Press Releases

The role of unshared songs in singing interactions between neighbouring song sparrows

sduncan — 2005-09-19T23:25:26Z

We examine how song sparrows use their long-distance songs to modulate territorial interactions. Like most species of songbirds, song sparrows have multiple song types, and because they learn their songs from their neighbors in their first year, a bird will typically share some, but not all, of his song types with any particular territorial neighbor. A song sparrow addresses his neighbor from a distance by singing a song he shares with that neighbor. The neighbour can then escalate the interaction by replying with the same song type (‘type matching’), maintain the interaction at the same level by replying with another but different song they share (‘repertoire matching’), or de-escalate the interaction by replying with a song they do not share.

Note: This research was described in Science News, 18/25 December 2004 (“Song fights: When male birds go tune to tune”, Vol 166, pp 397-399).

The evolution of herbal medicine: behavioural perspectives

sduncan — 2005-09-20T14:32:06Z

The popularity of herbal supplements, and evidence of scientific legitimacy in the use of some medicinal herbs, prompts a question about whether the origin of herbal medicine was the result of animals and humans learning that specific herbs are effective for preventing or treating
certain maladies, or a result of natural selection to seek out and use herbs with markers of efficacy such as a bitter taste? Examining the predictions and requirements of the learned and
evolutionary explanations points primarily to an evolutionary model, which accounts for the use
of ineffective as well as toxic medicinal herbs, and that was expanded by learning and social transmission.

Audience Effects on Food Calls in Captive Brown Capuchin Monkeys (Cebus apella)

sduncan — 2005-09-30T18:04:19Z

Brown capuchin monkeys vocalize when they discover tasty food. These calls, however, change as a function of how much food they have and who else is nearby. We tested how
the brown capuchin calls in the presence of a variety of different audiences, such as other females of different ranks, and the whole group. The results of the study indicate that the monkeys not only change how many calls they produce but also the acoustic features of
the call, such as pitch and loudness. This suggests that the monkeys’ calls may be more cognitively sophisticated than previously thought.

Emergence of division of labor in halictine bees: contributions of social interactions and behavioral variance

sdduncan_manager — 2005-10-04T21:20:53Z

A central question in the study of insect societies concerns the emergence of division of labor. Among the different models of division of labor, the threshold model postulates that it can emerge from initial inter-individual differences in propensity to perform a task. However, social interactions among members of the incipient groups are also likely to shape the genesis of division of labor. We compared task performance and social interactions during nest construction in forced associations of solitary or communal halictine bee. Our work suggests that behavioral asymmetry and social interactions, conditions that were likely to be present at the origins of sociality, might have significantly contributed to the emergence of division of labor in early social evolution.

Influence of plumage colouration on prey response: does habitat alter heron crypsis to prey?

sdduncan_manager — 2005-09-30T16:56:10Z

White plumage has been suggested to increase crypsis to aquatic prey for foraging wading birds. Under this hypothesis, a white-plumaged bird would be less easily
detected than a dark-plumaged bird to aquatic prey such as fish and crustaceans. We tested the hypothesis that white-plumaged herons (e.g. snowy egrets) would be more
cryptic than dark-plumaged herons (e.g. little blue heron) to two species of aquatic prey, mosquitofish and crayfish. Through laboratory and field experiments, we demonstrated
that mosquitofish avoided little blue herons whereas crayfish did not respond differently to the presence of snowy egrets or little blue herons. Our results suggest that plumage coloration in herons may influence crypsis to aquatic prey, specifically fish. These results have implications for the foraging behavior of wading birds.

The choice of arboreal escape paths and its consequences for the locomotor behaviour of four species of Anolis lizards

sdduncan_manager — 2005-10-04T21:44:27Z

We studied four species of arboreal lizards that are a classic example of niche-partitioning, in which species with shorter legs occur on narrower branches than species with longer legs. Accounting for branches encountered as well as chosen by anoles during escape locomotion in natural habitat and in standardized laboratory tests revealed remarkably uniform preference of all species for branches with the largest possible diameter, which is in contrast to the interspecific differences in niche. Thus, our results emphasize the need to account for both resources available and for resources used before making conclusions regarding proximate mechanisms of choice in
animals.

Evidence that 3-keto petromyzonol sulfate specifically attracts ovulating female sea lamprey (Petromyzon marinus)

sdduncan_manager — 2005-10-04T22:01:36Z

Research was conducted to clarify the function of a male sea lamprey sex pheromone. Results are the first to show that the male pheromone only attracts ovulating females.
Results are also the first to show that a synthetic copy of the male pheromone functions in a stream, which confirms the identity and makes this study one of the first in vertebrates
to successfully induce behaviors using a synthetic pheromone. These findings expand our knowledge of pheromone communication in vertebrates, and could lead to new ways
to control sea lampreys in the Great Lakes of North America where they are a destructive, invasive species.

A pair choice test to identify female mating pattern in relation to ovulation in long-tailed macaques (Macaca fascicularis)

sdduncan_manager — 2006-08-08T20:21:11Z

To better understand female mating strategies, male influence over females should be limited. We therefore conducted a pair choice test where female long-tailed macaques controlled access to males in order to identify how female behaviour and the ovarian cycle affect choice and number of mates. Six females and four males participated. Twice a day, females were presented with two males and allowed two choices. Females mated with multiple males in all ovarian cycle phases. They apportioned choices and copulations evenly across males and did not prefer dominant males. This contrasts with mating in the wild, where dominant males monopolize copulations.

Dietary Amino Acids Influence Plumage Traits and Immune Responses of Male House Sparrows (Passer Domesticus), but not as Expected

sdduncan_manager — 2005-10-04T22:17:50Z

Many birds have patches of black in their plumage. The size of these patches appears to
function as a signal, yet little is known about how the patch reveals information about the
bearer. One possibility is that melanin, the black substance in the plumage, requires
amino acids that are valuable for other functions, such as immune responses. We tested
this possibility in house sparrows by manipulating the amount of amino acids in their diet
during moult. We found that deficiencies of two amino acids appeared to reduce melanin
synthesis but did not alter its size. The distribution of amino acids also affected antibody
production, but the two involved in melanin synthesis did not. These results suggest that
development of informative signals depends on other processes.

Correlates of territorial boundary patrol behaviour in wild chimpanzees

sdduncan_manager — 2006-02-08T19:23:50Z

Male chimpanzees show a unique form of cooperative territorial defense that includes patrols of
territory boundaries and incursions into neighboring territories, where they may make lethal
attacks on conspecifics. Researchers have studied the functions of territoriality (e.g., defense of
food resources), but have not examined day-to-day decision-making about patrolling. Our
observations at Ngogo, in the Kibale National Park, Uganda, show that the number of males who
associate per day is the best predictor of whether males will patrol on any given day. Males
patrol more often when ripe fruit is abundant, but this is because they form large parties at such
times. The presence of estrous females has no apparent effect on the likelihood of patrolling.
Our data support the hypothesis that the risks associated with intergroup aggression, which
depend on the number of males present, are the main influence on willingness to make
potentially lethal attacks (the “imbalance of power” hypothesis). Because chimpanzees have a
fission-fusion social system, patrols can lead to low-cost opportunities for males to kill members
of neighbouring communities many males patrol together. Males at Ngogo reduce the risk of
patrolling and establish competitive asymmetries in their favour by patrolling in large parties.

Can the alternative male tactics 'fighter' and 'sneaker' be considered 'coercer' and 'co-operator' in coho salmon?

sdduncan_manager — 2005-11-10T16:52:31Z

In many species, there are alternative male types that look and behave differently. For example, some males are large and fight with other males for access to females for mating while other, smaller males apparently sneak matings. It is widely accepted that females of these species prefer to mate with large, fighter males. This paper re-examines that assumption in coho salmon, a species with alternative male types. The findings are that females apparently prefer small, sneaker males who cooperate with females. But females often mate with large males to avoid harassment by them. Who females mate with depends on the costs and benefits of any given situation.

Characterizing the mating behaviours of the Tamesi molly, Poecilia latipunctata: a sailfin with shortfin morphology

sdduncan_manager — 2005-11-10T17:13:25Z

The endangered Tamesi molly (Poecilia latipunctata), an unusual live-bearing fish, shows both sailfin and shortfin molly mating behaviours. Although genetically a sailfin molly, P. latipunctata lacks the enlarged dorsal fin. P. latipunctata males perform courtship displays to females to elicit cooperation similar to sailfin males. However, males also establish dominance hierarchies through agonistic acts and changes in colour like shortfin mollies. We found that both female receptivity and presence of other males influence type and intensity of male mating behaviours.
These context-dependent male mating strategies may have been important in the divergence of P. latipunctata from their sailfin molly ancestors.

Territory revisitation reduces intrusion during spawning trips by female yellowtail damselfish.

sdduncan_manager — 2005-11-10T17:35:17Z

Like humans, non-human animals are faced with difficult decisions about how to manage conflicting demands. For example, when we go to work or leave for vacation, we leave our homes unattended and thus exposed to intrusion. We solve this problem by using locks, guard dogs, alarms or by relying on neighbors. But, what if we these solutions were not available? Female yellowtail damselfishes aggressively defend territories that provide their food and shelter on Caribbean coral reefs but experience intrusion when they leave their territories at dawn to spawn in the territories of males. Spawning can last an hour or more allowing other members of the same species to invade the territory. Some, but not all, females return to their territories at intervals during spawning. We found that when females that returned during spawning were caged during the spawning period to prevent returns, they experienced more intrusion than when they were allowed to return to their territories. Returning reduced intrusion rates to levels similar to those occurring when the fish was continuously present in its territory on non-spawning days. Females that did not return during spawning did not experience an increase of intrusion during caging. Thus, female damselfish appear to resolve the conflict over protecting their territory while they have important business elsewhere by periodically returning home to check on things, but only if intrusion would be likely to increase significantly during a continuous absence.

Dominance rank relationships among wild female African elephants (Loxodonta africana)

sdduncan_manager — 2005-11-10T22:13:42Z

From savanna baboons to spotted hyenas, many female primates and social carnivores form close and enduring social relationships with their female kin. These relatives often help each other in conflicts. As a result, a young female comes to occupy a dominance rank just below her mother, eventually “inheriting” her dominance rank. Here we report that female African elephants—who
also have close and enduring relationships with kin—do not have these same “nepotistic” dominance hierarchies. Instead, rank is based on age and size. Our results suggest that in elephants, close female bonds probably evolved for sharing ecological and behavioral knowledge and skills rather than for within-group competition.

Coccidian oocyst parasitism in the blue-black grassquit: influence on secondary sex ornaments and body condition

sdduncan_manager — 2006-02-08T19:25:21Z

Female birds choose males that exhibit exuberant morphological characteristics and/or behavior, which may decrease survival of these males. Different hypotheses suggest that parasite-resistant males should have brighter plumage and more energetic behavioral displays, or should be in better physical condition than parasitised males. To test these hypotheses we evaluated behavioural and mophological characteristics of neotropical blue-black grassquits, and sampled their intestinal parasites. We found that heavily parasitised males have shorter display leaps and more patchy plumage when compared
with less parasitised males. However, we did not find that males in better condition exhibit brigher plumage or display more energetically.

The nature and representation of individual recognition odours in Belding’s ground squirrels

sdduncan_manager — 2006-02-08T19:21:25Z

Individually distinct cues are useful when animals interact repeatedly over time and when discrimination among multiple familiar individuals is beneficial. To understand how animals recognize each other socially, we need to know the sources and distribution of recognition cues, as well as how others perceive these cues. Here I show that Belding's ground squirrels, a highly social mammal, produce at least five individually distinct odors (from oral, dorsal, pedal and anal glands and from supraorbital areas), and that they incorporate multiple odours into their memories of conspecifics, suggesting a mental representation of familiar individuals. These odors may allow accurate discrimination of conspecifics along several social dimensions.

Development-related effects of an acanthocephalan parasite on pairing success of its intermediate host, Caecidotea intermedius (Isopoda)

sdduncan_manager — 2006-02-08T19:27:01Z

The acanthocephalan parasite, Acanthocephalus dirus, infects both an aquatic crustacean (first host) and a fish (second host) during its life cycle. Previous work has shown that development of the parasite correlates with changes in both the appearance (color) and behavior (activity, hiding) of the first host and that these changes increase conspicuousness to the second host. We examined whether parasite development also correlated with changes in the sexual behavior of the first host (aquatic isopod, Caecidotea intermedius). We compared the sexual behavior of males that differed in infection status (early-stage vs. late-stage parasites present) and found that parasite development correlated with variation in male sexual behavior. Specifically, that males infected with late-stage parasites were less likely to initiate mating attempts with females than males infected with early-stage parasites. We discuss the results in the context of both pathological effects of infection and strategic manipulation by the parasite.

Multiple breeding strategies in the swift fox, Vulpes velox

sdduncan_manager — 2006-02-08T18:57:09Z

Little is known of the mating system of the swift fox (Vulpes velox) or how it compares to other socially monogamous mammals. We used microsatellite analysis in conjunction with spatial observations to investigate swift fox mating strategies. The mating strategies employed by swift foxes were highly diverse. Previous field observations have indicated that the swift fox is socially monogamous. However, we found that extra-pair mating was a common breeding strategy, and there was also variation in the structure of social groups. In addition, swift foxes engaged in mate switching which refutes the prevailing hypothesis that they always mate for life. Thus, we found that the mating system of the swift fox is highly diverse and substantially more complex than previously believed. Factors that may influence which strategies are adopted and whether they are adaptive are discussed.

Alloparental feeding in the king penguin

sdduncan_manager — 2006-03-06T19:26:52Z

The austral ocean imposes severe limits in the accessibility to the food for many seabirds. In that context, breeders must periodically leave their offspring unattended. During parental absenteeism, fasting chick may gain allofeedings, i. e. supplements of food from other breeders than their own parents. We studied allofeeding in a king penguin colony, a seabird
in which parents leave their fasting chick in dense crèches up to several months running. During winter, more than 1/5 of adults allofed almost 2/3 of the chicks. Numerous breeders that have lost their own offspring became allofeeders, although successful breeders occasionally allofed. Chicks were allofed preferentially by adults that were their close neighbours when the colony was still organized into breeder territories. Although allofeeding is commonly associated with an altruistic behaviour, it was not strictly the case in king penguins because allofed chicks increase their survival without cost for the allofeeder.

Development of red-eyed treefrog eggs affects efficiency and choices of egg-foraging wasps

sdduncan_manager — 2006-01-20T19:05:50Z

Foraging theory predicts that predators choosing between prey of equal value will prefer those they are more likely to capture. Eggs are excellent and usually easy prey. However some embryos, such as red-eyed treefrogs, can escape from predators by hatching prematurely when attacked. Warkentin, Buckley and Metcalf asked if wasps foraging on red-eyed treefrog embryos prefer younger eggs that cannot yet hatch. They found that young eggs have a second defence mechanism: a thick jelly coat that becomes thinner as they developed. Wasps had difficulty extracting young embryos from this jelly, and in fact preferred to feed on older, more accessible eggs, even if they could hatch. This reduced the overall number of eggs killed, and shifted most of the mortality to intermediate stages, when eggs were losing their maternally-provided jelly defence, but had not yet developed the ability to escape by hatching. Eggs are not all equal to predators.

Non-random patterns of vigilance in flocks of the greater flamingo (Phoenicopterus ruber ruber)

sdduncan_manager — 2006-02-08T19:07:49Z

Animals gather information about predators when they interrupt feeding activities and raise their heads. Recent studies suggest that feeding activities should be interrupted at regular rather than unpredictable time intervals when foragers are threatened by predators that rely on surprise rather than stealth. Regular scanning has rarely been documented in
relation to predator behaviour. I examined vigilance patterns in greater flamingos foraging in a lagoon complex in Venezuela. Scanning behaviour was more regular than unpredictable in this large species where disturbance by people probably represents the most likely threat and which is therefore best detected using regular scanning.

Wounding, mortality and the lion's mane (Panthera leo)

sdduncan_manager — 2006-02-08T19:10:57Z

A protective role for the lion's mane has long been assumed but this assumption has never been tested. We compared patterns of injury, mane development and adult mane morphology in a population of
African lions and found no compelling evidence that the mane conferred effective protection against wounding. The mane area was not a specific target of attacks, and injuries to the mane area were not
associated with higher mortality than other injuries. Regions of the mane that were most frequently attacked did not show earlier onset of mane growth in subadult males, or longer/darker mane hair in adult males.
Adult males appeared to be wounded less frequently on the mane area than predicted by surface area, but it is unclear whether this trend was only caused by observer bias due to decreased visibility. We conclude
that while the mane may have conferred protection during the early evolution of the trait, protection appears to be secondary to the strong sexually-selected advantages of the mane as a condition-dependent ornament.

Sex differences in rates of territory joining and inheritance in a cooperatively breeding cichlid fish.

sdduncan_manager — 2006-02-08T18:19:12Z

In some species, called “cooperative breeders”, only male and one female in the group breed, while other group members (“helpers”) help them raise their young. Such cooperation and reproductive segregation raises many questions. How does an individual become a breeder in such a system? What do these helpers gain by helping? Stiver et al. investigate these questions by using underwater behavioural observations on a cichlid fish native to Lake Tanganyika, Africa. The researchers removed the breeding male from
some groups and the breeding female from others, and found that female helpers tended to inherit the breeding spot in the group they currently live in, while male breeding vacancies are typically filled by individuals that join the group. Helpers helped more when they were related to the new breeder. This study provides insights into how cooperation may have evolved and how changes in status influence individuals in social groups.

Mind the Gap: Means-End Discrimination by Pigeons

sdduncan_manager — 2006-02-08T19:12:06Z

Four experiments examined how pigeons learned two tasks designed to reveal their
understanding of means-end relations. The purpose of these experiments was to reveal
how different kinds of animals think about the world and how these capacities might have
evolved. The pigeons were required to retrieve out of reach food by selecting among a
ribbon attached to a food dish and one that was not. All of the pigeons came to select the
“connected” ribbon. Further tests designed to investigate how they learned this solution
suggested that it was solved based on the perceptual cues directly related to the ribbon
rather than a deeper conceptual understanding of the ribbon as a “means” to an end
(getting the food). Comparisons with similar results from primates suggest that some
differences between species may exist, but that caution is still needed in interpreting such
results because of procedural differences among the tests.

Site-dependent Aggression and Mating Behaviour in Three Species of Nasonia (Hymenpotera: Pteromalidae)

sdduncan_manager — 2006-03-06T18:58:19Z

We wanted to investigate the relationship between female mate availability and male aggression and area defense using three closely related species of the parasitoid wasp Nasonia. These three species differ in the frequency of females that emerge as virgins, and we wanted to determine if males will defend an area with females that are not virgin. We found that in one species, Nasonia vitripennis, 95% of females emerge as virgins and males are highly aggressive and stay on or near the host from which they emerge. One hundred percent of N. giraulti females emerge having already mated, and males do not defend the area and disperse. Finally, female N. longicornis are highly variable in the frequency of virgin females, but males are still aggressive. We believe this major difference between the species may have been caused by genetic or bacterial factors that limit successful reproduction between all three species.

Asymmetrical incest avoidance in the choice of social and genetic mates

sdduncan_manager — 2006-03-06T19:23:10Z

Even though incest generally results in lower reproductive success, it may occur if animals don’t have enough information about a prospective mate to estimate their relatedness or if the costs of avoiding inbreeding are too high. Over a 17-year period, Savannah sparrows (Passerculus sandwichensis) in an island population rarely paired incestuously (15 of 1609 nesting attempts). Most cases involved 1-year-old males breeding for the first time with aged females. Father- daughter matings (social and genetic) were avoided completely. These results suggest that there are fundamental differences in the likelihood of incestuous matings depending upon sex, age, and specific relationship.

Changing territories, changing tunes: male loons, Gavia immer, change their vocalizations when they change territories

sdduncan_manager — 2006-03-06T19:35:37Z

Male Common Loons produce a territorial vocalization called the "yodel". Each male loon has a characteristic yodel that is stable from year to year and differs from that of other male loons on other lakes. Of 13 male loons whose yodels we recorded before and after male loons changed territories, 12
substantially changed their yodels either the first or second year on the new territory. Further, this change was such that it increased the difference between their yodel and that of the previous resident of the territory. This result implies that loons not only change their vocalizations as the birds change territory but also that the new owner is familiar with the yodel of the resident that it replaces.

Variation in body temperature and the isolation calls of juvenile big brown bats (Eptesicus fuscus): consequences for individual recognition.

sdduncan_manager — 2006-03-06T19:48:15Z

In frogs and insects, communication sounds change as the individual’s body temperature changes. This complicates communication and individual identification. For most mammals, body temperature is constant and communication signals do not vary. However, in mammals that vary their body temperature as a means of saving energy, vocal communication may be compromised. We found that young big brown bats can vocalize even at body temperatures of 11^oC, but calls vary depending on body temperature. This may compromise a mother’s ability to identify her offspring. Maintaining body temperature by clustering, or using cues such as odour, may allow pups and mothers to reunite.

Sexual selection and social rank in bighorn rams.

sdduncan_manager — 2006-03-06T19:57:42Z

In many polygynous species, male reproductive success increases with social rank. Because rank is established through aggressive interactions among males, it should increase with body mass, because larger males should have a competitive advantage during fights. A positive effect of mass on social rank should select for high sexual dimorphism in body mass in ungulates. Because it is difficult to weigh free-ranging ungulates, however, empirical data on the relationship between mass and male social rank are scarce. We monitored individual mass, age and social rank of marked bighorn rams (Ovis canadensis) at Sheep River, Alberta, over 5 years. In this species, access to estrous ewes during the rut in mainly determined by ram social rank. We found that both mass and age were important determinant of social rank but the relative role of mass increased as rams aged. That is because up to about 6 years of age older rams are also inevitably heavier than younger rams. Once males reach their adult body mass, if they are large they can win fights again older conspecific. Our results support the idea that sexual selection may have led to the substantial sexual dimorphism seen in most ungulates.

Risk assessment by grasshopper mice (Onychomys spp.) feeding on neurotoxic prey (Centruroides spp.)

sdduncan_manager — 2006-04-13T21:09:33Z

Grasshopper mice are voracious arthropod predators in NA deserts and grasslands; many of their prey possess noxious defenses, including the sprays of stink beetles and the stings of scorpions. Some reports suggest grasshopper mice modify their attacks to neutralize the specific defenses of their prey (such as targeting a scorpion’s stinger), while other studies show the mice attack indiscriminately. We looked for prey-specific attack behavior using staged encounters with 38 wild-caught mice, testing each mouse with a bark scorpion (a dangerous, neurotoxin-wielding prey), with a stripetail scorpion (a non-neurotoxic prey), and a lab cricket (a defenseless prey). Mice attacked all three indiscriminately, but did have significantly more difficulty subduing bark scorpions. Our results suggest that grasshopper mice use a simple rule when attacking small invertebrates; i.e., if it moves and smells like food, attack! Moreover, our study demonstrates the mice are resistant to the potent neurotoxins of bark scorpions.

The role of testosterone in male downy woodpeckers in winter home range use, mate interactions, and female foraging behaviour

sdduncan_manager — 2006-04-13T21:19:02Z

We captured male downy woodpeckers in winter and inserted under the skin small implants filled with testosterone. We released them the same day and followed the males and their female mates regularly to determine what effect the elevated levels of
testosterone would have on male behavior, and what effect a change in male testosterone level might have on females associating with those males. Comparing our experimental males with normal males without elevated testosterone, we found that testosterone actually decreased the frequency of aggressive male-male encounters, it changed the way a male uses space within its home range (or territory), and it leads in some cases to increased male-female interactions. These interactions seemed to impact the female mates of testosterone-implanted males in several negative ways, including a reduction in
foraging behavior and a reduction in the frequency of a female’s social interactions with non-mate males.

Regulation of Space Use in a Solitary Field: Population Density or Prey Availability?

sdduncan_manager — 2006-04-13T21:34:42Z

Home range size in birds and mammals appears to be influenced by a number of factors including food availability, body mass, and population density. However, few studies have convincingly shown population density to influence the extent of space use in a population of free ranging carnivores without a corresponding increase in food availability. We investigated the relative effects of food availability, body weight, and increased density on the size of adult bobcat (Lynx rufus) home ranges and core areas in Mississippi, USA from 1989-1997. We observed an increase in population density and a decrease in annual mean home range and core area sizes for males and females during this 9-year study. Population density explained 64% and 56% of the variation in home range size for males and females, respectively, whereas food availability and body weight failed to explain the observed reduction in bobcat home range size. Population density was also the most important variable explaining variation in core areas for both sexes, although food availability also appeared to play a role, especially for females. We suggest that population density should be considered along with energy acquisition and metabolic factors such as food availability and body size when investigating variability in home range and core area sizes of mammals.

Polybia wasp biting interactions recruit foragers following experimental worker removals

sdduncan_manager — 2006-04-13T21:45:05Z

Communicative interactions among colony members, or worker connectivity, can affect division of labour in insect societies. In this study I used experimental forager removals to test whether biting interactions among wasp workers is a form of worker connectivity. I asked whether biting induces new recruits to enter the foraging force. I observed colonies with individually marked workers during a pre-treatment (control) period, then removed all arriving foragers on the following day. Foraging ceased in the colonies after several continuous hours of forager removals, and remained depressed on the following morning. I observed the colonies on one to three additional days, and I grouped the remaining workers into four behavioural categories: non-foragers, individuals that stopped foraging after the manipulation, continuing foragers that were active before and after the manipulation, and recruited foragers that began foraging after the manipulation. After the manipulation, the recruited foragers were bitten at similar rates to the continuing foragers. Workers in the other behavioural categories were bitten at lower rates. Most importantly, the recruited foragers were the only behavioural category that were bitten at significantly increased rates after the manipulation. The experiments show that biting plays a role in inducing foraging. Biting is a form of worker connectivity, serving as a mechanism of communication among Polybia workers that affects colony responses to changing conditions.

Line-following preferences of male crab spiders Misumena vatia

sdduncan_manager — 2006-04-18T17:36:07Z

Spiders, including the crab spider Misumena vatia, typically leave silken lines (draglines) behind them as they move. These lines allow spiders to prevent falls, as well as serving in a variety of other possible ways. Females of some species place sex-specific odors (pheromones) on these lines, which may also provide adult males with information that helps them to find virgin adult females. However, female Misumena do not produce odor cues that males can use. Adult males nevertheless respond positively to lines of their females, probably using tactile cues present on the lines. Immature males do not respond preferentially to these lines, which provide them with no advantages – following them would simply increase their vulnerability to the frequently cannibalistic females. Thus, draglines may function in more than one way, which may differ with both sex and age.

Effects of natal experience on habitat selection when individuals make choices in groups: a multilevel analysis

sdduncan_manager — 2006-04-18T17:47:48Z

When animals make choices in groups, an individual's decisions may be affected by the behaviour of other individuals in the same group. In this paper we demonstrate how one can use multilevel statistical models to study habitat preferences when animals make choices in groups, and when individual decisions are affected by the behaviour of other animals who are making choices in the same experiment. In particular, we show that when female Drosophila melanogaster select a new habitat, their habitat preferences are affected by a number of factors, including the type of habitat they experienced prior to making the choice, as well as the choices made by other females during the previous hour in the same trial. A comparison of analyses based on traditional statistical approaches (generalized linear model, GLM) with those based on the multilevel model indicates important discrepancies between the results of the two models, probably because the GLM was unable to include factors affecting choice that were shown to have important effects on choice in the multilevel analysis. This study demonstrates the utility of multilevel statistical models for addressing problems in animal behaviour.

Predator learning, experimental psychology, and novel predictions for mimicry dynamics

sdduncan_manager — 2006-04-18T18:12:21Z

The evolution of warning colouration and defensive mimicry is driven by predator avoidance learning and behaviour. Animal learning data from experimental psychology can further inform our predictions of predator behaviour and improve our conceptualization of predator behaviour and predictions for mimicry dynamics. I consider how relevant findings in animal learning, particularly the importance of contextual cues in mediating behaviour, may provide new insight for the evolutionary and ecological dynamics of defensive mimicry. Specifically, work in animal learning psychology predicts that (1) a Batesian mimic will be less disadvantageous for the model species than previously assumed, (2) contextual cues will be a selective agent in behaviour and/or distribution of model and mimic individuals, and (3) multimodal signals will contribute to model and mimic species context specificity, particularly in species with no opportunity for unique ecological cues. These predictions may help explain ecological/behavioural empirical data currently considered incongruous with mimicry theory
predictions.

Urban bioacoustics: it's not just noise

sdduncan_manager — 2006-04-18T18:26:46Z

The sound environment plays a major role in shaping the ways that animals communicate. Humans, particularly in cities, profoundly alter the sound environment. Humans increase noise levels through automobiles and other machines, and structures built by humans (homes, buildings, highways) alter the ways that sound moves through the environment, creating reflective surfaces and impediments to sound transmission. Several recent articles have identified effects of human-generated noise on animal communication and behaviour. These studies, however, serve to highlight the surprising lack of research on the behavioural responses of animals to altered sound environments. We describe several important characteristics of urban environments, all of which have parallels in natural environments. We suggest that cities are a fruitful area for future research on the evolution of animal communication systems, with implications for conservation in human-altered environments more generally.

Meat sharing among the Gombe chimpanzees: Harassment and reciprocal exchange

sdduncan_manager — 2006-07-06T18:35:23Z

Sharing food with unrelated individuals seems detrimental, yet it occurs in many species, including birds, bats and primates. Meat sharing among wild chimpanzees is a classic example of this phenomenon. I evaluated two explanations for nonkin meat sharing among wild chimpanzees at Gombe National Park, Tanzania. There was strong evidence supporting the idea that these chimpanzees share to avoid the costs imposed by persistent beggars. Meat possessors ate more slowly when faced with many beggars, and were more likely to share with beggars that persistently harassed them. Meat recipients stopped harassing the possessor. In contrast, there was mixed support for the idea that chimpanzees exchange meat for social “favours”. Males did not share preferentially with frequent male grooming partners or sexually receptive females. Possessors were more likely to share with frequent female grooming partners; however this was likely to be due to increased harassment by these females.

Contact call diversity in wild Orange-fronted parakeet pairs (Aratinga canicularis)

sdduncan_manager — 2006-07-06T18:47:20Z

Social animals rely on contact calls-- a type of vocalized sound-- to establish and maintain the connections so important to their life-style. Animals that live in stable social groups often share a common contact call, while animals that live in societies with more fluid structure often show individual distinctiveness. In these animals, such nametags could be used to address and make connections with specific individuals. Both parrots and dolphins live in fluid societies. Dolphins show both individually distinctive (signature) contact calls, and mimicking of other individuals' signatures while socializing. We examined the contact calls of wild Orange-fronted parakeets in Costa Rica, to see if they similarly produced signature contact calls, and if contact calls were shared within mated pairs, the only stable social grouping seen in this species. We found that individuals do produce signature calls, and that mated pairs, while not sharing a common call, do show call similarity.

Leaf-cutter ant species (Hymenoptera: Atta) differ in the types of cues used to differentiate between self and others self and others

sdduncan_manager — 2006-07-06T19:17:58Z

Ants are among the animals living in the most sophisticated societies. Here we search the chemical cues that these insects use when discriminating self from other. Nestmate recognition among most social insects is thought to be mediated by cuticular hydrocarbons. Here we show that among two closely related ant species, the chemical cues used for recognition vary between them and that they are not cuticular hydrocarbons, but chemicals secreted from the mandibular gland that produces their alarm pheromone and possibly another gland in the gaster. We performed experiments with free living colonies of Atta laevigata and Atta cephalotes using live and dead dummies, some impregnated with glandular extracts, allowed us to reconstruct the recognition cues Our results suggest that recognition mechanisms vary among ants, and may thus vary among other social insects, and are shaped by various evolutionary forces in addition to kin selection.

What makes information valuable: signal reliability and environmental uncertainty

sdduncan_manager — 2006-07-08T21:05:19Z

To acquire information, animals can track the likelihood of events, or pay attention to external signals. We developed mathematical predictions and then tested the value of different kinds of information to six captive blue jays (Cyanocitta cristata). The birds repeatedly chose to peck either a red or green key to obtain a food reward. We varied the overall probability that pecking red led to a food reward. A third key acted as a signal, and we varied how reliably this signal indicated the true colour from trial to trial. We found that blue jays used the signal when it reliably indicated the correct behaviour and the environment was uncertain. Blue jays ignored the signal when it indicated the true colour unreliably and when prior experience gave them a high level of certainty about the
true colour. Overall, we observed a bias towards using personally acquired experienc

A dynamic method to study the transmission of social foraging information in flocks using robots

sdduncan_manager — 2006-08-01T14:30:57Z

Robots could be excellent tools to investigate the dynamics of social behaviour in animals, such as, flock formation, social information transmission, etc. We assessed the potential use of robots in social contexts by studying the behavioural reactions of adult house finches (Carpodacus mexicanus) to robot behaviour. We found that the presence and motion of robots elicited responses that were similar to those given to live flock-mates. In general, house finches invested more time to foraging as the robots increased the duration of head-up bouts, which could be associated to the perception of foraging opportunities or to higher levels of flock anti-predator behaviour. We conclude that robots are a novel technique for animal behaviour with broad applications to the study of social behaviour and visual social cognition, because they allow detailed studies of the proximate and ultimate mechanisms underlying behavioural patterns and they have the potential to interact with live individuals.

Forager activation and food availability in harvester ants

sdduncan_manager — 2006-08-01T14:42:38Z

Ant colonies operate without central control, but are able to adjust foraging activity in response to food availability. In the field, we found that foraging activity increases with the return of successful foragers, and is unaffected by the return of unsuccessful foragers. We then compared our field observations to the outcomes of computer simulations. The computer model that best describes the results is one in which an inactive forager immediately joins a queue to leave the nest upon encountering a successful forager. This behaviour allows colony foraging to track food availability without memory or the capacity to monitor colony-level activity.

Montezuma oropendolas modify a component of song constrained by body size during vocal contests

sdduncan_manager — 2006-08-01T14:55:00Z

The sound frequencies of an animal's vocalization can reflect body size; larger
individuals are able to produce lower frequencies than smaller individuals. In some frogs, for example, individuals use these frequencies to assess the size of their opponents. Here we provide evidence for similar behavior in a bird. The Montezuma oropendola is a polygynous songbird in which male size is an important factor in mating success. During interactions at nesting colonies, males appear to lower the frequencies of some parts of their songs, suggesting that they have an important function in advertisement. Comparisons to other bird species indicate that these sounds are produced near the lower limit of what the birds can produce.

Taming of the skew: transactional models fail to predict reproductive partitioning in the paper wasp Polistes dominulus

sdduncan_manager — 2006-08-01T15:07:12Z

Behavioral ecologists have spent much of the past two decades trying to explain why and how cooperative groups can be stable when reproduction within the group is asymmetrically shared. Polistes paper wasps have been at the forefront of this investigation because of their colony-initiating behaviors. When females cooperatively initiate colonies, reproduction is often distributed unequally, and sometimes completely monopolized by one individual. Transactional models of reproductive skew assume a “social contract” where the dominant controls group
membership and may yield some reproduction to a subordinate as an incentive to stay. We tested predictions of these models in P. dominulus. The results were unsupportive. For example, we found no relationship between skew and relatedness, and observed colonies wherein reproduction was completely monopolized by dominants unrelated to subordinates. Overall, our results demonstrate that transactional skew models have little predictive power and are unlikely to yield further insight into Polistes wasp societies.

Reduced territorial responses in dark-eyed juncos, Junco hyemalis, following population establishment in a climatically mild environment

sdduncan_manager — 2006-08-02T15:16:50Z

Male songbirds respond to playbacks of their own species songs by aggressively
approaching the source of the playback. Here we show that male dark-eyed
juncos from different populations have different territorial responses throughout
the course of their breeding seasons. In southern California this species
normally inhabits the higher altitudes of the Sierra and males show very strong
responses to playback. By contrast males in a small population of juncos on the
coast in San Diego show much weaker responses. The San Diego population is
believed to have been founded by a small flock of birds from the Sierras in about
1980. We suggest that the weaker responses in San Diego are a consequence
of the much longer breeding season given the milder climate. The study
highlights how novel environments cause dramatic changes in social behavior.

The Role of Social Context and Individual Experience in Novel Task Acquisition in Cotton-top Tamarins (Saguinus oedipus)

sdduncan_manager — 2006-08-01T16:05:18Z

Many animals use social cues from conspecifics to help determine what to eat or how to find food. However, in many species dominance interactions limit opportunities for
individuals to closely observe and interact with skilled group members. We studied how naïve individuals learn novel foraging behaviour within the cotton-top tamarin, a new world monkey characterized by high levels of social tolerance. We designed a novel foraging task and trained some monkeys to be skilled in the task. We then exposed naïve tamarins to the foraging task either alone, with skilled mates, or with mates who did not know how to solve the task. Tamarins could not readily learn the novel task when they were tested alone, or with other naïve tamarins. However, tamarins could rapidly learn the task when they were tested with skilled mates. Our study shows that in a species with a tolerant social structure, individuals rely primarily on social cues to learn novel tasks.

Ontogeny of locomotory behaviour in the American locust, Schistocerca americana: From marathoner to broad jumper.

sdduncan_manager — 2006-08-01T16:15:20Z

The endurance and power output of running and swimming vertebrates improves with age. Do similar trends exist in invertebrates? American locust grasshoppers (Schistocerca americana) increase in body size by about 200-fold in the 7 seven weeks of development from hatching to adult. To determine if jumping performance varied during development, we forced grasshoppers of different ages (juveniles at 3 different stages and adults) to jump for twenty minutes. We measured their jump frequency, endurance, speed, and power output. Surprisingly, we found that younger grasshoppers had greater endurance, but like juvenile vertebrates, had lower power outputs than adults. The developmental changes in jumping performance match ecological and behavioural observations of foraging, dispersal, and migration, as juveniles only hop but adults can fly.

Intensity of interference affects the distribution of house sparrows Passer domesticus at food patches

sdduncan_manager — 2006-08-02T20:26:53Z

The Interference Ideal Free Distribution (IFD) model predicts that foragers should settle
in patches of high resource abundance when aggression/interference among competitors
is weak but should spread out evenly across patches when aggression/interference is
strong. We tested this prediction by observing house sparrows (Passer domesticus) at a
rich and a poor patch differing in seed density. We manipulated interference by altering
the size of the patches: two small (high aggression/interference) or two large (low
aggression/interference) patches. Birds preferred to feed at the rich patch when patches
were large and fighting infrequent. Birds aggressively interfered with each other at small
patches. As predicted, birds increased their use of poor patches to minimize interference
with half the birds feeding at the rich patch and the other half at the poor patch. Our study
is the first to support the Interference IFD prediction that consumer distributions can
become independent of resource distribution.

Sheep self-medicate when challenged with illness-inducing foods

sdduncan_manager — 2006-08-02T20:33:03Z

People learn to take aspirin for headaches, antacids for stomach aches, and
ibuprofen to relieve pain, and we often obtain prescriptions from doctors for
medications. Many of the drugs we use come from nature’s pharmacy and it has
been argued the desire to take medicines is the greatest feature that
distinguishes humans from the rest of the animals. But can other animals learn to
write their own prescriptions? Research at Utah State University suggests they
can. In these studies, sheep learned that sodium bentonite alleviates an acid
stomach from eating too much grain, that polyethylene glycol neutralizes the
adverse effects of foods high in tannins, and that dicalcium phosphate counters
the effects of foods high in oxalates. These medicines also enabled sheep to eat
more food, much as humans eat antacids before a spicy meal so they can eat
more and prevent an upset stomach.

Movements of male sockeye salmon, Oncorhynchus nerka, on spawning grounds: the effects of in-stream residency, density, and body size.

sdduncan_manager — 2006-08-02T20:47:36Z

We recorded the daily movements of male sockeye salmon from three populations during
their breeding season. We examined how movement varied among streams, among years
within streams, among males of different sizes, and as a function of how long the fish had
been living in the stream. This approach revealed that: 1) in all three streams, male
movement decreased as a function of time on the breeding grounds and was very limited
in most cases, 2) movement patterns, particularly initial exploratory movement, differed
among streams and among years within a stream but were unrelated to density, and 3)
large and small males showed equally limited movements. Most movement occurred in
the first few days in the stream, after which males seemed to wait for new females to
arrive rather than seek them elsewhere in the stream. These restricted movements have important implications for the evolution of salmon populations.

Aggressive Experience Alters Place Preference in Green Anole Lizards (Anolis carolinensis)

sdduncan_manager — 2006-08-03T06:09:05Z

Males of many species establish exclusive territories. We used a conditioned place
preference (CPP) procedure to determine whether engaging in aggression, was rewarding
for male green anole lizards and to determine whether aggressive experience could alter
spatial/contextual preferences. We repeatedly exposed male anoles to a mirror (which
frequently elicits aggressive displays) or the back of a mirror in opposing sides of a CPP
apparatus that consisted of two contextually distinct chambers connected by a tunnel.
Control animals were exposed to the back of the mirror in both sides of the apparatus.
Following conditioning, animals that exhibited aggressive behaviour when exposed to the
mirror increased the amount of time they spent in the side of the apparatus paired with the
mirror while the preferences of non-aggressive and control animals remained unchanged.
These findings suggest that aggression-related reward could play a role in the formation
and/or maintenance of stable territories.

Mate Recognition in a Simultaneous Hermaphroditic Shrimp, Lysmata wurdemanni (Caridea: Hippolytidae)

sdduncan_manager — 2006-08-03T06:15:58Z

Male crustaceans must find and identify receptive females in order to mate successfully.
Sex recognition mainly depends on sex pheromones, which are detected by antennae and
antennules. Distance (soluble) pheromone has been well documented to mediate mating behaviors
of some decapod crustaceans. Contact pheromone (an insoluble coating on the body surface) have
been proposed, but never been confirmed, to be used by male decapod crustaceans to detect
females. Here we report for the first time the involvement of both distance and contact
pheromones in the mating processes of a decapod crustacean, Lysmata wurdemanni. Females can
only mate during the small window of the post-molt period, during which they secrete both
distance and contact sex pheromone to attract males. Male shrimp tracked, recognized and
courted the receptive female shrimp based on both distance and contact sex pheromones, but
responded aggressively to newly molted male shrimp. Male shrimp with their chemosensory
appendages ablated appeared unable to identify EP shrimp, and neither courted nor copulated
with them. The outer flagella of the antennules house the receptors of the distance pheromone
whereas both antennae and antennules can detect the contact pheromone. Shrimp can still mate
successfully without the distance pheromone.

Behavioural mechanisms of invasion and displacement in Pacific island Geckos (Hemidactylus): evidence for interspecific reproductive interference

lopierce — 2006-08-03T19:11:39Z

Invasive species are a growing threat to global biodiversity. The increase in human travel and shipping over the last century has brought many exotic species to new lands. Many are thriving in their new habitats and their negative effect on native species may not be fully apparent for decades to come.

A recent study by Liz Dame and Ken Petren at the University of Cincinnati attempts to understand the role of behavior in animal invasions. They use Pacific gecko lizards as a model vertebrate system because they are easy to study in a controlled lab or field setting. Geckos occur in and on human houses across the world, thus they are very comfortable around humans and their structures. This team was able to understand how aggressive behavior and mating behavior affect each species’ ability to gather food and tip the tables in favor of the invading species.

Many scientists suspect that invaders succeed because they are better competitors for food, or because they are more aggressive and drive off native species. However, the Dame and Petren study suggests that something else is going on in their geckos. The invasive house gecko actually courts and mates with the native species. Although hybrids are not formed, some form of reproductive interference appears to be the most likely mechanism of displacement, because a number of other obvious possibilities were ruled out. Of course, it would be nice to extend these experiments to larger groups in a more natural setting, and that is the team’s plan. However this study clearly demonstrates that accounting for behavior will be a critical component in the goal to understand invasive species. It appears that it will be very difficult to predict or manage the affect of invasive animals without some knowledge of their behavior.

The queen is not a pacemaker in the small colony wasps Polistes instabilis and P. dominulus

sdduncan_manager — 2006-08-03T21:04:07Z

When individuals group together to rear young the work must be organized. In small social insect colonies it was thought that the queen orchestrated work, driving workers to forage, feed young, or build the nest. In this study we found otherwise. We observed natural colonies of two paper wasps, Polistes instabilis and Polistes dominulus. Work occurs in pulses, and who initiates activity can be said to be the orchestrator of work. A worker arriving at the nest or walking across the nest usually initiated these work pulses. The queen initiated no more pulses of activity than did the average worker. As there were far more workers than queens, this meant that nearly all active sessions were initiated by workers. These results change our view of the social integration in small wasp colonies. Their worker-initiated activity is like that of highly social colonies with thousands of wasps.

Inheritance of courtship song variation among geographically isolated populations of Drosophila mojavensis

sdduncan_manager — 2006-08-03T21:26:26Z

Many insect species communicate by means of acoustic signals. During courtship, males of many Drosophila species (sometimes called fruit flies) produce wing vibrations in order to achieve copulations. Thus, the acoustic properties of these male courtship songs are of great interest in terms of attractiveness to females, and possible differences in male mating success. These acoustic signals sometimes are used to avoid mating with the wrong species, or used by females to choose among potential mates with certain favorable song properties. Analysis of D. mojavensis songs has shown that this Sonoran Desert species is characterized by different songs in different parts of its species range. Study of male song differences was initiated to determine if they might be responsible for causing differences in mate choice among populations in addition to other signals exchanged between males and females during courtship. A genetic analysis of song differences was also performed.

Rhesus Monkeys (Macaca mulatta) Know What Others Can and Cannot Hear

sdduncan_manager — 2006-08-05T19:04:48Z

Although many animals use auditory information to functionally deceive other individuals, there has to date been little empirical verification that animals recognize how manipulating auditory information can alter what other individuals hear and know. Santos and colleagues are the first to show that at least one animal— the rhesus monkey (Macaca mulatta)— recognizes the connection between hearing and knowing. They presented monkeys with the opportunity to take grapes from a human competitor who was looking away. One of these two grapes was placed inside a silent container, while the other was placed inside a noisy container. Monkeys reliably took the grape from inside the silent container when the competitor was not looking, but not when the experimenter was looking and therefore already knew about the subject’s approach. These results demonstrate that monkeys preferentially attempt to obtain food silently only in conditions in which silence was relevant to obtaining food undetected.

On the evolution of hidden leks and the implications for reproductive and habitat selection behaviours

sdduncan_manager — 2006-08-05T19:10:57Z

Aggregations occur in all animal taxa, from insects to ungulates, and these aggregations can have
profound consequences for the ecology and evolution of organisms. While individuals might
have many reasons for being attracted to each other, an important link between mating strategies
and aggregations has not been adequately explored. In species with social pair bonds, infidelity
is common and results in ‘extra-pair’ copulations and paternity. The hidden lek hypothesis
suggests that aggregations of territorial males can result from female receptivity to extra-pair
copulations. We adapt four common models for the evolution of leks (aggregations of males that
females visit only for mating) to better understand the formation of hidden leks. Elaboration of
these models suggests distinct predictions that can be tested in situations where animals
aggregate in search of extra-pair copulations. Understanding the forces that shape hidden lek
formation and maintenance promises insight into habitat selection, aggregation, and reproductive
behaviours.

Prey crypticity reduces the proportion of group members searching for food

sdduncan_manager — 2006-08-05T19:20:43Z

Cryptic coloration protects against solitary predators but its efficiency against social predators is untested. Social predators are peculiar because they have the option of searching for their own food or exploiting others’ food. Consequently a group is a mixture of food searchers and exploiters. Using flocks of nutmeg mannikins we tested the hypothesis that cryptic coloration increases the predator’s search costs leading to lower proportions of searchers within groups. When we placed clumps of white millet seed on a background that made them cryptic, flocks of mannikins took longer to find the food, made more detection errors and significantly reduced the proportion of birds engaged in searching in three of four flocks. We conclude that
cryptic coloration provides a greater reduction in predation pressure when predators happen to be social because fewer social predators search for cryptic than non-cryptic prey.

Ecological and social influences on the hunting behaviour of wild chimpanzees (Pan troglodytes schweinfurthii)

sdduncan_manager — 2006-08-07T05:31:35Z

We used 25 years of data from Gombe National Park, Tanzania, to examine the factors affecting male chimpanzees’ decision to hunt red colobus monkeys. Our results provide evidence against social explanations for hunting in favour of more simple ecological alternatives. Upon encountering red colobus monkeys, male chimpanzees were less likely to hunt if sexually receptive female chimpanzees were present, indicating that they were not seeking meat to trade for sex. Instead, they may be forced to choose between hunting and mating. Males did not seek meat to trade with other males for social support, and hunting probability was not affected by diet quality. Hunts were more likely to occur, and to succeed, in woodland than in evergreen forest, emphasizing the importance of visibility and prey mobility. Finally, per capita meat availability decreased with adult male party size, suggesting that males did not benefit nutritionally by hunting cooperatively.

Testing central place foraging in eastern chipmunks (Tamias striatus) by altering loading functions

lopierce — 2006-08-07T18:24:08Z

Several earlier experiments lead us to believe that Eastern chipmunks (T. striatus) choose the number of seeds to carry back to the burrow in order to maximize their rate of delivery; as the distance to the burrow increases so does the number of seeds carried back. Confidence in this conclusion is tainted by the fact that chipmunks always collect loads that are considerably smaller than those expected of rate-maximizing foragers. This quantitative shortfall, however, could be due to problems involved in making reliable quantitative predictions. To circumvent this problem we chose to test an entirely new qualitative prediction. We experimentally manipulated the loading functions of 12 chipmunks by providing them with either natural sunflower seeds (Helianthus sp.) or sunflower seeds onto which we fastened an appendage that had to be removed before loading. As predicted by the model both load sizes and patch times were larger for seeds with an appendage and the effect on load size was greatest at 5 than at 20 m from the burrow. These results provide novel qualitative support that chipmunks behave as rate-maximizing CP foragers.

On seasonality in food caching behavior in parids: do we know the whole story?

lopierce — 2006-08-07T18:24:38Z

Food-caching tits and chickadees have been frequently used in many investigations into general questions concerning evolution of memory and the hippocampus, a part of the brain involved in memory processing. It has been generally assumed that these birds cache food very intensely during only a very brief period of time during autumn and results of many studies relied heavily on this assumption. Careful literature review, however, shows much more complex food caching patterns. During autumn, caching intensity may vary greatly between populations and during different years and these birds appear to cache food intensely over more than three-month period, from August through November rather than just during one moth of October as it has often been assumed. Chickadee and tits may also have a second peak in food caching during spring which suggests that food caching might be controlled by a suite of environmental factors related to food availability and energy balance in these birds rather than simply by photoperiod.

A state-dependent sex difference in spatial memory in pinyon jays (Gymnorhinus cyanocephalus): mated females forget as predicted by natural history

sdduncan_manager — 2006-08-07T19:14:34Z

We tested the prediction that female pinyon jays will be less accurate than males at finding their hidden seeds after many months. Pinyon jays rely on cached seeds for survival over the winter, and males provide all food for their mates at the nest. We first tested how well mated jays recovered seeds cached by themselves, their mates, or nonmates. Females outperformed males after one week, but both sexes performed with great accuracy. Males accurately located caches made by their mates; females did not. Next, we compared accuracies of mated males and females after 1 week, 2 months, and 4 months. Females performed at chance after 2 and 4 months; males remained accurate. We tested unmated birds and found that females were accurate at long intervals and that the sexes performed equally in a general spatial ability task. Spatial memory in pinyon jays may depend upon their mated status: mated females tend to forget, whereas unmated females remember.

Do food-hoarding animals have a cache recovery advantage?: determining recovery of stored food

lopierce — 2006-08-25T21:07:23Z

Food hidden by animals can be recovered by the hoarder or pilfered. We tested the hypothesis that yellow pine chipmunks recover more of their stored food than a naive forager. We allowed chipmunks to hide radio-labeled seeds and then established identical artificial caches nearby. We monitored 393 pairs of caches at ten sites. Removal of real caches represented the activity of the hoarder, foraging using spatial memory, plus the activities of pilferers, whereas removal of artificial caches represented the activities of pilferers. Seed-hoarding chipmunks were removed at four of ten sites after they prepared caches. Where hoarders remained, real caches disappeared 3.4-6.5 times faster than artificial caches, an effect that we attribute to the activity of the hoarder. Where cachers were removed, there were no significant differences in the removal of caches. We estimated that chipmunks retrieved 74% of their caches in 1997 and 56% of their caches in 1999-2002.

Male African elephants (Loxodonta africana) can distinguish oestrous status via urinary signals

lopierce — 2006-08-28T17:59:14Z

As adults, male and female African elephants, Loxodonta africana, often live separately in quite different social worlds. Males spend time searching for reproductively active females. In Asian elephants, females release a chemical signal called a pheromone, which indicates her approaching ovulation. No such pheromone has been identified yet in African elephants. Our goal was to determine if nine adult captive male African elephants housed in the USA could distinguish between urine from female African elephants in luteal (nonreproductive) and periovulatory (reproductively ready) oestrous stages as an indication that a pheromone is released in the urine. Males were presented with the two urine types and a control sample once a day over three days. All males showed greater chemosensory responses to the periovulatory urine by trial three, supporting the hypothesis that African elephants release an oestrous pheromone in the urine. Currently, we are pursuing the identity of this pheromone.

No preference for exaggerated courtship signals in a sensory trap

lopierce — 2006-08-04T14:32:00Z

Males usually court females with bright, loud, large and otherwise exaggerated signals because females prefer them over signals that are simply average. Male fiddler crabs Uca terpsichores build sand structures called hoods next to their burrows. Females have a preference for orienting to burrows with hoods because this allows them to move quickly from one male to the next and thereby avoid being caught and eaten by predatory birds. Other species of fiddler crabs also build structures but hoods are the largest. We replaced males’ hoods with concrete models of hoods of exaggerated size to see whether females prefer larger hoods. Surprisingly, they did not perhaps because females that attempt to discriminate between large and larger hoods must hesitate and this can be fatal. Hoods may be large not because females prefer them but because larger structures made of sand last longer.

Female hierarchy instability, male immigration, and infanticide increase glucocorticoid levels in female chacma baboons

lopierce — 2006-08-04T16:07:17Z

Over a period of 16 months, we measured the level of glucocorticoids (GCs), or stress
hormones, in the feces of wild female baboons. Their GC levels rose in response
to their reproductive states, new males joining the troop, males killing
infants, predation, and instability in the female hierarchy. A closer look at
their hormones revealed that they responded only when these events affected
their own lives, the lives of their offspring, or their social ranks. For
example, females with young infants that were at risk of being killed by new
males had increased GC levels whenever new males entered the troop or when
infanticidal attacks occurred. In contrast, GC levels of females without young
infants weren’t affected by these events. Although females mounted stress
responses frequently, stress-reducing friendships, egalitarian rank
relationships, and highly specific stress responses may have protected them
from many of the deleterious effects associated with chronic stress.
I’m also sending a photo of a female nursing her infant. Lactating females’ stress hormone levels increase when new males who might kill their infants enter the troop. Females without young infants do not experience a similar increase in stress hormones.

Mate Choice Rules in Animals

lopierce — 2006-08-04T16:17:29Z

We analyze experiments on female mate choice in frogs to learn what rules females use to decide between possible mates. The results show that none of the rules that
have been assumed in previous studies apply to this species. We also find that earlier studies of mate choice have not rigorously tested their assumptions of how females choose, so it is possible that mate choice rules have not been adequately describe for any species. The paper proposes ways that this problem can be studied using statistical tests.

Kin recognition and inbreeding avoidance in zebrafish is based on phenotype matching

lopierce — 2006-08-04T17:39:37Z

Differentiating kin from non-kin enables organisms of many species to allocate resources or altruistic behaviour towards related conspecifics and to avoid mating with close relatives. In this study, we tested which olfactory kin recognition mechanism is employed by zebrafish (Danio rerio). Juveniles of mixed sex groups preferred unfamiliar kin over unfamiliar non-kin indicating kin recognition based on a phenotype matching mechanism. They also preferred familiar kin to unfamiliar kin, showing that familiarity with individuals enhances kin preference. Adult females preferred the odour of unfamiliar, unrelated males to unfamiliar brothers indicating inbreeding avoidance. Adult male zebrafish showed no preference for the odour of related or unrelated females. To our knowledge, this is the first study testing different kin recognition mechanisms and ontogenetic switches of kin preference in the same species of fish.

Tracing the origins of signal diversity in anole lizards: phylogenetic approaches to inferring the evolution of complex behaviour

lopierce — 2006-08-04T17:49:54Z

Natural and sexual selection work together to shape the design of animal communicative systems, and sometimes act separately on different components to produce a single elaborate signal that works well in several contexts. Using evolutionary explicit methods and a dataset representing 53 taxa and four decades of research, we illustrate how different selective pressures have influenced the evolution of anole visual displays. Whereas evolutionary changes in display duration appear to be linked to the intensity of competition for resources, other display characteristics were more tightly associated with the need to facilitate species recognition and the type of environment in which the display is performed. We also found evidence that ecomorph distinctions, a major force in morphological evolution of anoles, have had an impact on the evolution of display structure. We contrast these findings with display evolution in other genera and discuss the evolution of visual communication in lizards more generally.

Functions of sibling aggression in the spotted hyena (Crocuta crocuta)

lopierce — 2006-08-25T21:11:19Z

Sibling aggression has long been assumed to serve as a mechanism for litter reduction in spotted hyenas. An alternate function for this behavior may be the establishment and maintenance of dominance between littermates. This study sought to test these two alternative hypotheses by observing wild spotted hyena litters during the first year of life. Siblings fought most during the first two months of life and rates of aggression then decreased, suggesting that once dominance is established there is little need to fight. Rates of sibling aggression peaked when competition for milk and meat was most intense, such as when prey were scarce. Dominant cubs were consistently heavier than their subordinate siblings, indicating one benefit of maintaining dominant status. Our data are consistent with the notion that hyena cubs are not demonstrating aggression in order to kill their siblings, but simply to establish rank relationships between littermates.

Asymmetric effects of experimental manipulations of social status on individual immune response

lopierce — 2006-08-04T18:32:52Z

Social animals are often at higher risk for pathogen infection, but little is known about which individuals in a group are most susceptible. I tested whether a bird’s social status directly influences its ability to mount an immune response to a non-pathogenic stimulus. I manipulated the natural social hierarchy of house finches by forcing dominant males lower in the flock’s hierarchy and allowing subordinate males to gain status. Changes in status caused striking changes in immunity within the same individual: dominant birds forced lower in the hierarchy mounted a proportionately lower immune response. Subordinate birds, on the other hand, did not change their immune response despite gaining social status, perhaps because this group did not alter their aggressive behavior in the new social context. Overall this study suggests that social status within a group can directly mediate the ability to mount an immune response, and may affect resistance to pathogens.

Female zebra finches prefer unfamiliar males but not when watching non-interactive video

lopierce — 2006-08-09T17:33:46Z

Video is a potentially powerful research tool in animal behaviour. If birds respond to video in the same way they respond to live birds then researchers could use video to assess the impact of subtle differences in behaviour and appearance through digital rather than physical means. Here we provide the first test of whether female zebra finches, a bird commonly used in behavioural studies, show the same mate preferences when watching video as when watching live males. To some extent the video worked. The male movies solicited large amounts of courtship from females. However, females fundamentally changed their mate preferences. When watching live males females courted an unfamiliar male in preference to their partner (pair-bonded) male—they seem to be looking for an extra-pair dalliance. However, when watching video they showed equal preference for these same two males. Therefore, video seems to promote courtship but can change who females prefer.

Territory owners discriminate between aggressive and non-aggressive neighbours

lopierce — 2006-08-04T18:53:19Z

Territorial animals live in a network of rivals, competing with each other for access to resources and for the attention of potential mates. In a territorial system where males vary in fighting ability or attractiveness to females, not all neighbours should be equally threatening to a territory owner. Territory owners would benefit by recognizing consistent individual differences between neighbours, assessing which neighbours represent greater threats, and responding appropriately when challenged. In this study, we examined whether male song sparrows assess the level of threat posed by individual neighbours and respond differently to neighbours that differ in their level of aggressiveness. Aggressive males should represent a greater threat because they are more likely to engage in fights over territorial boundaries, and may also be preferred by females as extra-pair mates. We used playback experiments to assay male territorial aggression, and then to test if males responded differently to their aggressive and non-aggressive neighbours. We found that male song sparrows respond more strongly to their aggressive neighbours than to their non-aggressive neighbours. Thus, male song sparrows differentiate between neighbours that differ in aggressive response and appear to respond adaptively based on their assessment of which individual posed the greatest threat.

A method to measure the development of song preferences in female cowbirds, Molothrus ater

lopierce — 2006-08-28T17:49:22Z

Male song development has been studied in detail across a range of different songbird species. Very little, however, is known about the development of preferences for songs in females. Here we describe a method to study female preferences outside the breeding season by documenting female responses to playbacks of songs of different developmental stages and of varying quality. We compared ‘wingstroke’ responses of juvenile and adult females in four groups across fall, winter, and spring. We found that adult, but not juvenile females showed preferences for variable song that was developmentally advanced. We assessed female preferences for the songs in the breeding season by playing back songs in sound attenuation chambers and recording the number of copulation solicitation displays females gave to each song. In the fall and winter, females of both age classes showed no tendency to wingstroke more to preferred song variants. In the spring, however, females did wingstroke more often to their preferred songs. Female preferences, similar to the song itself, appear to experience seasonal and developmental plasticity.

Physiological benefits as precursors of sociality: why banded geckos band

lopierce — 2006-08-25T21:02:52Z

Animals form groups for a variety of reasons. Some aggregate for social reasons such as grooming, reducing predation risks, or gaining access to mates. Aggregating could also provide a physiological benefit. Some nocturnal desert geckos aggregate in retreats during the day. We examined the factors, cues, and benefits of grouping in western banded geckos (Coleonyx variegatus). Geckos benefit from grouping by increasing the relative humidity in their retreats via the humidity generated by breathing, which in turn reduces their evaporative water loss (EWL). Grouping may be an important behavioral adaptation to living in deserts. Banded geckos are otherwise ill suited for life in this challenging environment because of their relatively low temperature preferences and high rates of EWL. Our study suggests a path for the evolution of social behaviour: as animals group for physiological benefits, the stage is set for the evolution of more complex social interactions.

Repeatability and consistency of female preference behaviors in a northern swordtail, Xiphophorus nigrensis

lopierce — 2006-08-11T18:30:09Z

Since we cannot ask animals other than ourselves whether or not they prefer certain mates, we often have to infer this preference by different behavioral displays. This study attempts to identify specific behaviors in swordtail fish that will inform researchers of a female’s intention to mate with different males of her species. The study involves two different experiments: one that identifies specific behaviors leading up to mating events. While the other investigates how consistently females perform these behaviors in successive mate choice trials. Our results indicate that the simple measure of time spent near the vicinity of males is the most repeatable and consistent measure of female preference in this species.

The emergency life-history stage and immunity in the cricket Gryllus texensis

lopierce — 2006-08-24T20:17:46Z

Both vertebrates and mollusks (e.g. oysters) become more susceptible to disease after stress. However, indirect evidence suggests that stress may make insects less susceptible to disease. If true, this would force us to reconsider our hypotheses about why stress-induced immunosuppression exists. We tested the effect of physical exercise, restraint, flying, heat, cold, fighting and elevated levels of the flight-or-fight hormone octopamine on disease resistance in the cricket Gryllus texensis. Physical exercise, restraint, flying, heat, fighting and the hormone octopamine produced a decline in disease resistance. One suggested advantage to stress-induced immunosuppression is that it enhances resistance to wound infections by decreasing resistance to systemic disease. However, we found that stress made crickets more susceptible to bacterial infection after wounding than controls. Nevertheless, the widespread occurrence of stress-induced immunosuppression suggests that it serves an important function.

Aggressive contests in house crickets: size, motivation and the information content of aggressive songs

lopierce — 2006-08-25T16:26:36Z

Many animals produce elaborate signals during aggressive contests. The function of these aggressive signals, including both their information content and the circumstances under which they cause resolution or escalation of conflict, continues to be controversial. We studied aggressive acoustic signals in house crickets to test their ability to inform opponents about ability and motivation to fight. We show that male crickets produce individually distinctive aggressive songs, which contain information about the ability of a male to win an aggressive contest. Song differed with male body size, and in two experiments relative size affected either the intensity or the outcome of fights. In contrast, we found no components of song that signal differences in male motivation to fight over a female. Although males were more aggressive and won more fights when they perceived females to be rare, their songs did not reflect this asymmetry in motivation to fight.

Inefficient task partitioning among nonhygienic honeybees (Apis mellifera L.) and implications for disease transmission

bruner854 — 2006-08-25T23:59:01Z

Hygienic behaviour in honeybee colonies involves the recognition, uncapping and removal of diseased brood by worker bees before the pathogen reaches the infectious stage. A colony with a high proportion of hygienic bees will detect infected brood, uncap the cells that contain the brood, and remove the diseased brood from these cells with relative speed and efficiency, limiting disease transmission. In contrast, a colony with a high proportion of non-hygienic bees will be slower in detecting infected brood, then may proceed to uncap, recap, and uncap these cells multiple times, succeeding in removing the diseased brood much later in time, if ever. This repetitive performance of the initial sub-task of uncapping increases the probability of these bees making repeated contact with the pathogen, increasing the probability of the pathogen being transmitted through the colony.

Photo explanation

The blue marked bee at the bottom is removing a dead pupa from a cell, as the last step in the hygienic process. Another blue marked bee at the top is inspecting a cell, the first detection step in the hygienic process.

The colony is in an observation hive, with Plexiglas walls and removable portal doors. A comb section of freeze-killed brood was introduced into the hive through a portal to elicit hygienic behavior. In this case, a portion of the capped brood (pupae sealed with a wax capping) was manually uncapped for experimental reasons (not related to this particular experiment).

Variation in female choice of mates: condition influences selectivity

bruner854 — 2006-08-28T17:42:34Z

The research investigated causes of variation in the mate preferences of female zebra finches, a small songbird that has long-term pair bonds and care of young by both parents. In zebra finches, both males and females participate in choosing their mate. The goal was to determine whether a female’s self-perception of her mate-getting ability, or attractiveness to males, affected her own mate selectivity. The prediction was that females with high mate-getting ability would be more selective; individuals with lower attractiveness would be less selective, because they cannot expect to attract highly desirable mating partners. A female’s quality was manipulated by slight trimming of her flight feathers, which increased the effort needed to fly. Females were less selective of mates following this manipulation than they were before the manipulation. Males did not appear to recognize the impaired flight capacity of females and did not discriminate against females with clipped flight feathers. Results support the prediction that individuals adjust their mate selectivity based on their self-assessment of mating quality. This research will help to understand why different individuals within a species vary in their behavior, and will aid development of better techniques to study the contributions of environment and genetic history to the expression of complex behaviors.

A complex plumage pattern as an honest social signal

bruner854 — 2006-08-28T17:39:12Z

Although there are numerous studies of the social significance of bird coloration, the vast majority of these deal with either variation in hue, or the amount of area of the body that is pigmented. Although it is common for birds to show intricate patterns by combining feathers of different colours, this has rarely been studied. We describe and analyse a bold pattern of black bands that cover the sides of the body of the red-legged partridge. By combining feathers of a specific length in a particular anatomical location, these bands align vertically during a display. The amount of black in each feather is correlated with body condition, and so may be used by other individuals (e.g. opponents during a territorial contest) to assess the quality of the bird. As social signals, patterns have the advantage of being able to be turned off and on when appropriate by behavioural modification.

Effects of heterospecific call overlap on the phonotactic behaviour of grey treefrogs

bruner854 — 2006-08-26T18:56:15Z

Communication plays an important role in the social lives of many organisms. Nevertheless, communication often takes place under less than ideal conditions. For most frogs, the successful coordination of reproductive behaviour depends upon the ability of females to assess and respond to the acoustic advertisement signals of males. A major problem of communicating in a frog chorus arises when the signals of neighbouring males overlap. We investigated the effects of overlap between the advertisement calls of two closely related and often-sympatric species of grey treefrogs on female phonotactic behaviour and signal selectivity. All females of one species, H. versicolor, approached a speaker broadcasting synthetic advertisement calls modelled after conspecific calls when the calls of the two species did not overlap. Surprisingly, the same females almost exclusively approached the source of synthetic calls modelled after the heterospecific advertisement calls when these calls completely overlapped the conspecific stimuli. Female H. chrysoscelis from the same population approached the source of synthetic conspecific calls even when these calls were overlapped by the heterospecific stimuli, indicating there may be differences between these closely related species in the susceptibility to the negative consequences of call overlap. When female H. versicolor were presented with conspecific advertisement calls that were completely overlapped by those of H. chrysoscelis, many females failed to approach either signal source. Response times of females that did respond were also longer, and the direction of phonotaxis was shifted in the direction of the heterospecific signal source. These negative influences of acoustic interference were reduced or eliminated as the degree of overlap between the calls of the two species was reduced. The results suggest that the effects of signal overlap in choruses on female phonotactic behaviour may be both negative and complex.

Seasonal variation in selection on male calling song

bruner854 — 2006-08-26T18:54:35Z

On a warm summer evening, you can often hear crickets singing, which they do to attract females. But all this singing also attracts a fly that lays her larvae (her eggs hatch inside her body) on the singing male that kill him within a few days. In Florida where this study was conducted, flies are around only during the autumnl but the crickets sing all year. This means that spring males can sing whenever and as much as they want but autumn males are constantly faced with death whenever they sing for females. We found that fewer autumn males sing (they search for females without singing) and they are less likely to sing at dusk when flies are most active, but if an autumn male does sing, he sings more than does a spring male. This is because singing is more effective at attracting females in the autumn than in the spring.

Copulatory dialogue: female spiders sing during copulation

bruner854 — 2006-08-26T18:53:19Z

Female signaling to the male during copulation has seldom been studied, but may be common in a variety of animals. Females of the spider Physocyclus globosus sing during copulation. Singing tends to occur when the male squeezes the female with his powerful genitalia (whose muscles are probably the strongest in his body); it apparently induces him to loosen this squeeze. When a female mated with two males, the male that responded more consistently to her singing by loosening was “rewarded” by fathering a greater proportion of her offspring. Greater numbers of squeezes also correlated with increased paternity. This is the first study to document apparent communication between male and female during copulation and show that it has reproductive consequences for the male. It thus opens a new field of inquiry regarding male-female sexual interactions, and confirms (once again) that females are more active in sexual interactions than previously appreciated.

A functional perspective on sexual selection: insights and future prospects

bruner854 — 2006-08-26T18:50:50Z

Studies of sexual selection in animals have traditionally focused on exaggerated male sexual traits that are used either as advertisements for attracting females, or as weapons in fights with other males over access to females. We review a growing literature showing how physiology and whole-organism performance (which includes phenomena such as locomotion or biting) play important roles both in determining the outcome of fights between males, and in constraining or promoting the expression of male sexual characters. For example, individual endurance capacities appear to be important determinants of victory in fights between males in several animal taxa. In some cases, performance abilities are linked to male displays, such that males might be able to glean information on another male’s fighting ability from his display. We also discuss several avenues for future research where greater consideration of physiological processes might help us to better understand how sexual selection operates.

Vocal mimicry by a passerine bird attracts other species involved in mixed-species flocks

bruner854 — 2006-08-26T18:50:00Z

Avian vocal mimicry has sparked both a great amount of interest and an equal amount of frustration, as researchers have often been unable to demonstrate the adaptive benefits of this behavior. While it is tempting to think that mimicry of other species influences the behavior of those species to benefit the caller, this has rarely been shown. We studied mimicry in the greater-racket tailed drongo (Dicrurus paradiseus), a frequent member of mixed-species flocks in the tropical rainforest of Sri Lanka. We found that drongos mimic the songs of other species at a high rate when they are outside of flocks. We then performed a playback experiment that showed that song mimicry was attractive to other species. Drongos benefit from associating with other species by catching insects that those species disturb and/or by stealing food from them. Thus, we suggest that mimicry can be adaptive for drongos by manipulating the behavior of other species.

Evaluation of predation risk by a caterpillar using substrate-borne vibrations

lopierce — 2006-09-13T18:24:31Z

Detection of predators and defensive responses are critical for the survival of most organisms. In this study, we determined whether caterpillars, which defend themselves from some predators by hanging on a silk thread, can detect predator threats and distinguish between different predators, other herbivores, and abiotic factors. Further, we determined how caterpillars distinguish among these. The hanging behavior of the caterpillars was exhibited in response to invertebrate predators (wasps and stink bugs) rather than to other herbivores, birds, or abiotic factors. Caterpillars distinguish among these by perceiving their vibrations that travel through plant leaves. The length of the silk thread produced by caterpillars in response to wasps was greater than that produced in response to stink bugs. Our results show that caterpillars are able to distinguish among the cues produced by abiotic factors, competitors and predators and respond specifically, in accordance with the potential risk embodied by a predator.

Sexually dimorphic grooming in bison: the influence of body size, activity budget, and androgens

lopierce — 2006-09-13T18:36:50Z

Sexual selection has favored both large body size and reduced grooming rates in male American bison. The ‘programmed grooming’ model proposes that an internal timing mechanism regulates tick-defense grooming in wild mammals. Sexually dimorphic males should groom less than smaller females for two reasons: (1) smaller animals suffer higher costs of parasitism and compensate by grooming more (body size principle), and (2) breeding males reduce grooming to maintain high vigilance for rival males and receptive females (vigilance principle). In bison, we found that body size and vigilance effects worked independently and additively to produce sexually-dimorphic grooming. Female grooming rate increased from 2-5 times greater than male grooming before the breeding season (rut) to 5-40 times greater than males during the rut. Breeding males groomed at only 7-40% of their pre-rut grooming rate. The suppression of grooming in rutting males was caused by elevated testosterone, rather than by conflicting time budgets.

Fighting for harems: assessment strategies during male-male contests in the sexually dimorphic Wellington tree weta

lopierce — 2006-09-14T18:11:00Z

Male animals often fight each other for mating access to adult females. Fights are often settled via ritualized display because actual fighting can be costly in terms of energy expenditure, injury or even death. In other cases, contests are settled with escalated brawls. In both cases it is important for the participating individuals to accurately assess a rival’s fighting ability so they can back-out before it gets too dangerous. It is not surprising that larger males tend to be better fighters and win most fights. But how do males assess their own fighting ability or that of their rivals, especially if they are closely matched? Mathematical theory suggests three ways: the energetic war of attrition, the sequential assessment model and the cumulative assessment model. I tested these models using the Wellington tree weta (Hemideina crassidens), a very large insect native to New Zealand. Male tree weta use their enormous mandibles as weapons in escalated fights for access to adult females. My data support the cumulative assessment model which suggests males continue to fight until they receive a certain amount of abuse from a rival.

Suppression of escape behaviour during mating in the cricket Acheta domesticus

lopierce — 2006-09-14T18:03:19Z

How does an animal decide what behaviour to perform when facing conflicting information from its environment? For example, information from the same mechanosensory inputs can trigger escape or mating behaviour in the cricket. We would like to determine how a cricket chooses which behaviour to perform, and how behavioural context may play a role in this decision-making process. To do this, we mechanically stimulated isolated male crickets with a small paintbrush and found that they responded with escape behaviours such as running, jumping or kicking. We then stimulated these same males after they had contacted a female and began mating behaviour and found that their escape responses were suppressed. We determined that physical, or chemosensory, contact between the male and female is required for this behavioural switch from escape to mating and that males must have visual contact with the female for this behavioural switch to be fully expressed.

Female swordtail fish use chemical cues to select well-fed mates

lopierce — 2006-09-14T18:35:55Z

The nutritional state of a potential mate is important since poor nutrition can be related to reduced sperm quality, low sperm quantity, and sexually transmitted diseases. In this study we show that female swordtail fish, Xiphophorus birchmanni, use information encoded in pheromones to select mating partners. Females of this species prefer chemical cues produced by males that are well fed over cues from food-deprived males. The females, however, showed no preference for odours of other well-fed females, which suggests that they respond to a nutritional-dependant mating signal, not simply to food excretions that could be produced by either sex. These results show that well-fed males can display their ability to acquire food to potential mates simply by releasing a pheromone, and that females use this information in selecting their mating partner.

Extraterritorial forays are related to a male ornamental trait in the common yellowthroat

lopierce — 2006-09-14T18:21:19Z

In many birds, females have young sired by neighbouring males, even though they are paired to another male. Little is known about the behaviours males and females use to seek (or avoid) copulations with these “extra-pair” partners. Our previous research on common yellowthroats (Geothlypis trichas) showed that males with larger black facial masks sired more young on neighbouring territories. Here we used radio-tracking to see how movements of birds off their territories related to mask size. We found that females only visited neighbouring males when they were fertilisable, and they usually visited males with larger masks than their own social mate. In contrast, males visited territories where the female was fertile and the resident male had a smaller mask than their own. The pattern of these visits suggests that both males and females are involved in seeking copulations with neighbours and they seek mating opportunities relative to mask size.

Spatially and temporally structured avian brood parasitism affects the fitness benefits of hosts' rejection strategies

lopierce — 2006-09-14T18:35:17Z

Cuckoos and cowbirds sneak eggs into nests of other species, and while many cuckoo hosts can spot the mimic parasite eggs, cowbird hosts typically do not reject the often odd-looking cowbird egg. We wondered how much individual females in two such non-rejecter cowbird host species, prothonotary warblers and red-winged blackbirds, would benefit if they were to become rejecters. We tracked the breeding activities of individually colorbanded female warblers and blackbirds and found that females who had already served as hosts to cowbirds in a prior year were more likely to be parasitized in a subsequent year, too. Our mathematical calculations showed that if such repeated cowbird parasitism is associated with a delay in the fitness benefit of rejecting cowbird eggs, then repeated misfortune with cowbird eggs may actually delay the evolution of effective antiparasite strategies in these and perhaps other host species.

Signalling and phosphorus: correlations between mate signalling effort and body elemental composition in crickets

lopierce — 2006-09-14T18:41:04Z

Phosphorus and nitrogen are limited in many ecosystems. Reducing their quantity in food appears to stifle invertebrate growth and reproduction. We hypothesized that an imbalance and a scarcity in nitrogen and/or phosphorus may cause variation in behavior. We investigated whether there was a relationship between long-distance mate attraction signalling of male field crickets and the amount of nitrogen and phosphorus found in their bodies. Calling behavior was strongly and positively correlated with the amount of phosphorus in the body, suggesting that the ability to obtain and/or retain phosphorus may influence variation in condition-dependent traits. We evaluate proximate hypotheses to account for the correlation. Overall, a stoichiometric perspective may help resolve several important problems in animal behavior.

Mechanisms of maternal investment by communal prairie voles (Microtus ochrogaster)

lopierce — 2006-10-18T18:00:25Z

Our objective was to explain our previous observation that the shared rearing of young by two mothers (i.e., plural breeding), but not a mother and female helper (i.e., singular breeding), enhances the weight gain of prairie vole (Microtus ochrogaster) young. We determined that young reared by singular and plural breeders are left alone 10 times less than and experience slightly warmer nests than young reared by single mothers. Young reared by plural breeders drink a greater volume of slightly more concentrated milk than young reared by single mothers. Young reared by singular breeders drink slightly more concentrated but not a greater volume of milk than young reared by single mothers. Moreover, young reared by singular breeders are groomed more than young reared by plural breeders and single mothers, but the differences are minimal. Most likely, improved thermoregulation and increased access to milk explain our previous observations.

Resource distribution and social structure in harem-forming Old World fruit bats: variations on a polygynous theme

lopierce — 2006-10-18T18:09:19Z

The prediction that the spatial dispersion of resources important to females should dictate female dispersion and male mating tactics is untested in harem-forming bats. We investigated the relationship between the spatial distribution of available roosts, harem size, male roost fidelity and the strength of social associations in two species of Old World fruit bats in the genus Cynopterus. We used radiotelemetry to study the daily movements of individuals and groups among roosts at two sites in peninsular Malaysia. High correspondence between the distribution of roost-sites, harem size and male behaviour supported the prediction that clumped resources would promote female aggregation and high roost fidelity in males. However, significant interspecific differences in the strength of male-female associations suggested that, where roosts are abundant and similar in quality, regardless of spatial distribution, the potential for males to monopolize mates depends on whether females switch roosts with, or independently of, males.

The nose knows: minnows determine predator proximity and density through detection of predator odours

lopierce — 2006-10-18T18:19:02Z

Prey animals have to spend time and energy to avoid being eaten by predators. However, while doing so, they cannot feed or reproduce. So, it would be beneficial for prey to develop efficient risk assessment abilities to increase time spent foraging and reproducing and decrease time spent avoiding predators. Prey that can match their intensity of antipredator behaviours to the threat they are exposed to, are said to be responding in a ‘threat-sensitive manner’. Many animals have been shown to respond to threats in such a way. Fishes, for example, can use concentration of odours of their predators to assess the risk they are exposed to. In our present study, we demonstrated that minnows coexisting with pike, have the ability to assess the density and proximity of the pike in their environment based on their odours only. These results demonstrate a high level of sophistication of predator recognition by prey species.

Experimental evidence of homing to site of incubation by mature sockeye salmon (Oncorhynchus nerka)

lopierce — 2006-10-19T13:21:37Z

Salmon and related fishes are famous for their ability and tendency to return from long migrations to breed at the same stream where they were spawned years earlier. However, the spatial precision of this homing ability has not been determined. To do so, we exposed larval salmon to changes in water temperature to induce marks on their ear bones before the embryos hatched. They were then buried in a small pond, connected to a creek by about 27 m of tiny creek. Four years later a number of the fish in the pond had marked otoliths and none of the fish sampled in the creek were marked. This demonstrated exceptionally fine-scale homing, though we cannot be sure that all the marked fish homed back to the pond. The ability to home to specific sections of a creek means that salmon populations can also evolve on very fine spatial scales.

Sexual selection in wild baboons: from mating opportunities to paternity success

lopierce — 2006-10-19T13:29:40Z

In mammals, high-ranking males usually mate more than lower-ranking males. However, the males that are observed to mate the most do not automatically produce the most offspring, for a variety of reasons. We performed a genetic analysis of paternity in a well-studied wild baboon population on a large sample across several groups and twelve years. We found that high-ranking males produced more offspring than lower-ranking males, but that male density and male rank stability also affected offspring production. We found little evidence for successful surreptitious mating, and no clear evidence of sperm competition or sperm selection. However, we found clear evidence that high-ranking males exhibited mate choice, concentrating their mating efforts on females experiencing conceptive, rather than non-conceptive cycles.