Mantella laevigata was investigated in the first long-term field study of anuran behavior in Madagascar. These small, diurnal, semi-terrestrial and aposematically colored frogs are mostly free of predation as adults, which has allowed them to cluster around limiting resources, and evolve a complex social system. For this, my dissertation work, I set out to explore the social and reproductive behavior of this little known species. 925 hours of observations were conducted on marked animals over the course of two wet seasons in Northeastern Madagascar. Several behaviors, some of which are stereotyped and largely invariable, but most of which are context-dependent, were discovered.

Males employ one of three reproductive/territorial strategies, the most successful of which is to defend water-filled treeholes or broken bamboo (wells), which are used as oviposition sites by pairs. Males emit loud, double-note advertisement calls from elevated perches in their territories. During 215 fights observed between males, they engaged in male-male amplexus, belly-to-belly wrestling, tumbling, leaping on to one another, chasing and calling; such fights often last more than half an hour.

Courtships follow a highly stereotyped sequence, including a “chinning” behavior not before observed in anurans. When a female approaches a calling male, his vocalizations drop in volume as he approaches her, and he places his throat on the top of the female’s head or dorsum. The male then leads the female to a potential oviposition site. Females often reject oviposition sites, at which point the stereotyped chinning and leading behavior resumes.

Successful courtships result in a single egg being laid above the water line. This is the lowest known clutch size for an anuran without direct development, and is suggestive of a high degree of parental care. Tadpoles cannibalize conspecific eggs. Their most common source of food is fertilized eggs, which are the result of courtships. Facultative maternal care occurs when mothers return, alone, to the wells they mated in, and deposit a single, unfertilized egg for their tadpole to eat.

Males and females have distinct interests during courtship and reproduction. Individuals of both sexes scout for oviposition sites when they are neither courting nor receptive to courtship. Males do not take females to wells which contain individuals or clutches of potential competitors, such as the two sympatric, well-breeding microhylid frog species. Males also discriminate against wells containing predatory crane-fly larvae, (Limonia renaudi Alexander, Tipulidae), which were often observed eating the eggs of M. laevigata and other well-breeding frogs. Females discriminate against wells that already contain M. laevigata tadpoles, which would attempt to cannibalize any eggs laid.

Courtships were most often abandoned by females after they investigated potential oviposition sites, and by males to engage in territorial defense. The quality of the oviposition site thus appeared to be critical to reproductive success, and a female choice experiment designed to discriminate between female choice of oviposition site (“good resources”), of unique male calls (“good genes”), and calls of different lengths (“good current condition”) failed to falsify this hypothesis. Females did not discriminate between males, or call length, but were significantly more likely to approach calls emanating from high-quality territories. I propose that anurans that breed in restricted, transient water bodies are a particularly likely group to display the evolution of mate choice for territory quality for three broad reasons:

1. The near universality of external fertilization in anurans means that the mating site is equivalent to the oviposition site, and is therefore where the offspring will develop (except in rare cases in which offspring are transported).
2. Derived breeding systems in which the young are traceable, such as in well- breeders, allow parents to identify their offspring on the basis of location.
3. Well-breeding, probably an adaptation to protect against predation, generates new risks, such as desiccation of eggs. Females are under pressure to find a place on land which has a reliable water-source, and it is often these oviposition sites, rather than food, which is limiting for such populations. Experimental results not reported here demonstrate that, in M. laevigata, oviposition sites do limit population size. Female choice for the limiting resource is predicted under these circumstances.

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Recent Founders’ Award Winners:
1999 Daniel Wiegmann and Douglas Wiegmann
1998 Renee Robinette and James Ha