ABS Media Information

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

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.