The battle of the sexes? Territory acquisition and defence in male and female fiddler crabs

Abstract

In many territorial species males invest substantially in weapons, which they use in fights to acquire and maintain territories that ultimately give them access to females. Females often live within male territories or in female-only areas that are segregated from males. Under these circumstances, females do not have to compete directly with males for space, and in the context of territory acquisition and defence there is therefore no cost to being weaponless. In fiddler crabs, however, weaponless females hold territories among well-armed males. How do they do this? Observations and replacement experiments were carried out on Uca annulipes to determine how males and females acquire and defend territories. Weaponless females were as capable as well-armed males of both acquiring and defending a burrow. Females acquired burrows by seeking out empty ones, while males acquired them by evicting male and female burrow owners. After acquiring a burrow, males mainly fought with male neighbours and females with female neighbours. Both sexes were equally likely to be evicted from their burrow and the likelihood that they remained on their territory for 24 h or more was the same. Males and females thus used different strategies of burrow acquisition and defence, and the male strategy appeared to be more costly. We discuss possible explanations for these differences