A farewell to arms: males with regenerated claws fight harder over resources

Physical strength and resource value are two key determinants of fighting success in most species. We investigated the role that resource value plays in determining fight outcome for a territory centred on a burrow in a fiddler crab, Uca annulipes. Males fought harder (escalated fights) for a territory during the mating period (when the burrow is also used for mating and breeding) than in the nonmating period (when it has value as a shelter). In both periods, having a burrow also allows access to the surrounding mudflat surface, where crabs forage. We confirmed earlier studies showing that males with regenerated claws are weaker competitors that are disproportionately evicted from their burrow during the nonmating period. Unexpectedly, however, males with a regenerated claw were not disproportionately evicted during the mating period. Fights at this time were also more escalated. We suggest this is because, when the disputed resource is also required for breeding, even weak males need to obtain and defend a burrow if they are to accrue any fitness. During the mating period, individuals with low resource-holding potential can improve their chances of mating if they escalate fights for burrows.

► We compared fiddler crab fighting behaviour during mating and nonmating periods.
► We confirm that males with regenerated claws are weaker competitors.
► Regenerated clawed males however, were not disproportionately evicted during the mating period.
► Weaker males may therefore improve their chances of mating by escalating fights.