More signalling for earlier mating: conspicuous male claw waving in the fiddler crab, Uca perplexa

The male courtship display of the fiddler crab Uca perplexa is a conspicuous claw waving that is directed at females to attract them to their burrows for mating. Like most other fiddler crabs, this species has an approximately biweekly reproductive cycle with mating spread over about 10 days. However, most mating takes place in the 3 days immediately preceding new and full moons. We examined the relation between the time males spend waving to females and the time they subsequently spend underground in their burrow, guarding their mates until they ovulate and then fertilizing their eggs. Early in the mating period, males courted females for about 3-5 s before the female entered their burrows, and males guarded these females for 3-5 days. During the 3 days of peak mating activity, courting time decreased significantly to about 2 s and guarding time decreased to about 1 day. This pattern cannot be explained by females preferring extended waving periods, decreased female choosiness towards the end of the mating period or variation in male waving over the mating period. We conclude that males of this species modulate their investment in courtship according to changing levels of female responsiveness to courtship.