Mating Behavior of Uca lactea perplexa (Decapoda: Ocypodidae)

Some fiddler crab species (genus Uca) are known to mate either on the surface or underground. Here we describe these two modes of mating in Uca lactea perplexa and compare them with these mating modes in other ocypodid crabs. All surface matings, which lasted from 1.2-5.1 min, occurred near the burrow entrance of the female. There was a weak, but significant, positive correlation between the sizes of surface-mating males and females. About 65% (44/68 pairs) of the males were larger, and 32% (22/68) smaller than their mates. Four of 36 (11%) females that were collected after surface mating and held in the laboratory ovulated fertile clutches. Females mated underground after they left their own burrows and either preceded or followed courting males into their burrows where they stayed, mated, and ovulated a clutch of eggs. Males significantly more often attempted to attract females to follow (67/75 courtships, 89%) rather than precede (8/75, 11%) them into their burrows, and relatively more of 44 females that mated in burrows of males followed (64%) than preceded (36%) their mates underground. However, this difference between the relative frequencies of the two kinds of courtship and their success suggests that females are more likely to mate in burrows that they enter first. All females that mated underground ovulated fertile clutches. Although individual males attempted both surface and underground mating, males that mated underground were larger than those that surface-mated. Unlike surface matings, they also were larger than their mates. The two different modes of mating, and sequences that lead to underground mating in U. lactea perplexa, are found in related ocypodid crabs, but the conditions governing their use are not yet clear.