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, oc curred near the burrow entrance of the female. There was a weak, but s ignificant, positive correlation between the sizes of surface-mating m ales and females. About 65% (44/68 pairs) of the males were larger, an d 32% (22/68) smaller than their mates. Four of 36 (11%) females that were collected after surface mating and held in the laboratory ovulate d fertile clutches. Females mated underground after they left their ow n burrows and either preceded or followed courting males into their bu rrows where they stayed, mated, and ovulated a clutch of eggs. Males s ignificantly more often attempted to attract females to follow (67/75 courtships, 89%) rather than precede (8/75, 11%) them into their burro ws, and relatively more of 44 females that mated in burrows of males f ollowed (64%) than preceded (36%) their mates underground. However, th is difference between the relative frequencies of the two kinds of cou rtship 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 su rface 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 seque nces 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.