Underground mating in the fiddler crab Uca tetragonon: the association between female life history traits and male mating tactics

Brood size and other life-history traits of females affect male investment in mating. Female Uca tetragonon, producing relatively small broods, were a ttracted to the burrows of males for underground mating (UM) while carrying eggs, Most UM females released larvae and ovulated new broods during the p airing, averaging 3.9 days. While a female was incubating one brood, anothe r brood was developing within the ovaries because the females were feeding adequately during incubation. These findings suggest that in U. tetragonon, a small-brood species, females increase the total number of broods produce d by breeding continually. In contrast, in large-brood species, feeding by ovigerous females is relatively brief and not enough to prepare the next br ood during incubation, inducing temporal separation between incubation and brood production. Unlike females in other ocypodids where females with larg e broods remain in thr breeding burrows of males, most female U. tetragonon left the male after UM. Wandering in female U. tetragonon after the pairs separate may occur because their small broods are adequately protected by a n abdominal flap. Relative brood size probably determines the vulnerability of the incubated broods to the females' surface behavior. Hence, male repr oductive success in large-brood species may decrease greatly if males expel their mates after ovulation, although this is not necessarily so in small- brood species. Whether the male drives away the female or not may depend on which behavior within tither small- or large-brood species yields the grea ter male reproductive success. In U. tetragonon some females extruded eggs in their own burrows after surface mating as well as in males' burrows afte r UM. It was unclear whether females chose a male with a larger burrow as a n UR I mate unlike several large-brood species. Burrows of both UM males an d ovigerous females in U. tetragonon were relatively smaller than those in some large-brood species, indicating that incubation of small broods does n ot require large burrows. Rather than benefits of UM by female choice, wand ering resulting from intersexual conflict, and sperm competition may explai n why some females mate in males' burrows in this small-brood species. (C) 2000 Elsevier Science B.V. All rights reserved.