Long searches for male-defended breeding burrows allow female fiddler crabs, Uca crenulata, to release larvae on time

When individuals benefit from highly selective mate choice and search costs are negligible, they should sample all or at least many potential mates. Most animals sample just a few mates, presumably because search costs override the benefits of lengthy searches. Observations on mate-searching female California fiddler crabs, Uca crenulata, showed that these crabs conducted much longer searches than have been reported for other animals. Moreover, large and small females used different sampling strategies. Searches may be long in this species because females use multiple criteria to select mates and benefit from finding a burrow of the right size. They chose mates that (1) were near to their size (2) had small claws given their body size, and (3) defended long burrows with entrances that matched the size of the female. Females sampled many burrows that did not match their size, indicating that they assessed burrows on contact and not before. An experiment examining why females use male burrow diameter as a mate choice criteria revealed that burrow opening diameter, or a correlate, affected incubation duration and therefore release time of larvae. Larvae were successfully released during high-amplitude nocturnal tides only when females incubated in burrows that allowed the larvae to exit the estuary swiftly and thus reduce predation risk, but not when females incubated in burrows that were too wide or narrow. The effect of burrow aperture on incubation duration may explain why females sampled many male burrows as they searched for a mate and why females of different size classes selected and sampled differently.