Time constraints and multiple choice criteria in the sampling behaviour and mate choice of the fiddler crab, Uca annulipes

Active female sampling occurs in the fiddler crab Uca annullipes. Females sample the burrows of several males before remaining to mate in the burrow of the chosen partner. Females time larval release to coincide with the following nocturnal spring tide and must therefore leave sufficient time for embryonic development after mating. Here we show how this temporal constraint on search time affects female choosiness, We found that, at the start of the sampling period (when time constraints are minimal), females selectively sample the larger males in the population. Towards the end of the sampling period (when the temporal constraints increase the costs of sampling), females are less selective. Furthermore, we suggest that the number of males sampled (and other indices of ''sampling effort'') may not be reliable indicators of female choosiness and may not reflect the strength of female mating preferences under certain conditions. Burrow quality also emerged as an important criterion in final mate choice. Burrow structure potentially influences reproductive success, and mate acceptance based on burrow structure appears to involve a relatively invariant threshold criterion. Since there is no relationship between male size and burrow quality, females are using at least two independent criteria when choosing potential mates. We envisage mate choice as a two-stage process. First, females select which males to sample based on male size. They then decide whether or not to mate with a male based on burrow features. This sampling process explains how two unrelated variables can both predict male mating success.