Can beggars be choosers? Male mate choice in a fiddler crab

In most species the operational sex ratio is male biased, so females can be choosy when selecting a mate. Male choosiness, however, may also be beneficial, especially in species where female quality is variable, male mating investment is high and there is a high probability of attracting additional females. We investigated male choosiness in the fiddler crab Uca mjoebergi. Clutch size was positively correlated with female size. Since male mating investment is high (prolonged mate guarding), males would therefore benefit by mating with large females. Males were capable of discriminating between large and small females, and under both natural and experimental conditions they preferentially courted larger females. They did not, however, forego mating opportunities with small females, probably because the operational sex ratio was highly male biased, which limited their opportunity for attracting a second mate. Thus male U. mjoebergi not only engaged in competition for matings, but also showed mate choice.