Abstract
Abstract: In the precopulatory phase, a male hermit crab Pagurus filholi guards a female by pinching the rim of the female's shell with his cheliped. We conducted two experiments to clarify the influences of the male-female size ratio and the sex ratio on the duration of precopulatory mate guarding. Larger males guarded females earlier and, consequently, performed longer precopulatory guarding than smaller males. Possible causes for these differences may include loading constraints(i. e. larger males appear to have a lower cost of mate guarding)and a size dependent conditional mating strategy(i. e. smaller males copulate without performing precopulatory mate guarding). Males also guarded females earlier and longer as the sex ratio became more male biased. When the male: female ratio increases, the chance of finding a female that will soon spawn may decrease, and intrasexual competition for the few receptive females may increase; under such circumstances, males may guard females that are not yet ready to mate. Relative male size and the sex ratio significantly affected the amount of time a male guarded a female. These results suggest that males might assess both female size and the sex ratio when deciding when to guard a female.
