Precopulatory mate guarding in the hermit crab Pagurus middendorffii (Brandt) (Decapoda: Paguridae): effects of population parameters on male guarding duration

Abstract

Abstract The effects of sex ratio, competitor size, and the encounter rate with females on the duration of male precopulatory guarding were tested in the hermit crab Pagurus middendorffii (Brandt, 1851) to examine how guarding duration varies in relation to social factors. Size and owner advantages in male–male contest competition were also examined. Larger and owner males were stronger competitors than smaller and challenger males, respectively. Males guarded females earlier and, consequently, longer when the sex ratio was more male biased, when size differences between competitor sizes were small, and when encounter rates were low, which are consistent with theoretical predictions. However, contrary to these predictions, small males did not guard earlier than large males when size differences were large. These results suggest that males might assess not only the operational sex ratio based on the encounter rate with females but also their competitive ability relative to other males and the possibility of successful guarding.