MATE SEARCHING BY MALES OF THE INTERTIDAL AMPHIPOD COROPHIUM VOLUTATOR (PALLAS)

In this paper we describe the mate-searching behaviour of male Corophi um volutator (Pallas), an intertidal amphipod. We expected male choice of mates because males invest in mating by mate guarding, and also be cause adult females greatly outnumber adult males at our study site. W e predicted that males would choose large females carrying many eggs a nd females close to moulting or close to being receptive. We found tha t individual males ''assessed'' an average of ca. 5 females in their r espective burrows before entering the burrow of a prospective mate. Ma les were more likely to cohabit with females that were close to being receptive than with females that were far from being receptive. Over t he season, the size of mate-searching males declined, whereas the numb er of females encountered by males increased, which may relate to the seasonal distribution of receptive females. However, there were no dif ferences in size between paired and unpaired females regardless of tim e of season. Our results support mate discrimination by males based on one criterion (stage of receptivity). The proximate and ultimate caus es of the biased sex ratios of C. volutator need to be determined befo re other predictions based on mate-choice theory can be made.