Male mate choice and insemination success under simultaneous versus sequential choice conditions

Theory predicts that males should be choosier when encountering potential mates simultaneously rather than sequentially because there is no opportunity cost. Consequently, when mate encounter rates vary across space and time males might benefit from plasticity in mate preferences to match prevailing social conditions, preferring high-quality mates when females are encountered frequently and showing no preferences when females are encountered rarely. Here we investigated how encounter type (i.e. simultaneous or sequential) alters male mate preferences for female size in the mosquitofish, Gambusia holbrooki. We found that male mosquitofish attempted to mate with a relatively large female significantly more often than a relatively small female when presented with two females simultaneously. In contrast, males showed no such preference when sequentially presented with two females. Further, males attempted more copulations with absolutely larger females irrespective of encounter type. Despite these behavioural patterns, however, neither male insemination success nor the number of sperm transferred was influenced by female size or the encounter type. Our results provide support for the prediction that male mate choice is stronger during simultaneous choice encounters, but suggest that insemination success in G. holbrooki is partly under female control.