Patterns of sperm precedence and predictors of paternity in the Trinidadian guppy

Despite its widespread occurrence in animals, sperm competition has been st udied in a limited range of taxa. Among the most neglected groups in this r espect are internally fertilizing fish in which virtually nothing is known about the dynamics of sperm competition. In this study, we examined the out come of sperm competition when virgin female guppies mated with two males. Behavioural cues were used to ensure that each male mated once (with female cooperation) and that sperm were successfully inseminated at copulation. T wo polymorphic microsatellite loci were used to estimate the proportion of offspring sired by the second male (P-2) and the results revealed a bimodal distribution with either first or (more often) second male priority. The o bserved P-2 distribution differed from that expected under the 'fair raffle ' model of sperm competition. Random sperm mixing is therefore unlikely to account for the observed variance in P-2 in this study. A further aim of ou r study was to identify predictors of male reproductive success. Using logi stic linear modelling, we found that the best predictors of paternity were time to remating and the difference in courtship display rate between first and second males. Males that mated quickly and performed relatively high n umbers of sigmoid displays obtained greater parentage than their slower and less vigorous counterparts. Since females are attracted to high-displaying males, our results suggest that female choice may facilitate sperm competi tion and/or sperm choice in guppies.