Female remating rate and pattern of sperm use suggest intense sperm competition in Drosophila antonietae (Diptera: Drosophilidae)

Abstract

Sperm competition is conceived as a powerful selective force which acts on genes related to reproduction, promoting the evolution of reproductive adaptations and inter-population divergence that may ultimately lead to speciation. Such selective pressure is believed to be particularly strong in species from the Drosophila repleta group since females of most of these species are highly promiscuous. However, sperm competition is determined by many other factors far less explored than female remating rate; consequently, its actual intensity as a selective pressure continues to remain unknown across most taxa. In this paper, we aim to estimate the intensity of sperm competition in Drosophila antonietae, a South American species from the D. repleta group, by means of behavioural and genetic analyses. In sum, our results, while failing to reveal sperm precedence in twice-mated females, show that sperm competition is likely to occur and may strongly reduce males’ reproductive output. In addition, using highly polymorphic microsatellite loci, we confirmed a high incidence of multiple paternity in wild-inseminated females. We discuss the results within an evolutionary context comparing the mating system between D. antonietae and closely related species.