A comparative study of virginity in fig wasps

In haplodiploid species, the presence of unmated (virgin) females that can produce only haploid male offspring may have several important effects on a range of phenomena such as reproductive strategies, the transmission of parasitic chromosomes and the evolution of eusociality. The strength of these effects will depend upon the prevalence of virgin females. Two theories make conflicting predictions concerning the importance of factors that should be associated with increased levels of virginity, emphasizing either the degree of local mate competition or brood size. In this paper, a model is presented which predicts that, under conditions of local mate competition, the prevalence of virginity should be negatively correlated with the average number of offspring developing in a patch. The different predictions were then tested using data from 53 species of fig wasps representing 15 genera from four continents. Across species, the estimated prevalence of virginity was significantly inversely related to brood size, but showed no correlation with sex ratio (an index of local mate competition), supporting the predictions of our model. Qualitatively similar results were found when a formal comparative analysis was carried out using a morphologically and molecularly based phylogeny.