PARTIAL LOCAL MATE COMPETITION AND THE SEX-RATIO - A STUDY ON NON-POLLINATING FIG WASPS

In many species, mating takes place in temporary patches where only a small number of females produce offspring. In this situation Local Mat e Competition (LMC) theory predicts that the optimal sex ratio (define d as proportion males) should become increasingly female biased as the number of females contributing offspring to a patch decreases. Howeve r, in a large number of these species, some mating is also likely to o ccur away from the natal patch (termed partial LMC). In this case the degree of LMC is reduced, and theory predicts a relatively less female biased sex ratio. We tested these two predictions with field data fro m 17 species of New World non-pollinating fig wasps representing three genera. We present a model which suggests that the average number of females ovipositing in a fruit (i.e. patch) is positively correlated w ith the proportion of fruit of a given tree species in which that spec ies of wasp occurs. Across species, the overall sex ratio was positive ly correlated with the proportion of fruit in which that species occur s. Furthermore, the males of some species are wingless, and in these s pecies all mating must take place before females disperse from their n atal fruit. In contrast, the males of other species are winged, and in these species mating may also take place away from the natal fruit. S pecies with winged males had less female biased sex ratios than specie s with wingless males that occurred in a similar proportion of fruit. Finally, the correlation between sex ratio and the proportion of fruit in which a species occurs was also observed within species when compa ring between the fruit crops of different trees. This suggests that in dividual females facultatively adjust the sex ratio of their offspring in response to variable LMC.