Alternative mating strategies, partial sibmating and split sex ratios in haplodiploid species

It is shown that when females can adjust their offspring sex ratios conditionally to the identity of their mates, i.e. sib or non-sib, split sex ratios are expected. These split sex ratios result from variation in relatedness between females and their daughters. Haplodiploid females' relatedness to their daughters increases as their relatedness to their mates increases. Therefore, sibmated females' optimal progeny sex ratio is more female biased than that of outbred females. Inbreeding depression that can result from complementary sex determination (CSD) is also considered. The genetic load caused by CSD can be so costly to sibmated females that they switch to the production of males only. The evolutionarily stable sex ratios for a sibmating model is found to be of a weak type. These weak equilibria and split sex ratios can lead to high variation about the mean and are an incentive for further studies on sex ratio variation in conjunction with mating behaviour. The occurrence of split sex ratios in haplodiploid taxa is important because it favours the evolution of eusociality. Partial local mating and alternative mating strategies can thus eventually lead to the evolution of eusociality.