Haplodiploid sex ratios and the mutation rate

Abstract

Deviations from a 1:1 sex ratio in species with haplodiploid genetics are well known and sociobiologists have produced various explanations1–8, all of which ignore the effect of mutations on haploid viability. Lethal recessive mutations can significantly increase male (haploid) mortality and their effect should be estimated to provide the appropriate null hypothesis with which to compare observed sex ratios before considering any more complex, sociobiological hypothesis. Prospective maternal care4 and local mate competition1,2 will also affect sex ratio, but increased haploid mortality due to mutation rate is the only effect common to all haplodiploid species. Using emergence data for some parasitoid species, the rate of mutation to lethal recessives is estimated to be about 0.035 per genome per generation giving a differential haploid mortality of 10%.