Genetic relatedness and evolution of insect sociality

Abstract

Genetic relatedness is a vital concept in the study of the evolution of social behaviour because it can be used to predict gene transmission into future generations. Any models using genetic relatedness to predict the course of social evolution have to take into account that this relatedness, when defined as genotypic regression, is affected by selection and that the evolution also depends on specific assumptions concerning the cost/benefit ratios. In this paper these problems are shown to exist in recent studies examining the evolution of worker behaviour in insects; these studies are reanalysed using allele frequency models, and the results compared with those from other models. It is shown that cyclic inbreeding (alternating outbred and inbred generations) can favour worker evolution in diploid populations but is a necessary condition only within a very limited range of the cost/benefit ratio. Male-haploid models show that both female and male workers evolve more easily if they can manipulate the brood produced by the queen by biassing the brood sex ratio in favour of females (the optimal proportion of females is ca. 0.75). The threshold for female workers to evolve is also lowered if they are allowed to produce some of the colony's male offspring (which arise from unfertilized eggs), in which case the optimal brood sex ratio becomes closer to 1:1. It is apparent that the two factors — sex-ratio bias and worker-produced males — are also important in the comparison of worker evolution in male-haploid and diploid insects.