Measuring the heritability of sex ratio in a social insect

Theories for how social behaviour evolves in animals, which represents a fundamental issue in evolutionary ecology, assume that social behaviour is influenced by genes. This critical assumption has rarely been tested, and very little is known about the genes underlying social traits. Experiments in which researchers subject traits to artificial selection, combined with modern genetic and genomic techniques, can help pinpoint and identify genes for these traits. In future, my group seeks to conduct such experiments in the bumble bee Bombus terrestris, using sex ratio (the ratio of new queens to males) as the social trait of interest. Although the value of the sex ratio in social insects is well predicted by evolutionary models, as with other social traits very little is known about its genetic basis. However, to conduct this work we first need to establish that sex ratio is indeed underpinned by genetic variation, i.e. is heritable, since non-heritable traits cannot respond to either natural or artificial selection. In the proposed work I therefore seek to measure the heritability of sex ratio in B. terrestris. This species is uniquely suited to the proposed work because of its simple, annual societies, its amenability to laboratory rearing and breeding, and the existence of increasingly sophisticated genetic information on its genomic architecture. I will measure heritability by comparing the sex ratios produced by daughter queens with those produced by their mothers. A positive association between daughter and maternal sex ratios will establish heritability (which is formally estimated as twice the regression coefficient of this association). As well as addressing a fundamental issue in evolutionary ecology, this proposal is novel, because the heritability of sex ratio has not previously been measured in any social insect. For this reason, and because it should lead to a future project that would also be novel and fundamental, the proposed research should substantially advance the field.