Molecular signatures of kin selection: Are sterile caste-associated genes nearly neutral?
Anna M Chernyshova, Anna M Chernyshova , Graham J. Thompson
Biology Department, Western University, London, Ontario, Canada; Biology Department, Western University, London, Ontario, Canada ; Biology Department, Western University, London Ontario Canada
In termite societies, sexual kings and queens are highly specialized for reproduction, while more-or-less sterile workers and soldiers perform non-reproductive roles that are associated with colony growth, colony maintenance and defence. Workers and soldiers can therefore be considered reproductively altruistic because they labour to help produce large numbers of non-descendent kin (i.e., siblings, half-siblings, etc.) at the expense of their own direct fitness. The evolution of altruism, in any taxon, is therefore intriguing because in theory it requires 'genes for altruism' to evolve indirectly via selection on reproducing relatives, who carry, but do not express these genes. Therefore, the notion of indirect selection is fundamental to our understanding of social evolution, yet surprisingly, we know little about how real genes might respond to this type of selection within living populations. The 'nearly neutral' hypothesis predicts that genes indirectly selected for subfertility may experience relaxed adaptive molecular evolution, relative to genes directly selected for reproduction. If so, we expect that the ratio of non-synonymous to synonymous substitutions will tend towards a neutral value of '1', relative to loci under direct selection for which this ratio will deviate from neutrality in either a purifying or positive direction. Here, we exploit newly available RNA sequence data for the eastern subterranean termite to test key predictions from the nearly neutral hypothesis.