Intragroup and intragenomic conflict over chemical defense against predators

Abstract

Insects are often chemically-defended against predators. There is considerable evidence for a group-beneficial element to their defences, and an associated potential for individuals to curtail their own investment in costly defence whilst benefitting from the investments of others, termed “automimicry”. Although females in chemically-defended taxa often lay their eggs in clusters, leading to siblings living in close proximity, current models of automimicry have neglected kin-selection effects, which may be expected to curb the evolution of such selfishness. Here we develop a general theory of automimicry that explicitly incorporates kin selection. We investigate how female promiscuity modulates intragroup and intragenomic conflicts over investment into chemical defence, finding that individuals are favoured to invest less than is optimal for their group, and that maternal-origin genes favour greater investment than do paternal-origin genes. We translate these conflicts into readily-testable predictions concerning gene-expression patterns and the phenotypic consequences of genomic perturbations, and discuss how our results may inform gene discovery in relation to economically-important agricultural products.