The evolution of male traits in social insects

Pair formation in social insects mostly happens early in adult life and away from the social colony context, which precludes promiscuity in the usual sense. Termite males have continuous sperm production, but males of social Hymenoptera have fixed complements of sperm, except for a few species that mate before female dispersal and show male-fighting and lifelong sperm production. We develop an evolutionary framework for testing sexual selection and sperm competition theory across the advanced eusocial insects (ants, wasps, bees, termites) and highlight two areas related to premating sexual selection (sexual dimorphism and male mate number) that have remained understudied and in which considerable progress can be achieved with relatively simple approaches. We also infer that mating plugs may be relatively common, and we review further possibilities for postmating sexual selection, which gradually become less likely in termite evolution, but for which eusocial Hymenoptera provide unusual opportunities because they have clonal ejaculates and store viable sperm for up to several decades.