Ancestral Monogamy Shows Kin Selection Is Key to the Evolution of Eusociality

Abstract

Close relatedness has long been considered crucial to the evolution of eusociality. However, it hasrecently been suggested that close relatedness may be a consequence, rather than a cause, ofeusociality. We tested this idea with a comparative analysis of female mating frequencies in 267species of eusocial bees, wasps, and ants. We found that mating with a single male, whichmaximizes relatedness, is ancestral for all eight independent eusocial lineages that weinvestigated. Mating with multiple males is always derived. Furthermore, we found that highpolyandry (>2 effective mates) occurs only in lineages whose workers have lost reproductivetotipotency. These results provide the first evidence that monogamy was critical in the evolution ofeusociality, strongly supporting the prediction of inclusive fitness theory.