Summary

African mole-rats of the family Bathyergidae are a powerful model system for the study of both ultimate and proximate factors affecting reproductive skew in mammals. They exhibit a range of cooperative breeding strategies and differing degrees of skew, culminating in eusocial behavior in two or possibly more species. Mating preferences encompass both facultative inbreeding/outbreeding and obligate outbreeding, and result in common features, but also some clear differences between mole-rat species in how their social systems and skew are maintained. Recent genetic studies have revealed that, in the species studied so far, colonies may contain unrelated immigrants and therefore there is the potential for reproductive conflicts of interest, because all mole-rats are reproductively totipotent. In naked mole-rats (Heterocephalus glaber), extreme socially induced suppression of reproductive physiology is apparent in both sexes, and is best explained by a dominantcontrol model, rather than by staying or peace incentives. The Damaraland mole-rat (Cryptomys damarensis) exhibits suppression of reproductive physiology in females, but not males, and in this species skew may be maintained by a combination of dominant control and incest avoidance. Other social species lack specific physiological blocks to reproduction, and skew may be maintained by incest avoidance and other, as yet unknown, behavioral means.

Introduction

The African mole-rats of the family Bathyergidae have received much attention from sociobiologists since the discovery of eusociality in the naked mole-rat (Heterocephalus glaber: Jarvis 1981). Following the announcement by Jarvis & Bennett (1993) that another mole-rat species, the Damaraland mole-rat (Cryptomys damarensis), also fitted the classical definition of eusociality (i. e. reproductive division of labor, cooperative care of offspring, and overlap of generations: Michener, 1969), it became apparent that the Bathyergidae were a model system for the study of social evolution and extreme reproductive skew.