Causes and consequences of incest avoidance in the cooperatively breeding mole-rat, Cryptomys darlingi (Bathyergidae)

A number of social mole-rat species maintain a strong reproductive skew (on ly one breeding pair in the group) solely through incest avoidance. Incest avoidance probably evolved for one of two reasons, namely for actually main taining a reproductive skew or, alternatively, to avoid high inbreeding dep ression. In the latter case a strong reproductive skew would result as a fo rtuitous by-product of the combination of a cloistral family life style of mole-rats and incest avoidance. We undertook breeding experiments in which the fertility of pairs of unrelated individuals were compared with that of pairs of double first cousins. Inbreeding depression was remarkably high an d an accompanying model suggests that it may be sufficient to support the i dea that strong incest avoidance evolved primarily to eliminate the costs o f inbreeding and subsequently facilitated the evolution of reproductive ske w.