REPRODUCTIVE SUPPRESSION IN SUBORDINATE, NON-BREEDING FEMALE DAMARALAND MOLE-RATS - 2 COMPONENTS TO A LIFETIME OF SOCIALLY INDUCED INFERTILITY

The Damaraland mole-rat Cryptomys damarensis exhibits an extreme repro ductive division of labour. Reproduction in the colony is restricted t o a single breeding pair, resulting from a two-fold control: (i) a red uced pituitary synthesis and/or secretion of luteinizing hormone leadi ng to a block to ovulation in non-reproductive females; and (ii) a str ong inhibition to breeding with familar kin. Circulating basal concent rations of luteinizing hormone as well as luteinizing hormone levels m easured in response to a single exogenous gonadotrophin releasing horm one challenge, were significantly lower in non-reproductive females in the presence of the reproductive female than those in colonies lackin g a reproductive female. Urinary progesterone concentrations before th e removal of the reproductive female were significantly higher in non- reproductives than the post removal values. Behavioural studies from s ib-sib and non-sib pairings provide evidence for a strong incest avoid ance, probably resulting from an inhibition of breeding with familiar colony members. A total of four pairings of non-sibs resulted in copul atory activity and eventual conception. In contrast, four couples of s ib-sib combinations failed to produce any sexual activity or offspring . Thus, suppression of reproduction in these non-reproductive, subterr anean bathyergids is complicated by the masking effect of familiarity that prevents incest, in addition to the physiological inhibition of f ertility in the presence of the reproductive female.