Pituitary sensitivity to exogenous GnRH in giant Zambian mole-rats, Cryptomys mechowi (Rodentia : Bathyergidae): support for the 'socially induced infertility continuum'

The giant mole-rat Cryptomus mechowi exhibits an extreme reproductive divis ion of labour. Reproduction in the colony is restricted to a single breedin g pair. Non-reproductive individuals do not breed unless removed from the c olony and paired with unfamiliar conspecifics. Circulating basal concentrat ions of luteinizing hormone (LH) as well as LH levels measured in response to a single exogenous gonadotropin hormone (GnRH) challenge are not signifi cantly different between the reproductive and non-reproductive groups of ei ther sex. Neither non-reproductive males nor females are physiologically su ppressed at the level of the pituitary, as they do not exhibit a reduced pi tuitary secretion of LH or decreased sensitivity to hypothalamic GnRH. Rath er, reproductive skew seems to result From an inhibition to mate with famil iar conspecifics. Familiar individuals housed in the absence of the breedin g pair did not breed, whereas pairing unfamiliar individuals of the opposit e sex resulted in sexual activity and recruitment. The results from the gia nt mole-rat suggest that reproductive skew may result from a predominantly behavioural repression in non-reproductive females arising from an incest a voidance mechanism.