Reproductive suppression and pituitary sensitivity to exogenous GnRH in the highveld mole-rat (Cryptomys hottentotus pretoriae)

The highveld mole-rat Cryptomys hottentotus pretariae exhibits an extreme r eproductive division of labour. Reproduction in this seasonally breeding so cial mole-rat is restricted to a breeding pair. The nonreproductive females seem to be physiologically suppressed from reproducing, whereas the non-re productive males are restricted from sexual activity through incest avoidan ce. Circulating basal concentrations of luteinizing hormone (LH) between re productive and non-reproductive females were not significantly different, y et the response to an exogenous gonadotrophin-releasing hormone (GnRH) chal lenge was significantly lower in non-reproductive females when compared to reproductive females. The mean basal LH concentration in non-reproductive f emales was not significantly different in and out of the breeding season. H owever, the magnitude of the LH response in non-reproductive females out of the breeding season was greater than in the breeding season. The ovaries o f reproductive females showed little change with respect to season. However , reproductive females had enhanced follicular activity in comparison to th eir non-reproductive counterparts. This suggests that non-reproductive fema les are under stricter control from the reproductive female when she is pre gnant. The tropical African mole-rats exhibit a continuum of socially induc ed infertility with differing social species inhabiting regions of varying degrees of aridity. In this spectrum, a predominantly behavioural repressio n is found amongst non-reproductive females in social mesic-adapted species , whereas a strictly physiological suppression is operative amongst nonrepr oductive females in arid-adapted social species. Here we show that the mesi c-adapted highveld mole-rat does not fit this trend in that the non-reprodu ctive females seem to be physiologically suppressed. We discuss this in lig ht of the seasonality of breeding and the ecological constraints that may o perate during times of drought.