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

Abstract

The highveld mole-rat Cryptomys hottentotus pretoriae exhibits an extreme reproductive division of labour. Reproduction in this seasonally breeding social mole-rat is restricted to a breeding pair. The non-reproductive females seem to be physiologically suppressed from reproducing, whereas the non-reproductive males are restricted from sexual activity through incest avoidance. Circulating basal concentrations of luteinizing hormone (LH) between reproductive and non-reproductive females were not significantly different, yet the response to an exogenous gonadotrophin-releasing hormone (GnRH) challenge was significantly lower in non-reproductive females when compared to reproductive females. The mean basal LH concentration in non-reproductive females was not significantly different in and out of the breeding season. However, the magnitude of the LH response in non-reproductive females out of the breeding season was greater than in the breeding season. The ovaries of reproductive females showed little change with respect to season. However, reproductive females had enhanced follicular activity in comparison to their non-reproductive counterparts. This suggests that non-reproductive females are under stricter control from the reproductive female when she is pregnant. The tropical African mole-rats exhibit a continuum of socially induced infertility with differing social species inhabiting regions of varying degrees of aridity. In this spectrum, a predominantly behavioural repression is found amongst non-reproductive females in social mesic-adapted species, whereas a strictly physiological suppression is operative amongst non-reproductive females in arid-adapted social species. Here we show that the mesic-adapted highveld mole-rat does not fit this trend in that the non-reproductive females seem to be physiologically suppressed. We discuss this in light of the seasonality of breeding and the ecological constraints that may operate during times of drought.