LH RESPONSES TO SINGLE DOSES OF EXOGENOUS GNRH BY SOCIAL MASHONA MOLE-RATS - A CONTINUUM OF SOCIALLY INDUCED INFERTILITY IN THE FAMILY BATHYERGIDAE

The Mashona mole-rat, Cryptomys darlingi, exhibits an extreme reproduc tive division of labour. Reproduction in the colony is restricted to a single breeding pair. The non-reproductive male and female colony mem bers are restrained from sexual activity by being familiar and related to one another and the reproductive animals. Circulating basal concen trations of luteinizing hormone (LH) as well as LH levels measured in response to a single exogenous gonadotropin releasing hormone (GnRH) c hallenge are not significantly different between the reproductive and non-reproductive groups of either sex. Socially induced infertility in both non-reproductive males and females does not result from a reduce d pituitary secretion of LH or decreased sensitivity to hypothalamic G nRH, but rather appears to result from an inhibition of reproductive b ehaviour in these obligate outbreeders. The African mole-rats exhibit a continuum of socially induced infertility with differing social spec ies inhabiting regions of varying degrees of aridity. In this continuu m a transition from a predominantly behavioural repression in a social mesic-adapted species through to complete physiological suppression l acking incest avoidance in an arid-adapted eusocial species occurs in this endemic African family of rodents.