Circulating LH Levels and the Response to Exogenous GnRH in the Common Mole-Rat: Implications for Reproductive Regulation in This Social, Seasonal Breeding Species

Abstract

The effects of breeding season and reproductive status on male and female reproduction were investigated in the common mole-rat, Cryptomys hottentotus hottentotus, a cooperatively breeding rodent which exhibits a unique combination of seasonal breeding and a reproductive division of labor. Pituitary function was examined by measuring the luteinizing hormone (LH) responses to single doses of 2 μg exogenous gonadotrophin-releasing hormone (GnRH) and physiological saline in 69 males and 58 females from 35 wild-caught colonies. Neither males nor females exhibited any apparent manifestation of season on basal LH concentrations or on pituitary sensitivity to stimulation by exogenous GnRH. The continuance of reproductive function during the nonbreeding period is essential in common mole-rat males and females, as this period coincides with the period of maximal dispersal opportunity in the winter rainfall area they inhabit. Normal circulating levels of reproductive hormones in dispersing animals may aid intersexual recognition, assist pair-bond formation, and thus prime animals for independent reproduction. Circulating basal concentrations of LH as well as LH levels measured in response to a single exogenous GnRH challenge were not significantly different between the reproductive and non-reproductive groups of either sex, suggesting the absence of a physiologically well-defined suppression of reproduction in subordinate common mole-rats.