Gonadal steroid Hormone concentrations in the solitary Cape mole-rat and the social Natal mole-rat

Urinary gonadal steroid concentrations were measured and compared in the summer and winter for both the Cape mole-rat (Georychus capensis) and the Natal mole-rat (Cryptomys hottentotus natalensis). The Cape mole-rat breeds seasonally, with sexual activity and pregnancy recorded during the winter months in the southern hemisphere. Despite the fact that it has a distinct breeding season, the seasonal differences in the urinary hormone concentrations in both male and female Cape mole-rats were not statistically significant. This suggests that the Cape mole-rat is an opportunistic breeder and is able to make use of favourable environmental conditions when they occur during the year. No seasonal differences in urinary sex steroid concentrations were found in either male or female Natal mole-rats. The endocrinology complements histological and post mortem data for presence of embryos in reproductive females recorded during the entire year and support the notion that the Natal mole-rat is not a seasonal breeder. Dominant, reproductive and subordinate, non-reproductive males displayed comparable testosterone levels and the reproductive and non-reproductive females exhibit comparable oestrogen concentrations. The comparable concentrations of sex steroids in reproductive and non-reproductive animals implies that lack of reproduction in subordinate animals is likely the result of incest avoidance rather than a physiological component of suppression. Urinary progesterone concentrations of the dominant, reproductive females were found to be significantly higher than that of the subordinate, non-reproductive females, and histological data indicate that follicular development does not progress to the stage of the corpus luteum. Furthermore a resultant Chapter 3 – Gonadal steroid hormones 35 LH surge to induce ovulation does not take place in subordinate animals. The reproductive physiology of the Natal mole-rat compares with loosely social mole-rat species inhabiting mesic areas.