Anovulation in non-reproductive female Damaraland mole-rats (Cryptomys damarensis)

Within colonies of Damaraland mole-rats (Cryptomys damarensis), anovulation in nonreproductive females is thought to play an important role in maintai ning reproductive skew. Pituitary sensitivity and ovarian structure were ex amined in three groups of females that differed with respect to their socia l environment and breeding status to determine whether anovulation is due t o inhibitory social cues or is merely the result of a lack of copulatory st imulation. The contribution of gonadal steroid negative feedback to neuroen docrine differences in the reproductive systems of the respective groups wa s also investigated. LH secretion after a 0.5 mu g GnRH challenge in female s that had been removed from the presence of the breeding individuals for a t least 6 months (removed non-reproductive females) was significantly highe r than in non-reproductive females in the colony, but significantly lower t han in reproductive females. In both removed nonreproductive females and re productive females, corpora lutes were observed in ovaries of seven of eigh t females, indicating that ovulation occurs spontaneously in subordinate fe males on removal from the breeding pair. Circulating progesterone concentra tions in removed non-reproductive females were significantly higher than in non-reproductive females, indicating that circulating progesterone is not responsible for infertility in non-reproductive females. Indeed, after hyst ero-ovariectomy, reproductive females continued to show significantly great er GnRH-stimulated LH secretion than non-reproductive females. Thus, differ ential inhibition of gonadotrophin secretion in breeding and non-breeding f emales occurs independently of gonadal steroids. It is concluded that femal e Damaraland mole-rats are spontaneous ovulators and that anovulation resul ts from inhibitory social cues within the colony, not a lack of copulatory stimulation. Since non-reproductive females are infertile, inhibition of th e hypothalamo-pituitary-gonadal axis has the potential to play a causal rol e in maintaining reproductive skew in colonies of C. damarensis.