Social suppression of reproduction in male naked mole-rats, Heterocephalus glaber

Abstract

Summary. To investigate possible anatomical and endocrine differences between breeding and non-breeding male naked mole-rats, 113 animals from 24 captive and 4 wild colonies were studied. While breeding males had larger reproductive tract masses compared to non-breeders relative to body mass (P < 0·01), spermatogenesis was active in all of the non-breeding males examined histologically (n = 9) and spermatozoa were present in the epididymides. Compared with non-breeders, breeding males had significantly higher urinary testosterone concentrations (mean ± s.e.m.: 23·8 ± 2·3 vs 5·2 ± 1·4 ng/mg Cr respectively; P < 0·001), and plasma LH (10·7 ± 1·7 vs 5·0 ± 0·8 mi.u./ml respectively; P < 0·01). Single doses of 0·1, 0·5 or 1·0 μg GnRH produced a significant rise in plasma LH concentrations 20 min after s.c. injection in breeding and non-breeding males at all doses (P < 0·001). However, there were differences in the magnitude of the LH response following administration of GnRH between breeding and non-breeding males, with non-breeding males showing a dose–response and having lower plasma LH concentrations 20 min after a single injection of 0·1 or 0·5 μg (P < 0·05), but not 1·0 μg, GnRH. This apparent lack of pituitary sensitivity of non-breeding males to single doses of exogenous GnRH was reversed by 4 consecutive injections of 0·5 μg GnRH at hourly intervals, suggesting that the reduced sensitivity may be the result of insufficient priming of the pituitary by endogenous GnRH. These results indicate that, despite the fact that non-breeding males were apparently producing mature gametes, clear endocrine deficiencies existed in male naked mole-rats. Keywords: reproductive suppression; naked mole-rats; hystricomorph rodent; testosterone; LH