Social suppression of ovarian cyclicity in captive and wild colonies of naked mole-rats, Heterocephalus glaber

Abstract

Summary. To investigate the endocrine cause of reproductive suppression in non-breeding female naked mole-rats, animals from 35 colonies were studied in captivity. Urinary and plasma progesterone concentrations were elevated in pregnant females (urine: 10·0–148·4 ng/mg Cr, 27 samples from 8 females; plasma: 3·6–30·0 ng/ml, 5 samples from 5 females; Days 21–40 of pregnancy) and cyclic breeding females (urine: 0·5–97·8 ng/mg Cr, 146 samples from 7 females; plasma: < 1·0–35·4 ng/ml, 25 samples from 7 females). The latter group showed cyclic patterns of urinary progesterone, indicating a mean ovarian cycle length of 34·4 ± 1·6 days (mean ± s.e.m.) with a follicular phase of 6·0 ± 0·6 days and a luteal phase of 27·5 ± 1·3 days (19 cycles from 9 breeding females). In non-breeding females urinary and plasma progesterone values were undetectable (urine: < 0·5 ng/mg Cr, 232 samples from 64 females; plasma: < 1·0 ng/ml, 7 samples from 6 females). Breeding females had higher (P < 0·001) plasma LH concentrations (3·0 ± 0·2 mi.u./ml, 73 samples from 24 females) than did non-breeding females (1·6 ± 0·1 mi.u./ml, 57 samples from 44 females). Urinary and plasma progesterone concentrations in non-breeding females from wild colonies situated near Mtito Andei, Kenya, were either below the assay sensitivity limit (urine: < 0·5 ng/mg Cr, 11 females from 2 colonies; plasma: < 1·0 ng/ml, 25 females from 4 colonies), or very low (plasma: 1·6 ± 0·6 ng/ml, 15 females from 4 colonies). In captivity, non-breeding females removed from their colonies (i.e. the dominant breeding female) and either paired directly with a non-breeding male (N = 2), or removed and housed singly for 6 weeks before pairing with a non-breeding male (N = 5) may develop a perforate vagina for the first time in as little as 7 days. Urinary progesterone concentrations rose above 2·0 ng/mg Cr (indicative of a luteal phase) for the first time 8·0 ± 1·9 days after being separated. These results suggest that ovulation is suppressed in subordinate non-breeding female naked mole-rats in captive and wild colonies, and show that plasma LH concentrations are significantly lower in these non-breeding females. This reproductive block in non-breeding females is readily reversible if the social factors suppressing reproduction are removed. Keywords: reproductive suppression; naked mole-rats; ovarian cycles; hystricomorph rodent