Summary. Eight male naked mole-rats, from three colonies were studied in captivity. When non-breeding male naked mole-rats were removed from their colonies and paired with a non-breeding female, or removed and housed singly for 6 weeks before pairing with a female, concentrations of urinary testosterone and plasma luteinizing hormone (LH) increased significantly (P < 0·05). Concentrations of these hormones were highest while the males were singly housed: urinary testosterone (mean ± s.e.m.) increased from 8·2 ± 1·3 ng/mg urinary creatinine (Cr) in a non-breeder in a colony to 49·1 ± 5·5 ng/mg Cr when singly housed and 21·8 ± 2·5 ng/mg Cr when paired with a female. Plasma LH concentrations increased from 4·7 ± 1·0 miu/ml when a non-breeder in a colony to 19·8 ± 4·0 miu/ml when singly housed and 9·9 ± 1·1 miu/ml when paired with a female. After pairing with a female, the pattern of urinary testosterone secretion in the male was synchronized with the ovarian cycle of the female mate, such that urinary testosterone concentrations were significantly higher during the early follicular phase of the female's cycle (P < 0·05).
These results suggest that active suppression of reproductive physiology by social cues occurs in non-breeding male naked mole-rats, and that this is readily reversible if social cues are removed and males are housed singly. When a male was subsequently paired with a female, endocrine suppression was partially reimposed on the reproductively active males, such that urinary testosterone concentrations were suppressed to values similar to those in non-breeding males, except for periods prior to mating. The breeding female may therefore control the reproductive physiology of both breeding and non-breeding males in colonies of naked mole-rats.
Keywords: reproductive suppression; naked mole-rats; hystricomorph rodent; testosterone; luteinizing hormone