Socially induced infertility in Ansell's mole‐rat: are there depressed hormone levels in non‐reproductive males and females?

Abstract

AbstractAnsell's mole‐rat, Fukomys anselli, is a social subterranean mammal and exhibits an extreme reproductive division of labour. Reproduction in the colony is restricted usually to a single female. Complete colonies captured throughout an entire calendar year were euthanased and the histology of the gonads and plasma hormone concentrations were measured in reproductive and non‐reproductive members of both sexes. In males, the circulating levels of testosterone were significantly higher in the reproductive male than the non‐reproductive males. The mean testes mass for the reproductive males corrected for body mass was not significantly greater than that of the non‐reproductive male. Similarly, the mean testes volume of reproductive males was not greater than that for the non‐reproductive males but the seminiferous tubule diameter was significantly greater in the reproductive males than the non‐reproductive males. Reproductive females characteristically possessed corpora lutea of ovulation and pregnancy in their ovaries and this was met with much higher progesterone concentrations in the reproductive females 34 nmol/L compared with 4 nmols/L in the non‐reproductive females. In contrast, non‐reproductive females showed a complete range of follicular genesis, but they did not possess corpora lutea of ovulation or pregnancy, in turn they show depressed progesterone concentrations. The current evidence suggests that in Ansell's mole‐rats, the non‐reproductive males and females refrain from sexual activity by being subordinate and moreover, related to the breeding pair.