Faulkes, Christopher Guy; (1990) Social suppression of reproduction in the naked mole rats, Heterocephalus glaber. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

In the unique, eusocial naked mole-rat, the only mammal with a reproductive strategy resembling that of the social insects, reproduction in colonies of up to 300 individuals is monopolised by a single dominant female, 'the queen', and one or two large males. The remaining mole-rats in a colony usually show no signs of sexual behaviour, are classed as non-reproductive, and show a behavioural division of labour. The aim of this thesis was to investigate the environmental and physiological factors involved in this extreme natural suppression of fertility. The physiological nature of the block to reproduction in non-breeding male and female naked mole-rats appeared to be mediated by a common mechanism, namely, reduced circulating LH concentrations, probably resulting from an inhibition of hypothalamic GnRH secretion. In non-breeding females, fertility was totally blocked by a failure of ovulatation. in male naked mole- rats, reproductive suppression was less clear-cut, because while breeding males had higher urinary testosterone and plasma LH concentrations, compared with non-breeding males, the latter still produced mature spermatozoa. Genetic fingerprinting studies of wild colonies revealed little genetic variation between individuals, suggesting that the reproductive strategy of the naked mole-rat has led to a high degree of inbreeding. The reproductive block in non-breeding naked mole-rats is readily reversible. Non-breeders removed from their colonies and housed singly, or paired with an animal of the opposite sex, became reproductively active approximately 8 days after removal from their colonies. Reproductive suppression in naked mole-rats did not appear to be mediated by pheromones, because maintaining odour contact between separated animals and their parent colonies neither delayed nor prevented the onset of reproductive activation in either sex. The extreme socially-induced infertility in both male and female naked mole-rats may therefore be mediated, at least in part, by a behavioural mechanism.

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