Social suppression of reproduction in the naked mole-rat, Heterocephalus glaber : -Plasma LH concentrations and differential pituitary responsiveness to exogenous GnRH

Master Thesis


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University of Cape Town

The naked mole-rat provides possibly the most extreme example of socially-induced reproductive suppression observed in any mammal. The majority of colony members remain reproductively suppressed for their entire lives, nevertheless they are not sterile, and can become reproductively active soon after removal from the colony. The breeding female controls reproductive suppression in the non-breeding animals, and both males and females are sensitive to her presence and reproductive state. The breeding female is thought to maintain reproductive suppression in the non-breeding animals by preferentially directing agonistic behaviour towards those animals that pose the greatest threat to her reproductive supremacy. Previous studies have investigated the phenomenon of reproductive suppression in the naked mole-rat, and have compared breeding and non-breeding animals selected at random from several colonies (Faulkes, 1990; Faulkes et al., 1990a; 1990b; Faulkes & Abbott, 1991), but none has looked at the individuals of entire colonies. Moreover, the time in the breeding female 's reproductive cycle when data have been collected has never been standardised. The aim of this study was to conduct the first large-scale investigation of reproductive suppression in the individuals of entire colonies of naked-mole-rats, over the reproductive cycle of the breeding female. The study was conducted on two colonies of naked mole-rats. In order to standardise the time in the breeding female's reproductive cycle during which data would be collected, the gestation period was divided into three time intervals, early (days 1-15), mid (days 30-40) and late (days 55-65) pregnancy, with the assumption that mating occurred on day 10 after parturition. During each time interval, behavioural data and blood samples were collected, and GnRH challenges were performed on all the colony members over 26 g. An in-vitro bioassay based on the production of testosterone by dispersed mouse Leydig cells was used to measure LH concentration in plasma samples collected before and 20 min after an exogenous dose of 0.1 μg GnRH. The results of this study support the findings of these previous studies, by providing conclusive evidence for reproductive suppression in non-breeding naked mole-rats, and by confirming that non-breeding females are more suppressed than non-breeding males.

Bibliography: pages 104-111.