Behavioural interactions, basal plasma luteinizing hormone concentrations and the differential pituitary responsiveness to exogenous gonadotrophin-releasing hormone in entire colonies of the naked mole-rat (Heterocephalus glaber)

Abstract

Agonistic and sexual interactions as well as plasma bioactive luteinizing hormone (LH) concentrations were monitored in all the adults of two colonies of the naked mole-rat Heterocephalus glaber at three phases in the pregnancy of the breeding female. Blood samples were collected at early (days 1–15), mid (days 30–40) and late (days 55–65) phases of her pregnancy, and the circulating basal plasma LH and the response to administration of 0.1 μg gonadotrophin-releasing hormone (GnRH) were examined. In both colonies it was found that non-breeding males and females showed depressed basal LH concentrations and responses to a GnRH challenge. However, there was considerable variation between individuals, in terms of both basal plasma and post-GnRH concentrations of LH, implying that certain individuals were more suppressed than others. The responses were more pronounced in non-breeding males than in non-breeding females, and this is discussed in light of the reproductive skew occurring within colonies. Few agonistic interactions occurred between the breeding female and the majority of the colony members, and overall, there was no clear relationship between plasma LH and the amount of aggression received from the breeding female. However, in one colony there was a significant positive correlation between basal plasma LH concentrations of non-breeding females and agonistic interactions received by them from the breeding female. In this same colony, older females and older and heavier males received most of the aggression from the breeding female. The second colony did not show this trend, possibly because it had recently lost many large animals during fighting for succession; in this colony sexual interactions were elevated.