Underlying behavioural and physiological determinants of dominance hierarchy in a eusocial mammalian species, the naked mole-rats (Heterocephalus glaber)

Abstract

The naked mole-rat (Heterocephalus glaber) is a subterranean mammal which occurs in colonies of up to 60 individuals. The animals have a distinct dominance hierarchy with breeders at the top specifically dominant breeding female (queen) and one to three breeding males, and the rest of the hierarchy is occupied by non-reproductive subordinates. The non-reproductive subordinates are able to reproduce, but are suppressed from reproducing by the queen.The aim of this thesis was to investigate how dominance-ranking position in naked mole-rats differs with animal personality traits, as well as stress-related and reproduction endocrine markers. However, to achieve this goal, the methods used to quantify animal personality traits, and the assays to determine stress- and reproduction-related hormone concentrations had to first be reliably validated. The validation steps are covered in the first three data chapters of the thesis. Thereafter, the last data chapters applied the novel validated methods in five naked mole-rat colonies. This study has revealed that the degree of reproductive suppression orchestrated at the level of the pituitary on various members of entire colonies is unequal, with some colony members being more suppressed than others that are closely linked to their position in the dominance hierarchy of the colony. Similarly, naked mole-rats experience differing levels of stress while in the colony and this may well be dependent upon their position in the dominance hierarchy and consequently interactions with the queen.