Behavior of the naked mole -rat (<italic>Heterocephalus glaber</italic>), with emphasis on factors related to the attainment of breeding status.

Abstract

I explored the evolution of eusociality through the study of naked mole-rats, small African rodents that are highly social: numerous non-breeding workers cooperate to raise the offspring of a single female, usually their mother. She breeds with a small number of males; the remaining colony members perform construction, maintenance, and defense of the colony. Though physiologically capable of reproduction, individuals delay doing so, such that many never directly reproduce. I investigated some of the factors underlying this extreme form of cooperation, especially traits correlated with future breeding status. The study utilized 200 captive individually-marked mole-rats, comprising 14 colonies. The chapters take up various topics related to naked mole-rat behavior. In chapter one I describe a tendency of the animals to hold a chip of wood behind their incisors when they dig, and discuss alternative hypotheses explaining the behavior. For chapter two I measured change over time in skin pigmentation, and found that breeders lose coloration faster than do non-breeders. Chapters three and four comprise a study of colony formation. I tested for correlations between future breeding status and four categories of behavior: eating and provisioning of food to colonymates under conditions of both abundant and restricted food availability, tendency to exit the colony, defense of the colony against foreign conspecifics, and time budgets for typical daily behavior. There was no evidence that animals that would eventually become breeders behaved differently in their natal colonies than did animals that remained non-breeders. I took several measures of physical size and body fat content, and found that only weight significantly predicted eventual breeding status. Mating pairs in experimental colonies consisted of unfamiliar distant kin (despite the equivalent presence of familiar close kin) which is surprising given that high levels of genetic similarity within colonies had suggested that close inbreeding was typical. Chapter five describes a rare case of colony-wide aggression in this normally highly cooperative species. Finally, chapter six synthesizes current evolutionary and medical approaches to understanding senescence, with ramifications for naked mole-rats and vertebrates in general.