Temporal changes in the social structure of a captive colony of the Damaraland mole-rat, Cryptomys damarensis: the relationship of sex and age to dominance and burrow-maintenance activity

Abstract

Crytomys damarensis is a eusocial subterranean rodent occurring in colonies in which a sole reproductive female and one to two males are involved in procreation; the remaining colony members are non-reproductive. Within each sex the reproductive animals are usually the largest and most dominant animals.

The dominance hierarchy of a young colony consisting of a founding reproductive pair of genetically unrelated animals and the first three successive litters, comprising 12 offspring, from this pair had a non-linear dominance hierarchy, h = 0.32. Dominance was found to be correlated positively to body mass as well as to the age of the animal. A subsequent study, which followed the incorporation of two subsequent litters and growth of the first three litters, and comprised 15 offspring, revealed that the dominance hierarchy had attained linearity, h = 0.9. Dominance was again positively correlated with the age and body mass of respective colony members. In both studies there was no clear relationship between dominance and sex within the colony.

The relationship between body mass and burrow-maintenance activity revealed that frequent workers in the colony had a greater mean body mass than infrequent workers. It is suggested that in establishing colonies, the older, stronger and hence larger animals may constitute the initial workforce. In addition the colony exhibits frequency-related work determination into frequent and infrequent workers. Gender was found to play no role in the frequency of work associated with burrow maintenance.

The social organization and temporal changes with recruitment are discussed in the light of events occurring in the field.