The social structure and dominance hierarchy of the highveld mole-rat Cryptomys hottentotus pretoriae (Rodentia: Bathyergidae)

Abstract

The highveld mole-rat Cryptomys hottentotus pretoriae occurs in the summer rainfall region of the highveld of South Africa. It lives in colonies of up to 10 individuals, in which reproduction is limited to one to two of the largest males and the largest female in the colony. Of three field captured colonies, the mean colony size was 10 ± 0 animals with a mean biomass of 900 ± 147 g. The study colony had a sex ratio of 1.5:1 in favour of males.

The social hierarchy of the highveld mole-rat is non-linear and has a value of 0.3 calculated from Landau's linearity index. Dominance was negatively correlated with capture order.

Histological examination of the gonads of reproductively active and sexually quiescent members of both sexes of two colonies provides further support of there being a single reproductive male and female responsible for procreation in the colony.

The non-reproductives of both sexes appear to be important in burrow maintenance activity and in foraging for geophytes upon which the mole-rats feed. The non-reproductive members of the colony cannot be subdivided into different worker groups based on body mass. The available evidence suggests that the highveld mole-rat is a transiently social species, at one extreme of a sociality continuum in the genus Cryptomys. The position of this subspecies in respect to the sociality continuum is discussed.