Relative age and reproductive status in Cryptomys hottentotus pretoriae (Rodentia: Bathyergidae) from South Africa

Abstract

The degree of molar eruption and wear were used to assign individuals of the social highveld mole-rat (Cryptomys hottentotus pretoriae) from South Africa into 9 relative age classes. Reproductive animals were found to be the oldest and heaviest members of colonies. Cranial morphometric analysis of 4 geographically disparate populations in South Africa generally showed lack of sexual dimorphism in cranial characteristics, but revealed 2 distinct groupings among the 9 relative age classes. The 1st grouping comprised individuals of age classes 1-4, which were all nonreproductive animals and considered to represent a combination of juveniles and subadults. The 2nd grouping included individuals of age classes 7-9, which included reproductive animals. Individuals of age classes 5 and 6, however, were largely intermediate, with some individuals included among both the younger and older age classes, but only a few of these animals were reproductive. These groupings suggest that if age classes are visualized as demarcating sections of variable and unknown length on a hypothetical growth curve, then individuals of age classes 5 and 6 appear to fall at a point on the curve just before it begins to stabilize. These results, together with a proposed microsatellite study, have the potential to provide additional tools to improve our current understanding of social structuring within colonies of the highveld mole-rat.