The biology and population ecology of the Namaqua dune mole-rat, Bathyergus janetta from the Northern Cape Province, South Africa

Abstract

Bathyergus Janetta is a solitary subterranean rodent that occurs in the very restricted areas of Namaqualand. This bathyergid is able to survive the arid environment due to the predictable winter rainfall that gives rise to the high abundance and diversity of geophytes in the area. Burrowing dynamics and burrow system configuration was studied by the monitoring of mound production and the excavation of six burrow systems in mole-rats which had been marked by toe-clipping. Bathyergus Janetta burrows are about 45cm below ground and comprise nesting chambers, food stores, defecation sites and bolt holes. Males have a more linear shaped burrow system than females, probably to increase home ranges in search of a possible mate. Burrow systems undergo consistent excavation and re-excavation of tunnels within the home range and it appears that mole-rats have an optimum burrow length that ranges from 71.2m to 165m with an average home range of 805.86 ± 375.52m2 • Bathyergus Janetta is a seasonal breeder. Females exhibit an elevation in urinary progesterone and oestradiol-17~ concentrations and males a rise in testosterone that correlates with seasonal rainfall figures. After the winter rainfall, the soil is soft and moist and easily excavated. Bathyergus Janetta makes use of this opportunity not only to extend their burrow systems but also to search for possible mates. Plural occupancy by adult mole-rats was observed during the onset of the winter and pups and pregnant females were caught at the end of October and November. Microsatellites were used in an attempt to determine parentage and elucidate relatedness within a population of B. Janetta. It was not possible to assign parentage within the scope of the statistical program CERVUS due to the large number of putative parents, although it seems that multiple paternity of litters may occur. Individual Bathyergus Janetta exhibit low relatedness values suggesting that the population is outbreeding and comprises related and unrelated individuals. A highly significant correlation between the isolation of genetic and geographical distances was found which supports the assumption that the subterranean niche poses a limitation on the dispersal abilities of mole-rats. A comparison between populations of B. Janetta and B. suillus shows a clear distinction between the two species. Surprisingly the two populations of B. suillus (although 15- 20km apart) show a distinct genetic differentiation and a high genetic diversity within the populations when compared to the B. Janetta population.