Data for Stable environments promote kin-based cooperative breeding in a mesic-dwelling social mole-rat

Social African mole-rats have been suggested as a model family to understand the role of ecological constraints on dispersal in the evolution of sociality in mammals. Group composition and sociality in African mole-rats exists on a spectrum and may differ between species and populations due to environmental conditions. Mole-rats of the genus Cryptomys have previously been considered less social than the more frequently studied naked (Heterocephalus glaber) and Damaraland mole-rats (Fukomys damarensis). In this study we assess within-group relatedness and dispersal patterns in a montane population of the Natal mole-rat (Cryptomys natalensis), which occur in a high rainfall region where the constraints on dispersal are presumably relaxed. Our results show that family groups of Natal mole-rats show distinct genetic clustering across the landscape, with group members more related to each other than to neighboring group members, similar to arid-dwelling mole-rat species. Both pairwise relatedness among individuals and genetic differentiation among groups exhibited significant effects with increasing distance. These effects were different between the sexes, indicting a male-biased dispersal pattern. However, geographic features present at the study site did not present absolute barriers to dispersal, with gene flow well maintained at the study site. The social structure of Natal mole-rats indicates that group-living and cooperative breeding are promoted through a combination of life-history traits and direct fitness benefits despite relatively benign environmental conditions. A consequence of relaxed ecological constraints may promote higher female immigration compared to arid-dwelling mole-rats, possibly due to a ‘dear enemy’ phenomenon.