Intra and intergroup patterns of relatedness and space use in the cooperative and promiscuous breeding Cape ground squirrel (Xerus inauris)
Group living is an important life-history tactic for many species and provides several benefits, such as predation protection and cooperative breeding, but can also incur costs. When groups become large, these costs can increase and can be detrimental to the reproductive success of gregarious females. Kin selection is one mechanism that may offset group costs. Hypotheses on the evolution of cooperative breeding predict these groups to be monogamous to maintain high relatedness within their family groups. In the case of promiscuous cooperative breeding species, relatedness may be highly variable both within and among groups, but little is known about if and how kin selection functions in these groups. Cape ground squirrels (Xerus inauris) are a cooperative breeding species with a promiscuous breeding system. Our objective was to first characterize the importance of kin selection within groups by examining relatedness within Cape ground squirrel family groups if kin bias was important during foraging away from safety, and if kin selection was an important factor when Cape ground squirrel females dispersed from their family group. Secondly, we characterized relatedness patterns among family groups across a landscape and determined if there was a kin bias or benefit to the sharing of spatial resources among family groups. We collected observational data on 15 different squirrel family groups in central South Africa. Results indicate that promiscuity influenced relatedness and group size, and that, over time, relatedness declined for males but not for females in a group. When females left their group, they usually did so with their offspring. When foraging, females did not show a spatial bias towards kin. Across a landscape, relatedness decreased with increasing distance, but we did not find that Cape ground squirrels showed a bias in spatial resources between kin, or that spatial resources contributed to reproductive success or survival of females. Overall, female Cape ground squirrels optimized direct fitness benefits when dispersing from their family groups, and overt kin biases were not apparent during foraging. Our study is important in understanding the evolution of cooperative breeding in a promiscuous species with a unique, tolerant, and non-aggressive social system.
Kin selection, Group splitting, Matrilines, Space use, Spatial resources, Promiscuous breeding, Cooperative breeding