Kinship in colonial tuco-tucos: evidence from group composition and population structure

Kinship plays a significant role in shaping the social and genetic structures of many vertebrate populations. Evidence of kinship, however, may be substantially influenced by the spatial and temporal scales over which co-ancestry is monitored. For example, while data on social group composition may yield little indication of relatedness among reproductive partners, data on the demographic structure of a population may reveal considerable shared ancestry among mates. We explored relationships among social group composition, individual movements, and population-level patterns of kinship using data from a 7-year field study of the colonial tuco-tuco (Ctenomys sociabilis), a group-living subterranean rodent that is endemic to southwestern Argentina. Our analyses indicate that social groups are composed of 1-4 generations of closely related females and a single, immigrant male, suggesting that reproductive partners are not related to one another. Monitoring individual movements, however, revealed that (1) most male dispersal occurs within the local population and (2) most new social groups are founded by females born in the study population, indicating that individuals reared in different burrow systems may share considerable co-ancestry. Simulation analyses revealed that up to 67% of reproductive partnerships consist of animals that share co-ancestry within the last 5-7 generations. Thus, while analyses of social group composition provide little evidence of kinship among reproductive partners, population-level analyses of dispersal and group formation suggest that co-ancestry among mates is common. These findings have important implications for interpreting social interactions and genetic structure in this species.