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

Kinship plays a significant role in shaping the social and geneticstructures of many vertebrate populations. Evidence of kinship,however, may be substantially influenced by the spatial andtemporal scales over which co-ancestry is monitored. For example,while data on social group composition may yield little indicationof relatedness among reproductive partners, data on the demographicstructure of a population may reveal considerable shared ancestryamong mates. We explored relationships among social group composition,individual movements, and population-level patterns of kinshipusing data from a 7-year field study of the colonial tuco-tuco(Ctenomys sociabilis), a group-living subterranean rodent thatis endemic to southwestern Argentina. Our analyses indicatethat social groups are composed of 1–4 generations ofclosely related females and a single, immigrant male, suggestingthat reproductive partners are not related to one another. Monitoringindividual movements, however, revealed that (1) most male dispersaloccurs within the local population and (2) most new social groupsare founded by females born in the study population, indicatingthat individuals reared in different burrow systems may shareconsiderable co-ancestry. Simulation analyses revealed thatup to 67% of reproductive partnerships consist of animals thatshare co-ancestry within the last 5–7 generations. Thus,while analyses of social group composition provide little evidenceof kinship among reproductive partners, population-level analysesof dispersal and group formation suggest that co-ancestry amongmates is common. These findings have important implicationsfor interpreting social interactions and genetic structure inthis species.