Burrow sharing in a second Patagonian species of tuco-tuco ( Ctenomys plebiscitum )

The tendency for conspecifics to live in groups is expected to reflect elements of both current ecology and evolutionary history. Evaluating the relative contributions of these factors to patterns of social behavior is facilitated by comparisons of closely related species that differ with regard to social organization. The Colonial Tuco-tuco (Ctenomys sociabilis) is 1 of 2 species of ctenomyids that has been shown to be group living. In contrast, initial reports suggest that the recently described and closely related C. plebiscitum may be solitary. To determine if comparative studies of these species can be used to explore factors contributing to divergence in social behavior, we employed radiotelemetry to characterize the social organization of a population of C. plebiscitum located near Esquel, Argentina. Our data indicate that contrary to expectation, C. plebiscitum is group living, with multiple adults sharing the same burrow system and putative nest site. Although this outcome is perhaps not surprising given the similar habitats in which C. plebiscitum and C. sociabilis occur, their close phylogenetic relationship makes it challenging to distinguish the effects of current versus historical factors in shaping the social organizations of these species. Our findings underscore the importance of using a phylogenetically informed approach to explore the ecological factors favoring group living in this and other lineages of mammals.