Ecology of sociality in rodents: A ctenomyid perspective

Group living is an important component of the social biology of numerous rodent species. For the past 2 decades, efforts to understand the ecological factors associated with group living in rodents have focused on subterranean taxa, in particular African mole-rats of the family Bathyergidae. Comparative analyses of the habitats occupied by solitary and social bathyergids suggest that group living occurs when the combined effects of sporadic rainfall, hard soils, and patchily distributed food resources render energetic costs of burrow excavation prohibitive for lone individuals. To determine whether these variables were associated with group living in other subterranean taxa, we characterized ecological differences between a solitary and a social member of a phylogenetically independent lineage of subterranean rodents, the Ctenomyidae. Specifically, we quantified soil conditions and spatial distributions. of food resources for I population each of the solitary Patagonian tuco-tuco (Ctenomys haigi) and the group-living colonial tuco-tuco (C. sociabilis), both of which occur in the Limay Valley of southwestern Argentina. Our analyses revealed that while members of both species occurred in relatively mesic mallin habitats, only C. haigi also occurred in and steppe habitat. No differences in spatial distributions of food resources were found between study sites. Significant differences in soil conditions, however, were detected; soils from steppe habitat were significantly harder to penetrate than soils from mallin areas, suggesting that costs of burrow excavation may be higher for the solitary C. haigi. Thus, data from ctenomyids in the Limay Valley are not consistent with explanations for group living developed for bathyergid mole-rats. Although ecological comparisons of ctenomyids over larger spatial scales are required, our data suggest that interactions between ecology and group living in subterranean rodents may be more diverse than previously realized.