Variable social organization among tuco-tucos (genusCtenomys) in theopimusclade

Abstract

Comparative studies of closely related species provide a powerful means of identifying the ecological and demographic factors associated with variation in mammalian social systems. Although most members of the subterranean rodent genus Ctenomys are thought to be solitary, the highland tuco-tuco (C. opimus) is group living, meaning that multiple adults share a burrow system and underground nest site. These animals are part of the opimus clade, a monophyletic collection of four named species that occur in northwestern Argentina and adjacent portions of Chile and Bolivia. As a first step toward generating a comparative assessment of social organization within this clade, we characterized spatial relationships among members of a population of Ctenomys at Antofagasta de la Sierra, Catamarca Province, Argentina. Based on geographic location and natural history, these animals were expected to be part of the opimus clade; analyses of mitochondrial cytochrome-b sequences from our study population confirmed this general phylogenetic placement. Radiotelemetry data indicated that the animals at Antofagasta were group living, with up to three adult females and one adult male sharing a burrow system. In contrast to other group-living ctenomyids, however, individuals did not consistently share nest sites. Comparisons of these data with re-analyses of spatial relationships among members of the population of C. opimus studied by O’Brien et al. (2020) revealed several intriguing differences in social organization, potential explanations for which include short-term responses to variable demographic and ecological conditions as well as more enduring responses to differences in local selective pressures. Further comparative analyses of these populations and, more generally, members of this subclade of Ctenomys will help to elucidate the factors contributing to variation in social behavior within this speciose and geographically widespread genus.

Group living in highland tuco-tucos (Ctenomys opimus) persists despite a catastrophic decline in population density

“…In C. sociabilis-the only other group-living tuco-tuco studied to date-per capita annual direct fitness is greater for lone females [53], as predicted if individuals live together due to constraints imposed by the habitat. However, the social organizations of highland and colonial tuco-tucos differ with respect to several key features, as do the habitats in which these animals occur [56][57][58][59], suggesting that the fitness consequences of group living may also differ between these species. Studies that compare the direct fitness of lone versus group-living individuals and that evaluate the effects of group size on direct fitness are needed to understand the adaptive consequences of sociality in the Pozuelos population and to place data from C. opimus within the larger, comparative context of adaptive variation in mammalian social behavior.…”