Facultative sociality in a subterranean rodent, the highland tuco-tuco (Ctenomys opimus)

Abstract

Understanding why social relationships vary among conspecifics is central to studies of animal behaviour. For many species, patterns of space use provide important insights into social behaviour. To characterize the social organization of the highland tuco-tuco (Ctenomys opimus), we used visual observations and radiotelemetry to quantify spatial relationships among adults in a population at Laguna de los Pozuelos, Jujuy Province, Argentina. Specifically, we sought to confirm anecdotal reports that these subterranean rodents are social, meaning that adults share burrow systems and nest sites. Our data indicate that the animals live in spatially distinct groups, although the number of individuals per group varies markedly. Although these relationships were robust with regard to location (above vs. below ground) and type of data (visual vs. telemetry), some groups identified during the daytime fissioned during the night. We suggest that the population of C. opimus at Pozuelos is facultatively social, meaning that individuals display predictable, adaptive differences in social relationships with conspecifics. More generally, our findings add to the growing number of subterranean species of rodents recognized as social, thereby generating new opportunities for comparative studies of these animals aimed at assessing the causes and consequences of variation in social organization.

Multi-year assessment of variability in spatial and social relationships in a subterranean rodent, the highland tuco-tuco (Ctenomys opimus)

“…The population of highland tuco-tucos (Ctenomys opimus) studied was located in Monumento Natural Laguna de los Pozuelos, Jujuy Province, Argentina (22° 34′ S, 66° 01′ W; elevation: 3600 m); this is the same population of C. opimus studied by O'Brien et al (2020). The ca.…”

“…Members of the study population were captured using tomahawk-style live traps baited with carrots (O'Brien et al 2020). Open traps were placed at active burrow entrances, as identified by the presence of recently excavated soil and fresh fecal pellets as well as observations of animals using those entrances.…”

“…Unlike most other tuco-tucos, C. opimus spends a substantial proportion of time foraging above ground, with the result that individuals are fully visible while feeding on salt grass (genus Distichlis) and other high Andean vegetation. Both direct observations and analyses of radiotelemetry data indicate that members of the population of C. opimus at Laguna de los Pozuelos, Jujuy Province, Argentina, are group-living, with multiple adults (mean = 3.7 ± 2.1 SD; range = 1-7) of both sexes sharing burrow systems and subterranean nests (O'Brien et al 2020). A social group may occupy several nest sites, resulting in variable combinations of group mates that share a nest on a given night (O'Brien et al 2020).…”

“…Both direct observations and analyses of radiotelemetry data indicate that members of the population of C. opimus at Laguna de los Pozuelos, Jujuy Province, Argentina, are group-living, with multiple adults (mean = 3.7 ± 2.1 SD; range = 1-7) of both sexes sharing burrow systems and subterranean nests (O'Brien et al 2020). A social group may occupy several nest sites, resulting in variable combinations of group mates that share a nest on a given night (O'Brien et al 2020). Importantly, these analyses have also revealed the presence of solitary individuals within this population, raising the possibility that C. opimus is facultatively social.…”

“…These findings were based on only a single season of fieldwork; and thus, O'Brien et al (2020) were unable to determine if the observed variation in social behavior is temporally persistent, with a mixture of solitary and groupliving individuals present in the population in multiple years. For the same reason, these authors could not evaluate how individual patterns of behavior contribute to population-level differences in social relationships.…”