Stable isotopes reveal differential patterns of Holocene environmental change among tuco-tucos (Rodentia: Ctenomyidae, Ctenomys) from Patagonia

Abstract

To explore the role of past environmental changes in shaping interspecific differences in genetic structure among tuco-tucos (Rodentia: Ctenomyidae, Ctenomys) from the Limay Valley of northern Patagonia, we compared δ13C and δ18O values for modern and historical tooth enamel from the colonial tuco-tuco (C. sociabilis) and the parapatric Patagonian tuco-tuco (C. haigi). Specifically, we sought to test the hypothesis that a mid-Holocene loss of genetic variation in C. sociabilis was associated with environmental change. For both species, the δ13C composition of tooth enamel differed significantly (~ 5.1‰ difference in mean δ13C values) between modern and Holocene (0.5–12 kyr B.P.) samples, suggesting marked temporal changes in the vegetation consumed. For C. sociabilis, no statistically significant differences in the δ13C composition of teeth were found among individuals from the early, middle, and late Holocene. In contrast, significant differences in δ13C values were found between middle and late Holocene samples from C. haigi. None of our analyses revealed statistically significant differences in δ18O values. Thus, although the diets of both study species have changed from the Holocene to the present, only C. haigi experienced significant dietary changes during the Holocene. We suggest that the ecologically more specialized C. sociabilis continued to consume the same food resources even as changing Holocene conditions caused preferred habitats to disappear. In contrast, the more generalized C. haigi altered its diet, allowing populations of this species to remain widespread despite changing Holocene environments.