At the edge of the burrow: The mitochondrial genetic structure and range dynamics of the yellow armadillo Euphractus sexcinctus in southern South America

Abstract

Armadillos are ecologically important but remain poorly studied in terms of population genetics and biogeography. The yellow armadillo (Euphractus sexcinctus) is among the most widespread species, yet its southern populations—at the distributional margin in Argentina and Uruguay—are poorly characterized despite their conservation relevance. Here, we integrate mitochondrial DNA analyses with ecological niche modeling (ENM) to investigate genetic diversity, population structure, and historical demography across the southern range. We found high mitochondrial diversity with incipient structuring into two main clusters: a western group and an eastern group. Demographic tests indicated recent expansions, particularly in the eastern cluster. ENMs revealed strong distributional shifts linked to Pleistocene climatic oscillations,with reduced suitability in the northwest during glacial periods and more stable refugial conditions in the southeast. These findings suggest that southern E. sexcinctus populations experienced repeated contractions and recolonizations, shaped by major rivers and regional environmental barriers. Comparisons with other armadillos and Neotropical mammals point to a shared history of postglacial southward expansions from northern refugia. Our results highlight the evolutionary significance of peripheral populations, which may harbor cryptic diversity, and underscore their vulnerability under ongoing environmental change.