Rivers as barriers to the subterranean rodent Ctenomys (Rodentia: Ctenomyidae) in northern Patagonia, Argentina

Geographical features can act as barriers to gene flow, promoting isolation, divergence, and ultimately speciation through vicariance. This process may be particularly pronounced in subterranean rodents of the genus Ctenomys, which exhibit limited vagility and often fragmented population distributions. In Argentine Patagonia, the taxonomy and distribution of many Ctenomys species remain unknown. Here, we evaluated the role of the Collón Curá and Limay Rivers in northwestern Patagonia as potential barriers to gene flow in Ctenomys. Animals were sampled on both riverbanks at different points along each river. Cytochrome b sequences were analysed using hierarchical AMOVAs, haplotype networks, and haplotype distribution mapping. We found high haplotype diversity, with only two haplotypes shared among sampling sites. Two well-differentiated haplogroups were identified: one corresponding to C. lentulus and the other probably representing a new, undescribed species. While some portions of the Collón Curá and Limay appear to limit gene flow between haplogroups, other portions of these rivers seem permeable, with potential contact between populations on opposite banks. These patterns probably reflect historical changes in river dynamics associated with glacial–interglacial cycles and geomorphological reorganization. Our results highlight the importance of integrating fine-scale geographical sampling and genetic analyses to uncover cryptic diversity and refine species limits in Ctenomys.