Distinct evolutionary lineages of Hoplisoma carlae (Siluriformes: Callichthyidae) due to dispersal barriers

The freshwater systems of South America have been strongly shaped by natural barriers and landscape fragmentation, driving high levels of endemism and diversification among Neotropical fishes. In this context, the subfamily Corydoradinae, particularly the genus Hoplisoma, offers an ideal model to investigate how geographic isolation has influenced evolutionary processes. This study focuses on Hoplisoma carlae, a species endemic to the Iguazú River basin, a region characterized by major dispersal barriers such as waterfalls, rapids, mountain ranges, and dams. We conducted an integrated analysis combining mitochondrial DNA (COI) sequences and morphological data from populations of H. carlae from Argentina and Brazil. Phylogenetic and population structure analyses revealed three well-differentiated groups corresponding to (1) the Urugua-í stream, (2) the upstream Iguazú River (“upstream A”), and (3) downstream sections of the Iguazú (including specimens from near the type locality of H. carlae) (“upstream B”). These groups are likely undergoing recent divergence driven by geographic isolation. The divergence time of H. carlae coincides with the formation of the Iguazu Falls. Our results suggest that natural barriers, including mountain ranges like the Sierra de la Victoria and historical waterfalls, along with recent anthropogenic barriers such as the Urugua-í dam, have contributed to population fragmentation and ongoing lineage divergence in H. carlae. These findings highlight the importance of preserving genetic diversity in fragmented freshwater ecosystems.