Diversity and evolutionary history in Characidium (Characiformes: Crenuchidae): description of a new species and phylogeography of the Characidium zebra complex.

Abstract

The Neotropical region harbors the greatest diversity of freshwater fishes worldwide, shaped by a complex geological history that influenced the formation of river basins and species dispersal. Within this context, the genus Characidium (Crenuchidae) stands out as one of the most diverse groups of Characiformes. Recent studies have uncovered substantial cryptic diversity and taxonomic uncertainty in this group, particularly within widespread species complexes. These findings highlight the need for integrative approaches that combine morphological, molecular, and biogeographic data to refine species delimitation and understand evolutionary processes. Geological events such as headwater captures may leave genetic signatures that help reconstruct the diversification history of freshwater fishes. Recognizing these patterns is essential not only for resolving taxonomy but also for conservation. Integrative taxonomy was thus employed to describe a new species of Characidium from the Upper Paraná River and to elucidate the biodiversity underlying the Characidium zebra complex. This approach generated new evidence for future research, clarified aspects of the evolutionary history of the genus, and demonstrated how biogeographic processes shaped the diversification of fish in the Neotropical region.