Multi-locus phylogeny and species delimitation in the catfish genus Ictalurus Rafinesque, 1820 (Actinopterygii, Siluriformes)

Background: Ictalurus is one of the most representative groups of North American freshwater fishes. Although this group has a well-studied fossil record, and has been the subject of several morphological and molecular phylogenetic studies, incomplete taxonomic sampling and insufficient taxonomic studies have produced a rather complex classification along with intricate evolutionary history patterns of the genus that are considered unresolved and remain under debate. Results Based on four loci and the most comprehensive taxonomic sampling analyzed to date, including currently recognized species, previously synonymized species, undescribed taxa, as well as poorly studied populations, this study produced a resolved phylogenetic framework that provided plausible species delimitation and an evolutionary time framework for the genus Ictalurus in North America. Conclusions Our phylogenetic hypothesis revealed that Ictalurus comprises at least 13 evolutionary units, partially corroborating the current classification and identifying populations that emerge as putative undescribed taxa. The divergence times of the species indicate that diversification of Ictalurus dates back to the early Oligocene, confirming its status as one of the oldest genera within the family Ictaluridae.