Polyploid Evolution, Phylogenetic Relationships, and Biogeography of Sub-Saharan Africa’s Only Tetraploid Fish Group – Pseudobarbus and Allies (teleostei: Cyprinidae)

The tetraploid smiliogastrines (Pseudobarbus & allies) constitute a small group of cyprinids that are endemic to freshwaters of southern Africa. How and when these polyploids originated has remained a mystery to researchers for years. Their phylogenetic relationships and biogeographical history also need further investigation. In this study, we reconstructed the phylogenetic relationships of this group using DNA sequences from both mitochondrial and nuclear genes. The initial split occurred between Namaquacypris hospes and all other tetraploid smiliogastrines. Amatolacypris is sister to the clade formed by Sedercypris and Cheilobarbus, which are reciprocally monophyletic. The clade formed by these three genera is sister to the monophyletic Pseudobarbus. For the three nuclear genes (i.e., RAG1, IRBP2, and EGR2B) used, we attempted to separate the two gene copies for each gene and each polyploid species. On the phylogenetic trees inferred from individual nuclear genes, one gene copy of Pseudobarbus & allies was clustered with African Enteromius & allies, whereas the other gene copy seen to be more closely related to Asian Puntius & allies. These results suggest that this tetraploid group likely originated through hybridization, although additional nuclear genomic data will be needed to rigorously test this hypothesis. The maternal progenitor of this group is likely a lineage from African Enteromius & allies, while the paternal progenitor likely came from an extinct Asian lineage ("Lineage P") closely related to Puntius & allies. Our results suggest that the Lineage P might have originated earlier than the common ancestor of all African smiliogastrines. The tetraploid smiliogastrines may have originated at late Paleogene to Eocene (58.9-36.5 Ma). They established themselves in the Orange River and later colonized all major rivers and lakes to the south. During this process, the tetraploid ancestor diverged into the current generic and specific diversity.