Diving into Diversity: The Complex Evolutionary History and Species Richness of the 'sawfin barbs' from Lake Edward and Adjacent Systems

Abstract

Enteromius Cope, 1867 is a species-rich genus of small cyprinids endemic to Africa, which includes the 'sawfin barbs'. This study explored the species diversity of this group within the Lake Edward system, including adjacent areas that belong to the Lakes Albert and Victoria systems. We used a multifaceted approach encompassing mitochondrial and nuclear DNA analyses, including a molecular clock analysis, and morphometrics. Additionally, broader regional relationships were investigated by including 'sawfin barbs' from other parts of the East Coast ichthyofaunal province and the Nile Basin, and from the Congo Basin, into the molecular analyses. In contrast to the previously reported three species from the Lake Edward system and adjacent areas, the results showed a fourfold increase in the number of species, thereby indicating that the three species actually constituted species complexes. Within these complexes, a consistent geographic pattern unfolded: if one species occurred at higher altitudes of the Lake Edward system, another closely related species occupied lower altitudes near Lakes Edward and George. This geographic consistency suggested an allopatric mode of speciation. Intriguingly, the revealed Pliocene-Pleistocene origin of nearly all species of 'sawfin barbs' from the Lake Edward system and neighbouring regions largely predated the important geological events that reshaped the hydrology in the western rift. This study offers a more detailed insight into the evolutionary patterns of the African small barbs representing a very high and unrecognized species diversity, accompanied by little morphological but high genetic divergence between species, indicating intriguingly old species origins.