A new endemic species Oreonectes weii sp. nov. (Cypriniformes, Nemacheilidae) within the Yangtze River Basin and its monsoon-driven evolutionary diversification

A new species Oreonectes weii sp. nov., is described that was collected from Shanggao County, Jiangxi Province, China, located at the upper reaches of the Yangtze River Delta. This naming honors the globally distinguished conservation biologist Fu-Wen Wei for his exceptional and pioneering contributions to biodiversity conservation and research. Morphologically, the new species can be distinguished from its congeners by a combination of meristic and morphological characters, including fin-ray counts, body coloration, eye normal, number of lateral-line pores, and gill-raker counts.

Genetically, it forms a distinct lineage in the mitochondrial Cyt b - based phylogeny and exhibits a genetic distance of 6.3 % from its sister species, O. polystigmus. We further estimated divergence time within the genus Oreonectes, which indicates an origin in the Late Oligocene (~ 27.06 Ma) and a most recent common ancestor at ~ 13.91 Ma. Our biogeographic analyses suggest that the Guijiang-Hejiang River Basin likely served as a source area for the genus’ dispersal into adjacent basins, and that the new species probably originated from a dispersal event of its ancestral population from the Pearl River Basin to the Yangtze River Basin during the Late Miocene (~ 6.78 Ma).

Lineage-divergence dynamics indicate that cladogenesis began around 28 Ma, accelerated markedly at ~ 18 Ma, peaked at ~ 6 Ma, and subsequently showed a gradual decline. The current diversity pattern of Oreonectes may have been shaped primarily by dispersal mediated by enhanced precipitation under the East Asian monsoon climate, with subsequent erosion-induced geographical isolation likely promoting speciation and diversification within the genus.