Evolution of the Yangtze River reconstructed from the largest molecular phylogeny of Cyprinidae

Abstract

The Yangtze River is the longest river in Asia, but its evolutionary history has long been debated, in particular the origin of the First Bend and formation of the Three Gorges. Diverse groups of endemic freshwater fishes have evolved in this river. Here we present the historical, spatiotemporal pattern of the endemic East Asian cyprinid clade based on the largest molecular phylogeny of Cyprinidae, including 1420 species and fossil records. Based on the evolution of egg types adapting to different hydrological conditions, we show that the ancestors of this endemic clade (laying adhesive eggs) were distributed in southern East Asia before ~24 Ma and subsequently dispersed to the Yangtze River basin to spawn semi-buoyant eggs at ~19 Ma. These results are consistent with the Yangtze River reversing its flow direction from southward to eastward to form the present river system around the Oligocene-Miocene boundary (~24–19 Ma). Some East Asian cyprinids evolved into fishes producing adhesive eggs again at ~13 Ma. This together with an increased net diversification rate, indicates that the river formed a potamo-lacustrine system during the Mid-Miocene. This new reconstruction of the history of the Yangtze River system through Cyprinidae phylogeny, together with the evolution of egg types in endemic East Asia cyprinids, improves the time resolution derived from geological studies.