Macro-evolutionary patterns of East Asian opsariichthyin-xenocyprinin-cultrin fishes related to the formation of river and river-lake environments under monsoon climate

Abstract

Although the East Asian monsoon is believed to be an important driver for the origin and evolution of the biotas in this region, the association has rarely been rigorously tested. Here, using phylogenetic comparative methods and analyses of key innovations of adaptive traits, we investigated evolutionary patterns of the East Asian cyprinid opsariichthyin-xenocyprinin-cultrin clade; the dominant species in lakes and rivers, which are the typical productions of monsoon climate. Our molecular phylogenetic analyses revealed the relationships as (Opsariichthys-tribe + (((Oxygaster-tribe ​+ ​Aphyocypris-tribe) ​+ ​Metzia-tribe) ​+ ​(Paralaubuca-tribe + (Squaliobarbus-tribe + (Hypophthalmichthys-tribe + (xenocyprinins ​+ ​cultrins)))))). Based on Bayesian relaxed-clock methods, we found that origins of the Squaliobarbus- and Hypophthalmichthys-tribes bearing the key adaptation of riverine spawning with drifting eggs occurred 22.5 and 21.1 Mya, respectively. These times are consistent with the Early Miocene origin of major rivers (e.g., Yangtze River) and the appearance of the East Asian monsoon climate. Diversification of the cultrins, characterized by spawning of adhesive eggs as well as swimming and feeding in lentic waters, were estimated to have evolved 16.6 to 0.2 Mya. This period covers three phases of enhancement of the East Asian monsoon from the Middle Miocene to the Pliocene (around 15–13, 10–7, and 3.5 Mya). The habitats of these cultrins and their evolution also suggest the appearance and development of a lake-river environment during those periods. Therefore, our results suggest close relationships between the evolution of these fishes and geological events in East Asia. Further, they provide knowledge that may help facilitate future conservation strategies such as the maintenance of high river flows during dam construction and operation.