Molecular Phylogeography Of Pampus Minor In The Coastal Waters Of China And Malaysia

The southern lesser pomfret（Pampus minor Liu and Li,1998）,belonging to Perciformes,Stromateidae and Pampus,is an offshore pelagic fish and mainly distributes in the southern Taiwan Strait,and has an important economic value.Due to the similar morphological characters and small size（adult length<150 mm）,P.minor was often mistaken for the juveniles of grey pomfret（P.cinereus）or silver pomfret（P.argenteus）in early studies.The incomplete taxonomic studies on Pampus fishes in traditional taxonomic references and books,thus many known Pampus fishes are often misidentified in current.In this study,we used the genetic structure and genetic diversity of the Pampus to analyze its distribution,and used morphological and DNA barcoding techniques to identify P.minor samples and determine the status of P.minor as a new species in the coastal waters of Wenzhou,China and Malaysia.The main findings are as follows.1.Redefinition of the northern and southern extremities of the occurrence of the P.minor based on mitochondrial CO1 sequences.Based on the morphological characteristics and DNA barcoding methods,our study constructed a neighboring phylogenetic tree of the P.minor CO1 sequences,under the premise of detailed and accurate morphological identifications,to accurately identify the P.minor samples collected in the coastal waters of Wenzhou and Malaysia and establish its status as a new record species in the waters of Wenzhou and Malaysia as well as to redefine the north-south extremities of the occurrence of the P.minor since sampling records were available as follows:it is mainly distributed in the south of the Taiwan Strait,the northern part of the South China Sea and the northern Gulf,the northernmost occurrence can reach the coastal waters of Wenzhou,and the southernmost occurrence can reach the coastal waters of Malaysia.The northward shift of the distribution range of the P.minor may be related to global warming,thus,the idea that global warming causes the northward shift of the species was verified.2.Genetic diversity analysis of the P.minor population based on mitochondrial DNA sequences（Cytb and CR）.The mitochondrial DNA sequences（Cytb and CR）were used to conduct a molecular phylogenetic study of 264 individual P.minor collected from 11 geographic populations in coastal China（Xiamen,Zhangpu,Taiwan,Zhuhai,Zhanjiang,Beihai,Weizhou Island,Haikou and Sanya）and Malaysia（Kuala Selangor,Mukah）from May2016 to December 2017.The molecular phylogeographic results showed high genetic diversity in the P.minor,suggesting that it may have experienced a population expansion event during its history,but lacked sufficient time for nucleotide variation to accumulate.The both mitochondrial fragments results indicated that the genetic diversity of the Chinese population was lower than that of the Malaysian population,which can be attributed to the higher fishing pressure in the Chinese population and the better habitat in the Malaysian population.By constructing a neighbor-joining phylogenetic tree and a minimum spanning tree,two clearly divergent phylogenetic lineages were detected within the P.minor species,but they did not differ significantly in spatial distribution,there was no geographical structure and genetic divergence mainly originated within the population.The F_ST results of the P.minor population showed significant divergence between the Chinese and Malaysian populations,and the AMOVA results indicated that genetic divergence was mainly originates from within the population.The geographic isolation caused by the Pleistocene ice age may have been one of the main factors in the differentiation of the P.minor population.During the Ice Age,the South China Sea formed a semi-blocked inland sea,providing glacial refuges for many marine organisms.And climatic oscillations during this period greatly influenced the geographic distribution pattern and genetic structure of the P.minor,with a significant reduction in the distribution of the pompano population,individuals survived in glacial refuges expanded rapidly during this period.For Chinese populations,genetic differentiation between populations was not evident,with the except for the Xiamen population.The ecological and geographic barriers formed by the Leizhou Straits,Hainan Island,Zhujiang River Diluted Water and the Taiwan Straits did not lead to the formation of phylogeographic patterns in the P.minor population.The genetic variation generated during this period is almost negligible,the Xiamen population can still be considered as a marginal population at the northern boundary of the range of the P.minor,and the marginal effect of a single species can help to analyse the genetic structure and evolution of the whole population in a limited spatiotemporal domain.The nucleotide mismatch distribution and neutrality tests for both mitochondrial fragments and the results of Bayesian skyline plots indicated that the population expansion did not deviate significantly from the expected distribution under the population expansion model.Therefore,it can be used to analyse the historical population dynamics of the P.minor populations.And the results suggest that the species experienced a population expansion event.The population expansion occurred during the late Pleistocene and the effective population size of the P.minor increased dramatically after the population expansion.