Morphological And Genetic Studies Of The Populations Of Ptychidio Jordani On The Main Stream Of Xijiang River In Guangxi

Ptychidio jordani,commonly known as the mouse fish,belongs to Cyprinformes,Cyprinidae,ptychidio,which mainly distributes on the main stream of Xijiang River in Guangxi.It is known as one of the four famous fishes in Xijiang River for its tender and delicious meat.Affected by overfishing,habitat retreat and deterioration of the water environment,the wild resources of P.jordani have declined sharply and have been listed as extremely endangered species in the Red List of China’s Vertebrates in 2016,so it is urgent to carry out the conservation and management of P.jordani.This research systematically explored the morphological differences of nine geographic populations（Tiane,Donglan,Dahua,Duan,Heshan,Wuxuan,Guiping,Pingnan and Wuzhou）on the main stream of Xijiang River in Guangxi based on morphology and genetics.Through the mitochondrial Cytb and D-loop region analyzed the genetic diversity and genetic structure and the formation mechanism of the geographical distribution pattern was systematically revealed.It aims to provide scientific reference for the population identification,the protection and rational utilization of P.jordani.1.Morphological study on the populations of P.jordani（1）Morphological analysis of P.jordani populationsIn this study,we conducted a multivariate statistical analysis of 333individuals from nine geographic populations of P.jordani by combining traditional morphology and measurement of truss network.Thereinto,principal component analysis extracted a total of four principal components（PC1～PC4）can explain 81.429%of the morphological differences.The contribution rates of top two principal components（PC1 and PC2）were 61.830%and 7.863%,and mainly reflected morphologic changes on the dorsal-ventral axis and tail of the fish.By making a scatter plot on the scores of Principal component,the morphological differences of most populations were easier to distinguish on the PC1 than PC2,Guiping,Pingnan and Wuzhou have deviated significantly from other populations.Further one-way ANOVA revealed that there were significance differences（P<0.05）in the characters of dorsal-ventral axis（D3-6and D5-8）of these three populations with most populations.In the discriminant analysis,the comprehensive discriminant accuracy of each geographical population was as high as 96.36%and it reached to 91.30%after cross validation.The scatter plot showed that Wuzhou,Guiping and Pingnan populations were relatively independent.Cluster analysis founded that Wuxuan population was most similar to that five populations from upstream with morphological characters,which first clustered into a single clade,then in turn clustered with far morphological distance of Wuzhou,Guiping and Pingnan populations together.The results of difference coefficient calculation showed that Pingnan,Wuzhou and Guiping populations from mid-down stream have reached the subspecies differentiation level with most populations on D5-8 and other character parameters,of which Pingnan had the largest degree of difference with other populations.In addition,the main scatter plot and the results of cluster analysis all found that the morphological distance between each population had a certain relationship with the actual geographical distribution,it was speculated that P.jordani may be affected by the local environment and produced the adaptive morphological differentiation.（2）Body length-body weight and fatness analysis of P.jordaniCorrelation of body length-body weight P.jordani showed that the growth of Guiping and Heshan populations were allometric growth,while other populations were uniform growth.The fatness of nine geographic populations of P.jordani showed that there was significant difference（P<0.05）between most populations,but no significant correlation with geographical distribution.Thereinto,the four populations from Donglan,Heshan,Guiping and Wuzhou were all relative fatness.There was significant difference in fatness（P<0.05）between Wuzhou and Guiping and other populations,it showed that Wuzhou and Guiping populations of P.jordani grew well.2.Genetic study on the populations of P.jordaniIn order to explore the genetic diversity and population structures of P.jordani,the mitochondrial D-loop region and Cytb sequences of 270 individuals from nine populations of P.jordani were sequenced.Results of genetic diversity of P.jordani population based on two mitochondrial gene showed the high haplotype diversities（h≥0.5）and low nucleartide diversities（π<0.005）characteristics;the genetic diversity of Hongshui River populations on the upstream were higher than that of the mid-down stream populations.the genetic differentiation index(F_st),gene flow（N_m）,the exact P text,the phylogenetic tree and the haplotype network map of P.jordani population based on mitochondrial D-loop region and Cytb sequences,it showed that there was a certain genetic differentiation between the upstream（Tiane,Donglan,Dahua,Duan and Heshan）and mid-down stream（Wuxuan,Guiping,Pingnan and Wuzhou）in two geographical regions.The genetic distance was less than 0.05 and subsequent analysis of molecular variance（AMOVA）showed that most genetic variation was found within populations.Thus,there was a certain differentiation among each geographic population of P.jordani on the main stream of Xijiang River in Guangxi,but it still belonged to the intraspecific differentiation.The neutrality test and mismatch distribution analysis based on two mitochondrial molecular markers D-loop region and Cytb sequences suggested that there was no population expansion event among P.jordani.In summary,most of the geographical populations of P.jordani on the main stream of Xijiang River in Guangxi exhibit high h and lowπphenomenon and the genetic structure among the populations were relatively single.In recent years,overfishing and the vulnerability of P.jordani to the environment changes such as construction of water conservancy facilities and the shipping channels make it instability and lead to the endangered resources of P.jordani.It is suggested that scientific protection and utilization should be carried out according to the current situation of P.jordani on the main stream of Xijiang River in Guangxi and the needs of economic development.