The Population Diversity And Conservation Of Endangered Chinese Cavefish,Sinocyclocheilus Microphthalmus

China is one of countries with the richest cavefish species diversity in the world.Sinocyclocheilus,a cyprinid genus,is endemic to China.All species in the genus have cave-dwelling behavior.Compared with the surface species,cavefish shows obvious morphological differences,which makes them become an excellent model for evolutionary study.However,most researches mainly focus on the species level in the past.And there is little attention to the populations of a given cavefish species.In this study,103 individuals from seven geographic populations of Sinocyclocheilus microphthalmus were selected as the research objects.Morphological and population genetic methods were applied to explore the morphological differences and genetic diversity among distinct populations.Depending on the research results,the endangered degree of S.microphthalmus was evaluated to provide reference and suggestions for population protection.Firstly,the study measured the morphology of populations of Sinocyclocheilus microphthalmus by using morphometric methods.Cluster analysis,principal component analysis,discriminant analysis and one-way ANOVA were applied to study the similarities and differences of morphological characteristics among diverse populations and environment influences on morphology.Population genetic research was based on the whole genome single nucleotide polymorphism data and 13 protein coding genes joint sequences in mitochondria to construct the phylogenetic relationship among populations of S.microphthalmus for exploring the genetic diversity and evolutionary relationship among populations.We also collected relevant environment information during field investigation.Based on the IUCN Red List assessment system,the endangered degree of species was re-assessed.Therefore,the protection countermeasures were put forward according to the assessment contents and results.According to the morphological differences of JQP,JZP,JYP,FYP and SCP,it was found that JQP was significantly different from JZP,JYP,FYP and SCP.The anal-fin base of JQP is close to the anus,different to other four populations with short distance to the anus.Morphological analysis showed that the five populations could be divided into two groups,JZP,JQP and JYP,FYP,SCP,JZP,JQP had significantly higher body height,head length and eyeball diameter than JYP,FYP,SCP(P < 0.001).Combined with habitat,JZP had relatively abundant food resources and light-coming,while the other three populations had the opposite micro-environments,indicating that the ecological environment played a certain role in promoting the morphological differentiation of species.The morphological similarity among populations within each group indicates that a similar environment may lead to similar adaptive characteristics among populations.Based on the molecular systematics of JZP,JYP,FYP,LLP,SMHP and SCP,it was found that the genetic diversity of Sinocyclocheilus microphthalmus was low at both species level and population level,indicating that the evolutionary potential of S.microphthalmus was low and its adaptability to environmental changes was weak.The genetic distances among six populations ranged from 0.00137 to 0.00448,among which JYP and JZP had the largest genetic distance,indicating that the two populations had the farthest genetic relationship.The differentiation coefficient among populations showed that only JYP and SMHP were moderately differentiated,and the rest were highly differentiated.The data of gene flow also confirmed this conclusion.The reasons for this may be the cave-dwelling behavior,weak diffusion ability and long-term geographical isolation,resulting in the lack of opportunities for gene exchange.The differentiation between populations of S.microphthalmus began in the Middle Pleistocene.The JZP firstly differentiated at about 0.46 Mya,and then differentiated into two branches before 0.33 Mya.One branch differentiated into LLP and SCP before 0.26 Mya,the other branch differentiated into JYP at about 0.24 Mya,and FYP and SMHP at about 0.07 Mya.The differentiation of the six populations may be affected by the geological uplift and climate change during the glacial periods,resulting in long-term geographical isolation,limiting gene exchange among populations and promoting the evolution of populations in different directions.The results of neutral test and mismatch analysis showed that the six populations had been in a stable state in history,and there was no noticeable population expansion.Re-evaluation of the endangered status for Sinocyclocheilus microphthalmus showed that its level was endangered(EN).The primary threats come from tourism development,underground water intake and over-fishing.It is therefore suggested that the protection of Sinocyclocheilus microphthalmus should be implemented as soon as possible by establishing protection areas,decreasing water pollution,scientifically managing cave tourism,and strengthening law enforcement.