Population Genetic Analysis Of Saurogobio.dabryi And S.punctatus In The Jialing River

Saurogobio dabryi and S.punctatus,a recently discovered new species,are small fishes that belong to the subfamily Gobioninae of the Cyprinidae,and widely distributed in the Jialing Rriver.The two species are similar in morphology,and also in distribution region.However,it was still unknown whether their genetic diversity and structure had similar characteristics in the Jialing River basin.Some researches had indicated that there were significantly discrepant in the biological characteristics in different sections of the Jialing River.In recent years,with nearing the completion of channelization project of Jialing River,the fragmentation of aquatic habitats,the decline of fish resources and other issues caused by the dams were becoming increasingly acute.Under the circumstances,it had been a worrying problem that whether the fish genetic diversity was affected.Therefore,113 S.dabryi and 109 S.punctatus that sampled from Chaotian district(CT)of the upstream,Cangxi county(CX)and Peng'an county(PA)of the midstream,Hechuan district(HC)of the downstream of the Jialing River were used to analyze their genetic diversity and structure,using the mt DNA control region sequences and 10 microsatellite loci to provide some references for the wild fish conservation in the Jialing River and the upper Yangtze River.The main results were as followed:(1)The mt DNA control region sequences of 113 tails S.dabryi in Jialing River were detected 39 haplotypes,haplotype diversity(h)of HC,CT,CX,PA were 0.940,0.929,0.877,0.875,nucleotide diversity(?)of HC,CT,PA,CX were 0.0264,0.0180,0.0120,0.0100,respectively.It can be seen that population genetic diversity of downstream was slightly higher than the upstream and midstream group.The analysis based on microsatellite data showed a similar trend: the microsatellite loci of the downstream HC population was highly polymorphic,while those of the midstream and upstream populations were moderately polymorphic.The AMOVA analysis showed that genetic differentiation mainly occurred between groups(69.38%)rather than between individuals within groups(22.23%).The genetic differentiation in the midstream and upstream(CX and PA,CT)was smaller,while the genetic differentiation between the downstream(HC)and the two river segments was larger.The population structure analysis,haplotype network diagram analysis and phylogenetic analysis all showed that the four S.dabryi populations can be divided into two genetic components,namely the midsream and upstream(CT,CX and PA),the other parts was downstream(HC)population.The mismatch distribution of nucleotide,BSP analysis and mode-shift tests to detect that four S.dabryi populations CX,PA,HC populations are in a stable state,while CT population has expanded trend,recently.(2)The mt DNA control region sequences of 109 tails S.punctatus in Jialing River were detected 33 haplotypes,haplotype diversity(h)of CT,HC,CX and PA were 0.997,0.960,0.779,0.703,nucleotide diversity(?)of HC,CT,CX and PA were 0.0482,0.0377,0.0284,0.0217,number of haplotype(H)of HC,CT,CX,PA were 24,11,8,8,respectively.Overall speaking,the genetic diversity of the downstream(HC)population was higher than upstream and midstream(CT,CX,PA)population.The results of microsatellite data analysis showed that four S.punctatus populations in Jialing River were highly polymorphic,and the genetic diversity parameters showed that the allele abundance(Ai=8.319),polypeptide information content(PIC=0.739)of the downstream(HC)population were at a high level,followed by the midstream(CX and PA)populations,and the upstream(CT)population was the lowest level.The AMOVA analysis showed that the genetic differentiation occurred between groups(63.65%)rather than between individuals within groups(0.78%).The genetic differentiation between midstream(CX and PA)was small,while that between other populations was at a high level.The population structure analysis,haplotype network diagram analysis and the phylogenetic analysis all showed that the four S.punctatus populations can be divided into three genetic components,namely,the upstream(CT),the midstream(CX and PA)and the downstream(HC)population.The mismatch distribution of nucleotide,BSP analysis and mode-shift tests to detect that in four S.punctatus populations,CT population experience expansion,recently,CX and PA populations are in a stable state,the population numberof HC is decline,may be experienced bottlenecks.Through comparison,it can be found that the genetic diversity of downsream(HC)in the jialing river was higher than that of the midstream and upstream,but there were also existed significant differences in population differentiation,populationstructure and population dynamics.In the analysis of population differentiation and population structure,the S.dabryi population in each section of Jialing River is divided into two genetic groups,one is the CT,CX and PA population,the other is the HC population.However,the S.punctatus population is divided into three genetic groups,CT,CX and PA,and HC.In the analysis of population dynamics,the HC population of S.punctatus is in a quantity disadvantage,while the S.dabryi recently.In addition,the division of S.dabryi on population differentiation,population structure were consistented with feeding habits,scales rings forming time,the mode of growth in different reaches in Jialing River,and there are differences in division of otolith morphology,so the phenomenon indicates that the natural geographical differences and genetic differences shaped the genetic pattern of two species together.But changes in hydrological condition,habitat fragmentation and other unfavorable factors caused by Water conservancy project may be changing the pattern.