Resources Evaluation Of Corbicula Fluminea In Poyang Lake And Population Genetics Based On Different Geographical Scales

The Corbicula fluminea is belonged to Bivalvia of Mollusca.It is widely distributed in freshwater and brackishwater,which often is one of dominant species in benthic community and has important economic values and ecological function.There is significantly declined of resources of C.fluminea due to the severe habitat destruction during recent decades.Previous studies about C.fluminea are mostly related to germplasm resources or benthic animal ecology.However,there are not clear related to the situation,process and its affected factors of resource decline.Our study takes Poyang Lake as the main research area to analyze the resources situation of C.fluminea in different habitats,and further evaluating its resources changes in main lakes.Then we study the demographic and genetic charactctristics of wild C.fluminea populations under harvest management,and analyze genetic diversity of C.fluminea of 13 geographical populations from major river basins in our country based on mitochondrial COI gene sequences.In order to provide theoretical basis for the resource conservation and scientific management of C.fluminea.The main results are as follows:1.There were four quantitative surveys in Poyang Lake during April 2019 to January 2020.The results show that average density of C.fluminea was 14.98±1.75 ind./m2,average biomass was 29.80±10.27 g/m2 in Poyang Lake.There was no significant difference of mean density or biomass among different seasons.Among them,the highest density was in October 2019,then was in April 2019,the lowest density was in January 2020;the highest biomass was in October 2019,then was in July 2019,the lowest biomass was in April 2019.From different habitats,there was no great difference of mean density or biomass between the main lake area of Poyang Lake and it connected the Yangtze River channel.The result of RDA showed that WD,TP,Chl-a and DO as the main environment variables were positively correlated with the stock of C.fluminea in Poyang Lake.Among them,DO had the greatest influence on the stock of C.fluminea in Poyang Lake.2.From the population structure,the annual shell length of C.fluminea in Poyang Lake was 1.82～36.00 mm,and the population structure was in a stable state.Shell-length(L)and body-weight(W)data were fitted to an exponential function.The value of the exponent(b)was 2.479,indicating isometrioc growth of C.fluminea in Poyang Lake.Seasonal length-frequency data was analysed using the ELEFAN I technique to evaluate the age structure and growth parameters of the population.The von Bertalanffy Seasonal Growth parameters were estimated as asymptotic length(L∞)was 37.28 mm,growth constant(K)was 0.46/year,theoretical age at zero length(t0)was-0.56 year,longevity(tmax)was 6.5 years,growth performance index(Φ’)was 2.81.Further analysis showed that the total mortality(Z)was 1.15/year,natural mortality(M)was 0.85/year,fishing mortality(F)was 0.30/year,the current exploitation rate(E)was estimated to be 0.26.3.Investigating the C.fluminea density and biomass of 8 areas under two kinds of harvest pressure from Poyang Lake Basin.The results showed that average shell length was 19.05±4.95 mm,and habitat types had no significant effect on size of C.fluminea,which density and biomass in lake habitat were higher than peripheral habitat.However,the biomass of peripheral habitat was higher than lake habitat when the density was similar.And the C.fluminea size in lake habitat was smaller than peripheral habitat.4.We analyzed the genetic diversity and genetic structure of C.fluminea from Poyang Lake Basin based on mitochondrial COI gene.The results showed that genetic diversity of C fluminea in lake habitat were higher than peripheral habitat.The genetic structure of two habitats was similar,and showed unclear geographical lineage.The analysis of molecular variance(AMOVA)showed that significant genetic differentiation among populations in peripheral habitat and no significant genetic differentiation between populations in lake habitat.Mismatch distribution analysis(MDA)and neutrality tests results showed C fluminea populations had not experienced population expansion,which indicated C.fluminea populations from Poyang Lake Basin were stable.5.We analyzed the genetic diversity and genetic structure of C.fluminea of 13 geographical populations from major river basins in China based on mitochondrial COI gene.The results showed the number of haplotypes among different populations ranged from 4 to 12.Among them,PY and YJ population were the most.Haplotype diversity(Hd)ranged from 0.424 to 0.878.Among them,WS population were with the highest haplotype diversity.Nucleotide diversity(π)ranged from 0.00230 to 0.04694.Among them,WS population were the hightest nucleotide diversity.Phylogenetic and haplotype network analysis showed that the 13 geographical populations of C.fluminea was unclear geographical lineage.AMOVA results showed that there was significant genetic differentiation among 13 populations.Neutrality tests and mismatch distribution analysis(MDA)results showed that the 13 geographical populations of C fluminea had not experienced population expansion.