The Population Genetics Of Mytilus Galloprovincialis And Hybridization Between Mytilus Galloprovincialis And Mytilus Coruscus

Mediterranean mussel?Mytilus galloprovincialis?is an introduced species for China and appeared only in Dalian,Liaoning province in 1950s.With the development of M.galloprovincialis aquaculture,the distribution of this species rapidly expanded to the coast of Zhejiang and Fujian province.However,M.galloprovincialis aquaculture declined sharply in southeast coast of China.In contrast,Mytilus coruscus became the major aquaculture species.“Relic”M.galloprovincialis still can be found in fragmentary areas along southeast coast of China,which provides a unique material for genetic structure study.On the other hand,the sympatry of M.galloprovincialis and M.coruscus facilitates the demonstration of introgression and species isolation mechanism.Population Genetic Study on Mytilus galloprovincialis in China CoastOur research analyzed the genetic diversity and population genetic structure of M.galloprovincialis in China coast.11 populations of M.galloprovincialis?Qinhuangdao,Zhuanghe,Dalian,Changdao,Kongtongdao,Rongcheng,Rushan,Aoshanwei,Jiaonan,Ganyu and Pingtan?were analyzed based on COI gene.5 typical populations of them?Zhuanghe,Dalian,Kongtongdao,Rongcheng and Pingtan?were further analyzed by means of 2b-RAD.According to the COI genetic differentiation coefficient for 11 populations,there are differentiations between Rushan and Qinhuangdao,Rushan and Kongtongdao,Rushan and Pingtan(F_st>0.05),respectively.We used Mantel test to find the correlation between geographic distance and genetic distance of 11 populations.COI data could not prove the existence of isolation by distance.The COI sequences of 11populations can be attributed to 13 haplotypes and then divided into 4 haplogroups according to their relationships.The ratios of 3 main haplogroups are similar in 11populations,revealing homogenous genetic structures for Chinese populations of M.galloprovincialis.We compared 13 COI haplotypes acquired with haplotypes from Mediterranean and northeastern Atlantic Ocean.The result showed that Chinese populations of M.galloprovincialis might be introduced from the Mediterranean Sea.We used 2b-RAD to test 5 typical populations and no differentiation was found.Mantel test showed a significant positive correlation between geographic distance and genetic distance.The genetic diversity parameters?H_o,H_e and PIC?calculated using2b-RAD data showed a low genetic diversity of 5 populations,however,there is a slightly increasing trend from north to south,especially that of the southernmost Pingtan population.Heatmap of differential SNPs clustering showed discrepant genetic relationships between 95 M.galloprovincialis and 5 M.coruscus,this might be an evidence of hybridization between the two mytilus species and introgression from native M.coruscus to M.galloprovincialis.Hybridization between Mytilus galloprovincialis and Mytilus coruscusIn order to clarify the feasibility of interspecific hybridization between the two commercially important mussel species,a diallel cross was conducted with 3replicates using the broodstocks of M.galloprovincialis from Dalian,Liaoning province and M.coruscus from Ningde,Fujian province respectively.Two cross groups?M.galloprovincialis?×M.coruscus?and M.coruscus?×M.galloprovincialis??were established,along with two control groups?M.galloprovincialis?×M.galloprovincialis?and M.coruscus?×M.coruscus??as controls.The development and growth were compared by monitoring of fertilization,hatching,survival and growth of the offspring from the four groups.Results showed that the fertilization rate exhibited notably asymmetric between the two cross groups.Mean fertilization rate of 88.87%was observed in the cross-group of M.galloprovincialis?×M.coruscus?,which was not significantly different from the two control groups.The fertilization and hatching rate of cross-group M.coruscus?×M.galloprovincialis?were significantly lower than all the other groups?P<0.05?,resulting in no offspring obtained eventually.The offspring from cross-group M.galloprovincialis?×M.coruscus?showed notable advantage in growth,as evidenced by the shell length of the planktonic larvae on day 9,11,13 and the juvenile on day 78 were significantly larger than the control groups?P<0.05?.The survival rate of cross-group M.galloprovincialis?×M.coruscus?had no significant difference from the control group M.galloprovincialis?×M.galloprovincialis?during the planktonic larvae stage,but significantly higher than the control group M.coruscus?×M.coruscus??P<0.05?.The results of this study provided valuable information for mussels breeding program in the future.