Systematic Taxonomy And Reproductive Characteristics Of Corbicula In The Dongting Lake

Corbicula has rich nutritional and medicinal value.It is an important human non-staple food and traditional Chinese medicine,and is also a natural food for livestock and fish.It has long been loved by the people of Southeast China,Japan and South Korea.In recent years,Corbicula has been fished for its increasing demand and economic value in domestic and foreign markets.The natural resources of Corbicula decreased gradually due to overfishing and habitat destruction,which seriously restricted the sustainable development of this industry.Tree synthesis analysis was carried out by using partial sequences of mitochondrial cytochrome oxidase subunit(CO I)and cytochrome b(Cyt b)gene as molecular markers to classify the Corbicula in the Dongting Lake.The gonad histology and sperm morphology of 126 Corbicula samples from the Dongting Lake were studied to determine the reproductive characteristics of Corbicula,especially the reproductive characteristics of androgenesis.The relationship between reproductive characteristics,species classification and haplotypes of Corbicula in the Dongting Lake was discussed,which will provide a reference for the rational exploitation and effective protection of its resources,and provide more comprehensive biological reproduction information for the study of reproductive characteristics of Corbicula in China.And it would be of great scientific significance to understand and explore the development and evolution of the androgenesis reproduction in nature.(1)A total of 5 haplotypes(DTH1-5)(MG546299-MG546303)were detected from 126 Cyt b gene sequences(531 bp)in the Dongting Lake,and 5 haplotypes were also detected in CO I gene sequences(614 bp),which were hap1-4(MG595699-MG595702)and hap5(KT893357),respectively.According to the ML phylogenetic tree of Cyt b and CO I genes in the Dongting Lake,they were both clustered into two branches.The Cyt b haplotypes DTH1 and DTH5 were corresponded to the CO I haplotype hap1(n=72).Besides,the Cyt b haplotypes DTH2-4 were identical to the CO I gene haplotypes hap2-5(n=54).By constructing the CO I phylogenetic tree,it was found that there were 2 lineages of Corbicula in the Dongting Lake.Meanwhile the CO I haplotype hap1 gene sequence was consistent with that of Corbicula leana,and the CO I hapoype hap2-5 gene sequence was consistent with that of Corbicula fluminea.The results showed that there might be two different species of Corbicula in the Dongting Lake,and they were C.leana and C.fluminea,respectively.However,the two Corbicula couldn’t be easily distinguished on the basis of their morphological characteristics alone,because univariate variance analysis of morphological parameters of the two populations of Corbicula showed no significant difference between them.(2)The results of gonadal histology and sperm morphology analysis of 126 Corbicula in the Dongting Lake were as follows.Gonadal histology results of C.fluminea(n=54)were as follows: 31 hermaphroditisms(57.4%),12 females(22.2%)and 9 males(16.7%),respectively.However there were 2 samples(3.7%)that their sex were unknown.Moreover there were only male individuals be found in C.fluminea haplotypes hap4 and hap5 individuals.And the gonadal histology results of C.leana(n=72)were as follows: 52 hermaphroditisms(72.2%),13 females(18.1%)and 7 males(9.7%).In the two species of Corbicula in the Dongting Lake,71 of the hermaphrodite individuals were biflagellate spermatozoa and 12 individuals could not determine the flagellum number.Among the 16 male individuals in the two species of Corbicula in the Dongting Lake,haplotype hap2 individuals of C.fluminea were biflagellate spermatozoa,while monotrichous spermatozoa was only found in haplotype hap3-5 individuals of C.fluminea.The male individuals of C.leana were all biflagellate spermatozoa,and there was no monotrichous spermatozoa.However,in these two species of Corbicula,there were 6 male individuals which could not determine the number of flagella.The results showed that the reproductive modes of two different species of C.fluminea and C.leana in the Dongting Lake were androgenesis predominantly,and other few individuals in sexual reproduction.However,the haplotype hap4 and hap5 individuals of C.fluminea had only male individuals and their reproductive mode were sexual reproduction.Besides both the two species of Corbicula in the Dongting Lake had hermaphroditism and dioecious.Meanwhile,the hermaphroditism was predominant reproduction in both two species.