| As an important economic and widely invasive bivalve species, the classification of the genus Corbicula clams have not been accurately resolved. Moreover, species delineation in Corbicula were even more complicated due to their androgenesis that resulting in the mismatch of mitochondrial/morphotype-nuclear genome. In addition, the complex classification of the genus Corbicula and the impacts of special geographical patterns in the Yangtze River may lead to the inaccurate resources assessment. Therefore, an integrated analysis that combining with the related interdisciplinary courses should be performed to provide more biogeographic information to further understand the detailed mechanism of the geographical structure and the correctly taxonomy of Corbicula in its native range in present study. The main results were as follows:(1) In present study, Corbicula clams were collected from six populations in the middle and lower of Yangtze River. The mitochondrial cytochrome c oxidase subunit I (COI) gene was employed to explore the phylogeographic patterns and genetic structure of the genus Corbicula. Results showed that 45 haplotypes were detected in 130 mt-COI fragments (614 bp) and identified 109 polymorphic sites. An analysis of molecular variance (AMOVA) of the 6 populations uncovered 49.14% of the genetic variation occurred among populations, and 50.86% within populations. Pairwise fixation index (Fst), gene flow (Nm) and genetic distance analyses indicated that the 6 populations were subdivided into two mainly groups. In addition, Hongze Lake (HZL) might have gene flows with Dianshan Lake (DSL) and Tai Lake (TL), respectively. Phylogenetic tree revealed the presence of five lineages (Lineage A, B, C, D, and E) among the haplotypes. The unimodal distribution in the lineages of A, B, C, and E indicated that the 6 populations of Corbicula might experience population expansion after bottleneck effect in 0.08-0.38 Mya.(2) Two color morphs (white and purple) of Corbicula sympatric in Datong Lake were compared by both morphometric (Shell length, Shell height and Shell width) and genetic analysis (based on the mitochondrial cytochrome c oxidase subunit I gene COI-mtCOI and 28S rDNA gene) to explore their taxonomic relationship. Morphological analysis showed that there were no significant differences in the three values of SH/SL, SW/SL, and SW/SH (P>0.05) between the two color morphs. Meanwhile, there were not significantly different in measurable parameters among the four mitochondrial COI haplotypes (DT-1, DT-7, DT-19 and DT-31) (P> 0.05). The sequences of four haplotypes (DT-1, DT-7, DT-19 and DT-31) were identical to FW1, FW5, FW4 and FW3 previously recorded in Asia, respectively. Restriction fragment length polymorphism (RFLP) analysis showed that only the sequence of haplotype DT-7 could be digested by the one-site restriction enzyme SacI into two fragments with 200/500 bp. The four haplotypes were shared with both white and purple color morphs. Phylogenetic analysis demonstrated that the four haplotypes were subdivided into two divergent clades among freshwater clade, and haplotype DT-7 was a divergent sister taxon to the other three. The results indicated that there were no distinct differences on morphological measures between the two color morphs, and each color morph shared with all four mitochondrial COI haplotypes. Two species (referred DT-7 as Corbicula fluminea and DT-1, DT-19 and DT-31 as Corbicula leana) might be coexisted in Datong Lake.(3) An preliminary analyses that combining the gonad histology, cell biology and molecular analysis were used to study the sex, chromosome ploidy, and the sperm morphology of the two different color morphs of Corbicula clams in Datong Lake. Results showed that there were only hermaphrodite and female individuals, no male were found existed in the Datong Lake. Both of the hermaphrodite and female ones were shared the white and purple color morphs. The phenomenon of unsynchronization development was found in gonad of the hermaphrodite individuals, and there were no effect on the development and growth process with each other. Then it speculated that the sexual reversal might be possibly existed in Corbicula clams. Chromosome ploidy analysis revealed the diploid (2n=36) and triploid (3n=54) of Corbicula clams may be coexisted in Datong Lake. The biflagellate sperm in this study indicated that the reproduction model of Corbicula clams in Datong lake were anadrogenesis. Phylogenetic analysis that constructed by the mitochondrial COI sequences of the histology, and cytology analysis samples recovered that only 4 haplotypes (DT-1, DT-7, DT-31, and DTI-3) were found in these studied samples, and the haplotype DT-7 was a sister clad to the remaining haplotypes. |
PDF Full Text Request