Molecular Identification And Phylogeny Of Larvalmugilids In Zhejiang Coastal Sea

Mugilidae is a speciose family in the Order Mugiliformes which have a worldwide distribution ranged from marine, brackish, to freshwater habitats of the tropical, subtropical and temperate regions. Despite their economic and ecological importance, the identification and phylogeny of mugilids still remains a challenge due to their morphologic conservativeness both at the intra- and intergenera level. In this study, the molecular identification and phylogenetic analysis were carried out for larva mugilids collected from Zhejiang Coastal waters using DNA sequences. In addition, population genetic and phylogeographical structure of Liza affinis were investigated. The results are summarized as follows:An alignment of CO Ⅰ gene obtained 611 nucleotides for 227 larva mugilid sequences with a consensus length. In the sequences, 183 variable sites were observed, 165 of which are parsimony informative. Haplotype diversity and nucleotide diversity were 0.700 and 0.04858, respectively. Additionally, 48 haplotypes were defined. Based on the sequence similarity suggested by the Gen Bank and BOLD database, these sequences represent six species of Mugilidae, which are Liza affinis, Liza haematocheila, Chelon macrolepis, Chelon subviridis, Moolgarda cunnesius and Moolgarda seheli. Among these species, L. affinis is the most common across the coastal waters, about 73% of all samples. It is first time that M. cunnesius and M. seheli are reported in East China Sea. In addition, Liza carinata used to be described in the region is probably L. affinis that we reported in this study. On average, the pairwise genetic distance based on Kimura 2-parameter(K-2-P) is 0.003 within species, and 0.079 within genera. The intraspecific K-2-P distances are significantly lower than intrageneric K-2-Ps(approximately 1 to 26).Neighbor-joining(NJ), Maximum-likelihood(ML) and Bayesian phygenetic trees of Mugilidae in Zhejiang Coast based on CO Ⅰ sequences, phylogenetic topology obtained with these three methods was highly consistent, in which three major clades formed with strong statistical supports, corresponding to three genera of Mugilidae. NJ and ML trees constcruted using cytochrome b(Cyt b) DNA sequences constructed for the seven species are similar in topology with the COⅠ trees. However, the ML tree of Mugilidae based on SNPs derived from RAD-seq shows some disparity from the Cyt b and CO I trees, especially in topology with genus Liza and Chelon. This may be because different genes have different evolutionary rates.A total of 166 L. affinis from 10 localities across four Zhejiang Coastal areas were analysed using COⅠ DNA sequences. The low levels of both haplotype diversity(0.468) and nucleotide diversity(0.00117) suggest that the populations may have experienced bottleneck or founder effect in recent history. The results of mismatch distribution and neutral test in addition to a star-like haplotype network together are in support of a recent population expansion after bottleneck or founder effect. Furthemore, AMOVA and pairwise φST analysis indicate no significant difference among populations. All the results suggest a lack of phylogeographic structure of L. affinis in Zhejiang Coastal sea.