| The sciaenid fishes (family Sciaenidae) are very important fisher resource andattractive species for aquaculture. China has the highest number of species in this family,with about30species in17genera. Due to a prolonged period of intensive fishing, theresources of sciaenid fishes have been remarkably declined, some species even was listedas endangered. In addition, sciaenid fishes commonly occur in temperate to tropical coastalwater and estuaries throughout the world, but are absent or poorly represented in oceanicislands group. Such pattern of distribution of sciaenid fishes provides a good model forstudying the fish evolution. In this study, the population genetic structure of miiuy croakerin East China Sea was investigated first. Secondly, ten mitochondrial genomes of croakerswere sequenced and characterized. Bioinformatic analyses were used to compare thecharacterization of coding regions and detect the variation in non-coding regions. Thirdly,phylogenetic relationships of eleven croakers were investigated and molecular datingtechnology was used to estimate the divergence time of those species with the aim to inferthe history of their origin and evolution.This thesis mainly contains three parts as followings:1. Weak genetic structure was detected among the six miiuy croaker populations, Fstanalysis revealed that ZS population showed significant genetic differentiations with theother five populations (RA, WL, WZ, YQ and XS). Neutrality test, mismatch distributionanalysis and minimum spanning network analysis indicated the miiuy croaker in the EastChina Sea might have experienced a rapid population expansion, and this event mayoccurred in late Pleistocene, about17,4000years ago. The climate change happened inPleistocene ice age and the resulting fluctuation of sea levels might explain the suddenexpansion of miiuy croaker population.2. The mitochondrial genomes of ten croakers are much conserved in genomecomposition, gene order, gene structure, base composition and codon usage frequency, andare similar to the typical vertebrate mitochondrial genome. Significant structure variationswere detected in the non-coding region. The pattern of loop and stem are different amongten mitochondrial genomes. The loop of OLhas three types: T-rich or partial T-rich, C-rich or partial C-rich, and no base-bias. Two type of conserved motif were identified in stem ofOL:5’-GCCGG-3’ and5’-ACCGG-3’. The complete central conserved sequence domainwas absence in the mitochondrial genome of spinyhead croaker, bighead croaker, smallyellow croaker and large yellow croaker. The incomplete central conserved sequencesdomain was detected in the mitochondrial genome of silver croaker, with absence of CSB-F.Although the central conserved sequence domain in goatee croaker was complete, but theCSB-E was5’-GTGAGG-3’, rather than the typical5’-GTGGGG-3’, all these resultsindicated that the control region in mitochondrial genomes of sciaenid fishes may evolveunder different pattern.3. The phylogenetic tree supported the monophyly of Sciaenidae and Pseudosciaeniae,but rejected the monophyly of Argyrosominae. Larimichthys and Collichthys have agenetically closet relationship, and the monophyly of both genera were rejected,introgressive hybridization may exits between Larimichthys and Collichthys fishes. Silvercroaker was found to be more evolutionarily older than goatee croaker, golden drum andyellow drum. Molecular dating analysis showed that the sciaenid fishes of coastal water ofChina may originate in the middle Pleistocene, about1.01million years ago (95%Posteriorprobability density0.7176mya to1.3132mya) and was obviously later than the ancestor ofAmerica sciaenid fishes documented by fossil record. This result could be another evidencefor the hypothesis that the common ancestor of family Sciaenidae may have a New Worldorigin, with subsequent dispersal of ancestor of the Old World group. |
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