The Phylogenetic Relationships And Hybridization Introgression Of Chinese Bream Fishes In Cultrinae(Teleostei:Cypriniformes:Cyprinidae)

The original definition of the Chinese bream fishes including the species from the genera Megalobrama and Parabramis which belonging to subfamily Cultrinae(Cypriniformes: Cyprinidae). They are commercial freshwater fishes with higher and compressed body size, while Sinibrama fishes belonging to the same subfamily, is a kind of small freshwater fishes inhabiting rivers and lakes. But their external morphology is similar to the species in Megalobrama and Parabramis with a compressed body size. Bǎnǎrescu(1970) has ever classified Sinibrama as a subgenus in Megalobrama. Regarding current studies on the phylogenetic relationships among Cultrinae, although there were some disputes, the three genera showed close relationship and formed a monophyletic group no matter what data(morphological characteristics or molecular sequences) used. So we renamed the Chinese bream fishes as a group including the genera Megalobrama, Parabramis and Sinibrama in the present study.To date, there is no comprehensive study on the phylogentic relationships of this group and some studies suggested that there were hybridization introgression among species in Megalobrama and Sinibrama. Hence, the main aims of the present study are composed by three parts. Fristly, we use mitochondrial(COI and Cytb) and nuclear(IRBP, RAG1 and RAG2) DNA sequences as molecular markers to reconstruct the phylogenetic relationships of the Chinese bream fishes and test the monophyly of Megalobrama and Sinibrama. Secondly, we use 9 polymorphic microsatellite makers combined with the phylogenetic analyses based on mitochondrial and nuclear DNA sequences to investigate the hybridization and introgression among Megalobrama and Sinibrama fishes. Finally, multivariate morphometric analysis was conducted on the genus Sinibrma in order to investigate the species validity and taxonomic status of S. taeniatus.The main results were as follows:1. We totally determined 208 COI sequences with 669 bp, 208 Cytb sequences with 1140 bp, 197 IRBP sequences with 849 bp, 181 RAG1 sequences within 1473 bp and 207 RAG2 sequences with 1224 bp in the Chinese bream fishes and its related groups. We reconstructed the phylogenetic trees by using Bayesian inference(BI) and maximum likelihood(ML) methods based either on a single genes or concatenated dataset with Hemiculter tchangi as outgroup. The phylogeny relationship based on the mitochondrial genes showed that the Chinese bream fishes form a monophyletic group and to be the sister group of a cluster composed of Chanodichthys dabryi, Culter mongolicus and Culter alburnus. Megalobrama and Sinibrama were not monophyletic groups with S. taeniatus grouping with species from Megalobrama. The results based on nuclear genes showed that the Chinese bream fishes was not a monophyletic group, while Megalobrama was a monophyletic group and to be sister group of Parabramis. Species S. taeniatus is not grouping with other species of Sinibrama and Megalobrama but locating at the basal position on the phylogenetic trees. The results based on the combination of the mitochondrial and nuclear gene sequences supported the monophyly of the Chinese bream fishes. S. taeniatus is the sister group of the species from Megalobrama except M. terminalis. We also suggest to use the interspecific hybridization introgression to explain the relationship between Megalobrama and Sinibrama. In addition, the results of all the datasets showed that S. melrosei was the sister group of S. wui collected from Min Jiang River, Ou Jiang River, Qiantang Jiang River and Longshan River. S. wui from other locations clustered with S. macrops as well as M. skolkoii clustered with M. amblycephala and can’t be separated on the phylogenetic tree.2. Nine polymorphic microsatellite markers were genotyped in S. taeniatus, M. terminal, M. skolkoii, M. pellegrini and M. amblycephala. The cluster analysis of these polymorphic microsatellite markers were conducted by the STUCTUER software. The results showed that the optimum genetic clustering number was K=5. The first genetic cluster mainly included S. taeniatus collected from Min Jiang River(tributary of Yangtze River), E’mei River and Pu Jiang River. All the species of S. taeniatus from other sites were belonging to the second cluster and few of the individuals from M. pellegrini, M. skolkoii and M. amblycephala joined into the two clusters of S. taeniatus. The third cluster included all the M. pellegrini individuals. The fourth genetic cluster was composed of the species of M. skolkoii and M. amblycephala but some individuals of M. pellegrini, M. terminal and S. taeniatus were joined into this cluster. The last genetic cluster included all the M. terminal specimens. The results of cluster analysis based on the polymorphic microsatellite markers showed that S. taeniatus and the Megalobrama species were distinct groups. The introgression has just occured in part of mitochondrial genes so far.3. Multivariate morphometric analysis was conducted on the species of Sinibrama. Principal component analysis(PCA) was performed respectively for 31 measurable characters and 6 countable characters based on 349 specimens. According to the results, there was no significant difference between the population of S. wui and S. macrops. It was reasonable to admit that S. macrops was senior synonym of S. wui. The results based on the metrical characters and countable characters showed that S. macrops, S. melrosei and S. taeniatus were valid species, but there was remarkable morphological variations between S. taeniatus and other species in Sinibrama. The results from molecular systematics showed that S. taeniatus was not clustered with other species in Sinibrama also and the minimum genetic distance based on COI gene sequences between S. taeniatus and other Sinibrama species was 6.9%. Therefore, we suggested that the Sinibrama taeniatus should be separated from the Sinibrama and to be an independent genus of Cultrinae. According to the nomenclature and its original name when it was first established, we named the genus with Rasborinus and take Rasborinus taeniatus as the species name.