The Mitochondrial Genome And Population Genetic Structure Of Chinese Freshwater Crab Sinopotamon Yangtsekiense

Freshwater crabs are special taxa in Brachyuran crabs which completely live in the freshwater. Sinopotamon yangtsekiense is an endemic species of China. We determined the mitochondrial DNA sequence of 5. yangtsekiense and discussed the phylogenetic status of freshwater crabs in Brachyuran according to gene arrangement features and sequence data sets. We also sequenced regions of mitochondrial COI and ND5 genes in order to address the genetic structure of S. yangtsekiense populations.1. The mitochondrial genome 5. yangtsekiense and phylogentic studies of Decapoda We determined the complete 11, 405 bp mitochondrial DNA sequence of S. yangtsekiense. It contains 11 protein coding genes (PCGs) and 12 tRNAs, typical of metazoan mitochondrial genomes. With respect to the ancestral mt gene order, there was only one tRNA (trnH) translocated out of the nad5-nad4 gene junction into the nad3-nad5 gene junction, just as two Portunoids and one Xanthoid. A duplication/ random loss model of a gene block F-nad5-H was proposed to account for the translocation. Based on two data sets of protein-coding genes (4PCGs: coxl~3, cob; UPCGs: except nadl and nad2 which were unsequenced ), Decapoda consisted of two suborders of Dendrobranchiata and Pleocyemata. The gene arrangement features at nad3-nad5 and nad5-nad4 junctions contain useful information for phylogenetic inference of the advanced groups within the Decapoda. According to either sequence data sets or gene arrangement features at both gene junctions, Brachyuran crabs were monophyletic and divergent between Heterotremata and Thoracotremata. Potamoidea represented by S. yangtsekiense were close to Portunoidea and Xanthoidea.2. Genetic structure of 5. yangtsekiense populations inferred from mitochondrial DNA sequences This study used molecular data (COI and ND5) to explore genetic structure of S. yangtsekiense. Eighty individuals were obtained representing 12 local polulations. Alignment of all sequences revealed 29 and 35 haplotypes for COI and ND5. Sequence analyses revealed two distinct clades, aYangtze-Huaihe clade (YH) including all S. y. yangtsekiense, and a Tongbai-Shanxian clade (TS) consisted of all S. y. tongbaiense and S. y. shanxianense by a high genetic divergence (8.35%). Nucleotide and gene diversity varied among the populations being highest in Yangtze and Huai, lowest in Shanxian and intermediate in Tongbai. According to the mismatch distribution of Yangtze and Huai populations, they were long-term stable. Tongbai population seemed to have undergone expansion 115,000-135,000 years ago. The maximum age of Shanxian population (0.12-0.14 Mya,) corresponded to the expansion time of Tongbai population and Shanxian population also underwent a recent expansion. Concordant geographical and genetic data point to a scenario of: (1) vicariance associated with uplifting of the Qinling and Tongbai-Dabie Mountains gives rise to the two separate clades; (2) Shanxian population is shown to be derived from Tonbai population; (3) the basins of lower Yangtze and Huai Rivers in East China are free from Quaternary glaciation, and inhabitable for 5. yangtsekiense since the later period of Tertiary. (4) The low genetic divergence of tongbaiense and shanxianense populations suggested that two subspecies would be combined to one.Three subspecies of S. yangtsekiense have been recognized based on morphological characteristics. The curve form of the terminal segment of the first pleopod of the male (or male pleopod 1) diagnose the three subspecies. The nominate subspecies S. y. yangtsekiense has straight terminal segment and occurs in the basins of lower Yangtze and Huai Rivers in East China. The terminal segment is slightly curved towards dorso-innerly in S. y. tongbaiense, and sharply curved in S. y. shanxianense. The former occurs in Tongbai County and surrounding areas in the Tongbai Mountains where the headwater of Huai River locate, while the latter in Shanxian County located south to the Yellow River in the eastern Qinling. According to our molecular evidence, we suggested that S. yangtsekiense should be recognized as two subspecies, one as S. y. yangtsekiense which has straight terminal segment and the other as S. y. tongbaiense (^shanxianense) which has curved terminal segment.