Study On Genetic Variation And Population History Of Odorrana Tormota In South Anhui Province Based On Mitochondrial DNA Cyt B Gene

The Chinese concave-eared frog (Odorrana tormota) is a rare speciesendemic to eastern China. Currently, the species distributes only in the restrictedregions of Anhui (Mt. Huangshan and Jing county) and Zhejiang (Jiande county)province. In this study, cyt b gene sequence was used as molecular geneticmarkers to evaluate the mtDNA genetic variation and genetic differentiationamong five local populations in Southern Anhui province, and to investigate therecent population history of the species. The main results were as follows.1. Complete sequences of mtDNA cyt b gene were determined from126individuals from Xiangxi (n=31), Fuxi (n=27), Chengkeng (n=21), Zhanghe(n=18) and Taoling (n=29) populations of the species. In the complete sequenceof cyt b gene (1146bp),39variable sites were identified and29distincthaplotypes were defined. Nucleotide differences among cyt b haplotypes rangedfrom0.0873%to0.785%, and genetic distance based on Kimura-2parametersvaried from0.1%to0.8%. The haplotype diversity of cyt b was0.855; whilenucleotide diversity was0.00211. Compared with those wide-distributed species,such as Rana nigromaculata and Pelophylax plancyi, mtDNA genetic diversity ofOdorrana tormota identified within the current study was much lower.2. Analysis of molecular variance based on cyt b gene showed that thedetected genetic variation mainly existed within populations (94.87%), but notamong populations (5.13%). And significant genetic structure was detectedamong populations. Pairwise analysis showed that no significant differentiationwas detected between Chengkeng and Zhanghe, but did between the twopopulations and the other populations. All gene flows between the fivepopulations were larger than4suggesting, historically, individuals dispersal between populations was considerable common. Results of Mantel test (r=0.390,P=0.126) showed that no significant correlation was detected between geneticdifferentiation and geographical distance.3. At the species level, both values of Tajima’s D and Fu’s Fs of cyt b genewere significantly negative. These statistical parameters showed thatconsiderable low frequency variations were accumulated in the species and thepopulations have historically undergone regional expansion events. Thisinference was also supported by results of mismatch distribution analysis. For cytb gene, the mismatch distribution curve of the whole population was bell shape,in line with the expected distribution curve of the population growth model.According to cyt b gene evolutionary rate of2%-4.4%Mry of Rananigromaculata, the time of population expansion of Odorrana tormota wasestimated to be occurred about8,394-18,466years ago following the last ice agein the Pleistocene. In accord with mismatch distribution results, Bayesian skylineplot analysis showed the initial population expansion occurred about15,500years ago followed with a long time of stability. It was about6,000years ago thatthe population began to decline and the population number decreased drasticallyabout2,500years ago.