Population genetic analysis and phylogeography of chinese liver fluke (Clonorchis sinensis Cobbold, 1875) from the Russia

In the present work, genetic diversity and phylogeography of the Far Eastern population of the liver fluke Clonorchis sinensis has been studied using nuclear rDNA internal transcribed spacer 1 (ITS1) sequences. C. sinensis is a causative factor of serious pathologies in humans. It is widely distributed in East Asia, but in Russia it is only found in the Far East. 26 metacercarian samples were collected at three distant localities in Khabarovsk and Primorsky Krai and were subjected to ITS1 sequencing. We also used 26 ITS1 sequences of C. sinensis from Primorsky Krai (two localities), which were previously deposited in GenBank. Statistical analysis was performed using the program DnaSP 4.5 and Arlequin 3.5. The median haplotype network was constructed by median joining using Network 4.6. Standard statistics showed low genetic diversity in the studied population: S, the number of polymorphic positions was 1.8%; Hd, haplotype diversity, was 0.21 ±0.05; and n, nucleotide diversity, was 0.0006 ± 0.0002. The obtained value of Fst was 0.045, which is indicative of low genetic differentiation. To establish the genealogical relationships between the haplotypes, we constructed a statistical parsimony network. It was found out that one major haplotype was identified in 88.5% of the sampled individuals. Of other five haplotypes, three were unique (singlets). The maximum distance between haplotypes was 3 SNP and one indel (5 substitutions). To estimate the population dynamics of C. sinensis in Russian part of the area, the analysis of pairwise nucleotide differences distribution was conducted. Unimodal mismatch distribution suggests a recent change in population size. Therefore, we believe that our data are consistent with a "founder effect" hypothesis, when a small number of migrants that were not genetically representative of the ancestral population have colonized a new area. To estimate the expected time of the species expansion, we used substitution rate (0.8%/MY) previously established for Schistosoma species (Schistosomatidae, Trematoda). Based on these data, C. sinensis expansion began approximately sooner than 4.5 kBP. We conclude that the outspread of the studied species to the Russian Far East territory could be due to the Holocene migration of the final hosts including humans.

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