Genetic structure analysis of Spirometra erinaceieuropaei isolates from central and southern China

Sparganosis caused by invasion of the plerocercoid larvae (spargana) of Spirometra erinaceieuropaei have increased in recent years in China. However, the population genetic structure regarding this parasite is still unclear. In this study, we used the sequences of two mitochondrial genes cytochrome b (cytb) and cytochrome c oxidase subunit I (cox1) to analyze genetic variation and phylogeographic structure of the S. erinaceieuropaei populations.

A total of 88 S. erinaceieuropaei isolates were collected from naturally infected frogs in 14 geographical locations of China. The complete cytb and cox1 genes of each sample was amplified and sequenced. Total 61 haplotypes were found in these 88 concatenated sequences. Each sampled population and the total population have high haplotype diversity (Hd), accompanied by very low nucleotide diversity (Pi). Phylogenetic analyses of haplotypes revealed two distinct clades (HeN+HuN+GZ-AS clade and GX+HN+GZ-GY clade) corresponding two sub-networks yielded by the median-joining network. Pairwise FST values supported great genetic differentiation between S. erinaceieuropaei populations. Both negative Fu's FS value of neutrality tests and unimodal curve of mismatch distribution analyses supported demographic population expansion in the HeN+HuN+GZ-AS clade. The BEAST analysis showed that the divergence time between the two clades took place in the early Pleistocene (1.16 Myr), and by Bayesian skyline plot (BSP) an expansion occurred after about 0.3 Myr ago.

S. erinaceieuropaei from central and southern China has significant phylogeographic structure, and climatic oscillations during glacial periods in the Quaternary may affect the demography and diversification of this species.