Demographic history and population genetic structure of Anisakis pegreffii in the cutlassfish Trichiurus japonicus along the coast of mainland China and Taiwan.

Studying the genetic diversity of nematode parasite populations is crucial to gaining insight into parasite infection dynamics and informing parasite phylogeography. Anisakiasis is a zoonotic disease caused by the consumption of infectious third-stage larvae (L3) of Anisakis spp. carried by marine fish. In the present study, a total of 206 mitochondrial DNA sequences (cytochrome c oxidase 2, cox2) were used to study the genetic diversity, genetic structure, and historical demography of twelve A. pegreffii populations from Trichiurus japonicas along the coast of mainland China and Taiwan. Two distinct evolutionary lineages of A. pegreffii and no significant genealogical structures corresponding to sampling localities suggested that isolation in the marginal seas shaped their patterns of phylogeographic distribution along the coast of mainland China and Taiwan during glaciation with lower sea levels. Furthermore, pairwise FST values and AMOVA did not indicate any significant genetic differentiation among groups with no relation to the geographic area, which might be attributed to fewer barriers to gene flow as well as large population sizes. The results of the neutrality test, mismatch distribution, and Bayesian skyline plot analyses showed that entire population underwent population expansion during the late Pleistocene. Analysis of the demographic history revealed that A. pegreffii underwent historical lineage diversification and admixture due to secondary contact based on ABC analysis. The present research represents the first definitive population structure and demographic history across sampling locations of A. pegreffii along the coast of mainland China and Taiwan.