Fine-scale population structure of Oncomelania hupensis in a highly urbanized area of the Yangtze River basin

Oncomelania hupensis distribution and dynamics determine schistosomiasis japonica transmission risk. The Yangtze River basin harbors the most extensive distribution of O. hupensis in China, including numerous highly urbanized habitats suitable for this snail. All previous whole mitogenome studies of O. hupensis have been conducted at provincial or watershed scales, leaving fine‑scale population structure within such urban settings overlooked. Using Suzhou as a representative case, we combined hierarchical Bayesian Analysis of Population Structure (hierBAPS) with maximum likelihood (ML) phylogenetics to make detailed inferences about the evolution and diversification of O. hupensis at a fine scale. Snails were collected from six locations in Suzhou. HierBAPS was used to partition mitogenome sequences into genetic groups, which were then projected onto a rooted ML phylogenetic tree to visualize clustering patterns. In addition, genetic diversity indices, neutrality tests, and population structure analyses were performed to infer matrilineal population characteristics and structure. A total of 40 high‑quality mitogenome sequences were retained. Based on hierBAPS Level 1 groups and clades defined in the ML tree, all Suzhou individuals formed three distinct clades, corresponding to lineages phylogenetically related to sequences reported from Hunan, Anhui, and Zhejiang. These were further subdivided into five local genetic groups, consistent with hierBAPS Level 2 clusters and subclades identified in the phylogeny. Genetic distance heatmaps and principal coordinate analysis also supported this fine‑scale population structure. Notably, patterns of mitochondrial genetic structure suggested possible maternal gene flow between two of the six sampled populations. Phylogenetic topology, genetic diversity indices, and neutrality tests suggested that one of these two populations could serve as a source or corridor of maternal lineages connecting surrounding populations, warranting particular attention in future surveillance. Even at the city scale, O. hupensis populations harbor considerable genetic diversity, and hierBAPS clustering robustly resolved the mitogenome sequences into phylogenetically meaningful subclades. These findings provide new insights into the maternal dispersal and population structure of O. hupensis in Suzhou and similar regions, providing a scientific basis for formulating precise and sustainable surveillance and control strategies for schistosomiasis japonica.