Genetic Structure of Water Chestnut Beetle: Providing Evidence for Origin of Water Chestnut

Water chestnut beetle (Galerucella birmanica Jacoby) is a pest of the water chestnut (Trapa natans L.). To analyze the phylogeny and biogeography of the beetle and provide evidence for the origin of T. natans in China, we conducted this by using three mitochondrial genes (COI, COII and Cytb) and nuclear ITS2 ribosomal DNA of G. birmanica. As for mtDNA genes, the beetle could be subdivided into three groups: northeastern China (NEC), central-northern-southern China (CC-NC-SC) and southwestern China (SWC) based on SAMOVA, phylogenetic analyses and haplotype networks. But for ITS2, no obvious lineages were obtained but individuals which were from NEC region clustered into one clade, which might be due to sequence conservation of ITS2. Significant genetic variation was observed among the three groups with infrequent gene flow between groups, which may have been restricted due to natural barriers and events in the Late Pleistocene. Based on our analyses of genetic variation in the CC-NC-SC geographical region, the star-like haplotype networks, approximate Bayesian computation, niche modelling and phylogeographic variation of the beetle, we concluded that the beetle population has been lasting in the lower, central reaches of the Yangtze River Basin with its host plant, water chestnut, which is consistent with archaeological records. Moreover, we speculate that the CC-NC-SC population of G. birmanica may have undergone a period of expansion coincident with domestication of the water chestnut approximately 113,900-126,500 years ago.