Genetic Differentiation and Population Structure of the Freshwater Snail Rivomarginella morrisoni (Gastropoda: Marginellidae) in Central and Southern Thailand

Rivomarginella morrisoni (Gastropoda: Marginellidae) is a narrowly distributed freshwater snail inhabiting drainage basins of central and southern Thailand. To clarify patterns of genetic differentiation across its range, 45 individuals from 11 sites across eight river basins were analyzed using two dominant molecular markers: sequence-related amplified polymorphism (SRAP) and inter-simple sequence repeats (ISSR). SRAP primers produced higher polymorphic information content (PIC) values than ISSR primers (0.35 vs. 0.27). Analysis of molecular variance (AMOVA) revealed strong population structure, with 80.29% of the genetic variation occurring among populations and 19.71% within populations Population differentiation statistic (PhiPT) = 0.803, p < 0.001). Unweighted Pair Group Method with Arithmetic mean (UPGMA) and principal coordinate analysis (PCoA) consistently separated central and southern populations, and STRUCTURE supported K = 2 as the most likely number of clusters. Similarly, principal component analysis (PCA) of morphological traits also distinguished specimens into two groups corresponding to these geographic regions, confirming region-specific divergence. Overall, the genetic and morphological patterns indicate restricted gene flow among basins and a clear separation between central and southern lineages of R. morrisoni. This study provides the first molecular evidence of population structure in this species and offers important baseline information for future taxonomic, ecological, and conservation research on freshwater marginellid snails.