Shell chirality and phylogeography of land snail Satsuma batanica species group (Gastropoda: Stylommatophora: Camaenidae)

Chirality has been recognised as a potentially important mechanism in the speciation of land snails because it leads to reproductive isolation between individuals with different coiling directions. The Satsuma batanica species group comprises the sinistral S. batanica and the dextral S. bacca, despite the observed sympatric distributions of the two chiral morphs. This study examines the population structure, phylogeographic history and taxonomy of the species group by analyzing mitochondrial COI gene sequences. A total of 127 haplotypes were identified from 367 individuals collected from 39 locations. The phylogenetic trees, constructed using Bayesian inference and maximum likelihood methods, along with the medianjoining network, identified 14 clades. The reconstructed ancestral states indicate that the most recent common ancestor of the S. batanica species group was sinistral. The frequent occurrence of the dextral morph, the shared haplotype, the sympatric distribution, and the co-occurrence of the two chiral morphs within the same phylogenetic clades recovered here do not support reproductive isolation and single-gene speciation based on chiral differences. All the names belonging to the S. batanica species group are considered synonyms because of their molecular and morphological similarities. This species is estimated to have originated approximately 615 thousand years ago from the northern margin of its current distribution. Two major genetic divergence stages occurred around 440 and 50-100 thousand years ago. The formation of ancient islands through orogenic activities is utilised to explain the phylogeographic history of the species.