Phylogenetics and species delimitations of the operculated land snail Cyclophorus volvulus (Gastropoda: Cyclophoridae) reveal cryptic diversity and new species in Thailand

Abstract

Recent conceptual and practical advances in phylogenetic species delimitation have enabled progressively robust biodiversity studies. Delimiting species in widespread taxa is an intriguing problem; the edible operculated land snail Cyclophorus volvulus (Müller, 1774) is a good example since it shows a high degree of shell and color variation along with a widespread distribution throughout Thailand. Taxonomic boundaries for C. volvulus were examined and clarified using a combined morphological and phylogenetic approach, the latter of which was based on both nuclear and mitochondrial gene sequences. Moreover, three species delimitation analyses were applied: Poisson tree processes (PTP), automatic barcode gap discovery (ABGD), and generalized mixed Yule-coalescent (GMYC). All phylogenetic trees revealed that C. volvulus was polyphyletic and comprised of three clades that coincided with their geographic distribution. The three species delimitation analyses concurred with the phylogenies and formed at least three groups. According to the results, C. volvulus s.l., as currently recognized, consists of three distinct species in Thailand: C. volvulus s.s., C. occultus sp. nov., and C. borealis sp. nov., which are described herein. Moreover, several of these highly distinct C. volvulus evolutionarily significant units (ESU) are likely to require urgent conservation attention.