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.

Integrative systematics reveals the new land-snail genus Taphrenalla (Eupulmonata: Ariophantidae) with a description of nine new species from Thailand

“…nov., respectively. In general, the results from the ABGD and PTP approaches recognized higher number of species than morphological distinctiveness (Jirapatrasilp et al, 2019;Nantarat et al, 2019). The ABGD analysis using the K2P model also yielded higher numbers of MOTUs than the JC69 model (Jirapatrasilp et al, 2019), which is similar to this study.…”

“…Therefore, the K2P model, which is popular for COI barcoding may yield biased results (Collins et al, 2012;Srivathsan & Meier, 2012;Jirapatrasilp et al, 2019). Also similar to our study, in the recent analysis of the operculated land snails, Nantarat et al (2019) reported that the PTP species delimitation revealed additional MOTUs relative to the ABGD method.…”

“…For inferring molecular phylogenies, the mitochondrial cytochrome c oxidase subunit I (COI) and the large subunit ribosomal (r)RNA gene (16S) have been widely and successfully used to study putatively closely related land snails (Hyman et al, 2007(Hyman et al, , 2017Wu et al, 2008;Liew et al, 2009;Köhler & Criscione, 2015;Hyman & Köhler, 2018). The partial 28S nuclear rDNA (28S) sequences are more conserved and become useful to resolve deep relationships within the family (Wade et al, 2001(Wade et al, , 2006Páll-Gergely et al, 2017;Nantarat et al, 2019).…”

New insights into the genetic diversity of the stone crayfish: taxonomic and conservation implications

“…Relatively high genetic divergence (Figs. 2 , 5 , Additional file 3 ) indicates that identified MOTUs are in the process of splitting and may evolve into different species in the future [ 100 ]. The single locus-based species delimitation approaches, as ABGD, GMYC, bPTP, are known to oversplit taxa and their performance is sensitive to many factors such as higher substitution rates, the number of species included, uneven sampling, varying population sizes, level of gene flow, the number of singletons in the input trees and unresolved nodes [ 36 , 37 , 42 , 97 , 101 – 105 ].…”

Annotated checklist of the land snail fauna from southern Cambodia (Mollusca, Gastropoda)

“…The demarcation among different species is poorly understood. Thus, both intensive and thorough revision and redescription require more effective taxonomic characters, e.g., morphometric analysis of large series of specimens and perhaps molecular phylogeny to clarify the exact species boundaries (see Nantarat et al 2019).…”