Morphometrics and phylogeography of the cave-obligate land snail Helicodiscus barri (Gastropoda, Stylommatophora, Helicodiscidae)

Abstract

Molecular studies have recently led to the detection of many cryptic species complexes within morphologically ambiguous species formerly undescribed by the scientific community. Organisms such as land snails are at a particularly higher risk of species misidentification and misinterpretation, in that gastropod systematics are based almost entirely on external shell morphology. Subterranean ecosystems are associated with especially high degrees of cryptic speciation, largely owing to the abiotic similarities of these systems. In this study, we attempt to diagnose the potential cryptic diversity in the troglobitic land snail Helicodiscus barri. Land snails are generally associated with having low vagility, and as such this species' broad, mosaic distribution indicates the misdiagnosis of this organism as a single species. We analyze both mitochondrial (16S, CO1) and nuclear (28S, H3) genetic data for 23 populations. Phylogeny for H. barri was reconstructed using both maximum-likelihood and Bayesian approaches to assess relationships among populations, and two species delimitation methods (mPTP and ABGD) were used to detect the presence of unique molecular operational taxonomic units (MOTUs). Species delimitation results revealed seven and sixteen MOTUs respectively, suggesting the presence of several cryptic lineages within H. barri. To assess how external shell morphology corresponds with patterns of genetic and environmental variation, two morphometric approaches were used incorporating 115 shells from 31 populations. Both morphometric approaches reveal a significant environmental influence on shell morphology, and one approach showed the significance of MOTU groups. We discuss the delimitation and morphometric results and additionally provide discussion on the taxonomic and conservation implications of this study.A peer-reviewed open-access journal Nicholas S. Gladstone et al. / Subterranean Biology 30: 1-32 (2019) 2

Molecular phylogenetic analysis of Punctoidea (Gastropoda, Stylommatophora)

“…Fossils of helicodiscid taxa are known from the Early Miocene of Europe (genus Lucilla Lowe, 1852;Nordsieck 2014;Salvador 2014) and the Late Miocene of North America (Liggert 1997;Gladstone et al 2019), indicating a former wider Laurasian distribution.…”

Redescription of Monacha pantanellii (De Stefani, 1879), a species endemic to the central Apennines, Italy (Gastropoda, Eupulmonata, Hygromiidae) by an integrative molecular and morphological approach

“…The conclusion that ten populations from the central Apennines form a different species is supported by the analysis of K2P genetic distances of COI sequences (Table 5). Although the utility of the 3% barcode threshold as a marker for species distinction, applied in the so-called "barcode method" based on COI sequences (Hebert et al 2003a(Hebert et al , 2003b(Hebert et al , 2018Pentinsaari et al 2020), is disputable (Davison et al 2009;Hausdorf 2010, 2012;Köhler and Johnson 2012;Batomalaque et al 2019;Koch et al 2020), COI sequences have been used to analyse taxonomic problems in different gastropod families (e.g., Remigio and Hebert 2003;Elejalde et al 2008;Duda et al 2011;Breugelmans et al 2013;Proćków et al 2013Proćków et al , 2019Čandek and Kuntner 2015;Walther et al 2016;Kruckenhauser et al 2017;Galan et al 2018;Gladstone et al 2019;Harl et al 2019;Kneubühler et al 2019;Bamberger et al 2020). They were also useful in our previous studies on Monacha species (Pieńkowska et al 2015(Pieńkowska et al , 2018a(Pieńkowska et al , 2019a(Pieńkowska et al , 2019b.…”

A new species of stygobitic snail in the genus Antrorbis Hershler & Thompson, 1990 (Gastropoda, Cochliopidae) from the Appalachian Valley and Ridge of eastern Tennessee, USA

“…Within the superfamily Truncatelloidea, observing paraphyly and high intraspecific divergence among species within other gastropod families (especially subterranean groups) is common when analyzing mitochondrial genes (Wilke et al 2013; Whelan and Strong 2016; Gladstone et al 2019). As a result, we cautiously provide these molecular results as only one of several lines of evidence for the species designation of A. tennesseensis and advise for the incorporation of additional genetic data in the future.…”