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 snailHelicodiscusbarri. 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 forH.barriwas 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 withinH.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.
Highlights
Caves provide a model system for studying the evolutionary processes and historical factors related to biogeography and speciation (Juan et al 2010)
The saturation of the land snail soft body with mucopolysaccharides inhibited the success of standard extraction procedures and subsequent sequencing
The CO1 dataset was assessed independently, as it was later utilized for the downstream species delimitation approaches
Summary
Caves provide a model system for studying the evolutionary processes and historical factors related to biogeography and speciation (Juan et al 2010). An increasing number of studies has examined population genetic and phylogeographic hypotheses of subterranean fauna (e.g., Moulds et al 2007, Snowman et al 2010, Weckstein et al 2016), which have greatly increased our understanding of colonization history, speciation, dispersal, and biogeography of troglobitic taxa (Juan et al 2010). Additional phylogeographic studies have uncovered considerable levels of cryptic diversity in subterranean species (Finston et al 2007, Juan and Emerson 2010, Niemiller et al 2012). Cryptic species complexes may be comprised of groups already at significant risk of extinction (Niemiller et al 2013)
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