Abstract
The genus Oxystele, a member of the highly diverse marine gastropod superfamily Trochoidea, is endemic to southern Africa. Members of the genus include some of the most abundant molluscs on southern African shores and are important components of littoral biodiversity in rocky intertidal habitats. Species delimitation within the genus is still controversial, especially regarding the complex O. impervia / O. variegata. Here, we assessed species boundaries within the genus using DNA barcoding and phylogenetic tree reconstruction. We analysed 56 specimens using the mitochondrial gene COI. Our analysis delimits five molecular operational taxonomic units (MOTUs), and distinguishes O. impervia from O. variegata. However, we reveal important discrepancies between MOTUs and morphology-based species identification and discuss alternative hypotheses that can account for this. Finally, we indicate the need for future study that includes additional genes, and the combination of both morphology and genetic techniques (e.g. AFLP or microsatellites) to get deeper insight into species delimitation within the genus.
Highlights
Molluscs comprise one of the largest marine phyla, comprising more than 50,000 described species, of which less than 10% are currently included in the global database of DNA barcodes (Radulovici et al 2010)
The mitochondrial cytochrome c oxidase subunit I gene (COI), used for barcoding purposes of animals is not efficient for all taxonomic groups, and pending the integration of the generation sequencing into the DNA barcoding technique (Taylor and Harris 2012), the barcoding approach has proved valuable in discriminating marine biodiversity (e.g. Sun et al 2012; see reviews in Radulovici et al 2010)
We determined the optimised threshold genetic distance (d) with which we tested the discriminatory power of COI sequences and delimited molecular operational taxonomic units (MOTUs)
Summary
Molluscs comprise one of the largest marine phyla, comprising more than 50,000 described species (marine species only), of which less than 10% are currently included in the global database of DNA barcodes (Radulovici et al 2010). DNA barcoding is a genetic technique designed to standardize and accelerate species identification as an instrument facilitating conservation efforts, ecosystem monitoring, and the identification of phylogeographic and speciation patterns (Radulovici et al 2010; but see Taylor and Harris 2012 for criticism) It has proved valuable in population genetics and phylogenetic analyses, identification of prey in gut contents, forensic and seafood safety, invasion biology (Armstrong and Ball 2005, Bucklin et al 2011) and in revealing cryptic species (Hebert et al 2004, Puillandre et al 2009, Lakra et al 2011). Five species are recognised (Branch et al 2010), but delimitation within the genus is still debated (Heller and Dempster 1991, Williams et al 2010), especially due to strong homoplasy in morphological characters traditionally used in identification keys (Hickman 1998)
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