DNA barcoding of reef brittle stars (Ophiuroidea, Echinodermata) from the southwestern Indian Ocean evolutionary hot spot of biodiversity

Abstract

In anticipation of the current biodiversity crisis, it has become critical to rapidly and accurately assess biodiversity. DNA barcoding has proved efficient in facilitating the discovery and description of thousands of species and also provides insight into the dynamics of biodiversity. Here, we sequenced a portion of the mitochondrial cytochrome c oxidase subunit I (COI) gene from all morphospecies of reef brittle stars collected during a large‐scale biodiversity survey in the southwestern Indian Ocean (SWIO). Three methods of species delineation (Automatic Barcode Gap Discovery, Generalized Mixed Yule Coalescent model, and Bayesian Poisson Tree Processes) showed concordant results and revealed 51 shallow reef species in the region. Mean intraspecific genetic distances (0.005–0.064) and mean interspecific genetic distances within genera (0.056–0.316) were concordant with previous echinoderm studies. This study revealed that brittle‐star biodiversity is underestimated by 20% within SWIO and by >40% when including specimens from the Pacific Ocean. Results are discussed in terms of endemism, diversification processes, and conservation implications for the Indo‐West Pacific marine biodiversity. We emphasize the need to further our knowledge on biodiversity of invertebrate groups in peripheral areas.

Unexpected high abyssal ophiuroid diversity in polymetallic nodule fields of the Northeast Pacific Ocean, and implications for conservation

“…The results obtained here were consistent with many other studies showing that different species delimitation methods can produce different delimitation scenarios when employing single-locus data (Hofmann et al, 2019). The single-locus species delimitation methods tested here, although they are extensively used throughout the literature, including for the Ophiuroidea (Khodami et al, 2014;Laakman et al, 2016;Boissin et al, 2017), are each subject to potential biases and differing https://doi.org/10.5194/bg-2019-360 Preprint. Discussion started: 26 November 2019 c Author(s) 2019.…”

“…Arguably, GMYC and especially the single-threshold version of the method is a robust species delimitation method (Fujisawa and Barraclough, 2013). GMYC performance depends on a single-locus ultrametric tree which tends to compress the coalescent events towards the tips of the tree, making it especially difficult to distinguish closely related species (Boissin et al, 2017). It has been argued that the PTP methods generate diversity estimates that are more robust to different phylogenetic methods, while GMYC is more sensitive, but provide consistent estimates for BEAST trees (Tang et al, 2014).…”

“…All ophiuroid individuals collected were morphologically identified to the lowest possible taxonomic level (primary species hypotheses, PSH, Puillandre et al, 2012;Boissin et al, 2017). Where possible, individuals were assigned to named species, however, in many cases because of their very small size, their early developmental stage (post-larval individuals) or their unique morphology, assignment in a morphological operational taxonomic unit was possible only at a higher taxonomic level, i.e.…”

“…Congruent support across a range of species delimitation approaches is assumedly provides more reliable results than a single method (Carstens et al, 2013;Fontaneto et al, 2015). Therefore, four different species delimitation analyses, including both distance-and tree-based approaches, were performed on the COI dataset, to allocate sequences into genetic species (secondary species hypotheses, SSH Puillandre et al, 2012;Boissin et al, 2017). Distance-based approaches detect the distance at which the 'barcode gap' occurs and sort the sequences into putative species based on this distance, whereas tree-based approaches use a phylogenetic tree from which the fit of speciation and coalescent processes are modelled to delineate species based on the branching rate of the tree (Carstens et al, 2013;Tang et al, 2014).…”

Species delimitation in the presence of strong incomplete lineage sorting and hybridization: lessons fromOphioderma(Ophiuroidea: Echinodermata)

“…(Hebert et al, 2003)) due to the numerous advantages of mitochondrial DNA such as its ubiquity, ease of amplification, high mutation rate and finally its reduced effective size compared to nuclear DNA which makes isolated populations diverge by genetic drift (and eventually reach reciprocal monophyly) more rapidly. In fact, it allowed in the first place the discovery of the O. longicauda species complex (Boissin et al, 2011;Stöhr et al, 2009), and it is still efficient to discover additional cryptic species, including brittle stars (Boissin et al, 2017). Nevertheless, mitochondrial lineages did not correspond to species (i.e.…”