DNA barcoding uncovers cryptic diversity in 50% of deep-sea Antarctic polychaetes

Abstract

The Antarctic marine environment is a diverse ecosystem currently experiencing some of the fastest rates of climatic change. The documentation and management of these changes requires accurate estimates of species diversity. Recently, there has been an increased recognition of the abundance and importance of cryptic species, i.e. those that are morphologically identical but genetically distinct. This article presents the largest genetic investigation into the prevalence of cryptic polychaete species within the deep Antarctic benthos to date. We uncover cryptic diversity in 50% of the 15 morphospecies targeted through the comparison of mitochondrial DNA sequences, as well as 10 previously overlooked morphospecies, increasing the total species richness in the sample by 233%. Our ability to describe universal rules for the detection of cryptic species within polychaetes, or normalization to expected number of species based on genetic data is prevented by taxon-specific differences in phylogenetic outputs and genetic variation between and within potential cryptic species. These data provide the foundation for biogeographic and functional analysis that will provide insight into the drivers of species diversity and its role in ecosystem function.

Distributional Patterns of Polychaetes Across the West Antarctic Based on DNA Barcoding and Particle Tracking Analyses

“…The genetic diversity of the DNA barcodes generated from the nine morphospecies was investigated in Brasier et al (2016). Phylogenetic and distance analyses found evidence for twelve cryptic species, increasing the number of species in this study from nine to seventeen.…”

“…Phylogenetic and distance analyses found evidence for twelve cryptic species, increasing the number of species in this study from nine to seventeen. In Brasier et al (2016) clades were assigned MB# to distinguish species, including cryptic species, e.g., Scalibregma sp. MB1 and Scalibregma sp.…”

“…These results are presented in Neal et al (2017) and all voucher specimens were deposited in the Natural History Museum London, details can be found online using the Darwin Core Archive https://doi.org/10.5519/0068114. DNA was extracted and sequenced from nine polychaete morphospecies (211 specimens in all); for details on the phylogenetic analysis of these sequences including the identification of cryptic species see Brasier et al (2016). Prior to DNA barcoding, a biogeographic distribution classification; cosmopolitan, circum-Antarctic or restricted, was allocated to each initial morphospecies analyzed (Table 1), where: "cosmopolitan" species are those that have been recorded throughout the majority of the world's oceans and both hemispheres; "cicrum-Antarctic" species are those that have been collected within different regions of the Southern Ocean and are considered to be widespread around the Antarctic and "restricted" species are those only recorded in one Antarctic region or location with no records within the Register of Antarctic Marine Species (RAMS) recorded or Basic Local Alignment Search Tool (BLAST) matches from other localities.…”

“…Schüller and Ebbe (2014), investigated all georeferenced Register of Antarctic Marine Species (RAMS) polychaetes within the Scientific Committee for Antarctic Research Marine Biodiversity Information Network (SCARMarBIN), concluding that while Southern Ocean polychaete taxonomy is improving with new species descriptions, there are still many "cosmopolitan" species which are most probably Antarctic species different to their Northern counterparts. This can be easily tested using DNA barcoding where comparative sequences exist (Brasier et al, 2016).…”

“…This study uses mitochondrial DNA barcoding data from one of the largest Antarctic polychaete barcoding projects to date (Brasier et al, 2016), to investigate the distributions of nine polychaete morphospecies previously considered to be cosmopolitan or circum-Antarctic. We combine our genetic analyses with particle tracking models to examine the directionality and distance of pelagic polychaete larvae and the potential to maintain genetic connectivity across widely distributed populations.…”