How much data is enough? 1 name, 5 nuclear clades, 6 mitochondria: resolving the Ophionereis schayeri complex

Cryptic species complexes are certainly not uncommon among the Australian marine inverterbrates, but the widely-distributed banded brittle star Ophionereis schayeri has exceeded expectations. This species enjoys a distribution... [ view full abstract ]

Cryptic species complexes are certainly not uncommon among the Australian marine inverterbrates, but the widely-distributed banded brittle star Ophionereis schayeri has exceeded expectations. This species enjoys a distribution in excess of seven thousand kilometres coastal distance along the southern coast of Australia, being found from Geraldton in Western Australia to Coffs Harbour in New South Wales, around the coast of Tasmania and more recently from the Kermadec Islands in the South Pacific, as well as a reported depth range of 0-200m. Initial low-resolution investigations involving mitochondrial DNA (partial COI sequences) and portions of the nuclear ribosomal array (28S ribosomal RNA and internal transcribed spacer-2: ITS-2) revealed four very clear and distinct species-level clades: one located among the Kermadec Islands, one at greater depths, one shallow-water clade restricted to New South Wales occurring in sympatry with its sister species, and finally, one shallow-water clade extending across the entire Australian range in shallow water. The latter clade is further subdivided into three additional clades exhibiting COI divergences of 4-8%, values normally indicating that a clade should be considered a separate species. However, one of these lineages is only distinct in mitochondrial DNA and is indistinguishable according to the ribosomal array data, while another is only 4% divergent from the most abundant clade. The question of which might be a separate taxon or a case of mitochondrial introgression was difficult to answer with the initial data. Additional sequencing of 16S rRNA excluded the possibility of one clade being represented by a pseudogene. However, nuclear introgression of the ribosomal array could not be ruled out with the extant data. Finally, a subset of individuals from each clade were added to an exon-capture analysis. Successful analysis of 1500 exons in 400 genes confirmed the original patterns of divergence and cyto-nuclear discordance. The wide distribution of Ophionereis schayeri and the locations of the clades within the complex has significant implications for our understanding of lineage generation on the southern coast of Australia.