Cryptic speciation and genetic structure of widely distributed brittle stars (Ophiuroidea) in Europe

Abstract

Pérez‐Portela, R., Almada, V. & Turon, X. (2012). Cryptic speciation and genetic structure of widely distributed brittle stars (Ophiuroidea) in Europe. —Zoologica Scripta, 00, 000–000. The development of molecular techniques has led to the detection of numerous cases of cryptic speciation within widely distributed marine invertebrate species and important taxonomic revisions in all the major marine taxa. In this study, we analysed a controversial marine species complex in the genus Ophiothrix, a widespread taxon in European waters traditionally assigned to two nominal species, Ophiothrix fragilis and O. quinquemaculata. These species are important components of the rocky shores and deep marine benthos along the North Atlantic and Mediterranean littoral. Their status (including variants of both species) has remained contentious due to overlapping variability in morphological characters. In this study, we analysed the genetic and morphological differences of Ophiothrix lineages along the Atlantic and Mediterranean coasts. We also assessed population genetic structure in the Atlantic and Mediterranean basins by sequencing two mitochondrial genes, the 16S rRNA gene and COI gene, of 221 specimens from 13 locations. Phylogenetic analyses demonstrated the existence of two genetically distinct lineages, attributable to two different species although unrelated to previous taxonomic distinctions. Morphological differences could also be detected between these lineages. Samples from the Northeast Atlantic and one from the deep Mediterranean grouped within Lineage I, whereas Lineage II pooled together the southern Atlantic and rocky shallow Mediterranean samples. In the northern region of the Iberian Peninsula and at a deep locality in the Mediterranean, both lineages overlap. Speciation processes likely happened during the Mio–Pliocene transition (about 4.8–7.5 million years ago), when marine‐level oscillations led to the blockage of major marine corridors in Europe and promoted genetic isolation by vicariance. Secondary contact between lineages following sea‐level increases and recolonization during the refilling of the Mediterranean after the Miocene salinity crisis could explain the present‐day distribution of genetic variability. No barriers to gene flow along the Atlanto‐Mediterranean area were detected for Lineage II, and the lack of genetic structure could be caused by a mixture of several factors, such as wide dispersal potential, recent demographic expansion and large population size.

Contrasted phylogeographic patterns on mitochondrial DNA of shallow and deep brittle stars across the Atlantic-Mediterranean area

“…II15. Effective population size estimations using the BSP confirmed the existence of larger population size in Ophiothrix sp.…”

“…II, originally preadapted to the warmer and shallower conditions of the southern basin of the North Atlantic, colonized the shallow intertidal-subtidal across the South European coast and the Mediterranean Sea after the opening of Gibraltar Strait following the Messinian Salinity Crisis. On the other hand, O. fragilis , preadapted to colder temperatures and deeper waters from the northern basin of the North Atlantic, subsequently colonized the deeper Mediterranean subtidal, where conditions are more similar in temperature to those currently found in the shallow Atlantic subtidal15. Thus, the distribution of these two Ophiothrix spp.…”

Comparative phylogeography and population genetic structure of three widespread mollusc species in the Mediterranean and near Atlantic

“…Species with a strong gene flow between the Western and the Eastern Mediterranean have been reported, such as brittle stars from the genus Ophiotrix (Pérez‐Portela et al . ) or the edible sea urchin Paracentrotus lividus (Calderón et al . ).…”

From metabarcoding to metaphylogeography: separating the wheat from the chaff

“…As before, we extracted haplotype information from all localities in Pérez‐Portela et al. (), spanning the Atlanto‐Mediterranean area, and compared with our results. We also obtained haplotype networks for the two closest populations studied in that work: Alcudia in the Balearic Archipelago and Ferrol in the Galician coast.…”