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Abstract(s)
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.
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Citation
Zoologica Scripta, 42(2), 151-169