Phylogeography of Ophryotrocha labronica (Polychaeta, Dorvilleidae) along Italian coasts

Species of the genus Ophryotrocha are a well-studied group of organisms but,
despite the relatively large body of biological studies, little is known about their
intra-specific patterns of genetic diversity. In the present study, we analysed the
patterns of genetic variation in samples of Ophryotrocha labronica (Polychaeta,
Dorvilleidae) collected along the Italian coasts within three regions with different
thermal regimes: the Northern Adriatic Sea (NAS), the Ligurian Sea (LS),
and the South/Southeast Sicilian Sea (SS). A partial sequence of the cytochrome
c oxidase subunit I (COI) gene was used as a genetic marker. An
analysis of molecular variance (AMOVA) showed significant genetic differentiation
between the NAS and the other regions. Conversely, little or no genetic
structuring was found between the LS and the SS or amongst locations within
a given region. A Bayesian phylogenetic tree and a median-joining network
provided evidence for the occurrence of two highly divergent genetic lineages
characterized by a high average sequence divergence (17.2%, Kimura twoparameter
distance). The spatial patterns of genetic variation found in O. labronica
may reflect the signature of past expansion events of the two genetic
lineages. Although the high sequence divergence suggested that cryptic speciation
within O. labronica may have occurred, other traits such as the absence of
reproductive isolation, pattern of phenotypic variation and habitat specificity
prompted us to regard the two groups as distinct COI lineages of O. labronica.