A multidisciplinary approach to the definition of species boundaries of the branching species of the coral genus Psammocora (Cnidaria, Scleractinia)

The Indo-Pacific coral genus Psammocora Dana (1846) has never been formally revised, and its phylogeny has only been partially explored. Several synonymies have been proposed for the 11 nominal species which have highly plastic branching growth forms. In the present study, the definition of genetic and morphologic boundaries among three currently recognized branching morpho-species, Psammocora stellata, Psammocora contigua and Psammocora obtusangula, is addressed through a joint morphometric and molecular study using corallite and branch measurements, and a portion of the -tubulin gene as a marker. The results show a morphological and partial phylogenetic distinction between P. stellata specimens and a complex composed of P. contigua and P. obtusangula, which is interpreted as a synonym species of P. contigua. Among the factors that could be responsible for the lack of reciprocal monophyly of the three species, hybridization is considered the most likely, due to the presence of interspecific recombinant sequences. Type material of nominal species of branching Psammocora is examined and classified based on genetically defined groups, and compared with synonym in the literature. Among the morphological characters used, corallite variables were best for discriminating between the two lineages and allow recognition of putative hybrid specimens. Psammocora stellata is reported for the first time in the western Indian Ocean (Mayotte), thus greatly extending its known distribution range. Finally, a hybrid swarm is identified in the Arabo-Persian Gulf, while no genetic structure is detected elsewhere in the Indo-Pacific region