Le problème des frontières entre espèces chez les coraux scléractiniaires : le cas du genre Psammocora
Publié le 21 avril 2009, mis à jour le 20 juillet 2009
Toutes les versions de cet article :
Ecole Pratique des Hautes Etudes (Paris) thesis - Francesca Benzoni - 14th of June 2007 at the EPHE lab. (Perpignan).
Le problème des frontières entre espèces chez les coraux scléractiniaires : le cas du genre Psammocora (PDF, 17.4 Mo, in french)
The validity of species boundaries definition in Scleractinia, traditionally based on the carbonate
skeleton morphology, has been questioned as the relative extent of ecological and evolutionary
influence on the skeleton variability is still to be clarified. Molecular techniques have provided new
possibilities to explore species boundaries and the phylogeny of coral taxa. Although in some cases
traditional coral classification was proved in accordance with the results of reproductive and/or
molecular studies, it was also shown that the direct correspondence between genetic cohesion and
morphologic information is not always real.
The Indo-Pacific scleractinian genus Psammocora Dana, 1846 has received scarce attention in recent
taxonomic works, and its phylogeny has been only marginally explored. As the genus was never
revised 23 nominal species have accumulated in the scientific literature over the last two centuries.
The relatively small number of nominal species with a wide distribution range makes the genus
Psammocora a good model to test the phylogenetic validity of the morphologic boundaries of
operational taxonomic units. The aim of this work is to review the morphologically defined
operational taxonomic units described in the genus and to assess to which extent they represent the
outcome of an underlying systematic order through a multidisciplinary approach.
The delineation of species boundaries on the basis of the joint results of morphologic and molecular
analysis largely agreed with the main results obtained from the type material morphometric analysis
based on corallite structures. Six distinct entities including a new species could be defined based on
matching morphometric and genetic information. However, boundaries proved to be well defined in
some cases and permeable in others. Hybridization between Psammocora contigua and P. stellata was
evidenced. The exploration of Psammocora phylogenetic relationships at the genus and family level
provided evidence that the genus as currently recognised is not monophyletic as P. explanulata is
phylogenetically closer to the family Fungiidae than to any other Psammocora species. A revision and
detailed description of the morphologic structures on which Psammocora taxonomy has been based
allowed the recognition of morphologic features that appear to be unique to this genus. The
phylogenetic implications of such distinctive morphological traits proved important to revise
Psammocora at and above the genus level and support the re-establishment of the family
Psammocoridae Chevalier & Beauvais, 1987. Hence, in the case of Psammocora, the combined
investigation of skeletal morphology and molecular phylogeny over a large set of specimens, including
types and museum collections material, allowed reconciling the results of traditional and novel tools.
However, several discrepancies between the previously proposed synonymies and the results of this
study demonstrated the need for a complete taxonomic revision of the genus.
Although several questions remain to be addressed and additional data is needed, the results of this
study provide the first detailed insight on species boundaries in the genus Psammocora and the basis
for a taxonomic revision of the genus. Moreover, this study shows that the re-evaluation of previously
disregarded morphologic characters can prove phylogenetically informative when combined with
molecular results. Therefore, this study demonstrates the value of a multidisciplinary approach to
clarify the complex issue of species boundaries in Scleractinia.
Keywords : Scleractinia, Psammocora, phylogeny, taxonomy, species boundaries