Genetic and morphometric evidence for unresolved species boundaries in the coral genus Psammocora (Cnidaria; Scleractinia)

A comparative morphological and molecular characterization of species boundaries between four species of the Scleractinian genus Psammocora, namely P. digitata, P. haimeana, P. profundacella and P. contigua was conducted. The definition of species boundaries in this genus has been the subject of few studies, in spite of the presence of ambiguous taxonomic distinction, and a revision of the genus has never been undertaken. The multivariate analyses of both descriptive and morphometric characters confirmed the distinction of P. digitata and P. contigua, conversely P. haimeana, P. profundacella and their intermediate morph differentiated on the basis of descriptive morphologic characters only. Morphometric characters alone allowed a less defined distinction between morphs, and morphological boundaries essentially intergraded in a gradient driven by enclosed corallite series characters. The phylogenetic analysis of a portion of the rDNA confirmed the morphological inferences, as P. digitata appears to be a distinct evolutionary lineage. Conversely, the other four morphs, P. contigua, P. haimeana, P. profundacella and their intermediate constitute a polytomic gene pool significantly distinct from P. digitata. Yet, P. contigua is significantly distinct from the other three morphs. Both morphological and molecular approaches suggested that P. haimeana, P. profundacella and their intermediate cannot be considered clearly distinct entities. Hybridization with other species of this genus not included in this study, or recent origin may have contributed to the polyphyly and lack of phylogenetic resolution of P. haimeana, P. profundacella and their intermediate morph. They appear to constitute a single gene pool showing morphological characters encompassing a gradient from the P. haimeana to the P. profundacella morphs. Such morphological variability possibly depends on environmental factors such as light conditions.