Taxonomy and species boundaries in the coral genus Favia Milne Edwards and Haime, 1857 (Cnidaria: Scleractinia) from Thailand revealed by morphological and genetic data

While Faviidae is a widely and uniformly distributed coral family throughout the Indo-Pacific, the extensive phenotypic plasticity of colony surface and corallite features often confounds the use of macromorphological characters in species identification, and contributes to conflict between traditional classification and molecular analyses of the group. Recent advances in morphological and molecular techniques now provide a suite of methods to re-address coral taxonomy in complex groups, such as that represented by the Faviidae. This study combines morphologic measurements including “3D coordinates landmarks” data with phylogenetic assessments of nuclear (ITS) and mitochondrial (COI-trnM) DNA to assess species boundaries in nine species of Faviidae with para-septothecal walls from Thailand. Strong concordance was found between morphological features and a priori groupings based on both morphospecies and genetically defined groups (ITS and COI-trnM). Favia truncatus was the most well-defined species based on morphological analyses, and it was also shown to be monophyletic using phylogenetic analyses. Besides F. truncatus, the only other species that was found to be monophyletic in analyses of both genes was F. cf. helianthoides, but its skeletal morphology overlapped with the F. favus species complex (comprised of F. favus, F. speciosa, F. matthaii and F. rotumana). Although not genetically monophyletic, the F. favus species complex and F. pallida were fairly well delineated morphologically. Morphospecies within the F. favus species complex are therefore possibly a result of genetic drift and/or stable polymorphisms driven by divergent selection. These results represent a first step toward a taxonomic revision of the Indo-Pacific Favia, which will integrate morphological methods with the study of type material, genetic information, reproductive data, and tests of phenotypic plasticity—given that multiple lines of evidence are needed to resolve ambiguous species and assign species names.