Resurrecting a subgenus to genus: molecular phylogeny ofEuphylliaandFimbriaphyllia(order Scleractinia; family Euphyllidae; clade V)
Authors: Luzon Katrina S. , Lin Mei-Fang , Ablan Lagman Ma. Carmen A. , Licuanan Wilfredo Roehl Y. , Chen Chaolun Allen 
Published: December 2017

Background

The corallum is crucial in building coral reefs and in diagnosing systematic relationships in the order Scleractinia. However, molecular phylogenetic analyses revealed a paraphyly in a majority of traditional families and genera among Scleractinia showing that other biological attributes of the coral, such as polyp morphology and reproductive traits, are underutilized. Among scleractinian genera, theEuphyllia, with nine nominal species in the Indo-Pacific region, is one of the groups that await phylogenetic resolution. Multiple genetic markers were used to construct the phylogeny of sixEuphylliaspecies, namelyE. ancora, E. divisa, E. glabrescens, E. paraancora, E. paradivisa,andE. yaeyamaensis.The phylogeny guided the inferences on the contributions of the colony structure, polyp morphology, and life history traits to the systematics of the largest genus in Euphyllidae (clade V) and, by extension, to the rest of clade V.

Results

Analyses of cytochrome oxidase 1 (cox1), cytochrome b (cytb), and β-tubulin genes of 36 colonies representingEuphylliaand a confamilial species,Galaxea fascicularis,reveal two distinct groups in theEuphylliathat originated from different ancestors.Euphyllia glabrescensformed a separate group.Euphyllia ancora, E. divisa, E. paraancora, E. paradivisa,andE. yaeyamaensisclustered together and diverged from the same ancestor asG. fascicularis.The 3′-end of thecox1gene ofEuphylliawas able to distinguish morphospecies.

Discussion

Species ofEuphylliawere traditionally classified into two subgenera,EuphylliaandFimbriaphyllia,which represented a dichotomy on colony structure. The paraphyletic groups retained the original members of the subgenera providing a strong basis for recognizingFimbriaphylliaas a genus. However, colony structure was found to be a convergent trait betweenEuphylliaandFimbriaphyllia,while polyp shape and length, sexuality, and reproductive mode defined the dichotomy better. Species in a genus are distinguished by combining polyp morphology and colony form. The cluster ofE. glabrescensof theEuphylliagroup is a hermaphroditic brooder with long, tubular tentacles with knob-like tips, and a phaceloid colony structure. TheFimbriaphylliagroup, withF. paraancora, F. paradivisa, F. ancora, F. divisa,andF. yaeyamaensis,are gonochoric broadcast spawners with short polyps, mixed types of tentacle shapes, and a phaceloid or flabello-meandroid skeleton. Soft-tissue morphology ofG. fascicularisandCtenella chagiuswere found to be consistent with the dichotomy.

Conclusions

The paraphyly of the original members of the previous subgenera justify recognizingFimbriaphylliaas a genus. The integrated approach demonstrates that combining polyp features, reproductive traits, and skeletal morphology is of high systematic value not just toEuphylliaandFimbriaphylliabut also to clade V; thus, laying the groundwork for resolving the phylogeny of clade V.