Resurrecting a subgenus to genus: molecular phylogeny of and (order Scleractinia; family Euphyllidae; clade V).

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, the , 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 six species, namely and 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 (), cytochrome b (), and β-tubulin genes of 36 colonies representing and a confamilial species, reveal two distinct groups in the that originated from different ancestors. formed a separate group. and clustered together and diverged from the same ancestor as The 3'-end of the gene of was able to distinguish morphospecies.

DISCUSSION

Species of were traditionally classified into two subgenera, and which represented a dichotomy on colony structure. The paraphyletic groups retained the original members of the subgenera providing a strong basis for recognizing as a genus. However, colony structure was found to be a convergent trait between and 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 of of the group is a hermaphroditic brooder with long, tubular tentacles with knob-like tips, and a phaceloid colony structure. The group, with and are gonochoric broadcast spawners with short polyps, mixed types of tentacle shapes, and a phaceloid or flabello-meandroid skeleton. Soft-tissue morphology of and were found to be consistent with the dichotomy.

CONCLUSIONS

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