Western Atlantic invasion of sun corals: incongruence between morphology and genetic delimitation among morphotypes in the genus Tubastraea

Abstract

The scleractinian corals of the genus Tubastraea Lesson, 1830 are currently globally dispersed and even so still present a confused taxonomy due to the overlap of morphological characters between the species. In this study, we investigate Tubastraea species previously found in the western Atlantic, based on the molecular marker (ITS gene) and morphology, to determine the accuracy of their descriptions. We identified three morphotypes from Brazil which were genetically delimited into two species: Tubastraea coccinea (Morphotypes I and II) and Tubastraea sp. (Morphotype III). Although morphotype I has morphological patterns of Tubastraea aurea (Quoy & Gaimard, 1833) there was no molecular divergence to support the species differentiation and continue to be recognized as a morphological variant of T. coccinea. The third morphotype is both morphologically and genetically distinct from T. coccinea and is also not representative of the species Tubastraea tagusensis Wells, 1982 despite earlier descriptions describing T. tagusensis in Brazil. Morphotype III exhibited distinct morphological characteristics among the other morphotypes, mainly due to greater polyp projection. In addition, it has fusions between septa, a characteristic that differentiates it from T. tagusensis. Nevertheless, molecular phylogenetic analyses showed that Brazilian Tubastraea fell into two well-supported monophyletic clades, and samples collected in the United States overlapped in both clades. Florida samples exhibited fewer morphotypes and showed greater genetic diversity, presenting haplotypes in four other internal clades. This study highlights the need for an integrative approach to conduct a deeper species delimitation of Tubastraea, essential for managing bioinvasion events by sun corals.