Evolution of the Caribbean subfamily Mussinae (Anthozoa: Scleractinia: Faviidae): transitions between solitary and colonial forms

Understanding evolutionary transitions in scleractinian corals is fundamental to predicting responses of coral reefs to climate change. We examine transitions between solitary and colonial corals in the fossil record, focusing on the Caribbean solitary reef coral <i>Scolymia</i> and members of the subfamily Mussinae. Fossil specimens are selected from a large well-documented collection of Neogene Caribbean corals, and a total of 23 species are distinguished using 15 morphological features. Ten of the 23 species are extant Caribbean species, seven are previously described extinct Neogene species, and six other extinct species are formally described as new. The 7 + 6 extinct species are added to a morphological data set consisting of 30 extant molecularly characterized species plus seven additional extinct (five Eocene, two Neogene) species. In addition to the Caribbean subfamily Mussinae, the extant species include the Indo-Pacific families Merulinidae and Lobophylliidae, and the Caribbean subfamily Faviinae. Phylogenetic analysis was performed on the data using maximum parsimony, and the results reveal four clades, which correspond with previously reported molecular clades. Solitary corals group most closely with Caribbean Mussinae and Indo-Pacific Lobophylliidae, whereas colonial corals are present in all four clades. Within Caribbean Mussinae, members of the colonial genera <i>Mycetophyllia</i> and <i>Isophyllia</i> form distinct subclades, as do the extinct solitary genera <i>Antillia</i> and <i>Antillophyllia</i>. The relationships within <i>Scolymia</i> are less well defined but its members appear more closely related to extinct solitary genera dating back to the Eocene. These results indicate that evolutionary transitions between solitary and colonial corals have been rare within the Mussinae. Except <i>Antillophyllia</i>, most Mussinae genera are restricted to the Caribbean. During the late Miocene, <i>Mycetophyllia</i> diversified and three other modern Mussinae genera (<i>Mussa</i>, <i>Scolymia</i>, <i>Isophyllia</i>) originated in association with increased Caribbean productivity. Mussinae that were more likely to survive Plio–Pleistocene extinction may have taken refuge in deep forereef habitats.