PATTERNS OF DIVERGENCE BETWEEN CARIBBEAN AND INDO-PACIFIC REEF CORALS

Traditional morphology-based systematics shows close evolutionary relationships between Caribbean and Indo-Pacific “faviid” and “mussid” reef corals; however, molecular phylogenies indicate three distinct family-level clades: (1) Caribbean faviids + mussids; (2) Indo-Pacific faviids; (3) Indo-Pacific mussids. The three clades diverged by middle Eocene time and are each regionally restricted. During the early Cenozoic, faviid and mussid corals also occurred in a third region, the Mediterranean, which was part of the westward flowing, pantropical Tethyan Seaway, but they became extinct in that region during the Miocene. Here we perform morphological phylogenetic analyses including Caribbean, Indo-Pacific, and Mediterranean fossil and Recent taxa to reconstruct the pattern of divergence between the three regions, and examine how it was related to the breakup of the Tethys. Preliminary analyses were performed on a dataset consisting of 73 taxa (67 Recent, 6 fossil) and 28 characters. In addition to traditional macromorphology, the characters include newly discovered micromorphological and microstructural features observed in transverse thin section. The results show that contrary to traditional systematics, the Mediterranean fossils group more closely with Indo-Pacific faviids than they do with Caribbean taxa. Indo-Pacific mussids form a distinct clade, and Caribbean taxa form two distinct subclades. However, Indo-Pacific faviids form numerous unresolved subclades, which are basal to the Caribbean subclades. This suggests that modern Caribbean taxa diverged from a more cosmopolitan pantropical fauna during one or two early Cenozoic evolutionary events associated with Tethyan breakup and Caribbean isolation, and they are thus evolutionarily unique.