SUCCESSIVE ISOLATION RATHER THAN EVOLUTIONARY CENTERS FOR THE ORIGINATION OF INDO-PACIFIC REEF CORALS

Biogeographic patterns are interpreted using relationships based on phylogenetic systematics in indo-Pacific reef corals (Scleractinia). A cladistic biogeographic analysis of the genera Symphyllia (Milne Edwards & Haime. 1848) and Coscinaraea (Milne Edwards & Haime, 1848) yielded three patterns. (1) Indo-Pacific reef coral species ranges overlap in a west to east stepwise fashion with the closest biogeographic relationships occurring between adjacent areas. These area relationships show a marked congruence with the Cenozoic geologic history of the Indo-Pacific. (2) The region represented by southeastern and southwestern Australia appears to be biogeographically distinct from both the north and western Indo-Pacific and the eastern Indo-Pacific. In Western Australia, controls over the biogeographic distribution of species of the two genera studied appear to be a function of latitudinally related environmental parameters. (3) Species with relatively derived character states display a higher degree of endemism than species which show relatively primitive character states. The relatively derived coral species showing the highest degrees of endemism exist at the periphery of Indo-Pacific reef coral distributions. Thus, many reef coral species must have originated far from the Indo-West Pacific centre of diversity. Congruence between the geologic history of the Indo-Pacific and the biogeographic area relationships suggest successive isolation as a working hypothesis for the origination patterns of Indo-Pacific reef corals. Species origination in reef corals was a response to geologic events that resulted in successive isolation of populations at various times and in various places during the Cenozoic history of the Indo-Pacific. It is suggested that future biogeographic studies do not confine themselves to diversity maps, but use species level phylogenetic information in constructing biogeographic hypotheses.