Historical biogeography of Indo-western Pacific coral reef biota: is the Indonesian region a centre of origin? Francesco Santini 1 * and Richard Winterbottom 2 1 Department of Zoology, University of Toronto, Toronto, Canada and 2 Centre for Biodiversity and Conservation Biology, Royal Ontario Museum, Toronto, Canada Abstract Aim To apply the modern theory of vicariant biogeography to the study of evolution of the coral reef fauna in the Indo-western Pacific region. Location Indian and western Pacific Oceans. Methods Use of taxa cladograms and Brooks Parsimony Analysis to reconstruct relationships between geographical areas. Results The analysis seems to indicate that the Indonesian region, long stated to be a ‘centre of origin’ for most of the Indo-West Pacific marine fauna, is a very derived area in the general area cladogram; and that most of the lineages may have originated in the western Indian Ocean, Australia, or the South-western Pacific (probably from lineages that had remained isolated after the breakup of the Gondwanan supercontinent, or because of the movement of island arcs). A series of events that fragmented an originally widespread biota seems to be highly congruent with geological events that caused the break up of Gondwanaland. Main conclusions Contrary to several previous claims, based mostly on descriptive, rather than analytical, studies, most lineages of coral reef fauna inhabiting the Indo- western Pacific region probably originated through vicariant events associated with, and following the break up of Gondwana. A general pattern of biotic distribution that is highly congruent with geological data shows that even if long range dispersal and sympatric speciation may in some cases have taken place, they have not probably been the predominant mechanism of speciation in the clades examined. Keywords Historical biogeography, vicariance, BPA, coral reefs, Indo-western Pacific. INTRODUCTION Historical biogeography is the branch of biogeography that deals with evolutionary and geological processes that occur over large temporal and spatial scales, and is often used to provide hypotheses for explaining discontinuous patterns of distribution of organisms (Morrone & Crisci, 1995). The assumption of earth’s stability resulted in dispersal being the dominant explanation for biogeographical distributions for centuries, with species supposedly having centres of origin from which they subsequently dispersed. With the discovery of plate tectonics, the concept of centres of origin has been strongly criticized and is now abandoned as an a priori explanation for current biotic distributions by many system- atists. Adherents to panbiogeography and vicariance bioge- ography believe that vicariance is the most parsimonious, and the only testable, explanation for the majority of speciation events, and should be used as the null hypothesis when trying to explain the distribution of taxa. According to this view, species do not have centres of origin; they were formed when the ancestral geographical range inhabited by an ancestral species was fragmented by vicariant events. Historical biogeograhy received a great impetus from the development of cladistic methodology, and, nowadays, cladistic biogeography is certainly the predominant *Correspondence: Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, M5S 3G5, Canada. E-mail: fsantini@zoo.utoronto.ca Journal of Biogeography, 29, 189–205 Ó 2002 Blackwell Science Ltd