The Sahul-Sunda floristic exchange: dated molecular phylogenies document Cenozoic intercontinental dispersal dynamics

AimThe aim was to characterize the temporal dynamics of the Sahul-Sunda floristic exchange using published dated molecular phylogenies. LocationThe Sahul and Sunda shelves in Australasia and Southeast Asia. MethodsDated molecular phylogenies were compiled from the literature for plant clades that contained at least one node representing a biogeographical disjunction between the Sahul and Sunda shelves. For these nodes the age, ancestral geographical area and propagule type were determined. ResultsWe analysed 49 clades from 21 published phylogenies representing a diverse set of angiosperm lineages. The inferred age of the disjunctions ranged from c.33Ma to c.1Ma; the earliest age marked the onset of the Sahul-Sunda floristic exchange. Disjunctions (resulting from dispersal/migration events) occurred at the rate of 0.41 per 2Myr between 34 and 12Ma. Thereafter the rate sharply increased, coincident with the shelves effectively merging. For nearly two-thirds (63%) of the nodes Sunda was the ancestral area, and for 90% the ancestral species possessed zoochorous propagules. Main conclusionsThere is strong support for a dynamic model of floristic exchange between Sahul and Sunda. Fewer (18%) disjunctions occurred prior to Sahul and Sunda merging around 12Ma, which we attribute to a combination of the effect of overwater dispersal barriers and relatively stable, saturated species assemblages resistant to the establishment of newly arrived lineages. The exchange, once underway, was strongly asymmetrical; eastwards migration into Sahul predominated over the reverse by a factor of c.2.4. As zoochorous lineages were overrepresented among the successful dispersers, we infer a strong role for localized animal dispersal across narrow water barriers.