RENNER, SUSANNE S.1 and THOMAS J. GIVNISH2.* 1Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121; 2Department of Botany, University of Wisconsin, Madison WI 53706. - Tropical intercontinental disjunctions: Gondwana break-up, immigration from the boreotropics, and transoceanic dispersal.
With the advent of molecular data - and particularly the use of
molecular clocks when warranted - biogeographers are re-examining the
roles of Gondwana break-up, immigration from the Laurasian tropics,
and transoceanic dispersal in shaping similarities among the world's
tropical floras. As increasing numbers of continental disjunctions are
analyzed, it has also become possible to ask whether there are regular
patterns in the direction(s) and timing of transoceanic dispersal
events. Wind and ocean surface currents (as well as tectonics) all
affect dispersal and are not randomly distributed in space and time;
they should thus leave an evolutionary trace provided that they have
been stable long enough to override lineage-specific differences in
dispersal and establishment capability. This symposium will assemble a
diverse set of researchers with phylogenetic data on disjunctly
distributed tropical lineages. The mix emphasizes continental
disjunctions and lineages that collectively display a variety of
dispersal mechanisms, and each contributor has been asked to address
three questions: (1) How much information about the timing and nature
of the events causing disjunctions can be obtained from molecular
data? (2) What appear to be the relative roles of dispersal and
vicariance, and how do these relate to aspects of earth history? And
(3) How can we crosscheck our inferences? This symposium honors Robert
Thorne for his outstanding contributions to biogeography and
especially the analysis of tropical plant disjunctions
Key words: angiosperms, boreotopics, Gondwana, Laurasia, long distance dispersal, molecular clocks