Colloquium: The flora of Madagascar: research needs and research progress
Koopman, Margaret M. , Baum, David A. .
Diversification and the maintenance of species boundaries in the tribe Hibisceae (Malvaceae) on Madagascar.
Madagascar is home to a substantial radiation within the Hibiscus tribe (Malvaceae; 86 species, 75% endemic). The group is morphologically diverse reflecting differences in pollination mode and a predisposition for ecological specialization to xeric environments. A well-resolved plastid phylogeny strongly supports an exclusively Malagasy clade (/Megistohibiscus) derived from an introduction in the Mid-Miocene and a second clade that arrived independently to the island 4-5mya. One interesting aspect of the /Megistohibiscus radiation is that one commonly finds multiple species occurring in sympatry. The segregate genus, Megistostegium, provides an excellent system to explore how such closely related species can persist in sympatry. Two, or even all three, of the recognized species of Megistostegium, may co-occur at a single site, yet they remain morphologically distinct despite overlapping flowering and similar pollination systems. Crossing experiments demonstrate a lack of pre-mating isolation and occasional intermediate individuals are encountered in the field. Sequence data from four nuclear genes and one chloroplast region suggest some degree of genetic cohesion to each species, but also historical and recent gene flow throughout the range of the genus. Given that these species boundaries are permeable, ecological selection is the most likely force maintaining genetic distinctions for at least a subset of the genome.
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1 - University of Wisconsin Madison, Department of Botany, Birge Hall, 430 Lincoln Drive, Madison, Wisconsin, 53706-1381, USA
Presentation Type: Symposium or Colloquium Presentation
Location: Blair B/Gage
Date: Tuesday, July 29th, 2008
Time: 9:45 AM