Systematics Section / ASPT
Ellis, A.G. , Weis, A.E. , Gaut, B. .
From fingers and thumbs to babies bums: Evolutionary process in the radiation of the Aizoaceae in the southern African deserts.
The radiation of the Aizoaceae (ice plants) in the winter rainfall deserts of southern Africa is unsurpassed in the plant kingdom, both in terms of the tempo of evolution (0.77-1.75 species per lineage per Myr) and the number of species involved (1563 species). The work reported in this paper is a first attempt to elucidate the evolutionary processes which have generated the remarkable species and growth form diversity in this group. Our work with Argyroderma, a genus within the Aizoaceae, has focused on understanding the structuring of genetic and morphological diversity along spatial, temporal and habitat axes. Argyroderma contains 11 taxa which are range restricted habitat specialists confined to quartz gravel plain habitats and one widespread “generalist” species which occurs sympatrically with all other species. The specialists have highly reduced growth forms, utilize edaphically distinct quartz habitats, are spatially restricted by the distribution of quartz in the landscape and have divergent flowering phenologies. AFLPs reveal a basal split between the generalist and the specialist clade, suggesting that selection across the boundary between non-quartz and quartz habitat has not driven diversification of the genus. Within the specialist clade we find that, whereas landscape structure contributes to neutral genetic divergence between spatially isolated populations, morphological divergence occurs across habitat (soil) boundaries. Growth form divergence in different edaphic environments in turn leads to shifts in the timing of flowering, resulting in temporal as well as spatial isolation between diverging populations. Divergent flowering phenologies promote further neutral genetic divergence and allow coexistence of previously spatially isolated species following range expansion.
1 - University of California, Irvine, Department of Ecology and Evolution, 321 Steinhaus Hall, UCI, Irvine, California, 92697, USA
Presentation Type: Paper
Location: Cottonwood A (Snowbird Center)
Date: Wednesday, August 4th, 2004
Time: 12:30 PM