PARENT SESSION
Oral Session # 46: Evolutionary Ecology I: Plants.
Presiding: P Minchin
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.
Differentiation in patterns of phenotypic plasticity among populations of Geranium carolinianum .
Bell, Daniela1, Galloway, Laura1, 1 University of Virginia, Charlottesville, VA, dlbell@virginia.edu
ABSTRACT- Phenotypic plasticity, the change in trait expression in response to the environment, may enhance reproduction and survival in a changing environment. Plasticity may be favored under variable environments while non-plastic responses may be favored under spatially uniform environments. Geranium carolinianum, an herbaceous annual plant, occurs in wood margins that are spatially variable for light and in old fields that are less variable for light. In a field common garden study with two light environments, I examined if wood margin populations demonstrate greater plasticity for morphological traits than old field populations. Three wood margin populations were compared with three old field populations. Surprisingly, wood margin plants were significantly less plastic for petiole length, internode length, and total plant height than were old field plants. Plants from wood margins had significantly lower fitness in low light relative to high light. In contrast, old field plants had constant fitness across both light environments. Selection analyses revealed significant directional selection on petiole length and selection differed significantly between the two light environments. These patterns suggest divergence for plasticity between wood margin and old field populations. Petiole length may be a shade-avoidance trait: the elongation of petioles may allow plants to escape shading by neighbors. Old field populations of G. carolinianum may experience substantial shading by neighboring herbaceous plants. Wood margin sites, in contrast, are characterized by shade from trees and other large woody plants. Responding to shade from trees by elongating petioles may be costly: fitness may be reduced because resources have been used to alter trait expression but the shade may not be avoided. Thus, wood margin plants may experience selection against plasticity while in old field sites selection favors plasticity.
Key words: Geranium carolinianum , phenotypic plasticity, light