Document: VIN-3-36-6

Evolutionary ecology of a petal-spot polymorphism in Clarkia xantiana ssp. xantiana (Onagraceae): Floral landmarks affect herbivore resistance, not pollinator visitation.

ECKHART, V.M.*, J.D.HANSEN, C.M.LA GRANGE and E.N.TWIEG

Grinnell College, Grinnell, IA 50112, USA ¹

Abstract:
Pigmented "landmarks" on flowers are often hypothesized to have evolved through selection to attract animal pollinators. Populations of Clarkia xantiana ssp. xantiana, a bee-pollinated annual, are highly polymorphic for the presence (and size) of dark spots on petals. This suggests that some form of balancing selection, imposed by pollinators and/or other factors, plays a role in maintaining the polymorphism. We investigated this possibility in studies of pollinator behavior, phenotypic selection, and quantitative genetics. In experimental arrays, petal-spot area had no effect on pollinator visitation rate (though total petal area had an expected positive effect). In some populations we detected significant stabilizing selection on petal-spot area (with respect to seed production). Two relationships contributed to this stabilizing selection. First, petal-spot area correlated negatively with fruit predation. Second, petal-spot area was found to be negatively genetically correlated with the node of first flowering, a trait that ongoing field studies have shown to be under upward directional selection in C. xantiana ssp. xantiana. These findings support recent ideas that herbivore resistance might influence the evolution of flower pigmentation and that trade-offs occur between herbivore defense and fecundity. Surprisingly, this study did not support the idea that the floral landmarks function as pollinator attractants.

Keywords: Clarkia xantiana, pollination, herbivory, flower color, natural selection

This abstract is being presented at: 10:45 AM in session:
Oral Session #6: Pollination Ecology.