PARENT SESSION
Poster Session # 15: Plant Ecology.
Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Survival and seed production of sticky and velvety Datura wrightii in the field.
Hare, J. Daniel*,1, Elle, Elizabeth1, 2, 1 University of California, Riverside, California, United States2 Simon Fraser University, Burnaby, British Columbia, Canada
ABSTRACT- Leaves of Datura wrightii in California are covered either with glandular trichomes (sticky plants) or non-glandular trichomes (velvety plants), and sticky plants are resistant to many of D. wrightii′s insect herbivores. Theoretical models suggest that variation in levels of resistance to herbivores may persist if resistance is costly and herbivore damage is variable. If so, then natural selection should favor resistant plants when herbivore damage is high and disfavor it when damage is low. However, without long-term equivalence between costs and benefits, then natural selection either should eventually drive the trait to fixation if the trait has a net benefit or eliminate it if the trait has a net cost. In previous short-term studies, we found that the production of glandular trichomes by D. wrightii had a net fitness cost even in the presence of herbivores. If always true, then natural selection should eliminate this expensive resistance trait. We monitored survival and seed production of sticky and velvety D. wrightii in the presence of herbivores in 11 natural populations over four or five years. In all populations where both types occurred, the finite rate of increase for velvety plants was from 60% to 274% greater than for sticky plants. Plant survival averaged between two and three years and did not differ significantly between plant types. Because seed production consistently favored velvety plants, we predict that the frequency of sticky plants should decline, and this prediction was met within five years in three of eight monitored populations where both types occur. Results strengthen our prediction that, in the absence of additional benefits to the suite of characters associated with the production of glandular trichomes, sticky plants should be eliminated from D. wrightii populations.
Key words: insect herbivory, trichomes, plant resistance, demography