PARENT SESSION
Poster Session #4: Herbivory.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Cost of glandular trichomes in Datura wrightii: A three-year study.

HARE, DANIEL^*,1, ELLE, ELIZABETH², VAN DAM, NICOLE³, ¹ University of California - Riverside, Riverside, California² Simon Fraser University, Burnaby, British Columbia, Canada³ Netherlands Institute of Ecology (NIOO - KNAW), Heteren, The Netherlands

ABSTRACT- Models of genetic variation for herbivore resistance within plant populations often postulate a balance between costs and benefits of resistance. Glandular trichome production by the perennial, Datura wrightii, is costly because plants producing glandular trichomes for herbivore resistance (sticky plants) produce 45% fewer seeds than susceptible plants producing nonglandular trichomes (velvety plants) in their first year. Sticky plants grow larger but produce fewer seeds per unit of biomass. Greater vegetative growth may allow sticky plants to compensate for low seed production efficiency, and resistance costs might decline over time. We monitored plant growth, survival and seed production for three years when exposed to and protected from herbivores and determined the net reproductive rate (R₀) and the finite rate of increase () of each trichome type. Most plants exposed to herbivores were killed by the end of the third year. When protected from herbivores, sticky plants were 187 - 245% larger than velvety plants but were consistently less efficient in producing seeds. The advantage of greater reproduction earlier in life by velvety plants increased by 55% - 230% over sticky plants, however. Although the there was a trade-off between growth and reproduction, no benefits accrued before most plants were killed by herbivores. The cost of glandular trichome production by sticky plants continued to exceed its benefits even after three years of differential vegetative growth favoring sticky plants.

KEY WORDS: herbivory, trichomes, cost of resistance, Datura wrightii