COMPETITION, HERBIVORY, AND REPRODUCTION OF TRICHOME PHENOTYPES OF DATURA WRIGHTII

Abstract

The trichome dimorphism of Datura wrightii is intriguing because glandular trichome production has a high fitness cost. Plants producing glandular trichomes (''sticky'' plants) are resistant to many insect herbivores that attack plants producing nonglandular trichomes (''velvety'' plants). When protected from herbivores, sticky plants initially pro- duce fewer seeds than velvety plants but grow to a larger size. In a three-year field ex- periment, we tested the hypothesis that sticky plants acquire a competitive advantage through greater vegetative growth. In the absence of herbivores, sticky and velvety plants grew to similar sizes in their first year, but sticky plants grew larger in the second and third years. Seed production of sticky plants was 46-60% less than velvety plants in their first year, and this caused a 13% reduction in their finite rate of increase overall, even though sticky plants produced more seeds than velvety plants did in later years. The impact of herbivory varied with plant density, and herbivores reduced plant fitness more at low plant density than at high plant density. The differences in growth associated with trichome morphology occurred too late to provide a competitive advantage to sticky plants and probably contribute little to the maintenance of D. wrightii's trichome dimorphism.