No benefit of glandular trichome production in natural populations of Datura wrightii?

Populations of Datura wrightii vary in the frequency of plants that produce glandular trichomes, a resistance trait under the control of a single gene . Such variation may be maintained if the production of glandular trichomes is costly in the absence of herbivory, and if selection imposed by herbivo re communities varies spatially or temporally. Here, we document costs in t he presence of herbivory for established glandular plants relative to estab lished non-glandular plants growing in natural populations from coastal mou ntain, Riversidian sage scrub, and Mojave desert habitats in southern Calif ornia. Damage caused by the herbivore community varied spatially, with sign ificant differences in herbivore-specific damage between plants of the two trichome types and among populations within habitats, although not generall y among habitats. Plants with greater canopy size and canopy persistence ha d higher viable seed production than smaller or more damaged plants, but th is relationship was statistically significant only for non-glandular plants . However, the relationship between viable seed production and canopy persi stence became significant for glandular plants when damage caused by sap su ckers, which do not remove leaf area, was pooled with undamaged leaf area. The high cost exhibited by glandular plants leads us to predict that in the absence of any additional, unknown benefits of producing glandular trichom es, the frequency of these plants should decline in all natural populations of D. wrightii.