title: Reliance on pollinators predicts defensive chemistry across tobacco species.
abstract: Defensive traits are typically studied in the context of avoiding antagonists, but may also mediate key interactions with mutualists. Plant chemical defences occur in flowers, suggesting pollinators may be agents of selection on defence. We hypothesised that floral defences would deter pollinators, and therefore, pollinators would select for lower defences in outcrossing than self-pollinating species. We measured pollinator reliance and alkaloid levels in 32 greenhouse-grown Nicotiana species. Using a comparative phylogenetic approach, we found significantly lower nectar, floral and leaf nicotine concentrations in outcrossing than selfing species, with a 15-fold decrease in leaf nicotine levels. Nicotine concentrations were positively correlated across tissues, suggesting that selection against floral defences could constrain the evolution of leaf defences. Thus, pollinators could shape the evolution not only of floral defences but also of defences in other tissues where herbivores have traditionally been considered the dominant agent of selection.
authors: Department of Plant, Soil and Insect Science, University of Massachusetts, Amherst, MA 01003, USA. lsadler@ent.umass.edu
authors: Lynn S
authors: LS
authors: Adler
authors: Megan G
authors: MG
authors: Seifert
authors: Michael
authors: M
authors: Wink
authors: Geoffrey E
authors: GE
authors: Morse
mesh_terms: D000222:Adaptation, Physiological; D000470:Alkaloids / Q000032:analysis; D005075:Biological Evolution; D035264:Flowers; D010802:Phylogeny; D018515:Plant Leaves / Q000737:chemistry*; D054817:Pollination; D012641:Selection, Genetic; D014026:Nicotiana / Q000737:chemistry*
chemical_list: D000470:Alkaloids