Attract or defend? Pollen and vegetative secondary chemistry of three pollen-rewarding lupines

PREMISE OF THE STUDY: Optimal Defense Theory predicts that selection should drive plants to differentially allocate resources for herbivore defense to tissues with high fitness values. As pollen’s primary role is the transport of gametes, plants may be expected to defend it from herbivory. However, for many animal-pollinated plants, pollen serves a secondary role as a pollinator reward. This may present a conflict between selection to defend pollen from herbivores and selection to reward pollinators. Here, we investigate whether pollen secondary chemistry in three pollen-rewarding Lupinus species better reflects the need to defend pollen or reward pollinators. METHODS: Lupinus (Fabaceae) species are nectarless, pollen-rewarding, and produce defensive quinolizidine and/or piperidine alkaloids throughout their tissues. We used gas chromatography to identify and quantitate the alkaloids in four above-ground tissues (pollen, flower, leaf, stem) of three western North American lupines: L. ar...