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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. argenteus, L. bakeri, and L. sulphureus, and compared alkaloid concentrations and composition among tissues within individuals. KEY RESULTS: Pollen alkaloid concentrations were 11-35% of those concentrations in other tissues in L. argenteus and L. sulphureus. We detected no alkaloids in L. bakeri pollen, though they were present in other tissues. Alkaloid concentrations were not strongly correlated among tissues within individuals. We detected fewer alkaloids in pollen compared to other tissues and pollen contained no unique alkaloids. CONCLUSIONS: Our results are consistent with the hypothesis that, in these pollen-rewarding species, pollen secondary chemistry may reflect the need to attract and reward pollinators more than the need to defend pollen from herbivory.
Knowledge graph centered on Data from: Attract or defend? Pollen and vegetativ with 16 nodes and 89 connections. Top connected: Bombus, plant-pollinator mutualism, pollinator foraging behavior, Lupinus, R. E. Irwin.
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