Patterns of Phytochemical Variation in Mimulus guttatus (Yellow Monkeyflower)
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The search for general patterns in the production and allocation of plant defense traits will be facilitated by characterizing multivariate suites of defense, as well as by studying additional plant taxa, particularly those with available genomic resources. Here, we investigated patterns of genetic variation in phytochemical defenses (phenylpropanoid glycosides, PPGs) in Mimulus guttatus (yellow monkeyflower). We grew plants derived from several natural populations, consisting of multiple full-sibling families within each population, in a common greenhouse environment. We found substantial variation in the constitutive multivariate PPG phenotype and in constitutive levels of individual phytochemicals within plants (among leaves of different ages), within populations (among full-sibling families), and among populations. Populations consisting of annual plants generally, but not always, had lower concentrations of phytochemicals than did populations of perennial plants. Populations differed in their plastic response to artificial herbivory, both in the overall multivariate PPG phenotype and in the individual phytochemicals. The relationship between phytochemistry and another defense trait, trichomes, differed among populations. Finally, we demonstrated that one of the PPGs, verbascoside, acts as a feeding stimulant rather than a feeding deterrent for a specialist herbivore of M. guttatus, the buckeye caterpillar (Junonia coenia Nymphalidae). Given its available genetic resources, numerous, easily accessible natural populations, and patterns of genetic variation highlighted in this research, M. guttatus provides an ideal model system in which to test ecological and evolutionary theories of plant-herbivore interactions.
KeywordsDefense Genetic variation Junonia coenia Kairomone Mimulus guttatus Phenylpropanoid glycoside Model system
The authors thank the Mimulus seed library (Duke University) and D. Lowry who generously provided some of the seeds used in this study. Thanks to E. Lewis and M. Crossley for help with sample processing and M. Arntz and R. Ecker for laboratory assistance. We are grateful for comments by several anonymous reviewers and J. Couture that substantially improved this manuscript. Z. HarnEnz was funded through the IBS-SRP (Integrated Biological Sciences Summer Research Program) at the University of Wisconsin, Madison. This work was supported in part by the National Science Foundation (grant numbers FIBR-0425908, DEB-0841609).
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