The Mechanisms of Adaptive Shifts in Allocation among Growth, Reproduction, and Defense

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One of the fundamental rules of life is that there are trade-offs associated with the adaptation of organisms to different environmental conditions. These trade-offs prevent individual biological species from dominating every habitat and climatic condition. However, while these trade-offs are prevalent, the understanding of what genetic and physiological mechanisms cause them is poor. Identifying the mechanisms underlying trade-offs in plants will provide knowledge of how evolution works and guidance for the improvement of crop species. This research focuses on understanding why trade-offs occur for adaptations of the yellow monkeyflower (Mimulus guttatus) to highly divergent coastal and inland climatic conditions in California. The coastal habitats of this region are inundated by a cool ocean fog during the summer months, which allows plants to survive year-round, but also means that there are more herbivores which eat them. In contrast, inland habitats are very hot and dry in the summer. The ways in which monkeyflowers have adapted to these different climates involves strong trade-offs, for which this research will establish the underlying mechanisms. The research will involve the mentorship of graduate students, postdocs, and underrepresented minority undergraduate students. Further, this award will support an ongoing partnership between investigators and the Michigan State University College of Education to create an inquiry-based learning module, focused on the monkeyflower system, for low-income middle school classrooms in Flint, MI. A website will be developed for distribution of this education module to classrooms nationwide. Whether to allocate resources to reproduction, growth, and/or defense is a fundamental dilemma faced by all plant species. This research will focus on the evolutionary divergence in allocation to rapid reproduction, long-term growth, and herbivore resistance between coastal and inland M. guttatus. Inland populations allocate resources primarily to rapid growth and reproduction to escape from seasonal drought while investing little in herbivore resistance. Coastal populations have evolved to invest more in vegetative growth and herbivore resistance as a result of higher herbivore pressure and a longer growing season. Aim 1 of the research will evaluate how two previously identified loci (DIV1 and DIV2) involved in adaptive divergence between coastal and inland populations contribute to concentrations of precursor and bioactive forms of the Gibberellin (GA) growth hormone and the defense hormone Jasmonic Acid (JA). The effects of the two loci on induced and constitutive levels of defensive phenylpropanoid glycosides (PPGs) will be evaluated. Aim 2 will elucidate the molecular mechanisms underlying adaptive variation in allocation among rapid reproduction, long-term vegetative growth, and herbivore resistance. Functional molecular studies of gibberellin biosynthesis and signaling genes will be conducted to evaluate their role in the evolution of trade-offs. Aim 3 will use hormone applications in the field to evaluate the role of those hormones in adaptive shifts in resource allocation across climatic conditions. Plants will be grown in manipulative reciprocal transplant experiments to assess the roles of GA and JA pathways on flowering time, biomass, and fitness in coastal and inland habitats.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.