Because most plants are unable to move, chemical and physical defenses against herbivores are critical to survival. Plant secondary compounds are exceptionally diverse, and can vary dramatically in concentration and diversity among plant tissues, across landscapes within species, and among species. However, the same compounds have often evolved multiple times within the same family or even in wildly divergent plant families. Our work seeks to understand the genetic mechanisms creating variation in defense, the evolutionary origins of variation in defense, and the selective factors that control geographic variation in their concentrations and diversity.

Research in the Kooyers lab current focuses on the evolution of a group of chemical defenses in Mimulus called phenopropanoid glycosides or PPGs. PPGs are a significant investment for annual M. guttatus populations, constituting ~8% dry leaf weight on average and up to 35% of dry leaf weight. PPG abundance and arsenal is highly variable across the species range with greater levels and different abundances of certain PPGs in areas with longer growing seasons and greater herbivory. Along with collaborator Liza Holeski, we are using QTL mapping experiments to elucidate the genes underlying variation in PPG abundance and arsenal and a number of manipulative experiments in the greenhouse and field populations to determine why this variation matters in natural populations. We also are being a large collaborative project with a number of labs examining growth/reproductive rate/defense tradeoffs across the entire Mimulus phylogeny.

Figure(above): PPG concentrations vary across a latitudinal gradient. Each color is a different PPG and size of pie represents total conc. of PPGs.
Figure (left): Conandroside - the most prevalent PPG in northern monkeyflower populations.