How Many More Thymes? A Case of Phytochemical Defense
Department of Biology and Department of Microbiology & Plant Biology
University of Oklahoma
This clicker case addresses several concepts related to the evolutionary ecology of herbivore defenses. A survey of several different studies that investigated chemical defenses in Thymus vulgaris (thyme) gives students the opportunity to develop hypotheses, pose potential experiments, and interpret data to develop a better understanding of not only herbivore deterrence, but also how natural selection can involve different pressures selecting for different phenotypes. The case study incorporates group discussion, analysis of experimental design, and data evaluation as central activities. It can be taught in a single 50-minute class session, an economy that is achieved in part by using a "flipped" approach. Students prepare outside of class by watching several short videos (one of which was made by the author) that teach the basics of herbivore deterrence and abiotic and biotic forces in the environment that can influence plant adaptations. The case study was designed for use in a large introductory-level class, but would also be appropriate for smaller classes or upper-level evolution courses.
- Describe and give examples of different categories of adaptations and strategies plants use for herbivore deterrence.
- Calculate inheritance probabilities in a monohybrid cross.
- Describe plant adaptations to ecological conditions of the Mediterranean region.
- Describe how plants use chemical defenses for herbivore deterrence.
- Explain how phenotype is related to genotype, and how this is influenced in an epistatic system.
- Describe how different selective pressures can favor maintenance of different phenotypes in a species or geographic region.
- Pose hypotheses to investigate herbivore deterrence.
- Predict outcomes of experiments.
- Analyze data and interpret experimental results in light of research results.
- Synthesize results from different studies and evaluate their larger significance.
KeywordsHerbivory; herbivore; deterrence; monoterpene; producer; genotype; phenotype; chemotype; Thymus vulgaris; thyme; Mediterranean ecosystem; chemical defenses; food webs;
Educational LevelHigh school, Undergraduate lower division, Undergraduate upper division
Type MethodsClicker, Flipped, Interrupted
Subject HeadingsBiology (General) Botany / Plant Science Ecology Evolutionary Biology Genetics / Heredity
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The following video(s) are recommended for use in association with this case study.
- Don’t Eat the Plants
This video shows actual examples of adaptations against herbivory in different plants growing at the University of Cambridge Botanic Garden. The video is particularly useful in that it provides specific examples of defenses in plants with which students are likely to be familiar. Running time: 6:35 min. Produced by Cambridge University. Uploaded to YouTube May 19, 2011.
- Mediterranean Vegetation—How Plants Survive
This excerpt from the Kingdom of Plants, a natural history documentary series written and presented by David Attenborough, provides a brief overview of the important abiotic features of the Mediterranean region, which is the native habitat of thyme, the focal species of the case study. Students should watch this video to learn about abiotic and biotic forces in the environment that can influence plant adaptations. Running time: 2:12 min. Produced by British Broadcasting Corporation (BBC), 2012.
- Plant Defenses Against Herbivory
This video, created by the author of this case study, examines the ecological niche plants fill as producers and then describes different categories of defenses that plants utilize against herbivores. Students should be advised to take notes from the video, specifically regarding the different physical and chemical defense strategies plants use. Running time: 8:01 min. Created by Phil J. Gibson for the National Center for Case Study Teaching in Science, 2015.
- Solving Genetics Problems
This optional video provides an overview of how to calculate probabilities in monohybrid, dihybrid, and trihybrid crosses (note however that detailed knowledge of inheritance is not essential to completing the case study). Running time: 13:35 min. Produced by ThePenguinProf, 2012.