Background
Carl Sagan suggested “it would be wryly interesting if, in human history, the cultivation of marijuana led generally to the invention of agriculture and thereby to civilization.” Sagan’s proposal may not be naive, since Cannabis cultivation dates back as far back as 12,000 years ago. The historical uses of Cannabis include food, fiber, oil, and a remedy for a variety of ailments, and the evolution of Cannabis as a multipurpose, chemically diverse plant is partly due to artificial selection during its long interaction with humans. Medicinal uses of Cannabis are potentially a result of compounds acting synergistically, which makes this plant an appealing system to examine effects of phytochemical diversity on organisms. One important but rarely-tested hypothesis is that plants with high phytochemical diversity, such as Cannabis, are better defended against a broad mix of natural enemies. However due to a dearth of ecological synergy studies, the phenomena and underlying mechanisms are still poorly understood.
Overview
Plant secondary metabolites (PSMs) potentially function as plant defenses both in isolation and when acting as part of a suite of compounds. However, many isolated PSMs are in fact not functional as defenses or toxins when tested in biological assays, while entire assemblages of compounds (e.g., measured as phytochemical diversity) can have powerful toxic and deterrent effects through synergy and other mechanisms. Hypotheses proposed to explain the effects of phytochemical diversity postulate that plants which possess multiple PSMs maintain a greater selective advantage when defending against diverse natural enemies and that synergistic effects are an important factor. However, our understanding of the mechanisms associated with phytochemical diversity and defense are insufficient because the literature is largely limited to the impacts of feeding experiments with isolated compounds. For my dissertation research, I am investigating a potentially widespread, but understudied, component of ecological interactions. Specifically, how abiotic and biotic environmental stressors affect phytochemical diversity.
Study Organism & Location
Cannabis sativa (Cannabaceae) is an ideal study plant because it has evolved a diverse mix of PSMs, with more than 480 compounds identified, including a number of classes of antiherbivore compounds (e.g., cannabinoids, flavonoids, terpenoids). Cannabis sativa is also characterized by high “intraclass” diversity, with extensive variations within classes of PSMs. This high interclass and intraclass diversity yields high functional diversity among cannabis populations and provides multiple opportunities to investigate effects of variation in functional diversity on arthropod communities.
Research Plan
By combining observational and experimental studies, I am characterizing effects of chemical variation on naturally occurring insect communities associated with Cannabis while taking advantage of controlled laboratory conditions to examine specific hypotheses about effects of plant chemistry on insect physiology. I am also conducting water-stress experiments on hemp grown at the UNR Greenhouse Complex under NDA permits. My research includes field collections, rearing experiments with herbivores and parasitoids, cultivation of hemp under experimental treatments, development of an infrared spectral library to characterize phytochemical diversity, and extraction of compounds to conduct Lepidopteran feeding experiments. Mixed linear models and structural equation modeling will be employed to analyze direct and indirect effects of phytochemical diversity on insect populations and arthropod community structure.
Study Organism & Location
Cannabis sativa (Cannabaceae) is an ideal study plant because it has evolved a diverse mix of PSMs, with more than 480 compounds identified, including a number of classes of antiherbivore compounds (e.g., cannabinoids, flavonoids, terpenoids). Cannabis sativa is also characterized by high “intraclass” diversity, with extensive variations within classes of PSMs. This high interclass and intraclass diversity yields high functional diversity among cannabis populations and provides multiple opportunities to investigate effects of variation in functional diversity on arthropod communities.
Research Plan
By combining observational and experimental studies, I am characterizing effects of chemical variation on naturally occurring insect communities associated with Cannabis while taking advantage of controlled laboratory conditions to examine specific hypotheses about effects of plant chemistry on insect physiology. I am also conducting water-stress experiments on hemp grown at the UNR Greenhouse Complex under NDA permits. My research includes field collections, rearing experiments with herbivores and parasitoids, cultivation of hemp under experimental treatments, development of an infrared spectral library to characterize phytochemical diversity, and extraction of compounds to conduct Lepidopteran feeding experiments. Mixed linear models and structural equation modeling will be employed to analyze direct and indirect effects of phytochemical diversity on insect populations and arthropod community structure.
