Genetic parallelism and allele reuse in herbivore-plant chemical phenotype matching

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Globalization of trade means the United States is under constant threat of invasion by foreign plant species, which, once established, can become invasive weeds. Such weeds can sometimes be managed through biocontrol, by importing insect enemies from their ancestral land. Impacts of an ancestral enemy on its host plant in new environments depend on the toxicity of the weed's chemical defenses and the efficacy of the insect's detoxification enzymes. Wild parsnips and parsnip webworms, both native to Europe, were accidentally introduced to North America and co-occur across the continent. This project will determine how the parsnip's chemical defense profile and the webworm's detoxification enzyme profile coevolve in response to each other and local conditions. This reciprocal adaptation may involve re-use of the same genetic variants or it may require different variants in different places. Understanding which of these options is most common can inform both basic research on the patterns and processes of coevolution and agricultural research about how invasive plants either escape from or succumb to herbivores. This project builds on past NSF funded research and will provide diverse training and outreach opportunities for students and the general public. Expression of cytochrome P450 detoxification genes in webworms and of cytochrome P450 biosynthetic genes in parsnips will be assayed by RNAseq in samples from different populations. Differentially expressed genes, their allelic variants, and their impact on chemical defense and detoxification will be characterized in parsnips and webworms across their range. Genotyping-By-Sequencing, another genome-enabled method, will be used to identify molecular polymorphisms in the interacting genomes in multiple environments. These data will be statistically analyzed to determine if these species re-use the same genetic variants when they interact or whether different genetic variants in different locations permit coadaptation.