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A Natural Experiment Testing the Role of Specialization in Speciation of Seed Beetles

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Species diversity varies across different insect lineages. One possible explanation for this diversity is that more diverse lineages are driven by intricate coevolutionary relationships. Many phytophagous insects must overcome significant plant defenses, such as accumulation of toxins, by developing specific adaptations of their own. This 'arms race' often leads to specialization and subsequent speciation within many insect taxa. Seed beetles in particular impose an intense selective pressure on plants by directly attacking plant offspring, contributing to widespread specialization between seed beetle species and highly specific host plants. Thus, it is highly unusual to come across seed beetles that are considered relative generalists. However, the Great Plains seed beetle, Acanthoscelides fraterculus, has been reared from host plants in different genera. To determine whether A. fraterculus is a true generalist or is actually composed of many specialist populations/species, I collected beetles at the same site from hosts in the genera Astragalus, Oxytropis, and Glycyrrhiza. This was repeated across eight localities in Colorado. I compared populations of the seed beetle reared from each host phenotypically and genotypically to determine whether the population structure is largely defined by host plant choice or geographic locality. Results from this experiment will provide insights into the mechanisms driving coevolution between phytophagous insects, which can contribute to understanding large scale community structuring.

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A Natural Experiment Testing the Role of Specialization in Speciation of Seed Beetles

Species diversity varies across different insect lineages. One possible explanation for this diversity is that more diverse lineages are driven by intricate coevolutionary relationships. Many phytophagous insects must overcome significant plant defenses, such as accumulation of toxins, by developing specific adaptations of their own. This 'arms race' often leads to specialization and subsequent speciation within many insect taxa. Seed beetles in particular impose an intense selective pressure on plants by directly attacking plant offspring, contributing to widespread specialization between seed beetle species and highly specific host plants. Thus, it is highly unusual to come across seed beetles that are considered relative generalists. However, the Great Plains seed beetle, Acanthoscelides fraterculus, has been reared from host plants in different genera. To determine whether A. fraterculus is a true generalist or is actually composed of many specialist populations/species, I collected beetles at the same site from hosts in the genera Astragalus, Oxytropis, and Glycyrrhiza. This was repeated across eight localities in Colorado. I compared populations of the seed beetle reared from each host phenotypically and genotypically to determine whether the population structure is largely defined by host plant choice or geographic locality. Results from this experiment will provide insights into the mechanisms driving coevolution between phytophagous insects, which can contribute to understanding large scale community structuring.