A Genomic and Macroevolutionary Approach to Studying Diversification in an Insect-Plant Arms Race

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The exuberant proliferation of herbivorous insects is often attributed to their association with plants, making their interactions of particular importance to understanding what is driving their vast diversity. Early biologists exploring the underlying factors proposed the hypothesis of coevolution (and the escape and radiate model). Despite general support for this hypothesis, the macroevolutionary and genomic consequences of the origins and evolutionary dynamics of host-plant shifts remain elusive. Recent results illustrate the need for a multidisciplinary approach to assessing the role of host plants in shaping insect diversity at macroevolutionary scales. Using the swallowtail butterflies (Papilionidae) and their host plants, this project will develop a macroevolutionary and genomic framework to studying the origin and evolution of an arms race through time and space. We will build a complete species-level phylogeny for Papilionidae relying on whole-genome sequencing for all species. This time-calibrated phylogeny will be combined with species traits to estimate ancestral host-plant preferences and subsequent host-plant shifts. We will reconstruct dated phylogenies of the main host-plant families to estimate whether the butterflies and their host plants diversified concurrently through time and space. Diversification rates will be estimated for shifting/non-shifting and prey/non-prey clades. A matching genomic survey will to look for genes under positive selection by comparing sets of phylogenetic branches that experienced a host-plant shift versus branches without such a shift. Transcriptomes will be characterized for caterpillars and their plants to identify and pinpoint the genes involved in the arms race, as well as to compare them across the swallowtail tree of life. With this ambitious research proposal, we aim to provide answers to longstanding and fundamental evolutionary questions on the mechanisms behind ecological interactions over long timescales.