Population Genomics of a Recent Rapid Host-Shift in the Introduced Pine Sawfly Diprion Similis

Population Genomics of a Recent Rapid Host-Shift in the Introduced Pine Sawfly Diprion Similis Biological invasions are natural experiments where organisms are introduced to novel environments that often demand adaptive responses, yet bottlenecks often restrict the variation required to adapt. Diprion similis is a pine sawfly from Europe that invaded North America in 1914 and saw a subsequent rapid shift to a morphologically novel host—the thin-needled white pine. Preliminary work on historical host-use in this system has revealed the shift to white pine was not widespread until the 1960s, when collection records show a dramatic shift to >90% white pine use. This observation is consistent with the hypothesis that a secondary successful invasion was the genetic catalyst for adaptation. Here, I propose sequencing a broad set of collected D. similis samples from North America to test the hypothesis that a second invasion event provided the necessary genetic variation for host-shift adaptation. We will use population structure and demographic modeling to infer the number of invasions and demographic parameters of a rapid, successful adaptation to a novel host. The proposed work could shed light on what makes a successful invasion and provide insights on the pattern and mode of rapid hostshifts in phytophagous insects and beyond.