Whole-genome resequencing data support a single introduction of the invasive white pine sawfly, Diprion similis

Authors: DAVIS, JEREMY - University Of Kentucky; Sim, Sheina; Geib, Scott; Scheffler, Brian; LINNEN, CATHERINE - University Of Kentucky

Submitted to: Journal of Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2023
Publication Date: 2/24/2023
Citation: Davis, J.S., Sim, S.B., Geib, S.M., Scheffler, B.E., Linnen, C.R. 2023. Whole-genome resequencing data support a single introduction of the invasive white pine sawfly, Diprion similis. Journal of Heredity. 114(3):246-258. https://doi.org/10.1093/jhered/esad012.
DOI: https://doi.org/10.1093/jhered/esad012

Interpretive Summary: The white pine sawfly is species recently introduced to the New England area where it was first recorded 110 years ago. Though it infests thick-needled pines in its native range in Eurasia, it now predominantly attacks the thin needles of the eastern white pine in its current introduced range in the North America. Due to its recent introduction and drastic host shift, the white pine sawfly, Diprion similis, represents a unique opportunity to test hypotheses on the mechanism of its invasion to determine if it represents a single or multiple introduction events and if there were patterns of genetic differentiation across populations. These questions were investigated by creating a high-quality and chromosome-length genome assembly for D. similis and generating whole-genome resequencing data for 64 individuals from introduced populations to evaluate population structure. Results from this study lead to support for the hypothesis that D. similis in North America represents a single-introduction event with implications for the ability of invading populations presumably depauperate of genetic diversity to adapt to a novel host.

Technical Abstract: Biological introductions can provide unique insights on evolutionary processes as unintended “natural experiments”. Invasion of phytophagous insects are of particular interest to evolutionary biologists studying adaptation, as introductions often require rapid adaptation to novel hosts. However, such rapid adaptation is expected to be limited by reduced genetic diversity common in invasions—a problem known as the “genetic paradox of invasions”. Many scenarios have been proposed for how organisms subvert this adaptive challenge, with the most studied being increased diversity generated by multiple invasive waves. Analyzing fine-scale population structure can be a powerful tool for evaluating the origin and number of invasion events that may have contributed to successful colonization and adaptation. Here, we present the reference genome and population structure for the introduced white pine sawfly, Diprion similis. This species was introduced to North America in 1914, where it has undergone a rapid host shift to the thin-needled eastern white pine (Pinus strobus), making it an ideal system for studying adaptation to novel environments. We obtained whole-genome sequences for 64 D. similis females to describe population structure in the introduced range and evaluate evidence for multiple introduction events. Our data reveal a single population in North America, and strong spatial patterns to population structure and genetic variation—consistent with expectations for a single-introduction event. We discuss implications of these findings for the adaptive history of this species, and next steps to develop D. similis as a model system in invasion biology.