Collaborative Research: Tracking fine-scale selection to temperature at the invasion front of a highly dispersive marine predator

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Marine invasive species pose a serious and ongoing risk to ocean ecosystems and the economies that rely on them. Understanding how such species adapt rapidly to new environments is key to preventing and managing invasions. Traditionally, the focus has been on inherent traits and flexibility of an invasive species, ignoring the potential for evolutionary change after introduction. However, recent research has shown that some marine species may evolve specific genomic features which allow highly efficient selection over as little as a single generation. This project tests the importance of genomic traits in allowing marine invasive species to survive and thrive on new shores. Its focus is on the high-impact invasive European green crab, which has spread over 1,500 km of the West Coast of North America since 1989 and has very recently begun expanding into the Salish Sea. This project tracks the earliest stages of green crab invasion into a new environment where the species is predicted to have substantial ecological and economic impacts. Genetic differences are followed over time and space across the entire West Coast, with a focus on crabs found in the Salish Sea where the species is currently expanding. Genetic data is complemented by oceanographic modeling to predict the spread of green crabs into the Salish Sea and across the West Coast. Finally, targeted sequencing and prior sampling are used to probe the genomic traits underlying these changes and determine if the same traits have played a role in the species' invasive success on other shores. Sampling for this project is conducted by Washington Sea Grant's Crab Team, an expansive outreach and monitoring program powered largely by hundreds of volunteers who monitor green crabs across 3,000 miles of coastline in the Salish Sea. The results of this project are shared with these volunteers and other stakeholders and is used to inform trans-boundary green crab management and spread prediction on the West Coast.Recent work has hypothesized that genomic architecture, which has been increasingly discovered to play a role in local adaptation, may also be key to a species' ability to adapt quickly when gene flow is high. This project integrates multiple approaches to track the speed and dynamics of adaptation-with-gene flow across a thermal gradient in an explicit oceanographic context using the invasive European green crab (Carcinus maenas). Prior work in this system identified a suite of genes that appear to constitute balanced polymorphisms whose allele frequencies correlate strongly with site temperature against a homogeneous neutral genetic background. This project has three main goals: 1) To examine fine-scale selection to temperature over a comprehensive spatial and temporal data set comprising most of the species' history on the West Coast, 2) To track the expanding range front in the Salish Sea, comparing the genetic trajectory of individuals at the range edge with oceanographic modeling of dispersal, and 3) To characterize the genomic regions surrounding putative balanced polymorphisms and examine the ubiquity of their association with temperature across globally replicated populations. This coupled evolutionary oceanography approach represents an unprecedented test of the speed and nature of rapid adaptation in a highly dynamic natural marine environment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.