Collaborative Research: LTREB: BEE: Long-term ecological and evolutionary dynamics of secondary contact.

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Populations of animals and plants are regularly isolated by natural processes and human activities. In isolation, populations adapt to local environments, and traits and genes may diverge. This adaptive divergence can create ecologically important variation that changes the role of species within ecosystems. Natural processes and human activities can also allow or force populations that have diverged in isolation to come back into contact - a process called secondary contact. The outcome of secondary contact is important for understanding how populations evolve and ecosystems function. This LTREB takes advantage of a whole-lake restoration project to study the decade-scale ecological and evolutionary dynamics of secondary contact between recently diverged lineages of alewife. Alewife are a well-studied and ecologically important fish found in lakes and in the coastal ocean of eastern North America. There are two divergent alewife life-history forms: the ancestral anadromous form that moves between lakes and the coastal ocean and a landlocked form that is resident in lakes. Many landlocked populations were formed by the construction of dams by colonial Americans. The recent removal of dams and construction of fishways create opportunities for secondary contact between landlocked and anadromous alewife populations. Findings will address questions fundamental to the generation and maintenance of biodiversity, the ecological impact of variation within species, and the impacts of human accelerated environmental changes including population fragmentation, restoration of habitat connectivity, and climate change. This project will inform the conservation and management of anadromous alewife, a critical resource in coastal freshwater and marine habitats, a species of conservation concern, and the focus of intensive restoration and conservation efforts. The genomic tools developed by this project will help resource managers address important questions, such as the impact of bycatch on anadromous alewife populations. The project will train graduate and undergraduate students, including students from underrepresented backgrounds, in a unique combination of advanced genomics techniques and whole-lake sampling. This project asks how climate change, anadromous alewife population recovery, and periodic major hybridization events (2-3 per decade), interact to determine the magnitude of hybridization and direction of gene flow, phenotypic differentiation among alewife forms, and whole-lake impacts. It focuses on the restoration of Rogers Lake, Connecticut and regional reference lakes. This project utilizes highly informative microhaplotype genetic markers to measure hybridization and gene flow; measures trophic morphology, individual growth rates, diets, and habitat use to assess phenotypic and ecological differentiation among forms; and samples inorganic nutrients, phytoplankton, and zooplankton to evaluate whole-lake impacts. This research provides a rare opportunity to track the ecological and evolutionary dynamics from the initiation of secondary contact, and the long-term research plan facilitates the detection of rare events and interactions between ecological and evolutionary process at the whole ecosystem scale.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.