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Potential local adaptation in populations of invasive reed canary grass (Phalaris arundinacea) across an urbanization gradient

Citation

Hovick, Stephen; Weston, Leah; Mattingly, Kali; Day, Charles (2022), Potential local adaptation in populations of invasive reed canary grass (Phalaris arundinacea) across an urbanization gradient, Dryad, Dataset, https://doi.org/10.5061/dryad.zgmsbccbh

Abstract

Urban stressors represent strong selective gradients that can elicit evolutionary change, especially in non-native species that may harbor substantial within-population variability. To test whether urban stressors drive phenotypic differentiation and influence local adaptation, we compared stress responses of populations of a ubiquitous invader, reed canary grass (Phalaris arundinacea). Specifically, we quantified responses to salt, copper, and zinc additions by reed canary grass collected from four populations spanning an urbanization gradient (natural, rural, moderate urban and intense urban). We measured ten phenotypic traits and trait plasticities, because reed canary grass is known to be highly plastic and because plasticity may enhance invasion success. We tested the following hypotheses: 1) source populations vary systematically in their stress response, with the intense urban population least sensitive and the natural population most sensitive, and 2) plastic responses are adaptive under stressful conditions. We found clear trait variation among populations, with the greatest divergence in traits and trait plasticities between the natural and intense urban populations. The intense urban population showed stress tolerator characteristics for resource acquisition traits including leaf dry matter content and specific root length. Trait plasticity varied among populations for over half the traits measured, highlighting that plasticity differences were as common as trait differences. Plasticity in root mass ratio and specific root length were adaptive in some contexts, suggesting that natural selection by anthropogenic stressors may have contributed to root trait differences. Reed canary grass populations in highly urbanized wetlands may therefore be evolving enhanced tolerance to urban stressors, suggesting a mechanism by which invasive species may proliferate across urban wetland systems generally.

Methods

These data are from a common garden experiment with reed canary grass (Phalaris arundinacea) collected from four populations along an urbanization gradient (5 individuals each). Clonal replicates of each individual were exposed to one of three urban-associated stressors (copper, zinc, salt) or stress-free controls. Plants were grown for one growing season and multiple traits recorded, including leaf and root functional traits and whole-plant biomass. Analyses were conducted to assess whether populations across our gradient differed in these traits or in trait plasticity, and whether plasticity was adaptive in stressful conditions.

Funding

Ohio State University