Abstract
Invasive species often exhibit either evolved or plastic adaptations in response to spatially varying environmental conditions. We investigated whether evolved or plastic adaptation was driving variation in shell morphology among invasive populations of the New Zealand mud snail (Potamopyrgus antipodarum) in the western United States. We found that invasive populations exhibit considerable shell shape variation and inhabit a variety of flow velocity habitats. We investigated the importance of evolution and plasticity by examining variation in shell morphological traits 1) between the parental and F1 generations for each population and 2) among populations of the first lab generation (F1) in a common garden, full-sib design using Canonical Variate Analyses (CVA). We compared the F1 generation to the parental lineages and found significant differences in overall shell shape indicating a plastic response. However, when examining differences among the F1 populations, we found that they maintained among-population shell shape differences, indicating a genetic response. The F1 generation exhibited a smaller shell morph more suited to the low-flow common garden environment within a single generation. Our results suggest that phenotypic plasticity in conjunction with evolution may be driving variation in shell morphology of this widespread invasive snail.
Highlights
IntroductionPhenotypic plasticity, which is environmentally sensitive production of alternative phenotypes by given genotypes (Stearns 1989), is widely thought to facilitate the spread of invasive species (Baker 1965; Agrawal 2001; Yeh and Price 2004; Richards et al 2006)
A small fraction of non-native taxa successfully establishes and becomes widespread (Mack et al 2000), leading to a key question in invasion ecology: what characteristics of a species determine its success at invading a range of new environments? Phenotypic plasticity, which is environmentally sensitive production of alternative phenotypes by given genotypes (Stearns 1989), is widely thought to facilitate the spread of invasive species (Baker 1965; Agrawal 2001; Yeh and Price 2004; Richards et al 2006)
There were no significant differences in aperture height and lower body whorl width among populations in the F1 generation (Appendices A3–A7). Like their parental-generation mothers, Green River snails were the largest, Bear River snails were intermediate, and Polecat Creek snails were the smallest in terms of shell height, aperture width, and upper body whorl width. This common garden experiment sought to determine the importance of phenotypic plasticity and adaptive evolution in shell morphology of P. antipodarum
Summary
Phenotypic plasticity, which is environmentally sensitive production of alternative phenotypes by given genotypes (Stearns 1989), is widely thought to facilitate the spread of invasive species (Baker 1965; Agrawal 2001; Yeh and Price 2004; Richards et al 2006). If invasive species exhibit or evolve greater plasticity than native species (McDowell and Lee 2002; Yeh and Price 2004), invasives might have a fitness advantage over natives in the invaded range (Schweitzer and Larson 1999; Legar and Rice 2003). Adaptive evolution in response to local regimes of natural selection leads to genotypes specialized for different local environments, and facilitates spread across an environmental gradient (Lee 2002; Lee and Gelembiuk 2008). There are still few studies that examine plastic versus evolved responses in permitting the spread of invasives into new ranges (Chevin and Lande 2011)
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