title: Evolution of plant growth and defense in a continental introduction.
abstract: Substantial research has addressed adaptation of nonnative biota to novel environments, yet surprisingly little work has integrated population genetic structure and the mechanisms underlying phenotypic differentiation in ecologically important traits. We report on studies of the common milkweed Asclepias syriaca, which was introduced from North America to Europe over the past 400 years and which lacks most of its specialized herbivores in the introduced range. Using 10 populations from each continent grown in a common environment, we identified several growth and defense traits that have diverged, despite low neutral genetic differentiation between continents. We next developed a Bayesian modeling approach to account for relationships between molecular and phenotypic differences, confirming that continental trait differentiation was greater than expected from neutral genetic differentiation. We found evidence that growth-related traits adaptively diverged within and between continents. Inducible defenses triggered by monarch butterfly herbivory were substantially reduced in European populations, and this reduction in inducibility was concordant with altered phytohormonal dynamics, reduced plant growth, and a trade-off with constitutive investment. Freedom from the community of native and specialized herbivores may have favored constitutive over induced defense. Our replicated analysis of plant growth and defense, including phenotypically plastic traits, suggests adaptive evolution following a continental introduction.
authors.affiliation: Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853.
authors.forename: Anurag A
authors.initials: AA
authors.lastname: Agrawal
authors.forename: Amy P
authors.initials: AP
authors.lastname: Hastings
authors.forename: Gideon S
authors.initials: GS
authors.lastname: Bradburd
authors.forename: Ellen C
authors.initials: EC
authors.lastname: Woods
authors.forename: Tobias
authors.initials: T
authors.lastname: Züst
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Harvey
authors.forename: Tibor
authors.initials: T
authors.lastname: Bukovinszky
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D031108:Asclepias / Q000235:genetics* / Q000254:growth & development* / Q000469:parasitology; D001499:Bayes Theorem; D005075:Biological Evolution; D002080:Butterflies; D005060:Europe; D014644:Genetic Variation; D060434:Herbivory; D058865:Introduced Species; D009656:North America; D010641:Phenotype; D063245:Plant Development