1. What drives the evolution of increased growth and fecundity in plants introduced to a novel range is not well understood.
2. We investigate between-range differences in performance for Verbascum thapsus, a weedy invader known to grow larger in its introduced than native range. Specifically, we question whether adaptation to herbivory or climate best explains increased performance of introduced populations.
3. We grew 14 native and 22 introduced populations of V. thapsus in two common garden locations: near Prague, Czech Republic (native range) and in Colorado, USA (introduced range). By removing herbivores from half of the plants within each garden we tested the prediction of the Evolution of Increased Competitive Ability (EICA) hypothesis: increased performance is driven by an evolutionary shift of resources away from defence against herbivory towards growth and reproduction. We then investigated whether genetically based clines in performance are expressed along climate gradients within both the native and introduced ranges.
4. On average, seeds produce larger rosettes when collected from the introduced versus native range. While this evolution of increased growth in introduced populations in part matches the prediction of EICA, climate, not herbivory, best explains this between-range difference. Specifically, seeds collected from the native range produce smaller rosettes as the climate of origin becomes cooler and drier, while there is no cline in performance in rosettes grown from seed collected from the introduced range, which are large regardless of climate of origin. Thus, a climate-based cline within the native range best explains lower average performance of native compared to introduced populations.
SYNTHESIS: The breakdown in a potentially adaptive cline emphasizes the need to more closely investigate the evolutionary processes that shape geographic structuring (or its absence) within the introduced range. In addition, EICA is not universally applicable to all invasion scenarios, and our findings underscore the importance of testing underlying assumptions alongside the predictions of this hypothesis.
Common Garden Performance Data
Includes data related to the performance of Verbascum thapsus rosettes grown in a common garden. Columns include: 'Plant' (unique ID associated with each rosette; numbers are not consecutive due to attrition before planting and plants that were excluded due to faulty irrigation), 'Population' (unique ID associated with each population; numbers are also not consecutive due to attrition before planting and plants that were excluded due to faulty irrigation), 'Origin' (continental range of seed collection; North American or European), 'Block' (1 or 2; a spatial block that coincides with maternal line), 'Treatment' (Ambient or Reduced Herbivory), 'PC1' (Principle Component associated mainly with temperature), 'PC2' (Principle Component associated mainly with precipitation during warm or wet periods), 'PC3' (Principle Component associated mainly with precipitation during warm and dry periods), 'Rosette.Area' (cm^2), 'Alive' (indicates where the rosette survived [1] or died [0] before September of the first growing season), 'Survival.to.Beginning.of.the.Second.Growing.Season' (0=no, 1=yes), 'Young.Leaf.Chewing.Damage' (estimate of average percent leaf tissue removed on young leaves by insect herbivores), 'Binomial.Young.Leaf.Chewing.Damage' (0=no visible damage, 1=visible damage on young leaves), 'Old.Leaf.Average.Chewing.Damage' (estimate of average percent leaf tissue removed on old leaves by insect herbivores), Binomial.Old.Leaf.Chewing.Damage (0=no visible damage, 1=visible damage on young leaves), 'Garden' (Garden Location; either U.S. or Czech Republic).
Performance Data.csv
Resistance to Herbivory Data
Includes data related to resistance against herbivory of native and introduced populations of Verbascum thapsus. Columns include: 'Garden' (Garden Location; either U.S. or Czech Republic), 'Block' (1 or 2; a spatial block that also coincides with maternal line), 'Population' (unique ID associated with each population; numbers are also not consecutive due to attrition before planting and plants that were excluded due to faulty irrigation), 'Origin' (continental range of seed collection; North American or European), 'Latitude' (of seed source), 'Longitude' (of seed source), 'PC1' (Principle Component associated mainly with temperature), 'PC2' (Principle Component associated mainly with precipitation during warm or wet periods), 'PC3' (Principle Component associated mainly with precipitation during warm and dry periods), 'Average.Rosette.Area.under.Reduced.Herbivory' (cm^2; rosette area for plants sprayed with systemic insecticide), 'Average.Ambient.Old.Leaf.Damage' (estimate of average percent leaf tissue removed on old leaves by insect herbivores when plants were sprayed with a water control).
Resistance Data.csv
Tolerance to Herbivory Data
Includes data related to tolerance to herbivory of native and introduced populations of Verbascum thapsus. Columns include: 'Garden' (Garden Location; either U.S. or Czech Republic), 'Block' (1 or 2; a spatial block that also coincides with maternal line), 'Population' (unique ID associated with each population; numbers are also not consecutive due to attrition before planting and plants that were excluded due to faulty irrigation), 'Origin' (continental range of seed collection; North American or European), 'Latitude' (of seed source), 'Longitude' (of seed source), 'PC1' (Principle Component associated mainly with temperature), 'PC2' (Principle Component associated mainly with precipitation during warm or wet periods), 'PC3' (Principle Component associated mainly with precipitation during warm and dry periods), 'Coefficient.of.Tolerance.Slope' (the slope of the line of log-transformed rosette area plotted against percent herbivore damage experienced by each plant), 'Variance.of.Tolerance.Slope'.
Tolerance Data.csv