Biological Invasions

, 13:2379 | Cite as

Evolution of growth but not structural or chemical defense in Verbascum thapsus (common mullein) following introduction to North America

  • Christina Alba
  • M. Deane Bowers
  • Dana Blumenthal
  • Ruth Hufbauer
Original Paper


Post-introduction evolution of increased growth or reproduction has been observed in many species of invasive plants; however, it is not consistently associated with a loss of defense, as predicted by the influential evolution of increased competitive ability (EICA) hypothesis. Inconsistent support for the EICA hypothesis likely reflects the fact that, although invasive plants are released from attack by some enemies, typically specialists, they often do not escape attack from generalists. Thus, different types of defense (e.g., structural versus chemical) may evolve in different directions following introduction. We used a common garden experiment to test whether a shift in allocation among defenses (as opposed to a simple increase or decrease in a single defense) is associated with increased growth in introduced Verbascum thapsus populations. Introduced populations had significantly greater shoot biomass than natives. However, root biomass was similar between ranges, and highly variable, resulting in only marginal differences in total biomass. Mean investment in all three defenses was remarkably similar between the native and introduced populations, providing no evidence for range-level, post-introduction evolution of defense. This finding was consistent with the fact that, despite significant population-level variability for all defenses, there was little evidence of trade-offs between growth and defense or among different types of defense. These results suggest that evolution of increased growth in V. thapsus is not fueled by decreased allocation to defense, and that selection on defense may vary more at the population scale than the continental scale.


Insect herbivores Iridoid glycosides Leaf toughness Trade-offs Trichomes 



We thank Alecu Diaconu, Brad Harmon, Hariet Hinz, John Parker, René Sforza, and Jennifer Williams for collecting seeds; Erik Hardy for measuring leaf toughness; and Christa Fettig and two anonymous reviewers for providing helpful feedback on an earlier version of the manuscript. We also thank the Colorado Native Plant Society for partial funding of the chemical analyses.


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  • Christina Alba
    • 1
  • M. Deane Bowers
    • 2
  • Dana Blumenthal
    • 3
  • Ruth Hufbauer
    • 1
  1. 1.Graduate Degree Program in Ecology and Department of Bioagricultural Sciences and Pest ManagementColorado State UniversityFort CollinsUSA
  2. 2.Department of Ecology and Evolutionary BiologyUniversity of Colorado at BoulderBoulderUSA
  3. 3.USDA-ARS, Rangeland Resources Research UnitFort CollinsUSA

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