Evolution of fast-growing and more resistant phenotypes in introduced common mullein (Verbascum thapsus)

Authors: KUMSCHICK, SABRINA - Colorado State University; HUFBAUER, RUTH - Colorado State University; ALBA, CHRISTINA - Colorado State University; Blumenthal, Dana

Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2012
Publication Date: 1/10/2013
Citation: Kumschick, S., Hufbauer, R., Alba, C., Blumenthal, D.M. 2013. Evolution of fast-growing and more resistant phenotypes in introduced common mullein (Verbascum thapsus). Journal of Ecology. 101:378-387.

Interpretive Summary: Species introduced into areas outside of their native range have to adapt to new biotic and abiotic conditions to be able to establish. Some of these introduced species are also more successful in their introduced than their native range. We used a common garden experiment to test whether introduced populations are better adapted to low water, more responsive to nitrogen availability, more competitive, faster-growing, or less resistant to herbivory than native populations. Results show that even though introduced mullein is not a better competitor, and is not better adapted to its drier introduced range, it grows larger in the absence of competition, and is better able to take advantage of high resource availability. Invasive mullein is more resistant to a generalist herbivore. These results demonstrate the usefulness of examining evolutionary responses of introduced species to both abiotic and biotic variables. Together, fast-growth, strong responses to high water-availability, and low root:shoot suggest that mullein has evolved to be more fast-growing and weedy in its introduced range. Furthermore, these traits were not evolved at the expense of resistance to generalist herbivores.

Technical Abstract: Species introduced into areas outside of their native range have to adapt to new biotic and abiotic conditions to be able to establish. Some of these introduced species are also more successful in their introduced than their native range, with increased growth and fecundity. We used a common garden experiment with 23 native and 27 introduced populations of common mullein (Verbascum thapsus) to test whether introduced populations are better adapted to low water, more responsive to N availability, more competitive, or faster-growing, than native populations. We also tested whether introduced mullein is less resistant to generalist herbivores in the introduced range. Results show that even though introduced mullein is not a better competitor, and is not better adapted to its drier introduced range, it grows larger in the absence of competition, and is better able to take advantage of high resource availability. Furthermore, invaders are also more resistant to a generalist herbivore. Synthesis: These results demonstrate the usefulness of examining evolutionary responses of introduced species to both abiotic and biotic variables. Together, fast-growth, strong responses to high water-availability, and low root:shoot suggest that mullein has evolved a fast-growing, weedy phenotype in its introduced range. At the same time, herbivory assays suggested that these traits were not evolved at the expense of resistance to generalist herbivores.