NY Botanical Garden Seminar, May 4: Phenotypic Plasticity and Plant Invasions.

“Examining the role of natural selection and phenotypic plasticity in plant invasions: a study of invasive Japanese knotweed (Fallopia japonica) and native woodland knotweed (Persicaria virginiana)”

Kelly O’Donnell, PhD., Postdoctoral Fellow
Columbia University

Friday, May 4, 2011
11am-12 noon
Watson 302
Refreshments at 10:45

Kelly O’Donnell

Dissertation Abstract

Determining the role of natural selection in plant invasions

The ecological and evolutionary study of plant invasion processes is of exceeding importance in today’s changing environment. However, few studies have addressed the impact of natural selection on invasive plant species. While scientists have been able to detect selection in natural populations, most studies are not replicated in space or time leading to unreliable statistical estimates and tentative causal analyses. My objective is to further our knowledge of selection dynamics in the wild by working in the area of invasion biology through studies that combine both field and controlled settings. Biological invasions may be thought of as natural evolutionary experiments that scientists can use to study the effects of possibly novel and intense selection pressures on species that are in the process of aggressively expanding their range. It has been suggested that plant invasion affords us the ability to better assess the speed and predictability of local adaptation by natural selection, and that there are at least two mechanisms by which species can become invasive: through rapid local adaptation and/or through augmented phenotypic plasticity. It remains to be seen if either or both of these statements are generally true, as they have been rarely tested in the field. I have conducted a multi-year selection analysis on field populations of invasive Japanese knotweed (Fallopia japonica) and a native relative, woodland knotweed (Persicaria virginiana) and found strong, but temporally variable, natural selection. I then assessed the level of local adaptation in Japanese knotweed and compared it to woodland knotweed via a reciprocal transplant experiment. Despite the strong selection pressure (but perhaps because of the variability), there was little evidence of local adaptation in either species. Finally, I examined both species to measure their plasticity for traits relating to light acquisition in a common garden experiment. Both species had plastic trait responses to shade, but they followed different plasticity strategies. Woodland knotweed followed a “jack-of-all-trades” approach; it was able to thrive under either light treatment. Japanese knotweed seemed to use the opportunistic “master-of-some” strategy; its trait plasticity allowed it to take advantage of a better quality environment. Overall, there was no clear distinction between the native and invasive species studied. Both experience strong selection, but do not seem to locally adapt to it. Both possess trait plasticity that allows them to thrive in different light conditions, although the strategy is different.

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