The role of allelopathy in plant invasion: evolutionary change vs. community response in Impatiens glandulifera
Final Report Abstract
Allelopathy has been suggested as a mechanism facilitating the invasive success of introduced plants. Particularly, the novel weapons hypothesis suggests that the allelochemicals produced by invasive plants are novel and more inhibitory to their invasiverange neighbours. However, this project examined a previously untested idea, according to which invasive populations could evolve the enhanced production of these allelochemicals due to either the greater advantage they confer against invasive-range neighbors, or due to the release of natural enemies at the invasive range, which could select for decreased herbivore resistance and a greater investment in allelopathy. Additionally, this study examined the consequences of invasion age and common evolutionary history with the local community on the evolution of both allelopathy and herbivore resistance. As a target species, this study investigated one of the most invasive plant species in Europe, Impatiens glandulifera, whose allelopathic effects, though recognized, were not yet fully established. The role of allelopathy in the invasive success of this species was determined in a set of experiments that compared both changes in the production of allelochemicals by native and invasive genotypes as well as the responses of the native and invasive-range communities to these chemicals. The most important results of the project were: Invasive I. glandulifera exerted a stronger inhibitory effect on the germination of their dominant neighbor, Urtica dioica compared to their native-range counterparts, providing support for the hypothesis that increased allelopathic ability could be selected for at the invasive range and facilitate invasion success. These results call for biogeographical studies that will examine not only the novelty but also the evolution of allelopathic effects in invasive plants. U. dioica from the native vs. invasive range of I. glandulifera exhibited no difference in the response to its allelopathic effect, either with leaf extracts or trained soil, thus not supporting the novel weapons hypothesis for this species, and suggesting that increased allelopathy in invasive I. glandulifera could have been selected for by other processes. When studied across its invasion chronosequence, I. glandulifera from native populations or older populations within the invasive range showed greater resistance to the generalist herbivore, Deilephila elpenor, coupled with greater production of the secondary defence compound 2-methoxy-1,4-naphthoquinone glycoside. Moreover, results from a field survey suggested that older populations within the invasive range incur greater attack rates from local herbivores compared to more recently-established populations. These findings support the idea that the selection pressure of enemy release at the introduced range might attenuate over time, leading to the evolutionary recovery of enemy resistance. This study emphasizes the importance of incorporating the effect of time since introduction when examining evolutionary or ecological processes of plant invasions.
Publications
- (2013) The role of allelopathy in plant invasion: evolutionary change vs. community response in Impatiens glandulifera. The Annual Plant Population Biology conference of the Ecological Society of Germany, Switzerland and Austria, Tartu, Estonia (Talk)
Gruntman M, Zieger S and Tielbörger K
- (2014) Competitive dominance of the invasive plant Impatiens glandulifera: using competitive effect and response with a vigorous neighbor. Biological Invasions 16: 141-151
Gruntman M, Pehl AK, Joshi S and Tielbörger K
(See online at https://doi.org/10.1007/s10530-013-0509-9) - (2014) Invasive success and the evolution of enhanced weaponry. The First International Adaptomics Symposium of the DFG Priority Research Program 1529, Bad Neuenahr, Germany
Gruntman M, Zieger S and Tielbörger K
(See online at https://doi.org/10.1111/oik.02109) - (2016) Evolution of plant defenses along an invasion chronosequence: defense is lost due to enemy release- but not forever. The Annual Plant Population Biology conference of the Ecological Society of Germany, Switzerland and Austria, Třeboň, Czech Republic
Gruntman M, Segev U, Glauser G and Tielbörger K
- (2016) Invasive success and the evolution of enhanced weaponry. Oikos, 125: 59-65
Gruntman M, Zieger S and Tielbörger K
(See online at https://doi.org/10.1111/oik.02109)
