High chemical diversity of a plant species is accompanied by increased chemical defence in invasive populations
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Mechanisms contributing to the invasive success of plants are still only partly understood. A main assumption is that an escape from specialized enemies in introduced ranges allows a reduction of chemical defences resulting in an increase in growth and reproduction and thus increased competitive ability of introduced plants. Not only variation in concentration but also variation in composition of chemical compounds between individuals may be a key advantage for plants introduced to novel areas impeding adaptation of different plant antagonists. To investigate quantitative and qualitative variation of putative defence compounds and investment of resources in growth, we conducted a common garden experiment in the native range with seeds of 13 native and 9 introduced populations of Tanacetum vulgare, an aromatic plant forming different chemotypes. After 3.5 months, plants of introduced populations had similar biomass but more stems and higher concentrations of volatile secondary compounds (mainly terpenes) than plants of native populations. Both native and invasive T. vulgare populations exhibited high chemotypic variation with nine chemotypes occurring on both continents, whereas several were found exclusively either in plants originating from the native (n = 10) or invasive (n = 2) range. Due to the known negative effects of many mono- and sesquiterpenes on various organisms, we propose that high concentrations of these secondary compounds accompanied by high chemotypic diversity may facilitate the invasion success of a plant species.
KeywordsBiological invasions Chemotype diversity Common garden experiment Shifting defence hypothesis (SDH) Tanacetum vulgare (common tansy) Terpenes
We thank K. Rondeau and B. Teichner for their lab and field assistance. Seeds were provided by G. Fayvush, R. Tanner, A. Sennikov, R. Wittenberg, S. Toepfer, A. Diaconu, I. Toševski, M. Dolgovskaya, M. Volkovitch, S. Mosyakin, A. McClay, S. Cesselli, S. Turner, B. Villegas, M. Pitcairn, M. Chandler, J. Story, R. Sforza and M. Cristofaro. We also thank A. Schwan for English correction. We gratefully acknowledge M. Chandler and A. McClay, co-leaders of the common tansy project in the U. S. A. and Canada, and the financial support of the Montana Noxious Weed Trust Fund through the Montana State University and the Minnesota Department of Agriculture in the U. S. A., and in Canada the Alberta Beef Producers, the Agriculture and Food Council of Alberta (Advancing Canadian Agriculture and Agri-Food Program), the Saskatchewan Agriculture and Food (Agriculture Development Fund), Enbridge Pipelines (Athabasca), EnCana Oil & Gas Partnership and the British Columbia Department of Forests and Range.
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