Evolution of traits explaining invasion success of Conyza canadensis (L)

Conyza canadensis (L.) is an annual world-wide successful invader, native to North America that has been introduced to mid-Europe about 350 years ago and has recently established in Asia and Australasia. Several life- history traits between native and invasive C. canadensis plants were compared to investigate whether invasive plants 1) have a higher competitive ability, i.e., win in head-to-head or diffused competition against native conspecifics and/ or 2) show a shift in allocation from defence to growth (EICA hypothesis). Resistance against herbivory of native and invasive populations with a native European generalist slug (Arion lusitanicus) and an invasive Nearctic specialist aphid (Uroleucon erigeronensis) were examined. Invasive populations from Europe and New Zealand were more attacked by the generalist Arion lusitanicus and lost an overall moderate, but significantly higher amount in rosette size due to herbivory than native American plants. However, final size of attacked plants was still higher in invasive populations than in plants from the native American range. In contrast, the invasive Conyza plants were less attacked by the Nearctic specialist Uroleucon erigeronensis (Aphidae). The infestation of the recently introduced specialist resulted in severe reduction of fitness in the infected native plants, while the generalist slug herbivory still resulted in thriving invasive C. canadensis. Invasive plants grew bigger after 70 days under identical conditions in the glasshouse and achieved a higher reproductive biomass, a key fitness- related trait in this annual species.