PARENT SESSION
Wednesday, August 9, 1:30-5:00 pm
COS 62 - Invasive species IV: trophic interactions and competition
Ballroom A, Ballroom Level, Cook Convention Center
Presiders: J Orrock

Evidence for evolutionary decreased defense against generalists in invasive horseweed Conyza canadensis.

Abhilasha, Dipti^*,1, Joshi, J¹, ¹ University of Zurich, Zurich, Zurich, Switzerland

ABSTRACT- Improved competitive ability in invasive plants through a shift in allocation in defense from defense to growth is one of the hypotheses explaining the success of non-indigenous invasive species. We compared resistance against a generalist herbivore and pathogen of native vs. invasive populations of Conyza Canadensis, one the most abundant invasive species in Europe. C. Canadensis is an annual species native to North America that has been introduced to mid-Europe about 350 years ago and recently established in New Zealand. In Europe, C. Canadensis is attacked by herbivores and contains mainly monoterpenes and sesquiterpenes, which have been shown to have anti-herbivore activity. In accordance with the EICA hypothesis, invasive populations from Europe and New Zealand were more attacked by Arion lusitanicus, a Southern European generalist slug (now invasive in mid-Europe) than native populations. Invasive populations suffered from a significantly higher reduction in rosette size due to herbivory than native American plants. Slug herbivory resulted also in an increased defense against fungi and invasive populations were more frequently infected by fungi than the natives. Invasive plants tended to grow bigger after 70 days under identical conditions in the glasshouse. European invasive plants had a higher number of leaves than the natives, whereas in New Zealand, polyploidisation might have led to bigger-sized leaves.

Key words: Conyza canadensis, Invasive Plants, Herbivory