PARENT SESSION
Contributed Oral Session 86: Herbivory: Genetic Variability in Insect - Plant Interactions
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal

Linking biotic interactions and soil conditions to local adaptation in Chamaecrista fasciculata (Fabaceae).

Abdala-Roberts, Luis^*,1, Marquis, Robert¹, ¹ University of Missouri-St. Louis, St. Louis, MO, U.S.A.

ABSTRACT- The selective pressures underlying the evolution of local adaptation often are not determined, especially the role of biotic interactions (e.g., herbivores and the third trophic level). The overall objectives of this study were to determine: 1) whether local adaptation is present in the ant-defended plant, Chamaecrista fasciculata (Fabaceae), and 2) the contribution of ant-plant-herbivore interactions and soil characteristics to such adaptation. We used three C. fasciculata populations and performed both a field and a greenhouse experiment. The first involved reciprocal transplants of seedlings from each population (to test for local adaptation) and experimental reduction of ant density and herbivory intensity (to test for effect of biotic interactions on study species fitness). Forty-five seedlings from each population were reciprocally transplanted to each site. Subsequently, three treatments were applied to 15 seedlings of each population source at each site: control, reduced ant density (blocking nectar production by extrafloral nectaries), and folivory reduction (using insecticide). The greenhouse experiment involved reciprocal transplants of population sources and soil sources (30 seedlings and 30 soil samples from each site) to test for a soil effect on C. fasciculata flower production, and the potential for local adaptation to soil conditions. Results showed that blocking nectaries significantly reduced ant density (thus increasing herbivory), and that the insecticide also reduced herbivore damage relative to controls; however, these manipulations did not impact C. fasciculata reproductive measures significantly (e.g., seed number). In contrast, soil source did have a significant effect on flower production. Overall, plants in both the field and greenhouse experiments, regardless of population source, had higher seed and flower production, respectively, at one specific site; native populations never showed higher fitness than non-native ones, thus causing us to reject the hypothesis of local adaptation. The absence of treatment effects on plant reproduction suggests a limited/inconsistent effect of ants and folivores on C. fasciculata fitness, which most likely restricts their capacity to promote local adaptation at the studied sites.

Key words: Chamaecrista fasciculata, local adaptation, ant-plant-herbivore interactions, soil