Dissertation Research: Impact of Environment on Plant Susceptibility to Leaf-Cutter Ants

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The proposed studies investigate the impact of environmental conditions on leaf quality and subsequent selection by leaf- cutter ants, Atta cephalotes, a dominant herbivore at the La Selva Biological Reserve in Costa Rica. Specifically the interactions of light and soil nutrient conditions will be studied to see if plant susceptibility is altered via changes in plant traits. Leaves from both field collected plants and cultivated seedlings (started from the seeds of a single parent tree, so as to control for genotypic effects) growing under different environmental conditions will be used. This study focuses on a tropical legume species, Inga edulis var. minitula, because it commonly occurs in a range of habitats, appears to change in quality in response to different environmental conditions, and experiences Atta attack. Field pickup and cutting bioassays, laboratory choice assays, and fungal inhibition assays will determine leaf acceptability and suitability to Atta. Both correlative analyses and experiments will be used to isolate the impact of specific leaf traits on the ant/fungus system. While previous research has been largely qualitative and interspecific, this study concentrates on the impact of quantitative intraspecific variation. Since the ant/fungus system is easily manipulated both in the field and in the laboratory, it offers a unique opportunity to quantify the effects of different environmentally induced leaf traits and to establish the mechanism behind leaf-cutter ant selectivity.