PARENT SESSION
Oral Session #78: Herbivory: Effects on Plants.
Presiding: C. Ivey
Thursday, August 8. 9:00 AM to 11:30 AM. Apache Meeting Room, TCC.
Population variation in plant traits associated with ant attraction in Chamaecrista fasciculata (Fabaceae).
Rios, Rodrigo*,1, Marquis, Robert1, 1 University of Missouri-St. Louis, Saint Louis, Missouri
ABSTRACT- Interactions among plants, herbivores, and predatory ants can result in the evolution of plant traits that attract ants as biotic defense agents against herbivores. We quantified spatial variation in traits that attract ants for eight populations of the extrafloral nectary (EFN) producing annual, Chamaecrista fasciculata. Our censuses in populations of this plant in Missouri and Illinois (USA) showed differences in ant attendance and herbivore pressure. We therefore expected differences in traits that influence tritrophic interactions among populations due to differing selective pressures. Seeds were collected from each population and plants were grown in a common greenhouse environment to measure several plant traits throughout the life of the plants. Populations where grouped into three regions according to the their geographical proximity to account for environmental variation. Nested-MANOVA results showed differences in measured traits among regions and among populations nested within the selected regions. Nectary size, nectar production, and leaf length explained most of the variation among regions and among populations. In addition, the number of leaf hairs, the first leaf to produce an EFN, and the first leaf to produce a functional EFN were also important in explaining differences. The two populations with the lowest insect abundance on C. fasciculata showed small nectaries and the lowest nectar production. These results suggest that differences in abundance of ants and herbivores has promoted differential evolution of extrafloral nectary-related traits among populations.
KEY WORDS: Tritrophic interactions, Extrafloral Nectaries, Ants, Herbivores