PARENT SESSION
Poster Session # 15: Plant Ecology.

Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Freshwater cyanobacterial resistance to herbivory: Chemical versus structural defense.

Camacho, Frank^*,1, Thacker, Robert¹, ¹ University of Alabama at Birmingham, Birmingham, AL

ABSTRACT- The freshwater cyanobacterium Lyngbya wollei forms dense mats in culturally impacted aquatic ecosystems in Alabama and produces saxitoxin, a carbamate alkaloid neurotoxin. We explored the palatability of L. wollei compared to a filamentous green alga, Rhizoclonium hieroglyphicum, in feeding assays using the freshwater amphipod Hyalella azteca as an herbivore. Three types of feeding assays were conducted: (a) whole mats of R. hieroglyphicum and L. wollei in the presence and absence of H. azteca, (b) ground L. wollei and R. hieroglyphicum, and (c) crude L. wollei extract coated onto artificial food strips. For the whole mat assay, H. azteca exhibited strong feeding preferences for R. hieroglyphicum compared to L. wollei treatments, significantly reducing R. hieroglyphicum growth rates. Amphipod density on a mat was negatively correlated with mat growth rate. Experiments using ground and extracted L. wollei showed that feeding deterrence was not due solely to the structural effect of the calcium carbonate sheath that surrounds the cyanobacterium. These results suggest that L. wollei may incur low rates of herbivory in freshwater ecosystems due to both structural and chemical defenses.

Key words: freshwater, saxitoxin, chemical ecology, cyanobacteria