Fig. 3

HPLC chromatograms for (a) seeds from the milkweed Asclepias syriaca, (b) a standard sample of the cardenolide ouabain, (c) the milkweed bug, O.fasciatus after feeding upon A. syriaca seeds, and (d) O. fasciatus after injection with ouabain. Numbered peaks are those identified as cardenolides. The peak at 20 min is that of an internal digitoxin standard of 1.5 μg. (c inset) Change in expression of α1A, α1B and α1C in O. fasciatus fed a diet devoid of cardenolides (sunflower seeds) versus milkweed seeds, and (d inset) change in expression when injected with ouabain compared to with a saline solution. Cardenolides that elute at the beginning of the chromatogram are highly polar, whereas those that elute near the end of the chromatogram are highly non-polar. Normalized fold change is relative to the non-cardenolide treatment in both cases. Error bars represent standard errors of mean values for three biological replicates