Raw data associated with "Potent nitrogen-containing milkweed toxins are differentially regulated by soil nitrogen and herbivore-induced defense" - Journal of Chemical Ecology

We tested effects of soil N and herbivore-damage on cardenolide profiles of two milkweed species differing in life-history strategies (<i>Asclepias syriaca</i> and <i>A. curassavica</i>), and the toxicity of their leaves. In particular leaf extracts were tested against the target enzymes (Na⁺/K⁺-ATPase extracted from neural tissue) from both monarch butterflies (<i>Danaus plexippus</i>) as well as less cardenolide-resistant queen butterflies, <i>D. gilippus</i>. Increasing soil N enhanced biomass of <i>Asclepias syriaca</i> but had weak effects on cardenolides, including causing a significant reduction in the N-cardenolide labriformin; feeding by monarch caterpillars strongly induced N-cardenolides (labriformin), its precursors, and total cardenolides. Conversely, soil N had little impact on <i>A. curassavica</i><b> </b>biomass, but was the primary driver of increasing N-cardenolides (voruscharin, uscharin and their precursors); caterpillar induction was weak. Butterfly enzyme assays revealed damage-induced cardenolides substantially increased toxicity of both milkweeds to both butterflies, swamping out effects of soil N on cardenolide concentration and composition. Although these two milkweed species differentially responded to soil N with allocation to growth and specific cardenolides, leaf toxicity to butterfly Na⁺/K⁺-ATPases was primarily driven by feeding-induced defense.