1. Figure S1: No relationship between proportion leaf damage and the A) latex or B) cardenolide response of common milkweed eaten by monarchs (solid circles) or Euchaetes(open circles). Control plants not shown. ABAB Latex exudation (mg) Cardenolides (  g/mg) proportion leaf damage

2. Figure S2: Reaction norm plots for the impact of monarch herbivory on 20 full-sibling families of common milkweed for A) latex and B) Cardenolides; the mean increase across families was >100% and >30% respectively (Figure 2) Latex exudation (mg) Cardenolides (  g/mg) Control Monarch Damage treatment A B

3. Figure S3: No correlation between latex and cardenolides (n=20 full-sibling families of common milkweed) in controls (diamonds), plants damaged by monarchs (squares), or plants damaged by Euchaetes (triangles). Latex exudation (mg) Cardenolides (  g/mg)