eLife Assessment: Cardenolide toxin diversity impacts monarch butterfly growth and sequestration

This important study investigates how structurally diverse cardenolide toxins in tropical milkweed, especially mixtures containing nitrogen-and sulfur-containing variants, influence monarch caterpillar feeding, growth, and toxin sequestration.The experiments provide solid evidence that chemical diversity within a single group of plant toxins can have combined effects on even highly specialized herbivores that differ from the effects of each toxin alone.However, as the mixture design does not fully separate true diversity effects from the influence of the N,S-cardenolides themselves and the ecological basis for the chosen natural ratios remains weakly justified.As a result, the broader conclusions would require more fully justified concentration regimes, mixture treatments that exclude N,S-cardenolides, and tests on living plants and non-adapted herbivores to firmly support the proposed coevolutionary interpretation.