Toxin resistance in the monarch butterfly expanded its milkweed host range

Weksler, N.; Astourian, M.; Yip, D.; Ordeman, E.; Verster, K.; Korablev, B.; Bernstein, S.; Agrawal, A. A.; Whiteman, N. K.; Karageorgi, M.

doi:10.64898/2026.05.25.727632

bioRxiv · 10.64898/2026.05.25.727632

Toxin resistance in the monarch butterfly expanded its milkweed host range

Weksler, N.·Astourian, M.·Yip, D.·Ordeman, E.·Verster, K.·Korablev, B.·Bernstein, S.·Agrawal, A. A.·Whiteman, N. K.·Karageorgi, M.

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Abstract

A central problem in ecology and evolution is to understand the extent to which herbivorous insect host plant specialization has been shaped by bottom-up natural selection from host-plant chemical defenses or top-down natural selection from natural enemies. Here, we show that the stepwise evolution of ATP target-site insensitivity (TSI) in the monarch butterfly lineage consistently tracked a dietary association with cardenolide-defended Asclepias host plants. We further show that Drosophila melanogaster flies edited with CRISPR-Cas9 genome engineering to carry the monarch butterflys more derived ATP genotype maintain survival across Asclepias host-plant diets that span a broad cardenolide defense gradient, whereas flies carrying early-diverging ATP genotypes in the monarch lineage show lower survival. We conclude that a resistance trait linked to sequestration and enemy protection also expanded dietary resistance to highly defended host plants, revealing how a single molecular adaptation may have been driven by both top-down and bottom-up selective pressures during herbivore specialization.

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Weksler, N., Astourian, M., Yip, D., Ordeman, E., Verster, K., Korablev, B., Bernstein, S., Agrawal, A. A., Whiteman, N. K., Karageorgi, M.. 2026-05-26. Toxin resistance in the monarch butterfly expanded its milkweed host range. https://doi.org/10.64898/2026.05.25.727632

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