Question Corner | Evolution through layers of food chain

How do monarch butterflies and their predators eat poisonous milkweed?

Scientists now understand how certain animals can feed on picturesque, orange monarch butterflies, which are filled from head to abdomen with milkweed plant toxins.

Milkweed produces toxic cardiac glycosides that can kill a horse, or a human, if consumed in high-enough concentration. However, monarch butterflies have evolved a set of unusual cellular mutations to be able to eat this plant. Now, a study carried out by researchers at the University of California, Riverside shows that the animals that prey on monarch butterflies too have evolved these same mutations (Current Biology).

The research revealed these mutations in four types of monarch predators — a bird, a mouse, a parasitic wasp, and a worm. “Plant toxins have caused evolutionary changes across at least three levels of the food chain. It's remarkable that concurrent evolution occurred at the molecular level in all these animals,” Simon C Groen, the first author says in a press release.

Milkweed toxins target a part of animal cells called the sodium–potassium pump, which helps enable heartbeats and nerve firing. When most animals eat milkweed, the pump stops working. Two years ago, these researchers discovered amino acid changes in three places on the pump that not only allow monarch butterflies to consume milkweed, but also to accumulate the milkweed toxins in their bodies as a defence against attacks. Groen’s team engineered these same amino acid changes in fruit flies, which then became as resistant to milkweed as monarchs. Based on the DNA sequence information, they found black-headed grosbeak, which eats up to 60% of the monarch butterflies in many colonies each year, had evolved the amino acid changes in their sodium pumps.

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Printable version | Jan 21, 2022 7:32:15 AM |

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