The same genetic changes in bugs, worms, mice, and birds were caused by the poisonous toxins of milkweed plants.
Monarch butterflies were among the first insects to use this special genetic twist to feed on milkweeds. The toxins are sequestered in parts of the butterfly's body to provide defense against the predator.
The black-headed grosbeak is a predator that migrates to Mexico during the winter to feed on monarch butterflies.
Scientists have suspected for a long time that this bird has evolved some of the same protective mechanisms as its meal, and now it appears that this animal has evolved some of the same mechanisms as its meal.
The black-headed grosbeak's genome was published last year, and researchers started looking for the same changes seen in monarch butterflies.
They were able to find two quirks in the butterfly's sodium pump genes that were not found in the other two genes.
Milkweed toxins can block the pump genes that are responsible for moving sodium and potassium out of a body's cells, causing chaos within the body.
If enough of the toxin is consumed, animals with hearts can die from heart failure.
If your main meal consists of milkweed toxins, there may be a need for pump genes to be changed.
The biology was pretty well worked out, but we couldn't go down to the lowest level of organization to see how grosbeaks are doing this.
"It looks like they are evolving resistance using the same kind of machinery in the same places in the genetic code as the monarch and the bugs and the beetles, that feed on milkweeds, as well."
Researchers were able to find these genomic changes in multiple layers of the food chain.
The wasp, which feeds on monarch eggs, has two different genes in it, one of which is the same one as the butterflies.
deer mice, which feed on monarch butterflies, have all three of the same defects as the nematode, which lives in the soil around milkweed plants.
The results show that at least two changes in the pump genes are needed to allow animals to prey on monarch butterflies.
Evolutionary systems biologist Simon 'Niels' Groen from the University of California Riverside says it's remarkable that convergent evolution occurred at the molecular level in all these animals.
Evolutionary changes were caused by plant toxins across the food chain.
The fact that all four of these animals are distantly related suggests that this predator-prey battle has deep evolutionary roots. Plant toxins may have caused a domino effect across the food web.
The authors hope to answer the question of whether these are the only genetic changes required to consume milkweed toxins with further research.
The black-backed oriole consumes up to a million monarchs each winter, but it tends to pick around the most toxic parts. The Grosbeaks should eat the whole butterfly.
When the orioles' genome is sequenced, it will be interesting to see if they have the same genetic changes in the pump genes or if they have adapted a different mechanism.
It's just a matter of time before they're discovered, as there are other parasites and predators that have evolved resistance to monarchs.
"We know that resistance to cardiac glycosides is not the only way, but targeting this particular pump seems to be the most efficient way to evolve resistance."
Current Biology published the study.
