A recent article confirms that scientists have researched that caterpillars are now eating milkweed (which is supposed to kill them). How is this happening? “Scientists have unraveled the sequence of gene mutations that enabled the monarch butterfly to thrive on toxic milkweed.” We learn at a young age that caterpillars turn into beautiful butterflies, so something must be happening before metamorphosis. There are three gene changing mutation amino acid sites including, 111, 119, and 122. Mutation 122 had the biggest boost in resistance. Another article states that ‘monarch flies’ continue to have small amounts of cardiac glycosides through metamorphosis, which is a trait that has been developed in monarch butterflies to restrain predators.
Monarch butterflies can eat milkweed due to a peculiarity in a crucial protein in their bodies, which is a sodium pump, that the cardenolide(steroid) toxins intervene with. How the pumps work? They move positively charged sodium atoms out of the cell resulting in the inside of the cell is negatively charged. In order for a heart to beat, the sodium pump has to build up enough electric charge and then nerves use the pumps to send signals to the brain.
What does milkweed have to do with this? In the study, they first addressed how milkweed is toxic to almost all insects, but caterpillars depend on milkweed. Females use milkweed to lay eggs and caterpillars eat as much as they can before chrysalis. In the article, they are referred to as “flying poison” because the milkweed toxin gets send from their gut to their wings and anything that tries to eat it immediately vomits it up. After these mutations, they now NEED milkweed to live and it altered the sodium pumps, so cardiac glycosides in the monarchs cells don’t affect them.
This mutation allowed butterflies to have their own food supply since milkweed is poisonous to other insects. Noah Whiteman, a biologist at the University of California, Berkely used CRISPR to try the mutations on fruit flies. The fruit fly experiment resulted in the findings that mutation 122 has bad side effects and is only useful if followed by another mutation. Other researchers say the order that mutations are done can make a big difference as well.