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Aye Tenger-Trolander

Monarch butterflies raised in captivity don’t migrate

In what may be a cautionary tale for citizen scientists trying to save North America’s iconic monarch butterfly, new research has found that butterflies raised in captivity are sometimes unable to migrate—some as a result of missing genes and others for want of the right environmental cues.

A graduate student discovered this genetic shortfall after buying dozens of monarchs and tethering them to a short pole—a common method to test what direction an insect wants to fly. Tethered wild-caught monarchs consistently headed south, the same direction they fly during their annual journeys from the United States and Canada to Mexico. But neither commercially sourced monarchs nor local individuals raised indoors did. They tended to head in random directions.

To see why the monarchs weren’t trying to fly south, the researchers sequenced the DNA of some of the butterflies and compared it with the already-sequenced monarch genomes. They found many differences but did not pin down any particular gene. But even with the right genes, the local butterflies raised indoors couldn’t head in the right direction; the researchers think that because outdoor-raised butterflies orient south, but ones raised indoors don’t, the latter are not getting the environmental cues that would signal them to fly south, they report today in the Proceedings of the National Academy of Sciences.

Over their long evolutionary history, monarchs that have spread to Africa, Australia, South and Central America, and Hawaii have ceased to migrate; with mild local conditions, they have no need to go anywhere else. But butterflies in colder climates such as North America don’t survive the winter if they don’t migrate.

Thus, the researchers say, the recent request for the U.S. government to list the species as threatened may be warranted. The findings also suggest school groups and hobbyists who raise monarchs to bolster the species’s population may want to source them locally and raise them outdoors for their entire life cycle.