Why Some Monarch Butterflies Migrate And Others Don’t

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Scientists who studied the genomes of monarch butterflies have discovered some interesting tidbits on how they have developed as they’ve dispersed throughout the globe over the years. The butterflies are found all over the world, but only the North American variety actually migrates en masse.

Clues to monarch butterflies’ migratory habits

Marcus Kronforst of the University of Chicago is one of the authors of the study, which was published in Nature, reports The New York Times. To complete the study, Kronforst and his team sequenced the genomes of 90 monarch butterflies from all around the globe.

One of their findings was a gene that seems to have a major impact on whether a particular variety of monarch is migratory. The gene also offers details on the origin of these butterflies, their migratory behavior and their color.

Changing views of monarch butterflies

Before the study, scientists believed that monarchs from South and Central America were older than those from North America. However, they now believe that the variety from North America is the oldest kind. According to Kronforst, at some point they “dispersed into South and Central America” and then crossed both the Pacific and Atlantic Oceans.

They learned that butterflies which migrate have lower levels of a certain collagen gene. That gene plays a role in forming the muscles the insects use to fly. The research team also used a flight monitor to learn that migratory butterflies use less oxygen.

Their metabolic rate is also lower, which is why they are able to fly such long distances. Some North American monarch butterflies fly from Canada as far south as Mexico, where they stay during the winter. Kronforst said he thinks of migratory monarchs as being marathoners rather than sprinters.

“The migratory ones are really marathon runners,” he said, according to The New York Times.

Other details about monarchs

Scientists also noted that most monarch butterflies are orange and black but that a very small percentage is white and black. That particular variety can be found in Hawaii.

They said there’s “one spot in one gene” in which all of the white monarchs differ from all of the orange monarchs.

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