The Genetic Secrets Behind the Monarch Marathoners

With their brightly colored wings, monarch butterflies are some of the most striking insects in the world. Yet these insects are facing a host of threats as climate shifts occur. Now, scientists have taken a closer look at the genes that underlie the monarch's famous traits in an effort to better understand the insect with one of the largest migrations in the world.

Each year, millions of monarchs fly from as far north as Canada to spend the winter in Mexico. While monarchs can be found in South and Central America, though, it's only North American monarchs that migrate. In order to better understand the genetics underpinning this migratory behavior, the researchers sequenced the monarch's genome.

In all, the scientists sequenced and compared the genomes of 101 butterflies, including migratory North American monarchs, non-migratory monarchs from around the world and a few closely related species. The researchers then analyzed the monarch's evolutionary origins by using genetic comparisons, tracing back the ancestral lineage of butterflies to a migratory population that likely originated in the southern U.S. or Mexico.

This finding in particular actually overturns the previous theory that the butterfly originated from a non-migratory tropical species, which later developed the ability to migrate. It seems that while historical records suggest that the monarch's dispersal across the Pacific and Atlantic occurred during the 1800s, the butterfly actually crossed the oceans thousands of years ago.

The researchers also uncovered the genetic basis for migration. In all, they identified more than 500 genes, most of which are involved in muscle, developmental and neural function, associated with migration. Yet a single gene disparity stood out. It turns out that migratory butterflies express greatly reduced levels of a gene involved in flight muscle formation and function. They consume less oxygen and have significantly lowered flight metabolic rates.

"Migration is regarded as a complex behavior, but every time that the butterflies have lost migration, they change in exactly the same way, in this one gene involved in flight muscle efficiency," said Kronforst, one of the researchers, in a news release. "In populations that have lost migration, efficiency goes down, suggesting there is a benefit to flying fast and hard when they don't need to migrate."

The findings reveal a bit more about monarchs in general. While this butterfly isn't in danger of extinction, its mass migration does appear to be in peril. The latest research could help scientists better understand these insects and perhaps help them develop strategies for conservationists.

The findings are published in the journal Nature.