Five Surprises That Emerged From Monarch Butterfly Genomes

Sequencing 101 butterfly genomes has revealed a few of the monarch’s secrets, including some keys to its epic annual migration

Monarch butterflies catching the sun on an oyamel tree in a Mexican overwintering site. (Jaap de Roode)

A monarch butterfly migration is a memorable sight. In North America, the iconic insects travel south to Mexico in the fall and north again in the spring. Wherever they stop, hundreds of fluttering bugs rest in the trees, and a sea of orange, white and black wings fill the sky.

But even though monarchs are perhaps best known for their migration, scientists had relatively little genetic data about the behavior. Now Marcus Kronforst, an evolutionary biologist at the University of Chicago, and his colleagues have used the latest statistical tools to delve into the monarch’s secrets. The team sequenced 101 genomes from monarch populations across the globe along with those of their close relatives, then ran comparisons looking for clues. Here are some of the revelations from the results, published yesterday in Nature:

Monarch butterflies originated in North America

(Sonia Altizer)

Until now, entomologists had suspected that the non-migratory southern monarchs were at the base of this butterfly’s evolutionary tree, and that migratory North American monarchs had evolved from their tropical brethren. But the genetic analysis shows that monarchs got their start in the north. “It was hard to wrap our heads around this new idea of where the monarchs came from,” says Kronforst. 

Three branches emerged from North American monarchs: one in Central and South America, one in the Pacific and one across the Atlantic. The researchers posit that monarchs spread from the southern United States or northern Mexico, headed south into Belize and Costa Rica, then ventured into South America and the Caribbean. Historical records put their spread across the Atlantic and Pacific around the early 1800s, but the genetic analysis suggests those populations split even earlier—between 2,000 and 3,000 years ago. Eastern monarchs crossed the Atlantic to Portugal, then Spain and Morocco. Western monarchs island-hopped from Hawaii to Samoa and Fiji, and eventually on to New Caledonia, Australia and New Zealand. These butterfly populations have grown considerably in the last 200 to 500 years, which could account for the discrepancy in the timing.

About Helen Thompson
Helen Thompson

Helen Thompson writes about science and culture for Smithsonian. She's previously written for NPR, National Geographic News, Nature and others.

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