Millenia of Evolution Produce Migrating Monarchs

- By Anne-Marie Luca

Monarchs, those large butterflies with the striking orange and black wings, are known for their impressive migration all the way to Mexico from southern Canada and the northern United States. While monarchs have been making this odyssey for several million years, their more than 4,000-kilometre route is actually only about 20,000 years old.

According to a 2014 American study on monarch genetics, published in Nature magazine, monarchs originated in the southern United States and northern Mexico. Their population spread at the end of the ice age, as the glaciers retreated and monarchs followed their host plant, milkweed, northward to the US Midwest and then into southern Canada. Some also ventured as far as South America and to many South Pacific and Caribbean islands.

But only North American monarchs make such a long journey. “After they moved north in the spring and summer, they were forced to adapt and head south again before winter. That’s how their migratory behaviour was reinforced, since those individuals that didn’t migrate in the fall all perished,” explains Maxim Larrivée, Head of Collections and Research at the Insectarium. The researchers identified the genes responsible for the muscular function used in flight, and that allow these migrants to use less oxygen and slow their metabolism.

The spread of milkweed played a role in their growth and dispersal, and now its eradication through the use of herbicides is one cause of the declining numbers of migrating monarchs. If you are concerned that these delightful butterflies are disappearing, keep in mind that you, too, can become an agent of change.