Downsizing: Could monarch butterflies actually lose their big, elongated wings?
As California’s visiting monarch butterf ly populations dwindle, will they lose their strikingly large wings?
In an article in the November edition of the journal Proceedings of the National Academy of Sciences, UC Davis biologist Micah Freedman suggests that very well might be the case.
Freedman studied two centuries of monarch collections and found that the butterflies’ wings change their characteristics when the monarchs’ migration patterns are altered.
Even when compared with other species of monarch butterflies, the wings of North American monarchs are exceptionally big and elongated. That enables the butterflies to generate more lift so they can fly long
distances.
Like airplane wings, a monarch’s “wing shape generates less drag,” Freedman said in an interview.
When Freedman looked at the wings of monarchs that settled on isolated land masses and islands such as Hawaii, Guam and Australia — where they no longer needed to migrate — the change in the shape of their wings was obvious. They became smaller and shorter over roughly 1,000 generations.
According to Freedman, islands are “discrete little pockets where you can study evolutionary processes,” making them particularly useful when looking at physical changes in animals as they adjust their behavior to fit their new environments.
Many of the nonmigrating monarchs Freedman studied were likely the descendants of the North American butterflies that overwinter in places such as Santa Cruz and Pacific Grove.
The monarchs in Australia have been there since at least 1871, Freedman said. From samples he obtained Down Under from museum collections over time, Freedman found that their wings had shrunk in area by 7.3% compared with their North American counterparts.
In addition to changing their appearance, migrational changes also affected the health of the monarchs. Recent research indicates that when monarchs “stopped migrating, they became much more susceptible to parasites,” Freedman said.
Freedman’s latest research has rattled conservationists.
“I’m really concerned that we’re going to lose the incredible uniqueness of the western migration,” said Emma Pelton, senior conservation biologist at the Xerces Society, an international organization dedicated to the conservation of invertebrates.
Part of Pelton’s job is tracking and counting monarchs on their yearly migration to the West Coast from the Rocky Mountains and other parts of the western U.S. where the winters are cold.
Because of the encroachment of humans on monarchs’ habitats and sources of food, Pelton has seen a drastic reduction of the monarch populations — from 300,000 in 2015 to under 10,000 this year.
“The migration in California is super unique and really worth protecting and fighting for,” she said. “We don’t know if we can get it back if we lose it.”