North American monarch butterflies bred in captivity may lose their ability to migrate southward, according to a new study published in the Proceedings of the National Academy of Sciences.
Famous for their winter migration to winter in California and Mexico, North American monarch populations have declined by more than 90 percent over the last two decades. Concerns over their decimated numbers have prompted a number of recovery efforts, including captive breeding programs that eventually lead to the release of butterflies during the summer and autumn months. However, the new findings suggest that such efforts may not work.
"We hope this will be an avenue into understanding how monarchs are losing migration," said senior study author Marcus Kronforst in a statement. "These monarchs have been brought into captivity and prevented from migrating for many generations, and they have genetically lost migration. It's a microcosm for what's happening naturally."
To come to their conclusions, researchers at the University of Chicago bought adult monarch butterflies from a commercial supplier and put them in enclosed mesh cages atop a rooftop that allowed the butterflies to be exposed to natural light, temperature, and other environmental conditions. Researchers collected eggs from these adults and raised them to adult butterflies so that they could test their internal navigation instincts by placing them in a “flight simulator” that used a computer to track their movements.
Butterflies should fly in a southward direction as their migration patterns indicate, but the butterflies bred from commercial monarchs did not. Furthermore, researchers genetically tested the commercially bought butterflies to ensure that they weren’t genetically different species. They found that while the butterflies did originate in North America, they are still genetically different enough to be considered a distinct population. This loss of migration may be in part caused by these genetic differences.
"We can't point to a single genetic change that did it because there are lots of them," said lead author Ayse Tenger-Trolander, a PhD student in Kronforst's lab. "But we think somewhere buried in the genome are changes that have broken it."
In a second test, researchers caught wild monarchs and reared their offspring completely indoors in a system that mimicked outdoor conditions. Though some individuals of the captive-bred monarchs would fly in a southward direction, the entire group lacked migratory instincts as a whole. The butterflies’ migratory instincts are so vulnerable that simply taking a butterfly’s chrysalis indoors was enough to disrupt their behavior.
"I thought there was no way that would matter, but it did," said Tenger-Trolander. "We know there are many hobbyists and enthusiast breeders who are trying to do their best husbandry and avoid buying from commercial breeders. But there could be an issue with the way they're raising them indoors too."