June 25 (UPI) -- Monarch butterflies bred in captivity may lose their sense of direction.
When researchers at the University of Chicago bought and released monarch butterflies from a commercial breeder, the butterflies failed to fly south. Even when the captive-bred monarchs were raised outdoors, the butterflies were unable to orient themselves.
Genetic analysis showed the captive-bred monarchs are genetically distinct from the migratory North American monarch population.
The new research, published this week in the journal PNAS, suggests captive breeding disrupts the species' ability to migrate.
Monarch butterfly numbers have been falling over the last 20 years. Scientists blame their decline on deforestation near their wintering grounds in Mexico, as well as pesticide exposure and habitat loss along their migratory routes through the United States.
In recent years, conservationists have spearheaded a variety of protection and rescue efforts, including the conservation of monarch habitat and the planting of milkweed fields and gardens. During their larval stage, butterflies only eat milkweed.
Conservationists have also tried releasing captive-bred butterflies into the wild throughout the summer and fall. But the latest research suggests the efforts are likely futile.
"We hope this will be an avenue into understanding how monarchs are losing migration," Marcus Kronforst, an associate professor of ecology and evolution at Chicago, said in a news release. "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."
After ordering several dozen monarch butterflies from a commercial supplier, Ayse Tenger-Trolander, a PhD student in Kronforst's lab, housed them in a rooftop garden and allowed them to mate. Mesh cages kept them from escaping, but they were able to enjoy the same outdoor conditions that they would in the wild.
Tenger-Trolander collected the eggs laid by the captive butterflies and raised them to adulthood in the same garden. Once mature, she tested the second generation in a flight simulator. The butterflies were tethered in a way that allowed them to fly in place and turn 360 degrees.
Butterflies with a healthy migratory impulse should fly mostly southward inside the simulator. During tests, the captive-raised butterflies failed to fly in any single dominant direction. Instead, they meandered. Even captive-bred butterflies raised entirely outdoors failed to exhibit migratory behaviors.
When researchers took chrysalises, monarch butterfly cocoons, from the wild to an indoor setting, just prior to the butterflies emergence, they found the relocation was enough to disrupt migratory 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."
Monarch butterflies populations have dispersed and settled throughout Central and South America, the Caribbean, southern Europe, northern Africa and across the Pacific Ocean to Australia. These disparate populations have also lost their migratory tendency.
When scientists sequenced the genome of the captive-bred butterflies, they determined the butterflies were genetically distinct from the North American population of migratory monarchs.
Researchers estimate the loss of migratory behavior can be explained by genetic changes.
"We can't point to a single genetic change that did it because there are lots of them," Kronforst said. "But we think somewhere buried in the genome are changes that have broken it."