A new study that suggests monarch butterflies fostered from the wild or cultivated by commercial breeders have trouble migrating and can exhibit unusual genetic traits hit the monarch butterfly community this week. The reaction has been intense.
“Boy, you gotta have thick skin to be part of this group!” said migration studies expert Andy Davis on the DPLEX, an email discussion group for about 800 monarch butterfly scientists, citizen scientists, hobbyists and others who follow monarch butterfly news and science. Davis edits the journal Animal Migration at the University of Georgia.
Davis then unpacked the study, published in PNAS, detailing for the layperson how University of Chicago researchers studied commercially bred monarchs and those caught in the wild and fostered in a “common garden experience.” The research took place in July of 2016. The scientists reared offspring of both groups over two generations through the summer and autumn, then tested the creatures for their flight orientation skills, and later, examined their offspring’s genetic traits.
Monarch butterfly lays eggs at Shady Oak Butterfly Farm. Photo courtesy Edith Smith
The researchers were looking for displays of directional flight, a characteristic typical of migratory monarchs late in the season. Generally, in late summer and early fall, migrating monarchs orient themselves to fly south; nonmigratory monarchs do not display such behaviour. The PNAS paper showed that the commercially bred butterflies and also those caught in the wild and reared indoors in less natural conditions, often do NOT display directional flight behaviors.
Perhaps more disturbing, when the researchers examined the DNA of the commercially reared butterflies, they found that the commercially bred monarchs’ genomes beared little resemblance to those of wild monarchs. They exhibited different traits, “genetic franken-monarchs,” as Davis said.
The study’s lead author Ayse Tenger-Trolander did not dispute Davis’ description.
“It is a franken monarch genetically,” said the evolutionary biologist who led the study. “It’s distinct, and comes up as its own branch on the tree of monarch life,” she said.
Tenger-Trolander speculated that the aberration likely resulted NOT from inbreeding, but from repetitive breeding of creatures that have had no generational exposure to migration. “The monarchs have likely lost migratory traits simply because they and their ancestors (also bred in captivity) haven’t been exposed to migration in many, many generations,” said Tenger-Trolander. “Without that selective event, monarchs that would never have survived in nature are allowed to mate and produce offspring in captivity.”
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However, Tenger-Trolander was careful to add that this study included a small sample from a single breeder. Future studies will likely include a more diverse mix of monarchs and breeders. The study also mentioned the many advantages of hobbyists fostering a few monarch butterflies. Rearing by summer hobbyists and schools groups, stated the paper, is a “net positive, especially in the link it creates between people and their natural environment.”
Conventional monarch butterfly science has held that butterflies raised in captivity without natural cues don’t have the Darwinian skill set to migrate.
Not surprisingly, the study provoked a heated online debate. As it moved through social and mainstream media, monarch butterfly fans challenged its claims, pushed back on its veracity and debated the very nature of scientific research. A post by Monarch Watch addressed the study and was shared on Facebook where it had more than 130 comments. Chip Taylor, founder of Monarch Watch, the citizen science tagging program at the University of Kansas at Lawrence, addressed the study’s claims.
“The system is resilient, complicated and still full of unexplained attributes–as well as unexplainable outcomes–e.g. indoor raised monarchs in Florida that were tagged and released in San Antonio with nine (not five as stated in the paper) recovered at the overwintering sites in Mexico,” wrote Taylor. “The article gives the impression that many of those who rear, tag and release get their stock from breeders. That’s not the case.”
When asked if she was surprised by the visceral reaction of the monarch community to the study, Tenger-Trolander, an evolutionary biologist at the University of Chicago, responded: “Yes, to a degree….I was hoping for a little more measured response.”
That said, Tenger-Trolander agreed that the study was imperfect and shared that she and colleagues are already strategizing on how to improve it.
One possibility is to replicate the experiment during monarch breeding and migration season along the migratory pathway, perhaps utilizing citizen scientists or universities in different locations. Training and uniformity of the experiment’s execution would be challenging, but doable. She added that any future study will likely focus on monarchs’ ability to see the sun and experience decreasing day length.
“But that’s the other question: is it one thing?” said Tenger-Trolander. “Is there some one environmental condition that’s kind of necessary and sufficient to cause migration…or is it a combination of everything? Like if you don’t get three of the five, you don’t do this behavior correctly, but if you get five out of five, you do.”
Bohlken and others were disappointed that the researchers refused to divulge the source of the butterflies. Tenger-Trolander, when pressed, said she didn’t want to thrown any one breeder “under the bus.”
“I can’t comment because I don’t know where the butterflies came from,” said Bohlken. When asked what best practices the IBBA recommends to its membership regarding how many generations of butterflies can be bred from an initial pair of “breeders,” as they’re known, before introducing new genetic material, Bohlken pleaded ignorance. “We preach hygiene to make sure monarchs are healthy…we do not get involved in genetics.”
Edith Smith, a commercial breeder at Shady Oak Butterfly Farm, one of the largest butterfly farms in the country, said she was most intrigued by the study’s claim that commercially bred monarchs have a separate set of genes, distinct from those in the wild.
Edith Smith at Shady Oak Butterfly Farm has mastered breeding the uncommon Blue Buckeye. Photo via Edith Smith, Shady Oak Butterfly Farm
Smith, who’s been breeding monarchs for decades and teaches classes to potential breeders at the Association for Butterflies, has experience in creating new strains of butterflies, such as her “Blue Buckeye.”
Years ago, whenever Smith noticed blue in the background of a Buckeye’s wings, she isolated the creature’s eggs for breeding. Over time, each generation of Junonia coeniaproduced a more pronounced iridescent blue in the background of the Buckeye’s wings. Eventually, Buckeye butterflies emerged with the entire backdrop of their wings a metallic blue in place of the original brown coloration.
As for the controversial study, Tenger-Trolander sees the take-home as a call for more research. We simply don’t know enough about how monarchs develop into their migratory habits yet, she said. In the meantime, she offers this advice: “If you want to be careful and really want to help monarchs, just put them on your porch instead of your kitchen.”
TOP PHOTO: Monarch butterfly getting tested for directional flight. Photo courtesy Ayse Tenger-Trolander