Each year, millions of monarch butterflies migrate across North America to fly far north of the U.S.-Canadian border to benefit central Mexico ̵1; covering as many as 3,000. mil. Meanwhile, on the other side of the Rocky Mountains, western monarchs generally fly 300 miles down to the Pacific Coast to spend the winter in California. It has long been believed that Eastern and Western monarchs were genetically distinct populations.
A new study, however, confirms that while Eastern and Western butterflies fly differently, they are genetically the same. The journal Molecular Ecology published the findings, led by evolutionary biologists at Emory University.
“It was surprising,” says Jaap de Roode, an Emory biology professor and senior author of the study. His lab is one of the fist in the world that studies monarch butterflies.
“You can expect organisms with different behaviors and ecologies to show some genetic differences,” says de Roode. “But we found that you can’t genetically distinguish between western and eastern butterflies.”
The current paper builds on previous work by the de Roode laboratory that found similarities between 11 genetic markers of Eastern and Western monarchs, as well as other more limited genetic studies and observation and tracking data.
“This is the first genome comparison across Eastern and Western monarchs to try to better understand differences in their behavior,” says Venkat Talla, the first author of the current study and a post- Emory doctorate in the laboratory.
Talla analyzed more than 20 million DNA mutations in 43 monarch genomes and found no evidence for genomic differentiation between Eastern and Western monarchs. Instead, he found identical levels of genetic diversity.
“Our work shows that Eastern and Western monarchs are coming together and exchanging much more genetic material than was previously realized,” says Talla. “And it adds to the evidence that there are likely to be differences in their environments that shape the differences in their migration patterns.”
Co-author Amanda Pierce, who led the previous study on 11 genetic markers, launched the project while a graduate student at De Roode Lab.
“Monarch butterflies are so fragile and so light, and yet they are capable of traveling thousands of miles,” Pierce says. “They are beautiful creatures and a great model system for understanding unique and intrinsic behavior. We know that migration is powered by their genetic wires in some way.”
After the monarchs leave their large sites, they fly north and lay eggs. The caterpillars change butterflies and then fly further, mating and laying another generation of eggs. The process repeats for many generations until the end, as the days grow shorter and the temperatures cool, the monarchs emerge from their chrysalis and begin to fly south. This migratory generation spends no energy on breeding or laying eggs, saving everything for the long journey.
“For every butterfly that makes it to California or to Mexico, that’s her first trip there,” Pierce points out.
Earlier work had identified a propensity for Eastern and Western monarchs to have slight differences in the shapes of their wings. For the current paper, the researchers wanted to identify any variation in their flight styles.
They gathered eastern monarchs from a migratory stop site in Saint Marks, Florida, and western monarchs from one of their closure sites near Oceano, California. Pierce conducted flight trials with the butterflies by tying them to a mill that limited their flight patterns to a circumference with a circumference of about 25 feet. The tests were performed in a laboratory under controlled light and temperature conditions that mimic welding sites. Artificial flowers were arranged around the circumference of the flying mills.
“The idea was to try to give them some‘ natural ’environment look to help them motivate and orient them,” Pierce explains.
The butterflies were released unscathed from the flight mills after short trials.
The results showed that Eastern monarchs choose to fly longer distances while Western monarchs fly shorter distances but with a sharp burst of speed. “The most powerful flight feature of the western monarch is like a sprinter, essentially,” says Pierce, “while the eastern monarchs display a more flight-like feature like marathon runners.”
Pierce has since graduated from Emory and now works as a geneticist for the Environmental Protection Agency in Washington, DC.
Talla, who specializes in bioinformatics, grew up in India where the rich diversity of wildlife inspired him to become an evolutionary biologist. He went to Sweden to take his Ph.D. where he studied the genomics of the European white wood butterfly. Although all the whites of the wood look visually identical, they are actually three different species.
“One of the big questions I’m interested in answering is how does an individual species end up becoming a multiple species?” Talla says. “I want to understand all the processes involved in that evolution.”
He jumped at the chance to join De Roode Lab. “Monarchs have always been at the top of my list of butterflies that I wanted to study because of their incredible migrations,” says Talla. “They’re a fascinating species.”
Last November, he joined De Roode on a lab trip to the change site on the eastern monarch, in and adjacent to the Monarch Butterfly Biosphere Reserve in central Mexico. Tens to hundreds of millions of monarchs sing the trees and the landscape during the winter. “It’s a sight that spends the mind,” Talla says. “It makes you wonder how they all know.”
Previous tracking and observation studies have shown that at least some western monarchs fly south to Mexico instead of west to California. The analysis of the entire genome suggests that more than a few of the Western monarchs may make the trip to Mexico where they mingle with the Eastern monarchs. And when the butterflies leave Mexico, some may fly west instead of east.
“Evidence from multiple directions is coming together to support the same thinking,” says de Roode.
The findings may help in the conservation of monarchs. Due to a combination of habitat loss, climate change and a lack of flowers, a number of Eastern and Western monarchs have declined in recent decades, with Western ones showing the further fall into haste. The U.S. Fish and Wildlife Service is currently considering whether butterflies need special protection.
“If environmental factors are all that drive the differences between Eastern and Western monarchs, it is possible that we can help the Western population by transplanting some of those from the East to the West, “de Roode says.
The De Roode lab is now planning to investigate what exactly is in butterfly environments that triggers different expressions of their genes.
Eastern monarch butterfly population pushes below extinction threshold
Venkat Talla et al, genomic evidence for gene flow between monarchs with divergent migratory phenotypes and flight performance, Molecular Ecology (2020). DOI: 10.1111 / mec.15508
Provided by Emory University
Citation: Butterfly Genomics: Monarchs migrate and fly differently, but meet and agree (2020, July 29) retrieved July 30, 2020 from https://phys.org/news/2020- 07-butterfly-genomics-monarchs-migrate-differently. html
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