Every year, millions of monarch butterflies migrate through eastern North America to fly from the far north as the US-Canadian border to invade central Mexico ̵1; covering up to 3,000 miles. Meanwhile, on the other side of the Rocky Mountains, Western monarchs usually fly 300 miles down the Pacific coast to spend the winter in California. It has long been believed that the Eastern and Western monarchs are genetically distinct populations.
However, a new study confirms that while eastern and western butterflies fly differently, they are genetically identical. Magazine Molecular ecology published findings led by evolutionary biologists at Emory University.
“It was surprising,” says Jaap de Roode, professor of biology at Emory and lead author of the study. His laboratory is one of the few in the world to study monarch butterflies.
“You would expect organisms with different behaviors and ecologies to show certain genetic differences,” says de Roode. “However, we have found that you cannot genetically distinguish between western and eastern butterflies.”
The current work builds on previous work by the de Roode Laboratory, which found similarities between the 11 genetic markers of Eastern and Western rulers, as well as other more limited genetic studies and observational and tracking data.
“This is the first comparison of Eastern and Western rulers trying to better understand their behavioral differences,” said Venkat Talla, the first author of the study and a postdoctoral doctor at Emory.
Talla analyzed more than 20 million DNA mutations in 43 monarch genomes and found no evidence of genomic differentiation between Eastern and Western rulers. Instead, he found the same levels of genetic diversity.
“Our work shows that the Eastern and Western monarchs are merging and exchanging genetic material to a much greater extent than previously thought,” says Talla. “And this contributes to the evidence that differences in their migratory forms are likely due to differences in their environments.”
Co-author Amanda Pierce, who led a previous study of 11 genetic markers, launched the project while she was a graduate student at De Roode Laboratory.
“Monarch butterflies are so fragile and so light, yet they are able to travel thousands of miles,” says Pierce. “They are beautiful creatures and a great model system for understanding unique innate behavior. We know that migration is somehow rooted in their genetic involvement. “
When the monarchs leave their wintering places, they fly north and lay eggs. The caterpillars turn into butterflies and then fly on, mating and laying the next generation of eggs. This process is repeated for several generations until the days shorten and the temperatures cool. The monarchs emerge from their chrysanthemums and begin flying south. This migratory generation does not expend energy on breeding or laying eggs, which saves everything for the long journey.
“For every butterfly that leads to California or Mexico, this is his first trip there,” Pierce wondered.
Previous work has revealed the tendency of Eastern and Western rulers to have slight differences in wing shapes. For the current work, the researchers wanted to identify any variations in their aviation styles.
They gathered the Eastern monarchs from a migratory stopover point in Saint Marks, Florida, and the Western monarchs from one of their hibernating locations near Oceano, California. Pierce performed flight tests with the butterflies by tying them to a mill, which limited their flight patterns to circles about 25 feet in circumference. The experiments were performed in the laboratory under controlled light and temperature conditions that mimicked overwintering sites. Artificial flowers were arranged around the flight mills.
“The goal was to try to give them some semblance of a ‘natural’ environment that would help them motivate and orient them,” Pierce explains.
After brief experiments, butterflies were eliminated unharmed from the flight mills.
The results showed that the Eastern monarchs would choose to fly longer distances, while the Western monarchs would fly shorter distances, but at a stronger speed. “The stronger flight characteristic of the Western monarch is essentially like a sprinter,” says Pierce, “while the Eastern monarchs show the flight line rather than the marathons.”
Pierce has since graduated from Emory and now works as a geneticist at the Environmental Protection Agency in Washington, DC
Talla, who specializes in bioinformatics, grew up in India, where his rich diversity inspired him to become an evolutionary biologist. He moved to Sweden to obtain a doctorate, where he studied the genomics of the European white wood butterfly. Although all white woods are visually identical, in reality they are three different species.
“One of the big questions I have answered is how does a species become multiple?” Talla says. “I want to understand all the processes involved in this development.”
He jumped on the occasion of entering the De Roode laboratory. “Monarchs have always been at the top of my list of butterflies that I wanted to study because of their incredible migration,” says Talla. “They’re a fascinating species.”
In November, he joined de Roode on a laboratory excursion to the site of an overmerg in the east of the monarchy inside and next to the Monarch Butterfly Biosphere Reserve in central Mexico. Tens to hundreds of millions of monarchs cover winter trees and landscapes. “It’s a charming sight,” Talla says. “It makes you think about how everyone knows how to get there.”
Previous surveillance and observation studies have shown that at least some Western rulers fly south to Mexico instead of west to California. Analysis of the complete genome suggests that more than a few Western rulers can travel to Mexico, where they mingle with Eastern rulers. And when the butterflies leave Mexico, some may fly west instead of east.
“Evidence from several directions is gathering to support the same view,” says de Roode.
Findings can help protect rulers. As a result of a combination of habitat loss, climate change and a lack of nectar flowers, the number of Eastern and Western monarchs has declined in recent decades, with Westerners declining the most. The U.S. Fish and Wildlife Service is currently considering whether butterflies need special protection.
“If environmental factors are driving the differences between Eastern and Western rulers, it is possible that we could help the Western population by moving some of the East to the West,” says de Roode.
The De Roode laboratory now plans to investigate what exactly causes the different expression of their genes in butterfly environments.
The butterfly population of the Eastern monarchy is falling below the extinct border
Venkat Talla et al., Genomic evidence of gene flow between rulers with different migratory phenotypes and flight performance, Molecular ecology (2020). DOI: 10.1111 / mec15508
Provided by Emory University
Citations: Butterfly genomics: Monarchs migrate and fly differently, but meet and mate (2020, July 29) retrieve July 30, 2020 from https://phys.org/news/2020-07-butterfly-genomics-monarchs-migrate- differently. html
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