RE: The monarch butterfly’s epic 3,000-mile migration

Dear Doron,

The article I sent was describing a professor at Univ of Cincinnati, but I can’t say that his research was any “big breakthrough” in the field. Hundreds of biologists have studied this migratory phenomenon for decades. I recall reading that the “magnetic compass” (determining the insect’s geographical position relative to the sun) is located in their antennae, and I suspect epigenetic factors –– that sense the length of day, temperature of the air, and host plant quality –– must play a role in the generation 3-4 times removed from the original generation.

One could conclude “this is an example if imprinting,” except that’s just the name of a biological process and still there is little to nothing known about the molecular explanation of this magnificent phenomenon.

When the late summer and early fall monarchs emerge from their pupae, they are physically and behaviorally different from those emerging in the summer. The shorter days, cooler air, and milkweed senescence (aging) of late summer trigger changes. In the northern part of their range, this occurs around the end of August, when monarchs begin to emerge in reproductive diapause. Diapause is controlled by the nervous system and by hormones. Environmental factors signaling the onset of unfavorable conditions are involved in triggering this physiological response.

Genetics: Upon dispersal, the Central and South American, Atlantic, and Pacific populations lost the ability to migrate. This prompted researchers to identify the gene regions in North American monarchs that appeared highly differentiated from non-migratory populations. Kronforst et al. (2014) identified 536 genes significantly associated with migration. One single genomic segment appeared to be divergent in the non-migrating populations and was extremely different from the North American population. One gene, collagen IV alpha-1, showed high divergence between migrating and non-migrating populations. Collagen IV alpha-1 is an important gene for muscle function, and divergence of this gene implicates selection for different flight muscles between migrating and non-migrating populations. Surprisingly, Collagen IV alpha-1 was down regulated in migratory monarchs, perhaps preparing them for lengthy flight. Furthermore, migrating monarchs had low metabolic rates compared to non-migrants as a consequence of flight muscle performance, lowering energy expenditure in migrating monarchs’ muscles. This evidence led researchers to conclude that changes in muscle function afforded migrating monarchs the ability to fly farther and use their energy more efficiently. Dr. Kronforst used the analogy of a marathon runner vs. a sprinter, “Migrating butterflies are essentially endurance athletes, while others are sprinters.”

Genetics: Genetic analysis is becoming an increasingly popular method to investigate the molecular-genetic basis of migration. Kronforst et al. 2014 used gene sequencing to compare 101 Danaus genomes from around the world. Comparative genomics analysis using Single Nucleotide Polymorphisms (SNPs) revealed variation in Danaus genomes that illustrated a monarch evolutionary tree. This tree revealed that the North American migratory population resided at the base of the tree signifying it as the most closely related species to the common ancestor of all monarchs. Their results suggest the monarch began in the southern USA or northern Mexico, making annual migrations as glaciers receded. These genetic analyses also allowed researchers to infer the distribution patterns of non-migratory monarch populations. Genetic analysis was also utilized to identify genes involved in migration (see “How do monarchs find the overwintering sites?).

One can find much more information at this URL, but still I see no definitive answers. 🙁 DwN

Subject: RE: The monarch butterfly’s epic 3,000-mile migration

Dear Dan,

As always, a pleasure to get your literature choices! Would you do me a great favor and tell me what was the migratory mechanism discovered? (-:
Prof. Doron Lancet


From: Nebert, Daniel (nebertdw) []
Sent: Friday, October 6, 2017 7:40 PM
Subject: The monarch butterfly’s epic 3,000-mile migration

This is a story of gene-environment interactions. Monarch butterflies winter over in the mountains of Mexico. Then they migrate as far north as southern Canada in late summer; however, because of their life span, it takes four generations to reach their destination 7-8 months later. And then, HOW do these great-grandchildren KNOW when to fly quicly all the way south and where to go –– to return to that same mountainside where their great-grandparents had been born?

Kings of navigation
Biologists are unravelling the mystery behind the monarch butterfly’s epic 3,000-mile migration.
By Michael Miller
Oct. 3, 2017

Monarch butterflies flutter to the same mountains in Mexico each winter even though neither they nor their parents or grandparents have ever been there. A University of Cincinnati biology professor is trying to unravel the mystery of the monarch’s multigenerational migration at UC’s Center for Field Studies. “What’s amazing about monarchs is they go to the same general area in Mexico year after year, but they’ve never been there before. It’s their great-grandparents who were last there,” said Patrick Guerra, assistant professor of biological sciences at UC’s McMicken College of Arts & Sciences.

Many creatures undergo epic migrations. Wildebeest travel 900 miles from the African Serengeti to the Maasai Mara and back in search of fresh pasture every year. Sea turtles return to the beaches where they hatched to lay their own eggs. And some shorebirds fly from the tip of South America to the high arctic and back every year in a 9,000-mile odyssey.

But Guerra said monarchs are special because their round-trip migration from the United States and southern Canada to central Mexico requires several generations to complete. “The butterflies have never been there before. Their sense of direction has to be hardwired,” he said.

Scientists know that monarchs navigate by the position of the sun in the sky — like an internal sundial. It’s the same way that ants and bees orient themselves. “We know they use the sun and the Earth’s magnetic field as guides. But we don’t know how they know when to stop,” Guerra said.

The mountains west of Mexico City are the perfect place for monarchs to spend the winter, he said. “They’ll roost in groups at these overwintering sites. It’s the perfect temperature,” Guerra said. “It’s neither too cold that they freeze to death nor too warm that their reproductive drive kicks in. When it gets hot, they turn to reproductive mode. So they’re trying not to be in that reproductive status to conserve their metabolic reserves.”

The butterflies cluster together on the pine and oyamel fir trees for warmth. Scientists estimated there were as many as 1 billion butterflies gathered in the mountains in 1996. That number has dropped precipitously since then. Last year, conservation groups estimated that 145 million butterflies roosted in the reserve, roughly an 85 percent decrease.

Scientists are trying to understand what’s behind the sharp decline. Possible culprits include ubiquitous pesticides used in agriculture and landscaping in North America and deforestation within the Mexican reserve. Some backyard gardeners plant nonnative milkweed that stays in flower longer in the fall, which could prompt some monarchs to linger in the north. A sudden cold snap could kill them.

“Its conservation status is either threatened or ‘species of concern,’ depending on whom you ask,” Guerra said. Today, western butterfly populations are most at risk. Conservation groups across North America are working to restore prairie habitat from Nova Scotia to California. Not all monarchs migrate. Populations in Florida remain in the Sunshine State year-round.

A monarch butterfly.

Guerra has studied a variety of insects prior to taking on butterflies. He has been studying monarchs for more than five years. “I was interested in dispersal, how insects disperse from certain areas and what they’re looking for,” he said. “But migration always interested me. This movement is more directed — they’re going to a place and back.” Guerra and his students are trying to determine what effect, if any, increasing urbanization has on the butterfly’s circadian rhythms and knack for navigation.

Students Alexis Moore and Jered Nathan captured monarchs at UC’s Center for Field Studies next to Miami Whitewater Forest in southwest Ohio. Butterflies were placed in mesh enclosures at nine places around the Tristate: three rural, three suburban and three urban. There the butterflies are subjected to the ambient light and noise of city life or the darkness and tranquility of rural living.

One site is a flower garden a few blocks from UC at the Cincinnati Zoo & Botanical Garden. Guerra’s students keep the monarchs in a three-foot-tall mesh box on a mulch bed next to the landscaping. Despite the busy city traffic just beyond the zoo security fence, monarchs and other butterflies flitted from flower to flower around the garden.

“Volunteers have adopted this garden. We have pollinator-friendly plants everywhere,” said Lyn Lutz, an exhibit manager at the zoo. The zoo has exhibits on native plants throughout its 69 acres to encourage and inspire people to plant their own butterfly gardens, she said. “Everyone should do their part,” she said. “You don’t need a big botanical garden. Anyone can do it.”

On a daily visit, students carefully removed a monarch from the enclosure. Each butterfly has its own identification number written in marker on a wing. The students feed their test subjects a honey solution each day while the butterflies get used to their new surroundings. After a few weeks, the monarchs will be released on a still afternoon at the UC field station to see how they orient themselves and whether researchers can discern any difference in flight trajectory among the city, suburban or urban groups, Guerra said.

“At this time of year, fall monarchs should always have the drive to fly south,” he said. “But if you live in the city, if your circadian clock is so disrupted that you can’t use [it] to keep track of the time of day, you might use the sun incorrectly. That’s our hypothesis. We’re predicting urbanization or its effects might affect their behavior.”

Light pollution interferes with wildlife in lots of ways. Turtle hatchlings on coastal beaches can mistake streetlights for the moon and scurry into traffic. Bright lights have been known to disorient migrating birds so badly that they fly into buildings. And when navigating such great distances, a couple degrees of navigation error could send the monarchs hundreds of miles off course. If the study determines that city monarchs are prone to disorientation, the next step will be to determine what it is about outdoor lights that disrupts their uncanny navigation system. “Is it the intensity of the light or is it LED versus incandescent or fluorescents?” Guerra said. “It could be that certain wavelengths of light matter. For example, a lot of moths and night insects use the moon to navigate at night.”

At the field station, researchers also harness butterflies and test them in a flight simulator, sort of a butterfly treadmill. Although flying in place, the butterflies can orient themselves 360 degrees. In flight-simulator trials, monarchs can be tested under various outdoor or indoor testing conditions, during which their flight behavior can be monitored and analyzed. The path of flight directionality they choose in the simulator trials helps researchers learn more about how butterflies orient themselves.

Student Moore, 21, is studying biomedical engineering. Her specialty is biomimicry or how engineers and designers can take natural cues molded by evolution to design better products. For example, the air intakes of fighter plane engines are shaped like the nares (or nostrils) of peregrine falcons, which can breathe even when stooping on prey at 200 mph. “These creatures have had hundreds of millions of years to evolve and find solutions to problems,” she said. “We can take those solutions and apply them to what we want to do.”

“The biggest surprise for me was just how big monarchs get. I’ve been dealing with the smaller summer monarchs in the lab,” Nathan said. “The migrating monarchs are much, much bigger.” Guerra plans to conduct the monarch study over several years to validate their findings. “I’m trying to understand how their brains work. What’s amazing is they have a brain the size of a pinhead, and they’re doing something that would take us all sorts of complex computations to do,” he said. “Monarchs are a cool model system.”

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