Monarch Butterflies Do Not Have to Migrate

When 101 butterfly genomes were compared, there were surprises.

Most people know about the amazing migration of Monarch butterflies across North America to their wintering grounds in Mexico, but not all may know that there are non-migrating species, too.  Why do some make the spectacular journey?  Is the secret in the genes?

To find out, Marcus Kronforst, an evolutionary biologist at the University of Chicago, analyzed the genomes of 92 Monarch butterflies and 9 other closely related species, Elizabeth Pennisi relates in Science Magazine.  “The samples came from different parts of North America, from places in South and Central America where the local monarchs stayed put all year round, and from elsewhere around the world.”  What he found was contrary to everyone’s expectations:

• “He [Kronforst] and his colleagues grouped the genomes by how similar they were to build a family tree. That tree revealed that, contrary to expectations, all the monarchs arose from a population in the southern United States or northern Mexico.”
• “The researchers expected that to make their long trips North American monarchs would need a lot more collagen” than the sedentary variety.  “Instead, the gene was less active in the migrants,” Pennisi writes.  Apparently, genes for efficient flight help the migrants more than genes for strength, National Geographic surmises.
• “Kronforst and Zahn’s team also sequenced genomes from Hawaiian monarchs, which come in white and orange forms. From breeding experiments, other researchers learned that a single gene was responsible for the color loss. Zahn and Kronforst expected that this gene would be involved in pigment-generating pathways. But instead, their analysis shows it was a gene that codes for myosin, a protein essential for muscle contraction. The butterfly myosin gene resembles a myosin gene that is mutated in a mouse strain that has light instead of dark fur. In the mouse, this myosin helps transport pigments into the hair, so Kronforst thinks the white morph’s myosin may fail to transport orange pigment into the wing scales.”

These results will be interesting to compare with other butterfly genomes as they become available, Pennisi says.  In the meantime, the study goes to show that expectations can be controverted by evidence.  There’s no substitute for data.

In addition, it shows that Monarch butterflies apparently do not need to migrate those thousands of miles.  The ones that don’t seem to get along just fine.  The migratory varieties may have been the original ones, from which the sedentary ones derived.  If so, “sedentary populations cannot easily restore migrating monarchs once the latter are lost,” making conservation efforts worthwhile.

The story was also covered by Science Daily and by National Geographic. The latter includes a video clip about the Monarch migration, with pictures of their Mexican retreat, and makes an appeal for conservation by encouraging people to plant the milkweed on which the butterflies depend.

A recent article on PhysOrg says that insects that undergo metamorphosis, like butterflies, tend to diversify more.  It does not explain, however, the origin of metamorphosis.  The extent of the diversification is also not specified.  Presumably, it refers to coloration patterns and other variations on the existing hardware and software.  Researchers at the University of New York recognize the importance of metamorphosis in diversification, but cannot explain its evolutionary function, even though the process has been studied since Darwin’s time.  “It might reduce competition between larvae and adults, it might promote dietary specialisation, it might reduce development times, it might improve survival in times of hardship, or something else,” Dr. Peter Mayhew, a senior lecturer at the university, speculated.  “Future work needs to address this question.”  In evolutionary thinking, apparently “might” makes right.

Meanwhile, with a more design focus, the BBC News posted an audio presentation from the Natural History Museum about how butterflies produce shimmering colors by structural properties of their wing scales.  Scientists there are working on ways to culture cells from butterfly wings to produce iridescent colors in the laboratory. “It’s really quite intricate,” the speaker said of the process.  It would “really reduce the energy requirements of our industries” to imitate the methods butterflies use.  A butterfly-mimic material “would never fade” as well, he said.

Monarch butterflies are featured stars in the Illustra film we highly recommend: Metamorphosis: The Beauty and Design of Butterflies.  The genetic news does not tell an evolutionary story or help it in any way.  It also offers no Darwinian solution to the miracle of metamorphosis.  The film shows how metamorphosis makes a powerful argument for intelligent design.  If you haven’t ordered the film, get it and share it… it’s beautiful, especially in a home theater with Blu-ray and 5.1 surround sound.  You will not be disappointed to watch it and to share it with thoughtful nature lovers.