Cassell, author of the just-published book Animal Algorithms: Evolution and the Mysterious Origin of Ingenious Instincts (2021), tackles one of the most remarkable mysteries of life forms:
It typically takes up to three generations of butterflies to make the complete journey.3 This means that the navigation information is genetically programmed. One of the unique aspects of the migration of the monarchs in eastern North America is that during their summer stay in Canada they occupy close to 400,000 square miles, while during their overwintering hibernation in Mexico they occupy less than half a square mile. As noted previously, they often migrate back to the same tree that their ancestor butterflies departed from in a mountainous region in Mexico. That means they must have an extremely accurate method of navigation to locate such a small target.
Navigating by Sun Compass
Monarchs navigate using a sun compass, and as previously described, this includes time compensation to account for the movement of the sun.4 The circadian clock used in the process is embedded within the butterfly’s antennae.5 The sun’s azimuth position is detected through the butterfly’s compound eyes.6 Researchers are only just beginning to decode the biological information required for these amazing feats. The genome of monarch butterflies has been decoded, including the genes related to the neurobiology and physical systems used for migration.7 Comparisons of migratory monarch genomes with the genomes of non-migratory monarchs has revealed that more than five hundred genes are involved in migratory behavior.8Eric Cassell, “For Evolution, Monarch Butterfly Migration Is a Mystery” at Evolution News and Science Today (November 22, 2021)
Now, about the evolution part, Cassell writes,
There exists no evolutionary model that satisfactorily explains its origin. That by itself does not prove that gradual evolution didn’t produce such programming, but the lack of such a model should at least give the open-minded pause for reflection.Eric Cassell, “For Evolution, Monarch Butterfly Migration Is a Mystery” at Evolution News and Science Today (November 22, 2021)
You may also wish to read: Book excerpt: Navigational genius of insects Eric Cassell: The Goulds call this curious dance “the second most information-rich exchange in the animal world,” second only to human language. That is quite a statement considering the communication is by insects with only 950,000 neurons, compared to humans with about eighty-five billion.
3 Replies to “Eric Cassell on the mystery of Monarch butterfly migration”
Sun and magnetism can’t account for such precision. The earth’s field moves around constantly. It’s good enough for a year-to-year memory, but not for a long-term ancestral memory.
Star references can be precise and long-lasting, especially when one star’s transit is marked and timed by a set of countable lines. Humans draw those lines by hand, but compound eyes have a built-in transit.
Alternatively, each destination tree might be a beacon transmitting a specifically shaped static field, which was ‘tuned’ by the butterflies. This would be testable. Switch two trees, roots and all. If the butterflies return to the old tree in the new location, there’s a beacon in the tree. If they return to the new tree in the old location, they’re using stars.
It may be something much simpler, as in: a million butterflies at one location leave behind a scent or pheromone signature that slowly diffuses out from the centre as it decays, providing a long lasting “beacon” for butterflies to follow (concentration gradient?) once they arrive in the general area, after their programmed flight south. Just a suggestion.
Well, yes, but there remains the origin for Migration itself.
That is, Migration can’t work Incrementally. How do you know South is warmer if you’ve never been there? In most cases, flying even 100 miles isn’t going to change the local weather very much. So I think this is another All or Nothing kinda thing.
Can you say “Magick”? I knew you could.