Natures wonders: dragonflies migrate like monarchs (Introduction)

by David Turell @, Thursday, January 10, 2019, 20:45 (9 days ago) @ David Turell

Same story over three generations:

https://www.sciencenews.org/article/green-darner-dragonflies-migrate-bit-monarch-butter...

"The monarch butterfly isn’t the only insect flying up and down North America in a mind-boggling annual migration. Tests show a big, shimmering dragonfly takes at least three generations to make one year’s migratory loop.

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"The study reveals that a first generation of insects emerges in the southern United States, Mexico and the Caribbean from about February to May and migrates north. Some of those Anax junius reach New England and the upper Midwest as early as March, says Hallworth, of the Smithsonian Migratory Bird Center headquartered in Washington, D.C.

"Those spring migrant darners lay eggs in ponds and other quiet waters in the north and eventually die in the region. This new generation migrates south from about July until late October, though they have never seen where they’re heading. Some of these darners fly south in the same year their parents arrived and some the next year, after overwintering as nymphs.

"A third generation emerges around November and lives entirely in the south during winter. It’s their offspring that start the cycle again by swarming northward as temperatures warm in the spring. With a wingspan as wide as a hand, they devote their whole lives to flying hundreds of kilometers to repeat a journey their great-grandparents made.

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"Although the darners’ north-south migration story is similar to that of monarchs (Danaus plexippus), there are differences, says evolutionary biologist Hugh Dingle of the University of California, Davis, who has long studied these butterflies. Monarchs move northward in the spring in stepwise generations, instead of one generation sweeping all the way to the top of its range.

"Also, Dingle says, pockets of monarchs can buck the overall scheme. Research suggests that some of the monarchs in the upper Midwest do a whole round trip migration in a single generation. As researchers discover more details about green darners, he predicts, the current basic migration scheme will turn out to have its quirky exceptions, too."

Comment: from uncommon descent website: "The question that it raises is, how do the insects “know” that they should migrate over several generations? When a larva becomes a pupa, the body completely dissolves and is reconstituted as an adult. Where and how exactly does the information survive? Reside?" I couldn't phrase the dilemma any better and remember it is the same for monarchs. These insects could not have worked this out stepwise. Only design fits. Obviously the genes survive the metamorphosis in the liquid phase.


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