Natures wonders: more on magnetic migration (Introduction)

by David Turell , Friday, May 19, 2017, 20:02 (2743 days ago) @ David Turell

It appears that most migration is handled by magnetite in an imals dahat travel far distances. this article is about trout:

https://phys.org/news/2017-04-genes-trout-home.html

"In the spring when water temperatures start to rise, rainbow trout that have spent several years at sea traveling hundreds of miles from home manage, without maps or GPS, to find their way back to the rivers and streams where they were born for spawning.

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"Generated by the flow of molten metal in its core, the Earth's magnetic field ranges from a mere 25 microteslas near the equator to 65 microteslas toward the poles—making it more than a hundred times weaker than a refrigerator magnet.

"Diverse animal species can detect such weak magnetic fields and use them to navigate. First identified in birds in the 1960s, this sense, called magnetoreception, has since been documented in animals ranging from bees and salamanders to sea turtles.

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"Disrupting the fish's internal compass with the magnetic pulse triggered changes in 181 out of the roughly 40,000 genes they examined.

"Notably, the brains of treated fish showed increased expression of genes involved in making ferritin, a protein that stores and transports iron inside cells. Treated fish also showed changes in genes involved in the development of the optic nerve.

"The results suggest that the detection system is based on iron that may be connected with or inside the eyes," Johnsen said.

"The findings are consistent with the idea, first proposed nearly 40 years ago, that animals have tiny magnetic particles of an iron-containing compound called magnetite in their bodies. The magnetite particles are thought to act like microscopic compass needles, relaying information to the nervous system by straining or twisting receptors in cells as they attempt to align with the Earth's magnetic field.

"'You can think of them as mini magnets that the body's cells can sense," Fitak said.

"Magnetite has been found in the beaks of birds, the brains of sea turtles, the tummies of honeybees, and the nasal passages of rainbow trout. Other studies have even found minuscule amounts of magnetite in the human brain, but recent research suggests most of it comes from air pollution rather than occurring naturally, and it's unclear whether they give humans a subconscious magnetic sense.

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"Next they plan to do similar experiments with other tissues, such as the retina, and additional species that live in the ocean but travel to their freshwater hatching grounds each spring to spawn, such as American shad.

"'Scientists don't know what proteins might be involved in magnetite-based magnetoreception, but now we have some candidate genes to work with," Fitak said."

Comment: It is logical that migratory animals would use the available magnetic field. What is an interesting issue is that the field reverses itself back and forth after roughly 200-300 thousand years. Does that disrupt the migrations? We don't know. What is not logical is how evolution arranged for this process. For dhw, how did cell communities know about the existence of a magnetic field and then find magnetite and place it in the right spots on the body? This system had to be put in place all at once. Saltation.