Magnetoreception in Animals

[BillTre]

For more than a hundred years people have been intrigued by how animals are able to do certain navigating tasks so well. Being able to sense magnetic fields has been one of several clues animals could use to figure out where they should go. Among possible magnetic sensory mechanisms have been:

1. light sensitive proteins (cryptochromes) in the retina that can also react to magnetic fields.
2. Microscopic magnetite crystals on found in various areas of the body (often the nose near nerves)
3. A new mechanism involving current flow in the semicircular canals where hairs cells used in sensing sound, orientation, acceleration, and other stuff. Other hair cells are found on the surface of various fish that have electro-sensory abilities.) The mechanism of transducing the magnetic signals into neural signals may involve currents induced in the semicircular canals. These could trigger voltage sensitive channels (in the hairs cells) as the cells experience differences in the voltages. The voltage difference could arise due to current changes in the varying magnetic fields. Magnetically evoked potentials were recorded from various nervous system regions.

The third option is described in the first shorter article. The research article has experimental detail. Some of these may be behind a paywall.

 

[sbrothy]

One wonders what they do when the field reverses back and forth....

 

[BillTre]

One wonders what they do when the field reverses back and forth....

You mean when the earth's geomagnetic field flips?
What they do could mean:

1. what does their nervous system do? (easiest)
2. What does their behavior do? (controls difficult, variability high)
3. How do they deal with it "mentally?" (most difficult)

Some of this could be approached experimentally.
Expect species differences.

 

[sbrothy]

Yeah, I kinda meant all of the above. Just a stray thought. It must confuse a lot of animals relying on magnetoreception.

EDIT: Dont get me wrong! I'm not sealioning you. I just wondered.

 

[BillTre]

Yeah, I kinda meant all of the above. Just a stray thought. It must confuse a lot of animals relying on magnetoreception.

The animals would probably have worked things out through generations of selection.
Confusion would be non-adaptive and eliminated.

Personally, I would expect something like an overlay on the normal visual field (which is also combined at some neural level with audio inputs). this would most likely be in the dorsal mid-brain, the visual tectum, the audio tectum or some other higher order sensory area. I might produce something like another color int he field.
Alternatively, specific sensory inputs could simply trigger directed actions toward or away from them, but the movements would usually get directed through the mid-brain tectum in some way.

 

[sbrothy]

Obviously I have no idea what I'm talking about compared to you, but perhaps a magnetic map still makes sense if you "sense" a complete reversal has taken place. And if not, I'm sure natural selection does it's ugly job. EDIT: I guess is basically what I "hear" you say.

 

[sbrothy]

Just thinking about being an about-to-spawn salmon almost gives me a headache though.

 

[BillTre]

Just thinking about being an about-to-spawn salmon almost gives me a headache though.

They also use sensing of complex sets of chemicals to identify the specific branches of streams they were in as a young fish.
So, the complexity can be headache inducing.

 

[Hornbein]

On Earth field reversal happens maybe twice in a million years. It takes millennia to complete, gradual adjustment is very possible so I think it wouldn't be a big deal. The field never collapses, it morphs. The poles wander around and there's more radiation at the poles but such regions are limited.

Field reversal on the Sun is periodic every 11 years but on Earth the iron core resists this so field reversal is chaotic, not periodic at all.

People in Bali are very good at knowing where north is. I think they should be tested for this. That's not that easy to do though : it's hard to isolate the subject from all mundane clues.

 

[256bits]

They also use sensing of complex sets of chemicals to identify the specific branches of streams they were in as a young fish.
So, the complexity can be headache inducing.

For navigation, what is needed is a map, the place where one is, where one was, and where one is heading. The principle of dead reckoning is termed for animals as path integration.
https://en.wikipedia.org/wiki/Dead_reckoning
https://en.wikipedia.org/wiki/Path_integration
As is said, what is happening in the brain, what sensors play a part, and what neurons fire as animals navigate is complex.

One can 'test' their own simple 'innate' simple navigation skills in your own house.
Shortly study the room you are in. Close the eyes. The map of the room resides somewhere in memory; you know where you are, and where you are going. Taking a step forward, you have a location update, and a location where you were ( for some animals this 'where you were' can be forgotten ), and a heading. Try to take as many steps as you think possible before you start becoming anxious ( about running into a wall, or banging a shin or toe ) and begin to feel unsafe. For most people, and a normal room with furniture, this would be a few steps. Stop, and open your eyes. Are you where you think you were in relation to the other objects in the room, and as close ( or as far away ) as you thought?
Try as many times as you like to see if you get better at it.
Try it outside in an open space with little chance of bumping into anything.

Humans rely on vision tremendously for location update on their map.
Other animals rely on other sensory input far more than just vision.
The fish, for example, has little in the way of visual clues that stand out in the way of navigation.

 

[BillTre]

For navigation, what is needed is a map, the place where one is, where one was, and where one is heading.

Alternatively, they could have a look up table of what behavior to do if certain cues are encountered. (Turn right at the 7-11, turn left at stop light, stop at the Big-5 store.)
This is similar to strategies used by neuronal growth cones as they navigate their way through the developing body to identify and form synapses on their target cells. Perhaps this is similar to your dead reckoning.

 

[Averagesupernova]

One can 'test' their own simple 'innate' simple navigation skills in your own house.
Shortly study the room you are in. Close the eyes. The map of the room resides somewhere in memory; you know where you are, and where you are going. Taking a step forward, you have a location update, and a location where you were ( for some animals this 'where you were' can be forgotten ), and a heading. Try to take as many steps as you think possible before you start becoming anxious ( about running into a wall, or banging a shin or toe ) and begin to feel unsafe. For most people, and a normal room with furniture, this would be a few steps. Stop, and open your eyes. Are you where you think you were in relation to the other objects in the room, and as close ( or as far away ) as you thought?
Try as many times as you like to see if you get better at it.
Try it outside in an open space with little chance of bumping into anything.

We did this as kids outdoors with a blindfold and being lead around. We knew the area well but it was very easy to get lost. Get lead around for twenty minutes while the person who was guiding tried their hardest to disorient the one blindfolded. No one ever got hurt or walked of a cliff.

 

[256bits]

Cliff ??? I would be ,,,,, my pants, you know.

 

[256bits]

Racoons and skunks have their nightly field trip for foraging, based on cues of where the best spots are, and make it back to their nest. At times, though, they would have to venture into unknown territory forming new cues. And teach their young the route to take by bringing them along.

Other animals such as bees transfer the route to, or rather the destination of, a food food supply by doing their little dance at the hive. The bees watching absorb this into memory somehow and are able to navigate to the food. What neurons are triggered by watching and what neurons are triggered by navigating I am not sure if any one thoroughly knows yet. Studies on fruit walking fruit flies are probably not directly applicable to other members of the animal kingdom.

Humans get lost in the woods.
I do wonder if some animals do actually get lost in the woods ( a contemplation just before going to sleep at bedtime meme )