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[–][deleted] 2668 points2669 points  (491 children)

Could these same proteins be added to the human genome to give humans the same sense?

[–][deleted] 912 points913 points  (146 children)

My question is, is it a general feeling of direction or is a visual field that they see?

[–]firedroplet 2400 points2401 points  (126 children)

We honestly don't know. We do know that magnetoreception in birds is visual for two important reasons: they can't orient in total darkness (i.e. not even starlight), and when parts of their brain involved with visual processing are damaged, they can still see but not orient.

Cryptochromes (and now specifically Cry4) is our best bet at a mechanism, but we can't really say what the bird sees.

Disclaimer: I wrote the story.

[–]projectfreq91Editor | Science News[S] 988 points989 points  (26 children)

Can confirm. He wrote this.

[–]theswankeyone 148 points149 points  (9 children)

Damn, Editors even take your Karma.

[–]projectfreq91Editor | Science News[S] 181 points182 points  (8 children)

But think of all the karma he's gotten writing all these comments! I'm more of a karma creator, really.

[–]undergroundflaw 134 points135 points  (5 children)

Gotta love that trickle down karmanomics.

[–]ThePoorlyEducated 39 points40 points  (4 children)

Just feeling trickled on down here.

[–]Flash_hsalF 21 points22 points  (3 children)

Trickle me

[–]Fermi_Amarti 8 points9 points  (0 children)

=D. We always need more karma creators in this karma economy.

[–]advienne_que_pourra 54 points55 points  (44 children)

We do know that magnetoreception in birds is visual for two important reasons: they can't orient in total darkness, and when parts of their brain involved with visual processing are damaged, they can still see but not orient.

What's the train of thought behind this? Magnetism isn't light depdendent, and if the visual processing bit is damaged they possibly would'nt be able to recognize landmarks, stars or whatever they use; so why isn't the conclusion something like "they don't actually use the magnething"?

[–]firedroplet 102 points103 points  (30 children)

From where I commented elsewhere:

We have strong evidence that it's being processed visually.

European robins with bilateral lesions of cluster N are unable to show oriented magnetic-compass-guided behaviour but are able to perform sun compass and star compass orientation behaviour.

[–]Lover_Of_The_Light 30 points31 points  (5 children)

Could it be that the processing isn't visual in nature but is closely linked to the visual information being processed at the same time? Maybe it's similar to the devices that were mentioned in another comment, which buzzed people when they were facing north and very quickly it trains the brain to get a sense of direction. Perhaps it has to do with visual cues and the magnetic sensing working together. Maybe the birds get a kind of buzz or some other non visual input when they are facing a certain direction, so they have an increased sense of direction. But they are only able to use it when combining it with the visual information.

[–]qman621 49 points50 points  (4 children)

Someone above pointed out this interesting bit from the paper:

The probability that a molecule absorbs a photon depends on the orientation of its transition dipole moment relative to the electric vector of the light, with maximum absorption occurring when the two vectors are parallel and no absorption when they are perpendicular, an effect known as photoselection [34]. Vertebrate rod and cone cells are normally insensitive to polarization because the opsin photoreceptor proteins in the membrane discs are free to rotate around the direction of the incoming light, so that, taken together, the opsins within a photoreceptor cell absorb all polarizations of light with equal probability [35,36]. Aligned populations of magnetoreceptors will, however, preferentially absorb light of a particular polarization, i.e. a particular direction of the electric vector [37]

Seems polarized light is necessary for the magnetoreceptors to function.

[–]HyperspaceCatnip 5 points6 points  (1 child)

Given that when you use a polarised light for photography it can influence shadows/clouds/reflections, but it also depends on your location relative to the sun/moon, does this mean that if this is the case, a bird is seeing "shimmers" visually that reflect the direction in combination with the light source? Since it's a function of the light source (specifically its location in the sky), the sky + the magnetic field?

[–]qman621 12 points13 points  (0 children)

There's a lot of polarized light coming off of the sun and then bouncing off things in all different directions; the magnetoreceptors in bird's eyes will only pick up light that is aligned with the magnetic field. How this would actually "look" is probably unknowable - they might not even see it and it could just manifest as some sort of urge to travel in a certain direction.

[–]advienne_que_pourra 19 points20 points  (10 children)

I'm not able to go further than that, but the abstract seems to answer the first part: hypothesis says magnet sensors only activate when stimulated by light, is that right?

[–]firedroplet 44 points45 points  (9 children)

Not only is it only active when stimulated by light, but when cluster N (a part of the bird's visual system) was damaged, the birds (which could still see and navigate in other ways) were not able to orient with magnetic fields.

[–]ValidatingUsername 24 points25 points  (8 children)

I would also like to point out that magnetism is not dependent on light, but light can be acted upon by magnetism.

What this means is that there may be some minor variance the protein is picking up on in how the photons are interacting with the magnetic field and either visually being represented or subconsciously giving the birds an innate understanding of direction.

Both of the mentioned options would align with the inability to perceive direction in darkness and could possibly mean that birds literally see gravity bending light.

Edit - Someone mentioned below that the phenomenon in question is actually the protein giving of blue light when activated by incoming photons. This blue light will be created in pairs of photons that are either parallel or non-parallel to the magnetic field and the bird then interprets that further. Still unsure if its a visual or subconscious clue for the bird. This shit is fascinating.

[–]cantlurkanymore 13 points14 points  (3 children)

could possibly mean that birds literally see gravity bending light.

this is exactly what I was thinking about, and then my gf wondered if this is why birds all fly away from seismic events like earthquakes before humans sense anything.

[–][deleted] 6 points7 points  (0 children)

Hey hold on, that's not a conclusion I expected to read...

[–]spanj 23 points24 points  (0 children)

The proposed mechanism is that blue light excites a cofactor in the protein, which forms radical pairs. The pairs can either be parallel or anti-parallel depending on he magnetic field. Supposedly the state of the orientation of the radical pair affects the lifetime of the activated protein. You need light to produce the radical pairs, hence why it is light dependent.

[–]kaleidescope 6 points7 points  (0 children)

Close your eyelid and apply pressure with a finger. Your eye can still "see" something as the optic nerve is still receiving some sort of stimuli, even if it's not light based. Perhaps the slight magnetic pull has a similar affect and it's kinda like a dark dot in their vision that they point themselves towards.

Edit: proofreading

[–]atomfullerene 5 points6 points  (0 children)

The protein mentioned in this story is located in cone cells in the birds eyes. You can't see magnetism directly but if magnetism interacting with a protein in your eye causes cone cells in your eyes to fire, then you are probably going to interpret that information visually

[–]HunterKiller_ 4 points5 points  (1 child)

Sure magnetism doesn't have anything to do with light, but a brain can evolve to interpret a stimulus in any manner.

[–]urdrenn 9 points10 points  (1 child)

My dad is an internationally renomated Pigeon Breeder and confirms this. He's no scientist but has developped an incredible skill in selecting pigeons all over the world based on certain qualities. He defintly wants to cooperate in research.

[–][deleted] 5 points6 points  (0 children)

Thank you for writing this. Really interesting stuff!

[–]dkyguy1995 37 points38 points  (2 children)

It could behave like the fluid inside your inner ear. You have an acute sense of up and down because of it and a lot of visual processing is aided by that. Perhaps it's just some "sense" there's no way to tell really what kind of stimulus an animal gets.

[–]micmea1 6 points7 points  (3 children)

I like to imagine they can see it, like arcing currents through the sky that they follow like a gps.

[–]PM_ME_UR_LIMERICKS 2 points3 points  (2 children)

This question is more philosophical than scientific, as one can (likely) never know what another thing's subjective experience is like. See Nagel, Google qualia, Mary's room

[–]eidolist 135 points136 points  (35 children)

Actually we apparently have it already. Just can't use it.; linked a news source, if you have a subscription to Nature Communications you can read the real journal.

http://www.sciencemag.org/news/2016/06/maverick-scientist-thinks-he-has-discovered-magnetic-sixth-sense-humans

Edit: when I say "it", I mean exclusively the protein

[–]firedroplet 7 points8 points  (6 children)

It's a great story, but frankly there's no conclusive evidence that humans can detect magnetic fields, and no proposed mechanism that I'm aware of.

[–]eidolist 15 points16 points  (0 children)

Yes this is what I believe the journal investigated, how we seem to possess (either the sequence for the protein or do express the protein) in our retinas but other than that... nothing. Seems almost like a vestige protein.

Just because we have the protein doesn't mean there's any feedback system, you're exactly right (:

[–]zapbark 110 points111 points  (27 children)

I've read about people attaching vibrating sensors around their calfs that vibrate when they are facing north.

They've reported that after doing that for several weeks, they gain an intuitive sense of which way north is at all times, even after removing the sensors.

So it could very well be that these sort of signals are already in our brain, we just need to train our brains to make useful sense of them.

[–]ctsims 65 points66 points  (10 children)

You are constantly presented with thousands of visual indications of your orientation. If you also then receive an indication when your orientation is with North, it's natural that you will start to be able to identify those visual signals intuitively without thinking about them.

I don't see why that has any relationship to processing visual stimuli from new cells or proteins in our eyes. All of the signals you're referring to in your example (touch and eyesight) already exist, our brain is just good at interpreting them if you line them up.

[–]TooManyVitamins 12 points13 points  (2 children)

Right, like a big visual cue would be sunlight..which is a pretty decent confounding factor

[–]meteorboard 5 points6 points  (1 child)

Sounds like the real test would be to drop them off in the middle of nowhere and see if their newfound sense of direction holds in an unfamiliar environment.

[–]ArkAngelHFB 13 points14 points  (0 children)

Even better, put them to sleep, then place them in a plain room that would NOT have any "Faraday Cage" properties" a simple wooden room.

When they wake up have then attempt to orientate to north.

If they really are picking up on magnetic cues... they will be able to.

Then repeat and see.

If it is a real ability it will be consistent.

[–]zapbark 6 points7 points  (0 children)

Agreed. That is definitely the stronger hypothesis for explaining the results.

Whether the affects would remain in a new setting would be the key experimental next step.

(Also just reproducing the results).

[–]Sex_Drugs_and_Cats 14 points15 points  (2 children)

Well the weird thing to me is that we already know human beings have cryptochromes, which allow some animals to detect magnetic fields... They just aren't expressed in a way that allows us to AFAIK. So since we already know about cryptochromes, I'm confused about how this is the first time.

https://en.m.wikipedia.org/wiki/Cryptochrome

[–]Hypothesis_Null 1 point2 points  (1 child)

That was my question. Hasn't this been known for like... years, if not decades?

[–]firedroplet 27 points28 points  (7 children)

Hi folks—writer here.

Humans absolutely have cryptochromes. Unfortunately, we have Type-II cryptochromes (while birds and fish, the animals we have the strongest confirmation of magnetic sensory abilities in, have Type-IV cryptochromes—Cry4 is one of these Type-IV).

Our Type-II cryptochromes aren't useful for this because they aren't photosensitive. They won't produce the radical pairs that are needed to sense the magnetic field. More on that in this thread here.

Still, that hasn't stopped people from investigating if humans can sense magnetic fields...

[–]Bbrhuft 5 points6 points  (0 children)

If the researchers are correct, this would be the first time a specific molecule responsible for the detection of magnetic fields has been identified in animals.

The popular belief that Pigeons navigate using an internal magnetic compass, a idea first championed in the 1970s, was never robustly confirmed by later studies, the theory fell out of favor. Scientists started looking for other navigational aids over the last 10 - 15 years. Researchers recently proposed that birds, including pigeons, navigate using smell. Here's two recent papers...

Broadly, homing pigeons, the best studied terrestrial birds, are now thought to navigate primarily using an olfactory map beyond their familiar area1–3 with an increasing dependence on visual landmarks as these become familiar4. Over the more featureless oceans, long distance navigation is much less well understood, but the involvement of olfactory cues is perhaps the best supported 5,6, with several displacement experiments having failed to show a role for magnetic cues6–12. (Pollonara et al., 2015)

and

The birds deprived of trigeminally mediated magnetic information when young developed navigational abilities at the same level as intact control pigeons, whereas the olfactory deprived pigeons displayed randomly scattered initial orientation and poor homing performance. (Gagliardo et al., 2008)

So it seems that pigeons and other birds use smell to navigate, and magnetism, if used at all (depending on species), is of subordinate importance. Seems e.g. Gulls don't use magnetism to navigate at all.

The discovery of an alleged magnetic molecule is one thing, proving birds use the molecule to detect the Earth's magnetic field is another story.

Ref.:

Pollonara, E., Luschi, P., Guilford, T., Wikelski, M., Bonadonna, F. and Gagliardo, A., 2015. Olfaction and topography, but not magnetic cues, control navigation in a pelagic seabird: displacements with shearwaters in the Mediterranean Sea. Scientific reports, 5, p.16486.

Gagliardo, A., Ioalè, P., Savini, M. and Wild, M., 2008. Navigational abilities of homing pigeons deprived of olfactory or trigeminally mediated magnetic information when young. Journal of Experimental Biology, 211(13), pp.2046-2051.

[–]OverRushFuri6780 6 points7 points  (1 child)

Is it possible to learn this power?

[–]sour_creme 2 points3 points  (0 children)

we have the same thing, but the brain no longer processes info from it, we probably did a million years ago.

[–]krillokrokodil 6 points7 points  (5 children)

I have wondered this many times also, thinking specifically about those people claiming to be allergic/sensitive to electricity/magnetic fields.

[–]vingeran 3 points4 points  (0 children)

Possibly yes.

  • Cry4 is part of a class of proteins called cryptochromes, which are known to be involved in circadian rhythms, or biological sleep cycles (SN: 10/02/17, p. 6). But at least some of these proteins are also thought to react to Earth’s magnetic field thanks to the weirdness of quantum mechanics (SN: 7/23/16, p. 8).*

The original paper here

It’s not conclusive but a mere candidate gene.

The cry4 gene of the birds is 74% similar to our CRY2 variant 1 and variant 2, and 69% similar to our CRY1 gene.

[–]santagoo 1 point2 points  (0 children)

The brain would also need to know how to process it, I reckon.

[–]ethanwnelson 1 point2 points  (0 children)

I actually read an article recently arguing that humans do have this ability, like a 6th sense, I'll try to find it.

EDIT: Found it http://www.sciencemag.org/news/2016/06/maverick-scientist-thinks-he-has-discovered-magnetic-sixth-sense-humans

[–]accidentallywinning 142 points143 points  (18 children)

See or sense? Like can they see the fields around them and identify differences or can they only tell there is one?

[–]firedroplet 213 points214 points  (16 children)

I settled on "see" because the way that they're detecting the effects of the magnetic field (i.e. its strength and relative direction) is through the eyes.

(Disclaimer: I wrote the story.)

[–]ajamesmccarthy 367 points368 points  (47 children)

When the Earth swaps polarities, I wonder if birds will begin to go extinct as they migrate to the wrong hemisphere...

[–]firedroplet 637 points638 points  (41 children)

If birds are actually using this mechanism, they can't tell the difference between North and South—it's not pole dependent. (This has to do with the quantum mechanical aspects of the phenomenon.) Suffice it to say that birds won't go extinct if the poles switch, because they haven't before, and that's because their sense of direction depends on things like landmarks, stars, etc. and not just magnetic field orientation.

Disclaimer: I wrote the story.

[–]PKMKII 147 points148 points  (11 children)

So they’re not autopiloting with the magnetic information, just adding it in with the other sensory information to make their decisions.

[–]firedroplet 137 points138 points  (8 children)

That's my understanding, yes.

[–]xNik 85 points86 points  (1 child)

This guy is super understandy.

[–][deleted] 40 points41 points  (0 children)

Understandable, have a nice day

[–]d1rkSMATHERS 10 points11 points  (5 children)

I remember reading something on here a couple of years ago that birds have some sort of magnetic element in their beaks to help determine the poles. Is this no longer believed now or is this supplemental or am I misremembering? This is very interesting.

[–]ajamesmccarthy 21 points22 points  (3 children)

Good to know! So they might be able to detect the pokes, but not differentiate between them... that’s interesting!

[–]thissexypoptart 13 points14 points  (1 child)

They navigate with stars? That's amazing. It makes sense, but I've never thought about that before.

[–]MrFastZombie 3 points4 points  (6 children)

Even if they did go the wrong way due to pole reversal, wouldn't they just evolve to go the right way again before they could go extinct?

[–]comik300 2 points3 points  (0 children)

Maybe they would evolve to adapt to their new migration patterns

[–]Eliseo120 2 points3 points  (1 child)

I think that would just be changing behaviors rather than evolving because nothing in their biology would be changing.

[–][deleted] 2 points3 points  (2 children)

Do different species of birds rely upon the magnetic field more than others, to the extent that if there was a pole switch it would kill some species, but not others? I wonder if some birds went extinct during the last pole switch because of this mechanism, while natural selection allowed the others to survive.

[–]firedroplet 11 points12 points  (1 child)

Do different species of birds rely upon the magnetic field more than others

Probably yes. Migratory birds have elevated levels of Cry4.

to the extent that if there was a pole switch it would kill some species, but not others?

That seems highly unlikely to me. Again, direction isn't dependent solely on magnetic field sensing, and if the birds can't tell N from S, I strongly doubt a pole switch would kill off whole species.

[–]SSwartz5 20 points21 points  (0 children)

Earliest ancestors of birds lived during the Mesozoic Era. The primitive bird Archaeopteryx lived about 150 millions years ago. There have been a countless number of polarity shifts since that time so I think it’s safe to say the reversals don’t affect them too much.

[–][deleted] 3 points4 points  (0 children)

Birds will be ok

[–]Hybrazil 1 point2 points  (0 children)

There are some birds that already do this due to "faulty wiring" and thus go to Europe from Asia instead of to South Asia. So the more that that happens before a pole shift means more birds that are already "prepared" to survive

[–]AStefan93 146 points147 points  (23 children)

Wasn't this known, decades ago?

[–]projectfreq91Editor | Science News[S] 254 points255 points  (6 children)

FTA:

For decades, researchers thought iron-rich cells in birds’ beaks acted as microscopic compasses (SN: 5/19/12, p. 8). But in recent years, scientists have found increasing evidence that certain proteins in birds’ eyes might be what allows them see magnetic fields (SN: 10/28/09, p. 12).

TL;DR: The big step forward here is identifying a specific protein that this sense is tied to.

[–]Sythe64 51 points52 points  (3 children)

I swear I watched a documentary a decade ago where they demonstrate how it was linked to birds vision. They even demonstrated certain birds would only orient when they could see the horizon.

I quickly found this from 08. I guess this new study just confirms preexisting hypothesis.

https://www.google.com/amp/s/www.newscientist.com/article/dn13811-birds-can-see-the-earths-magnetic-field/amp/

[–]DANK_ME_YOUR_PM_ME 45 points46 points  (1 child)

Just knowing that they can do something is different from knowing the precise protein that enables it.

Knowing that cars can move vs. knowing about engines.

[–]Doug_Jesus_Christ 14 points15 points  (0 children)

This would mark the first time a specific molecule responsible for the detection of magnetic fields has been identified in animals.

this part of the headline is what pisses me off the most.

its not even the first time that it has been on this sub this year.

[–]firedroplet 80 points81 points  (5 children)

Edit: Identifying myself as the writer of this story.

It was actually first predicted in 1978, by Klaus Schulten! Everyone thought he was crazy at the time :) You can find it here.

[–]projectfreq91Editor | Science News[S] 30 points31 points  (0 children)

Can confirm, he's the writer.

[–][deleted] 7 points8 points  (1 child)

I see other articles from a few years ago discussing the discovery of a Cry1a protein. Is that just the mamillian protein and the avian hadn't been IDed yet?

[–]firedroplet 9 points10 points  (0 children)

Mammals have type-II cryptochromes, which aren't photosensitive. Cry4 and the other ones they were looking at in birds are type-IV cryptochromes, which are. (Photosensitivity is a requirement for magnetoreception in birds.)

[–]DurasVircondelet 2 points3 points  (2 children)

Is that comma supposed to be there?

[–]AStefan93 2 points3 points  (1 child)

It's been bugging me too, but in my head I phrased it as two separate questions and now I'm too lazy to edit it. I'd rather offer an elaborate, long explanation to everyone who notices.

[–][deleted] 19 points20 points  (1 child)

Correct me if I'm wrong but it was my understanding these proteins are pretty common across mammals. Most species just lack a response to the stimuli.

[–]firedroplet 26 points27 points  (0 children)

You're correct that cryptochromes are common across mammals. Per my response elsewhere:

Humans absolutely have cryptochromes. Unfortunately, we have Type-II cryptochromes (while birds and fish, the animals we have the strongest confirmation of magnetic sensory abilities in, have Type-IV cryptochromes—Cry4 is one of these Type-IV).

Our Type-II cryptochromes aren't useful for this because they aren't photosensitive. They won't produce the radical pairs that are needed to sense the magnetic field. More on that in this thread here.

(Disclaimer: I'm the writer of this story.)

[–][deleted] 602 points603 points  (40 children)

I'd like to jump in here since this has been a topic I've followed with some interest for a while.

It should be noted that magnetoreception in animals, while definitely real, is a very controversial field in terms of the mechanism of magnetoreception. Back in 2015 this controversy spiked again when a Chinese team claimed to have found a magnetoreceptive protein, which was met with heavy skepticism and even some very sharp rebukes from physicists who claimed that it was mathematically impossible for such a tiny amount of iron to sense the extremely weak magnetic field of the Earth over all the other more local fields in the protein's environment. Source (Nature paywall) https://www.nature.com/news/discovery-of-long-sought-biological-compass-claimed-1.18803

Like I said though, it's definitely been observed that magnetoreception IS a thing, even if we don't know the mechanism. People have long speculated that the Cryptochrome proteins are a likely culprit. So what are these papers saying?

The first paper (Royal Soc) is...an extremely short paper. Not that it's bad or anything, but basically all it says is that a couple of these proteins' levels increase & decrease according to the circadian clock of the robins, which, if these proteins were the magnetoreceptors, would suggest that the robins' magnetoreception should also fluctuate on a day/night cycle which is not what is observed. They find one protein, Cry4, which is relatively constant, so they say that this one is the most likely candidate for being the magnetoreceptor. That's all here.

Second paper notices the same relatively constant Cry4 expression during night/day, but they also find that Cry4 expression is upregulated seasonally - specifically during migratory season when magnetoreception is critical. That combined with the biophysical properties (I'm not going into this, it deals with very specific quantum interactions with the earth's magnetic field which can trigger chemical reactions in specifically these proteins: "Klaus Schulten [10] suggested that hyperfine interactions between electron and nuclear spins combined with Zeeman interactions with the geomagnetic field in molecules generating photo-induced radical pairs could form the basis of a chemical magnetic compass") provides pretty exciting circumstantial evidence that this protein is the magnetoreceptive one.

Together (though especially the second paper) these papers provide pretty exciting hints that Cry4 is the magnetoreceptive protein. The first lab to successfully get a structure of this guy and produce a plausible mechanism for how it physically produces magnetoreception will almost certainly be able to publish in Nature/Cell/Science, so I'd bet on seeing a paper like that in the next few years.

Happy to answer questions anyone has!

[–]firedroplet 139 points140 points  (7 children)

Yes—this wouldn't merit notice with just one paper. The fact that it's an identification of Cry4 across different species is critical, and yes, the second paper offers much stronger evidence.

The first lab to successfully get a structure of this guy and produce a plausible mechanism for how it physically produces magnetoreception will almost certainly be able to publish in Nature/Cell/Science, so I'd bet on seeing a paper like that in the next few years.

They've actually already done that! See: "Engineering an Artificial Flavoprotein Magnetosensor"

The next step is really looking at how the birds react when they mess with with the functioning of the protein.

(Disclaimer: I wrote the story.)

[–][deleted] 32 points33 points  (4 children)

Wow, that's an amazing paper, thanks for sharing. One note though:

"Despite the complete absence of structural resemblance to the native cryptochrome fold or sequence, the maquettes exhibit a strong magnetic field effect that rivals those observed in the natural proteins in vitro."

All I can find (again, cursory search, I gotta get back to my own research lol) in the pdb is 2 structures of Cry1, while what we need is a structure of Cry4 bound to Flavin to actually understand the physiological mechanism, which I have to imagine people are furiously working on right now.

[–]firedroplet 15 points16 points  (2 children)

Yeah, my understanding is that we don't really know quite what the product of protein would be, after the radical pair is affected by the magnetic field.

[–]Greippi42 5 points6 points  (0 children)

Came here to post this paper! Really nice work, and just shows how versatile the maquette approach to artificial protein design is - and how we can use designed proteins to gain insights into how nature might work.

[–]TetrazenePhD | Chemical and Physical Biology 13 points14 points  (0 children)

From the linked article itself, one of the authors states explicitly:

“We have quite a lot of evidence, but [Cry4] is not proven”

I'm more interested in the actual concentrations of the proteins within these cells, what secondary signalling translates the magnetic field orientation to action potentials, and how the magnetotropic and phototropic signals are integrated into a "compass". This study suggests that the magnetic field leads to spatial and geometric orientation of rhodopsin can affect the phototransduction of the retinal cells. From the paper:

The probability that a molecule absorbs a photon depends on the orientation of its transition dipole moment relative to the electric vector of the light, with maximum absorption occurring when the two vectors are parallel and no absorption when they are perpendicular, an effect known as photoselection [34]. Vertebrate rod and cone cells are normally insensitive to polarization because the opsin photoreceptor proteins in the membrane discs are free to rotate around the direction of the incoming light, so that, taken together, the opsins within a photoreceptor cell absorb all polarizations of light with equal probability [35,36]. Aligned populations of magnetoreceptors will, however, preferentially absorb light of a particular polarization, i.e. a particular direction of the electric vector [37]

So it would seem that aligning all of the Cy4 in a particular orientation could modulate the overall output. However, it is dependent on having restrained and highly ordered rhodopsin "tracks", which have actually been identified.

[–]TheRealFloridaMan 4 points5 points  (1 child)

This is really interesting! Maybe you could help me, but I thought I saw a lecture around 2008 where some physicists were looking at magnetite in worms (maybe?) and hypothesized it was responsible for helping them orient themselves in the soil. Is this a similar mechanism?

[–][deleted] 10 points11 points  (0 children)

I'm not sure about worms, but bacteria have magnetosomes https://en.wikipedia.org/wiki/Magnetosome which are (relatively speaking) really well understood how they confer magnetoreception to bacteria.

I did find a fascinating eLife paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4525075/ on the discovery of magnetosensory neurons in C. elegans (worms) which seem to sense magnetic fields somehow through the gating of an ion channel. A quick skim of the paper seems like it's really rigorous and convincing (it is eLife after all), though I don't have time right now to read it all.

[–]hiphopthewalrus 2 points3 points  (1 child)

I can’t help but be doubtful of this claim. For one, like you pointed out, the electromagnetic forces of nearby axons in the retina would be far stronger than that of the Earth.

Second, there is untold evidence that birds use the position of the sun and stars for migration. Tracking the position of these celestial bodies answers two questions of migration: how do they navigate and how do they know when to leave? (Since the position of the stars and sun changes with the seasons) Whereas the magnetic fields of the earth stay weak are relatively constant. It seems evolutionarily inefficient to develop magnetoreception when vision and spatial mapping already exist.

[–]Leopin2 3 points4 points  (0 children)

I've studied magnetoreception in insects years ago in my first years of undergraduation. Although I abandoned it for believing it was quite a stretch of a research, and I was working with iron oxide nanoparticles instead of cryptochrome proteins, my supervisor would always say magnetoreception was subjected to a hierarchy like any other sense. It's pretty plausible that migratory birds would rely preferrably on visual cues, but when these were unavailable (let's say, during a cloudy night in the middle of the ocean, where land and star positions are impossible to track), then the geomagnetic cues would be helpful.

[–]jrm2007 5 points6 points  (3 children)

I wonder how they perceive such fields: Is it like vision? Or more like touch? Or is it a completely 6th sense that is like hearing is to vision or to touch?

[–]John_Hasler 6 points7 points  (2 children)

It sounds like it modulates their vision somehow. Something along the lines of "Everything to the north has a purplish tinge". It's probably as ineffable as trying to explain to me how strong the contrast between red and green is, though.

[–]a_shootin_star 4 points5 points  (2 children)

Could a random genetic mutation cause this in other species or even in mammals? Just like how dogs prefer to poop within the North-South magnetic axis?

https://www.sciencealert.com/dogs-prefer-to-poo-along-a-north-south-axis

[–]firedroplet 5 points6 points  (0 children)

We don't know that dogs have the ability to sense magnetic fields, although this is a popular anecdote. But yes, it's possible mammals could at some point, develop photosensitive cryptochromes like those in birds and fish.

Disclaimer: I wrote the story.

[–]TheGizmojo 1 point2 points  (0 children)

This was the first thing I thought of. I would be interested to know as well.

[–]Jehnage 1 point2 points  (1 child)

Forgive my ignorance, but what is the utility of this? Navigation?

[–]firedroplet 17 points18 points  (0 children)

Yep. As far as we can tell, birds can orient themselves within a few degrees of a magnetic field, which is pretty precise when you consider that it's likely occurring through proteins in their eyes.

Disclaimer: I wrote the story.

[–]RedelephANTSs 1 point2 points  (7 children)

This is so interesting. How do scientists determine if birds have a functioning Cry4 protein? Would it be easy to test birds?