tag:theconversation.com,2011:/us/topics/magnetoreception-18301/articlesMagnetoreception – The Conversation2021-11-15T20:00:44Ztag:theconversation.com,2011:article/1717382021-11-15T20:00:44Z2021-11-15T20:00:44ZHow do pigeons find their way home? We looked in their ears with a diamond-based quantum microscope to find out<figure><img src="https://images.theconversation.com/files/431890/original/file-20211115-17-gnk7bt.jpeg?ixlib=rb-1.1.0&rect=0%2C0%2C2899%2C2133&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><span class="source">Shutterstock</span></span></figcaption></figure><p>Homing pigeons are known for their uncanny ability to find their way home – navigating complex and changing landscapes. In fact, they do this so well they were used as a source of secure communication more than 2,000 years ago. </p>
<p>Julius Caesar <a href="https://www.asor.org/anetoday/2017/11/not-just-birds">reportedly sent</a> news of his conquest of Gaul back to Rome via pigeons, <a href="https://www.ft.com/content/255b75e0-c77d-11e2-be27-00144feab7de">as did Napoleon Bonaparte</a> following his defeat by England in the 1815 Battle of Waterloo. </p>
<p>We know pigeons use visual cues and can navigate based on landmarks along known travel routes. We also know they have a magnetic sense called “magnetoreception” which lets them navigate using Earth’s magnetic field. </p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/explainer-how-do-homing-pigeons-navigate-25633">Explainer: how do homing pigeons navigate?</a>
</strong>
</em>
</p>
<hr>
<p>But we don’t know exactly <em>how</em> they (and other species) do this. In <a href="https://www.pnas.org/cgi/doi/10.1073/pnas.2112749118">research</a> published today in the Proceedings of National Academy of Sciences, my colleagues and I tested a theory that attempts to link magnetoreception in homing pigeons with tiny lumps of iron-rich material found in their inner ears.</p>
<p>By using a new kind of magnetic microscope, we confirmed this isn’t the case. But the technology has opened the door for us to investigate the phenomenon in several other species. </p>
<h2>The current hypotheses</h2>
<p>Scientists have spent decades exploring the possible mechanisms for magnetoreception. There are currently two mainstream theories. </p>
<p>The first is a vision-based “free-radical pair” model. Homing pigeons and other migratory birds have proteins in the retina of their eyes called “cryptochromes”. These produce an electrical signal that <a href="https://www.nature.com/articles/s41586-021-03618-9">varies depending on the strength</a> of the local magnetic field.</p>
<p>This could potentially allow the birds to “see” Earth’s magnetic field, although scientists have yet to confirm this theory.</p>
<p>The second proposal for how homing pigeons navigate is based on lumps of magnetic material inside them, which may provide them with a magnetic particle-based directional compass.</p>
<p>We know magnetic particles are found in nature, in a group of bacteria called <a href="https://theconversation.com/magnetic-bacteria-and-their-unique-superpower-attract-researchers-100720">magnetotactic bacteria</a>. These bacteria produce magnetic particles and orient themselves along the Earth’s magnetic field lines.</p>
<p>Scientists are now looking for magnetic particles in a range of species. Potential candidates <a href="https://link.springer.com/article/10.1007%2Fs00114-007-0236-0">were found</a> in the upper beak of homing pigeons more than a decade ago, but <a href="https://www.nature.com/articles/nature11046">subsequent work</a> indicated these particles were related to iron storage and not magnetic sensing.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/new-evidence-for-a-human-magnetic-sense-that-lets-your-brain-detect-the-earths-magnetic-field-113536">New evidence for a human magnetic sense that lets your brain detect the Earth's magnetic field</a>
</strong>
</em>
</p>
<hr>
<h2>A peek inside a pigeon’s ear</h2>
<p>The new search is now underway in the inner ear of pigeons, where iron particles known as “cuticulosomes” <a href="https://www.sciencedirect.com/science/article/pii/S0960982213004338">were first identified</a> in 2013. </p>
<p>Single cuticulosomes have been located within distinct regions in the pigeon inner ear where other known sensory systems exist (such as for hearing and balancing during flight). In theory, if there were a magnetic sensing system in pigeons, it should be located close to other sensory systems.</p>
<p>But to determine whether iron cuticulosomes can act as magnetoreceptors in pigeons, scientists need to determine their magnetic properties. This is no mean feat, since cuticulosomes are 1,000 times smaller than a grain of sand. </p>
<p>What’s more is they are only found in 30% of the hair cells within the inner ear, making them difficult to identify and characterise.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/431870/original/file-20211115-6434-uzv76r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Diagram showing a homing pigeon's inner ear, with labels for hair cells and magnetic particles." src="https://images.theconversation.com/files/431870/original/file-20211115-6434-uzv76r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/431870/original/file-20211115-6434-uzv76r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=595&fit=crop&dpr=1 600w, https://images.theconversation.com/files/431870/original/file-20211115-6434-uzv76r.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=595&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/431870/original/file-20211115-6434-uzv76r.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=595&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/431870/original/file-20211115-6434-uzv76r.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=748&fit=crop&dpr=1 754w, https://images.theconversation.com/files/431870/original/file-20211115-6434-uzv76r.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=748&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/431870/original/file-20211115-6434-uzv76r.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=748&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">We conducted quantum magnetic imaging of iron-organelles in the pigeon inner ear.</span>
<span class="attribution"><span class="source">Robert W de Gille</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>To tackle this problem our group at the University of Melbourne, together with colleagues from Vienna’s Institute of Molecular Pathology and the Max Planck Society in Bonn, turned to a new imaging technology to explore the magnetic properties of iron cuticulosomes in the pigeon inner ear.</p>
<p>We developed a magnetic microscope that uses diamond-based sensors to visualise delicate magnetic fields emanating from tiny magnetic particles. </p>
<h2>Disproving the theory</h2>
<p>We carefully studied thin sections of the pigeon inner ear placed directly onto the diamond sensors. By applying magnetic fields of varying strengths to the tissue, we were able to gauge the magnetic susceptibility of single cuticulosomes.</p>
<p>Our results showed the magnetic properties of the cuticulosomes were not strong enough for them to act as a magnetic particle-based magnetoreceptor. In fact, the particles would need to be 100,000 times stronger to activate the sensory pathways required for magnetoreception in pigeons. </p>
<p>However, despite the search for the elusive magnetoreceptor coming up short, we are extremely excited by the potential of this magnetic microscope technology.</p>
<p>We hope to use it study a host of magnetic candidates across a variety of species including rodents, fish and turtles. And by doing so we can focus not only on cuticulosomes, but a range of other potentially magnetic particles.</p><img src="https://counter.theconversation.com/content/171738/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>David Simpson receives funding from the Australian Research Council. </span></em></p>In nature, one group of bacteria produces magnetic particles to orient themselves along Earth’s magnetic field lines.David Simpson, School of Physics, Senior Lecturer, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1135362019-03-18T17:01:05Z2019-03-18T17:01:05ZNew evidence for a human magnetic sense that lets your brain detect the Earth’s magnetic field<figure><img src="https://images.theconversation.com/files/264258/original/file-20190317-28505-1b1zf7w.jpg?ixlib=rb-1.1.0&rect=17%2C247%2C2849%2C1818&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Do you have a magnetic compass in your head?</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-illustration/moral-compass-career-path-concept-human-115938361">Lightspring/Shutterstock.com</a></span></figcaption></figure><p>Do human beings have a magnetic sense? <a href="https://www.springer.com/us/book/9783642797514">Biologists know</a> <a href="https://doi.org/10.1016/S0959-4388(00)00235-X">other animals do</a>. They think it helps creatures including bees, turtles and birds <a href="https://doi.org/10.1016/S0959-4388(02)00389-6">navigate through the world</a>.</p>
<p>Scientists have tried to investigate whether humans belong on the list of magnetically sensitive organisms. For decades, there’s been a back-and-forth between <a href="https://www.worldcat.org/title/human-navigation-and-the-sixth-sense/oclc/11022691&referer=brief_results">positive reports</a> and <a href="https://www.jstor.org/stable/1685499">failures to demonstrate</a> the trait in people, with <a href="https://www.springer.com/us/book/9781461379928">seemingly endless controversy</a>.</p>
<p>The mixed results in people may be due to the fact that virtually all past studies relied on behavioral decisions from the participants. If human beings do possess a magnetic sense, daily experience suggests that it would be very weak or deeply subconscious. Such faint impressions could easily be misinterpreted – or just plain missed – when trying to make decisions.</p>
<p>So our research group – including a <a href="https://maglab.caltech.edu/">geophysical biologist</a>, a <a href="https://neuro.caltech.edu">cognitive neuroscientist</a> and a <a href="http://www.isp.ac/index_e.html">neuroengineer</a> – took another approach. <a href="https://maglab.caltech.edu/human-magnetic-reception-laboratory/">What we found</a> arguably provides the first concrete neuroscientific <a href="https://doi.org/10.1523/ENEURO.0483-18.2019">evidence that humans do have a geomagnetic sense</a>. </p>
<h2>How does a biological geomagnetic sense work?</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=515&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=515&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=515&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=648&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=648&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264257/original/file-20190317-28479-jh5hpf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=648&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Life on Earth is exposed to the planet’s ever-present geomagnetic field that varies in intensity and direction across the planetary surface.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-vector/illustration-physics-magnetic-field-that-extends-1165968205">Nasky/Shutterstock.com</a></span>
</figcaption>
</figure>
<p>The Earth is surrounded by a magnetic field, generated by the movement of the planet’s liquid core. It’s why a magnetic compass points north. At Earth’s surface, this magnetic field is fairly weak, <a href="https://nationalmaglab.org/about/maglab-dictionary/tesla">about 100 times weaker</a> than that of a refrigerator magnet.</p>
<p>Over the past 50 years or so, scientists have shown that hundreds of organisms in nearly all branches of the bacterial, <a href="https://www.livescience.com/54242-protists.html">protist</a> and animal kingdoms have the ability to detect and respond to this geomagnetic field. In some animals – <a href="https://doi.org/10.1007/BF00611096">such as honey bees</a> – the geomagnetic behavioral responses are <a href="https://pdfs.semanticscholar.org/750f/ce1b8f4723b09dd2fb1324fc916c9578c77b.pdf">as strong as the responses</a> to light, odor or touch. Biologists have identified strong responses in vertebrates ranging from <a href="https://doi.org/10.1038/37057">fish</a>, <a href="http://jeb.biologists.org/content/205/24/3903.full">amphibians</a>, <a href="https://doi.org/10.1126/science.1064557">reptiles</a>, numerous birds and a diverse variety of mammals including <a href="http://jeb.biologists.org/content/120/1/1.short">whales</a>, <a href="https://doi.org/10.1038/srep09917">rodents</a>, <a href="https://doi.org/10.1371/journal.pone.0001676">bats</a>, <a href="https://doi.org/10.1073/pnas.0803650105">cows</a> and <a href="https://doi.org/10.7717/peerj.6117">dogs</a> – the last of which can be trained to find a hidden bar magnet. In all of these cases, the animals are using the geomagnetic field as components of their homing and navigation abilities, along with other cues like sight, smell and hearing.</p>
<p>Skeptics dismissed early reports of these responses, largely because there didn’t seem to be a biophysical mechanism that could translate the Earth’s weak geomagnetic field into strong neural signals. This view was dramatically changed by the <a href="https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/73/4/435/5435">discovery that living cells</a> have the <a href="https://doi.org/10.1126/science.472725">ability to</a> build nanocrystals of the <a href="https://doi.org/10.1126/science.201.4360.1026">ferromagnetic</a> <a href="http://jeb.biologists.org/content/140/1/35.short">mineral magnetite</a> – basically, tiny iron magnets. Biogenic crystals of magnetite were first seen in the teeth of one group of mollusks, later in <a href="https://doi.org/10.1126/science.170679">bacteria</a>, and then in a variety of other organisms ranging from protists and animals such as insects, fish and mammals, <a href="https://doi.org/10.1073/pnas.89.16.7683">including within tissues of the human brain</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=267&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=267&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=267&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=336&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=336&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264240/original/file-20190317-28475-1vhbs80.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=336&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Chains of magnetosomes from a sockeye salmon.</span>
<span class="attribution"><span class="source">Mann, Sparks, Walker & Kirschvink, 1988</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Nevertheless, scientists haven’t considered humans to be magnetically sensitive organisms.</p>
<h2>Manipulating the magnetic field</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=596&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=596&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=596&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=749&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=749&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264038/original/file-20190314-28479-1665yfc.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=749&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Schematic drawing of the human magnetoreception test chamber at Caltech.</span>
<span class="attribution"><span class="source">Modified from 'Center of attraction' by C. Bickel (Hand, 2016).</span></span>
</figcaption>
</figure>
<p>In our new study, we asked 34 participants simply to sit in our testing chamber while we directly recorded electrical activity in their brains with electroencephalography (EEG). Our modified <a href="https://science.howstuffworks.com/faraday-cage.htm">Faraday cage</a> included a set of 3-axis coils that let us create controlled magnetic fields of high uniformity via electric current we ran through its wires. Since we live in mid-latitudes of the Northern Hemisphere, the environmental magnetic field in our lab dips downwards to the north at about 60 degrees from horizontal. </p>
<p>In normal life, when someone rotates their head – say, nodding up and down or turning the head from left to right – the direction of the geomagnetic field (which remains constant in space) will shift relative to their skull. This is no surprise to the subject’s brain, as it directed the muscles to move the head in the appropriate fashion in the first place.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=513&fit=crop&dpr=1 600w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=513&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=513&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=645&fit=crop&dpr=1 754w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=645&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/264239/original/file-20190317-28492-1jg4d65.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=645&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Study participants sat in the experimental chamber facing north, while the downwards-pointing field rotated clockwise (blue arrow) from northwest to northeast or counterclockwise (red arrow) from northeast to northwest.</span>
<span class="attribution"><span class="source">Magnetic Field Laboratory, Caltech</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>In our experimental chamber, we can move the magnetic field silently relative to the brain, but without the brain having initiated any signal to move the head. This is comparable to situations when your head or trunk is passively rotated by somebody else, or when you’re a passenger in a vehicle which rotates. In those cases, though, your body will still register vestibular signals about its position in space, along with the magnetic field changes – in contrast, our experimental stimulation was only a magnetic field shift. When we shifted the magnetic field in the chamber, our participants did not experience any obvious feelings.</p>
<p>The EEG data, on the other hand, revealed that certain magnetic field rotations could trigger strong and reproducible brain responses. One EEG pattern known from existing research, called alpha-ERD (event-related desynchronization), typically shows up when a person suddenly detects and processes a sensory stimulus. The brains were “concerned” with the unexpected change in the magnetic field direction, and this triggered the alpha-wave reduction. That we saw such alpha-ERD patterns in response to simple magnetic rotations is powerful evidence for human magnetoreception. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/6Y4S2eG9BJA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Video shows the dramatic, widespread drop in alpha wave amplitude (deep blue color on leftmost head) following counterclockwise rotations. No drop is observed after clockwise rotation or in the fixed condition. <i>Connie Wang, Caltech</i></span></figcaption>
</figure>
<p>Our participants’ brains only responded when the vertical component of the field was pointing downwards at about 60 degrees (while horizontally rotating), as it does naturally here in Pasadena, California. They did not respond to unnatural directions of the magnetic field – such as when it pointed upwards. We suggest the response is tuned to natural stimuli, reflecting a biological mechanism that has been shaped by natural selection.</p>
<p>Other researchers have shown that animals’ brains filter magnetic signals, only responding to those that are environmentally relevant. It makes sense to reject any magnetic signal that is too far away from the natural values because it most likely is from a magnetic anomaly - a lighting strike, or lodestone deposit in the ground, for example. One early report on birds showed that robins stop using the geomagnetic field if the strength is more than about <a href="https://doi.org/10.1126/science.176.4030.62">25 percent different from what they were used to</a>. It’s possible this tendency might be why previous researchers had trouble identifying this magnetic sense – if they <a href="https://doi.org/10.1016/S1388-2457(02)00186-4">cranked up the strength of the magnetic field</a> to “help” subjects detect it, they might have instead ensured that subjects’ brains ignored it.</p>
<p>Moreover, our series of experiments show that the receptor mechanism – the biological magnetometer in human beings – is not electrical induction, and can tell north from south. This latter feature rules out completely the so-called <a href="https://doi.org/10.1146/annurev-biophys-032116-094545">“quantum compass” or “cryptochrome”</a> mechanism which is popular these days in the animal literature on magnetoreception. Our results are consistent only with functional magnetoreceptor cells based on the <a href="https://doi.org/10.1016/0303-2647(81)90060-5">biological magnetite hypothesis</a>. Note that a magnetite-based system <a href="https://doi.org/10.1098/rsif.2009.0491.focus">can also explain</a> <a href="https://doi.org/10.1098/rsif.2009.0435.focus">all of the behavioral effects in birds</a> that promoted the rise of the quantum compass hypothesis.</p>
<h2>Brains register magnetic shifts, subconsciously</h2>
<p>Our participants were all unaware of the magnetic field shifts and their brain responses. They felt that nothing had happened during the whole experiment – they’d just sat alone in dark silence for an hour. Underneath, though, their brains revealed a wide range of differences. Some brains showed almost no reaction, while other brains had alpha waves that shrank to half their normal size after a magnetic field shift.</p>
<p>It remains to be seen what these hidden reactions might mean for human behavioral capabilities. Do the weak and strong brain responses reflect some kind of individual differences in navigational ability? Can those with weaker brain responses benefit from some kind of training? Can those with strong brain responses be trained to actually feel the magnetic field? </p>
<p>A human response to Earth-strength magnetic fields might seem surprising. But given the evidence for magnetic sensation in our animal ancestors, it might be more surprising if humans had completely lost every last piece of the system. Thus far, we’ve found evidence that people have working magnetic sensors sending signals to the brain – a previously unknown sensory ability in the subconscious human mind. The full extent of our magnetic inheritance remains to be discovered.</p><img src="https://counter.theconversation.com/content/113536/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Shinsuke Shimojo received funding from Human Frontier Science Program (HFSP), Japanese Science and Technology Agency (JST), and currently receives funding from DARPA. </span></em></p><p class="fine-print"><em><span>Daw-An Wu receives funding from DARPA. </span></em></p><p class="fine-print"><em><span>Joseph Kirschvink receives funding from the RadioBio program of DARPA, and previous support for this work was from the Human Frontiers Science Program (HFSP).</span></em></p>Your brain’s sensory talents go way beyond those traditional five senses. A team of geoscientists and neurobiologists explored how the human brain monitors and responds to magnetic fields.Shinsuke Shimojo, Gertrude Baltimore Professor of Experimental Psychology, California Institute of TechnologyDaw-An Wu, California Institute of TechnologyJoseph Kirschvink, Nico and Marilyn Van Wingen Professor of Geobiology, California Institute of TechnologyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1007202018-09-13T10:47:26Z2018-09-13T10:47:26ZMagnetic bacteria and their unique superpower attract researchers<figure><img src="https://images.theconversation.com/files/236106/original/file-20180912-133898-1f7b9lz.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Magnetotactic bacteria owe their special property to the magnetic nanoparticles they contain.</span> <span class="attribution"><span class="source">Andy Tay</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>As a graduate student in the 1970s, microbiologist Richard Blakemore probably wasn’t expecting to discover a new bacterial species with a never-before-seen ability. While studying bacteria that live in muddy swamps, he observed that some tended to swim reliably toward the same geographical direction. Even when he rotated the microscope, they persisted in wiggling toward one direction. After confirming that their swimming behaviors were unaffected by light, Blakemore suspected they might be responding to the weak magnetic fields naturally present on Earth.</p>
<p>After further tests and observations, Blakemore confirmed the bacteria were reacting to magnetism. He <a href="https://doi.org/10.1126/science.170679">published a landmark paper</a> in the journal Science in 1975 introducing magnetotactic bacteria to the wider world. Later, researchers realized that another scientist, Salvatore Bellini, had <a href="https://doi.org/10.1016/j.micres.2012.04.002">previously discovered magnetotactic bacteria</a>, but his work received scant attention because it hadn’t been archived.</p>
<p>In the decades since, scientists have continued to study how these tiny magnetic creatures behave. Of course it’s just cool to learn more about these unique single-celled organisms. But researchers <a href="https://scholar.google.com/citations?user=22Jx6scAAAAJ&hl=en&oi=sra">like me</a> are also figuring out ways to harness their magnetic properties in medical and other engineering applications.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/3uUL4ooM6KI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Watch magnetotactic bacteria dance as the magnetic field around them changes direction.</span></figcaption>
</figure>
<h2>What makes them living magnets?</h2>
<p>You’ve probably stuck a magnet to the metal door of a refrigerator before. This unique group of prokaryotes basically contain super tiny versions of those fridge magnets. They pack either iron-oxide or iron-sulfide molecules into highly dense structures known as magnetic nanoparticles.</p>
<p>Each nanoparticle is about 100,000 times smaller than a grain of rice. Magnetotactic bacteria <a href="https://doi.org/10.1016/j.micres.2012.04.002">produce them in different shapes</a>: bullet, rectangular and spherical. Researchers aren’t sure of a reason for this variation, but a possible explanation is that differently shaped particles can interact differently with magnetic fields.</p>
<p>By clustering and aligning in chains, these magnetic nanoparticles enable magnetotactic bacteria to respond even to the weak magnetic fields of the Earth – a strength of about 0.5 Gauss, as opposed to the 100 Gauss of a refrigerator magnet.</p>
<h2>Where did magnetotactic bacteria come from?</h2>
<p>There are two main proposals for how magnetotactic bacteria emerged on Earth.</p>
<p>The first hypothesis suggests that this group of bacteria evolved a couple billion years ago, in a time of increasingly abundant oxygen. As the oxygen reacted with iron, the amount of iron dissolved in the oceans decreased. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/231798/original/file-20180813-2924-w0wau5.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/231798/original/file-20180813-2924-w0wau5.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/231798/original/file-20180813-2924-w0wau5.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=647&fit=crop&dpr=1 600w, https://images.theconversation.com/files/231798/original/file-20180813-2924-w0wau5.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=647&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/231798/original/file-20180813-2924-w0wau5.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=647&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/231798/original/file-20180813-2924-w0wau5.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=813&fit=crop&dpr=1 754w, https://images.theconversation.com/files/231798/original/file-20180813-2924-w0wau5.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=813&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/231798/original/file-20180813-2924-w0wau5.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=813&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A lipid membrane (looks like a translucent cloud in this image) wraps around magnetic nanoparticles to form a magnetosome in a magnetotactic bacterium.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1002/adfm.201703106">Tay et al., Advanced Functional Materials, 2017</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Living things need iron for metabolic activities such as respiration, so bacteria started storing it to prevent coming up short in times of scarcity. But high concentrations of freely diffusing iron are toxic for cells.</p>
<p>The idea is that evolution favored bacteria that wound up crystallizing iron into nanoparticles and wrapped a lipid membrane around them to form magnetosomes.</p>
<p>An alternative explanation is more widely accepted by biologists. It’s based on the observation that magnetotactic bacteria grow best in environments like the swamps where they were first discovered – places with very limited oxygen, at concentrations as low as 1 to 2 percent.</p>
<p>As a magnetotactic bacterium moves through a swampy bog, it’s likely to encounter sand or soil particles that could obstruct its path. A bacterium can actively use its <a href="https://www.britannica.com/science/flagellum">flagellum</a> – a whip-like appendage that propels it while swimming - to move past these sediments to reach its preferred growth environment.</p>
<p>But in some cases, the flagellum might not be powerful enough. Magnetic particles can provide some additional force for these bacteria, allowing them to make use of Earth’s magnetic field for navigation and a little extra thrust forward. Magnetosomes allow for more effective navigation.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/231799/original/file-20180813-2909-10x1fw5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/231799/original/file-20180813-2909-10x1fw5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/231799/original/file-20180813-2909-10x1fw5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=449&fit=crop&dpr=1 600w, https://images.theconversation.com/files/231799/original/file-20180813-2909-10x1fw5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=449&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/231799/original/file-20180813-2909-10x1fw5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=449&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/231799/original/file-20180813-2909-10x1fw5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=564&fit=crop&dpr=1 754w, https://images.theconversation.com/files/231799/original/file-20180813-2909-10x1fw5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=564&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/231799/original/file-20180813-2909-10x1fw5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=564&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Magnetotactic bacteria use Earth’s magnetic field to locate an environment where they can flourish.</span>
<span class="attribution"><a class="source" href="https://www.nature.com/scitable/knowledge/library/bacteria-that-synthesize-nano-sized-compasses-to-15669190">Nature Education</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Isolating and using magnetic genes in the lab</h2>
<p>For many years, scientists have been trying to determine whether animals including <a href="https://doi.org/10.1126/science.201.4360.1026">bees</a>, <a href="https://theconversation.com/leatherback-sea-turtles-use-mysterious-compass-sense-to-migrate-hundreds-of-miles-38519">sea turtles</a>, <a href="https://doi.org/10.1098/rsif.2004.0021">sharks</a> and <a href="https://doi.org/10.1038/nature03077">pigeons</a> are magneto-sensitive. Could this possible sense – <a href="https://doi.org/10.1016/j.cub.2010.03.045">called magnetoreception</a> – help them with amazing feats of navigation? So far studies have been mostly inconclusive.</p>
<p>Studying simpler organisms like the magnetotactic bacteria might be one way to better understand how genes regulate biomagnetism. </p>
<p>By creating mutations in the lab, microbiologists [have identified genes] that enable magnetotactic bacteria to produce magnetic nanoparticles. They’ve also found genes that control the nanoparticles’ <a href="https://doi.org/10.1038/nrmicro.2016.99">size, shape and alignment</a> in these bacteria.</p>
<p>One possible application is to use these magnetic genes as a tool to manipulate cells in a non-invasive way. They could allow a researcher to wirelessly control a cell. </p>
<p>Magnetogenetics could build on the <a href="https://theconversation.com/exciting-cells-and-controlling-heartbeats-could-optogenetics-create-drug-free-treatments-56539">technique of optogenetics</a>, a method that uses light to precisely manipulate cell activities. For instance, a researcher can trigger a genetically engineered neuron to fire by exposing it to light. Light cannot penetrate very far through tissue, though, so it can’t get into deep brain regions or the gut, for instance.</p>
<p>Magnetic fields, on the other hand, easily penetrate bodily tissues. By engineering magnetic cells and manipulating them, scientists hope to learn more about the functions of specific cell types. Ultimately this knowledge could help treat diseases. </p>
<p>Scientists haven’t yet had any success in creating magnetic cells, except in one strain of <a href="https://doi.org/10.1038/nnano.2014.13">photosynthetic bacterium</a>. Reports of <a href="https://doi.org/10.1002/mrm.21606">creating magnetic mammalian cells</a> are controversial. So far they only contain super-tiny magnetic nanoparticles that are randomly distributed in the cells.</p>
<p><a href="http://dicarlo.bol.ucla.edu/">My colleagues and I</a> worked on a way to help figure out which magnetism-related mutations might be useful. First, we used chemicals to randomly generate mutant bacteria with different numbers of magnetic nanoparticles. Then, using a magnetic device we developed that has unprecedented sensitivity, we were able to sort and separate mutants with no nanoparticles and those with up to three times more than the normal number.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/231800/original/file-20180813-2918-p8oe2y.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/231800/original/file-20180813-2918-p8oe2y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/231800/original/file-20180813-2918-p8oe2y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=430&fit=crop&dpr=1 600w, https://images.theconversation.com/files/231800/original/file-20180813-2918-p8oe2y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=430&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/231800/original/file-20180813-2918-p8oe2y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=430&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/231800/original/file-20180813-2918-p8oe2y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=541&fit=crop&dpr=1 754w, https://images.theconversation.com/files/231800/original/file-20180813-2918-p8oe2y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=541&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/231800/original/file-20180813-2918-p8oe2y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=541&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Schematic of the magnetic device that can separate bacteria mutants with different numbers of magnetic nanoparticles.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1002/adfm.201703106">Tay et al., Advanced Functional Materials, 2017</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We hope to use our <a href="https://doi.org/10.1002/adfm.201703106">mutation-selection protocol</a> to generate a library of mutants that we can then genetically sequence. Ultimately we want to identify the minimum number of genes we’d need to introduce into a mammalian cell to make it magnetic. Then we could manipulate its activity in deep tissues non-invasively using magnetic fields.</p>
<h2>Harnessing their magnetic powers</h2>
<p>Magnetotactic bacteria have useful applications even without genetic tweaking.</p>
<p>Researchers have used these bacteria as microrobots for <a href="https://doi.org/10.1038/nnano.2016.137">delivering drugs</a> and for <a href="https://doi.org/10.1002/jctb.5648">removing toxic metals from water</a>. The magnetic nanoparticles they synthesize have also been used in biomedical applications, including targeted drug delivery and killing cancer cells via generated heat, called hyperthermia. </p>
<p>It could be helpful to produce magnetotactic bacteria and magnetosomes on a large scale, particularly the mutants that overproduce magnetic nanoparticles. But scaling up has been difficult so far.</p>
<p>When cultured in large bioreactors, individuals at the top and bottom of the tank experience different amounts of hydrostatic pressure. This can cause them to grow slower and produce fewer nanoparticles. To overcome this problem, I designed a <a href="https://doi.org/10.1128/AEM.01308-18">magnetic microfluidic system</a> that can continually sort the bacteria based on their magnetic contents.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/231801/original/file-20180813-2891-1rc4j6l.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/231801/original/file-20180813-2891-1rc4j6l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/231801/original/file-20180813-2891-1rc4j6l.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=215&fit=crop&dpr=1 600w, https://images.theconversation.com/files/231801/original/file-20180813-2891-1rc4j6l.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=215&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/231801/original/file-20180813-2891-1rc4j6l.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=215&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/231801/original/file-20180813-2891-1rc4j6l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=270&fit=crop&dpr=1 754w, https://images.theconversation.com/files/231801/original/file-20180813-2891-1rc4j6l.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=270&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/231801/original/file-20180813-2891-1rc4j6l.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=270&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A magnetic microfluidic system could isolate bacteria with different amounts of magnetism.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1128/AEM.01308-18">Tay et al., Applied & Environmental Microbiology, 2018</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>The device consists of a few superfine channels. When magnetotactic bacteria flow in, they experience upward magnetic forces. Only individuals with a user-determined cutoff number of magnetic nanoparticles are collected, while bacteria that failed to reach the mark are disposed of.</p>
<p>This high-throughput cell separation platform allows me to continue culturing only the healthy bacteria which are producing a large number of magnetic nanoparticles. It’s an important step that will help scientists conduct further research in the lab with these intriguing organisms.</p><img src="https://counter.theconversation.com/content/100720/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Andy Tay does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>These single-celled organisms naturally respond to the Earth’s weak magnetic field. Scientists are untangling how it all works, looking to future biomedical and other engineering applications.Andy Tay, Postdoctoral Research Fellow in Materials Science and Engineering, Stanford UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/791662017-08-10T00:10:47Z2017-08-10T00:10:47ZSeeing without eyes – the unexpected world of nonvisual photoreception<figure><img src="https://images.theconversation.com/files/180942/original/file-20170803-5621-192em30.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Color-changing cells in an Atlantic squid's skin contain light-sensitive pigments.</span> <span class="attribution"><span class="source">Alexandra Kingston</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>We humans are uncommonly visual creatures. And those of us endowed with normal sight are used to thinking of our eyes as vital to how we experience the world. </p>
<p>Vision is an advanced form of photoreception – that is, light sensing. But we also experience other more rudimentary forms of photoreception in our daily lives. We all know, for instance, the delight of perceiving the warm sun on our skin, in this case using heat as a substitute for light. No eyes or even special photoreceptor cells are necessary.</p>
<p>But scientists have discovered in recent decades that many animals – including human beings – do have specialized light-detecting molecules in unexpected places, outside of the eyes. These “extraocular photoreceptors” are usually found in the central nervous system or in the skin, but also frequently in internal organs. What are light-sensing molecules doing in places beyond the eyes?</p>
<h2>Vision depends on detecting light</h2>
<p>All the visual cells identified in animals detect light using a single family of proteins, called the opsins. These proteins grab a light-sensitive molecule – derived from vitamin A – that changes its structure when exposed to light. The opsin in turn changes its own shape and turns on signaling pathways in photoreceptor cells that ultimately send a message to the brain that light has been detected.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/180938/original/file-20170803-27677-nk4xk0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/180938/original/file-20170803-27677-nk4xk0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/180938/original/file-20170803-27677-nk4xk0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=528&fit=crop&dpr=1 600w, https://images.theconversation.com/files/180938/original/file-20170803-27677-nk4xk0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=528&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/180938/original/file-20170803-27677-nk4xk0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=528&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/180938/original/file-20170803-27677-nk4xk0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=664&fit=crop&dpr=1 754w, https://images.theconversation.com/files/180938/original/file-20170803-27677-nk4xk0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=664&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/180938/original/file-20170803-27677-nk4xk0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=664&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Confocal microscope image of rod (green) and cone (red) photoreceptors in a human retina.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/nationaleyeinstitute/24912842829">Dr. Robert Fariss, National Eye Institute, NIH</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Most of our conscious vision stems from photoreceptors in the retina, the light-sensitive layer at the back of our eyeball. In animals with backbones (vertebrates), cells that detect light for vision are vaguely <a href="https://askabiologist.asu.edu/rods-and-cones">shaped like rods or cones</a>, giving them their familiar names. </p>
<p>We’ve known for a while that other vertebrates have additional photoreceptors in their brains. But scientists had long thought that rods and cones were pretty much the whole story of mammalian vision. Thus, the discovery in the early 2000s by <a href="https://neuroscience.brown.edu/Berson/">David Berson’s group</a> at Brown University of <a href="https://doi.org/10.1016/S0166-2236(03)00130-9">other cells in a mouse retina</a> that respond to light came as a shock.</p>
<p>Even stranger were associated discoveries in many laboratories demonstrating that these cells contained a new class of opsin proteins called the melanopsins, never before seen in vertebrates (but similar to those of many invertebrates). They seem not to be involved in conscious vision.</p>
<p>We can hardly call them extraocular since they’re right there in the eye. Instead they’re often referred to as “nonvisual” photoreceptors. That’s the term researchers use for all animal photoreceptors that aren’t associated with imaging pathways in nervous systems.</p>
<p>So now we know there are nonvisual photoreceptors in the eyes themselves in many – perhaps most – animals. Where else can we find them throughout body?</p>
<h2>The hunt for photoreceptors not in the eyes</h2>
<p>In general, identifying a potential extraocular photoreceptor means searching for the proteins that can detect light, the opsins. The advent of inexpensive and efficient molecular genetic technologies has made the search for opsins a cottage industry in laboratories worldwide.</p>
<p>Cells that contain opsins are probably active photoreceptors, but researchers use physiological or behavioral tests to confirm this. For example, they can search for electrical changes or look for a change in an animal’s activity when they expose the cell to light.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179688/original/file-20170725-30152-1e8eul.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179688/original/file-20170725-30152-1e8eul.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179688/original/file-20170725-30152-1e8eul.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=479&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179688/original/file-20170725-30152-1e8eul.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=479&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179688/original/file-20170725-30152-1e8eul.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=479&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179688/original/file-20170725-30152-1e8eul.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=601&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179688/original/file-20170725-30152-1e8eul.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=601&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179688/original/file-20170725-30152-1e8eul.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=601&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A photoreceptor cell in the brain of a horseshoe crab. Green indicates the presence of the photosensitive molecule peropsin. Membranes in the cell known to respond to light are red.</span>
<span class="attribution"><span class="source">Barbara Battelle</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>The photoreceptors scientists have found beyond the eyes are most commonly located in the central nervous system. Almost all animals have several types in the brain and often in the nerves as well. </p>
<p>The skin is where we see <a href="https://doi.org/10.1093/icb/icw106">most other light receptors</a>, particularly in active color-changing cells or skin organs called chromatophores. These are the black, brown or brightly colored spots sported by many fish, crabs or frogs. They reach their <a href="https://doi.org/10.1093/icb/icw022">highest development in the cephalopods</a>: octopus, squid and cuttlefish. Animals actively control their color or pattern for several reasons, most often for camouflage (to match the color and pattern of the background) or to produce bright, prominent signals for aggression or attracting a mate.</p>
<p>Surprisingly, there is a second class of light-sensitive molecules besides the opsins, never used for vision (as far as we know). They show up in some nervous structures, such as the <a href="https://doi.org/10.1093/molbev/msm011">brains or antennae of some insects</a> and even <a href="https://doi.org/10.1073/pnas.0405968101">in bird retinas</a>. These are the cryptochromes, well-named because their functions and methods of action are still poorly understood. Cryptochromes were <a href="https://doi.org/10.1126/science.284.5415.760">originally discovered in plants</a>, where they control growth and annual reproductive changes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/181224/original/file-20170807-25539-zs54k5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/181224/original/file-20170807-25539-zs54k5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/181224/original/file-20170807-25539-zs54k5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=376&fit=crop&dpr=1 600w, https://images.theconversation.com/files/181224/original/file-20170807-25539-zs54k5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=376&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/181224/original/file-20170807-25539-zs54k5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=376&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/181224/original/file-20170807-25539-zs54k5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=473&fit=crop&dpr=1 754w, https://images.theconversation.com/files/181224/original/file-20170807-25539-zs54k5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=473&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/181224/original/file-20170807-25539-zs54k5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=473&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A squid chromatophore in the skin detects light.</span>
<span class="attribution"><span class="source">Alexandra Kingston</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Why detect light outside the eyes?</h2>
<p>Now that we know that these photoreceptors can be found throughout animals’ bodies, what in the world are they actually doing? Obviously, their function depends in part on their location.</p>
<p>Generally, they regulate light-mediated behavior that exists below the level of consciousness and that doesn’t require having an extremely precise knowledge of a light source’s location in space or time. Typical functions include the timing of daily cycles of alertness, sleep and wake, mood, body temperature and numerous other internal cycles that are synchronized to the changes of day and night.</p>
<p>Biological clocks that maintain regular physiological cycles – and cause the discomforts of jet lag – nearly always are controlled by these photoreceptors. These detectors are also important for the opening and closing of the eye’s pupil to help adjust to varying light levels. Skin photoreceptors like those in fish or octopus often control color and pattern variations.</p>
<p>In some animals, they have a quite different, and rather amazing, task – providing magnetoreception, the ability to detect the Earth’s magnetic field. This capacity is based on the cryptochromes, which apparently underlie mechanisms for magnetic orientation in animals as different as birds <a href="https://doi.org/10.1073/pnas.1518622113">and cockroaches</a>. </p>
<h2>People have nonvisual photoreceptor abilities, too</h2>
<p>With the discovery of light-sensitive retinal cells in addition to rods and cones in mammalian retinas, it became obvious that humans, too, must use nonvisual pathways for control of behavior and function.</p>
<p>Pupil size varies with changing light, even in functionally blind humans. A joint British-American study, published in 2007, found that patients who have lost all rods and cones due to genetic disorders can <a href="https://doi.org/10.1016/j.cub.2007.11.034">still have light-responsive daily rhythms and pupils</a>. One patient could even report the sensation of “brightness” when shown a blue light, which should stimulate the retinal non-rod, non-cone photoreceptors.</p>
<p>Recent research with rodents at Johns Hopkins University by <a href="https://www.nimh.nih.gov/labs-at-nimh/principal-investigators/samer-hattar.shtml">Samer Hattar’s</a> group suggests that <a href="https://doi.org/10.1038/nature11673">nonvisual pathways can regulate</a> mood, learning ability and even the sensitivity of conscious vision.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/179689/original/file-20170725-20161-n7mpdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/179689/original/file-20170725-20161-n7mpdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/179689/original/file-20170725-20161-n7mpdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/179689/original/file-20170725-20161-n7mpdd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/179689/original/file-20170725-20161-n7mpdd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/179689/original/file-20170725-20161-n7mpdd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/179689/original/file-20170725-20161-n7mpdd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/179689/original/file-20170725-20161-n7mpdd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A photosensitive nerve cell in the retina of a mouse. The green color shows the location of the photosensitive pigment melanopsin, which is responsible for most nonvisual photoreception in mammals.</span>
<span class="attribution"><span class="source">Maureen E. Stabio</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Finally, an unexpected recent finding in research led by <a href="http://neuroscience.jhu.edu/research/faculty/83">Solomon Snyder</a> and <a href="http://anesthesiology.hopkinsmedicine.org/cardiac-anesthesia/dan-berkowitz/">Dan Berkowitz</a>, also at Johns Hopkins University, found that blood vessels in mice contain melanopsin, the opsin used in retinal nonvisual photoreception. They found that this light-sensitive protein can regulate <a href="https://doi.org/10.1073/pnas.1420258111">blood vessels’ contraction and relaxation</a>. Since humans are likely to have the same system, this could partially explain the <a href="http://dx.doi.org/10.1016/S0733-8651(05)70271-X">increase in heart attacks in the morning</a>, which are perhaps associated with blood pressure changes occurring at that time.</p>
<p>We know nonvisual light detection is ubiquitous and significant in the lives of animals. Future research will continue to untangle its effects on human health and well-being.</p><img src="https://counter.theconversation.com/content/79166/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Thomas Cronin has received funding from the National Science Foundation and the Air Force Office of Scientific Research in the past.</span></em></p>We’re used to thinking of our eyes detecting light as the foundation of our visual system. But what’s going on in other cells throughout the body that can detect light, too?Thomas Cronin, Professor of Biological Sciences, University of Maryland, Baltimore CountyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/429852015-06-30T10:16:25Z2015-06-30T10:16:25ZI’m stuck like glue: why I love magnets and you should too<figure><img src="https://images.theconversation.com/files/86641/original/image-20150628-1431-ac980z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The invisible force and visible effects of magnetism.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/archeon/12857404305"> Hans Splinter</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>I have a confession: I’m obsessed with magnets.</p>
<p>We rely on magnets every day, but seldom give them a second thought. There are magnets in your credit card, your cellphone, your car, microwave oven and computer – and perhaps also pasted all over your refrigerator. </p>
<p>Probably the last time you thought about a magnet was in <a href="https://www.nde-ed.org/EducationResources/HighSchool/Magnetism/twoends.htm">a high school science class</a>. But you should realize they’re the unsung heroes of our world. Someone needs to stand up for magnets, and that person is me.</p>
<p>Don’t get me wrong. I’m not a magnet stalker or a magnet groupie. I’m a scientist, and I study magnetism for a living.</p>
<h2>Universally magnetic</h2>
<p>My main interest is in “<a href="https://www.skatelescope.org/magnetism/">cosmic magnetism</a>” – magnets in outer space. </p>
<p>Incredibly, magnetism is everywhere in the cosmos: planets, stars, gaseous nebulae, entire galaxies and the overall universe are all magnetic. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/86775/original/image-20150629-9054-170w15l.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/86775/original/image-20150629-9054-170w15l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/86775/original/image-20150629-9054-170w15l.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=563&fit=crop&dpr=1 600w, https://images.theconversation.com/files/86775/original/image-20150629-9054-170w15l.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=563&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/86775/original/image-20150629-9054-170w15l.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=563&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/86775/original/image-20150629-9054-170w15l.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=707&fit=crop&dpr=1 754w, https://images.theconversation.com/files/86775/original/image-20150629-9054-170w15l.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=707&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/86775/original/image-20150629-9054-170w15l.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=707&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Our planet is one big magnet.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Earths_Magnetic_Field_Confusion.svg">TStein</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>What does it mean to say that a heavenly body is magnetic? For a solid body like the Earth, the idea is reasonably simple: <a href="http://www.geomag.nrcan.gc.ca/mag_fld/fld-eng.php">the Earth’s core is a giant bar magnet</a>, with north and south poles.</p>
<p>But farther afield, things get weird.</p>
<p><a href="http://phenomena.nationalgeographic.com/2014/12/08/magnetic-milky-way/">Our entire Milky Way galaxy is also a magnet</a>. Just like for the Earth, the Milky Way’s magnetism is produced by electrical currents. But while the Earth has a molten core to carry these currents, our galaxy’s magnetism is powered by uncounted numbers of electrons, slowly drifting in formation through space. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/86774/original/image-20150629-9102-wyi1lf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/86774/original/image-20150629-9102-wyi1lf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/86774/original/image-20150629-9102-wyi1lf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=300&fit=crop&dpr=1 600w, https://images.theconversation.com/files/86774/original/image-20150629-9102-wyi1lf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=300&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/86774/original/image-20150629-9102-wyi1lf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=300&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/86774/original/image-20150629-9102-wyi1lf.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=377&fit=crop&dpr=1 754w, https://images.theconversation.com/files/86774/original/image-20150629-9102-wyi1lf.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=377&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/86774/original/image-20150629-9102-wyi1lf.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=377&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The magnetic field of our Milky Way galaxy as seen by the Planck satellite. Darker regions correspond to stronger polarized emission, and the striations indicate the direction of the magnetic field projected on the plane of the sky.</span>
<span class="attribution"><a class="source" href="http://www.mpa-garching.mpg.de/mpa/institute/news_archives/news1502_aaa/fig3.jpg">ESA and the Planck Collaboration</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The result is a magnet like nothing you’ve ever seen. </p>
<p>First, the Milky Way’s magnetism is unimaginably weak, around a million times weaker than the Earth’s. What’s more, instead of having a single north–south pole, there is seemingly <a href="http://www.mpifr-bonn.mpg.de/research/fundamental/cosmag">a separate magnet in each spiral arm</a> of our galaxy’s glowing pinwheel: different galactic neighborhoods have their own local definitions of north and south.</p>
<h2>Cosmic questions about cosmic magnets</h2>
<p>My own research has two focuses. First, what do galactic magnets look like? Where are all the north and south poles in our Milky Way, and in the millions of other galaxies scattered throughout the universe?</p>
<p>Second, and more importantly, where did all these magnets come from? How did the first cosmic magnets come into existence billions of years ago, and how have they survived through to the present day?</p>
<p>These questions are not quite as esoteric as they sound. </p>
<p>Magnetism is vital for <a href="https://www.cfa.harvard.edu/news/2009-20">stars like our sun to form</a>. The Earth’s magnetism <a href="http://www.esa.int/Our_Activities/Space_Science/Cluster/Earth_s_magnetic_field_provides_vital_protection">protects our atmosphere from harmful radiation</a>. And cosmic magnets generate energetic high-speed particles which, on arrival at Earth, <a href="http://www.space.com/7193-death-rays-space-bad.html">can cause random genetic mutations</a> and hence drive evolution.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/DRR3IPfTXiE?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Faraday rotation is an effect through which light is rotated as it passes through magnetized regions of space. (Swinburne Astronomy Productions / CAASTRO: The ARC Centre of Excellence for All-sky Astrophysics)</span></figcaption>
</figure>
<p>On the other hand, the answers are elusive. The big challenge is that magnetism is invisible: point a powerful telescope at a cosmic magnet, and you won’t see it. Instead, we use indirect approaches, relying on the fact that <a href="http://dunlap.utoronto.ca/%7Ebgaensler/papers/stories/301Gaensler-3.pdf">background light is subtly changed</a> as it passes through magnetic regions of foreground gas. I think of it as trying to do the ultimate cryptic crossword puzzle, but blindfolded and with your hands tied behind your back. </p>
<h2>A magnetic sixth sense</h2>
<p>Of course, one can’t spend one’s whole life just thinking about cosmic magnets. Every scientist has a secret unfulfilled ambition: a completely different scientific career that perhaps, if things had been different, they would have pursued instead.</p>
<p>So what’s my secret alternative vocation? </p>
<p>In a parallel universe, I would still be obsessed with magnets. But I would not be an astronomer. Instead I would study “magnetoreception.” </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/86643/original/image-20150628-1438-3k8odr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/86643/original/image-20150628-1438-3k8odr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/86643/original/image-20150628-1438-3k8odr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/86643/original/image-20150628-1438-3k8odr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/86643/original/image-20150628-1438-3k8odr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/86643/original/image-20150628-1438-3k8odr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/86643/original/image-20150628-1438-3k8odr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/86643/original/image-20150628-1438-3k8odr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Birds’ long migrations can be tied to their magnetic ‘sixth sense.’</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/wolfraven/3108329398">Jack Wolf</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Magnetoreception is the ability of some animals to <a href="http://www.the-scientist.com/?articles.view/articleNo/36722/title/A-Sense-of-Mystery/">respond or react to magnetism</a>: a “sixth sense” that allows them to see the unseen. The best-known examples are birds, some species of which <a href="http://www.nytimes.com/2012/04/27/science/study-sheds-light-on-how-pigeons-navigate-by-magnetic-field.html">navigate using the Earth’s magnetic field</a> during their spectacular globe-spanning migrations. </p>
<p>But in recent years, scientists have found that a whole host of other species can sense magnetism. Perhaps the most extraordinary case is that of <a href="http://www.nature.com/news/the-mystery-of-the-magnetic-cows-1.9350">magnetic cows</a>. Using images from Google Earth, researchers have claimed that cows around the world tend to align their bodies with the Earth’s magnetic field whenever they are grazing or resting.</p>
<p>Other studies, covering everything from <a href="http://www.smithsonianmag.com/smart-news/earths-magnetic-field-draws-sea-turtles-their-nests-180953926/?no-ist">the swimming patterns of sea turtles</a> to the <a href="http://www.pbs.org/newshour/rundown/dogs-poop-in-alignment-with-earths-magnetic-field-study-finds/">directions dogs face when they defecate</a>, have similarly revealed that animals can somehow sense magnetism. </p>
<p>Even humans might have some vestigial sensitivity to magnets. <a href="http://www.ncbi.nlm.nih.gov/pubmed/11976892">Vision quality seems to depend</a> on whether you’re facing north–south or east–west. Dreams are more likely to be <a href="http://www.newscientist.com/article/dn16871-sweet-dreams-are-made-of-geomagnetic-activity.html">mundane rather than bizarre</a> when the Earth’s magnetism is going through a period of high activity. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/86645/original/image-20150628-1428-liw6y9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/86645/original/image-20150628-1428-liw6y9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/86645/original/image-20150628-1428-liw6y9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=307&fit=crop&dpr=1 600w, https://images.theconversation.com/files/86645/original/image-20150628-1428-liw6y9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=307&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/86645/original/image-20150628-1428-liw6y9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=307&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/86645/original/image-20150628-1428-liw6y9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=386&fit=crop&dpr=1 754w, https://images.theconversation.com/files/86645/original/image-20150628-1428-liw6y9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=386&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/86645/original/image-20150628-1428-liw6y9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=386&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The pluses of magnets.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Bar_magnet.jpg">Aney</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<h2>Well-known but so mysterious</h2>
<p>It’s now been around 2,600 years since <a href="http://galileoandeinstein.physics.virginia.edu/more_stuff/E&M_Hist.html">the Greek philosopher Thales noticed that magnets attract iron</a>. We understand almost completely how magnets work, right down to <a href="http://magician.ucsd.edu/essentials/WebBookse16.html">the detailed atomic level</a>. Once a curiosity, magnetism is now at our beck and call, and <a href="http://www.northeastern.edu/sunlab/mom/technology.html">underpins our entire modern world</a> of convenience and technology. </p>
<p>We might have completely tamed magnets for our purposes, so much so that we almost never give them a moment’s thought. But both up in the heavens and down here on the ground, there’s still a huge amount we don’t understand about magnets. Where did magnets come from? How have they shaped the universe? And what roles do they play for life on Earth? </p>
<p>So please don’t overlook magnets. Magnets are marvelous, mysterious and magical, and deserve both your affection and your respect.</p><img src="https://counter.theconversation.com/content/42985/count.gif" alt="The Conversation" width="1" height="1" />
<h4 class="border">Disclosure</h4><p class="fine-print"><em><span>Bryan Gaensler receives funding from the Natural Sciences and Engineering Research Council of Canada.</span></em></p>I have a confession: I’m obsessed with magnets. We rely on magnets every day, but seldom give them a second thought. There are magnets in your credit card, your cellphone, your car, microwave oven and…Bryan Gaensler, Director, Dunlap Institute for Astronomy and Astrophysics , University of TorontoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/385192015-03-11T11:08:31Z2015-03-11T11:08:31ZLeatherback sea turtles use mysterious ‘compass sense’ to migrate hundreds of miles<figure><img src="https://images.theconversation.com/files/74339/original/image-20150310-13539-4146qb.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A leatherback sea turtle pauses for air on its long migration.</span> <span class="attribution"><span class="source">Connie Merigo (NMFS Permit #1557-03)</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span></figcaption></figure><p>Imagine yourself swimming in the Sargasso Sea in the Atlantic. The color blue dominates this part of the world - there’s nothing to see but a vast expanse of water and sky in all directions. The winds are calm. The water is warm, clear and deep. You have a destination in mind, but how do you choose your direction, and maintain it, day and night, for thousands of miles? Without a compass or GPS for guidance, this would be an impossible task for a human being. Yet many marine animals routinely achieve this feat during their yearly migrations between breeding and feeding habitats. </p>
<p>Sea turtles are known for their spectacular long-distance migrations. After many years at sea, they can pinpoint their natal nesting beaches after crossing entire ocean basins. We don’t know the distance covered during their developmental journeys but this period can last several decades, and they likely cover tens of thousands of miles. The largest, fastest and deepest-diving species of sea turtle is the <a href="http://www.nmfs.noaa.gov/pr/species/turtles/leatherback.htm">leatherback (<em>Dermochelys coriacea</em>)</a>. Leatherback sea turtles can grow to over a thousand pounds on a <a href="http://dx.doi.org/10.1371/journal.pone.0033259">diet of watery jellyfish</a>. They <a href="http://dx.doi.org/10.1098/rspb.2005.3110">travel extensively</a> between tropical and temperate habitats to gorge on seasonally abundant gelatinous prey. It’s a mystery how they maintain their headings to travel direct migratory paths over such vast distances.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/74326/original/image-20150310-13539-1p90vkx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/74326/original/image-20150310-13539-1p90vkx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/74326/original/image-20150310-13539-1p90vkx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74326/original/image-20150310-13539-1p90vkx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74326/original/image-20150310-13539-1p90vkx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74326/original/image-20150310-13539-1p90vkx.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74326/original/image-20150310-13539-1p90vkx.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74326/original/image-20150310-13539-1p90vkx.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Large Pelagics Research Center scientists collaborate with commercial fishermen to find and tag leatherback turtles at sea. Captain Mark Leach checks out a 800-pound male leatherback turtle with a GPS-linked satellite tag on its back.</span>
<span class="attribution"><span class="source">Kara Dodge (NMFS Permit #1557-03)</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Satellite tags to track turtles</h2>
<p>To understand the behavior and migratory patterns of these enigmatic turtles, we set out to locate and tag them in their northern foraging grounds in the northwest Atlantic. Productive waters off the coast of Massachusetts’ Cape Cod attract a rich diversity of marine life, including the jellyfish-eating leatherback turtle. Working with a skilled team of professionals – including commercial fishermen, a spotter pilot, veterinarians and field biologists – we placed <a href="http://dx.doi.org/10.1371/journal.pone.0091726">satellite tags on 20 leatherback sea turtles over three years</a>.</p>
<p><a href="http://www.int-res.com/articles/esr2008/theme/Tracking/TMVpp21.pdf">Satellite telemetry</a> has revolutionized scientists’ ability to track far-ranging marine animals for relatively long periods of times (months to years), often in otherwise inaccessible habitats. Virtually following animals via tracking tag has provided insight on migration timing and routes of a wide variety of ocean-dwelling species, including <a href="http://dx.doi.org/10.1016/j.cub.2009.04.019">sharks</a>, <a href="http://dx.doi.org/10.1139/F10-033">tunas</a>, <a href="http://dx.doi.org/10.1007/s00227-010-1578-2">ocean sunfish</a>, <a href="http://faculty.washington.edu/glennvb/fish475/Zerbini%20et%20al%202006%20published%20paper.pdf">whales</a>, <a href="http://dx.doi.org/10.1890/0012-9615(2000)070%5B0353:FEONES%5D2.0.CO;2">seals</a>, <a href="http://dx.doi.org/10.1073/pnas.0603715103">seabirds</a> and <a href="http://dx.doi.org/10.1007/s00227-009-1279-x">sea turtles</a>. Over the last decade, the integration of <a href="http://adsabs.harvard.edu/abs/2006AGUFMOS33C1716R">GPS</a> antennas into traditional satellite tags has greatly improved the accuracy and precision of location data, allowing us to track migrating animals with less error.</p>
<p>In our <a href="http://dx.doi.org/10.1371/journal.pone.0091726">research off Cape Cod</a>, we used satellite tags that collected location, depth and temperature information. When a turtle surfaces to breathe air, this data is transmitted from the tag to orbiting satellites. Satellites then relay the data to the satellite-based service <a href="http://www.argos-system.org">ARGOS</a> where the data is processed and then, ultimately, it’s sent to us for analysis. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/74343/original/image-20150310-13550-15vur6d.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/74343/original/image-20150310-13550-15vur6d.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/74343/original/image-20150310-13550-15vur6d.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74343/original/image-20150310-13550-15vur6d.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74343/original/image-20150310-13550-15vur6d.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74343/original/image-20150310-13550-15vur6d.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74343/original/image-20150310-13550-15vur6d.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74343/original/image-20150310-13550-15vur6d.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Somehow this young leatherback knows the way.</span>
<span class="attribution"><span class="source">Kara Dodge (NMFS Permit #1557-03)</span>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Swimming straight ahead, but how?</h2>
<p>One goal of our study was to identify the migratory routes of male and female adult and juvenile leatherback turtles. In our recently published <a href="http://dx.doi.org/10.1098/rspb.2014.3129">paper in Proceedings of the Royal Society B</a>, we used location data from satellite tags on 15 leatherback turtles to reconstruct their tracks and analyze their migratory orientation as they traveled south to the tropics. They didn’t swim along the coast where they could use landmarks and topographic features on the seafloor to orient themselves. Instead, these turtles struck out for open ocean, swimming offshore into the subtropical gyre. The North Atlantic gyre is a large circle of ocean currents stretching from the equator to near Iceland, and from the east coast of North America to Europe and Africa. We focused our analysis on turtle movements in the middle of the gyre, in an area known as the Sargasso Sea.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/74490/original/image-20150311-24206-1q4lti.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/74490/original/image-20150311-24206-1q4lti.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/74490/original/image-20150311-24206-1q4lti.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=606&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74490/original/image-20150311-24206-1q4lti.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=606&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74490/original/image-20150311-24206-1q4lti.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=606&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74490/original/image-20150311-24206-1q4lti.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=762&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74490/original/image-20150311-24206-1q4lti.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=762&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74490/original/image-20150311-24206-1q4lti.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=762&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Map of leatherback turtle tracks. Segments in the subtropical gyre are highlighted in red (observed) and green (corrected for the effect of currents).</span>
<span class="attribution"><a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>In the deep blue realm of the Sargasso Sea, these turtles were able to maintain remarkably consistent compass headings for over 600 miles (1000 km). Individual turtles followed widely-spaced parallel paths within the gyre. It looked as if the turtles shared the same directional orientation despite being in different parts of the gyre at different times. These consistent headings suggest that leatherback turtles migrating within the gyre use a common compass sense. It remains a mystery just what that compass sense could be.</p>
<p>Within the gyre interior, leatherback turtles have access to limited known sensory information. The seafloor is inaccessible at such depths. Weak ocean currents and lack of stationary reference points make hydrodynamic cues improbable. Wind- or current-borne cues such as odor plumes disperse rapidly over long distances. And sea turtles’ <a href="http://dx.doi.org/10.1242/jeb.015792">poor eyesight above water</a> likely reduces the utility of celestial cues such as stars. They lack all these bathymetric, hydrodynamic, celestial and chemosensory modes of guidance.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/74337/original/image-20150310-13543-12pt2ld.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/74337/original/image-20150310-13543-12pt2ld.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/74337/original/image-20150310-13543-12pt2ld.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74337/original/image-20150310-13543-12pt2ld.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74337/original/image-20150310-13543-12pt2ld.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74337/original/image-20150310-13543-12pt2ld.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74337/original/image-20150310-13543-12pt2ld.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74337/original/image-20150310-13543-12pt2ld.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stay on target, stay on target….</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/myfwc/6948027070">Florida Fish and Wildlife Conservation Commission, NOAA Research Permit #15488</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<h2>Invisibly orienting by solar or magnetic compass</h2>
<p>We hypothesize that leatherbacks migrating through the subtropical gyre may orient to some aspect of the earth’s geomagnetic field and/or the position of the sun on the horizon. Leatherbacks could have a time-compensated sun compass, similar to what has been proposed for <a href="http://dx.doi.org/10.1242/jeb.00657">loggerhead turtles</a> and exists in some <a href="http://dx.doi.org/10.1016/S0022-5193(05)80452-7">birds</a>, <a href="http://dx.doi.org/10.1073/pnas.152137299">butterflies</a> and other animals. These animals orient themselves using the time of day from their circadian clocks and the position, or azimuth, of the sun. Solar and magnetic features are ubiquitous and vary in a predictable way from north to south in this region, making them potentially useful for compass orientation.</p>
<p>Magnetic orientation has been demonstrated in many long-distance migrants, including <a href="http://dx.doi.org/10.1038/ncomms5164">monarch butterflies</a>, <a href="http://dx.doi.org/10.1007/BF00610853">yellowfin tuna</a>, <a href="http://jeb.biologists.org/content/199/1/29.short">birds</a>, <a href="http://dx.doi.org/10.1007/BF00657119">sockeye salmon</a> and <a href="http://jeb.biologists.org/content/199/1/73.abstract">sea turtles</a>. In laboratory experiments where leatherback hatchlings were exposed to reversed magnetic field conditions in a darkened room, the turtles oriented in approximately the opposite direction, suggesting they possess a <a href="http://www.biolbull.org/content/185/1/149.full.pdf">light-independent magnetic compass</a>. If leatherbacks retain this compass into adulthood, it could explain their ability to orient consistently day and night in the gyre. Evidence for a <a href="http://dx.doi.org/10.1242/jeb.00657">solar compass</a> has also been found in other sea turtles, and leatherback turtles may be able to interchangeably use magnetic and visual (solar) compasses during migration.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/74347/original/image-20150310-13539-1y8oxed.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/74347/original/image-20150310-13539-1y8oxed.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/74347/original/image-20150310-13539-1y8oxed.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/74347/original/image-20150310-13539-1y8oxed.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/74347/original/image-20150310-13539-1y8oxed.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/74347/original/image-20150310-13539-1y8oxed.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/74347/original/image-20150310-13539-1y8oxed.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/74347/original/image-20150310-13539-1y8oxed.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Starting out on the journey, baby leatherbacks in Trinidad.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/quintenquestel/14767799655">Quinten Questel</a>, <a class="license" href="http://creativecommons.org/licenses/by-nc-nd/4.0/">CC BY-NC-ND</a></span>
</figcaption>
</figure>
<p>At this stage, we can only speculate on the importance of different compass senses during leatherback migration. But there’s no doubt that adult and juvenile leatherback turtles are capable of remarkable compass orientation in the seemingly featureless expanse of the Sargasso Sea. How they actually accomplish these feats remains a mystery, but our study provides some tantalizing clues. Future work should focus on understanding the sensory systems that allow leatherbacks, and other ocean navigators, to find their way across the open sea.</p><img src="https://counter.theconversation.com/content/38519/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kara Dodge does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>How do these massive sea turtles stay on target as they migrate hundreds of miles through featureless open ocean?Kara Dodge, Postdoctor Investigator in Biology, Woods Hole Oceanographic InstitutionLicensed as Creative Commons – attribution, no derivatives.