Animal Magnetism Comes to Light
Perhaps you saw them in Living Waters: sea turtles navigating alone for thousands of miles in the open sea, then returning to the exact beach where they had hatched; salmon swimming from Canada halfway to Japan, then finding their way back to the mouth of their natal stream.
The only global force available to make long-distance migration possible for sea creatures is the Earth's magnetic field -- something humans cannot sense. A compass can point a hiker north, but it cannot tell her the intensity of the field at any given point. A map can tell her companion where he is, but cannot tell him which bearing to take. Both tools are necessary, and both are available to many animals with input from the magnetic field.
At long last, Chinese investigators recently reported in Nature Materials the putative discovery of the physical basis of the magnetic sense in animals: "A Magnetic Protein Biocompass." If their findings are correct, the capability resides in a rod-shaped complex of iron-rich proteins inside particular cells. The abstract explains:
Here, we report a putative magnetic receptor (Drosophila CG8198, here named MagR) and a multimeric magnetosensing rod-like protein complex, identified by theoretical postulation and genome-wide screening, and validated with cellular, biochemical, structural and biophysical methods. The magnetosensing complex consists of the identified putative magnetoreceptor and known magnetoreception-related photoreceptor cryptochromes (Cry), has the attributes of both Cry- and iron-based systems, and exhibits spontaneous alignment in magnetic fields, including that of the Earth. Such a protein complex may form the basis of magnetoreception in animals, and may lead to applications across multiple fields. [Emphasis added.]
"It's an extraordinary paper," one biochemist remarked in Nature News. It may settle long-standing debates about the source of this incredibly accurate sense. David Cyranoski describes the system as "a biological compass needle: a rod-shaped complex of proteins that can align with Earth's weak magnetic field." The Nature News piece includes a diagram of the proposed magnetic receptor (MagR), looking like a rod of ring-shaped proteins rich in iron surrounded by cryptochromes. The Chinese researchers watched these rods orient themselves to magnetic fields. New Scientist takes us into the lab:
The researchers then identified and isolated this protein complex from pigeons and monarch butterflies.
In the lab, the proteins snapped into alignment in response to a magnetic field. They were so strongly magnetic that they flew up and stuck to the researchers' tools, which contained iron. So the team had to use custom tools made of plastic.
The solution looks intriguing, but Cyranoski writes that other scientists remain skeptical. Controversies have gone on for years about the roles of cryptochromes v. particles of magnetite. New Scientist reviews the history of the debate:
There used to be two competing theories about magnetic sense: some thought it came from iron-binding molecules, others thought it came from a protein called cryptochrome, which senses light and has been linked to magnetic sense in birds.
Xie's group was the first to guess these two were part of the same system, and has now figured out how they fit together.
Some skeptics are not convinced that such small amounts of iron in MagR can respond to magnetic fields. Some want to see the magnets work in vivo. Others doubt that the team's research was free of contamination. At best, this may represent "a major step forward towards unravelling the molecular basis of magnetoreception."
What the articles fail to address is the bigger picture of stimulus and programmed response. A compass is useless without eyes to read it and a brain to interpret it. If MagR is a compass needle, how does the animal sense its orientation and respond appropriately? The response mechanism must be able to discern not only the direction of the needle, but the angle of inclination of the field line at a given point as well as its intensity. Even with all this equipment, the animal must have a map inherited at birth to tell it where to go. Magnetosensation is networked with other senses, such as olfaction, proprioception and biological clocks. Without doubt, years of additional work will be required to put all the pieces together.
It immediately becomes apparent that we have here an astonishing example of convergence:
The biocompass -- whose constituent proteins exist in related forms in other species, including humans -- could explain a long-standing puzzle: how animals such as birds and insects sense magnetism....
Many organisms -- ranging from whales to butterflies, and termites to pigeons -- use Earth's magnetic field to navigate or orient themselves in space.
Animals known to have magnetoreception skills range from worms to mammals, insects to fish, bacteria to reptiles. Cows have been observed to prefer to stand in a north-south direction. Even humans appear to possess these protein complexes, suggesting we could develop the skill to a degree. Don't some people have a keener sense of direction than others?
There is an astonishing range of magnetosensing creatures that are unrelated according to Darwinian theory. Maybe that's why none of the articles tried to explain how this ability evolved. Will they say all these lineages hit upon the same systems independently? Or will they claim that bacterial ancestors developed it, but some descendent lineages lost it? Either answer seems dubious.
Intelligent design, on the other hand, predicts that organisms will be equipped with complex systems that can take advantage of environmental cues and respond with precision. That's exactly what we observe. We see similar equipment in our own remote sensing machines like spacecraft and weather instruments, so we are not surprised to find it in living creatures.
Image credit: Illustra Media.