Many migratory species use the Earth’s magnetic field to keep their journeys on track. Now a study of a very non-migratory animal, the Drosophila fruit fly, shows the same capacity exists in some unexpected places. Perhaps humans are the rare ones because we don’t have this capability; if so, why?
In the quest for survival, access to information about the world, particularly information your rivals lack, is exceptionally valuable. So it is not surprising animals have developed an astonishing array of ways to observe the world around them. Magnetic fields are one of these, but before humanity’s invention of powerful electromagnets these were generally very weak. The effort required to detect them was much greater than for light or sound.
Consequently, biologists thought that only those animals that really needed to know their place on Earth – migratory pigeons or turtles for example – had exploited magnetoreception. However, a paper in Nature calls this into question.
The possibility that Drosophila are capable of magnetoreception was raised in 2015 with the identification of a MagR protein produced by the flies that orientates itself to align with magnetic fields.
The newly-published paper goes past this, revealing two methods by which the flies’ cells appear able to detect fields. The previous work identified photoreceptor proteins known as cryptochromes as being the sensors used by Drosophila to detect fields, with the capacity apparently failing in flies engineered not to produce cryptochromes leaving them magnetically blind.
The authors of the new paper point to work showing cryptochromes do this by harnessing the powers of quantum super-positioning. However, the team also question the need for cryptochromes, showing their role may be substituted by a molecule that occurs in all living cells, humans included.
Dr Alex Jones (no, not that one) of the National Physics Laboratory said in a statement, "The absorption of light by the cryptochrome results in movement of an electron within the protein which, due to quantum physics, can generate an active form of cryptochrome that occupies one of two states. The presence of a magnetic field impacts the relative populations of the two states, which in turn influences the 'active-lifetime' of this protein."
The authors showed the molecule flavin adenine dinucleotide (FAD) binds to the cryptochromes to create their sensitivity to magnetism. However, they also found the cryptochromes may be an amplifier of FAD’s capacity, not essential to it.
Even without cryptochromes, fly cells engineered to express extra FAD were able to respond to the presence of magnetic fields, as well as being highly sensitive to blue light in the presence of these fields. The magnetoreception required nothing more complex than an electron transfer to a side chain. The authors think cryptochromes may have evolved to take advantage of this.
"This study may ultimately allow us to better appreciate the effects that magnetic field exposure might potentially have on humans,” said co-lead author Professor Ezio Rosato of the University of Leicester.
Migratory animals not only detect fields, but can feel their direction, using the fact fields point at different angles depending on location. Whether the flies still get a benefit, or if this is a trait left over from some migratory ancestor, is not known.
The paper is published open access in Nature.