The ability to naturally perceive Earth’s magnetic field is something humans don’t have. Some animals, on the other hand, do: birds, some bats, turtles, ants, and even sharks are able to detect it. The molecule sometimes responsible for this ability has now been found in the eyes of a whole host of additional mammals, perhaps hinting that more creatures can sense the magnetic field than previously thought.
A new study, published in the journal Scientific Reports, has revealed that this particular protein – a “cryptochrome” known as Cry1a – has been found lurking in the retinas of dogs, wolves, bears, foxes, and badgers, but not in cats, lions, or tigers. It was also detected in primates, including the Bornean orangutan and two species of macaque monkey.
It’s well-known that migratory birds are able to detect the angle of the magnetic field relative to the ground, effectively giving them an on-board compass. This “magnetoreception” appears to be related to their visual system, which contains Cry1a, located in the retina's cone cells, which are responsible for color vision.
Finding this compound within a range of mammals suggests that they might have magnetoreception too – indeed, some of them have been shown to exhibit this ability. Red foxes, for instance, are more successful at catching mice when they pounce on them along magnetic field lines. Nevertheless, the distribution of Cry1a within a slightly unexpected range of mammals shocked the research team.
“We were very surprised to find active [Cry1a] in the cone cells of only two mammalian groups,” said Christine Nießner, a researcher from the Max Planck Institute for Brain Research in Frankfurt, and a coauthor of the study, in a statement. She also notes that “species whose cones do not contain active [Cry1a], for example some rodents and bats, also react to the magnetic field.”
There are multiple ways that an organism can react to or utilize the magnetic field. For example, magnetotactic bacteria are able to use tiny particles of magnetite or iron sulfide within their cells to orient themselves along field lines. The big brown bat is shown to be confused and disorientated when exposed to strong magnetic fields – once again, magnetite particles are thought to be the culprit here.
The researchers aren’t yet sure why this light-activated protein is present in these specific mammals; in fact, they cannot definitely say if this protein is used for magnetoreception in these species. However, following the process of elimination, this seems the most likely explanation.
Although Cry1a can play a role in the circadian rhythm – the innate awareness of a 24-hour cycle – this is unlikely to be the case here: Cry1a was found on the outer segments of the cone cells, not within the nucleus where circadian rhythms are regulated. Cry1a can act as an additional visual pigment used to perceive certain colors, but the researchers found this to also not be the case in these examples.
The next step will be trying to verify if all of these Cry1a-enhanced mammals do have a sense of magnetoreception.