Last Updated on April 23, 2023 by Coral Realm

It’s the question that has been at the forefront of sensory biology for decades. How exactly do animals sense the magnetic field of the Earth? 

“The search for a mechanism has been proposed as one of the last major frontiers in sensory biology and described as if we are ‘searching for a needle in a haystack,'” said Robert Fitak, one of the studies authors.

A new paper has shed some light on this mystery! Hopefully this is a huge step forward towards fully understanding the complex systems behind magnetoreception.

Animals Sixth Sense – Bacteria The Reason Behind The Magnetic Sixth Sense?

A new study by a collaboration of research from the UK, USA, and Israel published in the Philosophical Transactions of the Royal Society B journal has provided a new answer for how many animals can sense the Earth’s magnetic field. 

There is no question on whether a magnetic sense in animals exists; it is well documented in many species. Turtles use this ability to navigate thousands of miles back to the very beach they were born on to lay their eggs. 

The hypothesis by Natan, Fitak, Werber, and Vortman proposes that the animals sixth sense stems from a symbiotic relationship with magnetotactic bacteria. 

Magnetotactic bacteria are a very broad and diverse group of prokaryotic bacteria which have their movement affected and influenced by magnetic fields. 

There have been two main theories behind the magnetoreception in animals until this recent proposal; the magnetite-based magnetoreception hypothesis and the ‘radical-pair’ hypothesis. The former proposes that magnetic structures which are attached to proteins pick up the magnetic field of the Earth. The proteins then let the signal be passed on. The latter proposes that a molecule such as the cryptochrome protein which contains two unpaired electrons could function to sense the magnetic field.

There have been multiple cases for and against both of these hypotheses, but the authors lay out new evidence for their symbiotic magnetic-sensing hypothesis. 

They have trawled through a mountain of data from MGRAST (Metagenomic Rapid Annotations using Subsystems Technology) which is a huge bank of metagenomic data. Using this data they could estimate the abundance of magnetotactic bacteria in different animals. 

It was found that magnetotactic bacteria are indeed associated with animals, and actually that similar animal species may host similar bacteria species. 

For instance penguins and loggerhead sea turtles (Caretta caretta) were regularly found to host Candidatus Magnetobacterium bavaricum. While the two mammalian species, brown bats (Myotis sp.) and Atlantic right whales were found to instead commonly host different magnetotactic bacteria of the genera Magnetospirillum and Magnetococcus.

It is still unknown where exactly these magnetotactic bacteria would live in the host animal, or how indeed they would relay their magnetic sensings on to their host. 

The authors describe four ways in which the magnetotactic bacteria could potentially pass on the information. 

The first is via physical aggregations. This could be used in small organisms such as protists; as the bacteria move with the magnetic field and accumulate in one area the host cell also moves in that direction. 

The second is aggregations facilitating a neural response. This could be utilized by larger animals. The bacteria could be found in an organ such as cilia, and when the bacteria move along magnetic fields the cilia then communicate this to the host which then generates a neural response accordingly.

The third is cell to cell communication. In this scenario the magnetotactic bacteria directly communicate with the host cells. This communication will most likely occur via hormones or other small molecules.

The fourth is through the avian visual system. Magnetoreception in birds has been associated with both the nervous and visual systems. The authors suggest that it could be both. In this case birds could actually see the magnetotactic bacteria moving with the Earth’s magnetic field! Which is very interesting indeed!

While there is still research to be done to get to the bottom of the mystery of how animals perceive the Earth’s magnetic field, this is a big step forward. Fully understanding how animals and organisms interact with magnetic fields could improve and change the way that we humans utilize magnetic fields, also in navigation for instance.

We are also in the dark with how our modifications of magnetic fields affect animals. The construction of power lines alters the local magnetic environment for example, and understanding how this affects the behavior of animals could aid conservation efforts, and help in increasing biodiversity.

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Eviatar Natan, Robert Rodgers Fitak, Yuval Werber, Yoni Vortman. Symbiotic magnetic sensing: raising evidence and beyond. Philosophical Transactions of the Royal Society B: Biological Sciences, 2020; 375 (1808): 20190595 DOI: 10.1098/rstb.2019.0595

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