Plegadis falcinellus

Magnetotactic bacteria in animals

How do Birds Navigate?

Ground breaking new study identifies Magnetotactic bacteria in animals, strengthening controversial symbiotic magnetic navigation hypothesis

Tadorna ferruginea
Dror Galili- nature photographer

How exactly do animals, especially migratory birds, navigate across vast reaches of the earth to their precise seasonal abodes? One hypothesis is that they utilize the earth’s magnetic field to navigate through the air, land and sea. But in spite of numerous studies indicating animals do indeed sense the geomagnetic field, the identity of the magnetic sensor remains enigmatic – “a sense without a sensor”. Recently Dr. Natan from Oxford University and Dr. Vortman from Tel-Hai College raised an exciting new hypothesis: that the sensor lies not in the animals themselves, but in symbiotic magnetotactic bacteria - a group of bacteria characterized by possessing an “iron needle” which causes them to swim along with the magnetic field. Animals hosting such bacteria, might just sense the bacteria and acquire a “magnetic sense” indirectly, without possessing any magnetic sensing capability of their own. This hypothesis offers a satisfying resolution to the often contradictory and puzzling results of previous research - and also explain how this much touted sensor has yet to be found.


 Pelecanus onocrotalus
Dror Galili- nature photographer

The gap in this neat hypothesis, however is that no magnetotactic bacteria have been identified within animal samples – up to now. In this new contribution, researchers from the UK, University of Central Florida USA, and Tel-Hai College Israel (Natan, Fitak, Werber and Vortman), show that since the hypothesis has been raised, new, previously neglected findings have come to light. “Apparently evidence has always been around and was waiting for someone to shine a light on “says Vortman. Contrary to "common knowledge" in the scientific community, they found, within an existing public metagenomics database that many animal samples do in fact contain a wide variety of magnetotactic bacteria species.

This supports the hypothesis by refuting one of its major criticisms. Further, “for a given host, specific magnetotactic bacteria species are most commonly found. In addition, the magnetotactic bacteria of mammals such as bats and whales are more similar to each other than to penguins and sea turtles – strengthening the possibility that these bacteria are truly symbiotic to specific hosts and reducing the possibility that arbitrary environmental contamination is the cause of the presence of these magnetotactic bacteria” Fitak adds. The authors also demonstrate that current knowledge on the diversity of these bacteria is far from comprehensive, and that the number of identified species has grown logarithmically over the past few years. The next challenge is to prove experimentally that these bacteria are indeed the basis for the transcontinental animal navigation capabilities. “It is possible that the ability of birds to find their way while migrating across continents, sea turtles crossing oceans and salmons finding their way from the ocean to the creeks, is also possible due to the tinny bacteria which reside within them”, sums Natan.   

Sturnus vulgaris
Dror Galili- nature photographer

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