No sense of direction? Consider consulting some carp

The ability to navigate using the earth’s magnetic field is a skill that is not unique to humans.  Over the last few decades, scientists have discovered that numerous organisms have an ability to tell which way is north.  And the list is growing.

In one study, “Magnetic Alignment in Carps: Evidence from the Czech Christmas Fish Market,” Hart et al. reported that carp tend to align themselves along a north-south axis.  The authors photographed over 14,000 carp swimming in plastic tubs at pre-Christmas fish markets and found that, on average, the fish positioned themselves facing either the North Pole or the South Pole.

While the authors have not yet proven that carp can sense the geomagnetic field, they did rule out other possible orientation cues, including light, wind, temperature, and water flow. What benefit a common orientation may provide the fish remains unknown.  One possible explanation the authors present is that it may help the fish coordinate their movement when they swim in a school.

Some other organisms also have an ability to detect localized magnetic fields.  In a paper titled “Desert Ants Learn Vibration and Magnetic Landmarks,” Buehlmann et al. demonstrated that ants can sense a strong magnetic field created by two small magnets and use this as a landmark to find their nest.

In the absence of any other landmark (such as a vibrational, visual, or olfactory cue), ants who had been trained to associate the magnetic field with the nest entrance spent a lot more time near the magnetic field than ants who were naive to this landmark.  It is unclear how relevant this experiment is to ants in their natural environment, but the study nevertheless highlights the ants’ ability to sense a magnetic field.

While little is known about how carp align with the earth’s magnetic field or how ants sense a localized magnetic field, more is known about how some tiny organisms, aptly named magnetotactic bacteria, orient with a magnetic field.  These bacteria form straight chains of nano-size magnetic particles within the cells. The magnetic chains are attached to intracellular structures, thus allowing the bacteria to align passively with the earth’s magnetic field, like compass needles.

In a paper published earlier this month, Kalirai et al. showed that some magnetotactic bacteria form anomalous magnetic chains, with some sections of the chain oriented north and others south.  This finding contradicts scientists’ previous understanding that all the magnetic particles in a single chain would have the same alignment.  The study raises many questions: Would bacteria with anomalous magnetic chains have a competitive disadvantage in their natural environment?  Is there a single genetic mutation that leads to the anomalous magnetic chains?

All three of these studies raise intriguing questions, and we look forward to future discoveries from these scientists.

Image: Arrows indicate the orientation of carp swimming in a plastic tub (Hart et al. PLOS ONE 2012)

References:

Hart V, Kušta T, Němec P, Bláhová V, Ježek M, et al. (2012) Magnetic Alignment in Carps: Evidence from the Czech Christmas Fish Market. PLoS ONE 7(12): e51100. doi:10.1371/journal.pone.0051100

Buehlmann C, Hansson BS, Knaden M (2012) Desert Ants Learn Vibration and Magnetic Landmarks. PLoS ONE 7(3): e33117. doi:10.1371/journal.pone.0033117

Kalirai SS, Bazylinski DA, Hitchcock AP (2013) Anomalous Magnetic Orientations of Magnetosome Chains in a Magnetotactic Bacterium: Magnetovibrio blakemorei Strain MV-1. PLoS ONE 8(1): e53368. doi:10.1371/journal.pone.0053368

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