Wednesday, 26 April 2017

Researchers identify genes that help trout find their way home

April 26, 2017 by Robin A. Smith
 
Scientists have identified genes that enable rainbow trout to use Earth’s magnetic field to find their way back to the streams where they were born. Credit: Eric Engbretson, U.S. Fish and Wildlife Service

In the spring when water temperatures start to rise, rainbow trout that have spent several years at sea traveling hundreds of miles from home manage, without maps or GPS, to find their way back to the rivers and streams where they were born for spawning.

In a study published April 26, 2017 in Biology Letters, researchers have identified genes that enable the fish to perform this extraordinary homing feat with help from Earth's magnetic field.

Generated by the flow of molten metal in its core, the Earth's magnetic field ranges from a mere 25 microteslas near the equator to 65 microteslas toward the poles—making it more than a hundred times weaker than a refrigerator magnet.

Diverse animal species can detect such weak magnetic fields and use them to navigate. First identified in birds in the 1960s, this sense, called magnetoreception, has since been documented in animals ranging from bees and salamanders to sea turtles.

But despite more than half a century of research, the underlying molecular and cellular machinery remains a mystery.

To work out the genetic basis, Duke University postdoctoral associate Bob Fitak and biology professor Sönke Johnsen and colleagues investigated changes in gene expression that take place across the rainbow trout genome when the animal's magnetic sense is disrupted.

In a basement aquarium on the Duke campus, they randomly scooped up one fish at a time from a tank into a small holding container, and placed the container inside a coil of wire. The coil was connected to a capacitor, which discharged an electric current to create a split-second magnetic pulse inside the coil, about 10 times weaker than the magnetic field generated by an MRI machine in a hospital.

Next the researchers sequenced all the gene readouts, or RNA transcripts, present in the brains of 10 treated fish and 10 controls to find out which genes were switched on and off in response to the magnetic pulse.

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