Researchers have discovered the basis for the magnetic personalities of migratory ants. These social insects integrate magnetic soil nanoparticles into their antennae to help them navigate the forests of South America, according to a study published online today (May 20) in the Journal of the Royal Society Interface.
A Pachycondyla marginata ant attacking a termite Image: Alex Wild
The study is a "great integration of physics and biology," Robert Srygley, a physiological ecologist with the USDA-Agricultural Research Service in Sidney, Montana, who did not participate in the research findings, told The Scientist.
Most ants communicate through pheromones and other chemical signals to find their way. But some ant species map-read by responding to geomagnetic forces.Pachycondyla marginata,a black, inch-long, termite-hunting ant that ranges from Bolivia to southern Brazil, is one such species. During the cold and dry season, which spans from April to September, P. marginata ants migrate at a 13º angle askew from the magnetic north-south axis. Based on behavioral and magnetic measurements, researchers had suggested that the ants carry a "magnetoreceptor" in their antennae, but it wasn't known what magnetic materials gave the animals their compass bearings.
Using light microscopy and transmission electron microscopy imaging techniques, Jandira Ferreira de Oliveira and her colleagues at the Brazilian Center for Physics Research in Rio de Janeiro found that the ants collect ultra-fine-grained iron oxide and aluminum silicate crystals from the soil and incorporate them into three main joints of their antennae. The researchers then devised a theoretical model of the antennae's magnetic sensitivity, and concluded that the amount of magnetic nanoparticles the ants pick up is sufficient to underlie their migratory sixth sense.
"They finally localized where [the magnetoreceptor] might be," said Srygley, although the researchers still need to pin down which of the three antennal joints holds the magnetic sensor, he added. Oliveira noted that the second antennal segment is home to the Johnston's organ, which is known to detect motion and might be responsible for sensing magnetic fields, too.
The next step, said Oliveira, is to show how the magnetic sensors in the antennae hook up to the nervous system. The iron oxide particles "should be coupled to mechanosensitive structures so as to transmit the information on the geomagnetic field in the form of a torque or force into the nervous system," she wrote in an email.
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