Any diver who might witness a sea turtle revolving wildly in the water is watching an instinctive ‘dance’ as the animal works to orientate itself with Earth’s magnetic field.
Scientists at the University of North Carolina (UNC) at Chapel Hill have just published what they believe is a groundbreaking study of how turtles navigate.
Biologist and lead author of the study Kayla Goforth, a recent UNC doctoral candidate, came up with a hypothesis concerning turtles’ ability to return repeatedly to the same feeding sites, even if it meant swimming halfway round the Earth.
“Kayla began to wonder if we could get the turtles to associate the magnetic signature of a geographic area with food — and therefore act out this turtle dance behaviour,” said Prof Kenneth Lohmann, who with his wife Catherine runs the biology department’s Lohmann Lab.
“She really took the lead in this,” he said of Goforth’s experiment to test the hypothesis. “I wasn’t at all sure in the beginning whether it would work, but we were happy to have her try – and it turned out remarkably well.”
The team conditioned captive loggerhead turtles to certain magnetic fields by replicating those of various oceanic locations, repeatedly feeding the turtles in some places but not in others.
When later exposed to the fields in which they had previously been fed, their wild “turtle dancing behaviour” indicated that they associated the magnetic signature with food.
When excited by a familiar magnetic signature the turtles would lift their heads out of water, mouths open, slap their flippers and sometimes spin in circles.
According to Goforth’s team they are using their “magnetic map sense”, but also have a “magnetic compass sense” that enables them to move in particular directions.
Map or compass sense?
Working with UNC’s physics and astronomy department, the team investigated the effects of radio-frequency oscillating magnetic fields on the turtles’ magnetic senses. They were surprised to find that while the fields had no effect on map sense they would disrupt the turtles’ ability to use compass sense and orientate themselves.
“It suggested that there are two different mechanisms for the magnetic map and compass, and they might have evolved separately,” said Goforth.
She is now continuing postdoctoral research at Texas A&M University to explore these processes further, though now using monarch butterflies rather than turtles.
“We know that for the visual sense, you have eyes; for the sense of smell, you have a nose; and for hearing, you have ears, but no receptor like that has been identified for the magnetic sense, and the mechanism remains unknown,” says Goforth.
The study has just been published in Nature.
Also on Divernet: THE MIRACLE OF MARINE TURTLES, SEA TURTLES ON THE BRINK, 400 HOURS’ DIVING AS BIO-STUDENT STANDS UP FOR TUMOROUS TURTLES, TRACKING TROPICAL TURTLES – DEEP DOWN, GREEN TURTLE SEX-BIAS: NEW CAUSE FOR CONCERN
