In the wake of swimming for a considerable length of time in a mammoth circle from settling grounds in North Carolina and Florida to North Africa, the turtles discover their way back to settle on shorelines inside around 40 to 50 miles of where they were conceived.
Traditionally, scientists have thought that animals living near each other are more likely to have things in common genetically. But the best predictor of genetic similarities among loggerhead turtles is not their location or the nature of their habitat, but the magnetic field of the beach where they were born.
"A lot of different animals including sea turtles detect Earth's magnetic field and then derive navigational information from it and use it to find their way across or throughout long-distance migrations", Brothers says. Since turtles ordinarily return to their birthplaces to lay their eggs, it's no surprise that their offspring will be genetically similar to others in that area.
Biologist J. Roger Brothers is coauthor of the paper.
These sea turtles use magnetic fields like Global Positioning System
By utilizing already revealed hereditary data from in excess of 800 settling Florida loggerheads, Dr. Lohmann and Mr. Siblings could demonstrate that there was more hereditary similitude among turtles that home on shorelines with comparable magnetic marks than there was among turtles that home on shorelines that were physically near each other. This acts like a kind of compass for them, he says, even as they leave the East Coast of the US and travel hugely long distances, in some cases all the way to Africa.
"Eventually, they return to nest on the beach where they hatched - or else, as it turns out, on a beach with a very similar magnetic field", said Kenneth Lohmann, professor of biology in the College of Arts and Sciences at UNC-Chapel Hill. This seems to explain the unusual pattern of genetic similarities among turtles. With magnetic fields running across the peninsula, individual turtles might be making navigational errors and nesting on beaches that are magnetically similar to their home beach, but on opposite coasts, he said.
And the turtles appear more likely to get disoriented and go to the beach with the familiar magnetic field and breed, than going to a closer beach with a different magnetic field. "The difference in the Earth's magnetic field is a really strong predictor of how genetically similar or different the two nesting populations are".
The research, that appears in Current Biology, provides valuable insight into the turtles' navigation and nesting behaviors that could advance future conservation efforts. Sea turtles don't begin to reproduce until they are about 20, and only one out of 1,000 hatchlings survives to reproduce, so scientists would need to run an unrealistically long and large experiment, he said. Although we have plenty of behavioral evidence than many animals, from fruit flies to foxes, have magnetoreceptive abilities, it's tough for us to imagine what it must be like to be able to navigate by some sort of internal magnetic compass. "It might have important applications for the conservation of sea turtles, as well as other migratory animals such as salmon, sharks, and certain birds", Lohmann says.