Lobsters find their way with magnets

Jan. 1, 2003 at 2:05 PM   |   0 comments

CHAPEL HILL, N.C., Jan. 1 (UPI) -- Lobsters can find their way home in the ocean over long distances using Earth's magnetic field as a detailed map to navigate by, research released Wednesday reveals.

There are two requirements for an animal to demonstrate "true navigation," said Larry C. Boles, a Ph.D. candidate in biology at the University of North Carolina, who conducted the research with Kenneth J. Lohmann of the same school. One is directional ability, in which the animal possesses an internal compass. The other is positional ability, which allows the creature to determine its location relative to where it wants to go.

In the case of lobsters, Boles said, "the way they find this position is using the Earth's magnetic field." Lobsters have a "magnetic map sense" that allows them to use the magnetic field to collect information about their position in the ocean. A similar sense has been demonstrated in the past in salamanders, some birds, salmonid fish and sea turtles.

As described in the Jan. 2 issue of the British journal Nature, in experiments conducted in waters around Florida's Keys, captured Caribbean spiny lobsters -- Panulirus argus -- first were tethered to a central post in a salt water tank with a smooth fiberglass surface.

As soon as a lobster was captured, divers covered its eyestalks with rubber eye caps so it could no longer see its surroundings. Then a plastic cable tie was wrapped around its midsection between the fourth and fifth pairs of walking legs. A small brass non-magnetic swivel was threaded through the tie and arranged so it was directly over the dorsal midline of the lobster. A monofilament line tied to the swivel could then be used to tether the lobster in the orientation arena.

Each tethered lobster was released onto the slippery fiberglass surface of the arena. While the lobster's feet slid across the floor, a computerized tracking system recorded the direction of pull on the tether. As long as they did not touch the sides of the tank, most of the lobsters continued to walk at the end of their tethers in a particular direction for more than an hour, the researchers said.

"We kidnap the lobsters, then tether them to this ridiculous setup," Boles said. "Despite all the things we've tried to do to them, they walk toward home."

In a second part of the experiments, the captured lobsters were transported distances greater than 5 miles along circuitous routes to a testing site. At first, the lobsters were transported only by boat. Then the researchers increased the distance lobsters and conducted part of the trip in a truck. Some lobsters also were exposed to strong and variable magnetic fields created by attaching magnets to the transport container. All the actions were meant to confuse the lobsters as much as possible during transport so they could not use any environmental cues.

Although the lobsters exposed to magnetic disturbances changed their walking directions often and appeared to be disoriented, the non-disturbed lobsters walked a straight course toward home.

"It was assumed that this navigation ability was unique to vertebrates," said John Phillips, an associate professor of biology at Virginia Polytechnic Institute in Blacksburg, who demonstrated salamanders possessed magnetic map sense a few years ago. The fact that Boles and Lohmann have demonstrated it in an invertebrate "is part of the excitement about this new work," he told United Press International.

Phillips said the magnetic map sense of salamanders and spiny lobsters appears to be different and more detailed than that of birds and turtles. "Migratory birds will shift when they meet a magnetic variation," he said, somewhat like using the variation as a signpost that says, "change direction here."

However, lobsters and salamanders appear to learn to map their areas and can detect spatial variations in the magnetic field, much like a person would know to go up or down a hill to reach a destination. Lobsters and salamanders will follow, up or down, the magnetic variations they sense.

"What the salamander work and the spiny lobster work demonstrates is that (the animals have) a map sense that is more flexible than position-fixing," Phillips said.

Developing a magnetic map sense is difficult for any creature because Earth's field contains only very tiny variations. "The change in the field is on the order of about 1-100th of 1 percent in intensity per kilometer ... and a 100th of a degree of inclination," Phillips said. "We're trying to map (Earth's) magnetic topography and we haven't succeeded, which gives you some idea of how hard it is for an animal to do it."

As Boles explained, "Earth's magnetic field is omnipresent in the environment, but it varies from area to area, with slight part-per-thousand differences. If you can detect those differences, you can come up with a representation of something like a magnetic longitude and latitude -- different places have different addresses."

The experiments, he said, "created magnetic fields in the lab that represented fields that existed far away, and the animals acted as if they were in that faraway location ... We have shown that if you pick up a lobster and move it from its home, it tries to go back."

More details about the experiment are available online at unc.edu/depts/oceanweb/lobsters/.

The question most asked researchers in this field is whether humans have a comparable magnetic map sense. Some controversial research was published in the 1970s from England indicating humans might possess this ability.

However, Kraig Adler, professor of Biology and vice provost for Life Sciences at Cornell University in Ithaca, N.Y., said he participated in a demonstration of the techniques used in those original experiments and "found absolutely nothing to it. The original techniques were flawed."

Phillips added although several group have attempted it, no one has been able to reproduce any results indicating humans have developed a magnetic map sense.

--

(Reported by Dan Whipple, UPI Science News, in Broomfield, Colo.)

© 2003 United Press International, Inc. All Rights Reserved. Any reproduction, republication, redistribution and/or modification of any UPI content is expressly prohibited without UPI's prior written consent.
Trending News
Join the conversation
Most Popular
Photos
Video
x
Feedback