麻豆淫院

Open water swimming can be strangely claustrophobic. Immerse your face in cloudy water and your view might dwindle to a few centimeters. Yet, harbor seals (Phoca vitulina) manage to negotiate the turbid coastal waters in which they reside with ease, detecting their surroundings through various senses, including their dexterous whiskers.

But Frederike Hanke from the University of Rostock, Germany, wondered whether the resourceful creatures may also use their vision to determine which direction they are maneuvering in, despite the opaque view.

"We wanted to know whether harbor seals can determine their heading from optic flow fields鈥攖he pattern of motion on the retina generated as a seal moves past visible objects, including particles in the water, in their surroundings," she says.

But to do so, she and her colleagues, Laura-Marie Sandow, Ann-Kathrin Thimian (both from the University of Rostock) and Markus Lappe (University of M眉nster, Germany), would have to set some harbor seals a gaming challenge.

They published their discovery in the Journal of Experimental Biology that images of particles in cloudy water moving across the retina at the back of the eye are sufficient to tell diving seals which direction they are moving in.

The team designed three computer simulations to show their seal "colleagues": one which simulated a seal moving through the open sea with blocks of dots streaming toward them out of the screen; the second simulating the seabed passing beneath them with a plane of dots rushing toward the viewer; and the final one simulating the surface of the sea flowing above the viewer's head with another plane of dots.

Then, the team encouraged three seals, Nick, Luca and Miro, to shuffle into place in front of a large screen showing the simulations so that they could indicate which side, left or right, they appeared to be moving toward, based on the movement of the dots, by touching a red ball on either side of their heads in return for a reward of tasty sprats.

Fortunately, Nick and Luca were gaming veterans, so they picked up the task with ease, but Miro was a novice, so it took a while for him to learn鈥攂ut Hanke recalls that Miro is a very open-minded seal, "so coped with all new situations easily."

Once the seals were comfortable with the game, Sandow and Thimian kept track of the seals' choices as they watched the dot simulations, which appeared to show the seal heading in a direction that was 22, 18, 14, 10, 6 or 2 deg to the left, or similar positions to the right.

Then, the team plotted the animals' successes as they determined which direction they appeared to be traveling in, although Hanke explains that they sometimes made mistakes.

"These are living animals, not robots. Errors are most likely due to inattentiveness or sometimes a drop in motivation," she chuckles. And when the team plotted the seals' successes, it was clear that the animals were perfectly capable of determining which direction they were traveling in based simply on the dots streaming in their view; exactly as the cloudy water, seabed or water surface would appear to move when they are swimming.

Even in the faintest light, harbor seals are able to use their vision and take advantage of cloudy water to determine which direction they are traveling in based on the apparent movement of objects and particles in the water streaming past their eyes. And now Hanke is keen to find out whether the skillful creatures are able to use this visual effect to determine how far they have traveled, "which is interesting in the context of navigation," she says.