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Sharks are famous for their seemingly relentless movement – a small handful of species, such as great white sharks, have to swim to breathe and hold their gills in the water. Still, all these movements do not prevent the sharks from resting. Sleeping in the animal kingdom manifests itself in many strange ways. Birds whose brains are sleeping one by one or bats that sleep almost every hour of the day.
And An article published Wednesday in Current BiologyThe researchers reported that the draft shark, a small nocturnal shark endemic to New Zealand, appears to sleep during periods of calm, and that their metabolism and posture change significantly during these resting bouts.
However, with a touch of dread, they keep their eyes open for many.
More research will be required to show that other shark species capture underwater z’s, such as the draft shark. But the new study supports the hypothesis that one reason organisms evolved sleep was as a means to conserve energy.
draft sharks they were identified as sleepers in the past year By this same group of researchers based in New Zealand and Australia. They watched the captured sharks carefully in the tanks and tested their response to disturbances during their rest periods. (These sharks are not among those that swim for breath; they hang on the ocean floor and pump water through their gills.) The team found that it was more difficult to activate the sharks when they were inactive for long periods of time. makes you think they are actually asleep.
This time, researchers are trying to compare the metabolisms of sharks during these calm periods, defined as longer than five minutes, said Craig Radford, professor of marine science at the University of Auckland and author of the new paper. , when they rest for a shorter period of time and swim actively. As a way to indirectly measure metabolism, they used a custom-made tank that allowed the sharks to monitor how much oxygen they were using. Each of the seven sharks spent 24 hours in the tank, and the researchers found that these situations were indeed quite different.
Dr. “When they’re asleep, they show a pretty low metabolic state compared to when they’re either on alert or moving around the tank,” Radford said.
In evolutionary terms, sleep is a somewhat mysterious behavior, since it’s hard to imagine what could be so beneficial for an organism that regularly forgoes a chance to feed, mate, and escape predators. As far as we know, many less complex organisms never enter a dormant period. One hypothesis is that sleep originated as a way to conserve energy: If you don’t move, you burn fewer calories. Some have even suggested that the ability to get a better night’s sleep helps. primitive primates evolve into Homo sapiens. In the case of these sharks, it seems to allow them to get along with less energy expenditure.
The researchers found that when sharks sleep, they usually take a flat position at the bottom of the tank, similar to how other animals curl up or lie down when they’re asleep. But they were intrigued to discover that sharks don’t bother to constantly close their eyes for a snooze. And then they sometimes close their eyes during periods of waking rest. The team hypothesizes that the sharks may close their eyes in response to daylight rather than facilitating sleep.
“It’s human work to be done, isn’t it?” said Radford.
However, sharks do everything in their own way, including when they sleep.
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