Science & Technology

Investigating the response to visual changes during the midnight

At night in the Arctic, you can see diffuse sunlight, moonlight, aurora borealis, and artificial light, including near Kongsfjorden in the Svalbard Islands. Svalbard is an archipelago northeast of Greenland. At the lightest of the Arctic polar nights, usually in the middle of the day known as noon twilight, Arctic krill (insets) know to swim to the bottom to hide from predators. At the darkest of the Arctic polar nights, they swim to the surface in search of bioluminescent food.Credits: Photo by Geir Johnsen, Photo Illustration by Tammy Beeson

A new study is investigating the visual rhythms of animals in the polar nights of the Arctic.

Some people may want lunch around 11:30 am. The reason for this is that our biological rhythms are trained to convey ourselves when we are hungry, and when we get that craving, we know that our bodies are time to eat. Because it is. The same applies to visual rhythms.

It is usually brighter during the day than at night. For this reason, our visual system is modified to be ready to operate under brighter light conditions. At night, our eyes become more sensitive to adapt to the lack of available light.

It turns out that the same thing happens with Arctic krill. At the brightest polar nights in the Arctic (at high latitudes, when the sun stays below the horizon for the entire 24 hours), we know that the Arctic krill swims in the middle of the day, usually called noon twilight. Go down to the bottom to hide from predators. The darkest of the Arctic polar nights are when they swim to the surface in search of bioluminescent food.

New research published in PLOS Biology I saw this visual sensitivity rhythm in Arctic krill during the Arctic polar night.

Jonathan Cohen, an associate professor of marine science policy at the University of Delaware’s Faculty of Global and Marine Environment, said he was the lead author of this paper, leading to greater research into the biological processes that occur. .. During the Arctic polar night.

“For a long time, there was a doctrine that when the sun stayed below the horizon, biology became an interrupted animation, and when the sun returned above the horizon in the spring, everything was back again,” Cohen said. I am saying. “In our work, we have found that this is not the case. Instead, there are creatures that are active throughout the polar nights when the sun is below the horizon. Even when the sun is below the horizon, you There is more light than you think, and it has a biological effect. ”

One of those biological effects lies in the visual sensitivity rhythm of krill.

To carry out the survey, Cohen traveled to the Svalbard Islands in the Arctic Ocean (northeast of Greenland if searching for a globe) to conduct surveys on both offshore research vessels and onshore optical stations. I did it.

Using underwater acoustics technology, researchers were able to learn that krill was active and present during the polar nights of the Arctic.

“In this paper, we really ask this question. Is there enough light in the polar nights of the Arctic to draw in their biological rhythms? And it turns out to be there.” Cohen said.

Krill used outside light in a variety of ways. It not only assists the visual system in moving up and down in the water column to find food, but also helps control its bioluminescence so that it cannot be eaten by predators.

Unlike low latitudes, in the Arctic Circle, where there are distinct periods of bright and dark nights, there are different light sources such as moonlight and aurora (aurora) during the polar nights, providing light at different times. This expands and shifts the amount of light available.

“There is still a difference between day and night, but it’s a bit blurry due to the presence of the moon and aurora, because these light levels are basically enough to get pretty close to what you see at noon time. Cohen said.

Polar night light in the Arctic does not fluctuate as much as low latitude light, but it does. While the sun is below the horizon, it still produces vibrations of light intensity, and these changes in light are perceived by krill.

Animals and people synchronize their biological clocks with visual cues such as periodic light (light dims or brightens) that directs certain genes to be turned on or off. ..

Looking for these visual mechanisms of krill, researchers as extracellular retinal electrocardiographic recordings under constant darkness to better understand how krill adapts to changes in light. I used what is known. The researchers conducted two experiments. One is a laboratory experiment in which oysters are exposed to flashes of different light intensities to measure sensitivity, and the other is an experiment in which flashes of the same intensity are exposed to different times of the day to measure the effect of time on visual sensitivity. is.

“We’re doing this with animals that we’ve collected and placed in the dark, so we can determine how well the krill can detect the flash,” Cohen said. “So we know that we were only exposed to the light of the environment they had at the time of collection, and that was the light that set their body clock.”

In addition to laboratory experiments, researchers relied on acoustic data showing when krill was moving vertically and optical data collected both on land and in the sea. Arctic polar night.

Cohen said this new discovery about krill has some implications. One is that Arctic krill can set its body clock using very small changes in light 24 hours a day. This is one of the lowest ever measured.

This study also helped to speculate how krill use external light and their own bioluminescence to protect themselves from potential predators. When swimming in the water, krill put their backs up and their bellies down. Their belly produces bioluminescence — like a krill that illuminates a small light bulb from its belly.

Underwater, light can only be detected from directly above. So by shining this light from their belly, they erase the shadows they would present when viewed from below.

“This is called counter-illumination and creates a light that blurs the shadows so that predators cannot see it from below,” Cohen said. “What we think this rhythm does is allow them to better adjust their bright shadows.”

They can also save energy and stay safe by staying low in the water column until feeding. Other animals may move up and down in response to passing clouds that look like dark shadows overhead, but krill can ignore those shadows and save energy.

With these new discoveries, Cohen will return to the Arctic in January 2022 and continue to investigate the effects of Arctic polar night artificial light on Arctic marine life.

Reference: “The photophysiological cycle of Arctic krill by Jonathan H. Cohen, Kim S. Last, Corey L. Charpentier, Finlo Cotier, Marine Darth, Laura Hobs, Gaia Jonssen, Jorgen Berge, Get caught up in the weak midday dusk of the polar night “October 19, 2021 PLOS Biology..
DOI: 10.1371 / journal.pbio.3001413

This project was funded by the Norwegian Research Council and the UK Natural Environment Research Council.

Investigating the response to visual changes during the midnight Investigating the response to visual changes during the midnight

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