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Animal eyesight is needs-driven

“Do you want to see what a box jellyfish sees and experiences when it rides a roller-coaster?”
“We humans believe that what we see is reality, but it isn’t. It is an eminently human reality, filtered through our eyes. The visual world of animals shows different realities”, says Dan-Eric Nilsson.
“We humans believe that what we see is reality, but it isn’t. It is an eminently human reality, filtered through our eyes. The visual world of animals shows different realities”, says Dan-Eric Nilsson.

Almost 40 years have passed since Dan-Eric Nilsson arrived in Lund from Gothenburg as a doctoral student. Today he is one of the top vision researchers and his vision team at the Department of Biology attracts attention from all over the world. His interest in the subject has not waned over time; there is no mistaking his enthusiasm as he quickly locates the short video showing what a gelatinous blob would see if it rode a roller-coaster.

A few minutes later, after an animated ride best described as a greyish haze in slow motion, Dan-Eric Nilsson bluntly reveals a piece of news which is potentially transformative for the well-being of both humans and animals.

He and other researchers in the team have developed a completely new light-measuring system, which they are in the process of patenting through LU Innovation. According to Dan-Eric Nilsson, the new light measurement system provides much more relevant information compared to the current lux meter and can be used in connection with light ergonomics, for example. A company has embraced the business concept and is in the process of applying the measurement technology to create better lighting.

The greatest benefit will be to enable natural outdoor light to be simulated indoors in everything from schools, housing for the elderly and private homes to animal barns. The outcome seems to be increased well-being for both humans and animals.

“Currently all lightbulbs, diodes and fluorescent lamps give unnatural light indoors. We have categorised various light environments around the world. We have measured light in the tropical rainforest, in deserts, under water on coral reefs and in all other possible sorts of environments. We have measured at different times of year, at different times of day and in different weather conditions. Soon it will be possible to choose what sort of outdoor light you want indoors”, says Dan-Eric Nilsson, continuing:

“We could never have imagined that the measurements would turn out to have these applications when we started out, four or five years ago.”

The two hottest projects in Dan-Eric Nilsson’s research at the moment both address the evolution of the eye, albeit in completely different ways. One project uses a unique type of camera which sees the world as birds see it. In the other, researchers are attempting to figure out what various animals can see.

“There is no immediate benefit to knowing what birds use their eyes for, but it will emerge eventually”, says Dan-Eric Nilsson with a smile.

Whereas the human eye contains three colour receptors enabling us to perceive red, green and blue, birds have four (red, green, blue and ultraviolet). In addition, there are two variants of colour vision in birds, which is why the “bird’s eye camera” is equipped with eight different filters through which it sees simultaneously. This enables the camera to provide an image of how birds perceive the world through their eyes.

“We humans believe that what we see is reality, but it isn’t. It is an eminently human reality, filtered through our eyes. The visual world of animals shows different realities”, says Dan-Eric Nilsson.

Working out what animals can see is a potentially successful approach. This was proven not least by Dan-Eric Nilsson’s and his colleague Eric Warrant’s search for the deep-sea squid. The giant of the depths had long been a mystery which baffled the two researchers. There were no fresh specimens to be found. The only ones available were carcasses which had floated up from depths of 1000 metres and rotted on a beach before they ended up in a tub of formalin.

“You know, there was nothing usable, no eyes. Not until we heard about a fisherman in Honolulu in Hawaii who had caught an injured specimen. Then we heard that someone had photographed it in the harbour. But who was that and where was the photograph?”

After quite some detective work, they found out that the man they were looking for was Ernie Choy. They phoned and then paid a visit to him. He was more than happy to show the photograph.

“It was a head with a giant eye. The good thing about the picture was that there was a fuel tank nearby and the fuel hose lay across the eye. So once we found out the diameter of the hose, the calculation was easy. The pupil turned out to be 9 centimetres and the whole eye 27 centimetres in diameter.”

Several years later, Dan-Eric Nilsson and Eric Warrant were in Wellington, New Zealand, when a colossal squid captured in the depths of the Antarctic was thawed after having been kept frozen for a few years. The colossal squid’s eye turned out to be as large as that of the giant squid.

No other creature even comes close. Several species have eyes the size of oranges, then there is nothing, nothing, nothing… and then these giants’ 27-centimetre eyes.

Their size is explained by the need to detect danger at depths of 1000 metres. There is no daylight at those depths, only light from bioluminescent organisms such as plancton.

“Large eyes look for large objects. These squids’ eyes have become this large to enable them to detect their worst enemy, the sperm whale. They can see it at a distance of 120 metres and when they do, they position themselves laterally and wait. When the sperm whale is close, the squid shoots off to the side. The whale has no chance of turning fast enough to follow.”

The deep-sea squid’s eye and vision are perfect, in Dan-Eric Nilsson’s view. “The same can be said of all creatures’ eyes, they are perfect for the world which those creatures inhabit. Even the eyes of the box jellyfish are perfect and work excellently – provided that it sticks to its element and gives up any notion of riding on roller-coasters.

They use their eyes to detect mangrove roots and avoid swimming into them. They navigate around the roots at a distance of a few centimetres. If they had sharper eyesight, they would alter their course unnecessarily early. They would spend their entire lives turning and that wouldn’t make sense.”

In one way, knowledge about what box jellyfish use their eyes for symbolises all the work conducted within the six autonomous research teams included in the vision group.

“This is how we work: we simply try to understand how visually driven behaviours occur on the basis of the information available in the surrounding world. If we can understand that, we can understand the evolution of the eye.”

 

Text: Jan Olsson

Photo: Gunnar Menander

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