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Posted: 18th August 2015

Pupil shape helps animals survive
Cat eye
Species with vertically elongated pupils, like domestic cats and foxes, are very likely to be ambush predators.
Strong relationship between pupil shape and how animals feed

The pupil shape of an animal can be directly linked to their place on the food chain, a new study has found.

Researchers at Durham University and the University of California, Berkeley examined the eyes of over 200 land species to decipher why animals have evolved with different shaped pupils.

They discovered that species with vertically elongated pupils, like domestic cats and foxes, are very likely to be ambush predators, while species with horizontally elongated pupils, such as sheep and deer, are more likely to be prey.

“Our research is the first to offer a quantitative explanation as to why some animals have vertically elongated pupils and others horizontal," explains Professor Gordon Love from Durham University.

"We looked at the visual benefits of different pupil orientation and found a strong relationship between this and how animals feed – in short whether they are the hunter or the prey,” he added.

In the study, researchers produced computer models of animal eyes to assess the visual benefits of different pupil orientations and how this indicates whether they are predators or prey.

They noted that animals with vertically elongated pupils hide at close distance before striking their prey and tend to have eyes on the front of their head. Vertically elongated pupils allow these animals to judge distance without having to move their head which would risk giving away their position.

Meanwhile animals with horizontally elongated pupils tend to have eyes on the side of their head, rather then the front. Horizontally aligned pupils allow more light to be received from both in front and behind, while limiting light from above and below.  Together with the location of the eyes, this gives these animals panoramic vision along the ground to help detect and flee from predators.

The study also found that when grazing animals bend their head to eat, the pupil can rotate, enabling them to keep their pupils horizontal to the ground and therefore maintain their panoramic vision.

Professor Love said: “This work tells us more about why animals may have evolved in certain ways, in response to their place on the food chain. It also further reveals just how remarkable their eyes and vision are and helps us to further understand how our eyes work.”

The study is published in Science Advances. 



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