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Content archived on 2023-03-23

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Trending science: Animals’ eyes may reveal place in the pecking order

A new study proposes that the pupil shape of an animal indicates whether they are the hunter or the hunted.

It seems that the eyes are not only the window to the soul but may also a dead giveaway of your position on the food chain. That’s according to a recently-published study which found a striking correlation between terrestrial species’ pupil shape and ‘ecological niche’ – that is, foraging mode and time of day they are active. The study, which was published in Science Advances last week, analysed the pupils of more than 200 land species. It found that species with vertically elongated pupils are very likely to be ambush predators and active day and night. Meanwhile, species with horizontally elongated pupils are very likely to be prey and to have laterally placed eyes. According to the study, vertically elongated pupils are advantageous for ambush predators to use stereopsis (the perception of depth and 3-D structure) to estimate distances of vertical contours and defocus blur to estimate distances of horizontal contours. On the other hand, the benefit of horizontally elongated pupils for prey is that they create sharp images of horizontal contours ahead and behind, allowing for a horizontally panoramic view that facilitates detection of predators from various directions and forward locomotion across uneven terrain. The study also found that when an animal of prey drops its head, the pupil can rotate by up to 50 degrees to stay horizontal. Martin Banks, one of the study authors and professor of optometry at Berkeley, noted to the Guardian, ‘The first key visual requirement for these animals is to detect approaching predators, which usually come from the ground, so they need to see panoramically on the ground with minimal blind spots. The second critical requirement is that once they do detect a predator, they need to see where they are running. They have to see well enough out of the corner of their eye to run quickly and jump over things.’ And vertically or horizontally elongated pupils are not the only possibility. As Science magazine reports, there are some species whose pupils are circular. These are generally the animals that chase down their prey, including such as cheetahs, lions and tigers. The magazine notes, ‘This suggests that above a certain shoulder height—about 42 cm—the functional advantages of vertical pupils are lost. The will to survive, it seems, has helped the eye of the tiger—and the fox and the horse—evolve pupils best suited to helping them do just that.’ For further information, please visit: http://advances.sciencemag.org/content/1/7/e1500391

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