Eye Shape May Help Distinguish Predator From Prey for Animals

Jenny Read, a vision scientist of Newcastle University in Britain, was more supportive, calling the new research “an incredibly neat example” of natural selection at work – how competition between predators and prey can influence eons of development. Look to the eyes.

While the diversity of eye shapes throughout the animal kingdom is well known, it seems like there’s a considerable difference between the eyes of grazing animals and those of predators, who have vertical slits rather than horizontal pupils.

Animals with vertical elongated pupils such as cats are also hunters – but tend to wait in the sidelines and ambush their prey.

The oblong shape of pupils inside the eyes of hunters like cats allow them to see in a wide range of light conditions.

They found that the horizontal pupils expanded the effective field of view. Instead, the pupils are nearly always horizontal or vertical, which suggests there must be other benefits which explain this orientation.

“A surprising thing we noticed from this study is that the slit pupils were linked to predators that were close to the ground”, said Dr Sprague. In this study, Walls explained that slit-shaped pupils enabled different musculatures, as well as a greater range in the total amount of light entering the eye. Pupils that are stretched horizontally allows them to receive more light from the front, back and sides, while also limiting the amount of light from the sun so they can better see the ground. Vertical-slit pupils maximize both cues, the researchers said.

“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”, Martin Banks, a professor of optometry at the University of California – Berkeley, said in a press release. “The second critical requirement is that once they do detect a predator, they need to see where they are running”. Circular pupils are generally found on animals that chase down their prey, such as cheetahs, or on taller ambush predators like lions and tigers.

These vertically enhanced cues are especially beneficial for predators close to the ground.

Researchers also learned that domesticated cats can narrow their pupils by 135-fold, while humans can only reduce pupils by 15 times.

“If an animal becomes nocturnal, they’re likely to develop a vertical pupil, if they become diurnal, they have a round pupil”. Like dogs, their pupils were round.

The research found that vertical slits, meanwhile, give the predator the improved depth of field and the ability to judge distances that helps them secure their prey. After analyzing the pupils of more than 200 land species including canines, felines, reptiles, and ungulates, the scientists found that short ambush predators such as alligators and foxes are more likely to have vertical pupils, whereas prey species-like gazelles or sheep-are more likely to have horizontal pupils.

Then again, there’s a find to that thinking: when the goat twists its head to touch, the flat understudy would change to take an opposite shape in connection to the ground. This trick would only work if the animal’s pupils were parallel with the horizon.

“It allows them to see better in front and behind, and maybe not to be dazzled by sunlight from above”, Banks said. Of these, 44 had vertical pupils and 82% had shoulder heights less than 42 cms or 16.5 inches.

Needless to say, scientists want to know why all these different shapes evolved. “It also further reveals just how remarkable the eyes and vision are and is another piece in the jigsaw puzzle of understanding how eyes work”.

The authors noted that this research focused on terrestrial species.

Other co-authors of this study are Jürgen Schmoll and Jared Parnell at Durham University.