Could animal eyes be impacted by size and diet?
A study of 214 species indicates animal size and dietary habits as main factors in determining eye appearance.
Some animal eyes have round pupils, while others have vertical slits and still others are horizontal. While there are far more than three types of pupils present in nature (such as the distinctive “W” of the cuttlefish) researchers decided to focus on these major categories mentioned above in their study, published in the journal Science Advances.
According to their findings, vertical pupils may help some animals hunt, while round or horizontal pupils help spot threats from a distance. The study was conducted in part by using computer models designed to mimic a sheep’s eyes. Horizontal animal eyes filter more light to the creature’s sides, but are less helpful for looking up and down. This creates a broader field of view while scanning the area for potential dangers.
Vertical slits tend to belong to ambush predators because it’s the optimal shape for judging distance accurately. Lastly, round pupils were mainly associated with predators that are taller in stature and are able to chase down their prey; tigers and humans are both examples of predators with round pupils.
These findings puzzled researchers. They only offer an explanation for animals whose vision remains fixed at the horizon line. But animals are constantly moving and altering their perspective. By observing horses and other grazing species, scientists came to an interesting possible conclusion:
“When they pitch their head down, their eyes rotate in the head to maintain parallelism with the ground. And that’s kind of remarkable, because the eyes have to spin in opposite directions in the head,” said Martin Banks, a vision specialist at University of California, Berkeley.
Critics of the paper have been quick to point out that there are numerous exceptions to these conclusions regarding the correlation between pupil shape and food chain status. One notable example is the chinchilla, which has slit pupils despite its lack of predatory tendencies.
Looking to integrate this study into your classroom? Here’s a great idea for showing your students “the big picture” of animal eyes.
Activity: The aperture of a camera resembles the pupil of an eye in many ways. What happens to the photograph when you experiment with the aperture to let in more or less light?
Have any of your students shown interest in vision as a career path? Or perhaps having a greater understanding of physiology? Here are some cool careers to talk with them about.
Jobs: Biologist, Optician
Photo Credit: Creative Commons