“Form equals function” is a fundamental principle of biology. This means that the physical characteristics of a part of the body are associated with its purpose and that we can predict the function of something by paying attention to its appearance. When we see the muscular and very long hind quarters of a greyhound and compare them to the same body parts of a Bichon Frize, we can determine which of these dogs would win a race in between. Likewise, when we compare the large ears of bats to those of squirrels, it is easy to conclude that the hearing of bats is much sharper than that of squirrels.
A study of canine eyes found that their shape unexpectedly correlates with their function. The researchers behind the study “A comparison of facial color pattern and gazing behavior in canid species suggests gazing communication in gray wolves (Canis lupus) “ concluded that the more visible canine eyes are in a particular species, the more that species uses its eyes to communicate with each other. Species with highly visible eyes are able to effectively communicate the direction of their gaze with other members of the species. This “gaze signaling” is widespread in highly social species.
For the study, the researchers used photographs of 320 adults from a total of 25 species to analyze the color patterns of their faces and eyes. After careful measurements, they divided all species into three general categories of eye visibility: 1) The position of the pupil in the eye and the position of the eye in the face were remarkable. 2) Only the position of the eye in the face was visible. 3) Neither the pupil nor the eye had a visible appearance.
For each species studied, they drew on previous work to unravel some aspects of their social behavior. Do they hunt alone or in pairs, or do they hunt in groups of three or more? Outside of the breeding season, do they live alone or in pairs, or do they live in groups of three or more during this part of the year? The data revealed a pattern: more social species tended to have more visible eyes than less social species.
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Scientists studied a representative species with each type of eye visibility: gray wolves, fennec foxes and bush dogs. They found that gray wolves (high eye visibility) spent more time looking at other members of their social group than fennec foxes (medium eye visibility) who, in turn, spent more time exhibiting this gazing behavior. than bush dogs (poor eye visibility). The more visible the eyes, the more time animals spend looking directly at each other. The longer duration of this gazing behavior in more social species suggests that they use them to communicate more with each other.
There may be a trade-off related to eye visibility in predators. Many species that hunt in pairs or alone have inconspicuous eyes. It has been hypothesized that such eyes prevent prey from being alerted if the predator has them in the eye. For group hunters and social species, the advantages of communication within the species may outweigh this disadvantage.
This study suggests that we should be able to predict the level of gazing behavior and sociality of other canine species based on the visibility of their eyes.