How do different types of animals see?

A research team led by the University of Arkansas has recently gathered extensive data on hundreds of vertebrate and invertebrate species in order to shed more light on the specificity of the visual systems of various animals. The experts found that terrestrial animals are able to distinguish more colors than their aquatic counterparts, while animals adapted to open terrestrial habitats see a wider range of colors than those adapted to live in forests. 

Most importantly though, evolutionary history appears to be a key factor structuring which colors different types of animals can see. For instance, the scientists discovered that invertebrate species see shorter wavelengths of light compared to vertebrate ones, due to the distinct evolution of some of their retinal cells.

“Scientists have long hypothesized that animal vision has evolved to match the colors of light present in their environments,” said study co-author Erica Westerman, an assistant professor of Biology at the University of Arkansas. “But this hypothesis is difficult to prove, and there is still so much we don’t know about animal vision. Gathering data for hundreds of species of animals living in a wide range of habitats is a monumental task, especially when considering that invertebrates and vertebrates use different kinds of cells in their eyes to turn light energy into neuronal responses.”

According to the researchers, animals’ ability to detect and process visual information depends on the wavelengths and intensity of light in specific environments, together with the sensitivity of a type of retinal proteins called opsins, which determine the spectrum of light a species can see. By collecting data for 446 animal species spanning four phyla, Professor Westerman and her doctoral student Matthew Murphy found that vertebrates and invertebrates use phylogenetically distinct opsins in their retinae. 

Due to the physiological difference between ciliary opsins in vertebrates and rhabdomeric opsins in invertebrates, the latter appear to be better at seeing short wavelength light, even in cases when habitats should select for vertebrates to also be able to detect similar patterns. However, this difference could occur due to stochastic genetic mutations found in vertebrates, which may limit the range of light that they can perceive.

“Our study answers some important questions, but it also generates more questions that could help us understand animal vision even better. We can do more to assess differences in the structure of the vertebrate and invertebrate retinae, or how their brains handle visual information differently. These are exciting questions,” concluded Murphy.

The study is published in the journal Proceedings of the Royal Society B Biological Sciences.

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By Andrei Ionescu, Earth.com Staff Writer