By gathering vision data from hundreds of vertebrates and invertebrates, biologists at the University of Arkansas have deepened scientists’ understanding of animal vision, including the colors they see.
Researchers have determined that land-adapted animals are able to see more colors than water-adapted animals. Animals adapted to open terrestrial habitats see a wider range of colors than animals adapted to forests.
However, evolutionary history – primarily the difference between vertebrates and invertebrates – significantly influences the colors a species sees. Invertebrates see shorter wavelengths of light than vertebrates.
Biological sciences doctoral student Matt Murphy and assistant professor Erica Westerman recently published these results in Proceedings of the Royal Society B. Their paper, “Evolutionary History Limits Species’ Ability to Match Color Sensitivity to Habitat‘s Available Light,” discusses how environment, evolution, and to some extent, genetic makeup influence how animals see colors and what colors they see.
“Scientists have long hypothesized that animal vision evolved to match the colors of light present in their environment,” Westerman said. “But this hypothesis is difficult to prove, and there is still so much we don’t know about animal vision. Collecting data for hundreds of species of animals living in a wide range of habitats is a monumental task, especially considering that invertebrates and vertebrates use different types of cells in their eyes to transform light energy into neural responses.”
An animal’s ability to detect visual information depends on the wavelengths and intensity of light in a given environment. The amount and wavelength sensitivity of a family of retinal proteins, called opsins, govern the spectrum of light an animal sees – from ultraviolet to far-red light.
However, invertebrates and vertebrates use phylogenetically distinct opsins in their retinas, and researchers have not determined whether these distinct opsins influence what animals see or how they adapt to their light environment.
Murphy and Westerman collected vision data for 446 animal species spanning four phyla. One of these phyla contained vertebrates – animals that have backbones, like fish and humans. The rest of these phyla contained animals that were invertebrates, those that lack a backbone, such as insects, squids, and jellyfish.
The researchers’ study showed that although animals adapt to environments, their ability to adapt may be physiologically limited. While vertebrates and invertebrates largely use the same type of cell, opsins, to see, they build these cells differently. This physiological difference – what biologists call ciliary opsins in vertebrates and rhabdomeric opsins in invertebrates – could explain why invertebrates are better at seeing short-wavelength light, even when the habitat should select for that. vertebrates also see short wavelengths of light.
However, the difference could be due to stochastic genetic mutations occurring in vertebrates but not invertebrates, Westerman said. These mutations could also limit the range of light in vertebrate vision.
“Our study answers some important questions,” Murphy said, “but it also generates more questions that could help us better understand animal vision. We can do more to assess differences in the structure of vertebrate retinas and invertebrates, or how their brains process visual information differently.These are exciting questions.