What Colours Do Animals See? Study Throws Light On Animal Vision

Evolutionary history, primarily the difference between vertebrates and invertebrates, significantly influences which colours a species sees. Terrestrial animals see more colours than aquatic animals.

Cat looking at a butterfly on a flower | Representative photo

Source : Getty

Have you ever wondered what colours animals see? Biologists from the University of Arkansas in the United States have deepened scientists' understanding of animal vision, including colours they see, by gathering vision data for hundreds of vertebrates and invertebrates. The researchers have determined that animals adapted to land are able to see more colours than animals adapted to water, and that animals adapted to open terrestrial habitats see a wider range of colours than animals adapted to forests. 

The study titled "Evolutionary history limits species' ability to match colour" was recently published in the journal Proceedings of the Royal Society B: Biological Sciences. 

What Influences The Colours A Species Sees?

Evolutionary history, primarily the difference between vertebrates and invertebrates, significantly influences which colours a species sees. For instance, invertebrates can see shorter wavelengths of light, compared to vertebrates, the study said.

The researchers have explained how environment, evolution, and to some extent, genetic composition influence how and what colours animals see. 

In a statement released by University of Arkansas, Erica Westerman, one of the authors on the paper, said scientists have long hypothesised that animal vision has evolved to match the colours of light present in their environments, but the hypothesis is difficult to prove, and there is still so much that is not known about animal vision.

Westerman added that 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. 

What Determines Animals’ Ability To Detect Visual Information?

According to the study, an animal's ability to detect visual information depends on the wavelengths and intensity of light in a given environment, and the quantity and wavelength sensitivity of a family of retinal proteins, called opsins, governs the spectrum of light an animal sees, from ultraviolet to far red light.

Invertebrates And Vertebrates Use Distinct Opsins

The study said that invertebrates and vertebrates use phylogenetically distinct opsins in their retinae, and scientists have not determined whether these distinct opsins influence what animals see or how they adapt to their light environments. Phylogenetic is an adjective relating to the evolutionary development of a species, or of a particular feature of an organism.

Matt Murphy, the lead author on the paper, along with Westerman, collected vision data for 446 species of animals spanning four phyla. 

The word phylum, which is singular for phyla, is used to refer to a group of related living organisms that ranks above the class and below the kingdom in scientific classification.

Which Animals Were Considered?

One of the four phyla contained vertebrates such as fish and humans. Meanwhile, the rest of the phyla contained animals that were invertebrates, such as insects, squid and jellyfish.

Though animals do adapt to their environment, their ability to adapt can be physiologically constrained, the study stated. Both vertebrates and invertebrates broadly use the same cell type, opsins, to see. However, they build the cells differently. 

Difference Between Opsins Of Vertebrates And Invertebrates

There is a physiological difference between the opsins of vertebrates and invertebrates. Biologists call opsins in vertebrates as ciliary opsins, and those in invertebrates as rhabdomeric opsins. The eyes of certain animals contain rhabdomeric photoreceptors which enable the larvae to detect and swim towards light sources. 

Why Invertebrates Are Better At Seeing Short Wavelengths Of Light

According to the study, the physiological difference between vertebrates and invertebrates may explain why invertebrates are better at seeing short wavelength light, even when habitat should select for vertebrates to also see short wavelengths of light. 

Westerman said that the difference could be due to stochastic genetic mutations occurring in vertebrates but not in invertebrates. Stochastic means having a random probability distribution which may not be predicted precisely. Due to these mutations, the range of light in vertebrates' vision may have become limited.

Murphy said the study answers some important questions but also generates more questions that could help us understand animal vision even better. He said scientists can do more to assess differences in the structure of the vertebrate and invertebrate retinae, or how their brains handle visual information differently.