A few years ago, Professor Liz Tibbetts stumbled upon something surprising. She noticed that wasps had striking facial features—including fake eyelines and distinctive marks. At the time, people didn’t believe that wasps were able to see this kind of fine scale variation, but in the years since, her wasps have become a model system of how individual identities are displayed and perceived even in animals with tiny brains.
“Animals use color in every context in very meaningful ways, you can look at social behavior, partners, enemies, or you can look at reproductive behavior, sexual selection, mate choice, escaping behavior and crypsis—every aspect of their life is impacted by color,” said Mark Hauber, Professor of Animal Behavior at the University of Illinois, Urbana-Champaign and one of the authors of a new review paper on the biology of color.
Researchers know that animals are able to see and produce colors that humans cannot, specifically in the ultraviolet and infrared zone, but until recently they were not able to view the world as animals themselves see it. In the paper released in Science this week, scientists showed that we are starting to understand how animals produce color and integrate information about it, and what implications that has for evolution. “We have tools which allow us to see how the bird sees a fruit item or how a predator sees an egg in a nest, instead of seeing the world through photographs,” said Hauber.
Colors can emerge from pigments and chemicals (like traditional paints, or the fluorescence that gives us highlighters) or from structures (in which physical features manipulate light and allow us to perceive colors), and different species sometimes develop very similar features. Humans, for instance, experience pigmentation changes due to the same signaling molecule as stickleback fish.
We perceive light and color through hue, saturation, and lightness using cones and rods. Other animals experience different portions of the light spectrum, according to the paper. Birds have three cone types and can see in the ultraviolet. Certain types of fish can see different colors based on what they eat and many can see infrared light.
A group of scientists ranging from evolutionary biologists to behavioral ecologists and anthropologists collaborated at a workshop in Berlin, exploring the role of color across animals. By collectively examining hundreds of species, they examined color on scales as small as nanoscale features and cellular mechanisms, and as large as fully visible arrays. The team connected the sensory, cognitive, and neural bases of color in animals with the adaptive and evolutionary implications of coloration. “We can now ask questions about color from every angle, from the evolutionary to the mechanistic, to the perceptual and developmental aspects,” said Hauber.
The team pieced together a full picture due to advances in technology such as spectrophotometry, digital imaging, and computational tools that allow scientists to better quantify the full spectrum of colors, not just those visible to humans. The methods reveal the way that nanoscale features interact with light, how animal colors change over time, and what causes coloration.
They also drew from advances in neuroscience and genetics, illuminating the way animals perceive color and the genetic changes that allow unrelated species to develop parallel or convergent phenotypes, which in this context means they developed similar observable colored features (like the fish and humans). Connecting these concepts allows scientists to ask questions about how one animal may develop camouflage based on what its predators can see, how great reed warbler birds distinguish their own eggs from parasitic cuckoo eggs, or about why some wasps can distinguish faces. “People are using these tools understand how social structures for instance in starlings effects colorfulness of females,” said Hauber. “The more equitable and social a starling species is, the more colorful a female starling is because sexual selections works both ways.”
This roadmap allows us to understand how our animal counterparts see color, and will help scientists develop new biomaterials or bio-inspired designs with applications for design, architecture, medicine, clothing, or security. Beyond obvious applications for camouflage, by understanding how color is produced in nature, researchers can generate new materials with higher energy efficiency or that perform multiple functions, much like the colors present in animals.
Hauber says scientists now need to explore pattern generation and recognition, diving deeper into how creatures like wasps can recognize facial features, and understanding the neurological aspects, and even probing color production in plant species. “Both in insects with tiny brains and with monkeys and humans with facial recognition, we need to have a model for how color and pattern are perceived.”