We Could Be on the Threshold of a New Era of Color Science
New insights on the role of color in animals could lead to innovation in fields as varied as clothing design and the security industry.
An international team of 27 scientists has just declared that we are on the threshold of a new era of color science that could have far-reaching impacts on everything from the security industry to our understanding of animal and human behavior.
The declaration, published in the journal Science, follows multiple advances in the study of animal and plant coloration.
“New technology is opening new windows into exploration of color perception, production, and function,” senior author Tim Caro of the University of California, Davis, said.
Co-author Justin Marshall of the University of Queensland recently determined that mantis shrimp have four times as many color receptors as humans do. He explained that we have three — red, green, and blue — while the shrimp have twelve.
Lead author Innes Cuthill of the University of Bristol said mantis shrimp use those extra color channels to analyze light coming from objects in ways much different than humans and most other animals.
“They analyze light like a machine called a spectrometer, which a physicist would use to measure how much light there is in a set of wavebands,” he said. “We, and most other animals, instead transform the relative amounts of light in different wavebands into a single continuous percept: the sensation we call color.”
Animals see the world differently than we do. For example, no human has yet set eyes on “bird white.” What we think of as “white” could also be something completely different to a bird.
“Objects that all look white to us may look different to a bird depending on how much ultraviolet light there is,” Cuthill said. “If there’s as much UV as blue, green, and red, that would be ‘bird white.’ If there was no UV, then that would be a saturated primary color to a bird, one we cannot imagine.”
Another recent finding in the field of color biology suggests patterns of color on a species can signal how well an individual can fight. Co-author Elizabeth Tibbetts of the University of Michigan first noted that black facial patterns vary on paper wasps. She then discovered that females with larger or a greater number of irregular black marks on their faces tended to win fights with their rivals.
Tibbetts explained that the facial signals help reduce the costs of conflict.
“Lots of animals have color patterns that convey information about fighting ability: birds, lizards, fish, mammals, insects,” she said. “It’s the animal version of advertising your fighting prowess with karate belt color. If you are a wimpy wasp, it doesn’t make sense to challenge the strongest wasp in the neighborhood to a fight.”
Body coloration can be tied to many behaviors. Humans are not exempt from the color-behavior connection. In fact, many people who head to a sunny climate for spring or summer vacation may exemplify the phenomenon.
Caro explained that skin color in humans is the result of a trade-off between avoiding the harmful effects of ultraviolet radiation and the beneficial effects of vitamin-D production caused by sunlight hitting the skin.
“This trade-off can affect behavior,” he continued. “For example, people in northern European climates like to take advantage of the sun in spring and sunbathe to produce vitamin D after the long winter.”
Color in nature is usually tied to honest visual information. Human heritage, in this way, is reflected in an individual’s skin color.
It would seemingly be easy for a weak paper wasp to evolve prominent facial markings, giving them a tough look in the wasp world. Others of its kind would soon figure this out, Caro said, adding that over evolutionary time, such “false” markings would be lost from the population.
Coloration that misleads others, however, remains in certain species. Co-author Alison Davis Rabosky of the University of Michigan studies red-and-black banded coral snakes, which are often deadly. Rabosky recently reported that more than 150 snake species mimic its color pattern, and she used geographic data to pinpoint where these faux poisonous snakes emerged.
Many US homeowners continue to be fooled by false black widow spiders, which look like actual black widows, but have a much less dangerous bite. For these spiders and the coral snake mimics, looking like a deadly creature can keep many predators at bay.
Scientists are also learning that coloration patterns can serve multiple functions at once.
“A single-color patch may signal one thing to a mate, another to a rival, or be seen by a member of your own species, but not by a predator because of their different visual systems,” Caro said.
“The review brings new order to this idea, showing that color can double between warning coloration and camouflage, and sexual signals and physiological functions, and social signals,” he added. “Interactions between color and both odor and auditory signals are a new frontier in the study of animal coloration, too.”
Still other advances in how plants and animals generate both pigment-based and structural colors could benefit humans. Structural coloration is the production of color by tiny surfaces that are fine enough to interfere with visible light. The brilliant, iridescent colors of a peacock’s tail feathers are created by structural coloration, as are the shimmering throat feathers of many hummingbird species.
“Understanding the intricacies of how color is produced may allow these steps to be replicated in the production of sensors in medicine and security,” Caro said.
Color research might also improve human nutrition, given that colors in plants are often tied to health benefits. There has been great interest in recent years in anthocyanin pigments that, depending on their pH, may appear red, purple, or blue. Numerous studies show that they and associated flavonoids — biologically active, water-soluble plant compounds — help to protect against a myriad of human diseases.
Scientific advances could also reveal when colors first emerged on Earth. A chicken and egg-type question could be: Which came first, color or the ability of any species to see it?
Recent studies have taken color science back to the Dinosaur Age, given that pigments can be preserved in the archaeological record. They have enabled researchers to recreate the colors of certain dinosaurs. Some, like maniraptoran dinosaurs, could be quite flashy, while others like a species of armored dinosaur, sported mellower reddish-brown hues.
Paleontologists have not yet determined what these different colors and patterns might have meant. Even for living animals, color patterns largely remain a mystery. Caro, for example, is currently conducting research on why biting flies are reticent about landing on black and white striped surfaces — one reason why zebras look the way they do. In the future, certain patterns on clothing could help to deter particular insects from bothering humans.
Caro is also studying the principles that govern coloration in plants and animals, not only for insect deterrence, but also for camouflage, warning signals, sexual cues, signaling to other species, thermoregulation, and more.
“We take color for granted, yet it is an important part of life,” Caro said. “We use color to recognize, plants, animals, and individual people, but most of the time we never stop to ask why is the giant panda is black and white or the giraffe dappled?”
“Understanding the functions of coloration,” he added, “can provide a new window into appreciating beauty in nature, and also encourage children to enjoy nature and the environment — something that is disappearing in western societies.”