Evrim Yazgin
Cosmos science journalist
Many animals today use bright colour displays as a means of attracting potential mates or to warn off would-be predators.
The classic case of sexual selection using colour signalling is found in peacocks which proudly show off their vibrant tails to attract peahens for courtship.
Bright colours are also displayed by toxic species including venomous snakes and poisonous frogs. This is a way of telling predators to stay away or risk getting a potentially fatal mouthful.
Some other animals may even have evolved to mimic their toxic cousins to ward off predators.
For example, the non-venomous false coral snake (Erythrolamprus mimus) and Mexican milk snake (Lampropeltis triangulum annulata) closely resemble the bright red, yellow (or white) and black bands of the highly venomous coral snake (Micrurus tener).
A new study published in the journal Biological Reviews maps the development of colour signals in animals, relating these dazzling displays to the evolution of colour vision itself.
The research focused on “conspicuous colours” like red, yellow, orange, blue and purple which stand out against most natural backgrounds. This is the opposite of camouflage colours like green, grey and brown which help animals blend in with their surroundings.
“We wanted to know when bright coloration evolved and what was the purpose of that coloration,” says co-author Zachary Emberts, an assistant professor at Oklahoma State University, US. Emberts was a postdoctoral scholar at the University of Arizona when the study was conducted.
The study found that colour vision in animals evolved about 500 million years ago. This predates the evolution of colourful fruits by about 150 million years and the evolution of flowers only about 200 million years ago.
“There has been a dramatic explosion of both warning and sexual colour signals in the last 100 million years,” says study lead John Wiens, a professor at the University of Arizona.
It is not clear why this explosion began about 400 million years after colour vision evolved.
Wiens’s team identified 3 main groups responsible for this explosion: ray-finned fishes in marine environments, and birds and lizards on land.
They found that warning colour signals are at least 5 times more widespread among animals than sexual signals which are only seen among arthropods (the group that includes spiders and insects) and vertebrates.
The team theorises that warning colour signals may be more prevalent because the animal itself doesn’t need to have colour vision to ward off predators. But for sexual colour signals to be effective, the species must also be able to see in colour.
“In the future, it would be even more interesting to study what drives the ability of animals to see specific colours like red or blue,” Emberts says.
