As dazzling as it often seems, fashion in the animal kingdom can be frighteningly repetitive. There are only so many color templates screaming “look at me” between the grays and greens of foliage and dirt.
So it shouldn’t come as a surprise that animals often use the same colors for very different purposes.
The brilliant purple of a male northern cardinal (Cardinalis cardinalis) serves as a signal for potential partners to get closer; in strawberry poison dart frogs (Oophaga pumilio), this red blast is a stern warning to stay away or you’ll take a gulp of powerful, deadly ones toxin.
Evolutionary biologist Zachary Emberts, currently of Oklahoma State University, and his colleague John Wiens of the University of Arizona wondered what prompted the same colors to evolve to serve such different purposes in different animals.
They conducted a study of 1,824 species of terrestrial vertebrates (aquatic animals may be quite a different one fish kettle), categorized their coloration as either come here or get lost, and they found the common thread that connected each group.
The animals that came here, such as birds and lizards, descended from ancestors that were diurnal or diurnal. The stray animals like snakes and amphibians are descended from nocturnal ancestors.
“Characteristics that we see in species today may be a result of their evolutionary history,” says Emberts. “We were looking for evolutionary patterns, so we ran two separate analyses, one that used their current day-night activity and one that used their ancestral day-night activity.”
They found that today there is no correlation between day and night activity and the colouration of the animals; Instead, the connection is purely ancient. But it seems to be the same for all terrestrial vertebrates, whose evolution dates back about 350 million years.
“It doesn’t matter how a species produces the colors”, Says Wiens. “The way a bird colors red is different than the way a lizard colors red, but this general pattern of day-night activity still works.”
According to the researchers’ analysis, most of the ancestors of the animals they studied started out rather plain and monotonous and developed their vivid hues over time, and most of them live in environments where their vivid colors stand out. The most reasonable explanation is that more colorfully colored animals were better able to survive and passed their genetic material to generations that continued the trend.
The colors analyzed included red, orange, yellow, purple and blue, and the researchers found that for all colors except blue, the colors were fairly evenly split between sex signals and warnings. What could be causing this is currently unclear.
“It’s interesting to see that some colors like red, orange, and yellow are used with similar frequency to evade predators and attract mates.” says Emberts.
“On the other hand, blue coloration has been associated more often with mating than with predator avoidance.”
The coloring of diurnal animals makes sense: a conspicuous animal will be seen by other animals, including potential mates, in daylight. That may also make them greater targets for predators, but it seems that finding a mate and reproducing is more important than not being eaten. The females of these species are often drab in comparison and therefore better able to hide from predators and survive to raise offspring.
But nocturnal animals sneak and sniff around in the dark. A male nocturnal snake doesn’t have much use for a bright color as a sexual signal if the females can’t see them.
“Warning colors have also developed in species without eyes” Says Wiens. “It’s debatable whether most snakes or amphibians can see color, so their bright colors are generally used as signals for predators rather than members of the same species.”
Instead, the researchers suggest, the coloring may have evolved to tell diurnal predators that might stumble upon the sleeping animal to stay away. However, future research may reveal more details. The team hopes to delve deeper into the development of bright colors to see if their functions have changed over time.
In the meantime, however, research shows that delving into the evolutionary history of animal traits can uncover patterns that are outdated today.
The team’s research was published in evolution.