As dazzling as it may seem, fashion in the animal kingdom can be frighteningly repetitive. There are so many colorful stencils that scream “look at me” amidst the grays and greens of foliage and dirt.
So it should come as no surprise that animals often use the same colors for very different purposes.
The brilliant crimson of a male Northern Cardinal (cardinalis cardinalis) serves as a signal for potential partners to approach; in strawberry poison dart frogs (Oophaga pumilio), that burst of red is a stern warning to stay away, or you’ll ingest a mouthful of powerful and deadly toxin.
Evolutionary biologist Zachary Emberts, now of Oklahoma State University, and his colleague John Wiens of the University of Arizona wondered what makes the same colors evolve to serve such different purposes in different animals.
They conducted a study of 1,824 species of terrestrial vertebrates (aquatic animals may be another sack, bag), categorizing their coloration as come-hither or get-lost, and found the common thread connecting each group.
The animals that come here, such as birds and lizards, are descended from ancestors that were diurnal or active during the day. Lost animals, such as snakes and amphibians, are descended from nocturnal ancestors.
“The traits we see in species today may be the result of their evolutionary history,” emberts says. “We were looking for evolutionary patterns, so we did two separate analyses, one that used their current day and night activity and one that used their ancestral day and night activity.”
They found that there is no correlation between daytime and nighttime activity and the coloration of the animals today; instead, the bond is purely ancestral. But it is one that appears to be consistent across all terrestrial vertebrates, whose evolution dates back some 350 million years.
“It doesn’t matter how a species produces colors,” vienna says. “The way a bird turns red is different from how a lizard turns red, but this general pattern of day and night activity still works.”
According to the researchers’ analysis, most of the ancestors of the animals they studied started out fairly simple and drab, their vivid hues evolved over time, and most of them live in environments where their vivid colors stand out. . The most reasonable explanation is that brighter colored animals could survive better and pass on 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 colorations were fairly evenly split between sexual cues and warnings. It is currently unclear what could be the reason for that.
“It is interesting to see that some colors such as red, orange and yellow are used with similar frequency as a form of predator avoidance and as a form of mate attraction.” Emberts says.
“On the other hand, blue coloration was more frequently associated with mating than with predator avoidance.”
The coloration of diurnal animals makes sense: a conspicuous animal, in daylight, will be seen by other animals, including potential mates. That can also make them bigger targets for predators, but it seems that being able to find a mate and reproduce is more important than not being eaten. The females of these species are often drab by comparison, and thus are better able to hide from predators and survive to raise offspring.
But nocturnal animals slither and sniff in the dark. A male nocturnal snake doesn’t have much use for a bright color for sexual signaling if the females can’t see it.
“Warning colors have evolved even in species without eyes,” vienna says. “It’s questionable whether most snakes or amphibians can see colors, so their bright colors are usually used to signal predators rather than members of the same species.”
Instead, the researchers suggest, the coloration may have evolved as a way to tell daytime predators that may encounter the sleeping animal to stay away. But future research may reveal more details. The team hopes to delve into the evolution 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 reveal patterns that are no longer current.
The team’s research has been published in Evolution.
