As dazzling as it often looks, fashion in the animal kingdom can be horribly repetitive. There are only a limited number of color models that scream “look at me” amid the grays and greens of foliage and mud.
It is therefore not surprising that animals often use the same colors for very different purposes.
The brilliant crimson of a male Northern Cardinal (Cardinal-Cardinal) serves as a signal to potential mates to get closer; in Strawberry Poison Frogs (Oophaga pumilio), this burst of red is a stern warning to avoid or you will 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 causes 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 a whole different group of fish), categorizing their coloration as coming here or getting lost, and they found the common thread connecting each group.
The animals that came here, such as birds and lizards, are descended from diurnal or daytime active ancestors. 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,” says Emberts. “We were looking for evolutionary patterns, so we performed two separate analyses, one that used their current day-night activity and one that used their ancestral day-night activity.”
No correlation, they found, exists between daytime and nighttime activity and animal coloration today; on the contrary, the link is purely ancestral. But it’s the one that seems to be consistent for all terrestrial vertebrates, whose evolution dates back about 350 million years.
“It doesn’t matter how a species produces colors,” says Wiens. “The way a bird makes red is different from the way a lizard makes red, but that general pattern of day-night activity still works.”
According to the researchers’ analysis, most of the ancestors of the animals they studied started off rather plain and dull, evolving their vivid hues over time, and most of them live in environments in which their colors come out vividly. The more reasonable explanation is that brighter colored animals were better able to survive 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, colorations were roughly evenly split between sexual signaling and sexuality. Warning. It is not currently known what could be the reason.
“Interestingly, for certain colors like red, orange and yellow, they are used with similar frequency both as a means of avoiding predators and as a means of attracting mates,” says Emberts. .
“On the other hand, blue coloration was more frequently associated with mating than predator avoidance.”
The coloring of diurnal animals makes sense: a flashy animal, in daylight, is going to be seen by other animals, including potential mates. It may also make them more important targets for predators, but it seems that being able to find a mate and reproduce is more important than not being eaten. Females of these species are often dull in comparison, and therefore better able to hide from predators and survive to raise their offspring.
But nocturnal animals crawl and snoop in the dark. A male nocturnal snake doesn’t need a bright color much for sexual signaling if the females can’t see it.
“Warning colors have evolved even in species without eyes,” Wiens explains. “It’s debatable 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 coloring may have evolved as a way to tell daytime predators that might stumble upon the sleeping animal to move away. But future research may reveal more details. The team hopes to dig deeper 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 relevant today.
The team’s research has been published in Evolution.
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