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Why did bright colors evolve in the animal kingdom?

Scientists have long been puzzled by a strange natural phenomenon: the fact that vibrant color patterns in various animal species seem to serve different roles. While some animals use these patterns to attract mates, others employ them to ward off predators. 

By examining the role of color patterning in all the major groups of land vertebrates – amphibians, mammals, birds, crocodilians, turtles, lizards, and snakes – a team of researchers from the University of Arizona has identified a strong and consistent link between the function of animals’ bright colors and the activity patterns of their evolutionary ancestors. The experts found that species which use their bright colors as a sexual signal were descended from ancestors that were active during the day, while those that use such colors to deter predators had ancestors which were active during the night.

“This pattern generally seems to hold across land vertebrates, a group with about 40,000 species that evolved over 350 million years,” said study senior author John Wiens, a professor of Ecology and Evolutionary Biology at the University of Arizona. “It doesn’t matter how a species produces the colors. The way that a bird makes red is different from how a lizard makes red, but this general pattern of day-night activity still works.”

The scientist discovered that vividly colored lizards and birds typically use their coloring as a sexual signal to attract mates, while colorful amphibians and snakes usually wear them as a warning signal for predators. While many of these amphibians and snakes are currently diurnal, their ancestors were nocturnal. Thus, there is no clear connection between warning colors and present-day diurnal or nocturnal activity.

Early in their evolution, most of the ancestors of modern species started out drab and dully colored. However, vivid coloration evolved over time across many different lineages and, since they helped animals survive and reproduce, they became established and passed on to future generations. 

“Traits that we see today in species can be a result of their evolutionary history,” said study lead author Zachary Emberts, a postdoctoral fellow at the University of Arizona. “We were looking for evolutionary patterns, so we did two separate analyses, one that used their current day-night activity and one that used their ancestral day-night activity.”

Since ancestors of amphibians and snakes spent time interacting and mating with their conspecifics in the dark, having bright colors offered them no sexual advantage. Thus, their intense coloring may have evolved for a very different purpose: a warning sign for predators. “Animals generally use these colors either as a sexual signal or as a warning signal – rarely both,” Professor Wiens concluded.

The study is published in the journal Evolution.

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By Andrei Ionescu, Staff Writer

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