Because some use them to impress and others to intimidate

Poison dart frogs are found in the humid tropical forests of Central and South America. They are known to exhibit a wide range of bright colors starting from birth. These bright warning colors allude to a deadly toxin found inside their skin. Individuals of some species carry enough toxin to kill, in theory, up to 10 adults. Credit: Da Vinci Science Center

High up in a tree stands a bright vermilion red flycatcher. Males of this songbird species use their red feathers to attract females. Meanwhile, a king snake from the Arizona mountains crawls between the rocks below. Its vivid red, yellow and black coloring mimics that of the venomous coral snake to keep predators away. But why did these two species develop similar colors to send completely different messages?

Researchers at the University of Arizona set out to better understand how bright colors evolved in terrestrial vertebrates. They found a strong and consistent link between the function of animals’ bright colors and the activity patterns of their ancestors. Species that use their bright colors as a sexual signal were found to be descended from daytime active ancestors. Conversely, species using aposematism, a bright coloring that warns predators that the species are toxic, were found to have ancestors that were active at night.

The research, published in the journal Evolution, was made by Zachary Emberts and John J. Wiens, both of the Arizona Department of Ecology and Evolutionary Biology. Their findings open a door to understanding the evolutionary differences between many of today’s colorful species.

“This pattern generally appears to hold true in all terrestrial vertebrates, a group of about 40,000 species that have evolved over 350 million years,” said Wiens, professor of ecology and evolutionary biology and senior author of the paper. “It doesn’t matter how a species produces colors. The way a bird does red is different from how a lizard does red, but this general pattern of day-night activity still works.”

According to the researchers, brightly colored lizards and birds typically use their coloring as a sexual cue for mates. Conversely, colorful amphibians and snakes generally wear them as a warning sign for predators. Many of these amphibians and snakes are diurnal, which means they are active during the day, but their ancestors were nocturnal or active during the night.

The results did not show a clear connection between the warning colors and today’s day or night activity. However, when scientists used evolutionary relationships and statistics to estimate day-night activity patterns in the ancestors of these species, a pattern emerged: sexual coloration was associated with ancestors who were active during daylight, while the warning coloring was associated with ancestors who had a nocturnal lifestyle.

At the beginning of their evolution, most of the ancestors of the studied species began to be gray and faded. Over time, the vivid coloring has evolved separately across many different lineages. Because they helped the animals survive and reproduce, the bright colors settled and passed on to future generations, said Emberts, postdoctoral research associate in EEB and first author of the paper.

“The traits we see in species today may be a result of their evolutionary history,” he said. “We were looking for evolutionary models, so we did two separate analyzes, one using their current day-night activity and one using their ancestral day-night activity.”

The ancestors of amphibians and snakes spent time mating and interacting with members of their own species in the dark. Having bright colors offered them no sexual advantage because the colors could not be seen by potential mates. According to the researchers, this absence of visual sexual cues at night may have opened up the possibility that intense colors evolve for a very different purpose: a warning sign for predators.

“Warning colors have also evolved in eyeless species,” Wiens said. “Whether most snakes or amphibians can see colors is debatable, so their bright colors are generally used to signal predators rather than members of the same species.”

Bright colors in the animal kingdom: why some use them to impress and others to intimidate

King snakes of the Arizona mountains are found in the southwestern United States and northern Mexico. Non-poisonous, they are similar in color to poisonous coral snakes. This coloring has evolved as a predator protection mechanism. Credit: John J. Wiens

The researchers have another idea that could help explain the findings.

“The simplest potential explanation for this trend is situations where an animal is disturbed in moments of inactivity,” said Emberts. “When they sleep during the day and a predator disturbs them, that bright color becomes important.”

Wiens pointed to the example of the red-eyed tree frog, a predominantly green frog found in the tropical rainforests of Central America. During the nap, its uniform green color blends with the surrounding foliage. When startled by a predator, the frog may exhibit its red eyes, bright orange hands and feet, and vibrant blue and yellow flanks. The unexpected display of bright colors could buy the frog enough time to escape.

Researchers analyzed data from 1,824 terrestrial vertebrate species, looking for correlations between being diurnal and nocturnal and the function of the animals’ bright coloration.

They classified the colors as warning signs if one species qualified as poisonous or objectionable or mimicked another species with these deterrent characteristics. Colors were classified as sexual cues if one sex, commonly males, developed vibrant coloration at sexual maturity while the other sex did not.

“Animals generally use these colors as a sexual signal or a warning sign, rarely both,” Wiens said.

The researchers analyzed whether a species was diurnal or nocturnal, whether or not it had obvious colors, and whether those colors were used as warning or sexual signals. The “obvious” colors included red, orange, yellow, blue and purple. Few species reside in colorful environments, so the striking colors of the animals stand out from the natural background. The results indicated that this color palette was used for the two different purposes to more or less equal extent, with blue being the exception.

“It is interesting to see that for some colors such as red, orange and yellow, they are used with a similar frequency both as a way to avoid predators and as a means of companion attraction,” Emberts said. “On the other hand, blue coloring was more frequently associated with mating than predator avoidance.”

The researchers’ analyzes included all major groups of terrestrial vertebrates: amphibians, mammals, birds, crocodiles, turtles, lizards and snakes.

Wiens and Emberts intend to further study the evolution of color in other animals, insects and plants. Additionally, they hope to determine when flashy colors first evolved and how their functions have changed over time.


The faces and feet of the dinosaurs could be colored


More information:
Zachary Emberts et al, Why are animals so colorful? Evolution of sexual versus warning signals in terrestrial vertebrates, Evolution (2022). DOI: 10.1111 / evo.14636

Provided by the University of Arizona

Citation: Vibrant Colors in the Animal Kingdom: Why Some Use Them to Impress and Others to Intimidate (2022, October 18) Retrieved October 18, 2022 from https://phys.org/news/2022-10-bright-animal-kingdom -intimidate .html

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