Why Do Animals, Especially Males, Have So Many Different Colors?

Why Do Animals, Especially Males, Have So Many Different Colors?

ScienceDaily (Nov. 9, 2009) — Why do so many animal species -- including fish, birds and insects -- display such rich diversity in coloration and other traits? In new research, Gregory Grether, UCLA professor of ecology and evolutionary biology, and Christopher Anderson, who recently earned his doctorate in Grether's laboratory, offer an answer.

At least since Charles Darwin, biologists have noticed that species differ in "secondary sexual traits," such as bright coloring or elaborate horns, Grether said. Darwin attributed this diversity to sexual selection, meaning the traits increased an animal's ability to attract mates.

But Grether and Anderson, writing in the Oct. 28 issue of the journal Proceedings of the Royal Society B: Biological Sciences, emphasize another evolutionary factor.

"The cost of attacking the wrong type of male and of being attacked by the wrong type of male favors the rich diversity of coloration and of birdsong and chemical cues, such as odors, to identify rivals," Grether said.

Grether and Anderson studied several species of the Hetaerina damselfly (closely related to dragonflies) and found that differences in coloration served to help damselflies distinguish males of their own species, who are rivals, from those of other species, who are not.

"We found that male Hetaerina damselflies use species differences in wing coloration to distinguish between intruders of their own species and intruders of other damselfly species, but only at sites where the two species naturally occur together," he said. "This provides one of the clearest demonstrations yet of an evolutionary process that is probably very prevalent in nature but which has largely been overlooked. We tested for shifts in what animals recognize as competitors."