© University of California - Los AngelesThis male Hetaerina damselfly from the occisa species has red spots at the base and tip of its wings but no black pigmentation.
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.