Scientists once thought that female mate choice alone accounted for the eye-catching color patterns seen in some male fish. But for orangethroat darters, male-to-male competition is the real force behind the flash, a new study finds.

The research, reported in the Royal Society journal Proceedings B, suggests that separate populations of orangethroat darters are evolving differing color patterns as a result of the males’ ability to distinguish their own from other species.