Brain May Play Critical Role in Controlling Sexual Aggressiveness

The brain may be more important than testosterone produced by the testes in controlling male sexual aggressiveness, according to North Carolina State University researchers studying a gender-bending coral reef fish called the Caribbean bluehead wrasse. The wrasse are able to change sexes between male and female in response to environmental and social stimuli. Either females or nonaggressive males can turn into a macho, sperm-producing, sexually aggressive supermale when no dominant male is present.

Zoologist John Godwin and his colleagues reported in the Dec. 22 Proceedings of the Royal Society that they removed the ovaries from selected wrasse and placed the fish in a colony that had no dominant male. They found that the altered females were still able to become sexually aggressive supermales, although they could not produce sperm and lacked some normal coloration. The findings, they say, indicate that the male behavior is controlled by the brain, not the testes.