Stress can get you down. Worse: Stress can keep you down at least that's what happens to the male African cichlid fish when a bigger, rowdier male controls a coveted patch of lake-bottom territory.
In a study published Aug. 15 in the Journal of Neuroscience, a research team led by Stanford neurobiologist Russell Fernald has shown that continuous high levels of a stress hormone, cortisol, work to prevent most male cichlids from developing the bright, warlike colors, the extra muscles and the fully mature sex organs of a dominant "territorial" male.
Stress appears to prevent all but the dominant males from achieving reproductive success. Fernald said that since many species have evolved dominant and non-dominant males, the role of stress hormones in social systems may be widespread. "The interesting new thing we have found is that stress depends not only on the social state of the individual male but also on the stability of the community," Fernald said.
Fernald is the Benjamin Scott Crocker Professor of Human Biology and director of the Human Biology program at Stanford. He is also a professor of psychology and a member of the Neurosciences program faculty. He and members of his laboratory already have shown that for cichlid fish, social position determines physiology. It's not so much that the biggest, brightest fish becomes dominant. Instead, a fish must earn his bright "macho" colors by proving to himself and others that he can control and defend a patch of food-laden gravel.
Those males that prove themselves Fernald and his students call them "territorial" experience a dramatic transformation, switching color within minutes from a camouflaged sandy gray to bright blue or yellow. Within days, they put on weight, mature sexually and sport a threatening, warpaint-like stripe next to their eyes.