Teenagers aren't the only species that suffer from social pressure. In fact some creatures even change sex when the social equilibrium shifts. Some male cichlid fish don't go that far, but their behaviour, appearance and fertility alter as the social hierarchy changes. Russell Fernald wondered whether a shift in social status was the trigger for the physiological changes that accompany well-established behavioural changes. Working with Stephanie White and Tuan Nguyen, he monitored male cichlid reproductive status after the fish were transferred to a new social environment. Tracking the fish as their dominance rose and fell, the scientists discovered that changing the fish's social status drove changes in the level of a key sex hormone that controls the fish's sexual maturity (p. 2567).
In the shore pools of Lake Tanganyika, only territorial, brightly coloured male cichlid fish are fertile. The remaining males, who haven't succeeded in winning a patch...
