Biologists generally agree that female choosiness drives the males of their species to ever-greater heights of showmanship, from having brighter feathers and more sprawling antlers to driving faster cars. Now, in a striking validation of the cosmetics and fashion industries, Trond Amundsen and Elisabet Forsgren at Swedens Goteborg University demonstrate, at least in fish, that male choice matters too.

Amundsen and Forsgren, who published their results in yesterdays Proceedings of the National Academy of Sciences, found that male two-spotted gobies stuck in a partitioned tank between two contrasting femalesone with a bright yellow-orange belly, the other drabspent twice as much time in the side of their chamber next to the flashier female, even if the color was markered on. They were also four times more likely to display their willingness to mateby shivering up close to the female or undulating toward the nestfor the more brightly colored female fish. These results, the authors write, "suggest that the colorful belly of female two-spotted gobies has evolved, at least partly, as a response to male mate choice."

But male gobies aren't just interested in beauty. A female's color, which comes from carotenoids in her eggs and to a lesser extent her skin, may indicate to the male the quality of her eggs, the authors note. Males gobies are far outnumbered by females at the end of the mating season and nurture the eggs by themselves, so they have a strong incentive to recoup their investment by choosing a mate who produces eggs more likely to survive.

The authors point out that mate choice on the part of male animals is relatively widespread. For that reason, they write, "we suggest that more attention be directed at the largely unstudied phenomenon of female 'beauty' in fish and other animals."