Do male sticklebacks prefer females with red ornamentation?

In general, females are less ornamented than males and until recently female ornaments have been regarded as non-adaptive correlated effects of selection on males. This view is challenged and the alternative hypothesis that females' ornaments have evolved independently of male showiness, by intersexual selection for example, is supported. I tested these hypotheses experimentally using threespine sticklebacks (Gasterosteus aculeatus) from a population in which both sexes have red pelvic spines. Two females differing in red spine colour extravagance were presented simultaneously to a male under white and green light, and the male's courtship activity towards each female was quantified. Green light prevented the use of red cues by sticklebacks. The results show that red colour on the pelvic spines of female sticklebacks has value as a signal to males in this population, and males actually courted females with drab pelvic spines more than females whose pelvic spines had a redder hue, but only when illuminated by white light. The interpretation that best accounts for this result is that spine colour has a strong function in male–male aggressive interactions. This interpretation favours the hypothesis of non-adaptive correlation that has been proposed to explain the evolution of red spines in female sticklebacks.