Variation in mating preference within a wild population influences the mating success of alternative mating strategies

The evolutionary importance of variation in female preferences has been ignored until recently, in part because evidence that variation in specific female preferences results in variation in mate choice in the wild has been lacking. In the laboratory, females of the swordtail fish Xiphophorus multilineatus prefer large males that court (courters) to small males that sneak (sneakers). However, variation in this preference is related to female size, with the strength of preference for courter males increasing with female size. In this study we found that both a femaleʹs size and her strength of preference for courter males were significantly related to whether or not she mated with a courter male. These results provide strong evidence for variation in female mate preference influencing the mating success of males in the wild. When combined with previous results demonstrating a correlation between female size distribution and frequency of the two types of males across populations, our results suggest that variation in female preference helps to promote variation in male alternative mating behaviours, and ultimately heritable variation in male traits.