Frequencies of alternative mating strategies influence female mate preference in the swordtail Xiphophorus multilineatus

While studies demonstrating variation in female mating preferences are increasing, we still know very little about the factors that contribute to this variation, and we are therefore unable to predict how selection on males will vary due to female preference. A previous study of Xiphophorus multilineatus detected variation in female mate preference, where smaller females had a weaker strength of preference for males that court (courters) as compared to small males that use sneak-chase behaviour (sneakers). We tested the hypothesis that female experience with biased frequencies of courter and sneaker males would result in negative frequency-dependent selection on these male alternative mating strategies through female mate choice. We examined the preferences of naïve females, females given experience with different frequencies of courter/sneaker males in laboratory mesocosm treatments, and wild-caught females collected when the frequencies of males were sneaker biased and equal. The frequency of courter to sneaker males experienced in the laboratory significantly influenced female preference for courter males, but not in the direction we predicted for one end of the frequency distribution: the weakest strength of preference for courter males was from the treatment where courter males were less frequent. The pattern detected in wild-caught females was similar to the pattern detected in the laboratory-mated females, and together they suggest that when frequencies are biased towards either type of male, smaller females have a weaker preference for courter males.