Mating preferences do not maintain the tailspot polymorphism in the platyfish, Xiphophorus variatus

Negative assortative, or disassortative, mating describes the scenario when individuals tend to mate with dissimilar phenotypes more often than by random chance alone. This form of nonrandom mating has the power to select for the maintenance of polymorphism in conspicuous traits, for example, when females prefer mates that have a different trait value than their own. The livebearing variable platyfish, Xiphophorus variatus, exhibits high polymorphism for a melanic pigmentation trait called tailspots, which results in variation in a conspicuous visual cue. Livebearers often exhibit female mating preferences based on morphological traits and disassortative mating has been suggested in a related species. Whether mating choice contributes to the maintenance of tailspot variation has never been tested. Here, we examined mating preferences of wild-caught females for pairs of male stimuli differing in their tailspot pattern. Females showed no evidence for either assortative or disassortative association preferences, spending equal time with males of different patterns. These results corroborate data on natural mating patterns in X. variatus, suggesting that mate choice for tailspots is either nonexistent or at least insufficient to account for the maintenance of tailspot variation.