Multivariate male traits misalign with multivariate female preferences in the swordtail fish, Xiphophorus birchmanni

Mate choice represents the outcome of a complex decision that is most often based on the integration of information on multiple traits expressed by potential mates. Multiple traits, however, can show phenotypic correlations, which may coincide with, or oppose, female preference for individual traits. Thus, if multivariate preferences are misaligned with trait covariation, variation in single traits can persist because of weakened net sexual selection. Male swordtails, Xiphophorus birchmanni, show positive covariation among three sexually dimorphic visual traits: body size, vertical bars and dorsal fin size. Using synthetic video animations, we isolated each trait and found that females preferred males with large bodies and vertical bars, but small dorsal fins, thus conflicting with male trait covariation. We then tested females using live wild-caught males and found that females preferred smaller dorsal fins on larger males. We suggest that multivariate discordance between traits and preferences results in weak sexual selection on male visual traits, and may help explain the maintenance of variation in sexually dimorphic phenotypes.