Variation, but no covariance, in female preference functions and male song in a natural population of Drosophila montana

Studies of the variance and covariance between female mating preferences and sexually selected male traits in natural populations are rare. In D. montana, male courtship song is an important target of sexual selection. We analysed the variance in components of song and preferences among F1 families from a natural population. All song traits varied substantially, with among-family variance components ranging from 30 to 65%. The greatest variation was in carrier frequency, which is the most important predictor of mating success. This is compatible with the trait capturing mutational and other components of genetic variance in condition because of condition-dependent expression. There was also variation for some components of preference variation, with significant variation among sisters within families, and among families. Females varied in overall responsiveness, but not in the slope of the linear female preference function for male song carrier frequency. Such variation might be expected to generate assortative mating, with more choosy females mating with higher quality males, but there was no covariance across families between female responsiveness and male carrier frequency. Substantial variation in the level of responsiveness might allow low-quality males to achieve some mating success and counteract the build-up of a strong genetic covariance between preferences and traits.