Data from: Sex chromosome linked genetic variance and the evolution of sexual dimorphism of quantitative traits

Theory predicts that sex chromsome linkage should reduce intersexual genetic correlations thereby allowing the evolution of sexual dimorphism. Empirical evidence for sex linkage has come largely from crosses and few studies have examined how sexual dimorphism and sex linkage are related within outbred populations. Here we use data on an array of different traits measured on over 10,000 individuals from two pedigreed populations of birds (collared flycatcher and zebra finch) to estimate the amount of sex linked genetic variance (h2z). Out of 17 traits examined, eight showed a non-zero h2Z estimate but only four were significantly different from zero (wing patch size and tarsus length in collared flycatchers, wing length and beak colour in zebra finches). We further tested how sexual dimorphism and the mode of selection operating on the trait relate to the proportion of sex linked genetic variance. Sexually selected traits did not show higher h2Z than morphological traits and there was only a weak positive relationship between h2Z and sexual dimorphism. However, given the relative scarcity of empirical studies it is premature to make conclusions about the role sex chromosome linkage in the evolution of sexual dimorphism.