Digest: Neo-sex chromosome underlying the Faster-Z effect in a species of Lepidoptera .

Do Z chromosomes evolve at a faster rate than autosomes in Lepidoptera? Mongue et al. show that Z-linked genes in two Lepidopteran species evolve faster than autosomal genes. However, the neo-sex chromosome differs from the ancestral chromosome and shows adaptive evolution for genes with a biased expression in the heterogametic sex. These findings indicate that studying molecular evolutionary patterns in sex-linked sequences at different evolutionary stages is essential to understand the dynamics of sex chromosome evolution.