Exploring the W chromosome: accumulation of retrotransposons contributes to sex chromosome differentiation in the willow beauty Peribatodes rhomboidaria (Lepidoptera: Geometridae)

Abstract The evolution and molecular differentiation of heteromorphic sex chromosomes involves the accumulation of different repetitive DNA sequences due to restricted recombination. This also applies to moths and butterflies (Lepidoptera), which mostly have the WZ sex chromosome system. The female-specific W chromosome is typically rich in heterochromatin, harbours few or no genes and carries a large number of repetitive sequences. Molecular cytogenetic approaches such as comparative genomic hybridization (CGH) or fluorescence in situ hybridization (FISH) have shown that the W chromosome has evolved rapidly and varies widely among species. However, our knowledge of the composition of the W chromosome is still very limited. Here we present the analysis of repeats on the W chromosome in the willow beauty, Peribatodes rhomboidaria (Geometridae). RepeatExplorer comparative analysis of male and female genomes identified 10 putative W chromosome-enriched repeats, most of them being LTR or LINE mobile elements. We analysed two repeats with the largest difference between sexes: PRW LINE-like and PRW Bel-Pao. The results of FISH mapping and bioinformatic analysis confirm their W chromosome enrichment, thus supporting the hypothesis that mobile elements are the driving force of W chromosome differentiation in Lepidoptera.