Rewinding the ratchet: Rare recombination locally rescues neo-W degeneration and generates plateaus of sex-chromosome divergence

Natural selection is less efficient in the absence of recombination. As a result, non-recombining sequences, such as sex chromosomes, tend to degenerate over time. Although the outcomes of recombination arrest are typically observed after many millions of generations, recent neo-sex chromosomes can give insight into the early stages of this process. Here we investigate the evolution of neo-sex chromosomes in the Spanish marbled white butterfly, Melanargia ines, where a Z-autosome fusion has turned the homologous autosome into a non-recombining neo-W chromosome. We show that these neo-sex chromosomes are likely limited to the Iberian population of M. ines, and that they arose around the time when this population split from North-African populations, around 1.5 million years ago. Recombination arrest of the neo-W chromosome has led to an excess of premature stop codons and frameshift mutations, and reduced gene expression compared to the neo-Z chromosome. Surprisingly, we identified two r..., , , # Data from: Rewinding the ratchet: rare recombination locally rescues neo-W degeneration and generates plateaus of sex-chromosome divergence

[https://doi.org/10.5061/dryad.fj6q57435](https://doi.org/10.5061/dryad.fj6q57435)

These data are associated with the population genomic analyses in Decroly et al. (2024).

## Repeat intervals

The file `melanargia_ines.PT_MI_8.v2_0.sequences.red_repeats.bed` contains intervals of the genome identified as repeats using the software Red (Girgis, 2015).

## Gene annotation

The file `melanargia_ines.PT_MI_8.v2_0.sequences.red_repeats.augustus.gt.gff3` contains a gene annotation generated with braker2.1.5 (Hoff et al. 2019).

## VCF

The file `melanargia_ines.vcf.gz` contains filtered variant calls for 15 individuals sampled throughout Iberia and the Maghreb (see Decroly et al. 2024 for details).

## Callable intervals

The file `melanargia_ines.callable.bed.gz` contains intervals of the genome where genotypes are callable in a specific subset of i...