The Hypolimnas misippus genome supports a common origin of the W chromosome in Lepidoptera

Orteu, A.; McCarthy, S. A.; Hornett, E. A.; Gemmel, M.; Reynolds, L. A.; Warren, I. A.; Gordon, I. J.; Hurst, G. D. D.; Durbin, R.; Martin, S. H.; Jiggins, C. D.

doi:10.1101/2023.03.24.533969

bioRxiv · 10.1101/2023.03.24.533969

The Hypolimnas misippus genome supports a common origin of the W chromosome in Lepidoptera

Orteu, A.·McCarthy, S. A.·Hornett, E. A.·Gemmel, M.·Reynolds, L. A.·Warren, I. A.·Gordon, I. J.·Hurst, G. D. D.·Durbin, R.·Martin, S. H.·Jiggins, C. D.

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Abstract

Moths and butterflies (Lepidoptera) have a heterogametic sex chromosome system with females carrying ZW chromosomes and males ZZ. The lack of W chromosomes in early diverging lepidopteran lineages has led to the suggestion of an ancestral Z0 system in this clade and a B chromosome origin of the W. This contrasts with the canonical model of W chromosome evolution in which the W would have originated from the same homologous autosomal pair as the Z chromosome. Despite the distinct models proposed, the rapid evolution of the W chromosome has hindered the elucidation of its origin. Here, we present high-quality, chromosome-level genome assemblies of two Hypolimnas species (Hypolimnas missipus and Hypolimnas bolina) and use the H. misippus assembly to explore the evolution of W chromosomes in butterflies and moths. We show that in H. misippus the W chromosome has higher similarity to the Z chromosome than any other chromosome, which could suggest a possible origin from the same homologous autosome pair as the Z chromosome. However, using genome assemblies of closely related species (ditrysian lineages) containing assembled W chromosomes, we present contrasting evidence suggesting that the W chromosome might have evolved from a B chromosome instead. Crucially, by using a synteny analysis to infer homology, we show that W chromosomes are likely to share a common evolutionary origin in Lepidoptera. This study highlights the difficulty of studying the evolution of W chromosomes and contributes to better understanding its evolutionary origins. SignificanceButterflies and moths have a sex determination system in which females carry two different sex chromosomes, Z and W, while males carry two copies of the Z. The evolutionary origin of the W chromosome has been elusive, with many possible scenarios being suggested, such as the independent evolution of W chromosomes in many butterfly and moth species. Here, we present genome assemblies of two Hypolimnas butterfly species and use one of them to shed light on the evolution of the W chromosome. We show that W chromosomes across butterflies and moths are very similar which suggests a shared common origin.

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Orteu, A., McCarthy, S. A., Hornett, E. A., Gemmel, M., Reynolds, L. A., Warren, I. A., Gordon, I. J., Hurst, G. D. D., Durbin, R., Martin, S. H., Jiggins, C. D.. 2023-03-24. The Hypolimnas misippus genome supports a common origin of the W chromosome in Lepidoptera. https://doi.org/10.1101/2023.03.24.533969

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