For the first time the whole genome of the British Swallowtail (Papilio machaon britannicus) has been sequenced (Ref). The genome-wide analyses demonstrates that the British Swallowtail butterfly is genetically isolated and distinct from other Papilio machaon populations. This supports its status as a valid subspecies and justifies special conservation efforts.
The major molecular study reveals several key points about the genetics of Papilio machaon britannicus that are directly relevant to its informed conservation:
- There is evidence of genetic drift and reduced genetic diversity, and some evidence of inbreeding.
- there has been some gene flow with continental subspecies – however, the genomic distinctiveness of britannicus (currently) remains differentiated
- there is no evidence of increased genetic load (deleterious mutations)
This is overall good news regarding the status of what is a small population, or group of populations, confined to the Norfolk Broads.
Principal component analysis of genetic variance made with 10% of the SNP randomly selected. The figure shows the difference between Papilio machaon (from Europe to Lebanon) and on the first axis, and the difference between the subspecies is represented along the second axis. The data for Papilio machaon britannicus is on the far right of the figure.
Photo credit. Martin Partridge/Swallowtail & Birdwing Butterfly Trust
Additional work included in this study includes a through whole-genome sequencing of Papilio machaon populations across Europe. We demonstrate that Papilio machaon britannicus forms a genetically distinct and isolated lineage. In contrast, continental subspecies, such as Papilio machaon machaon, Papilio machaon gorganus and Papilio machaon aestivus, are genomically indistinguishable and should be considered a single, widespread subspecies.
Reference
Nabholz, B., Reboud, E.L., Lafon, B.J., Cotton, A.M., Partridge, M.G., Collins, N.M., Condamine, F.L. (2026)
Endemic but not eroded: Genomic distinctiveness and conservation genomics of the British swallowtail butterfly (Papilio machaon britannicus). Insect Conservation and Diversity, 1–15. Available from: https://doi.org/10.1111/icad.70102
