British swallowtail split from European cousins much earlier than thought, study finds — SkimNews
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- Papilio machaon britannicus separated from continental swallowtails 200,000 to 1.7 million years ago — far earlier than the 8,000 years since Doggerland's flooding previously assumed — according to whole-genome sequencing published in Insect Conservation and Diversity.
- Mark Collins, president of the Swallowtail and Birdwing Butterfly Trust and study co-author, argues britannicus's distinctiveness justifies conservation over introducing the continental gorganus, which could hybridise britannicus out of existence.
- The study detected inbreeding in britannicus populations but concluded they carry no damaging mutations, suggesting the subspecies is not genetically inviable despite being confined to the Norfolk Broads.
- Rising seas are salinating the Norfolk Broads and killing milk parsley — britannicus's sole larval food plant — making translocation to protected inland wetland sites urgent.
- The continental gorganus subspecies is increasingly reaching Britain via warmer climates and regularly breeds in Kent and Sussex during fine summers, with some lepidopterists arguing eventual hybridisation is inevitable.
- Collins described britannicus as 'a relict population...not just a relict for Britain but a relict from a once much wider distribution in wetlands across Europe,' with candidate translocation sites including Lakenheath (Suffolk), Shapwick (Somerset), and Yorkshire wetlands.
Why it matters: The genetic finding reframes britannicus as an ancient, irreplaceable lineage rather than a recent wetland variant — bolstering arguments against introducing continental swallowtails and for funding active translocation programmes. The binding extinction constraint is loss of milk parsley, britannicus's sole larval food plant, to saline intrusion in the Norfolk Broads as sea levels rise.
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