British swallowtail split from European cousins much earlier than thought, study finds

The British swallowtail. Papilio machaon britannicus, is found nowhere else in Europe and is vulnerable to extinction. Photograph: Geoff du Feu/Alamy View image in fullscreen The British swallowtail. Papilio machaon britannicus, is found nowhere else in Europe and is vulnerable to extinction. Photograph: Geoff du Feu/Alamy British swallowtail split from European cousins much earlier than thought, study finds Finding that Norfolk butterfly has been distinct subspecies for 200,000 years could transform conservation approach The endangered swallowtail butterfly Papilio machaon britannicus , which is only regularly found breeding in Britain on the Norfolk Broads, has been a distinct subspecies for at least 200,000 years, according to a study. Smaller, darker in colour and much rarer than the continental swallowtail, britannicus was previously considered to have developed its distinctive form during its confinement in the wetlands of eastern England over the last 8,000 years, after the flooding of Doggerland. But the new genetic study suggests britannicus is a wetland specialist and may have once occurred much more widely in north European wetlands, separating from its continental cousins between 200,000 and 1.7m years ago. Nominate your invertebrate of the year Read more The whole-genome sequencing of swallowtail populations across Europe, published in Insect Conservation and Diversity , found some evidence of inbreeding in britannicus but concluded that its surviving populations were not suffering from damaging mutations. The study is likely to transform conservation approaches to the swallowtail in Britain. Some butterfly experts have recently argued that the continental swallowtail, Papilio machaon gorganus , which is much more common because its caterpillars feed on a variety of plants including fennel and wild carrot, could be introduced into Britain and become much more widespread, potentially hybridising the “less successful” britannicus out of existence. But Mark Collins, the president of the Swallowtail and Birdwing Butterfly Trust and a co-author of the paper, said the genetic distinctiveness of britannicus made it worthy of a renewed conservation effort. Britannicus is found nowhere else in Europe and is vulnerable to extinction because global heating is causing rising sea levels that threaten its freshwater wetland habitats. “We’re looking at a relict population in the Norfolk Broads that’s not just a relict for Britain but a relict from a once much wider distribution in wetlands across Europe,” Collins said. “ Britannicus is part of our own natural heritage, it’s protected by law for good reason because it’s a unique thing, and we should not allow it to be wiped out.” View image in fullscreen Papilio machaon britannicus feeding on thistle flower. Photograph: Kevin Elsby/Alamy In the wild, the caterpillars of britannicus will only reliably eat a rare wetland plant, milk parsley, which is the reason the butterfly is so scarce in Britain. B