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

A recent study has revealed that the British swallowtail butterfly, Papilio machaon britannicus, has been a distinct subspecies for at least 200,000 years, much earlier than previously thought. This subspecies is found only in the Norfolk Broads in Britain and is characterized by its smaller size and darker color compared to its continental cousins. The study, which involved whole-genome sequencing of swallowtail populations across Europe, suggests that britannicus may have once been more widely distributed in north European wetlands, but is now confined to a small area due to rising sea levels and habitat loss.

The findings of the study have significant implications for conservation efforts, as britannicus is vulnerable to extinction due to its limited range and specialized habitat requirements. The caterpillars of britannicus only feed on a rare wetland plant, milk parsley, which is also threatened by rising sea levels and salination of the Norfolk Broads. To ensure the survival of britannicus, conservationists will need to identify new wetland sites that are protected from rising seas and can support the growth of milk parsley.

The study's results also challenge the idea that introducing the continental swallowtail, Papilio machaon gorganus, into Britain could help increase the population of swallowtails in the country. Some experts had suggested that introducing the continental subspecies could lead to hybridization and potentially wipe out the britannicus subspecies. However, the study's authors argue that britannicus is a unique and valuable part of Britain's natural heritage, and that conservation efforts should focus on protecting and preserving this subspecies.

The president of the Swallowtail and Birdwing Butterfly Trust, Mark Collins, emphasized the importance of conserving britannicus, stating that it is a "relict population" that is not just unique to Britain, but also a remnant of a once wider distribution in wetlands across Europe. Collins argued that britannicus can survive in wetlands if given a helping hand, and that hybridization with the continental subspecies may occur on the fringes, but the subspecies can endure if its habitat is preserved.

The study's findings highlight the need for urgent conservation action to protect britannicus and its habitat. Rising sea levels and global heating are major threats to the survival of this subspecies, and conservationists will need to work to identify and protect new wetland sites that can support the growth of milk parsley and the survival of britannicus. By taking action to conserve this unique subspecies, Britain can help preserve its natural heritage and ensure the long-term survival of the British swallowtail butterfly.

The conservation of britannicus will require a coordinated effort to identify and protect suitable habitats, as well as to introduce the butterfly to new sites. The study's authors are already planning a project to identify the best sites for conservation and to introduce britannicus to these areas, with potential sites including Lakenheath in Suffolk, Shapwick in Somerset, and sites in Yorkshire. By working to conserve britannicus, conservationists can help ensure the long-term survival of this unique and valuable subspecies.