The British swallowtail butterfly is the UK’s only native swallowtail and largest native butterfly. It may look similar to other swallowtails found across Europe, but its DNA tells a different story.A new study has found that the British swallowtail, also known as Papilio machaon britannicus, is a genetically distinct population that is found nowhere else in the world.The butterfly which is known for its light yellow-and-black wings with blue and red markings, is mainly found in the marshes and wetlands of eastern England, particularly the Norfolk Broads. Its survival is linked to a single plant called milk-parsley.Researchers carried out whole-genome resequencing on three British swallowtail butterflies and compared the results with existing genetic data from swallowtail populations across Europe and North Africa.They hoped to answer two big questions- whether the British swallowtail is truly a different lineage and whether its small habitat has resulted in harmful genetic decline over time.The results, published in the journal Insect Conservation and Diversity, revealed that the British swallowtail is genetically distinct. The study found that it has around 20% less genetic diversity than its European relatives.However, despite its limited range and lower genetic diversity, researchers found that the butterfly has not accumulated a large number of harmful mutations.At the same time, the study found significantly higher levels of inbreeding in the British population compared with swallowtail populations in mainland Europe. Researchers said this could create challenges for the butterfly’s long-term survival.The question of whether the British swallowtail is truly distinct has been debated for years. Although the butterfly is classified as vulnerable and is legally protected in the UK, its taxonomic status has remained uncertain.Researchers noted that this is not unusual. The genetic diversity of many insect species is still poorly understood because genetic studies often focus on identifying hidden species rather than measuring the genetic health of populations.In recent years, genetic research has helped scientists better understand swallowtail butterflies around the Mediterranean region. Earlier studies confirmed that the North African swallowtail Papilio saharae is a separate species even though it closely resembles the European swallowtail.Previous genetic studies of the British swallowtail produced mixed results. According to the researchers, clear genomic evidence is important because it helps conservation planners decide how best to protect small and isolated populations.For the new study, scientists collected DNA from three British swallowtails in the Norfolk Broads. They removed a tiny section from one foreleg of each live butterfly and then released the insects back into the wild. The team also collected DNA samples from swallowtails in Sweden and Russia for comparison.Rather than examining a small number of genetic markers, the researchers used whole-genome sequencing, which helped them to study complete genetic blueprint.The team then measured the amount of genetic variation in each population, checked for evidence of inbreeding and examined whether harmful mutations were building up over time.The findings showed that the British swallowtail population is both genetically distinct and isolated. Researchers estimated that its population size is about 8.8 times smaller than populations found on the European mainland. They also found that the British butterflies have nearly one-fifth of the genetic diversity seen in their continental relatives.One of the clearest signs of inbreeding was the presence of longer “runs of homozygosity.” These are long stretches of DNA where the genetic material inherited from both the parents are identical, mostly because the parents share a common ancestor.Researchers also used demographic modelling, a method that helps scientists study population history. While the analysis did not clearly show recent changes in population size, it suggested that there may have been limited gene flow between British and mainland European swallowtails in the past.The researchers said the study helps settle a long-running debate about the genetic uniqueness of the British swallowtail. They added that genomic research could become an important tool for conservation efforts, especially as climate change, habitat loss and intensive farming continue to put pressure on vulnerable butterfly populations.
