Urbanization-associated range expansion genetically homogenizes a butterfly species

The appearance of invasive species putting native species under pressure is a common cause forbiodiversity loss. Genetic diversity may also be lost within species, however, when a populationbecomes expansive and mixes with native local populations. We address this scenario in ahistorically sedentary butterfly species in which a population has become invasive across CentralEurope in tight association with urbanization. Based on genome-wide sequence data fromhistorical museum specimens and contemporary samples from the same sites, we demonstratethe erosion of historical native populations by genetic mixing with the invasive population. Thismixing causes the loss of unique genetic variation and the spread of ubiquitous genetic variationwithin the species. Our study illustrates that human-driven environmental change can result in thecryptic decline of biodiversity within a species despite geographic range expansion.