A new genetic study overturns the myth of the “London Underground Mosquito,” revealing that this common urban insect originated not below the cities of modern Europe, but in ancient Mediterranean civilizations more than a thousand years ago, according to a new study. Modern cities are reshaping ecosystems, driving rapid adaptation in many species. A striking example is the northern house mosquito, Culex pipiens, which exists in two forms: the bird-biting C. pipiens f. pipiens (pipiens), adapted to open-air, seasonal environments, and the human-biting C. pipiens f. molestus (molestus), which thrives in urban belowground spaces. Molestus mates in confined areas, remains active in winter, bites humans, and can lay eggs without a blood meal, yet is morphologically indistinguishable to pipiens. This species is also known to be a potent vector for several mosquito-borne diseases, including West Nile virus. The origin of molestus is debated, however. One hypothesis suggests that it evolved rapidly in the London Underground during World War II. However, historical records describe molestus-like mosquitoes in European cellars and Mediterranean aboveground habitats far earlier and perhaps centuries before the rise of modern cities. Too better understand the origin of molestus, Yuki Haba and colleagues sequenced the whole genomes of 357 C. pipiens mosquitos (both contemporary and historical samples) from across Europe and North Africa. Their findings reveal that molestus did not evolve rapidly in northern European subways or within the last few centuries. Instead, genomic evidence shows that molestus adapted to human habitats aboveground environments in the Mediterranean or Near East over a period of a thousand or more years, possibly in association with the rise of early dense agricultural settlements along the banks of the Nile in Egypt. Key traits enabling urban belowground success, such as biting mammals, mating in confined spaces, and laying eggs without a blood meal, were present in these ancient aboveground populations, arguing for the importance of preexisting traits in urban adaptation. While ancient origins primed molestus for urban environments, additional modern evolution likely occurred after colonizing subterranean urban habitats, Haba et al. note. These findings underscore that adaptation to human-altered environments can build on traits evolved long before modern cities and may involve multiple, independent colonization events globally. In a related Perspective, Jason Munshi-South and Ann Evankow discuss the study in greater detail.
