The northern house mosquito, commonly thought to have evolved in the London Underground, actually has roots tracing back to the Mediterranean, according to a new genetic study published in the journal Science, reports BritPanorama.
The myth surrounding this mosquito originated during World War II, when Londoners taking refuge from German air raids in subway stations endured bites from these pests. Over the decades, biologists proposed that the mosquitoes were adapted to the subterranean environment of the Tube.
This mosquito exists in two forms: one, Culex pipiens form pipiens, bites birds and inhabits open air; the other, Culex pipiens form molestus, primarily bites humans and thrives underground. It was previously hypothesized that the latter variant had evolved specifically to occupy London’s metro system.
“That theory was made really famous by a genetic study published in 1999, which claimed, based on what I would say was limited evidence, that the ‘London Underground mosquito’ seemed to have evolved (on site) from an aboveground population,” said Yuki Haba, a postdoctoral researcher at Columbia University and lead author of the new study. The latest research challenges this view, showing that molestus did not rapidly evolve underground but has a much longer history.
Haba and colleagues analyzed the DNA sequences of hundreds of mosquitoes globally, including historical samples from World War II. Their findings indicate that the lineage of molestus developed far earlier in history than previously thought.
“It’s a lot older than the London Tube, and it seems to have evolved around the Mediterranean region, particularly in the Middle Eastern region,” Haba explained. The divergence between the aboveground pipiens and the underground molestus could have occurred as early as 10,000 years ago or as recently as 1,000 years ago, with the most likely timeframe being between 3,000 and 2,000 years ago.
Migrating north
The research team began their investigation into the “London Underground mosquito” hypothesis in 2018. They reached out to authors of previous papers and sourced samples from 50 countries. Due to restrictions, they could not collect live specimens from the London Underground itself; instead, they used historical samples from the Natural History Museum in London, analyzed by the Wellcome Sanger Institute.
Ultimately, the researchers analyzed 357 contemporary mosquito specimens and 22 historical specimens, amassing a total of about 800 samples from various studies.
“Our data shows that molestus is descended directly from pipiens populations that still thrive in the Mediterranean region,” noted Lindy McBride, a senior author of the study and associate professor of evolutionary genomics at Princeton University. This suggests the mosquito evolved at Mediterranean latitudes but likely originated from the Middle East, an area too arid for the bird-biting variant.
At that time, the development of agricultural communities using irrigation systems provided suitable breeding grounds for the mosquito. Additionally, historical documentation indicates that molestus was first described as a distinct species in Egypt in 1775, and evidence suggests it was present in Southern Europe by the 1800s.
“This sequence of detection suggests that molestus traveled north, finding refuge underground in colder climates, whereas it could only survive in warmer areas without access to subterranean environments,” McBride added.
Mosquito opportunities
Richard Nichols, a genetics professor at Queen Mary University of London and co-author of the 1999 study, expressed that the new research, while presenting different conclusions, contributes to scientific understanding. He emphasized how the 1999 study showed underground mosquitoes had distinct genetic traits suited for surviving in confined spaces.
Finally, Cameron Webb, an associate professor of medical entomology in Australia, highlighted that the new findings shed light on how these mosquitoes adapt to urban environments. He cautioned that as city designs evolve due to climate change, it is crucial to understand these adaptations to prevent increased health risks associated with mosquitoes.
