Dear Readers, I was much taken by an article in New Scientist about the evolution of urban species by Rob Dunn this week, and in particular his thoughts about the infamous London Underground mosquito. During the Second World War, unfortunate civilians who spent nights on the platforms of Underground stations to avoid the Blitz complained about being bitten unmercifully, but it’s only recently that genetic technology has advanced to a point where we can really work out what’s going on.
The original LU Mosquito came from the Fertile Crescent in the Middle East and lived above ground. These insects are active only during the warmer months, require a meal of blood before they can reproduce, and feed mainly on the blood of birds. However, as the mosquito spread north into colder climes, it survived by living in cities, particularly their underground regions such as sewers. The insect evolved new genetic characteristics, such as odour recognition, digestion and immunity, that would be useful in environments rich in organic waste.
However, it wasn’t just the genes that changed, behaviour did too. Both the underground and the above-ground mosquitoes are thought to be the same species, but the underground ones are active all year round, can reproduce without a blood meal, and prefer to feed on mammals: rats and mice in particular, but humans where they can find them. The underground mosquitoes are isolated from other mosquitoes, and their habitat can be compared to an island, as Dunn points out: the mosquitoes cannot disperse, and so they become more and more specialised. Cities such as Paris, Minsk, Tokyo and New York all have their own ‘Underground Mosquitoes’.
However, the isolation can have another, even more extreme, effect – it’s been shown that where LU Mosquito populations are isolated within the Underground network, they can start to become genetically distinct from one another. So, it was found that the mosquitoes found on the Victoria Line were different from those found on the Bakerloo Line. It’s quite possible that every underground line could have its own mosquito, though I suspect that lines with a larger proportion of stations which are above ground might be less distinct, because their mosquitoes can actually disperse and interbreed.
For us, though, as humans, it means that the old Petula Clark song ‘Don’t Sleep in the Subway’ has never been better advice.