Many people are aware of stories of 'tube mice', but there is another species that are not so well known for there Underground homes.
The London Underground mosquito is a genetically distinct subspecies. It was first reported during the Blitz of World War 2, when the Tube's tunnels were used as overnight bomb shelters. Over the course of the war, almost 180,000 people sheltered in the Underground. They were ravaged by all sorts of insects.
"The Tube then was a very different place than it is now," says Steven Judd, Head of Environment for the London Underground. With standing water and different pest controls, flies, ticks, lice and fleas were a lot more common than they are now, he says. After the war, other that occasional complaints of bites, made by mainly maintenance workers, these sub-terrarium insects were given little attention.
UNTIL NOW!
Katherine Byrne decided to study these animals as part of a doctoral study. collecting mosquito's from a range of 7 sights, over 180 KM ranging network. The mosquito's that were collected underground were found to be fundamentally different to their surface dwelling relations, the Culex pipiens on the surface is known to feed on birds, he underground mosquitoes were classified as Culex pipien molestus - named primarily due to the fact they 'molest' people, for there blood.
Whilst these species look very similar to each other they have complacently different behaviors, for example while the surface mosquitoes form big swarms in order to pair off and breed, underground ones are not as abundant so it is just individuals who choose each other to mate.
"These differences can be interpreted in a straightforward way as adaptations to a subterranean life," wrote Byrne. Since there were no birds to feed on, they began feeding on mammals, mostly rats and humans. They mated in closed areas, because they had to – and they lost their tendency to hibernate in winter because there are no obvious seasons underground. The reason for these separations is due to when the Underground systems construction finished the tunnels were largely sealed off from the surface, with some mosquitoes becoming trapped, with this physical barrier preventing breeding causing a divergent evolution to occur within the last 100 years.
Byrne also found the underground mosquitoes are now so distinct they can no longer interbreed with other mosquitoes.
"There are differences in both the mating behaviour and the reproductive biology," says David Reznick, a biologist at the University of California in Riverside.
"People usually think of speciation as being very slow and as something you can't see happening," says Reznick. "But in this example, you can sort of see it happening. It's a relatively recent phenomenon and you can see a clear start date" – when construction of the London Underground began in 1863.
Not everyone is convinced though.
"It's unclear if it evolved there or was brought into the Underground system… from the freight and fruit movement into the docks of London," says Judd. There is not enough research to give us an indication, he adds.
What is clear is that the molestus mosquito is not unique to the London Underground, says Gomes.
It is actually found in all sorts of human underground constructions, from water systems to the basements of large houses. It has been found in similar enclosed environments, such as caves and sewers, across Western Europe, particularly temperate countries such as Spain and Portugal. It is also found in metropolitan Tokyo and in the New York subway.
Still, Reznick argues there are a number of genetic factors that suggest the underground mosquito first evolved in London.
For instance, Byrne's research involved sampling 12 surface mosquito populations near Underground sites. She compared the genetic makeup of overground and underground mosquitoes and found their alleles, or gene variants, to be incredibly similar.
"If they [the subterranean mosquitoes] had come from Spain, you would expect them to have distinct alleles to those above ground," says Reznick. The underground insects should then have been most closely related to Spain's above-ground mosquitoes. But this was not the case: London's underground and overground mosquitoes are each other's closest relative.
What's more, the Underground mosquitoes are all quite genetically similar.
"If you have a big population of humans and then 20 go and colonise an island somewhere, the colonisers will only have genes that are a small subset of the initial population," says Reznick.
A few hundred years in the right circumstances can form a new species
The underground mosquitoes are so similar to each other that it "suggests a small number of genetic individuals created this population", he says.
I just love that it happened on Darwin's own turf and began almost the same year he wrote his book
Still, with no one having examined the London Underground mosquito since Byrne in the late 1990s, he says work needs to be done to bring our understanding up to scratch. "The genetic tools that they were using aren't the ones we'd use today. The truth is – it would be nice if someone studied the mosquitoes more closely."
While Reznick has followed this speciation process in a number of organisms – from moths to flies to invasive plants – the London Underground mosquito has such a special spot in his heart that he devoted a chapter to the insects' evolution in a 2010 book he wrote on the subject of Darwin's 1859 classicOrigin of Species.
"I just love that it happened on Darwin's own turf and began almost the same year he wrote his book."