London Underground mosquito

The London Underground mosquito is a species of mosquito in the genus Culex found in the London Underground. It is thought to have evolved from the overground species Culex pipiens recently.^[when?] Biologists named the London Underground mosquito Culex pipiens molestus due to its voracious biting. Notably the London C.p. molestus assaulted Londoners sleeping in the Underground during the Blitz,^[1] although similar populations were already known. The name seems to already have been given to a species of mosquito found in Australia, named as long ago as 1775.^[2] The London Underground mosquito, although first discovered in the London Underground system, has been found in underground systems around the world. It is suggested that it may have adapted to human-made underground systems since the last century from local above-ground Culex pipiens,^[3] although more recent evidence suggests that it is a southern mosquito variety related to Culex pipiens that has adapted to the warm underground spaces of northern cities.^[4]

The evidence for this mosquito being a different species from Culex pipiens comes from research by Kate Byne and Richard Nichols. The species have very different behaviours,^[1] are extremely difficult to mate,^[3] and with different allele frequency consistent with genetic drift during a founder event.^[5] More specifically, this mosquito, Culex pipiens molestus, breeds all-year round, is cold intolerant, and bites rats, mice, and humans, in contrast to the above ground species Culex pipiens that is cold tolerant, hibernates in the winter, and bites only birds. When the two varieties were cross-bred the eggs were infertile suggesting reproductive isolation.^[1][3]

Since that paper more information has accumulated. The fundamental results still stand: the genetic data indicate that the molestus form in the London Underground appeared to have a common ancestry, rather than the population at each station being related to the nearest above-ground population (i.e. the pipiens form). Byrne and Nichols' working hypothesis was that adaptation to the underground environment had occurred locally in London once only – since there are many hurdles to jump in order to become adapted to the subterranean environment, it is understandable that it would occur rarely. This hypothesis implies that local adaptation would be expected in different locations around Europe and beyond, as each local pipiens population evolved an offshoot that overcame the problems of living underground.

However, more recently-collected genetic evidence suggests that a single molestus form has spread throughout Europe and beyond, since populations over a large area share a common genetic heritage. These widely separated populations are distinguished by very minor genetic differences, which suggest that the molestus form developed recently: a single mtDNA difference shared among the underground populations of ten Russian cities;^[6] a single fixed microsatellite difference in populations spanning Europe, Japan, Australia, the middle East, and Atlantic islands.^[4] This worldwide spread might have occurred after the last glaciations or be even more recent, due to the insects hitch hiking on world trade routes. One possibility is the international second-hand tire trade. The tires retain water in which the larvae can survive (Completely removing water from an old tire can be difficult).

What has always been more intriguing about the molestus story was that the reproductive isolation in north European populations appears to be almost complete, whereas there is clearly gene flow between them in populations to the south. Byrne and Nichols attributed this pattern to the inability of the underground form (and perhaps their hybrids) to survive above ground in harsh northern winters.

Now it appears that the persistence of hybrids in northern climates may be another evolutionary problem that can be solved but only rarely: the Fonseca paper obtained genetic evidence that the recent colonization of America by Culex mosquitoes actually involves a strain derived from a rare successful hybridization between pipiens and molestus. They suggest that hybridization may explain why the American form bites both birds and humans (this interpretation is controversial, see letter from Spielman et al.^[7] and the response that follows it in Science). The consequences of this more indiscriminate feeding hit the news in 1999 with the outbreak of human encephalitis in New York, caused by West Nile virus. It was the first documented introduction of this virus into the Western Hemisphere; perhaps because in the longer established populations the old world northern above-ground pipiens almost exclusively bite birds, the human biting ones being incarcerated below ground.

New York outbreak

In the summer of 2011, an invasion of Culex Pipiens Molestus appeared on the Upper West Side in the borough of Manhattan, New York City. The mosquito is well known for being in commonly found in sewers of New York and thrive throughout the year feeding off of humans. Residents of older bownstones found the mosquitos coming from the underground into basements and then through air vents and other openings into the homes. The city government did not make this infestation of the pest a top priority because they tested negative for West Nile Virus and the high cost of mosquito control.^[8]

See also

• Nylon-eating bacteria
• E. coli long-term evolution experiment
• Radiotrophic fungus
• Urban wildlife

References

1. ^ ^{a b c} Alan Burdick (2001). "Insect From the Underground - London, England Underground home to different species of mosquitos". Natural History. http://findarticles.com/p/articles/mi_m1134/is_1_110/ai_70770157. 
2. ^ "Culex molestus Forskal, 1775". Discover Life. University of Georgia. http://pick4.pick.uga.edu/mp/20q?search=Culex+molestus&guide=Culicidae. 
3. ^ ^{a b c} "London underground source of new insect forms". The Times. 1998-08-26. http://www.gene.ch/gentech/1998/Jul-Sep/msg00188.html. 
4. ^ ^{a b} Fonseca DM, Keyghobadi N, Malcolm CA et al. (March 2004). "Emerging vectors in the Culex pipiens complex". Science 303 (5663): 1535–1538. doi:10.1126/science.1094247. PMID 15001783. http://www.mosquitocatalog.org/files/pdfs/wr380.pdf. 
5. ^ Byrne K, Nichols RA (January 1999). "Culex pipiens in London Underground tunnels: differentiation between surface and subterranean populations". Heredity 82 (1): 7–15. doi:10.1038/sj.hdy.6884120. PMID 10200079. 
6. ^ Vinogradova EB and Shaikevich EV (2007). "Morphometric, physiological and molecular characteristics of underground populations of the urban mosquito Culex pipiens Linnaeus f. molestus Forskål (Diptera: Culicidae) from several areas of Russia European Mosquito Bulletin". Journal of the European Mosquito Control Association 22: 17–24. ISSN 1460-6127. 
7. ^ Spielman A, Andreadis TG, Apperson CS et al. (November 2004). "Outbreak of West Nile virus in North America". Science 306 (5701): 1473c–1475c. doi:10.1126/science.306.5701.1473c. PMID 15567836. 
8. ^ Carlin, Dave (November 3, 2011). "Exclusive: Upper West Side Mosquito Mystery". CBS New York (CBS Local Media). http://newyork.cbslocal.com/2011/11/03/exclusive-upper-west-side-mosquito-mystery/. Retrieved November 4, 2011.