Wednesday, August 6, 2008

Little Dudes: Culex molestus

Besides having a bitching name, the Culex molestus mosquito, which lives in the London underground tube network, is cool because it seems to have evolved extremely rapidly. According to this archived London Times article, the species that went underground over a hundred years ago when the tubes were first being constructed was Culex pipiens -- a species that preyed upon birds primarily. It has changed enough in these short years that it is now considered a whole new species.

The rapid evolution is partially thought of being dependent upon the environment in the tubes -- very good for mosquitos. There is plenty of water, steady temperature, and lots of mammalian prey. So, these mosquitos got to breed year-round and plentifully, increasing the rate of genetic mixing. This would, hypothetically, speed up evolution.

Culex molestus now fits the classic model of speciation, Allopatric or Geographic speciation, in which there is a physical barrier to breeding within one species (some are above ground some below, in this case) and over time different conditions in the two places cause different selection pressures and the species divides. An example of one difference between these mosquitoes is that the tube mosquitos prey almost exclusively on mammals now, including rats and mice, whereas Culex pipiens still preys primarily on birds.

The Biological Species Concept then comes into play as to whether the two populations of bugs are in fact two separate species. Simply, do they interbreed? In this case, the tube mosquitos and Culex pipiens can breed when intermixed, but it is very rare even under lab conditions which are specifically designed to encourage the behavior. This means that, functionally, they don't breed in nature. Boom, the hallmark of a separate species.

If you are a more visual person, here is a short video on the situation:

Enjoy evolution,


[photo via NSW health site]

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