We've probably all heard about bacteria that "develop" a resistance to drugs. Often it turns that the resistence is the result of a genetic information-loss that makes the bacteria less robust in general, but which happens to confer an advantage against certain drugs.
is a recent article from Nature (in turn reporting on an article in PNAS) about mosquitoes that have "evolved" a resistance to DEET -- a component used in many insect repellents. In fact, the trait was bred rapidly, going from 13% to 50% of the population in a single generation under controlled breeding. This suggested that the DEET resistance was a dominant trait, and that there was probably only a single gene involved. So have these mosquitoes somehow evolved to become a superior breed of bug? Not from what I can tell.
First of all, why are mosquitoes repelled by DEET? According to wikipedia
, it seems that mosquitoes really don't like the smell for some (unknown) reason. Mosquito antennae have special sensor cells that are triggered by DEET.
More recent evidence shows that DEET serves as a true repellent in that mosquitoes intensely dislike the smell of the chemical repellent. A type of olfactory receptor neuron in special antennal sensilla of mosquitoes that is activated by DEET as well as other known insect repellents... has been identified.
But what about these "resistant" mosquitoes? According to Nature:
The researchers have not identified the gene that they propose is responsible for DEET resistance, or precise details about its workings. They did, however, find a type of odour-sensing cell that responds to DEET in most mosquitoes but is less sensitive to the repellent in the resistant ones.
The team found that odour-sensing cells in general were less sensitive
to DEET in resistant females compared with cells in nonresistant females. But they also spotted one type of neuron that showed distinctly lower responses to high DEET concentrations in the repellent-insensitive females. Any gene responsible for this effect might alter that cell so that it could not recognize DEET or it might mutate an odorant-binding protein that delivers DEET to a receptor, the team speculates.
Amazing! These supposedly-evolved super-mosquitoes actually have less-functional sensors! No new features or systems have been gained. Instead, an existing one has been lost. That's not called evolution; that's called de-evolution. In fact, it's called "breaking stuff". These mosquitoes have a mutation that results in the loss of genetic information, which then breaks their DEET detectors. This allows them to ignore the insect repellent, but only at the cost of a fully-functioning sensory system. As usual, mutations are a destructive force, not a creative force.