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Malaria-carrying mosquitoes might be splitting into new species

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malaria mosquito two types that might become different speciesBy any other name, the Anopheles gambiae mosquito would still bear—with its tiny buzzing wing beats—the deadly threat of malaria, which can be passed to humans in a single blood-sucking bite. But what if this species were to split in twain?

Two new studies, published online October 21 in Science, have found evidence that A. gambiae, which is one of the major carriers of the malaria parasite in sub-Saharan Africa, is evolving in two directions. The species has long been known to consist of several different subtypes of closely related mosquitoes. After careful genetic analysis, it appears that the Mopti (M) and Savanna (S) varieties of this insect might be on a path to become distinct species.

The two types are physically and developmentally "indistinguishable"—they have been observed "even flying in the same mating swarms," noted the researchers of one study. Only genetic differences reveal a difference between them.

"We can see that mosquitoes are evolving more quickly than we thought," Mara Lawniczak, of the Division of Cell and Molecular Biology at the Imperial College London and co-author of the first study, said in a prepared statement. She and her colleagues studied the genomes of the two varieties and detected more genetic differences between the two strains than would have been expected given their frequent geographical overlap.

The second group of researchers compared key genetic differences between these two A. gambiae types (in addition to the Bamako strain, which falls into the S subtype). Their study found that, based on genetic sites that seemed to have changed the most, the mosquitoes might be diverging in part due to habitat differences.

"It’s important to identify and monitor these hidden genetic changes in mosquitoes if we are to succeed in bringing malaria under control by targeting mosquitoes," Lawniczak said. Some 247 million people were infected with malaria as of 2008, according to the World Health Organization, and it is implicated in about one million deaths each year.

"Unfortunately, strategies that might work against one strain of mosquito might not be effective against the other," Lawniczak said. Nevertheless, a more refined picture of mosquito genetic makeup—and mutation—could lead to more targeted intervention in the future.

"Our studies help us to understand the makeup of the mosquitoes that transmit malaria," George Christophides, also of Imperial College London and co-author of the first study, said in a prepared statement. And that, in turn, they hope will help them "find new ways of preventing them from infecting people."

Image of two types of Anopheles gamiae mosquito courtesy of Jim Gathany/CDC

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  1. 1. frgough 11:08 am 10/22/2010

    Considering we don’t even have a mathematically precise definition of what a species is (the current method is for biologists to get together and take a vote), arguing that mosquitos are splitting into different species is a bit ridiculous.

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  2. 2. eosimias 6:39 pm 10/22/2010

    I believe frgough is being disingenuous. It is not true that biologist vote to decide on a when a species is a species. The standard definition of a species (at least sexually producing ones) says that organisms within a species are able to breed. In other words, genes within a species should be able to freely exchange across the population. If you have two subspecies that no longer freely exchange genes amongst the population, even though they inhabit the same geographic location, then one can begin to consider them two separate species. My understanding from this article is that this is exactly what has been observed.

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  3. 3. eosimias 4:05 am 10/23/2010

    Sorry for the typo. I meant "sexually reproducing ones".

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  4. 4. Daniel35 2:52 pm 10/23/2010

    But eosimias, aren’t there often some individuals within one species that can interbreed with some in other species? Where do you draw the line in these cases? I’m one for drawing fewer lines, thinking less in categories and more in continua, spectra and gradations.

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  5. 5. eosimias 3:00 pm 10/23/2010

    Daniel35, Do you have examples? The offspring of interbreeding have to be themselves fertile, for them to be considered within the same species. Donkeys and horses can produce offspring, but their offspring, mules, are not fertile. Thus, the genomes of donkeys and horses do not actually mix in the population at large. I’d love to hear of examples of interbreeding between individuals of different species, which result in viable, fertile offspring.

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  6. 6. ItsMe 7:13 am 10/24/2010

    The word "species" does seem to be a human construct, and not an actual reality.

    By your definition of species allopatric species shouldn’t happen, but most "species" of plants are thought to arise this way.

    What about other types of reproductive isolation, besides breeding within your "species"? For example: "species" that reproduce asexually. E.coli or any other bacteria is a good example. Applying the biological species concept to these guys gets problematic.

    Dogs are considered a subspecies of the wolf, but should they be? They are reproductively isolated, in that wolves eat dogs, but if locked in a cage together they get bored… have nothing else to do… and fertile puppies are born. In the wild the chance of these two having puppies is slim to none. There is probably little to none genetic flow between these two in the wild.

    There are lots of problems with the biological species concept and these are only a few off the top of my head. This is why I think that "species" is a word made by humans because we like to categorize everything, and not a word that actually means anything.

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  7. 7. eosimias 10:00 am 10/24/2010

    Dear ItsMe! While I would agree that most taxonomic or biological classifications (i.e. genus, class, family, phylum, etc) are human constructs, this is somewhat less so for the concept of a species. Undoubtedly, classifying species which only reproduce asexually becomes problematic (actually some bacteria can reproduce sexually). This is also true when considering species across time or even across space (i.e. allopatric species). However this is not the case for sympatric species (such as the case described in this article), which coexist in the same location and time. I do not see your logic, which says that according to my definition allopatric species shouldn’t happen. The fact that species occupy different areas and do not exchange genetic information does not, in of itself, mean that they are different species. This could, of course, over time result in speciation, but just the act of being separate does not make them different species. I doubt any biologist would say it did. However, if two subspecies coexist within the same geographic location, but they no longer breed with each other, then this CAN be considered the beginnings of a speciation event. What could cause two subspecies to become genetically isolated, even when they occupy the same geographic location? The answer can be changes in behavior, such that male and females of the different subspecies no longer mate. Or perhaps, the cause could be translocations or other chromosomal changes, which would render hybrids of the two subspecies no longer fertile, etc. It is true that dogs are considered a subspecies of the wolf, but this is so because dog / wolf hybrids can produce fertile offspring. The fact that interbreeding might not occur in the wild does not mean that they are two separate species. Having said that, the fact that they would be unlikely to breed naturally in the wild could make them genetically isolated and, as such, could result in the beginnings of speciation between these two subspecies of Canis lupus. Over time, genetic changes in each subspecies might accumulate to the extent that the two would no longer be able to produce viable, fertile offspring. This has not yet happened, so they are still considered the same species.

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  8. 8. eosimias 4:13 pm 01/9/2011

    I found an interesting article on the issue of speciation, and when should one call two separate subspecies two separate species. It seems quite relevant to the discussions we have had, so here it is:

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