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Species of microbe begins to diverge in Russian hot spring - Scientists literally watch as a single-celled microorganism population evolves into two distinct spe

By Mali Wiederkehr | February 22, 2012

Evolutionary biologists may as well ditch their books and race to Russia, where they can now observe the live-action speciation of a single-celled microbe population known as Sulfolobus islandicus. Speciation is the evolutionary process by which new species form, and in this case, it means that Sulfolobus islandicus is on its way to becoming two distinct, new species.
Differentiating between species is a challenging business. In sexually reproducing organisms, a species is primarily defined by the ability of its members to mate with one another and exchange genetic information. For instance, humans and chimpanzees are considered two separate species because their members cannot produce viable offspring. Although evolution holds that these two species once shared a common ancestor, significant genetic differences now render them as separate.
Classifying species becomes more tricky when one ventures into domains of life that reproduce asexually or by cloning. These species do not mate with other organisms in their population and are, therefore, difficult to distinguish from one other. Scientists classify asexual species using other criteria, including morphological (or structural) differences, behavior observation and DNA sequencing.
Sulfolobus islandicus falls into this "difficult to classify" category because it belongs to the domain known as Archaea, whose organisms reproduce asexually. In addition to being asexual, archaeons are single-celled microbes that live in extreme environments. Scientists found Sulfolobus islandicus living on a Russian volcano, in a spring full of boiling, acidic water.
Although they live in the same water, some organisms belonging to Sulfolobus islandicus began to show marked genetic changes, and scientists noticed that the shared portions of their genome were decreasing with time. This led them to believe that Sulfolobus islandicus is diverging into two species, which they termed the Red and Blue groups.
The scientists concluded that the microbes were structurally identical. However, after observing the archeon behavior, they noticed that organisms belonging to the Blue group grew less rapidly than those in the Red and that Blue group's colonies were subsequently less dense.
After collecting strains of Sulfolobus islandicus from the hot spring, they sequenced the microbes' genome and examined their evolutionary relationships. They noticed that the highest difference between the genomes of any two strains totaled to a mere 0.35 percent. Despite being so similar, the strains were telling of a clear movement towards two species, with each individual analyzed bearing a resemblance toward only some of the members.
Furthermore, the scientists found that microbes only shared their DNA with some of the members of Sulfolobus islandicus. Namely, they observed that the Blue group began to donate less DNA to the Red one. This was another clue that led them to believe that speciation was indeed taking place.
It may seem surprising that microbes can share DNA despite being unable to sexually reproduce. Unlike organisms, who share genetic information through sexual reproduction, however, microbes exchange DNA through a process known as lateral gene transfer. This method of gene transfer stands in contrast to vertical gene transfer, where genes are passed from parents to offspring.
Scientists are perplexed as to why Sulfolobus islandicus is rapidly evolving into two separate species. The most common reason for speciation is that organisms become separated by a geographic barrier, such as a mountain or a river, and are subsequently subjected to different selection pressures, thus causing them to evolve.
The quintessential example of this phenomenon, known as allotropic speciation, concerns Darwin's finches of the Galapagos Islands. The finches used to share a common ancestor but evolved into separate species after migrating to different islands where they experienced selection pressures like new food sources.
In contrast to the finches that underwent allotropic speciation, Sulfolobus islandicus is evolving in one geographic region under the same environmental conditions. This form of speciation, called sympatric speciation, is more difficult to account for and is undergoing further scientific investigation. According to Rachel Whitaker, lead author of the study from the University of Illinois, this is the first known example of sympatric speciation in a microorganism. She believes that the study highlights the extensive genetic diversity that occurs in microbial populations.

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