Termites and teeth bacteria

A German scientist has solved the mystery of Namibia’s “fairy circles”, rings of perennial grasses with a bare centre, which persist for decades in extremely arid territory.

A sand termite called Psammotermes performs this feat of “ecosystem engineering”, according to a paper by Norbert Juergens of the University of Hamburg in the journal Science. Studying fairy circles over a wide area, he found that the termites were the only organism present in every ring, young or old.

The rings form because termites eat the roots of shortlived grasses and other plants, preventing them establishing themselves within the ring. Without vegetation, rainwater is not lost by evaporation through plant leaves but instead is stored within the sandy soil. This water sustains the termites during the dry season while allowing a ring of longer-lived perennial grasses to grow outside the barren circle.

Once established, the fairy circles are a magnet for other species of plant and animals. Like oases in the desert, they increase biodiversity at least tenfold. “Psammotermes turns wide desert regions of predominantly ephemeral life into landscapes dominated by species-rich perennial grassland,” Juergens says.

An oral history

Teeth bacteria are the latest organisms to be studied through “ancient DNA” technology, which allows scientists to extract and amplify tiny traces of genetic material from specimens thousands of years old. The conclusions are bad news for modern oral health.

An international team led by Alan Cooper of the University of Adelaide extracted DNA from tartar (calcified dental plaque) from 34 north European skeletons, spread over 7,500 years, from the last hunter-gatherers, through the first farmers, to Bronze Age, medieval and modern times.

“Oral bacteria in modern man are markedly less diverse than historic populations, and this is thought to contribute to chronic oral and other disease in post-industrial lifestyles,” says Cooper, in the journal Nature Genetics.

“The composition of oral bacteria changed markedly with the introduction of farming and again around 150 years ago,” he adds. “With the introduction of processed sugar and flour in the Industrial Revolution, we can see a dramatically decreased diversity in our oral bacteria, allowing domination by caries-causing strains. The modern mouth basically exists in a permanent disease state.”

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