GENETIC STUDY UNCOVERS HIDDEN WORLD IN THE SAND

Created on 30 November 2010 by tidingsadmin
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Sediment samples from a Scottish beach turn out to harbour ecosystems far richer and more diverse than anyone had previously suspected.

A team of researchers wanted to understand the communities of metazoans that live in the sand of the seabed and shoreline. These multi-celled creatures - like flatworms and nematodes - are bigger and more complex than bacteria, but still mostly too small to see with the naked eye. They are among the most numerous animals in existence, but we know comparatively little about them.

Rather than examining each metazoan under the microscope, the study used genetic analysis to reveal the sheer number of new species found in one small area, as well as the ecological relationships that bind these communities together. The technique, called 'environmental metagenetics', could now let scientists quickly assess the range of living things found in many other kinds of environments.

'The sequencing techniques are orders of magnitude faster and cheaper than traditional approaches,' says Vera Fonseca, a PhD student at Bangor University and lead author of the paper, published in Nature Communications. 'To complete the same work using traditional methods would take unquantifiable centuries to manually identify each individual species in a sample.'

The team took samples of sand along an 800m stretch of the beach at Prestwick in western Scotland. They used modern genetic sequencing technology to analyse the animals present. Their discoveries include identifying the genetic signatures of at least 182 kinds of nematode worm. Only 450 species had previously been described across the whole British Isles, so this is a major advance achieved by looking at a distance equivalent to just 0.004 per cent of the nation's coastline.

Nematodes are already believed to be the commonest multi-cellular creatures in existence, accounting for some 80 per cent of all the individual animals in the world. The latest research suggests they are even more varied and numerous than has been suspected. This may be partly because of the time-intensive methods that taxonomists have to use to investigate them have so far not been a match for the diversity out there.

A further big surprise was the importance of another group of metazoans, the flatworms. These occurred in numbers second only to those of nematodes and although they are often top predators in the ecosystem, until now, their role had largely been overlooked.
'It's as if grassland ecologists were suddenly to realise the whole cat family had been missed out from their previous studies of the savannah ecosystem,' says Dr Simon Creer of Bangor, who led the research team.

Rapid advances in DNA sequencing technology have made research like this possible. Just a few years ago, the process of sequencing genes was extremely slow and laborious, with researchers having to prepare and test each small piece of genetic material individually. Trying to use these methods to handle samples of a whole ecosystem would have taken far too long to be practicable.

But the new generation of sequencing machines let scientists sequence large amounts of DNA at once. 'In the early eighties, I spent three years studying ten thousand microscopic worms from the Firth of Clyde by eye, one at a time, using high power light microscopes, and identified 113 species,' says Professor John Lambshead of the University of Southampton, another author. 'Our new DNA study identified 182 types of nematode worm from the same region in just one month.'

Over the last few years, these advances in gene sequencing technology have revealed previously-unimagined diversity in communities of microbes. The team behind this latest study wanted to use similar methods to understand the bigger creatures known as metazoans.

These are still tiny by human standards, but they're complex multi-celled animals with comparatively complex behaviour and ecosystems. They form a crucial link between the microbial world and that of big animals like us.

It's still not clear just why nematodes are so incredibly numerous and successful in environments ranging from the sediment of the deep seabed to the soils of forests and grasslands. Creer speculates that the worm-like shape they share with the flatworms may just be uniquely effective for moving around and finding food in a three-dimensional environment made up of grains of various sizes and the gaps between them.

The group pioneered this set of techniques for analysing metazoan biodiversity, setting out its basic framework in a Molecular Ecology paper earlier in 2010.

Team members are now using it in different environments. 'Adding the DNA sequence of the samples to a database will ultimately enable scientists to track where individual species occur, and over time to gauge their reaction to climate change or to pollution or other human induced events,' Creer explains.

For example, Professor Kelley Thomas of the University of New Hampshire, who led the team's bioinformatic analysis, is applying it to assess the effect of the recent oil spill on the metazoan communities of the Gulf of Mexico.

This article originally appeared in Planet Earth Online, and is reproduced here with their permission.

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