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Opening a can of worms

13 October 2008


Earthworms are far more diverse in the UK than previously thought, according to new University findings which could have important consequences for agriculture.

Dr Bill Symondson, of the School of Biosciences, along with Dr Andrew King and undergraduate student Amy Tibble, found that that many of the common earthworm species in gardens and on agricultural land are actually made up of a number of distinct species. Each species could have its own individual roles in food chains, soil structure and ecology.

The discovery was made after efforts to develop better tools to identify earthworm DNA in slug and worm-eating beetles produced some unexpected results.

Dr Symondson said: "We started getting results that were not really what we expected to see and that indicated the presence of several new earthworm species. After investigating this further we eventually found that there are significant numbers of what we call ‘cryptic species’. These different species live in the same environment and have the same outward appearance, but do not interbreed and have clearly distinct DNA sequences.

"Earthworms play a major role in the agricultural environment because they are involved in many soil processes such as soil turnover, aeration and drainage, and the breakdown and incorporation of organic matter. For this reason, they have often been the subject of research into, for example, ecology and toxicology. It is vitally important that we know exactly which species we are studying, in case they respond differently from one another – to agrochemicals or heavy metals in the soil, for example."

Dr Symondson and his team studied nine different species of common earthworm and collected samples from Britain and mainland Europe. They found evidence that four of the nine species are made up of complexes of multiple species. Furthermore, detailed analysis of one common species – Allolobophora chlorotica – shows that it is made up of at least three species in Britain and one additional species in central Europe.

Dr Symondson added: "Any further earthworm research will now have to be done with the knowledge that in many cases there are multiple species where we thought there was just one. We need to establish for certain whether the different cryptic species play different roles in the ecology of our agricultural land or have different tolerances to potential environmental stresses such as toxins, parasites, or extremes of temperature."

The research is published in the journal Molecular Ecology, and was funded by the Biotechnology and Biological Sciences Research Council.