Danish research team leads the way for future biodiversity monitoring using DNA traces in the environment to keep track of threatened wildlife  a lake water sample the size of a shot-glass can contain evidence of an entire lake fauna.

Global biodiversity is plummeting while biologists are fighting to keep score and reliable monitoring of threatened animals remains a major challenge. The biologist toolset has changed little on this area for a hundred years - still relying on expensive expert surveys basically finding and counting the animals. However, this situation is now set to change according to a recent study by researchers at the Natural History Museum of Denmark published as a cover story in the acclaimed scientific journal Molecular Ecology. The results of the study show that a new method can be used to monitor rare and threatened animal species from DNA traces in their freshwater environments.

The development of the innovative DNA species monitoring was accomplished by PhD student Philip Francis Thomsen and Master's students Jos Kielgast and Lars L. Iversen at Centre for GeoGenetics headed by professor Eske Willerslev.

"We have shown that the DNA detection method works on a wide range of different rare species living in freshwater - they all leave DNA traces in their environment which can be detected in even very small water samples from their habitat. In the water samples we find DNA from animals as different as an otter and a dragonfly," says Philip Francis Thomsen.

By studying the fauna of one hundred different lakes and streams in Europe with both conventional methods - counting individuals - and the new DNA-based method the research team documents that DNA detection is effective even in populations where the animals are extremely rare. The study also shows that there is a clear correlation between the amount of DNA in the environment and the density of individuals meaning that the DNA detection method can even be used to estimate population sizes. This is crucial in the monitoring of rare animals, where one often wants to know whether the population is large or small.

"The UN has agreed to halt the decline of biodiversity, but a prerequisite to do so is that we are capable of properly documenting the status of threatened species. Our new approach is a huge step forward making it cheaper and faster to monitor the endangered species, and thus prioritise efforts to the benefit of biodiversity at a broad scale," says Jos Kielgast.

The researchers have documented that DNA traces of animals are nearly ubiquitous in the freshwater environment and, as a proof-of-concept, these findings may have wider implications reaching disciplines far beyond threatened species monitoring. With DNA sequencing technology advancing at rapidly dropping costs, environmental DNA research is set to change from being merely a scientific curiosity to become an important tool in applied biology. It is for example conceivable that fishing quota may in the future be based on DNA traces rather than fish catches.

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