Species ID challenged by DNA analysis

Identifying species: looks are no longer enough. Increasingly common problem for 21st century biologists

November 2010: What happens when a species isn't the one it looks like? It is a problem being faced increasingly by biologists. Although Linnaean taxonomy is still a cornerstone of biology, modern DNA techniques have erased many of the established boundaries between species, making it far more difficult, in practice, to know exactly what you are looking at.

Emma Vodoti, of the University of Gothenburg, says work on identification may have to change to take account of increased knowledge of DNA

A researcher from Sweden's University of Gothenburg is now highlighting the potential pitfalls this can cause. ‘If you can't recognise a species by looking at it, this can have serious consequences,' says Emma Vodoti from university's Department of Zoology. ‘For example, there is a species of leech that is widely used in medical studies, and it was discovered recently that sometimes a leech was being used that looks the same but has a different genetic make-up. This naturally has an effect on the results of the studies conducted. All work based on having to be able to identify species may have to change.'

Three hundred and fifty years after Linnaeus created his system for organising and categorising species of plants and animals, the system is being pulled apart. Newly discovered organisms are still categorised and named in line with his system, but there is a big difference between species described before and after the discovery of DNA. Until the 1980s, scientists had to rely entirely on appearance, anatomy and other characteristics, such as a bird's song. Since then, genetic patterns have also been taken into account when identifying new species.

Genetic studies have erased many established boundaries between species
'Ironically, these genetic studies have erased many of the established boundaries between species and even disproved the existence of previously described species that have turned out not to be related. Attempts have been made to establish universal boundaries between species by quantifying how much DNA needs to be different between two organisms in order for them to be viewed as separate species, but this doesn't always work.'

In her thesis, Vodoti looks at the practical problems with species identification today, after having studied the relationship between the genetic relatedness and the appearance and geographical distribution of various sea creatures. The common horse mussel Modiolus modiolus found in the Atlantic and on the west coast of Sweden turns out to be totally different genetically from the one found on the Pacific coast of the USA, despite looking identical. Nemertean worms may have similarities in appearance but turn out to consist of a hotchpotch of different species, more or less independent of looks. Nemerteans include worms just a few millimetres in length to one of the world's longest creatures, Lineus longissimus, which can grow up to 15 metres.

‘It's probably impossible to find a universal way of defining, identifying and delimiting species,' says Vodoti. ‘My thesis shows that there is a need for individual assessment on a case-by-case basis when identifying species, taking account of both appearance and genes.'