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Mitochondrial DNA Sequencing of Butteflies on Iberian Peninsula Reveals High Level of Potentially New Species; DNA Barcode Reference Library Established; Libray Should Aid Critical Conservation Efforts

Since 2006, a team of researchers has sequenced the mitochondrial DNA of all the known species of butterflies on the Iberian peninsula (228) and its main populations. The result is a report that compiles more than 3500 genetic sequences of all the species, which have been compared to the genetic sequences of other European buttefly populations. The open-access article was published online on July 24, 2015 in Scientific Reports. It is titled “DNA Barcode Reference Library for Iberian Butterflies Enables a Continental-Scale Preview of Potential Cryptic Diversity.” The paper has 277 pages of supplementary material, including pictures and 80 maps of the geographical distribution of the butterfly genetic lineages identified. This is the first time that the butterfly community of two entire countries (Spain and Portugal) has been thoroughly analyzed. Surprisingly, the mtDNA sequences obtained suggest that up to the 28% of the analyzed species could be totally new to science. These species could have been undetected until now because of the difficulties in distinguishing them from others that are morphologically very similar. The results of this research will be very useful to guide future studies of butterfly biodiversity and improving their conservation, establishing priorities, and avoiding the mixing up of divergent lineages. "Knowing the exact number of species and differentiating them is essential for their protection," says the article’s senior author Dr. Roger Vila, Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra, Barcelona, Spain). The CSIC is the Spanish National Research Council. Also, adds Dr. Vila, "it will allow genetic identification of any butterfly sample, like small fragments (legs or wings), eggs or even the remains in the stomachs of animals that have eaten butterflies." This will be very useful for ecological studies on species interactions, adds the scientist.

One of the goals of the project was to discover whether there are unknown species still to be discovered. The scientists have compared the mtDNA sequences obtained in this work with other sequences of European butterflies and have seen that 28% of the studied species have DNA sequences of very divergent lineages, which might belong to still-undiscovered species.

Scientists say this could be explained because there are different cryptic species that are morphologically very similar and might have been classified as a single species. But DNA analysis demonstrates that an important fraction of these populations has had a long independent evolution.

In other words, "this implies that within this 28% of species we might find species that have been overlooked," says Dr. Vila. "Now we are starting the hard work of studying each case individually in order to see which butterflies are really a new species and which others are just new sub-species. I don't think that all of them will be new species, but we already have promising data for a few of them."

Dr. Vila adds: "We see nature with our human eyes, and many butterflies are indistinguishable to us because they have characteristics we cannot see. But DNA sequencing techniques enable a level of differentiation unimaginable until a few years ago."

Similar to the current situation with bees, there are figures that clearly demonstrate that butterflies are in a critical situation. In the last twenty years, the butterfly population in Europe has been reduced by half.

"And this is taking into account that twenty years ago the butterfly population had already declined compared to previous decades. We are in a race against time to know and protect their diversity," concludes Dr. Vila.

The image here shows the butterfly Zerythia rumina. (Credit: Vlad Dinca).

[Press release] [Scientific Reports abstract]