Wednesday, November 21, 2012

Barcoding types

When describing a new species, taxonomists provide us with a species name and designate a type specimen to which this name will be permanently attached. In other words, a type is an example that serves to anchor the defining features of a particular taxon. 

DNA Barcodes can be used both to attribute species names to a given specimen and to flag genetic clusters for which no name is available. In an ideal situation this can be achieved by sequencing type specimens. However, the majority of the type specimens that are in our Natural History Museums is fairly old and not necessarily stored under DNA-friendly conditions. Many are conserved in formalin which destroys DNA over time. Others, like many insects, are pinned and boxed. From time to time researchers were able to extract DNA from such specimens but mostly they focused on considerably younger specimens (collected and described more recently) or addressed a very small number of samples as it is a more  laborious process.

Eois isographata (credit
In a new study researchers from Austria and Germany report successful sequencing of DNA Barcodes from 96 historical specimens (92 type specimens +4 non-types) of the moth genus Eois (in the 79 to 157 year age range). They used six primer combinations (recovering between 109 and 130 bp each) to assemble a full-length barcode sequence for each specimen. And indeed they were able to generate sequences with an average length of ~500 bp. Furthermore, they developed a non-destructive DNA extraction which means that the often very valuable type is not destroyed in the sense that no additional damage compared to conventional preparation of genitalia slides is inflicted on the specimen. Genitalia slides are usually necessary for morphology-based identification and description. This is still possible after the extraction procedure.

What strikes me is the fact that they were still able to retrieve enough DNA to apply the primer sets they had designed to come up with DNA Barcodes of reasonable length albeit they had to admit that the work is considerably more expensive than 'regular' DNA Barcoding. Nevertheless, a big step forward to anchor another defining feature to some types. Only this time it is one far more objective than many morphological characters out there.

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