A Plea for Standardized Nuclear Markers in Metazoan DNA Taxonomy

The ease of sequencing DNA barcodes promoted a species identification system universally applicable across animal phyla. However, relying on a single mitochondrial DNA fragment has a number of drawbacks that can mislead species delimitation and identification. Implementation of multiple nuclear markers would mitigate the limits of the current barcoding system if these markers are universally applicable across species, carry sufficient information to discriminate between closely related species, and if sequencing and analyzing these markers can be automatized. As sequencing costs continue to fall, we believe that the time is right to extend DNA barcoding. Here we argue that nearly universal single-copy nuclear protein-coding genes deliver the desired characteristics and could be used to reliably delimit and identify animal species.