Background: DNA barcoding is a popular tool in taxonomic and phylogenetic studies, but for most animal lineages protocols for obtaining the barcoding sequences--mitochondrial cytochrome C oxidase subunit I (cox1 AKA CO1)--are not standardized. Our aim was to explore an optimal strategy for arachnids, focusing on the species-richest lineage, spiders by (1) improving an automated DNA extraction protocol, (2) testing the performance of commonly used primer combinations, and (3) developing a new cox1 primer suitable for more efficient alignment and phylogenetic analyses.
Methodology: We used exemplars of 15 species from all major spider clades, processed a range of spider tissues of varying size and quality, optimized genomic DNA extraction using the MagMAX Express magnetic particle processor-an automated high throughput DNA extraction system-and tested cox1 amplification protocols emphasizing the standard barcoding region using ten routinely employed primer pairs.
Results: The best results were obtained with the commonly used Folmer primers (LCO1490/HCO2198) that capture the standard barcode region, and with the C1-J-2183/C1-N-2776 primer pair that amplifies its extension. However, C1-J-2183 is designed too close to HCO2198 for well-interpreted, continuous sequence data, and in practice the resulting sequences from the two primer pairs rarely overlap. We therefore designed a new forward primer C1-J-2123 60 base pairs upstream of the C1-J-2183 binding site. The success rate of this new primer (93%) matched that of C1-J-2183.
Conclusions: The use of C1-J-2123 allows full, indel-free overlap of sequences obtained with the standard Folmer primers and with C1-J-2123 primer pair. Our preliminary tests suggest that in addition to spiders, C1-J-2123 will also perform in other arachnids and several other invertebrates. We provide optimal PCR protocols for these primer sets, and recommend using them for systematic efforts beyond DNA barcoding.