To test for universality of primers and cycling conditions, we performed parallel experiments in three different laboratories (Berkeley, Cologne, Konstanz) using the same primers but different biochemical products and thermocyclers, and slightly different protocols.
The selected primers for
16S [30 ] amplify a fragment of ca. 550 bp (in amphibians) that has been used in many phylogenetic and phylogeographic studies in this and other vertebrate classes: 16SA-L, 5' - CGC CTG TTT ATC AAA AAC AT - 3'; 16SB-H, 5' - CCG GTC TGA ACT CAG ATC ACG T - 3'.
For
COI we tested (1) three primers designed for birds [7 (
link)] that amplify a 749 bp region near the 5'-terminus of this gene: BirdF1, 5' - TTC TCC AAC CAC AAA GAC ATT GGC AC - 3', BirdR1, 5' - ACG TGG GAG ATA ATT CCA AAT CCT G - 3', and BirdR2, 5' - ACT ACA TGT GAG ATG ATT CCG AAT CCA G - 3'; and (2) one pair of primers designed for arthropods [2 (
link)] that amplify a 658 bp fragment in the same region: LCO1490, 5' - GGT CAA CAA ATC ATA AAG ATA TTG G - 3', and HCO2198, 5'-TAA ACT TCA GGG TGA CCA AAA AAT CA-3'. Sequences of additional primers for
COI that had performed well in mammals and fishes were kindly made available by P. D. N. Hebert (personal communication in 2004) and these primers yielded similar results (not shown).
The optimal annealing temperatures for the
COI primers were determined using a gradient thermocycler and were found to be 49–50°C; the 16S annealing temperature was 55°C. Successfully amplified fragments were sequenced using various automated sequencers and deposited in Genbank. Accession numbers for the complete data set of adult mantellid sequences used for the assessment of intra- and interspecific divergences (e.g. in Fig.
5) are AY847959–AY848683. Accession numbers of the obtained COI sequences are AY883978–AY883995.
Nucleotide variability was scored using the software DNAsp [31 (
link)] at
COI and
16S priming sites of the following complete mitochondrial genomes of nine amphibians and 59 other vertebrates:
Cephalochordata: AF098298,
Branchiostoma.
Myxiniformes: AJ404477,
Myxine. Petromyzontiformes: U11880,
Petromyzon.
Chondrichthyes: AJ310140,
Chimaera; AF106038,
Raja; Y16067,
Scyliorhinus; Y18134,
Squalus.
Actinopterygii: AY442347,
Amia; AB038556,
Anguilla; AB034824,
Coregonus; M91245,
Crossostoma; AP002944,
Gasterosteus; AB047553,
Plecoglossus; U62532,
Polypterus; U12143,
Salmo.
Dipnoi: L42813,
Protopterus.
Coelacanthiformes: U82228,
Latimeria.
Amphibia, Gymnophiona: AF154051,
Typhlonectes.
Amphibia, Urodela: AJ584639,
Ambystoma; AJ492192,
Andrias; AF154053,
Mertensiella; AJ419960,
Ranodon.
Amphibia, Anura: AB127977,
Buergeria; NC_005794,
Bufo; AY158705;
Fejervarya; AB043889,
Rana; M10217,
Xenopus.
Testudines: AF069423, NC_000886,
Chelonia;
Chrysemys; AF366350,
Dogania; AY687385,
Pelodiscus; AF039066,
Pelomedusa.
Squamata: NC_005958,
Abronia; AB079613,
Cordylus; AB008539,
Dinodon; AJ278511,
Iguana; AB079597,
Leptotyphlops; AB079242,
Sceloporus; AB080274,
Shinisaurus.
Crocodilia: AJ404872,
Caiman.
Aves: AF363031,
Anser; AY074885,
Arenaria; AF090337,
Aythya; AF380305,
Buteo; AB026818,
Ciconia; AF362763,
Eudyptula; AF090338,
Falco; AY235571,
Gallus; AY074886,
Haematopus; AF090339,
Rhea; Y12025,
Struthio.
Mammalia: X83427,
Ornithorhynchus; Y10524,
Macropus; AJ304826,
Vombatus; AF061340,
Artibeus; U96639,
Canis; AJ222767,
Cavia ; AY075116,
Dugong; AB099484,
Echinops; Y19184,
Lama; AJ224821,
Loxodonta; AB042432,
Mus; AJ001562,
Myoxus; AJ001588,
Oryctolagus; AF321050,
Pteropus; AB061527,
Sorex; AF348159,
Tarsius; AF217811,
Tupaia; AF303111,
Ursus (for species names, see Genbank under the respective accession numbers).
16S sequences of a large sample of Madagascan frogs were used to build a database in Bioedit [32 ]. Tadpole sequences were compared with this database using local BLAST searches [33 (
link)] as implemented in Bioedit.
The performance of
COI and
16S in assigning taxa to inclusive major clades was tested based on gene fragments homologous to those amplified by the primers used herein (see above), extracted from the complete mitochondrial sequences of 68 vertebrate taxa. Sequences were aligned in Sequence Navigator (Applied Biosystems) by a Clustal algorithm with a gap penalty of 50, a gap extend penalty of 10 and a setting of the ktup parameter at 2. PAUP* [34 ] was used with the neighbor-joining algorithm and LogDet distances and excluding pairwise comparisons for gapped sites. We chose these simple phenetic methods instead of maximum likelihood or maximum parsimony approaches because they are computationally more demanding and because the aim of DNA barcoding is a robust and fast identification of taxa rather than an accurate determination of their phylogenetic relationships.
Vences M., Thomas M., van der Meijden A., Chiari Y, & Vieites D.R. (2005). Comparative performance of the 16S rRNA gene in DNA barcoding of amphibians. Frontiers in Zoology, 2, 5.