The HTS barcode checkerpipeline, a tool for automated detection of illegally traded species from high-throughput sequencing data
© Lammers et al.; licensee BioMed Central Ltd. 2014
Received: 14 November 2013
Accepted: 30 January 2014
Published: 6 February 2014
Mixtures of internationally traded organic substances can contain parts of species protected by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). These mixtures often raise the suspicion of border control and customs offices, which can lead to confiscation, for example in the case of Traditional Chinese medicines (TCMs). High-throughput sequencing of DNA barcoding markers obtained from such samples provides insight into species constituents of mixtures, but manual cross-referencing of results against the CITES appendices is labor intensive. Matching DNA barcodes against NCBI GenBank using BLAST may yield misleading results both as false positives, due to incorrectly annotated sequences, and false negatives, due to spurious taxonomic re-assignment. Incongruence between the taxonomies of CITES and NCBI GenBank can result in erroneous estimates of illegal trade.
The HTS barcode checker pipeline is an application for automated processing of sets of ‘next generation’ barcode sequences to determine whether these contain DNA barcodes obtained from species listed on the CITES appendices. This analytical pipeline builds upon and extends existing open-source applications for BLAST matching against the NCBI GenBank reference database and for taxonomic name reconciliation. In a single operation, reads are converted into taxonomic identifications matched with names on the CITES appendices. By inclusion of a blacklist and additional names databases, the HTS barcode checker pipeline prevents false positives and resolves taxonomic heterogeneity.
The HTS barcode checker pipeline can detect and correctly identify DNA barcodes of CITES-protected species from reads obtained from TCM samples in just a few minutes. The pipeline facilitates and improves molecular monitoring of trade in endangered species, and can aid in safeguarding these species from extinction in the wild. The HTS barcode checker pipeline is available at https://github.com/naturalis/HTS-barcode-checker.
KeywordsBiodiversity informatics High-throughput sequencing Taxonomy Wildlife forensics
The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) entered into force in 1975, and aims to control and regulate trade in endangered species. The convention produces appendices that list taxa (at various taxonomic levels, e.g. species, genera, families) in which trade is controlled or prohibited. These appendices are agreed upon and amended at the Conference of Parties meetings and are available online . There are three appendices: Appendix I includes taxa threatened with extinction; Appendix II contains taxa not threatened with immediate extinction but for which regulation is required to avoid overexploitation that might threaten survival in the wild; Appendix III includes taxa for which one CITES member country requested the involved CITES parties for assistance in controlling the international trade.
CITES appendix-listed taxa cannot be traded internationally without permits from the exporting and importing country. Monitoring of trade in CITES taxa is a challenge to customs authorities worldwide and is especially difficult when parts such as antlers, horns, leaves, roots, or powders are used in mixtures such as in Traditional Chinese Medicines (TCMs). During manufacturing of TCMs, parts are often processed (ground, heated, dried, blended with other products), and this makes taxonomic identification based on chemical, chromatographic or morphological methods challenging [2, 3]. Labels often do not provide sufficient warranties about the actual contents of a product, because listed ingredients may be absent whereas others may be included. New methods are therefore needed to protect both consumers and producers from fraud, and endangered species from overexploitation.
DNA barcoding  is a powerful new tool in the emerging field of wildlife forensics since species composition of mixtures can be reconstructed by sequencing and identifying variable barcoding markers. The mitochondrial marker COI is frequently used for animals; for plants, the official Barcode of Life (BoLD) plastid markers matK and rbcL are used in addition to the nuclear ribosomal Internal Transcribed Spacer (nrITS). DNA barcodes can be identified by querying them against databases such as NCBI GenBank or BoLD , to which reference sequences of animal and plant species have been submitted over the past 10 years. (The latter database includes images of reference specimens and additional sampling details in addition to sequence data). The availability of increasingly complete reference databases has opened up the way for DNA barcoding to become a standard tool for regulatory institutions worldwide to control illegal trade in endangered species.
High-throughput sequencing (HTS) techniques, e.g. those based on platforms such as Illumina HiSeq, IonTorrent, PacBio and Roche 454 [6, 7], yield increasingly large volumes of barcode sequences. This leads to a greater identifying potential for complex species samples such as TCMs, at low cost. The process of going through a set of identified sequences and manually comparing them to the CITES appendices is labor intensive and error prone for several reasons. Firstly, HTS continues to increase the volume of reads, which in turn increases the time to process the data. Secondly, the CITES appendices are only available as HTML documents on the internet, which makes manual verification of sequencing results against the appendix-listed taxa labor intensive. Thirdly, the CITES appendices often list higher taxa (e.g. genera, families) whereas reference sequences are annotated to species level, requiring the correct expansion of the CITES taxa to the level to which sequences are annotated. Fourthly, false positive hits can occur for DNA barcodes deposited in NCBI GenBank, as it occasionally has incorrect taxonomic name annotations. Lastly, taxonomies of the CITES appendices and NCBI GenBank are not always congruent, and this can lead to erroneous conclusions about illegal trade in endangered species.
To address these challenges we have developed an open-source, freely available pipeline that automates the identification and CITES listing verification steps to enable efficient scanning of large sample sequence datasets, and allows for quick detection of presence of DNA barcodes derived from protected species.
The HTS barcode checker is written in python and uses the biopython, beautiful-soup and requests packages to handle FASTA sequences and communicate with the various APIs and web services used, such as NCBI GenBank and the PhyloTastic TNRS service. The steps of the pipeline are shown in Figure 1 and are explained in more detail below.
Local names databases
As an offline process, a local database is maintained containing the NCBI taxon IDs of CITES-listed taxa. The distribution contains a ready-to-use copy of this database; at the time of writing this copy is based on the CITES appendices of June 12th 2013.
By default the HTS barcode checker will compare the CITES database to the latest version of the online CITES appendices during steps that are automatically carried out by the Retrieve_CITES.py script (Figure 1 – step 1-3, section A). If the local version is out of date a new version will be created by scanning the CITES appendices and retrieving the names of CITES-protected species and the appendix numbers in which they occur (Figure 1 – step 4-5). For each entry in the CITES appendix the corresponding taxon ID is initially retrieved using approximate string searches in the NCBI taxonomic database (Figure 1 - step 6). Since an entire genus or family can be listed in the CITES appendix (for example: Dendrobium or Orchidaceae), higher taxa are expanded into the lower, terminal ranks to which GenBank sequences are annotated. When no taxon ID can be obtained, a taxonomic name resolution web service (TNRS) [13, 14] is used (Figure 1 - step 7) to obtain a list of synonyms, based on which the pipeline retries to obtain and expand taxon IDs. During testing, synonyms were successfully retrieved for the CITES-protected plant species Euphorbia capsaintemariensis (syn. E. cap-saintemariensis), Laelia jongheana (syn. Cattleya jongheana), Crysaldiocarpus decipiens (syn. Dypsis decipiens), Sarracenia rubra ssp. jonesii (syn. S. jonesii), and Platymiscium pleiostachyum (syn. P. parviflorum). The resolved, species-level NCBI taxon IDs for CITES-protected taxa are locally stored along with CITES appendix information and NCBI taxon names in a comma-separated values (CSV) file that can be read with standard spreadsheet software.
User-specified, additional names database
Panax omeiensis J. Wen, ined.
Panax sinensis J. Wen, ined.
To identify putative CITES-listed taxa from DNA barcode sequence data, the HTS-barcode-checker script (Figure 1 – section B) takes a set of sequences in FASTA format and searches these either using BLAST against the NCBI GenBank database (Figure 1 - step 4) or a local BLAST search with the NCBI-BLAST + tool  (Figure 1 – step 9-11). All GenBank databases and BLAST algorithms are supported; by default the nucleotide database nr is searched using the blastn algorithm.
It is recommended that large NGS sets (thousands to millions of reads) are first clustered into Operational Clustered Taxonomic Units (OCTUs) with tools such as CD-HIT . CD-HIT is a relatively fast cluster program that clusters sequences based on sequence similarity. Sequences are sorted based on decreasing sequence length, with the first sequence acting as a cluster seed. All subsequent sequences are matched against the seed, depending on the similarity threshold they are placed in the same cluster or serve as a new cluster seed.
By clustering the sequences redundancy is reduced, which will decrease BLAST time. For example a sample containing 79,000 IonTorrent reads could be clustered to a set of of 3,845 representative sequences at 97% sequence similarity. Overloading of the NCBI servers is prevented by a default timeout between BLAST submits, however for larger datasets it is recommended to use a local BLAST database in combination with the NCBI-BLAST + tool (obtainable from ). The update_blastdb.pl tool that comes with the NCBI-BLAST + package can be used to download and maintain local copies of the GenBank databases (18GB for the nucleotide dataset).
Current (erroneous) annotation
Summarized test cases
Identification (% identity)
Aquilaria sinensis (98.76%)
A. rugosa (98.35%)
Dendrobium cariniferum (98.2%)
D. dixanthum (97.63%)
D. williamsonii (99.18%)
With the default settings the sequences are matched against the NCBI GenBank nr database using a blastn search. BLAST hits are filtered with the aforementioned criteria: hits must have a maximum e-value of 0.05, a minimum hit length of a 100 bp and a minimum hit identity of 97%. The 10 hits with the lowest e-value are returned. These default settings can be altered if needed, use the argument for more details.
To force or avoid updating the local CITES database, add or , respectively. Use the argument for a full list of available arguments.
Besides running the pipeline from the command-line interface it is also possible to make it available in more user-friendly environments: the pipeline can be installed as a standalone Common Gateway Interface (CGI) web application or be installed onto the galaxy platform [22, 23] (necessary scripts and configuration files are provided with the distribution). In both cases the functionality of the pipeline is then available to end-users by interacting with a simple, graphical user interface.
Results and discussion
The reliability and accuracy of using BLAST as a method for identification depends on several factors. Firstly, the completeness of the reference database is of importance. Very few entire genomes of CITES-listed species have been sequenced: so far only 130  out of a total of 30713 species. Our pipeline is therefore not intended to handle Whole Genome Shotgun (WGS) data.
Secondly, for the standard DNA barcoding markers not all CITES-listed taxa have so far been sequenced. Species in diverse groups such as Orchidaceae or Primates are sometimes similar, and differences between their standard barcodes may therefore be small. To prevent both type I and type II errors in the identification of difficult to distinguish species, specialists of various CITES committees decided that for species that cannot be discriminated based on DNA barcodes the entire genus (that can be recognized by DNA barcoding) rather than the individual species (that cannot) should be placed on the CITES Appendices. The CITES organization annually updates the contents of its appendices for this reason.
An example case is Cyclemys spp., a genus of freshwater turtles (Geoemydidae): one widespread species, C. dentata, is heavily exploited for food while other species in the genus are rarely traded. The entire genus was placed on appendix II in 2013. In the criteria for amendment of the appendices  it is explicitly stated that this action was carried out because enforcement officers are unlikely to be able to distinguish traded material of C. dentata from close relatives (look-alike criteria set out in Annex 2b). In response to this, the default settings of the HTS pipeline use a cut-off value of 3% sequence similarity to distinguish species from each other by DNA barcodes obtained. This approach generally works to keep endangered and non-CITES protected close relatives apart from each other. We explicitly state the cases to which this does not apply below. A cut-off value was chosen based on earlier studies that found this divergence to be sufficient to keep the majority of plants and animals apart using the standard matK, rbcL and COI DNA barcoding markers [19, 20].
Thirdly, the quality of identification depends on the length of the DNA barcode sequence used for identification. Smaller fragments have been shown to lack the discriminatory power to distinguish between species in a genus or higher taxon . For this reason, the pipeline discards identifications obtained from matches shorter than 100bp by default. Finally, to minimize the chance that identifications are based on an erroneous entry the user should look, where possible, at multiple BLAST results and verify that they are in agreement with each other. The pipeline by default returns the 10 BLAST hits with the lowest e-value (after BLAST filtering); based on multiple identifications per sequence the end-user should validate whether an identification is reliable. We recommend that users select BLAST hits with the highest sequence similarity and match length wherever possible. If multiple hits are obtained with identical quality results, but different assigned species, the fragment lacks the discriminatory power to describe the hit to species level. In these cases the user should refrain from assigning a single species but stick to the genus instead.
In our experience, virtually no situations have yet occurred in which a non-CITES-protected species could be mixed up with a CITES-protected taxon. The only exceptions concern taxonomic groups that contain domesticated species from Bovidae (wild cattle, goats and sheep) and Canidae (wolves and foxes). The wild species in these taxonomic groups cannot always be distinguished from their domesticated relatives (cows, dogs, domestic goats and sheep) so identification using standard barcoding markers fails. Similar issues arise when trying to determine whether a species is cultivated or not, as standard barcodes do not provide the necessary resolution to distinguish cultivars from samples collected in the wild.
The HTS barcode checker pipeline is the first tool for automated searches for DNA barcodes of CITES-protected taxa in HTS data. On the CITES website, several other online tools are available, such as databases that can be queried for information about trade, management systems, export quota, publications, identification manuals and photographs, but none as yet to search for hits in HTS datasets. The Chinese Academy of Medical Sciences in Beijing produces DNA barcodes from ingredients from Traditional Chinese Medicines and lists these on its website, but here too automatic search tools are not provided.
To compare speed of the pipeline to current practices we presented a spreadsheet file with ten taxonomic names (among which two CITES-listed taxa) obtained from a TCM HTS dataset to ten colleagues and let them search for CITES-listed taxa by scrolling through the CITES Appendices using the ‘search and find’ option in Adobe Reader. Processing time ranged between little over one minute to slightly under five minutes among the ten participants and did not result in full recovery of CITES-listed taxa in all cases. The HTS barcode checker pipeline processed the same dataset in less than ten seconds and successfully retrieved all protected species.
Here we report the pipeline results for three sequence sets that were based on material confiscated by Dutch customs officials. For each sample the Internal Transcribed Spacer 1 (nrITS1) region was amplified and sequenced using the IonTorrent PCM platform. The reads were clustered using CD-HIT  at 97% sequence similarity. The clusters were identified with the HTS barcode checker pipeline under default settings (max e-value of 0.05, minimum of 97% sequence similarity and a hit length of at least a 100 bp). The full pipeline results are available in Additional file 1. The clustered FASTA files for all cases are available with the pipeline distribution in the /data folder.
An incense cone was sequenced and clustered of which the manufacturer provided us with all ingredients among which a protected taxon (Aquilaria). Clustering produced a total of 175 non-singleton OCTUs. A total of 99 unique identifications could be obtained by BLASTing using the pipeline. The results, listed in Table 3, indicate that the cone indeed contained species of Aquilaria (Thymeleaeceae), which are all placed on CITES Appendix II. The not protected plant species specified by the manufacturer were identified as well, thus validating the method.
Wood chips from a confiscated agarwood sample were sequenced. Clustering resulted in a total of 51 non-singleton OCTUs. A total of 26 unique identifications could be obtained by BLASTing the OCTUs, including an identification for Aquilaria species which is listed on CITES appendix II. The majority of the other OCTU identifications were from Citrullus and Pseudomonas.
A confiscated Dendrobium stem was sequenced and clustered, this produced a total of 3845 non-singleton OCTUs. A total of 159 unique identifications could be obtained by BLASTing using the pipeline; these included three different Dendrobium species, listed in Table 3. The results indicate that the stem indeed belongs to a member of the Dendrobium genus, though the barcode lacks the discriminatory strength to determine the exact species. Since all Orchidaceae are on CITES appendix II the sample was lawfully confiscated. Other sequence results included various fungal species.
Although the pipeline presented here is ready to use, several enhancements are possible that would increase usability and impact. For example, although incorrect taxonomic identifications of NCBI GenBank records have previously been noted, no community project exists to record and track such errors . The blacklist used by the HTS barcode checker could be used for communal record keeping, especially as our usage of git as a decentralized revision control system provides the ideal infrastructure for this. Conversely, should an alternative community-wide blacklist of NCBI GenBank come into existence, HTS barcode checker could be modified to make use of it. We expect the number of users to grow once the HTS barcode checker project is linked from the CITES Virtual College , which would build a community that could ‘crowd source’ such a blacklist.
Though the HTS barcode checker can be setup to run via CGI or platforms such as galaxy, a publicly hosted web service would make the pipeline accessible to non-expert users such as customs officers as it would remove the need for local installations. In addition, this web application could be configured to update the local databases of additional names and the blacklist at frequent intervals, thereby guaranteeing that the user always operates on state-of-the-art knowledge.
Lastly, DNA barcodes of CITES-protected species collected from well-identified specimens should be uploaded in larger numbers to BoLD, where taxonomic names can be updated as needed by third parties. The number of CITES-protected species is currently 820 for mammals, 605 for birds, 722 for reptiles, 81 for amphibians, 20 for sharks, 132 for fishes, 3 for lungfishes, 1 for sea cucumbers, 25 for scorpions and spiders, 69 for insects, 2 for leeches, 37 for clams and mussels, 10 for snails and conches, 1636 for corals and sea anemones, 260 for sea ferns, fire corals and stinging medusae, and 26290 for plants (counts based on [28–37] and the latest proposed changes to the CITES Appendices). From this total of 30713 CITES-protected species, roughly 16830 (55%) are present in NCBI GenBank with DNA barcodes, and 13883 (45%) remain to be sequenced. Multiple initiatives carried out at The Field Museum and Missouri Botanical Garden (USA), Naturalis Biodiversity Center (the Netherlands), Muséum National d’Histoire Naturelle (France), Smithsonian’s National Museum of Natural History (USA), Zoological Institute of the Russian Academy of Sciences (Russia) and University of Johannesburg (South Africa) are currently producing additional barcode sequences of CITES-listed species. We therefore expect that the current number of 45% not yet covered in NCBI GenBank or BoLD will decrease.
High-throughput sequencing of DNA barcodes has improved identification potential of traded endangered species. Taxonomic errors in reference databases such as NCBI GenBank, and incongruences in the taxonomies of the CITES appendices and DNA barcode reference databases, can lead to incorrect conclusions on illegal trade. The HTS barcode checker pipeline is developed for automated identification from mixtures of illegally traded species, and includes functionality for correcting and standardizing taxonomic names to overcome the caveats discussed above. The pipeline alleviates the identification process by eliminating error-prone human search and matching steps, and provides a repeatable method for assessing the presence of CITES-protected taxa by analysis of HTS data. Tests demonstrate the potential of the HTS barcode checker pipeline for saving manual labor, reducing taxonomic errors and increasing integration between the NCBI GenBank reference database and the CITES appendices.
Availability and requirements
Project name: HTS barcode checker
Project home page: https://github.com/naturalis/HTS-barcode-checker
Operating systems: Platform independent
Programming language: Python (version 2.7 or 3.0 and higher)
Other requirements: Python packages biopython, beautiful-soup and requests.
Any restrictions to use by non-academics: No
Application programming interface
Basic local alignment search tool
Barcode of life database
Convention on international trade in endangered species of wild fauna and flora
Comma separated values
High throughput sequencing
National Center for Biotechnology Information
Operational clustered taxonomic unit
Traditional Chinese medicine
Taxonomic name reconciliation service
Tab separated values.
The authors would like to thank Denise Rijkeboer and Elza Duijm for kindly providing us with Ion Torrent data to test the pipeline, Thomas Bolderink, Alex Hoogkamer and Roeben Vink for development of a first prototype, Sigrid Beiboer for co-mentoring them during the internship out of which this project evolved, Rene Dekker and Chris Schürmann for providing us with the most recent updates of the CITES Appendices. Marcos Regis Silva of the CITES Secretariat granted us permission of using the term HTS barcode checker for automatic identification of CITES protected species.
- Appendices I, II and III. [http://www.cites.org/eng/app/appendices.php]
- Coghlan ML, Haile J, Houston J, Murray DC, White NE, Moolhuijzen P, Bellgard MI, Bunce M: Deep Sequencing of Plant and Animal DNA Contained within Traditional Chinese Medicines Reveals Legality Issues and Health Safety Concerns. PLoS Genetics. 2012, 8 (4): doi:10.1371/journal.pgen.1002657Google Scholar
- Gathier G, van der Niet T, Peelen T, van Vugt RR, Eurlings MCM, Gravendeel B: Forensic Identification of CITES protected Slimming Cactus (Hoodia) using DNA barcoding. J Forensic Sci. 2013, 58 (6): 1467-1471. 10.1111/1556-4029.12184.View ArticlePubMedGoogle Scholar
- Savolainen V, Cowan RS, Vogler AP, Roderick GK, Lane R: Towards writing the encyclopaedia of life: an introduction to DNA barcoding. Roy Soc B Biol Sci. 2005, 360: 1805-1811.View ArticleGoogle Scholar
- Hebert PDN, Cywinska A, Ball SL, deWaard JR: Biological identifications through DNA barcodes. Roy Soc B Biol Sci. 2003, 270 (1512): 313-321. 10.1098/rspb.2002.2218.View ArticleGoogle Scholar
- Shendure J, Ji H: Next-generation DNA sequencing. Nat Biotechnol. 2008, 26 (10): 1135-1145. 10.1038/nbt1486.View ArticlePubMedGoogle Scholar
- Glenn TC: Field guide to next-generation DNA sequencers. Mol Ecol Resour. 2011, 11: 759-769. 10.1111/j.1755-0998.2011.03024.x.View ArticlePubMedGoogle Scholar
- Benson DA, Karsch-Mizrachi I, Lipman DJ, Ostell J, Sayers EW: GenBank. Nucleic Acids Res. 2009, 37: D26-D31. 10.1093/nar/gkn723.View ArticlePubMed CentralPubMedGoogle Scholar
- Altschul SF, Gish W, Miller W, Myers EW, Lipman DJ: Basic local alignment search tool. J Mol Biol. 1990, 215: 403-410.View ArticlePubMedGoogle Scholar
- Cock PJA, Antao T, Chang JT, Chapman BA, Cox CJ, Dalke A, Friedberg I, Hamelryck T, Kauff F, Wilczynski B, de Hoon MJL: Biopython: freely available Python tools for computational molecular biology and bioinformatics. Bioinformatics. 2009, 25 (11): 1422-1423. 10.1093/bioinformatics/btp163.View ArticlePubMed CentralPubMedGoogle Scholar
- Beautiful Soup. [http://www.crummy.com/software/BeautifulSoup/]
- Requests: HTTP for Humans. [http://docs.python-requests.org/en/latest/]
- Stoltzfus A, Lapp H, Matasci N, Deus H, Sidlauskas B, Zmasek CM, Vaidya G, Pontelli E, Cranston K, Vos R, Webb CO, Harmon LJ, Pirrung M, O'Meara B, Pennell MW, Mirarab S, Rosenberg MS, Balhoff JP, Bik HM, Heath T, Midford P, Brown JW, McTavish EJ, Sukumaran J, Westneat M, Alfaro ME, Steele A: Phylotastic! Making Tree-of-Life Knowledge Accessible, Re-usable and Convenient. BMC Bioinformatics. 2013, 14: 158-10.1186/1471-2105-14-158. doi:10.1186/1471-2105-14-158.View ArticlePubMed CentralPubMedGoogle Scholar
- Boyle B, Hopkins N, Lu Z, Garay JAR, Mozzherin D, Rees T, Matasci N, Narro ML, Piel WH, McKay SJ, Lowry S, Freeland C, Peet RK, Enquist BJ: The taxonomic name resolution service: an online tool for automated standardization of plant names. BMC Bioinformatics. 2013, 14: 16-10.1186/1471-2105-14-16. doi:10.1186/1471-2105-14-16.View ArticlePubMed CentralPubMedGoogle Scholar
- Camacho C, Coulouris G, Avagyan V, Ma N, Papadopoulos J, Bealer K, Madden TL: BLAST+: architecture and applications. BMC Bioinformatics. 2009, 10: 421-10.1186/1471-2105-10-421.View ArticlePubMed CentralPubMedGoogle Scholar
- Li W, Godzik A: Cd-hit: a fast program for clustering and comparing large sets of protein or nucleotide sequences. Bioinformatics. 2006, 22: 1658-1659. 10.1093/bioinformatics/btl158.View ArticlePubMedGoogle Scholar
- BLAST+ executables. [http://blast.ncbi.nlm.nih.gov/Blast.cgi?PAGE_TYPE=BlastDocs&DOC_TYPE=Download]
- Hajibabaei M, Smith MA, Janzen DH, Rodriguez JJ, Whitfield JB, Hebert PDN: A minimalist barcode can identify a specimen whose DNA is degraded. Mol Ecol Notes. 2006, 6: 959-964. 10.1111/j.1471-8286.2006.01470.x.View ArticleGoogle Scholar
- CBOL Plant Working Group: A DNA barcode for land plants. Proc Natl Acad Sci USA. 2009, 106: 12794-12797.View ArticlePubMed CentralGoogle Scholar
- Ratnasingham S, Hebert PDN: A DNA-based registry for all animal species: The Barcode Index Number (BIN) System. PLoS One. 2013, 8: doi:10.1371/journal.pone.0066213Google Scholar
- Groenenberg DSJ, Neubert E, Gittenberger E: Reappraisal of the “‘Molecular phylogeny of Western Palaearctic Helicidae s.l. (Gastropoda: Stylommatophora)’”: When poor science meets GenBank. Mol Phylogenet Evol. 2011, 61: 914-923. 10.1016/j.ympev.2011.08.024.View ArticlePubMedGoogle Scholar
- Giardine B, Riemer C, Hardison RC, Burhans R, Elnitski L, Shah P, Zhang Y, Blankenberg D, Albert I, Taylor J, Miller W, Kent WJ, Nekrutenko A: Galaxy: a platform for interactive large-scale genome analysis. Genome Res. 2005, 15 (10): 1451-1455. 10.1101/gr.4086505.View ArticlePubMed CentralPubMedGoogle Scholar
- Goecks J, Nekrutenko A, Taylor J, The Galaxy Team: Galaxy: a comprehensive approach for supporting accessible, reproducible, and transparent computational research in the life sciences. Genome Biol. 2010, 11 (8): R86-10.1186/gb-2010-11-8-r86.View ArticlePubMed CentralPubMedGoogle Scholar
- Genome information by organism. [http://www.ncbi.nlm.nih.gov/genome/browse/]
- Criteria for amendment of Appendices I and II. [http://www.cites.org/eng/res/09/09-24R15.php]
- Pennisi E: Proposal to “Wikify” GenBank Meets Stiff Resistance. Science. 2008, 319 (5870): 1598-1599. 10.1126/science.319.5870.1598.View ArticlePubMedGoogle Scholar
- The CITES Virtual College. [https://cites.unia.es/cites/]
- Wilson DE, Reeder DM: Mammal Species of the World. A Taxonomic and Geographic Reference (3rd ed). 2005, Baltimore: Johns Hopkins University PressGoogle Scholar
- Clements JF, Schulenberg TS, Iliff MJ, Sullivan BL, Wood CL, Roberson D: The eBird/Clements checklist of birds of the world: Version 6.7. 2012, http://www.birds.cornell.edu/clementschecklist/downloadable-clements-checklist,Google Scholar
- Zug GR, Vitt LJ, Caldwell JP: Herpetology. 2001, San Diego: Academic Press, 2Google Scholar
- Frost DR: Amphibian Species of the World: an Online Reference. 2013, http://research.amnh.org/herpetology/amphibia/index.html,Google Scholar
- Compagno LJV: Sharks of the world. An annotated and illustrated catalogue of shark species known to date. 2002, Food and Agriculture Organizations of the United Nations: RomeGoogle Scholar
- Fishwise 2013. Universal Fish Catalogue. [http://www.fishwise.co.za]
- Rein JO: The Scorpion Files. Trondheim: Norwegian University of Science and Technology. 2012, http://www.ntnu.no/ub/scorpion-files/,Google Scholar
- Platnick NI: The World Spider Catalog, version 13.5. 2013, http://research.amnh.org/iz/spiders/catalog,Google Scholar
- Veron JEN: Corals of the World. 2011, http://coral.aims.gov.au/,Google Scholar
- Mabberley DJ: Mabberley's Plant-Book. A portable dictionary of plants, their classification and uses. 2008, Cambridge: Cambridge University PressGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.