The Barcode Blog

A mostly scientific blog about short DNA sequences for species identification and discovery. I encourage your commentary. -- Mark Stoeckle

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Archive for June, 2008

Freshwater fish DNA data debut

Sunday, June 22nd, 2008

In June 2008 PLoS ONE, thirteen researchers from nine Canadian universities, museums, and federal agencies report on mtDNA sequences from 1360 individuals representing 195 (95%) of Canada’s 205 freshwater fish species. Hubert et al follow “best practices” established for DNA barcode records (similar criteria would enhance the value of other genetic reference data as well), namely each sequence is derived from a vouchered specimen and the barcode record includes:

  • “Bi-directional sequences of at least 500 base-pairs from the approved barcode region of COI, containing no ambiguous sites
  • Links to electropherogram trace files available in the NCBI Trace Archive
  • Sequences for the forward and reverse PCR amplification
  • Species names that refer to documented names in a taxonomic publication or other documentation of the species concept used
  • Links to voucher specimens using the approved format of institutional acronym:collection code:catalog ID number”

The researchers analyzed an average of 7.6 specimens/species, with an effort to sample across species ranges. A first pass look at genetic distances among and within Canadian freshwater fish shows results similar to those of other animal groups: average variation within species, 0.3%; average minimum distance between congeneric species (nearest neighbor), 8.3%; species with overlapping mtDNA sequences, 7% (4 species pairs and 1 flock of 5 species; one of the overlapping species pairs represents probable introgression. ) Five species showed divergent clusters differing by 1-2% in different parts of their geographic ranges, and 2 species showed larger divergences (3%, 7%); some or all of these might represent distinct species. 

A challenge for science publishing is disseminating the large data sets that are increasingly generated. Restricting publication to only those studies with novel findings can lead to a kind of distortion, sometimes with serious consequences. The bias against negative studies, for example, is one factor contributing to the misculation of risks of medicines. As biodiversity genetics moves forward, we need ways to ensure high-quality work, receive appropriate academic credit, and disseminate results in a timely manner.  PLoS ONE describes itself as “an international, peer-reviewed, open-access, online publication…that welcomes reports on primary research from any scientific discipline.” It seems to me that this sort of forum with a focus on quality rather than novelty is needed as a home for publication of large genetic data sets including DNA barcode records. Making this information available in a timely manner will in turn help drive development of analytic and display tools and enable scientific applications, such as identification of fish eggs and larva shown above. 

DNA helps sort out really big animals, crowding Ark

Friday, June 13th, 2008

How many giraffes were onboard the Ark?  Giraffes are classified as a single species, Giraffa camelopardalis, with five to nine subspecies proposed based on regional variation in pelage (coat pattern). In 21 dec 2007 BMC Biology (open access) researchers from University of California, Los Angeles; Center for Conservation Research, Omaha Zoo; and Mpala Research Centre, Kenya, investigate genetic variation in giraffes across African continent. 

Using biopsy darts, the authors collected skin specimens from 266 giraffes at 19 localities in West, East, and South Africa. A 654 nucleotide region of mtDNA spanning cytb and control sequences was analyzed, revealing 35 haplotypes, and the remainder of the cytb gene (1709 bp total) was sequenced from one individual from each of the 35 haplotypes. The mtDNA sequences clustered into six reciprocally monophyletic lineages, which corresponded to groupings according to pelage pattern and regional location, and were largely concordant with subspecies designations.  Genetic distances suggested these groups have been reproductively isolated for 0.3 to 1.6 MY, similar to calculated divergence times among other closely-related mammals.

Analysis of 14 nuclear microsatellites from 381 individuals at 18 locations (it is not clear whether these are the same individuals as above) recovered the same six groups and suggested additional genetic subdivisions within some groups. Although at least some of the genetically and pelage-defined clusters have overlapping or adjacent ranges without geographic barriers, only three (0.8%) of individuals were identified as hybrids. These findings raise interesting questions about giraffe biology; for example, is there behavioral isolation perhaps based on visual recognition of pelage patterns? 

It is impressive that species can be overlooked in such large, boldly patterned, iconic animals.  Might there be similar divisions within the numerous species of small, brown, rarely seen mammals? Routine DNA analysis of a standardized mtDNA region (aka DNA barcoding) will help discover how finely divided animal biodiversity is.  Wilson and Reeder’s Mammal Species of the World, Third Edition lists 5,419 species, so this appears to be an achievable goal for our mammalian kin (list available online http://nmnhgoph.si.edu/msw/).  I hope the authors include barcode region COI in their next analyses, so their data can be easily combined with other data sets, including the 28,560 mammalian barcode records in BOLD to date. 

High school students help demonstrate practicality, utility of DNA barcoding

Wednesday, June 4th, 2008

High school students in San Diego are using DNA barcoding to survey life in San Diego Bay, ranging from invasive mussels, to gastropod egg masses on eel grass, zooplankton and endangered species. Under leadership of Dr. Jay Vavra, students developed a simplified protocol for DNA extraction and amplification that can be performed in the high school’s biotechnology laboratory, and successfully identified dried jerky meat from ostrich, turkey, and beef. They have established a collaboration with East African graduate students to apply this approach to identifying bushmeat from endangered species in local African markets.

Just two years ago, in Syst Biol 55: 844, 2006 some taxonomists worried whether DNA barcoding would ever be useful: “The truth is that DNA barcoding will not have any meaningful use for the general public and even when a portable barcoder becomes available it will not lead to any increase in the biological literacy of the man in the street.” Authors Cameron et al might want to visit their local high school!

For high school students DNA barcoding seems as natural as texting. You can analyze DNA to identify species? Sure. You only need a trace sample, like a hair or a bit of dried skin? Sure, just like CSI shows. On the other side, many identification keys are not practical for most persons who would like to identify what is in their backyard.


Contact: mark.stoeckle@rockefeller.edu

About this site

This web site is an outgrowth of the Taxonomy, DNA, and Barcode of Life meeting held at Banbury Center, Cold Spring Harbor Laboratory, September 9-12, 2003. It is designed and managed by Mark Stoeckle, Perrin Meyer, and Jason Yung at the Program for the Human Environment (PHE) at The Rockefeller University.

About the Program for the Human Environment

The involvement of the Program for the Human Environment in DNA barcoding dates to Jesse Ausubel's attendance in February 2002 at a conference in Nova Scotia organized by the Canadian Center for Marine Biodiversity. At the conference, Paul Hebert presented for the first time his concept of large-scale DNA barcoding for species identification. Impressed by the potential for this technology to address difficult challenges in the Census of Marine Life, Jesse agreed with Paul on encouraging a conference to explore the contribution taxonomy and DNA could make to the Census as well as other large-scale terrestrial efforts. In his capacity as a Program Director of the Sloan Foundation, Jesse turned to the Banbury Conference Center of Cold Spring Harbor Laboratory, whose leader Jan Witkowski prepared a strong proposal to explore both the scientific reliability of barcoding and the processes that might bring it to broad application. Concurrently, PHE researcher Mark Stoeckle began to work with the Hebert lab on analytic studies of barcoding in birds. Our involvement in barcoding now takes 3 forms: assisting the organizational development of the Consortium for the Barcode of Life and the Barcode of Life Initiative; contributing to the scientific development of the field, especially by studies in birds, and contributing to public understanding of the science and technology of barcoding and its applications through improved visualization techniques and preparation of brochures and other broadly accessible means, including this website. While the Sloan Foundation continues to support CBOL through a grant to the Smithsonian Institution, it does not provide financial support for barcoding research itself or support to the PHE for its research in this field.