Rockefeller University

Program for the Human Environment

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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Some Fret Over Exceptions to Barcoding

The springboard for a recent news@nature.com item by Hannah Hickey “Butterflies poke holes in DNA barcodes” is a report by Gompert et al in press in Mol. Ecology on genetic differences between two subspecies of Melissa blue butterfly, Lycaeides melissa melissa and L. m. samuelis. The latter subspecies is commonly known as “Karner blue” and is listed under the USA Endangered Species Act. Analysis of mitochondrial DNA revealed some populations of Karner blue have distinct COI sequences but those populations adjacent to the range of L. m. melissa subspecies do not. This result is not surprising. For one, DNA barcoding does not aim to separate subspecies. Subspecies are geographic variants within species whose differences shade into one another so it would be surprising if any single gene showed a sharp demarcation between populations. Most subspecies do not show diagnostic genetic differences, and when such differences are found, it has often led to proposals to elevate them to species status.

Regarding the utility of DNA barcoding, the findings with Melissa blues are unremarkable, as there are cases in all animal groups studied so far in which barcoding narrows identification to a few closely-related species, but no further. For example, see my earlier entry on comparing barcode performance. It may be helpful to point out that DNA barcoding is an instrument, not a theory. Cases of partial resolution do not “disprove” barcoding or invalidate its use. In fact, one application of DNA barcoding will be to quickly highlight such cases which may be biologically interesting as they likely represent recent speciation, ongoing hybridization, or synonymy.

A more relevant Nature article that Ms. Hickey might have cited is Als et al study of Maculinea large blues, a related group morphologically similar, taxonomically confusing, and highly endangered butterflies. Large blues have “extraordinary parasitic lifestyles…later instars live in ant nests where they either devour the brood (predators), or are fed mouth-to-mouth by adult ants (cuckoos)”. Genetic analysis using mitochondrial and nuclear DNA uncovered numerous cryptic species with unsuspected host specificity, thereby both multiplying the challenge and providing the key to conservation, the need to conserve both ant hosts and butterflies.

As highlighted by the large blue study, the larger and more exciting challenge for biodiversity science will be how to incorporate the enormous number of genetically and biologically distinct forms whose discovery is facilitated by large-scale barcoding.

Photo of Rebel’s large blue Maculinea rebeli and phylogeny showing cryptic species among predatory Maculinea from Nature article by Als et al.

This entry was posted on Tuesday, March 28th, 2006 at 11:05 am and is filed under barcode performance, General. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

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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.