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DNA Barcoding Helps Expose Wasp Diversity

NEW YORK (GenomeWeb News) – A new study that weds traditional taxonomy, morphology, and ecology with DNA barcoding has uncovered more than a hundred previously unrecognized parasitic wasp species — and provided insights into their host specificity.
 
In a paper that will appear online this week in the Proceedings of the National Academy of Sciences, a team of North American researchers applied DNA barcoding to thousands of parasitoid wasps from a decades-old collection in northwestern Costa Rica. Their results illustrate the potential benefits of combining different types of biological data to document and understand biodiversity. And, researchers say, this approach could ultimately yield clues about the patterns that drive biological systems.
 
“Ultimately, we’re interested in understanding the rules that promote the rise and fall of species,” senior author Paul Hebert, director of the Biodiversity Institute of Ontario at the University of Guelph, told GenomeWeb Daily News.
 
A DNA barcoding pioneer, Hebert was among the first to propose using a standard, predetermined stretch of DNA to catalogue and identify as many eukaryotic organisms as possible. The goals of such efforts, he said, are to create a digital identification system for life that is based on DNA sequences and to find rules that scientists can apply when going into new regions and trying to understand species diversity.
 
For the latest paper, Hebert and his team focused on six genera from a subfamily of parasitoid wasps called the Microgastrinae, which parasitize caterpillars. About 1,500 Microgastrinae species have been described to date, but biologists estimate it may actually consist of more than five to ten thousand species. There is also relatively little known about just how specialized the parasites are — partly due to an incomplete understanding of their species diversity.
 
“Efforts to estimate parasitoid host specificity that do not include DNA-based discrimination of the parasitoid species are likely to underestimate host specificity because of the inadvertent labeling of morphologically similar but genetically isolated lineages as being a single species,” the authors wrote.
 
For the study, the researchers turned to a unique resource — Costa Rica’s Area de Conservacion Guanacaste — which includes caterpillars and associated parasitoid wasps collected over 30 years. The collection, which houses approximately 400,000 wild-caught and reared caterpillars, proved invaluable for the study, Hebert explained, because a wealth of morphological and taxonomic information and ecological correlates had been collected for the specimens.
 
Biologists were able to integrate this information with new genetic technology, Hebert explained, barcoding 2,597 parasitoid wasp specimens. Usually, he said, the goal is to get about 650 base pairs of sequence information. But since some specimens had degraded DNA from sitting on pins for decades, the researchers generally settled for sequences longer than 500 base pairs.
 
Based on morphological and taxonomic assessments, the parasitoid wasps fell into 171 provisional species groups. DNA barcoding increased the detected species richness in this group by some 70 percent, uncovering nearly 150 new provisional species. In the most striking example of hidden, cryptic species found by barcoding, the researchers identified 36 provisional species that had originally been classified as one.
 
In another case they identified wasps that shared a nearly identical DNA barcode but had distinct hosts, parasitizing caterpillars in different families.
 
Together, the combination of morphology, DNA barcodes, and host/ecological records revealed 313 provisional wasp species in the collection, each parasitizing just one, two, or a few closely related caterpillar species. “This kind of host specificity is so strongly correlated with the host’s ecology that the wasps cannot be labeled as generalists in any useful sense of the word,” the authors argued.
 
This specialization may eventually change the way in which community ecologists look at food webs as well, Hebert noted. “[B]arcoding can provide a rapid and relatively inexpensive first screen of a large, diverse, and understudied biota in a way that dramatically improves understanding of species richness and trophic webs,” he and his colleagues wrote.
 
Eventually, Hebert and others involved in the International Barcode of Life project would like to see barcoding applied to millions of specimens in order to characterize 500,000 species. That undertaking is expected to provide information that can be used to understand species diversity and increase the rate of new species discovery. And, Hebert noted, DNA barcoding is being applied to other fields as well. For instance, DNA barcodes are being used for tracking food products and in efforts to curb poaching.

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