Download Hidden Diversity: DNA `barcoding`

27-Sep-2004
Hidden diversity: DNA 'barcoding' reveals a common butterfly is actually 10 different
species
PHILADELPHIA – A common butterfly, found
in a variety of habitats from the southern United
States to northern Argentina, is actually
comprised of at least 10 separate species,
according to researchers from the University of
Pennsylvania.
Astraptes fulgerator, a medium-large skipper
butterfly, is a routine visitor to urban gardens and
tropical rainforests. While the "species" has been
known to science since 1775, only now has
examination of a small and standardized
signature piece of the genome – a technique
called DNA barcoding – shown that this
"species" is really an amalgam of a number of
genetically distinct lineages, each with different caterpillars and preferences in food plant and
ecosystem.
However, as many as six species can live in the same place, which strongly suggests mating
segregation. Because the adults differ at best only slightly in appearance -- so slightly that it was
attributed to ordinary "variation" -- this finding may have larger implications for maintaining
biodiversity.
"It raises the questions of how many other species out there are really multiple species like this
one and what that might mean to wildlife conservation," said Daniel Janzen, co-author of the
study and professor in the Department of Biology in Penn's School Arts and Sciences. "We
might lament the local extinction of a plant or animal but take comfort in the notion that the
species lives on elsewhere. Well, what if that extinct animal was the only example of a
genetically distinct species, hiding inside a morphology similar to the surviving species?"
Janzen and his colleagues report their findings in the Sept. 29 issue of the Proceedings of the
National Academy of Sciences. Their research began during 25-year-long inventory of the
wildlife in the Area de Conservación Guanacaste, a large conservation zone of dry, rain and
cloud forests in northwestern Costa Rica. They noticed that, amid the more than 2,500 wildcaught caterpillars of A. fulgerator, many could be separated by slight variations in color, which
then could be linked to the particular plants the caterpillars ate.
It soon became obvious that A. fulgerator was, indeed, a complex of a number of separate
species whose adult forms looked remarkably similar. When the centuries-old method of telling
insects apart -- the examination of their genitalia by John Burns at the Smithsonian Institution –proved inconclusive, the team turned to a recently emerging method for discriminating species:
DNA "barcoding,"
In much the same way that supermarket barcoding can distinguish one brand of canned beets
from another, DNA barcoding is an attempt to classify species by variations in a small signature
and standardized portion of gene called cytochrome c oxidase I, common to all life. Based at the
University of Guelph in Canada, the Barcode of Life Database can determine patterns of COI
gene variation within a given group of specimens. If the specimens in question differ by more
than a few percent in their base pairs of DNA in this gene, it is likely that they have come from
different populations.
Paul Hebert and Erin Penton at Guelph were able to extract the necessary DNA from 484 adult
butterflies deposited at the Smithsonian –- all raised from the much larger pool of caterpillars
caught in Costa Rica by Janzen, Winnie Hallwachs and a team of 17 Costa Rican
parataxonomists –- despite the fact that these butterflies have been dried museum specimens for
as long as 23 years. Where possible, they included at least 20 individuals from each group of
food plant, color variation and preferred habitat. As a result, they found 10 distinct species within
the group known as A. fulgerator in an area the size of the greater Philadelphia area and as many
as six species in a place no larger than the 262-acre Penn campus.
"Given the vast range of the supposed A. fulgerator species, it doesn't take much imagination to
realize that there are probably a great many more hidden species out there," Janzen said. "Our
results add to the evidence that cryptic species are prevalent, which I believe is of critical
importance if we are to document the health of the environment and the richness of global
biodiversity."