Biology Reference
In-Depth Information
organisms that require microscopic examination for morphological traits or that
have a variety of life stages.
Smith et al. (2006)
reported that parasitoid tachinid
flies have cryptic host specificity when subjected to DNA barcoding.
However, COI sequences in many organisms (algae, protists, and plants) are
not informative and indicate that COI is
not
a universal barcode for all life.
Furthermore, the method used to separate species with barcode data has been
criticized (
DeSalle et al. 2005
). The original expectation was that intraspecific
divergences in COI sequences are less than interspecific divergences and that
there is a “barcoding gap” between species. However, there clearly is not such
a gap between all animal species, and the degree of difference in distance that
is needed is debated. The use of barcoding to identify new species is particu-
larly controversial if it is the only attribute used to identify the new species. DNA
barcoding should create the hypothesis that a population is a new species and
additional data (morphological, molecular, behavioral) should be developed to
support the hypothesis.
Yassin et al. (2010)
used 68 species of
Drosophila
as a model to test DNA bar-
coding and tree- and character-based methods of species identification. They
analyzed 1058 COI sequences of the 68 species and found that “DNA bar-
coding of
Drosophila
shows no reason to alter the 250 year old tradition of
character-based taxonomy.” By contrast,
Ball and Armstrong (2006)
found that
DNA barcodes provided a highly accurate means of identifying 20 lymantriid spe-
cies.
Derocles et al. (2012)
studied 50 species of parasitoids that attack aphids in
northwestern Europe. They used both COI and a nuclear gene (long wavelength
rhodopsin) for their analyses and found that some species were indistinguishable
on the basis of their COI sequences, whereas the nuclear gene failed to discrimi-
nate between other species and concluded that “no unique locus but a combina-
tion of two genes should be used to accurately identify members of Aphidiinae.”
To work well, a library of DNA barcodes needs to be developed so that iden-
tifications can be made. This requires developing a large-scale database and
the ability to access voucher specimens for confirmation of identifications
(
Borisenko et al. 2009
). Thus, specimens are collected, prepared, sequence data
obtained, data are entered into databases, and the collection managed so that
data and specimens can be compared.
DNA barcoding is a “method of identifying previously described taxa” and
“reference sequences lie at the very heart of the DNA barcoding initiative”
because “Without verified reference sequences from voucher specimens that
have been authenticated by qualified taxonomists, there is no reliable library
for newly generated query sequences to be compared with” (
Taylor and Harris
