88 K. Sreedevi et al.
rate of molecular evolution that is about three
times that of 12S or 16S rDNA, its third position
nucleotides showing a high incidence of base
substitutions. The success of universal primers
for this gene enables the analysis of amino acid
substitutions to initially designate an unidentified
organism to a higher taxonomic group before ex-
amining nucleotide substitutions to determine its
species identity (Hebert et al. 2003 ).
Hebert et al. ( 2003 ) named this technique
“DNA barcoding.” Then, the Barcode of Life
project was proposed to promote DNA barcod-
ing as a global standard for sequence-based iden-
tification of eukaryotes. Recently, the Barcode
of Life project entered a new phase with the
launch of the International Barcode of Life proj-
ect (IBOL; International Barcode of Life 2012).
The IBOL is a huge international collaboration of
26 countries that aims to establish an automated
identification system based on a DNA barcode
library of all eukaryotes. In the first 5 years, the
IBOL will focus mainly on developing a barcode
library, including 5 million specimens of 500,000
species. The DNA sequences are used as genetic
“barcodes” that may potentially be used as a bi-
oidentification system for all animals and have
proven to be a useful identification tool for ver-
tebrates such as birds (Hebert et al. 2004 ), fish
(Ward et al. 2005 ), and hexapod orders such as
Lepidoptera (Hajibabaei et al. 2006 ), Coleoptera
(Greenstone et al. 2005 ), Diptera (Smith et al.
2007 ), Hymenoptera (Smith et al. 2008 ), Ephem-
eroptera (Ball et al. 2005 ), and Hemiptera (Lee
et al. 2011 ). DNA barcoding does not substi-
tute but complement conventional taxonomical
studies.
The three main taxonomic applications that
DNA barcoding has been previously used are: (1)
the identification of species previously defined
by other criteria, including rapid identification,
as well as linking specimens to established spe-
cies that are unidentifiable by other means; (2)
the description of new species by interpreting
DNA diversity as an indicator of species diver-
sity; (3) the definition of operational units for
ecological studies (Rubinoff 2006 ).
DNA should be an excellent tool for inferring
phylogenies: large number of homologous char-
acters that should be less subject to convergent
evolution than other characters that might lead to
a confusion of grade and clade. A character can
be phylogenetically informative when nucleotide
changes are shared by two or more taxa. A char-
acter can be phylogenetically uninformative when
all nucleotides are the same among taxa, or when
only a single taxon has a different nucleotide.
According to Hillis et al. ( 1996 ) three main
applications of molecular systematics are,- Reconstruction of phylogenetic relationships
of organisms. - Studies of population structure, including geo-
graphic variation, mating systems, heterozy-
gosity, and individual relatedness. - Identification of species boundaries including
hybridization.
There are many methods to understand these mo-
lecular variations; few molecular methods with
their applications were explained in Table 1
Molecular Markers Used in Systematics
A diverse range of novel molecular (DNA)
markers are now available for taxonomic inves-
tigations. Both DNA and protein markers have
revolutionized the biological sciences and have
enhanced many fields of study, especially sys-
tematics. This has been possible because of the
rapid advances in molecular biological methods
and bench-level protocols for wider application.
The utility of molecular markers as additional
tools in systematic has led to “molecular system-
atics”. Over a long time, significant contributions
have been made in the field of insect systematics
through morphometric traits, wherein a number
of difficulties were encountered due to geno-
type–environment interactions. The limitations
in using morphological, physiological, and cy-
tological markers for assessing genetic diversity
and population dynamics have been largely cir-
cumvented by the developments in DNA-based
markers. Molecular markers, by nature, are neu-
tral to the stage of development, physiological
status, and environmental influences. Isozymes
and other proteins as markers are often expressed
codominantly and discriminate homozygous and