Biology Reference
In-Depth Information
interspecific genetic diversity. The methodology used to analyze data and to
develop phylogenetic trees continues to improve. However, considerable con-
troversy may surround specific conclusions because the use of different analysis
tools or different DNA sequences can result in different phylogenetic trees.
In 2003, DNA barcoding was proposed as a method to obtain rapid and
accurate identification of a broad range of organisms, including insects. The
Consortium for the Barcode of Life was initiated in 2004, and in 2010 the
International Barcode of Life project was established to develop an automated
identification system based on a DNA barcode library, based on the COI mitochon-
drial sequences, of most eukaryotes. Projects for the Lepidoptera, Trichoptera,
Formicidae, and Apidae were developed. The automated system requires
advances in information technology for the huge datasets produced and one
(Barcode of Life Database [BOLD]) is freely available to all scientists. However,
even Barcoding has limitations and its validity has been questioned due to the
discovery of nuclear copies of the mitochondrial genes (called numts), which can
result in erroneous conclusions about the diversity of arthropod species.
12.2 Introduction
The methods and concepts used to classify arthropods, and other organisms, are
themselves undergoing evolution. Classification started when Linnaeus estab-
lished a formalized hierarchical system of binomial nomenclature in 1758. Carolus
Linnaeus, a Swedish botanist, published
Systema Naturae
in 1758 and proposed
basic principles for organizing newly described species into groups and for assign-
ing these groups to specific taxonomic categories. This resulted in a ranking clas-
sification, typically ascending from species to genus, family, order, class, super
class, subphylum, phylum, and kingdom. See
Table 12.1
for two outlines of the
higher classification of the Phylum Arthropoda (others are available). One outline
was presented in the second edition of
Insect Biology and Diversity
(
Daly et al.
1998
), and the third edition was just published by
Whitfield and Purcell (2013)
,
indicating how rapidly concepts can change with the addition of new, mostly
molecular, data. The classification of the orders also changed between edition 2
and 3 (
Table 12.2
), with termites and cockroaches now included in the Blattodea
and with Homoptera and Hemiptera now collapsed into Hemiptera.
The Linnaean system made no provision for naming and classifying organisms
based on evolutionary relationships and Linnaeus assumed the living world was
limited to
≈
10,000 species. The notion that a classification should be based on
phylogenetic, or evolutionary, relationships developed only after Darwin's pub-
lication of
The Origin of the Species
in 1859. The identification, description, and
explanation of the diversity of organisms are known as systematics.
