Biology Reference
In-Depth Information
there are 3.7 million arthropod species (
Strain 2011
), so there will be systematics
work required for a long time to come. An understanding of arthropod system-
atics and phylogeny requires the combined use of the fossil record, traditional
morphological data, and molecular data and many relationships within the
Arthropoda remain to be resolved (
Giribet and Edgecombe 2012
).
12.9 Molecular Analyses of Arthropod Phylogeny
12.9.1 Evolution of the Ecdysozoa
The superphylum Ecdysozoa is an evolutionary clade that includes the Insecta,
Crustacea, Myriapoda, Chelicerata, Onychophora, Tardigrada, and five phyla
of worms, including the Nematoda. The Ecdysozoa is the largest clade of spe-
cies and occupies the greatest diversity of ecological niches, with an estimated
total of
>
4.5 million living species (
Telford et al. 2008
).
Telford et al. (2008)
reviewed the molecular data supporting the Ecdysozoa as a natural, monophy-
letic group.
12.9.2 Relationships among the Arthropoda
Regier et al. (2010)
evaluated 75 arthropod species using 62 single-copy nuclear
protein-coding genes. The data were analyzed using likelihood, Bayesian, and
parsimony methods. The 75 species included every major arthropod lineage plus
five species of tardigrades and onychophorans. The results strongly supported
the Pancrustacea (Hexapoda plus Crustacea) hypothesis and the morphology-
based Mandibulata (Myriapoda plus Pancrustacea).
12.9.3 The Phylogeny of the Holometabola
Wiegmann et al. (2009)
examined the evolutionary relationships of 11 orders
of holometabolous insects. These include the Neuroptera, Raphidioptera,
Megaloptera, Trichoptera, Lepidoptera, Diptera, Strepsiptera, Mecoptera,
Siphonaptera, Coleoptera, and Hymenoptera, all of which are thought to have
originated in the late Carboniferous (318-300mya). Six nuclear protein-coding
genes were analyzed using maximum likelihood and Basesian methods. The
results indicated that all orders are monophyletic, and the Hymenoptera are
the basal-most lineage of the Holometabola, originating approximately when
the Holometabola diverged. The Strepsiptera were found to be a sister group
to the Coleoptera, resolving the controversial placement of this order as a sister
group of the Neuroptera. Fleas (Siphonaptera) recently have been hypothesized
to be members of the Mecoptera, but the data from
Wiegmann et al. (2009)
do
not support collapsing the Siphonaptera into the Mecoptera. Based on molecu-
lar data, the holometabolous orders diverged rapidly, between 274 and 213 mya
(although the fossil record does not always reflect these dates).
