Molecular Biology and Evolution, Vol 16, 1645-1653, Copyright © 1999 by Society for Molecular Biology and Evolution
T Wirth, RL Guellec and M Veuille
The cytochrome oxidase subunit II (COII) gene was sequenced for six
dermapteran species. The nucleotide composition of this gene is biased in
most animals. While the CG content of other insect orders is low (mean,
27.6%; range, 19.5%-33.1%), species from the Forficula genus showed
unusually high values (mean, 42.4%; range, 37.3%-44.1%), mostly due to high
CG frequencies at third codon positions: the mean CG content at these
positions was around 45% (range, 43.9%-46.9%) for Forficula, compared with
only 13.3% for other insects. This effect was so strong that in one
species, Forficula lesnei, there was no significant difference between the
frequencies of the four bases. During evolution, this loss of bias has
involved a significant increase in the synonymous substitution rate and an
increase of transitions over transversions compared with other insects. A
strong directionality of substitutions has favored T-->C and A-->G
changes. This phenomenon was also observed between two conspecific
populations of Forficula auricularia. A species from a closely related
genus, Anechura bipunctata, was intermediate between Forficula and other
insects for these parameters, while two remotely related dermapteran
species, Labidura riparia and Euborellia moesta, were similar to other
insects. These results suggest that the evolution of Forficula DNA content
has been both rapid and recent.
ORIGINAL ARTICLE
Directional substitution and evolution of nucleotide content in the cytochrome oxidase II gene in earwigs (dermapteran insects) Citation]
Laboratoire d'Ecologie and Ecole Pratique des Hautes Etudes, Paris 6 University, France.
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