Evolution of the Mitochondrial Cytochrome Oxidase II Gene in Collembola |
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Authors: | Francesco Frati Chris Simon Jack Sullivan David L Swofford |
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Institution: | (1) Dipartimento di biologia Evolutiva, Università di Siena, via P.A. Mattioli 4, 53100, Siena, Italy, IT;(2) Department of Ecology and Evolutionary Biology, U-43, University of Connecticut, 75 North Eagleville Road, Storrs, CT 06269-3043, USA, US;(3) Laboratory of Molecular Systematics, MSC, MRC-534, Smithsonian Institution, Washington, DC 20560, USA, US |
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Abstract: | The sequence of the mitochondrial COII gene has been widely used to estimate phylogenetic relationships at different taxomonic
levels across insects. We investigated the molecular evolution of the COII gene and its usefulness for reconstructing phylogenetic
relationships within and among four collembolan families. The collembolan COII gene showed the lowest A + T content of all
insects so far examined, confirming that the well-known A + T bias in insect mitochondrial genes tends to increase from the
basal to apical orders. Fifty-seven percent of all nucleotide positions were variable and most of the third codon positions
appeared free to vary. Values of genetic distance between congeneric species and between families were remarkably high; in
some cases the latter were higher than divergence values between other orders of insects. The remarkably high divergence levels
observed here provide evidence that collembolan taxa are quite old; divergence levels among collembolan families equaled or
exceeded divergences among pterygote insect orders. Once the saturated third-codon positions (which violated stationarity
of base frequencies) were removed, the COII sequences contained phylogenetic information, but the extent of that information
was overestimated by parsimony methods relative to likelihood methods. In the phylogenetic analysis, consistent statistical
support was obtained for the monophyly of all four genera examined, but relationships among genera/families were not well
supported. Within the genus Orchesella, relationships were well resolved and agreed with allozyme data. Within the genus Isotomurus, although three pairs of populations were consistently identified, these appeared to have arisen in a burst of evolution from
an earlier ancestor. Isotomurus italicus always appeared as basal and I. palustris appeared to harbor a cryptic species, corroborating allozyme data.
Received: 12 January 1996 / Accepted: 10 August 1996 |
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Keywords: | : Collembola — mtDNA — Cytochrome c oxidase subunit II — Among-site rate variation — A + T bias — Phylogeny — Likelihood models |
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