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1.
Noboru Sueoka 《Journal of molecular evolution》1999,49(1):49-62
The relative contribution of mutation and selection to the G+C content of DNA was analyzed in bacterial species having widely
different G+C contents. The analysis used two methods that were developed previously. The first method was to plot the average
G+C content of a set of nucleotides against the G+C content of the third codon position for each gene. This method was used
to present the G+C distribution of the third codon position and to assess the relative neutrality of a set of nucleotides
to that of the G+C content of the third codon position. The second method was to plot the intrastrand bias of the third codon
position from Parity Rule 2 (PR2), where A=T and G=C. It was found that whereas intragenomic distributions of the DNA G+C content of these bacteria are narrow in the majority
of species, in some species the G+C content of the minor class of genes distributes over wider ranges than the major class
of genes. On the other hand, ubiquitous PR2 biases are amino acid specific and independent of the G+C content of DNA, so that
when averaged over the amino acids, the biases are small and not correlated with the DNA G+C content. Therefore, translation
coupled PR2-biases are unlikely to explain the wide range of G+C contents among different species. Considering all data available,
it was concluded that the amino acid-specific PR2 bias has only a minor effect, if any, on the average G+C content. In addition,
PR2 bias patterns of different species show phylogenetic relationships, and the pattern can be as a taxal fingerprint.
Received: 5 November 1998 / Accepted: 1 March 1999 相似文献
2.
Base composition is not uniform across the genome of Drosophila melanogaster. Earlier analyses have suggested that there is variation in composition in D. melanogaster on both a large scale and a much smaller, within-gene, scale. Here we present analyses on 117 genes which have reliable intron/exon
boundaries and no known alternative splicing. We detect significant heterogeneity in G+C content among intron segments from
the same gene, as well as a significant positive correlation between the intron and the third codon position G+C content within
genes. Both of these observations appear to be due, in part, to an overall decline in intron and third codon position G+C
content along Drosophila genes with introns. However, there is also evidence of an increase in third codon position G+C content at the start of genes;
this is particularly evident in genes without introns. This is consistent with selection acting against preferred codons at
the start of genes.
Received: 24 February 1997 / Accepted: 10 November 1997 相似文献
3.
Langenkämper G Fung RW Newcomb RD Atkinson RG Gardner RC MacRae EA 《Journal of molecular evolution》2002,54(3):322-332
We present phylogenetic analyses to demonstrate that there are three families of sucrose phosphate synthase (SPS) genes present
in higher plants. Two data sets were examined, one consisting of full-length proteins and a second larger set that covered
a highly conserved region including the 14-3-3 binding region and the UDPGlu active site. Analysis of both datasets showed
a well supported separation of known genes into three families, designated A, B, and C. The genomic sequences of Arabidopsis thaliana include a member in each family: two genes on chromosome 5 belong to Family A, one gene on chromosome 1 to Family B, and
one gene on chromosome 4 to Family C. Each of three Citrus genes belong to one of the three families. Intron/exon organization of the four Arabidopsis genes differed according to phylogenetic analysis, with members of the same family from different species having similar
genomic organization of their SPS genes. The two Family A genes on Arabidopsis chromosome 5 appear to be due to a recent duplication. Analysis of published literature and ESTs indicated that functional
differentiation of the families was not obvious, although B family members appear not to be expressed in roots. B family genes
were cloned from two Actinidia species and southern analysis indicated the presence of a single gene family, which contrasts to the multiple members of
Family A in Actinidia. Only two family C genes have been reported to date.
Received: 17 April 2001 / Accepted: 27 August 2001 相似文献
4.
Abdelaziz Heddi Hubert Charles Chaqué Khatchadourian Guy Bonnot Paul Nardon 《Journal of molecular evolution》1998,47(1):52-61
The principal intracellular symbiotic bacteria of the cereal weevil Sitophilus oryzae were characterized using the sequence of the 16S rDNA gene (rrs gene) and G + C content analysis. Polymerase chain reaction amplification with universal eubacterial primers of the rrs gene showed a single expected sequence of 1,501 bp. Comparison of this sequence with the available database sequences placed
the intracellular bacteria of S. oryzae as members of the Enterobacteriaceae family, closely related to the free-living bacteria, Erwinia herbicola and Escherichia coli, and the endocytobiotic bacteria of the tsetse fly and aphids. Moreover, by high-performance liquid chromatography, we measured
the genomic G + C content of the S. oryzae principal endocytobiotes (SOPE) as 54%, while the known genomic G + C content of most intracellular bacteria is about 39.5%.
Furthermore, based on the third codon position G + C content and the rrs gene G + C content, we demonstrated that most intracellular bacteria except SOPE are A + T biased irrespective of their phylogenetic
position. Finally, using the hsp60 gene sequence, the codon usage of SOPE was compared with that of two phylogenetically closely related bacteria: E. coli, a free-living bacterium, and Buchnera aphidicola, the intracellular symbiotic bacteria of aphids. Taken together, these results show a peculiar and distinctly different DNA
composition of SOPE with respect to the other obligate intracellular bacteria, and, combined with biological and biochemical
data, they elucidate the evolution of symbiosis in S. oryzae.
Received: 8 September 1997 / Accepted: 24 October 1997 相似文献
5.
Wolbachia are obligatory intracellular and maternally inherited bacteria, known to infect many species of arthropod. In this study,
we discovered a bacteriophage-like genetic element in Wolbachia, which was tentatively named bacteriophage WO. The phylogenetic tree based on phage WO genes of several Wolbachia strains was not congruent with that based on chromosomal genes of the same strains, suggesting that phage WO was active and
horizontally transmitted among various Wolbachia strains. All the strains of Wolbachia used in this study were infected with phage WO. Although the phage genome contained genes of diverse origins, the average
G+C content and codon usage of these genes were quite similar to those of a chromosomal gene of Wolbachia. These results raised the possibility that phage WO has been associated with Wolbachia for a very long time, conferring some benefit to its hosts. The evolution and possible roles of phage WO in various reproductive
alterations of insects caused by Wolbachia are discussed.
Received: 28 January 2000 / Accepted: 3 August 2000 相似文献
6.
Relationships Between Genomic G+C Content,RNA Secondary Structures,and Optimal Growth Temperature in Prokaryotes 总被引:11,自引:0,他引:11
G:C pairs are more stable than A:T pairs because they have an additional hydrogen bond. This has led to many studies on the
correlation between the guanine+cytosine (G+C) content of nucleic acids and temperature over the last 20 years. We collected
the optimal growth temperatures (Topt) and the G+C contents of genomic DNA; 23S, 16S, and 5S ribosomal RNAs; and transfer RNAs for 764 prokaryotic species. No
correlation was found between genomic G+C content and Topt, but there were striking correlations between the G+C content of ribosomal and transfer RNA stems and Topt. Two explanations have been proposed—neutral evolution and selection pressure—for the approximate equalities of G and C (respectively,
A and T) contents within each strand of DNA molecules. Our results do not support the notion that selection pressure induces
complementary oligonucleotides in close proximity and therefore numerous secondary structures in prokaryotic DNA, as the genomic
G+C content does not behave in the same way as that of folded RNA with respect to optimal growth temperature.
Received: 25 September 1996 / Accepted: 21 January 1997 相似文献
7.
Analysis of DNA sequences of 132 introns and 140 exons from 42 pairs of orthologous genes of mouse and rat was used to compare
patterns of evolutionary change between introns and exons. The mean of the absolute difference in length (measured in base
pairs) between the two species was nearly five times as high in the case of introns as in the case of exons. The average rate
of nucleotide substitution in introns was very similar to the rate of synonymous substitution in exons, and both were about
three times the rate of substitution at nonsynonymous sites in exons. G+C content of introns and exons of the same gene were
correlated; but mean G+C content at the third positions of exons was significantly higher than that of introns or positions
1–2 of exons from the same gene. G+C content was conserved over evolutionary time, as indicated by strong correlations between
mouse and rat; but the change in G+C content was greatest at position 3 of exons, intermediate in introns, and lowest at positions
1–2 in introns.
Received: 23 December 1996 / Accepted: 1 April 1997 相似文献
8.
Nucleotide Composition Bias Affects Amino Acid Content in Proteins Coded by Animal Mitochondria 总被引:16,自引:0,他引:16
We show that in animal mitochondria homologous genes that differ in guanine plus cytosine (G + C) content code for proteins
differing in amino acid content in a manner that relates to the G + C content of the codons. DNA sequences were analyzed using
square plots, a new method that combines graphical visualization and statistical analysis of compositional differences in
both DNA and protein. Square plots divide codons into four groups based on first and second position A + T (adenine plus thymine)
and G + C content and indicate differences in amino acid content when comparing sequences that differ in G + C content. When
sequences are compared using these plots, the amino acid content is shown to correlate with the nucleotide bias of the genes.
This amino acid effect is shown in all protein-coding genes in the mitochondrial genome, including cox I, cox II, and cyt b, mitochondrial genes which are commonly used for phylogenetic studies. Furthermore, nucleotide content differences are shown
to affect the content of all amino acids with A + T- and G + C-rich codons. We speculate that phylogenetic analysis of genes
so affected may tend erroneously to indicate relatedness (or lack thereof) based only on amino acid content.
Received: 3 July 1996 / Accepted: 6 November 1996 相似文献
9.
Near Homogeneity of PR2-Bias Fingerprints in the Human Genome and Their Implications in Phylogenetic Analyses 总被引:1,自引:0,他引:1
Noboru Sueoka 《Journal of molecular evolution》2001,53(4-5):469-476
Genes of a multicellular organism are heterogeneous in the G+C content, which is particularly true in the third codon position.
The extent of deviation from intra-strand equality rule of A = T and G = C (Parity Rule 2, or PR2) is specific for individual amino acids and has been expressed as the PR2-bias fingerprint. Previous
results suggested that the PR2-bias fingerprints tend to be similar among the genes of an organism, and the fingerprint of
the organism is specific for different taxa, reflecting phylogenetic relationships of organisms. In this study, using coding
sequences of a large number of human genes, we examined the intragenomic heterogeneity of their PR2-bias fingerprints in relation
to the G+C content of the third codon position (P
3
). Result shows that the PR2-bias fingerprint is similar in the wide range of the G+C content at the third codon position
(0.30–0.80). This range covers approximately 89% of the genes, and further analysis of the high G+C range (0.80–1.00), where
genes with normal PR2-bias fingerprints and those with anomalous fingerprints are mixed, shows that the total of 95% of genes
have the similar finger prints. The result indicates that the PR2-bias fingerprint is a unique property of an organism and
represents the overall characteristics of the genome. Combined with the previous results that the evolutionary change of the
PR2-bias fingerprint is a slow process, PR2-bias fingerprints may be used for the phylogenetic analyses to supplement and
augment the conventional methods that use the differences of the sequences of orthologous proteins and nucleic acids. Potential
advantages and disadvantages of the PR2-bias fingerprint analysis are discussed.
Received: 21 December 2000 / Accepted: 16 February 2001 相似文献
10.
Sawada H Kanaya S Tsuda M Suzuki F Azegami K Saitou N 《Journal of molecular evolution》2002,54(4):437-457
Phytopathogenic Pseudomonas syringae is subdivided into about 50 pathovars due to their conspicuous differentiation with regard to pathogenicity. Based on the
results of a phylogenetic analysis of four genes (gyrB, rpoD, hrpL, and hrpS), Sawada et al. (1999) showed that the ancestor of P. syringae had diverged into at least three monophyletic groups during its evolution. Physical maps of the genomes of representative
strains of these three groups were constructed, which revealed that each strain had five rrn operons which existed on one circular genome. The fact that the structure and size of genomes vary greatly depending on the
pathovar shows that P. syringae genomes are quite rich in plasticity and that they have undergone large-scale genomic rearrangements. Analyses of the codon
usage and the GC content at the codon third position, in conjunction with phylogenomic analyses, showed that the gene cluster
involved in phaseolotoxin synthesis (argK–tox cluster) expanded its distribution by conducting horizontal transfer onto the genomes of two P. syringae pathovars (pv. actinidiae and pv. phaseolicola) from bacterial species distantly related to P. syringae and that its acquisition was quite recent (i.e., after the ancestor of P. syringae diverged into the respective pathovars). Furthermore, the results of a detailed analysis of argK [an anabolic ornithine carbamoyltransferase (anabolic OCTase) gene], which is present within the argK–tox cluster, revealed the plausible process of generation of an unusual composition of the OCTase genes on the genomes of these
two phaseolotoxin-producing pathovars: a catabolic OCTase gene (equivalent to the orthologue of arcB of P. aeruginosa) and an anabolic OCTase gene (argF), which must have been formed by gene duplication, have first been present on the genome of the ancestor of P. syringae; the catabolic OCTase gene has been deleted; the ancestor has diverged into the respective pathovars; the foreign-originated
argK–tox cluster has horizontally transferred onto the genomes of pv. actinidiae and pv. phaseolicola; and hence two copies of only the anabolic OCTase genes (argK and argF) came to exist on the genomes of these two pathovars. Thus, the horizontal gene transfer and the genomic rearrangement were
proven to have played an important role in the pathogenic differentiation and diversification of P. syringae.
Received: 22 May 2001 / Accepted: 26 September 2001 相似文献
11.
12.
Capsular polysaccharides are important virulence factors both in Gram-positive and Gram-negative bacteria. A similar cluster
organization of the genes involved in the synthesis of bacterial exopolysaccharides has been postulated in both cases, suggesting
that these clusters evolved by module assembly. Horizontal gene transfer has been postulated to explain the polymorphism found
in these cellular polymers. The cap1K and cap3A genes coding for the pneumococcal type 1 and type 3 UDP-glucose dehydrogenases, respectively, have been compared with other
UDP-sugar dehydrogenases. We have observed that the evolutionary distance between Cap1K and Cap3A is approximately equal to
that found between Cap1K (or Cap3A) and other UDP-GlcDH of families evolutionarily distant like KfiD, the dehydrogenase from
Escherichia coli K5. On the basis of comparisons of G + C content, patterns of synonymous and nonsynonymous substitutions, dinucleotide frequencies,
and codon usage bias, we conclude that the kfiD gene has been introduced into E. coli from an exogenous source, probably from a streptococcal species.
Received: 26 May 1997 / Accepted: 30 July 1997 相似文献
13.
Wang B 《Journal of molecular evolution》2001,53(3):244-250
Genes with atypical G+C content and pattern of codon usage in a certain genome are possibly of exotic origin, and this idea
has been applied to identify horizontal events. In this way, it was postulated that a total of 755 genes in the E. coli genome are relics of horizontal events after the divergence of E. coli from the Salmonella lineage 100 million years ago (Lawrence and Ochman, 1998). In this paper we propose a new way to study sequence composition
more thoroughly. We found that although the 755 genes differ in composition from other genes in the E. coli genome, the difference is minor. If we accepted that these genes are horizontally transferred, then (1) it would be more
likely that they were transferred from genomes evolutionarily closely related to E. coli; but (2) the dating method used by Lawrence and Ochman (1997, 1998) largely underestimated the average age of introduced sequences
in the E. coli genome, in particular, most of the 755 genes should be introduced into E. coli before, instead of after, the divergence of E. coli from the Salmonella lineage. Our study reveals that atypical G+C content and pattern of codon usage are not reliable indicators of horizontal
gene transfer events.
Received: 27 September 2000 / Accepted: 9 April 2001 相似文献
14.
We compared the codon usage of sequences of transposable elements (TEs) with that of host genes from the species Drosophila melanogaster, Arabidopsis thaliana, Caenorhabditis elegans, Saccharomyces cerevisiae, and Homo sapiens. Factorial correspondence analysis showed that, regardless of the base composition of the genome, the TEs differed from the
genes of their host species by their AT-richness. In all species, the percentage of A + T on the third codon position of the
TEs was higher than that on the first codon position and lower than that in the noncoding DNA of the genomes. This indicates
that the codon choice is not simply the outcome of mutational bias but is also subject to selection constraints. A tendency
toward higher A + T on the third position than on the first position was also found in the host genes of A. thaliana, C. elegans, and S. cerevisiae but not in those of D. melanogaster and H. sapiens. This strongly suggests that the AT choice is a host-independent characteristic common to all TEs. The codon usage of TEs
generally appeared to be different from the mean of the host genes. In the AT-rich genomes of Arabidopsis thaliana, Caenorhabditis elegans, and Saccharomyces cerevisiae, the codon usage bias of TEs was similar to that of weakly expressed genes. In the GC-rich genome of D. melanogaster, however, the bias in codon usage of the TEs clearly differed from that of weakly expressed genes. These findings suggest
that selection acts on TEs and that TEs may display specific behavior within the host genomes.
Received: 2 May 2001 / Accepted: 29 October 2001 相似文献
15.
Along the gene, nucleotides in various codon positions tend to exert a slight but observable influence on the nucleotide
choice at neighboring positions. Such context biases are different in different organisms and can be used as genomic signatures.
In this paper, we will focus specifically on the dinucleotide composed of a third codon position nucleotide and its succeeding
first position nucleotide. Using the 16 possible dinucleotide combinations, we calculate how well individual genes conform
to the observed mean dinucleotide frequencies of an entire genome, forming a distance measure for each gene. It is found that
genes from different genomes can be separated with a high degree of accuracy, according to these distance values.
In particular, we address the problem of recent horizontal gene transfer, and how imported genes may be evaluated by their
poor assimilation to the host's context biases. By concentrating on the third- and succeeding first position nucleotides,
we eliminate most spurious contributions from codon usage and amino-acid requirements, focusing mainly on mutational effects.
Since imported genes are expected to converge only gradually to genomic signatures, it is possible to question whether a gene
present in only one of two closely related organisms has been imported into one organism or deleted in the other. Striking
correlations between the proposed distance measure and poor homology are observed when Escherichia coli genes are compared to Salmonella typhi, indicating that sets of outlier genes in E. coli may contain a high number of genes that have been imported into E. coli, and not deleted in S. typhi.
Received: 16 January 2001 / Accepted: 30 August 2001 相似文献
16.
Base Composition Skews, Replication Orientation, and Gene Orientation in 12 Prokaryote Genomes 总被引:21,自引:0,他引:21
Michael J. McLean Kenneth H. Wolfe Kevin M. Devine 《Journal of molecular evolution》1998,47(6):691-696
Variation in GC content, GC skew and AT skew along genomic regions was examined at third codon positions in completely sequenced
prokaryotes. Eight out of nine eubacteria studied show GC and AT skews that change sign at the origin of replication. The
leading strand in DNA replication is G-T rich at codon position 3 in six eubacteria, but C-T rich in two Mycoplasma species. In M. genitalium the AT and GC skews are symmetrical around the origin and terminus of replication, whereas its GC content variation has been
shown to have a centre of symmetry elsewhere in the genome. Borrelia burgdorferi and Treponema pallidum show extraordinary extents of base composition skew correlated with direction of DNA replication. Base composition skews
measured at third codon positions probably reflect mutational biases, whereas those measured over all bases in a sequence
(or at codon positions 1 and 2) can be strongly affected by protein considerations due to the tendency in some bacteria for
genes to be transcribed in the same direction that they are replicated. Consequently in some species the direction of skew
for total genomic DNA is opposite to that for codon position 3.
Received: 2 February 1998 / Accepted: 15 June 1998 相似文献
17.
Seiichi Taguchi Shuichi Kojima Mahito Terabe Yoshinori Kumazawa Hiroshi Kohriyama Masayuki Suzuki Kin-ichiro Miura Haruo Momose 《Journal of molecular evolution》1997,44(5):542-551
We previously found that proteinaceous protease inhibitors homologous to Streptomyces subtilisin inhibitor (SSI) are widely produced by various Streptomyces species, and we designated them ``SSI-like proteins' (Taguchi S, Kikuchi H, Suzuki M, Kojima S, Terabe M, Miura K, Nakase
T, Momose H [1993] Appl Environ Microbiol 59:4338–4341). In this study, SSI-like proteins from five strains of the genus Streptoverticillium were purified and sequenced, and molecular phylogenetic trees were constructed on the basis of the determined amino acid
sequences together with those determined previously for Streptomyces species. The phylogenetic trees showed that SSI-like proteins from Streptoverticillium species are phylogenetically included in Streptomyces SSI-like proteins but form a monophyletic group as a distinct lineage within the Streptomyces proteins. This provides an alternative phylogenetic framework to the previous one based on partial small ribosomal RNA sequences,
and it may indicate that the phylogenetic affiliation of the genus Streptoverticillium should be revised. The phylogenetic trees also suggested that SSI-like proteins possessing arginine or methionine at the
P1 site, the major reactive center site toward target proteases, arose multiple times on independent lineages from ancestral
proteins possessing lysine at the P1 site. Most of the codon changes at the P1 site inferred to have occurred during the evolution
of SSI-like proteins are consistent with those inferred from the extremely high G + C content of Streptomyces genomes. The inferred minimum number of amino acid replacements at the P1 site was nearly equal to the average number for
all the variable sites. It thus appears that positive Darwinian selection, which has been postulated to account for accelerated
rates of amino acid replacement at the major reaction center site of mammalian protease inhibitors, may not have dictated
the evolution of the bacterial SSI-like proteins.
Received: 23 August 1996 / Accepted: 20 November 1996 相似文献
18.
Phylogenetic Analysis of Invertebrate Lysozymes and the Evolution of Lysozyme Function 总被引:22,自引:0,他引:22
Bachali S Jager M Hassanin A Schoentgen F Jollès P Fiala-Medioni A Deutsch JS 《Journal of molecular evolution》2002,54(5):652-664
We isolated and sequenced the cDNAs coding for lysozymes of six bivalve species. Alignment and phylogenetic analysis showed
that, together with recently described bivalve lysozymes, the leech destabilase, and a number of putative proteins from extensive
genomic and cDNA analyses, they belong to the invertebrate type of lysozymes (i type), first described by Jollès and Jollès
(1975). We determined the genomic structure of the gene encoding the lysozyme of Mytilus edulis, the common mussel. We provide evidence that the central exon of this gene is homologous to the second exon of the chicken
lysozyme gene, belonging to the c type. We propose that the origin of this domain can be traced back in evolution to the origin
of bilaterian animals. Phylogenetic analysis suggests that i-type proteins form a monophyletic family.
Received: 21 May 2001 / Accepted: 22 October 2001 相似文献
19.
Syvanen M 《Journal of molecular evolution》2002,54(2):258-266
The deduced amino acid sequences from 1200 Haemophilus influenzae genes was compared to a data set that contained the orfs from yeast, two different Archaea and the Gram+ and Gram− bacteria,
Bacillus subtilis and Escherichia coli. The results of the comparison yielded a 26 orthologous gene set that had at least one representative from each of the four
groups. A four taxa phylogenetic relationship for these 26 genes was determined. The statistical significance of each minimal
tree was tested against the two alternative four taxa trees. The result was that four genes significantly supported the (Archaea,
Eukaryota) (Gram+, Gram−) topology, two genes supported the one where Gram− and Eukaryota form a clade, and one gene supported
the tree where Gram+ and Eukaryota define one clade. The remaining genes do not uniquely support any phylogeny, thereby collapsing
the two central nodes into a single node. These are referred to as star phylogenies.
I offer a new suggestion for the mechanism that gave rise to the star phylogenies. Namely, these are genes that are younger
than the underlying lineages that currently harbor them. This hypothesis is examined with two proteins that display the star
phylogeny; namely onithine transcarbamylase and tryptophan synthetase. It is shown, using the distance matrix rate test, that
the rate of evolution of these two proteins is comparable to a control gene when rates are determined by comparing closely
related species. This implies that the genes under comparison experience comparable functional constraint. However, when the
genes from remotely related species are compared, a plateau is encountered. Since we see no unusual levels of functional constraint
this plateau cannot be attributed to the divergence of the protein having reached saturation. The simplest explanation is
that the genes displaying the star phylogenies were introduced after Archaea, Eukaryota, and Bacteria had diverged from one
another. They presumably spread through life by horizontal gene transfer.
Received: 12 July 2001 / Accepted: 27 July 2001 相似文献
20.
Francesco Frati Chris Simon Jack Sullivan David L. Swofford 《Journal of molecular evolution》1997,44(2):145-158
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 相似文献