Differences In Evolutionary Rates Research Articles

Phylogenetic relationships and remarkable radiation in Parartemia (Crustacea: Anostraca), the endemic brine shrimp of Australia: evidence from mitochondrial DNA sequences

The Australian continent is notable for the faunal radiations which have occurred in its saline inland waters. The endemic brine shrimp genus Parartemia inhabits many of these habitats. The complex pattern of morphological variation in parartemiids has impeded the establishment of a sound scheme of species relationships. The present study provides an explicit hypothesis of relationships for the genus based on nucleotide sequence data from a segment of mitochondrial DNA coding for the large subunit rRNA gene. Phylogenetic analyses indicated that the eight known species are genetically distinct, and revealed the existence of at least two new species. The molecular data support certain morphology-based relationships among species, but are inconsistent with other hypotheses. There is evidence that most members of the genus arose in a short interval, followed by remarkable genetic divergence. Comparisons of levels of mt DNA sequence divergence between lineages from saline inland waters and freshwaters using representative crustacean groups from Australia that included parartemiids indicated profound differences in rates of evolution, with halophiles exhibiting greater rates of change than their counterparts from freshwaters.

Molecular evolution of Mycobacterium tuberculosis: phylogenetic reconstruction of clonal expansion

Setting: M. tuberculosis isolates were collected from patients attending health clinics in a high incidence urban community and in a low incidence rural setting in South Africa.Objective: To reconstruct the evolutionary history of a group of closely related M. tuberculosis isolates using IS 6110, DRr and MTB484(1) restriction fragment length polymorphism (RFLP) data.Design: Mycobacterium tuberculosis isolates containing an average of ten IS 6110 elements, with a similarity index of ⩾65% were genotypically classified by DNA fingerprinting using the IS 6110 derived probes IS-3′ and IS-5′, as well as the DRr and MTB484(1) probes, in combination with Pvu II or Hin fl endonuclease digestion. These RFLP data were subjected to phylogenetic analysis using both genetic distance and parsimony algorithms.Results: Phylogenetic analysis predicted the existence of two independently evolving lineages, possibly evolving from a common ancestral strain. The topology of the phylogenetic tree was supported by comprehensive bootstrapping and the specific partitioning of DNA methylation phenotypes. The observed difference in the branch lengths of the two lineages may suggest differential evolutionary rates. Isolates collected from different geographical regions demonstrate independent evolution, suggesting that it is highly unlikely that strains have been recently transmitted between the two regions. The number of evolutionary events identified in this strain family differs significantly from that of previously characterized strain families, implying that evolutionary rate may be strain family dependent.Conclusion: Based on this analysis we propose that the algorithm used to calculate recent epidemiological events should be revised to incorporate the evolutionary characteristics of individual strain families, thereby enhancing the accuracy of molecular epidemiological calculations.

Molecular cloning, characterization and expression analysis of a catalase cDNA from hot pepper ( Capsicum annuum L.)

We report the cloning of a catalase cDNA from hot pepper ( Capsicum annuum L.) and its expression patterns. CaCat1 is consisted of 1837 bp containing one open reading frame (ORF) of 1479 and 45 bp/313 bp of 5′/3′-untranslated region. Deduced amino acid sequence of CaCat1 showed the 95% and 78% identity with that of Nicotiana tabacum Cat1 and Nicotiana plumbaginifolia Cat2, respectively. Northern hybridization shows that CaCat1 transcripts are more abundant in stems than in leaves and roots, and in early stages than in mature stage of fruit development. In roots its transcripts are induced in response to aluminum and NaCl. In addition, its transcription levels under light (12 h)/dark (12 h) cycle and constant light conditions exhibit circadian rhythm, reaching a maximum at late in the dark period or early in the light period. The morning specific circadian regulation of CaCat1 was also observed in NpCat1, but not in NtCat1, suggesting difference in evolutionary rates between coding region and regulatory region of the catalase genes.

Cytochrome b phylogeny and the taxonomy of great apes and mammals.

In the Linnaean system of classification, the generic status of a species is part of its binomial name, and it is therefore important that the classification at the level of genus is consistent at least in related groups of organisms. Using maximum-likelihood phylogenetic trees constructed from a large number of complete or nearly complete mammalian cytochrome b sequences, I show that the distributions of intrageneric and intergeneric distances derived from these trees are clearly separated, which allows the limits for a more rational generic classification of mammals to be established. The analysis of genetic distances among hominids in this context provides strong support for the inclusion of humans and chimpanzees in the same genus. It is also of interest to decipher the main reasons for the possible biases in the mammalian classification. I found by correlation analysis that the classification of mammals of large body size tends to be oversplit, whereas that of small mammals has an excess of lumping, which may be a manifestation of the larger difficulty in finding diagnostic characters in the classification of small animals. In addition, and contrary to some previous observations, there is no correlation between body size and rate of cytochrome b evolution in mammals, which excludes the difference in evolutionary rates as the cause of the observed body size taxonomic bias.

Long-branch attraction phenomenon and the impact of among-site rate variation on rodent phylogeny

The phylogenetic relationships among major lineages of rodents is one of the issues most debated by both paleontologists and molecular biologists. In the present study, we have analyzed all complete mammalian mitochondrial genomes available in the databases, including five rodent species (rat, mouse, dormouse, squirrel and guinea-pig). Phylogenetic analyses were performed on H-strand amino acid sequences by means of maximum-likelihood and on H-strand protein-coding and ribosomal genes by means of distance methods. Also, log-likelihood ratio tests were applied to different tree topologies under the assumption of rodent monophyly, paraphyly or polyphyly. The analyses significantly rejected rodent monophyly and showed the existence of two differentiated clades, one containing non-murids (dormouse, squirrel and guinea-pig) and the other containing murids (rat and mouse). Long-branch attraction between murids and the outgroups could not be responsible for the existence of two different rodent clades, as no significant differences in evolutionary rate have been observed, except in the case of the squirrel, which shows a lower rate. The impact of among-site rate variation models on the phylogeny of rodents has been evaluated using the gamma distribution model. Results have shown that relationships among rodents remained unchanged, and the general topology of the tree was not affected, even though some branches were not properly resolved, most likely due to a lack of fit between estimated and real rate heterogeneity parameters.

An updated and comprehensive rRNA phylogeny of (crown) eukaryotes based on rate-calibrated evolutionary distances.

Recent experience with molecular phylogeny has shown that all molecular markers have strengths and weaknesses. Nonetheless, despite several notable discrepancies with phylogenies obtained from protein data, the merits of the small subunit ribosomal RNA (SSU rRNA) as a molecular phylogenetic marker remain indisputable. Over the last 10 to 15 years a massive SSU rRNA database has been gathered, including more then 3000 complete sequences from eukaryotes. This creates a huge computational challenge, which is exacerbated by phenomena such as extensive rate variation among sites in the molecule. A few years ago, a fast phylogenetic method was developed that takes into account among-site rate variation in the estimation of evolutionary distances. This "substitution rate calibration" (SRC) method not only corrects for a major source of artifacts in phylogeny reconstruction but, because it is based on a distance approach, allows comprehensive trees including thousands of sequences to be constructed in a reasonable amount of time. In this study, a nucleotide variability map and a phylogenetic tree were constructed, using the SRC method, based on all available (January 2000) complete SSU rRNA sequences (2551) for species belonging to the so-called eukaryotic crown. The resulting phylogeny constitutes the most complete description of overall eukaryote diversity and relationships to date. Furthermore, branch lengths estimated with the SRC method better reflect the huge differences in evolutionary rates among and within eukaryotic lineages. The ribosomal RNA tree is compared with a recent protein phylogeny obtained from concatenated actin, alpha-tubulin, beta-tubulin, and elongation factor 1-alpha amino acid sequences. A consensus phylogeny of the eukaryotic crown based on currently available molecular data is discussed, as well as specific problems encountered in analyzing sequences when large differences in substitution rate are present, either between different sequences (rate variation among lineages) or between different positions within the same sequence (among-site rate variation).

Sponge proteins are more similar to those of Homo sapiens than to Caenorhabditis elegans

We compared 42 phylogenetically conserved proteins from four marine sponges [Porifera] with almost the complete set of Caenorhabditis elegans proteins and all known proteins from humans. The majority of the sponge proteins arc significantly more similar to human than to C. elegans orthologucs/homologues. This finding reflects the accelerated evolutionary rate in the C. elegans lineage, since sponges split off first from the common ancestor of all multicellular animals. Furthermore, three sponge/human proteins were not found in C. elegans: (2–5)A synthetase, DNA repair helicase and lens βγ-crystallin. Sponges arc the source of the most ancient proteins already present in the common ancestor of all multicellular organisms. Some of these proteins were lost later during the evolution of individual animal lineages. These ‘found/lost’ proteins may serve as molecular markers for an improved systematics of Metazoa. In addition, phylogenetically conserved sponge proteins can be very helpful for the evaluation of differences in evolutionary rates in different animal lineages. We therefore propose sponges as the reference animals in molecular evolutionary studies of Metazoa.

Sponge proteins are more similar to those of Homo sapiens than to Caenorhabditis elegans

We compared 42 phylogenetically conserved proteins from four marine sponges [Porifera] with almost the complete set of Caenorhabditis elegans proteins and all known proteins from humans. The majority of the sponge proteins are significantly more similar to human than to C. elegans orthologues/homologues. This finding reflects the accelerated evolutionary rate in the C. elegans lineage, since sponges split off first from the common ancestor of all multicellular animals. Furthermore, three sponge/human proteins were not found in C. elegans: (2–5)A synthetase, DNA repair helicase and lens βγ -crystallin. Sponges are the source of the most ancient proteins already present in the common ancestor of all multicellular organisms. Some of these proteins were lost later during the evolution of individual animal lineages. These «found/lost» proteins may serve as molecular markers for an improved systematics of Metazoa. In addition, phylogenetically conserved sponge proteins can be very helpful for the evaluation of differences in evolutionary rates in different animal lineages. We therefore propose sponges as the reference animals in molecular evolutionary studies of Metazoa.

Testing the hypothesis of a recombinant origin of human immunodeficiency virus type 1 subtype E.

The human immunodeficiency virus type 1 (HIV-1) epidemic in Southeast Asia has been largely due to the emergence of clade E (HIV-1E). It has been suggested that HIV-1E is derived from a recombinant lineage of subtype A (HIV-1A) and subtype E, with multiple breakpoints along the E genome. We obtained complete genome sequences of clade E viruses from Thailand (93TH057 and 93TH065) and from the Central African Republic (90CF11697 and 90CF4071), increasing the total number of HIV-1E complete genome sequences available to seven. Phylogenetic analysis of complete genomes showed that subtypes A and E are themselves monophyletic, although together they also form a larger monophyletic group. The apparent phylogenetic incongruence at different regions of the genome that was previously taken as evidence of recombination is shown to be not statistically significant. Furthermore, simulations indicate that bootscanning and pairwise distance results, previously used as evidence for recombination, can be misleading, particularly when there are differences in substitution or evolutionary rates across the genomes of different subtypes. Taken jointly, our analyses suggest that there is inadequate support for the hypothesis that subtype E variants are derived from a recombinant lineage. In contrast, many other HIV strains claimed to have a recombinant origin, including viruses for which only a single parental strain was employed for analysis, do indeed satisfy the statistical criteria we propose. Thus, while intersubtype recombinant HIV strains are indeed circulating, the criteria for assigning a recombinant origin to viral structures should include statistical testing of alternative hypotheses to avoid inappropriate assignments that would obscure the true evolutionary properties of these viruses.

Multiple nuclear insertions of mitochondrial cytochrome b sequences in callitrichine primates.

We report the presence of four nuclear paralogs of a 380-bp segment of cytochrome b in callitrichine primates (marmosets and tamarins). The mitochondrial cytochrome b sequence and each nuclear paralog were obtained from several species, allowing multiple comparisons of rates and patterns of substitution both between mitochondrial and nuclear sequences and among nuclear sequences. The mitochondrial DNA had high overall rates of molecular evolution and a strong bias toward substitutions at third codon positions. Rates of molecular evolution among the nuclear sequences were low and constant, and there were small differences in substitution patterns among the nuclear clades which were probably attributable to the small number of sites involved. A novel method of phylogenetic reconstruction based on the large difference in rates of evolution at different codon positions among mitochondrial and nuclear clades was used to determine whether different nuclear paralogs represent independent transposition events or duplications following a single insertion. This method is generally applicable in cases where differences in pattern of molecular evolution are known, and it showed that at least three of the four nuclear clades represent independent transposition events. The insertion events giving rise to two of the nuclear clades predate the divergence of the callitrichines, whereas those leading to the other two nuclear clades may have occurred in the common ancestor of marmosets.

Evolutionary relationships among Europan newts (genus Triturus) as inferred from two mtDNA fragments

European newts (genus Triturus) are widely studied, but their phylogeny is not yet unambiguously resolved. Fragments of mitochondrial DNA experiencing different rates of evolution (the ATPase and 12S rDNA genes) were sequenced in order to test a phylogenetic hypothesis derived from biochemical and behavioural data. Well supported branches of the existing phylogeny also gained support in our study. Within the subgenus Palaeotriton (the group of small-bodied newts) the monophyletic origin of the hypothesized T. boscai - T. italicus clade remained ambiguous, whereas strong support was gained for the sister-taxon relationship of T. vulgaris and T. montandoni. The position of T. vittatus within the subgenus Triturus as a sister taxon to the clade of big-bodied newts (T. marmoratus and T. cristatus superspecies) was also supported. However, the phylogenetic position of the medium-sized newt, T. alpestris could not be clarified.

Comparative Genomics of Mitochondrial DNA in Members of the Drosophila melanogaster Subgroup

In this study, a comparative genomics approach is employed to investigate the forces that shape evolutionary change in the mitochondrial DNA (mtDNA) of members of the Drosophila melanogaster subgroup. This approach facilitates differentiation of the patterns of variation resulting from processes acting at a higher level from those acting on a single gene. The mitochondrial genomes of three isofemale lines of D. simulans (siI, -II, and -III), two of D. melanogaster (Oregon R and a line from Zimbabwe), and D. mauritiana (maI and -II), and one of D. sechellia were sequenced and compared with that derived from D. yakuba. Data presented here indicate that at least three broad mechanisms shape the evolutionary dynamics of mtDNA in these taxa. The first set of mechanisms is intrinsic to the molecule. Dominant processes may be interpreted as selection for an increased rate of replication of the mtDNA molecule, biases in DNA repair, and differences in the pattern of nucleotide substitution among strands. In the genes encoded on the major strand (62% of the coding DNA) changes to or from C predominate, whereas on the minor changes to or from G predominate. The second set of mechanisms affects distinct lineages. There are evolutionary rate differences among lineages, possibly owing to population demographic changes or changes in mutational biases. This is supported by the heterogeneity found in synonymous, nonsynonymous, and silent substitutions. The third set of mechanisms differentially affects distinct genes. A maximum-likelihood sliding-window analysis detected four disjunct regions that have a significantly different nucleotide substitution process from that derived from the complete sequence. These data show the potential for comparative genomics to tease apart subtle forces that shape the evolution of DNA.

Complete nucleotide sequence of Japanese flounder (Paralichthys olivaceus) mitochondrial genome: structural properties and cue for resolving teleostean relationships.

We cloned and sequenced the complete mitochondrial genome of Japanese flounder (Paralichthys olivaceus). A circular 17,090 bp mitochondrial genome from the flounder contains 37 structural genes as in other vertebrates so far reported. This is the first report of the complete mitochondrial sequence from a higher teleostean fish (Acanthopterygii). The organization including gene order is quite similar to that of other teleostean fishes as well as placental mammals. The putative control region of the Japanese flounder mitochondrial genome contains a length variable region of about a 74 bp tandem repeat cluster. As a preliminary study we adopted the maximum likelihood and neighbor-joining inference methods to examine phylogenetic relationships among teleostean and related fishes. Comparisons of amino acid sequences of protein-coding genes and nucleotide sequences of tRNA genes resolved some middle to deep branches among some teleostean fishes. The flounder mitochondrial genome does not show an indication of evolutionary rate difference among teleosts leading to difficulty in phylogenetic analyses, and our data is useful for future evolutionary studies dealing with higher teleostean fishes.

Lineage-specific evolutionary rate in mammalian mtDNA.

The existence of a lineage-specific nucleotide substitution rate in mammalian mtDNA has been investigated by analyzing the mtDNA of all available species, that is, 35 complete mitochondrial genomes from 14 mammalian orders. A detailed study of their evolutionary dynamics has been carried out on both ribosomal RNA and first and second codon positions (P12) of H-strand protein-coding genes by using two different types of relative-rate tests. Results are quite congruent between ribosomal and P12 sites. Significant rate variations have been observed among orders and among species of the same order. However, rate variation does not exceed 1.8-fold between the fastest (Proboscidea and Primates) and the slowest (Perissodactyla) evolving orders. Thus, the observed mitochondrial rate variations among taxa do not invalidate the suitability of mtDNA for drawing mammalian phylogeny. Dependence of evolutionary rate differences on variations in mutation and/or fixation rates was examined. Body size, generation time, and metabolic rate were tested, and no significant correlation was observed between them and the taxon-specific evolutionary rates, most likely because the latter might be influenced by multiple overlapping variable constraints.

Evolutionary relationships among Europan newts (genus Triturus) as inferred from two mtDNA fragments.

European newts (genus Triturus) are widely studied, but their phylogeny is not yet unambiguously resolved. Fragments of mitochondrial DNA experiencing different rates of evolution (the ATPase and 12S rDNA genes) were sequenced in order to test a phylogenetic hypothesis derived from biochemical and behavioural data. Well supported branches of the existing phylogeny also gained support in our study. Within the subgenus Palaeotriton (the group of small-bodied newts) the monophyletic origin of the hypothesized T. boscai - T. italicus clade remained ambiguous, whereas strong support was gained for the sister-taxon relationship of T. vulgaris and T. montandoni. The position of T. vittatus within the subgenus Triturus as a sister taxon to the clade of big-bodied newts (T. marmoratus and T. cristatus superspecies) was also supported. However, the phylogenetic position of the medium-sized newt, T. alpestris could not be clarified.

The rooting of the universal tree of life is not reliable.

Several composite universal trees connected by an ancestral gene duplication have been used to root the universal tree of life. In all cases, this root turned out to be in the eubacterial branch. However, the validity of results obtained from comparative sequence analysis has recently been questioned, in particular, in the case of ancient phylogenies. For example, it has been shown that several eukaryotic groups are misplaced in ribosomal RNA or elongation factor trees because of unequal rates of evolution and mutational saturation. Furthermore, the addition of new sequences to data sets has often turned apparently reasonable phylogenies into confused ones. We have thus revisited all composite protein trees that have been used to root the universal tree of life up to now (elongation factors, ATPases, tRNA synthetases, carbamoyl phosphate synthetases, signal recognition particle proteins) with updated data sets. In general, the two prokaryotic domains were not monophyletic with several aberrant groupings at different levels of the tree. Furthermore, the respective phylogenies contradicted each others, so that various ad hoc scenarios (paralogy or lateral gene transfer) must be proposed in order to obtain the traditional Archaebacteria-Eukaryota sisterhood. More importantly, all of the markers are heavily saturated with respect to amino acid substitutions. As phylogenies inferred from saturated data sets are extremely sensitive to differences in evolutionary rates, present phylogenies used to root the universal tree of life could be biased by the phenomenon of long branch attraction. Since the eubacterial branch was always the longest one, the eubacterial rooting could be explained by an attraction between this branch and the long branch of the outgroup. Finally, we suggested that an eukaryotic rooting could be a more fruitful working hypothesis, as it provides, for example, a simple explanation to the high genetic similarity of Archaebacteria and Eubacteria inferred from complete genome analysis.

Molecular Systematics of the Grackles and Allies, and the Effect of Additional Sequence (Cyt B and ND2)

Within the New World blackbirds, the lineage of grackles and their allies contains several species that have been extremely well studied by avian biologists. Using mitochondrial DNA (mtDNA) sequences, we present a phylogeny for the grackles and allies that serves as a basis for comparative studies in this group. We compare two gene regions and determine that ND2 is evolving more rapidly than cytochrome b. However, this difference in evolutionary rate does not result in significant incongruence between phylogenies derived from the two gene regions independently. A combined weighted analysis provides a completely resolved phylogeny for this group. In general, this phylogeny has higher support than the phylogenies derived from the two genes independently. Two major clades are identified in this combined phylogeny (1) a completely South American clade, and (2) a largely North American/Caribbean/Central American clade. This phylogeny has important implications for the study of behaviors and morphology.

Microsatellite and trinucleotide-repeat evolution: evidence for mutational bias and different rates of evolution in different lineages.

Microsatellites are stretches of repetitive DNA, where individual repeat units comprise one to six bases. These sequences are often highly polymorphic with respect to repeat number and include trinucleotide repeats, which are abnormally expanded in a number of diseases. It has been widely assumed that microsatellite loci are as likely to gain and lose repeats when they mutate. In this review, we present population genetic and empirical data arguing that microsatellites, including normal alleles at trinucleotide-repeat disease loci, are more likely to expand in length when they mutate. In addition, our experiments suggest that the rates of expansion of such sequences differ in related species.

To be horizontally transferred or not

Horizontal gene transfer is undoubtedly a major factor in prokaryotic genome evolution. However, not all genes are equally likely to be transferred: the probability of a gene being transferred is correlated with its function. Horizontal transfer has occurred frequently for operational (housekeeping) genes but rarely for informational genes involved in transcription, translation and related processes. Jain et al.1 Jain R. Rivera M.C. Lake J.A. Horizontal gene transfer among genomes: the complexity hypothesis. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 3801-3806 Crossref PubMed Scopus (879) Google Scholar investigated the temporal aspects of horizontal transfer using phylogenetic analysis of six complete prokaryotic genomes. They observed that operational genes have been horizontally transferred continuously since the divergence of the prokaryotes, rather than being exchanged in one, or a few, transfer events early in their evolution. In agreement with earlier studies, the differences in rates of evolution (measured by nucleotide substitution rates) between operational and informational genes are minimal, suggesting that factors other than the rate of evolution are responsible for the observed differences in horizontal transfer frequency. They propose that a major factor in the frequent horizontal transfer of operational genes is that, while informational genes are typically members of large, complex systems, operational genes are not; the horizontal transfer of informational genes is therefore less probable than that of operational genes.

The transmission and effects of Wolbachia bacteria in parasitoids

AbstractWolbachia bacteria are obligatory intracellular parasites of arthropods and have been detected in about 70 species of parasitic wasps and three parasitoid flies. Wolbachia are transmitted cytoplasmically (maternally) and modify host reproduction in different ways to enhance their own transmission: parthenogenesis induction (PI), cytoplasmic incompatibility (CI), or feminization (F) of genetic males. Only PI and CI are known in parasitoids. PI‐Wolbachia cause thelytoky in otherwise arrhenotokous parasitoids by generating diploid (rather than haploid) unfertilized wasp eggs. CI‐Wolbachia cause incompatibility of crosses between infected males and uninfected females because the paternally derived chromosomes fail to decondense and are destroyed after syngamy. More complex situations arise when hosts harbor multiple infections, which can lead to bidirectional incompatibility and may be involved in parasitoid speciation. The relative fitness of infected and uninfected hosts is important to the population dynamics of Wolbachia, and more data are needed. Evolutionary conflict should be common between host genes, Wolbachia genes, and other “selfish” genetic elements. Wolbachia‐specific PCR primers are now available for several genes with different rates of evolution. These primers will permit rapid screening in future studies of spatial and temporal patterns of single and multiple infection. Molecular phylogenies show that CI‐ and PI‐Wolbachia do not form discrete clades. In combination with experimental transfection data, this result suggests that host reproductive alterations depend on the interaction between attributes of both Wolbachia and host. Moreover, Wolbachia isolates from closely related hosts do not usually cluster together, and phylogenies suggest that Wolbachia may have radiated after their arthropod hosts. Both results support considerable horizontal transmission of Wolbachia between host species over evolutionary time. Natural horizontal transmisson between parasitoids and their hosts, or with entomoparasitic nematodes or ectoparasitic mites, remains a tantalizing but equivocal possibility.