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Results for “systematic evolution”

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At least 343 records · Page 19Linked to original sources

PubMed2006

Effectiveness of hip protectors for preventing hip fractures in elderly people: systematic review.

OBJECTIVES: To present the updated results of systematic review of the current evidence for the effectiveness of hip protectors from reports of completed randomised trials, and to explore the evolution of that evidence. DESIGN: Systematic review with meta-analysis. DATA SOURCES: Cochrane Bone, Joint, and Muscle Trauma Group trials register (January 2005), Cochrane central register of controlled trials (Cochrane Library Issue 1, 2005), Medline (1966 to January 2005), Embase (1988 to January 2005), and CINAHL (1982 to December 2004). Other databases and reference lists of relevant articles were searched and some trialists were contacted. REVIEW METHODS: Randomised or quasirandomised controlled trials reporting the incidence of hip fractures, pelvic fractures, and other fractures in elderly people offered hip protectors compared with a control group that was not. RESULTS: Outcomes for fracture were available from 14 randomised and quasirandomised trials. Pooling of data from 11 trials carried out in nursing or residential care settings, including six cluster randomised studies, showed evidence of a marginally statistically significant reduction in incidence of hip fracture (relative risk 0.77, 95% confidence interval 0.62 to 0.97). Pooling of data from three individually randomised trials of 5135 community dwelling participants showed no reduction in hip fracture incidence with provision of hip protectors (1.16, 0.85 to 1.59). No evidence was found of any significant effect of hip protectors on incidence of pelvic or other fractures. No important adverse effects of hip protectors were reported, but compliance, particularly in the long term, was poor. CONCLUSIONS: On the basis of early reports of randomised trials, hip protectors were advocated. Accumulating evidence indicates that hip protectors are an ineffective intervention for those living at home and that their effectiveness in an institutional setting is uncertain.

Aged↗

PubMed2004

Myostatin rapid sequence evolution in ruminants predates domestication.

Myostatin (GDF-8) is a negative regulator of skeletal muscle development. This gene has previously been implicated in the double muscling phenotype in mice and cattle. A systematic analysis of myostatin sequence evolution in ruminants was performed in a phylogenetic context. The myostatin coding sequence was determined from duiker (Sylvicapra grimmia caffra), eland (Taurotragus derbianus), gaur (Bos gaurus), ibex (Capra ibex), impala (Aepyceros melampus rednilis), pronghorn (Antilocapra americana), and tahr (Hemitragus jemlahicus). Analysis of nonsynonymous to synonymous nucleotide substitution rate ratios (Ka/Ks) indicates that positive selection may have been operating on this gene during the time of divergence of Bovinae and Antilopinae, starting from approximately 23 million years ago, a period that appears to account for most of the sequence difference between myostatin in these groups. These periods of positive selective pressure on myostatin may correlate with changes in skeletal muscle mass during the same period.

Amino Acid Sequence↗

PubMed1980

An unusual case of "somatosensory epilepsy".

The "somatosensory spike" epilepsy is still little known, except in highly specialized places. It depends on two factors: a) it is rare (mean incidence: 1 case in 1,000 new EEGs); b) the evoked spikes that constitute the first sign for the evolution of the syndrome are not systematically sought, also many months can pass before finding one "positive" case. The evolution of a "positive" case towards epilepsy is represented by a 15% possibility. An unusual case of this syndrome is presented, which is of interest both because it constitutes the first case in the literature and because of the neurophysiological problems that it reveals. The case is represented by a 10-year-old girl, who presented a particular form of "somatosensory spike" epilepsy; the focal motor seizures were localized at the first three fingers of the right hand and the EEG finding was a focus of spikes on the left temporo-central region. She arrived at this stage after going through the four classical states of "somatosensory spike" epilepsy.

Child↗

PubMed1982

A particular evolution of two cases of somatosensory spike epilepsy.

"Somatosensory spike epilepsy" is still little known, except in highly specialized places, because of two factors: 1) it is rare (the incidence in our experience is one case in 1,000 new EEGs); 2) the evoked spikes, that constitute the first sign for the evolution of the syndrome, are not systematically sought, and many months can pass before finding one "positive" cases. The evolution of a "positive" case towards epilepsy is represented by a 15% possibility. In this report we present two unique cases of this syndrome; they are of interest because they constitute the first such cases in the literature and also because of the neurophysiological problems that they reveal. The cases are represented by an eight year old girl and by an eleven year old boy, who suffered from the typical form of "sensitive spike epilepsy" characterized by its classical evolution in four stages, with a clinical phase of about one year. Two years after the cessation of previous seizures, they presented a new "bouffee" of partial motor seizures. The EEG abnormalities were in the parietal parasagittal region the first time, while they were situated in the temporoparietal region in the second time. The somatosensory spikes were evoked from the foot the first time and from the fingers the second time. In the second case the trigger zones were only on the left side of the body.

Carbamazepine↗

PubMed1995

Evolution of segmentation genes in insects.

Systematic genetic analysis of the segmentation process in Drosophila has established a paradigm for the molecular control of the formation of metameric segments. However, it has been suggested that some of the mechanisms involved in this process in Drosophila are uniquely adapted to the syncytial mode of embryogenesis in such higher dipterans. A particularly contentious problem is the role of early segmentation genes in short-germ insects, in which development proceeds by sequential addition of segments in a cellular environment. However, analysis of the expression of presumptive homologs of segmentation genes in holometabolous short-germ insects suggests that they do indeed have a role in segmentation and that the Drosophila paradigm may be more widely applicable than is usually assumed. Most interestingly, these results suggest that the molecular mechanisms of pattern formation in noncellular and in cellular environments may not be as radically different as it is often thought to be.

Animals↗

PubMed1999

The recognition and evaluation of homoplasy in primate and human evolution.

Homoplasy has been a prominent issue in primate systematics and phylogeny for as long as people have been studying human evolution. In the past, homoplasy, in the form of parallel evolution, was often considered the dominant theme in primate evolution. Today, it receives blame for difficulties in phylogenetic analysis, but is essential in the study of adaptation. This paper reviews the history of study of homoplasy, methods of defining homoplasy, and methodological and biological factors that generate homoplasy. A post hoc definition of homology and homoplasy, based on patterns of character distributions and their congruence or incongruence on a cladogram, is the most consistent method of recognizing these phenomena. Defined this way, homology and homoplasy are mutually exclusive. However, when different levels of analysis are examined, it is seen that homoplasy at one level, such as adult phenotype, often exists simultaneously with homology at a different level, such as developmental process. Thus, in some cases, patterns of homoplasy may point to underlying similarities that reflect the shared heritage of a particular clade. This is an old concept that is being renewed on the strength of recent trends in developmental biology. Factors that influence homoplasy include character definition and a host of biological factors, such as developmental constraints, allometry, and adaptation. These interact with one another to provide explanations of homoplastic patterns. Because of the repetition of events, explanations of homoplastic features are often more reliable than those for homologous features, and serve as effective tests for hypotheses of evolutionary process. In some cases, particular explanations of homoplasy lead to generalizations about the likelihood of homoplasy in a type of structure. The structure may be adaptive or highly epigenetic, or it may belong to an anatomical system considered to be more prone to homoplasy than others. However, our review shows that these generalizations are usually based on theory, and contradictory expectations can be developed under different theoretical models. More rigorous empirical studies are necessary to discover what, if any, generalizations can be made about the likelihood of homoplasy in different types of characters.

Adaptation, Physiological↗

PubMed1994

Advances in the theory and practice of DNA-hybridization as a systematic method.

DNA hybridization continues in the 1990s to provide insight into phylogeny and evolution. The resilience of this 30-year-old distance technique may be attributed to its fundamental power as a comparative method, as well as to advances in our understanding of its operation and improvements in experimental design and data analysis. These attributes and advances, along with the assumptions and limitations of DNA hybridization, are discussed in this paper. Examples are provided of recent DNA hybridization studies of molecular, morphological, and behavioral systematics and evolution.

Animals↗

PubMed2003

Anatomical features of Leiopelma embryos and larvae: implications for anuran evolution.

A controversial issue in anuran systematics is the relationship of Leiopelma to other anurans because recent phylogenetic constructions imply different relationships among the basal frogs. Of particular evolutionary interest is whether early development of Leiopelma resembles an ancestral salamander-like larva, an anuran tadpole, or neither. In the 1950s, Neville G. Stephenson hypothesized that direct development is the primary mode of development in amphibians, based on the fact that Leiopelma spp. lack a free-living (=feeding) larval stage. Although this hypothesis has not been generally accepted, it has not been formally refuted. We review Stephenson's work on Leiopelma and examine the anatomy of embryos/"larvae" of the four extant Leiopelma species for evidence of vestigial larval features that might refute the "direct-developing ancestor" hypothesis. We describe internal oral features in early developmental stages of Leiopelma and compare Leiopelma with a closely related basal anuran, Ascaphus, to assess whether their early developmental stages share any derived features. In Leiopelma hochstetteri, embryos/larvae have open gill slits and some faint rugosities around one gill slit that may be vestiges of gill rakers or filters. They also have more intestinal loops, indicative of an elongated alimentary tract, at earlier rather than late embryonic/larval stages. Collectively, these features support the view that the ancestor of Leiopelma had a free-swimming, free-feeding, aquatic larva. The palatoquadrate of Leiopelma archeyi reorients approximately 40 degrees from a more horizontal to a more vertical position through embryonic/"larval" development. This amount of cranial remodeling is intermediate between that seen in salamanders (17-27 degrees) and that reported for Ascaphus (64 degrees ) and other basal frogs (71-78 degrees) at metamorphosis. We found no internal oral features that Leiopelma shares specifically with Ascaphus. However, Leiopelma embryos have a ventrally positioned mouth and a downturned rostrum, characteristic of Ascaphus and other stream-adapted tadpoles.

Animals↗

PubMed2007

Banding patterns and chromosomal evolution in five species of neotropical Teiinae lizards (Squamata: Teiidae).

Karyotypes of five species of South American teiid lizards from subfamily Teiinae: Ameiva ameiva, Kentropyx calcarata, K. paulensis, K. vanzoi (2n = 50, all acrocentric), and Cnemidophorus ocellifer (2n = 50, all biarmed), are herein described and compared on the basis of conventional and silver staining, and CBG and RBG banding patterns. Meiotic data are also included. Karyotypes of K. paulensis, K. vanzoi, and C. ocellifer are reported here for the first time. Inter-generic variability in Ag-NORs location was detected with NORs occurring at the end of long arm of pair 1 in K. calcarata, K. paulensis, and K. vanzoi; pair 5 in C. ocellifer and pair 7 in A. ameiva. The location of NORs, along with the karyological differences between A. ameiva and the Central American species (A. auberi), corroboretes the molecular-based hypothesis that the genus Ameiva is paraphyletic. Inter-populational heteromorphism in Ag-NORs size was detected between populations of C. ocellifer. RBG and CBG banding data demonstrated that the biarmed condition of the C. ocellifer chromosomes is due to multiple pericentric inversion events instead of addition of constitutive heterochromatin. Differential-staining techniques used here revealed valuable information about Teiinae karyotypic diversity and made it possible to compare these species, contributing to both the better comprehension of their chromosomal evolution and issues on taxa systematics.

Animals↗

PubMed2004

Multidimensional vector space representation for convergent evolution and molecular phylogeny.

With growing amounts of genome data and constant improvement of models of molecular evolution, phylogenetic reconstruction became more reliable. However, our knowledge of the real process of molecular evolution is still limited. When enough large-sized data sets are analyzed, any subtle biases in statistical models can support incorrect topologies significantly because of the high signal-to-noise ratio. We propose a procedure to locate sequences in a multidimensional vector space (MVS), in which the geometry of the space is uniquely determined in such a way that the vectors of sequence evolution are orthogonal among different branches. In this paper, the MVS approach is developed to detect and remove biases in models of molecular evolution caused by unrecognized convergent evolution among lineages or unexpected patterns of substitutions. Biases in the estimated pairwise distances are identified as deviations (outliers) of sequence spatial vectors from the expected orthogonality. Modifications to the estimated distances are made by minimizing an index to quantify the deviations. In this way, it becomes possible to reconstruct the phylogenetic tree, taking account of possible biases in the model of molecular evolution. The efficacy of the modification procedure was verified by simulating evolution on various topologies with rate heterogeneity and convergent change. The phylogeny of placental mammals in previous analyses of large data sets has varied according to the genes being analyzed. Systematic deviations caused by convergent evolution were detected by our procedure in all representative data sets and were found to strongly affect the tree structure. However, the bias correction yielded a consistent topology among data sets. The existence of strong biases was validated by examining the sites of convergent evolution between the hedgehog and other species in mitochondrial data set. This convergent evolution explains why it has been difficult to determine the phylogenetic placement of the hedgehog in previous studies.

Animals↗

PubMed2004

A systematic-heuristic approach for space trajectory design.

In this paper a novel algorithm is proposed for space trajectory design that combines a systematic and a heuristic method for global optimization. For the systematic part of the algorithm a branching technique is used, whereas a particular implementation of evolution programming forms the core of the heuristic part. The idea is to use a limited population evolving for a small number of generations, according to specific evolution rules, in subregions of the solution space defined by a branching procedure. On the other hand the branching rules are functions of the outcome from the evolution optimization. The proposed combined systematic-heuristic global optimization performs quite well on the cases analyzed in this paper, suggesting the possibility of more complex applications.

Journal Article↗

PubMed1998

Evolution of the protists and protistan parasites from the perspective of molecular systematics.

Unlike prokaryotes, the Protista are rich in morphological and ultrastructure information. Their amazing phenotypic diversity permits assignment of many protists to cohesive phyletic assemblages but sometimes blurs relationships between major lineages. With the advent of molecular techniques, it became possible to test evolutionary hypotheses that were originally formulated according to shared phenotypic traits. More than any other gene family, studies of rRNAs changed our understanding of protist evolution. Stramenopiles (oomycetes, chrysophytes, phaeophytes, synurophytes, diatoms, xanthophytes, bicosoecids, slime nets) and alveolates (dinoflagellates, apicomplexans, ciliates) are two novel, complex evolutionary assemblages which diverged nearly simultaneously with animals, fungi, plants, rhodophytes, haptophytes and a myriad of independent amoeboid lineages. Their separation may have occurred one billion years ago and collectively these lineages make up the "crown" of the eukaryotic tree. Deeper branches in the eukaryotic tree show 16S-like rRNA sequence variation that is much greater than that observed within the Archaea and the Bacteria. A progression of independent protist branches, some as ancient as the divergence between the two prokaryotic domains, preceded the sudden radiation of "crown" groups. Trichomonads, diplomonads and Microsporidia are basal to all other eukaryotes included in rRNA studies. Together with pelobionts, oxymonads, retortamonads and hypermastigids, these amitochondriate taxa comprise the Archaezoa. This skeletal phylogeny suggested that early branching eukaryotes lacked mitochondria, peroxisomes and typical stacked Golgi dictyosomes. However, recent studies of heat shock proteins indicate that the first eukaryotes may have had mitochondria. When evaluated in terms of evolution of ultrastructure, lifestyles and other phenotypic traits, the rRNA phylogenies provide the most consistent of molecular trees. They permit identification of the phylogenetic affinity of many parasitic groups as well as a means to integrate molecular and cell biological information from diverse eukaryotes. We must place greater emphasis upon improved phylogenetic inference techniques and investigations of genomic diversity in protists.

Animals↗

PubMed2005

Determinants of simulated RNA evolution.

Models of RNA secondary structure folding are widely used to study evolution in theory and simulation. However, systematic studies of the parameters involved are rare. In this paper, we study by simulation how RNA evolution is influenced by three different factors, namely the mutation rate, scaling of the fitness function, and distance measure. We found that for low mutation rates the qualitative evolutionary behavior is robust with respect to the scaling of the fitness function. For efficient mutation rates, which are close to the error threshold, scaling and distance measure have a strong influence on the evolutionary behavior. A global distance measure that takes sequence information additively into account lowers the error threshold. When using a local sequence-structure alignment for the distance, we observed a smoother evolution of the fitness over time. Finally, in addition to the well known error threshold, we identify another threshold of the mutation rate, called divergence threshold, where the qualitative transient behavior changes from a localized to an exploratory search.

Animals↗

PubMed2025

The plastid genome of the critically endangered Valeriana trinervis (= Centranthus trinervis) and insights from comparison with other Valeriana plastomes (Caprifoliaceae).

The first complete plastid genome of the critically endangered species Valeriana trinervis was sequenced, assembled and compared with other published Valeriana plastomes. In this study, we assembled the plastid genome of the critically endangered, endemic species Valeriana trinervis (= Centranthus trinervis) and compare it with all published plastomes of Valeriana. We found not only differences in the inverted repeats boundaries, in the type and abundance of repeats, but also similarities in codon usage and microsatellite numbers. We detected non-canonical start codons in several genes and identified variation in several regions that could be useful for phylogenetic and phylogeographic studies. The phylogenetic tree inference based on both full plastomes and coding sequence data indicated that V. trinervis is sister to all Eurasian Valeriana accessions confirming the phylogenetic position recently investigated. This is the first plastome available for a species of the Mediterranean clade of Valeriana previously known as Centranthus, and it adds further data to understand the evolution and diversification of this systematically debated genus.

Genome, Plastid↗

PubMed1987

Phylogenetic comparison of the photoaffinity-labeled benzodiazepine receptor subunits.

The late evolutionary appearance of the benzodiazepine receptor (BZR) allows an experimental approach for evaluation of the qualitative development of its subunits. Photoaffinity labeling of brain membranes with [3H]flunitrazepam followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography offers a suitable method for tracing the qualitative evolution of the BZR. A systematic comparison of the subunit patterns in fishes, amphibians, reptiles, birds, and mammals revealed that the subunit of 53K is phylogenetically the oldest photoaffinity labeled subunit; whereas it is the only band present in the lungfish and most amphibians, additional bands are apparent in higher tetrapods. In fishes, the evolution of the BZR subunits leads to the loss of the 53K subunit. KD values are discussed in relation to specific subunit patterns. Possible explanations for the observed variation of the subunits are discussed, with special emphasis placed on the possible evolution by gene duplication and subsequent divergence.

Amphibians↗

PubMed2026

Global epidemiology, genomic evolution, and clinical implications of dual- and multiple-carbapenemase-producing Klebsiella pneumoniae: A systematic qualitative review.

BACKGROUND: The global emergence of dual- and multiple-carbapenemase-producing Klebsiella pneumoniae, particularly isolates co-harbouring blaNDM and blaOXA-48/OXA-48-like determinants, represents a critical threat to global health because of limited therapeutic options and expanding genomic complexity. METHODS: This systematic qualitative review synthesized evidence from 44 English-language peer-reviewed studies published between 2017 and 2026 and indexed in Scopus, with a focus on genomic evolution and spatiotemporal distribution. RESULTS: High-risk clones ST147, ST101, and ST11 were identified as major drivers of dissemination. Genomic analysis revealed key adaptive mechanisms, including stable IncL 96-kb fusion plasmids and IS10-mediated truncation of blaNDM-1, potentially reducing fitness costs while preserving resistance. Convergence events were also documented in which dual-carbapenemase-producing isolates acquired additional colistin resistance determinants (mcr-1 or mgrB alterations) and virulence-associated markers such as iuc1. Importantly, related resistance determinants were identified beyond hospital settings, including community, environmental, and food-associated reservoirs. CONCLUSION: The shift from single to dual and multiple carbapenemase production in K. pneumoniae underscores the need for integrated genomic surveillance, improved antimicrobial stewardship, and broader reservoir monitoring to address this evolving public health threat.

Klebsiella pneumoniae↗

PubMed2006

Wide-band tracheids in genera of Portulacaceae: novel, non-xylary tracheids possibly evolved as an adaptation to water stress.

Wide-band tracheids (WBTs) are novel tracheids with wide, lignified secondary walls that intrude deeply into the cell lumen when viewed in transverse sections. These tracheids are found in a few genera in related families in the order Caryophyllales: Aizoaceae, Cactaceae, and Portulacaceae. WBTs in these three families vary in (1) systematic occurrence (found in more highly derived genera in each family), (2) location in plant organs, and (3) structure and dimensions. In addition, an analysis was conducted of WBT cell walls to test the hypothesis that WBTs evolved as an adaptation to water stress (i.e., the wide secondary walls should prevent collapse of the primary wall during water stress). The cell wall data show that primary cell walls in WBTs cannot inwardly collapse to occlusion, thus providing support for the water stress hypothesis of WBT evolution. With consideration of their systematic occurrence, the molecular phylogenetic data, and data here showing support for a water stress adaptive origin, it is logical to assume that WBTs evolved in genera that were adapting to environments undergoing a rapid trend toward aridification.

Adaptation, Physiological↗

PubMed2003

Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics.

It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 +/- 0.3) and the Moon (17.0 +/- 0.8) are below the chondritic ratio of 19.9 +/- 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago.

Earth, Planet↗