SEARCH · PubMed Health

Results for “evolution”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,153 records · Page 64Linked to original sources

PubMed1992

Evolution of developmental decisions and morphogenesis: the view from two camps.

Modern developmental biology largely ignores evolution and instead focuses on use of standard model organisms to reveal general mechanisms of development. Evolutionary biologists more widely hold developmental biology to be of major consequence in providing potential insights into evolution. Evolutionary insights can enlighten our views of developmental mechanisms as much as developmental data offer clearer views of mechanisms which underlie evolutionary change. However, insights have been limited by the long-term disengagement of the two fields dating to the rise of experimental embryology in the 1890s. Molecular genetics now provides a powerful tool to probe both gene function and evolutionary relationships, and a greater connection has become possible. The expansion of experimental organisms beyond the standard model animals used in most studies of development allows us to ask deeper questions about the interaction of development and evolution. This paper presents an analysis of the complementary uses of the resulting data in the two fields as they grope for accommodation. Analysis of the radical changes in early development seen in closely related sea urchins with alternate modes of development illustrate the complementarity of developmental and evolutionary data. These studies show that what have been thought to be constrained mechanisms of axial determination, cell lineage patterning, and gastrulation in fact evolve readily and provide the means for the rapid evolution of development.

Animals↗

PubMedDate not supplied

[Evolution of sex: role of deleterious mutation and mobile elements].

Prevalence of sexual reproduction is still enigma. The main character of sex is alleles mixing that could be advantageous either in unstable environment (in this case sex provides high temp of evolution) or in unstable genotype (in this case sex provides purge of genome from deleterious mutations). As long as not all species inhabit highly changeable environments, variation of genotypes is more important factor. As the majority of new mutations is deleterious, effective mechanism of genome purging is needed. Maintenance of "purging mechanism" may be a single role of sex. Two promising mutational hypotheses--clade selection (Muller's ratchet and Nunney's hypothesis) and mutational deterministic hypothesis of Kondrashov claim that more effective elimination of slightly-deleterious mutations provides main advantage to sexual population in comparison with asexual. Despite prima facie similarity, these hypotheses differ in mechanisms, work at different temporal scales and have different consequences. Kondrashov's hypothesis reveals short-term advantage of sexual reproduction, and thus, based on the individual selection. Clade selection displays long-term advantage of sexual reproduction that could be realized only by group selection. The role of mobile elements in evolution of sexual reproduction is also discussed. Firstly, mobile elements ("sexual molecular parasites") can complicate the problem: having been domesticated in asexual genomes and remaining active in sexual genomes they lead to higher mutational rate in sexual organisms and so violate assumption critical for both mutational hypotheses of "other things being equal". Secondly, mobile elements could be leader factor of origin of sex (hypothesis proposed by Hickey). Because theory of group selection could explain maintenance of sex, but not its origin, mobile elements could induce the origin of sex but were not able to maintain it, so the next scenario of evolution of sex is proposed: mobile elements induced origin of sex, which was established later by group selection because provided long term benefit (Muller's ratchet and Nunney's hypothesis). So, on all stages of evolution, sex was not advantageous for the organism per se.

Animals↗

PubMed2003

Origins and plasticity of neural crest cells and their roles in jaw and craniofacial evolution.

The vertebrate head is a complex assemblage of cranial specializations, including the central and peripheral nervous systems, viscero- and neurocranium, musculature and connective tissue. The primary differences that exist between vertebrates and other chordates relate to their craniofacial organization. Therefore, evolution of the head is considered fundamental to the origins of vertebrates (Gans and Northcutt, 1983). The transition from invertebrate to vertebrate chordates was a multistep process, involving the formation and patterning of many new cell types and tissues. The evolution of early vertebrates, such as jawless fish, was accompanied by the emergence of a specialized set of cells, called neural crest cells which have long held a fascination for developmental and evolutionary biologists due to their considerable influence on the complex development of the vertebrate head. Although it has been classically thought that protochordates lacked neural crest counterparts, the recent identification and characterization of amphioxus and ascidian genes homologous to those involved in vertebrate neural crest development challenges this idea. Instead it suggests thatthe neural crest may not be a novel vertebrate cell population, but could have in fact originated from the protochordate dorsal midline epidermis. Consequently, the evolution of the neural crest cells could be reconsidered in terms of the acquisition of new cell properties such as delamination-migration and also multipotency which were key innovations that contributed to craniofacial development. In this review we discuss recent findings concerning the inductive origins of neural crest cells, as well as new insights into the mechanisms patterning this cell population and the subsequent influence this has had on craniofacial evolution.

Animals↗

PubMed2003

Haplodiploidy, sex, and the evolution of pesticide resistance.

The assumption that males and females are equally tolerant to pesticides in haplodiploid arthropods led to the prediction that the evolution of resistance is faster in haplodiploid than in diploid arthropods. However, in this review, it was found that the ratio of male to female tolerance is substantially smaller in haplodiploid than in diploid arthropods, indicating that resistance alleles are not strongly up-regulated in haploid males. In addition, males were generally less tolerant than females in both haplodiploid and diploid arthropods. Factors such as sexual size dimorphism and sex-dependent selection may account for the lower tolerance in males than in females. Little among-population variation in the ratio of male to female tolerance was found in three species. Moreover, the tolerance ratio generally remained unchanged by selection for resistance to pesticides, although significant among-species variation was present within arthropod orders. This indicates that sexual dimorphism in pesticide tolerance evolves at a slower rate than resistance to pesticides. Simulations considering between-sex differences in pesticide tolerance showed that resistance evolution can be slower in haplodiploids than in diploids. Recessive resistance, low male tolerance to pesticides, fitness costs expressed in males, and the use of refuges contributed in substantially delaying the evolution of resistance in haplodiploid arthropods. These findings cast a new perspective on the evolution of pesticide resistance in haplodiploid herbivores and natural enemies.

Alleles↗

PubMedDate not supplied

[Origin and evolution of the hamuli in the monogeneans].

The hypothesis of the origin and evolution of the hamuli in monogeneans is proposed. It is suggested that the hamuli originated as the adult attachment organs of protomonogeneans inhabited the gills of the first vertebrates. Primarily they were represented by two lateral pairs of large hooks disposed anterior to the larval haptor. The fundamental direction in the evolution of monogeneans was the concentration of all attachment structures on the growing haptor. It the course of this evolutionary process, the hamuli onchoblasts migrated to the haptor, in which they had reached the position in the hind part of the haptor. The neotenic evolution of the Dactylogyridea and Gyrodactyloidea resulted in the forming new hamuli pairs. The hooks of opposite sides of the haptor are joined in a single complex within each side by the transverse plates (bars). So the presence of 4 hamuli is plesiomorphy for all the monogeneans and the presence of the transverse bars and new hamuli pairs are apomorphy for the Dactylogyridea and Gyrodactyloidea, whose evolution was linked with that of the Teleostei. The origin of the new hamuli pairs and transverse bars in the Dactylogyridea and Gyrodactyloidea appears to be a convergence.

Animals↗

PubMed2004

Intra-host evolution of human immunodeficiency virus type 1 and viral fitness.

RNA viruses are frequently tolerant to high levels of mutagenesis. In contrast, DNA viruses are less errorprone and coevolve along with their specific hosts over long time periods. Although both strategies have been successful, the "RNA-strategy" (directly linked to the pathogenic potential of these agents) most often generates novelty (new variants, new strains, and even new viral pathogens). For several decades, intra-host virus evolution has been considered to be a speculative field, far from the main issues of clinical virology. This concept is now changed, due to the evidence that RNA virus evolution is intimately linked to failures in viral disease control and prevention. Antiviral strategies using single and fixed elements (i.e. treatments using one antiviral compound, immunizations using a single recombinant protein) have been unable to control highly dynamic quasispecies, such as human immunodeficiency virus type I (HIV-1) and hepatitis C virus (HCV). The development of combinatorial treatments in HIV-1 infection and the recognition that vaccines should be multivalent are important steps in adapting disease control strategies to the complexity of viral populations. The present report summarizes the strategies adopted to address HIV-1 evolution and its phenotypic consequences, including changes in susceptibility to antiviral compounds, viral fitness, and pathogenic potential. In particular, it is highlighted that sequence-function analyses of the intra-host HIV-I evolution, including studies of viral fitness, have opened up new perspectives not only to studying the pathogenic mechanisms and the virus-host relationships, but also to designing new strategies for monitoring antiviral therapies.

AIDS Vaccines↗

PubMed2004

Immune reconstitution in HIV-1 infected children with discordant response to antiretroviral therapies: patterns of HIV-1 env gene evolution driven by restoration of thymic function.

The evolution of human immunodeficiency virus type 1 (HIV-1) env gp120 region was addressed in HIV-1 infected children showing virological failure to antiretroviral therapy (ART). Sequence analysis of the replicating plasma virus at baseline and after one year of therapy documented evolution of gp120 in all subjects but one. Analysis of the host's selective pressure showed that the values of Ka/Ks ratios were higher in the V3 sequence than in the whole C2-V5 region in 4 of 5 children with improvement of thymic output. Moreover, in 2 of the 4 chidren, the V3 evolution paralleled with a reverse shift of the viral phenotype (from CXCR4-tropic to CCR5-tropic). These results suggest that, under ART, the V3 evolution towards less pathogenic viral variants may be driven by the host's increased selective pressure following restoration of thymic function and immune reconstitution.

Amino Acid Sequence↗

PubMed2004

[The evolution of plant disease resistance gene].

The evolution of plant disease resistance genes has shaped in some kinds of common forms. The duplication of plant progenitor disease resistance gene creates disease resistance gene loci. The intragenic and extragenic recombination results in variation. Recombination also is involved in generation novel resistance specificities. In addition, the leucine-rich repeats (LRRs) involved in recognitional specificity are subject to adaptive selection. Insertion of transposable elements into several resistance gene loci result in further evolution of resistance genes. With the evolution of plant disease resistance genes, the R genes (resistance genes)-mediated response shows diversification which represents different stages in the oscillating evolution between plants and their pathogens.

Adaptation, Physiological↗

PubMed2005

Constrained camouflage facilitates the evolution of conspicuous warning coloration.

The initial evolution of aposematic and mimetic antipredator signals is thought to be paradoxical because such coloration is expected to increase the risk of predation before reaching a stage when predators associate it effectively with a defense. We propose, however, that constraints associated with the alternative strategy, cryptic coloration, may facilitate the evolution of antipredator signals and thus provide a solution for the apparent paradox. We tested this hypothesis first using an evolutionary simulation to study the effect of a constraint due to habitat heterogeneity, and second using a phylogenetic comparison of the Lepidoptera to investigate the effect of a constraint due to prey motility. In the evolutionary simulation, antipredator warning coloration had an increased probability to invade the prey population when the evolution of camouflage was constrained by visual difference between microhabitats. The comparative study was done between day-active lepidopteran taxa, in which camouflage is constrained by motility, and night-active taxa, which rest during the day and are thus able to rely on camouflage. We compared each of seven phylogenetically independent day-active groups with a closely related nocturnal group and found that antipredator signals have evolved at least once in all the diurnal groups but in none of their nocturnal matches. Both studies lend support to our idea that constraints on crypsis may favor the evolution of antipredator warning signals.

Animals↗

PubMed2006

Evolution of HVR-1 quasispecies after 1-year treatment in HIV/HCV-coinfected patients according to the pattern of response to highly active antiretroviral therapy.

Hepatitis C virus (HCV) variability is mainly attributed to the ability of the virus to respond to host immune pressure, acting as a driving force for the evolution of quasispecies. This study was aimed at studying the changes in HVR-1 heterogeneity and the evolution of HCV quasispecies in HIV/HCV-coinfected patients according to the pattern of response to highly active antiretroviral therapy (HAART). Sixteen HIV/HCV-coinfected patients harbouring HCV genotype 1 and who had been on HAART for at least 1 year, 8 showing increasing CD4+ T-cell counts (immunological responders) and 8 showing a stable or decreasing CD4+ T-cell counts (immunological nonresponders), were selected from a prospective cohort study. After 1 year of HAART, 11 patients showed HIV viral load <2.6 log10 cp/ml (virological responders), and 5 showed HIV viral load above this value (virological non-responders). Plasma samples, collected before starting therapy and after 1 year of HAART, underwent clonal sequence analysis for HVR-1 region of HCV. Nonsynonymous/synonymous substitutions ratio (Ka/Ks), aminoacidic complexity (normalized Shannon entropy) and diversity (p-distance), were considered as parameters of quasispecies heterogeneity. After 1 year of HAART, heterogeneity of HVR-1 quasispecies significantly decreased in virological non-responders, whereas the heterogeneity tended to increase in virological responders. The differences in the evolution were less stringent, when considering immunological response. On the other hand, profound qualitative modifications of HVR-1 quasispecies were observed only in patients with both immunological and virological HAART response. On the whole, these findings suggest that, in patients undergoing HAART, the extent of HCV variability and the evolution of HVR-1 quasispecies is influenced by the pattern of response to antiretroviral therapy.

Adult↗

PubMed2006

Cross-generational environmental effects and the evolution of offspring size in the Trinidadian guppy Poecilia reticulata.

The existence of adaptive phenotypic plasticity demands that we study the evolution of reaction norms, rather than just the evolution of fixed traits. This approach requires the examination of functional relationships among traits not only in a single environment but across environments and between traits and plasticity itself. In this study, I examined the interplay of plasticity and local adaptation of offspring size in the Trinidadian guppy, Poecilia reticulata. Guppies respond to food restriction by growing and reproducing less but also by producing larger offspring. This plastic difference in offspring size is of the same order of magnitude as evolved genetic differences among populations. Larger offspring sizes are thought to have evolved as an adaptation to the competitive environment faced by newborn guppies in some environments. If plastic responses to maternal food limitation can achieve the same fitness benefit, then why has guppy offspring size evolved at all? To explore this question, I examined the plastic response to food level of females from two natural populations that experience different selective environments. My goals were to examine whether the plastic responses to food level varied between populations, test the consequences of maternal manipulation of offspring size for offspring fitness, and assess whether costs of plasticity exist that could account for the evolution of mean offspring size across populations. In each population, full-sib sisters were exposed to either a low- or high-food treatment. Females from both populations produced larger, leaner offspring in response to food limitation. However, the population that was thought to have a history of selection for larger offspring was less plastic in its investment per offspring in response to maternal mass, maternal food level, and fecundity than the population under selection for small offspring size. To test the consequences of maternal manipulation of offspring size for offspring fitness, I raised the offspring of low- and high-food mothers in either low- or high-food environments. No maternal effects were detected at high food levels, supporting the prediction that mothers should increase fecundity rather than offspring size in noncompetitive environments. For offspring raised under low food levels, maternal effects on juvenile size and male size at maturity varied significantly between populations, reflecting their initial differences in maternal manipulation of offspring size; nevertheless, in both populations, increased investment per offspring increased offspring fitness. Several correlates of plasticity in investment per offspring that could affect the evolution of offspring size in guppies were identified. Under low-food conditions, mothers from more plastic families invested more in future reproduction and less in their own soma. Similarly, offspring from more plastic families were smaller as juveniles and female offspring reproduced earlier. These correlations suggest that a fixed, high level of investment per offspring might be favored over a plastic response in a chronically low-resource environment or in an environment that selects for lower reproductive effort.

Animals↗

PubMed2006

Male pregnancy and the evolution of body segmentation in seahorses and pipefishes.

The evolution of complex traits, which are specified by the interplay of multiple genetic loci and environmental effects, is a topic of central importance in evolutionary biology. Here, we show that body and tail vertebral numbers in fishes of the pipefish and seahorse family (Syngnathidae) can serve as a model for studies of quantitative trait evolution. A quantitative genetic analysis of body and tail vertebrae from field-collected families of the Gulf pipefish, Syngnathus scovelli, shows that both traits exhibit significantly positive additive genetic variance, with heritabilities of 0.75 +/- 0.13 (mean +/- standard error) and 0.46 +/- 0.18, respectively. We do not find any evidence for either phenotypic or genetic correlations between the two traits. Pipefish are characterized by male pregnancy, and phylogenetic consideration of body proportions suggests that the position of eggs on the pregnant male's body may have contributed to the evolution of vertebral counts. In terms of numbers of vertebrae, tail-brooding males have longer tails for a given trunk size than do trunk-brooding males. Overall, these results suggest that vertebral counts in pipefish are heritable traits, capable of a response to selection, and they may have experienced an interesting history of selection due to the phenomenon of male pregnancy. Given that these traits vary among populations within species as well as among species, they appear to provide an excellent model for further research on complex trait evolution. Body segmentation may thus afford excellent opportunities for comparative study of homologous complex traits among disparate vertebrate taxa.

Animals↗

PubMed2006

[The significance of mutations in genomic evolution].

One of the fundamental questions in biological sciences and key problem to be solved in evolutionary biology is that how intra-and interspecific genomic diversity formed, accumulated and preserved in the long history of evolution. It is well known that mutation is the major driving force that has shaped genomes. Moreover mutation research forms the basis for the study of genome evolution. So a full understanding of mutation is necessary to unravel the mechanisms of genome evolution. In the review, we summarize the progress of mutation research and latest development in this field with an emphasis on the property of mutation and its profound significance toward genomic evolution.

Animals↗

PubMed2006

Evolutionary persistence of phenotypic integration: influence of developmental and functional relationships on complex trait evolution.

Examination of historical persistence of integration patterns provides an important insight into understanding the origin and evolution of complex traits. Specifically, the distinct effects of developmental and functional integration on the evolution of complex traits are often overlooked. Because patterns of functional integration are commonly shaped by selection exerted by the external environment, whereas patterns of developmental integration can be determined by relatively environment-independent selection for developmental homeostasis, examination of historical persistence of morphological integration patterns among species should reveal the relative importance of current selection in the evolution of complex traits. We compared historical persistence of integration patterns produced by current developmental versus ecological requirements by examining the evolution of complex mandibular structures in nine species of soricid shrews. We found that, irrespective of phylogenetic relatedness of species, patterns of developmental and functional integration were highly concordant, suggesting that strong selection for developmental homeostasis favors concordant channeling of both internal and external variation. Overall, our results suggest that divergence in mandible shape among species closely follows variation in functional demands and ecological requirements regardless of phylogenetic relatedness among species.

Animals↗

PubMed2006

The evolution of genetic architecture under frequency-dependent disruptive selection.

We propose a model to analyze a quantitative trait under frequency-dependent disruptive selection. Selection on the trait is a combination of stabilizing selection and intraspecific competition, where competition is maximal between individuals with equal phenotypes. In addition, there is a density-dependent component induced by population regulation. The trait is determined additively by a number of biallelic loci, which can have different effects on the trait value. In contrast to most previous models, we assume that the allelic effects at the loci can evolve due to epistatic interactions with the genetic background. Using a modifier approach, we derive analytical results under the assumption of weak selection and constant population size, and we investigate the full model by numerical simulations. We find that frequency-dependent disruptive selection favors the evolution of a highly asymmetric genetic architecture, where most of the genetic variation is concentrated on a small number of loci. We show that the evolution of genetic architecture can be understood in terms of the ecological niches created by competition. The phenotypic distribution of a population with an adapted genetic architecture closely matches this niche structure. Thus, evolution of the genetic architecture seems to be a plausible way for populations to adapt to regimes of frequency-dependent disruptive selection. As such, it should be seen as a potential evolutionary pathway to discrete polymorphisms and as a potential alternative to other evolutionary responses, such as the evolution of sexual dimorphism or assortative mating.

Alleles↗

PubMed2004

HIV evolution and escape.

Human immunodeficiency virus (HIV) exemplifies the principles of Darwinian evolution with a telescoped chronology. Because of its high mutation rate and remarkably high rates of replication, evolution can be appreciated over periods of days in contrast to the durations conceived of by Darwin. Certain selective pressures that drive the evolution of HIV include chemotherapy, anatomic compartmentalization and the immune response. Examples of these selective forces on HIV evolution are described.

AIDS Vaccines↗

PubMedDate not supplied

[Molecular evolution of glycogen phosphorylase and aminotransferases of vertebrate muscle tissue].

Comparative biochemical studies on phosphorylase b, aspartate aminotransferase and alanine aminotransferase in muscles of various vertebrates (the lamprey Lampetra fluviatilis, dogfish Squalus acanthias, rays Dasyatis pastinaca and Raja clavata, teleosts Scorpaena porcus, Spicara smaris, Esox lucius, Tinca tinca, Abramis brama, Lucioperca lucioperca, Cyprinus carpio, Salmo ischchan, frog Rana temporaria, tortoise Testudo horsfieldi) revealed some peculiarties of their molecular evolution. It was shown that isoenzyme PH-II, which comprises in most on the investigated lower vertebrates the main bulk of phosphorylase b, disappears in evolution of the type. Isoenzyme PH-I which is found in fisches in small amounts, increases in evolution becoming the sole form of phosphorylase b in skeletal muscles of endothermic animals. Mitochondrial and cytoplasmic isoenzymes of aspartate aminotransferase were found in all the vertebrates studied. Cytoplasmic isoenzyme from ectothermic and endothermic animals does not differ significantly, whereas the mitochondrial one undergoes considerable changes in the evolution of vertebrates.

Alanine Transaminase↗

PubMedDate not supplied

[Evolution of the DNA structure: direction, mechanism, rate].

On the basis of the analysis of frequencies of occurence of pyrimidines of different length, the degree of clustering of DNA of a hundred species belonging to different taxons has been determined. A tendency towards increase in the index of DNA clustering was revealed in the sequence: bacteria, invertebrates, fishes, amphibians, reptiles, birds, mammals. A mechanism is postulated, according to which an increase in the degree of clustering of DNA in the process of progressive evolution of species may be due to accumulation of mutations, Pyr in equilibrium Pur transversions, resulting in an increase in the degree of asymmetry of the complementary chains of DNA. That this mechanism does exist is proved by a positive correlation between the degree of clustering of DNA and the degree of asymmetry of natural DNA chains. The mean frequency of mutation of vertebrates is about 4,6-10(-8) substitutions per nucleotide per year. Evolution of different groups of organisms may be accompanied with an increase in the rate of evolution of DNA structure. With the help of a special computer program, proceeding from the amino acid sequence of cytochromes c in 40 species belonging to different taxons, the degree of clustering of pyrimidines and the degree of asymmetry of complementary chains of DNA cistrons coding for cytochrome c was determined. A general tendency towards an increase in the mean values of the corresponding parametres of structure was found in the following: bacteria, invertebrates, fishes, amphibians, reptiles, birds and mammals. Thus, it was established that "neutral" amino acid substitutions in cytochromes are based on the selection of mutations leading to accumulation of pyrimidines in sense H-chain of DNA, and purines--in the corresponding mRNA. The frequency of mutation in cytochrome c of chordates is about 5,2-10(-8) of amino acid residues per year. It is assumed that the evolution modification of DNA structure may be due to increase in the disturbance stability of translation.

Amino Acids↗