Female participation in the labour force of selected Latin American countries.
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Age Factors↗
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Results for “selective forces”
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[Adaptability of patients to freely selected and forced physical exercise after myocardial infarction].
In 45 patients with myocardial infarction in the rehabilitative period in health resort centers, bicycle ergometric tests with forced routine continuously gradually increasing exercise or without forced graded exercise in accordance with the "free option" motor motivation test were performed at the beginning and at the end of treatment. The work performed at the beginning and at the end of treatment. The work performed with free option is characterized by substantial differences in its volume, duration, intensity, and rate. Free option exercise is submaximal, close to tolerant, but simultaneously shows lower values in heart rates, systolic blood pressure, "double product" and cost-effective index. The free option exercise test is a more sensitive indicator of alterations in the status of a patient with myocardial infarction during health resort rehabilitation.
Adaptation, Physiological↗
Joint moments of force in selected sports and rehabilitation exercises.
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Exercise Therapy↗
Forces determining selection of uremia therapy.
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Age Factors↗
Evolution of balanced genetic polymorphism.
Extreme genetic polymorphism maintained by balancing selection (so called because many alleles are maintained in a balance by a mechanism of rare allele advantage) is intimately associated with the important task of self/non-self-discrimination. Widely disparate self-recognition systems of plants, animals and fungi share several general features, including the maintenance of large numbers of alleles at relatively even frequency, and persistence of this variation over very long time periods. Because the evolutionary dynamics of balanced polymorphism are very different from those of neutral genetic variation, data on balanced polymorphism have been used as a novel source for inference of the history of populations. This review highlights the unique evolutionary properties of balanced genetic polymorphism, and the use of theoretical understanding in analysis and application of empirical data for inference of population history. However, a second goal of this review is to point out where current theory is incomplete. Recent observations suggest that entirely novel selective forces may act in concert with balancing selection, and these novel forces may be extremely potent in shaping genetic variation at self-recognition loci.
Animals↗
Rapid evolution of fertilization selectivity and lysin cDNA sequences in teguline gastropods.
Proteins mediating intercellular recognition face opposing selective forces as they evolve: purifying selection to maintain function, and diversifying selection to alter specificity. Lysin is a 16-kDa protein which enables sperm of free-spawning marine snails to make a hole in the vitelline layer (VE) surrounding conspecific eggs. Previous work on abalone (Haliotis spp.) has shown that positive selection promotes rapid interspecific divergence of lysin. Here, we present data on the specificity of VE dissolution by four species of teguline gastropods, along with lysin cDNA sequences. The teguline and abalone lineages diverged over 250 MYA. As in abalone, VE dissolution by lysin in tegulines is species-selective, and positive selection promotes rapid interspecific divergence over the entire mature protein. Nonsynonymous substitution rates, calculated using a mtCOI molecular clock calibrated by two Tegula species separated by the Isthmus of Panama, are high (> 25 substitutions per site per 10(9) years). However, the extensive replacements in teguline lysins are overwhelmingly conservative with respect to type, charge, and polarity of residues. Predictions of secondary structure suggest that the size and position of alpha-helices are also conserved, even through pairwise amino acid identities between Haliotis rufescens and the different tegulines are less than 15%.
Amino Acid Sequence↗
Genetic variation in response to an indirect ecological effect.
Indirect ecological effects (IEEs) are widespread and often as strong as the phenotypic effects arising from direct interactions in natural communities. Indirect effects can influence competitive interactions, and are thought to be important selective forces. However, the extent that selection arising from IEEs results in long-term evolutionary change depends on genetic variation underlying the phenotypic response-that is, a genotype-by-IEE interaction. We provide the first data on genetic variation in the response of traits to an IEE, and illustrate how such genetic variation might be detected and analysed. We used a model tri-trophic system to investigate the effect of host plants on two populations of predatory ladybirds through a clonal aphid herbivore. A split-family experimental design allowed us to estimate the effects of aphid host plant on ladybird traits (IEE) and the extent of genetic variation in ladybird predators for response to these effects (genotype-by-indirect environmental effect interaction). We found significant genetic variation in the response of ladybird phenotypes to the indirect effect of host plant of their aphid prey, demonstrating the potential for evolutionary responses to selection arising from the prey host.
Animals↗
Evolution of the complementary sex-determination gene of honey bees: balancing selection and trans-species polymorphisms.
The mechanism of sex determination varies substantively among evolutionary lineages. One important mode of genetic sex determination is haplodiploidy, which is used by approximately 20% of all animal species, including >200,000 species of the entire insect order Hymenoptera. In the honey bee Apis mellifera, a hymenopteran model organism, females are heterozygous at the csd (complementary sex determination) locus, whereas males are hemizygous (from unfertilized eggs). Fertilized homozygotes develop into sterile males that are eaten before maturity. Because homozygotes have zero fitness and because common alleles are more likely than rare ones to form homozygotes, csd should be subject to strong overdominant selection and negative frequency-dependent selection. Under these selective forces, together known as balancing selection, csd is expected to exhibit a high degree of intraspecific polymorphism, with long-lived alleles that may be even older than the species. Here we sequence the csd genes as well as randomly selected neutral genomic regions from individuals of three closely related species, A. mellifera, Apis cerana, and Apis dorsata. The polymorphic level is approximately seven times higher in csd than in the neutral regions. Gene genealogies reveal trans-species polymorphisms at csd but not at any neutral regions. Consistent with the prediction of rare-allele advantage, nonsynonymous mutations are found to be positively selected in csd only in early stages after their appearances. Surprisingly, three different hypervariable repetitive regions in csd are present in the three species, suggesting variable mechanisms underlying allelic specificities. Our results provide a definitive demonstration of balancing selection acting at the honey bee csd gene, offer insights into the molecular determinants of csd allelic specificities, and help avoid homozygosity in bee breeding.
Alleles↗
Signature of selective sweep associated with the evolution of sex-ratio drive in Drosophila simulans.
In several Drosophila species, the XY Mendelian ratio is disturbed by X-linked segregation distorters (sex-ratio drive). We used a collection of recombinants between a nondistorting chromosome and a distorting X chromosome originating from the Seychelles to map a candidate sex-ratio region in Drosophila simulans using molecular biallelic markers. Our data were compatible with the presence of a sex-ratio locus in the 7F cytological region. Using sequence polymorphism at the Nrg locus, we showed that sex-ratio has induced a strong selective sweep in populations from Madagascar and Réunion, where distorting chromosomes are close to a 50% frequency. The complete association between the marker and the sex-ratio phenotype and the near absence of mutations and recombination in the studied fragment after the sweep event indicate that this event is recent. Examples of selective sweeps are increasingly reported in a number of genomes. This case identifies the causal selective force. It illustrates that all selective sweeps are not necessarily indicative of an increase in the average fitness of populations.
Alleles↗
Sexual selection: an evolutionary force in plants?
Sexual selection has traditionally been used to explain exaggerated sexual traits in male animals. Today the concept has been developed and various other sexually related traits have been suggested to evolve in the same manner. In nearly all new areas where the theory of sexual selection has been applied, there has been an intense debate as to whether the application is justified. Is it the case that some scientists are all too ready to employ fashionable ideas? Or are there too many dogmatic researchers refusing to accept that science develops and old ideas are transformed? Maybe the controversies are simply a reflection of the difficulty of defining a theory under constant re-evaluation. Thus, we begin by summarizing the theory of sexual selection in order to assess the influence of sexual selection on the evolution of plant morphology. We discuss empirical findings concerning potentially affected traits. Although we have tried to address criticisms fairly, we still conclude that sexual selection can be a useful tool when studying the evolution of reproductive traits in plants. Furthermore, by including the evidence from an additional kingdom, a fuller understanding of the processes involved in sexual selection can be gained.
Biological Evolution↗
The roles of antibody variable region hypermutation and selection in the development of the memory B-cell compartment.
Somatic hypermutation and selection of immunoglobulin (Ig) variable (V)-region genes, working in concert, appear to be essential for memory B-cell development in mammals. There has been substantial progress on the nature of the cis-acting DNA elements that regulate hypermutation. The data obtained suggest that the mechanisms of Ig gene hypermutation and transcription are intimately intertwined. While it has long been appreciated that stringent phenotypic selection forces are imposed on the somatically mutated Ig V regions generated during a T-cell dependent B-cell response, the mechanisms involved in this selection have remained enigmatic. Our studies have questioned the role of foreign antigen deposited on follicular dendritic cells in affinity-based positive selection of V regions, and have shown that this selection takes place in a "clone-autonomous" fashion. In addition, our data strongly suggest that affinity for antigen alone is not the driving force for selection of B-cell clones into the memory compartment. In contrast, we suggest that a combination of positive selection for increased foreign antigen binding, and negative selection of antibody V regions that are autoreactive at the onset of the response, or have acquired autoreactivity via hypermutation, results in the "specificity maturation" of the memory B-cell response.
Animals↗
Evidence for Selection of more Adapted Human Immunodeficiency Virus Type 1 Recombinant Strains in a Dually Infected Transfusion Recipient.
Human immunodeficiency virus type-1 (HIV-1) genetic diversity is one of the remarkable characteristics of these viruses, and the mechanisms involved in the selective forces driving HIV-1 evolution are of great interest. Samples from hosts infected with multiple distinct strains represent a valuable in vivo resource to investigate the role of recombination in the natural evolution of HIV-1. This work describes a detailed study regarding the evolution of the envelope gene (env) (C2-V5 region) in a dually infected child who received blood transfusions simultaneously from two distinct HIV-1 infected donors. In this study, we were able to directly compare the data obtained from the dually infected recipient with data obtained from two other singly HIV-1 infected children who had received blood transfusion from each of the two donors. Sequences from the singly infected children clustered into two distinct groups, each related to the respective donor-derived sequence by phylogenetic analysis, and hence were consistent with the epidemiological data. In the case of the dually infected child, a high degree of recombination between the two donor-derived sequences was observed at the C2-V3 region, whereas in the V4-V5 region selection of only one derived donor sequence was seen. Measurement of nonsynonymous versus synonymous substitution rates at each region revealed that negative selection was the main evolutionary force acting on the viral population of the dually infected child, regardless of the genetic mechanism by which each region evolved. Based on direct comparison with data obtained for the two singly infected children we propose that the higher amount of viral diversity observed in HIV-1 multi-infection events, as in the case of the dually infected patient, might contribute to maximizing selective advantage and possibly minimizing immune response. We conclude that recombination shaped by selective forces may increase the adaptive potential of HIV-1.
Adaptation, Physiological↗
The asymmetry of life.
Stereoselective physical phenomena and their possible importance for the prevalence of D-sugars and L-aminoacids in living matter are reviewed. A classification is presented according to which a selective force provides a microscopic or macroscopic selection depending on its generality when taken over a macrosystem (a 'unitary biosphere' such as the Earth). The microscopic 'selections' are not genuine selections because the final sense of asymmetry is here determined by chance, in other words the initial choice is 'random', while it is 'directed' in the macroscopic selection. Two macroscopic selections appear possible: 1. selection due to an intrinsic energy difference between enantiomorph configurations, 2. selection accomplished by elliptically polarised radiation.
Amino Acids↗
Positive Darwinian selection on two homologous fertilization proteins: what is the selective pressure driving their divergence?
Most examples of positive selection inferred from nucleotide sequence data involve hostpathogen interactions. However, positive selection also promotes the divergence of proteins mediating sperm-egg recognition in marine invertebrates. The abalone spermatozoon has a large acrosomal vesicle containing two proteins of 16 kDa and 18 kDa. Lysin, the 16-kDa protein, exhibits species-specificity in dissolving a hole in the egg vitelline envelope through which the sperm swims to reach the egg plasma membrane. The 18-kDa protein coats the sperm acrosomal process and probably mediates fusion of the two gametes. In this review, we compare sequences of both proteins from five species of California abalones. Both proteins show extensive divergence which has been promoted by positive Darwinian selection. The ratios of nonsynonymous to synonymous nucleotide substitutions may be the highest yet discovered for full-length sequences. Although extensive divergence has occurred, there is conservation of the shape and polarity of residues in both proteins. The two acrosomal proteins arose by a gene duplication followed by their extensive divergence. Five hypotheses are presented which attempt to explain the nature of the unknown selective force responsible for the robust positive selection. The positive selection may, in some unknown way, be related to the establishment of prezygotic barriers to reproduction. Because positive selection promotes the divergence of unrelated, species-specific gamete recognition proteins in both abalones and sea urchins, we predict that positive selection may be a general phenomenon in the evolution of gamete recognition systems in marine invertebrates.
Amino Acid Sequence↗
HIV evolution: CTL escape mutation and reversion after transmission.
Within-patient HIV evolution reflects the strong selection pressure driving viral escape from cytotoxic T-lymphocyte (CTL) recognition. Whether this intrapatient accumulation of escape mutations translates into HIV evolution at the population level has not been evaluated. We studied over 300 patients drawn from the B- and C-clade epidemics, focusing on human leukocyte antigen (HLA) alleles HLA-B57 and HLA-B5801, which are associated with long-term HIV control and are therefore likely to exert strong selection pressure on the virus. The CTL response dominating acute infection in HLA-B57/5801-positive subjects drove positive selection of an escape mutation that reverted to wild-type after transmission to HLA-B57/5801-negative individuals. A second escape mutation within the epitope, by contrast, was maintained after transmission. These data show that the process of accumulation of escape mutations within HIV is not inevitable. Complex epitope- and residue-specific selection forces, including CTL-mediated positive selection pressure and virus-mediated purifying selection, operate in tandem to shape HIV evolution at the population level.
Adult↗
The potential for adaptive evolution of pollen grain size in Mimulus guttatus.
We tested whether pollen grain size (PGS) shows heritable variation in three independent populations of Mimulus guttatus by imposing artificial selection for this character. In addition, we looked for correlated responses to selection in a range of 15 other floral characters. Heritable variation in PGS was found in all three populations, with heritabilities of between 19 and 40% (average 30%). After three generations, upward and downward lines differed on average by 30% in pollen volume. No consistent patterns of correlated response were found in other characters, indicating that PGS can respond to selective forces acting on PGS alone. Possible selection mechanisms on PGS in this species could include intermale selection, if large pollen grains produce more competitive gametophytes; or optimization of patterns of resource allocation, if local mate competition varies.
Adaptation, Physiological↗
Can internal models of objects be utilized for different prehension tasks?
We examined if object information obtained during one prehension task is used to produce fingertip forces for handling the same object in a different prehension task. Our observations address the task specificity of the internal models presumed to issue commands for grasping and transporting objects. Two groups participated in a 2-day experiment in which they lifted a novel object (230 g; 1.2 g/cm3). On Day One, the high force group (HFG) lifted the object by applying 10 N of grip force prior to applying vertical lift force. This disrupted the usual coordination of grip and lift forces and represented a higher grip force than necessary. The self-selected force group (SSFG) lifted the object on Day One with no instructions regarding their grip or lift forces. They first generated grip forces of 5.8 N, which decreased to 2.6 N by the 10th lift. Four hours later, they lifted the same object in the manner of the HFG. On Day Two, both groups lifted the same object "naturally and comfortably" with the opposite hand. The SSFG began Day Two using a grip force of 2.5 N, consistent with the acquisition of an accurate object representation during Day One. The HFG began Day Two using accurately scaled lift forces, but produced grip forces that virtually replicated those of the SSFG on Day One. We concur with recent suggestions that separate, independently adapted internal models produce grip and lift commands. The object representation that scaled lift force was not available to scale grip force. Furthermore, the concept of a general-purpose object representation that is available across prehension tasks was not supported.
Adult↗
Nonretarded and mentally retarded children's performance on a manual-control task with and without visual feedback.
Performance differences between 10 nonretarded and 10 retarded persons on a manual-control task were examined. More specifically, the focus was on possible relationships between the subjects' abilities to control their response forces and the focus of their attention. The subjects, who were closely matched for MA, were required to exert force on a transducer within a selected force bandwidth for 3 seconds to obtain a reinforcer. Results suggested that the ability to discriminate internal cues is related to IQ differences.
Achievement↗