Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “fluctuating selection”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 37 records · Page 2Linked to original sources
PubMed2006

Site-specific amino acid frequency, fitness and the mutational landscape model of adaptation in human immunodeficiency virus type 1.

Analysis of the intensely studied HIV-1 gp120 V3 protein region reveals that the among-population mean site-specific frequency of an amino acid is a measure of its relative marginal fitness. This surprising result may arise if populations are displaced from mutation-selection equilibrium by fluctuating selection and if the probability of fixation of a beneficial amino acid is proportional to its selection coefficient.

Acclimatization↗
PubMed1989

Rubidium and zinc fluctuations in selected tissues during the development of the BW7756 murine hepatoma.

In separate studies, radioisotopes 65Zn and 86Rb were used to monitor trace element fluctuations from normal in C57L/J mice throughout the progression of a murine hepatoma. Amounts too small to upset normal levels were injected directly into the blood stream. After an equilibration period, the whole mouse and various resected organs and tissues were counted. Compared to normal levels, rubidium in diseased mice was lower in kidney and blood, and elevated in skin and muscle. Diseased mice showed depressed levels of zinc in skin and muscle. Large fluctuations during different stages of tumor growth were observed for various other tissues and organs of diseased mice.

Animals↗
PubMed2004

Maintenance of clonal diversity in Dipsa bifurcata (Fallén, 1810) (Diptera: Lonchopteridae). I. Fluctuating seasonal selection moulds long-term coexistence.

The deterministic maintenance of clonal diversity in thelytokous taxa can be seen as a model for understanding how environmental heterogeneity both can stabilize genetic diversity and can allow coexistence of competing species. We here analyze the temporal fluctuations in clonal diversity in the thelytokous Lonchopterid fly, Dipsa bifurcata (Fallén, 1810), at four localities in Sweden over an 8-year period. Estimated fitness values for clones are cyclical, synchronous among populations and correlated with seasonal changes in the environment. Differential winter viability and emergence from overwintering along with differential reproductive rate during the summer appear to be the selective mechanisms by which long-term clonal diversity is maintained. In a companion paper (Tomiuk et al, 2004), we present a model for the maintenance of clonal diversity through the mechanism of differential diapause among clones, utilizing fitness values estimated from the data presented here. In general, our results imply that fluctuating seasonal fitnesses can maintain stable genetic polymorphism within populations, as well as coexistence between closely related competitors, when coupled with differences in diapause phenology.

Analysis of Variance↗
PubMed1994

Seasonal fluctuations of selected physiological characteristics of elite alpine skiers.

The effects of heavy resistance training and jumping exercise were examined during the 1989-1990 season in 12 international level alpine skiers. The athletes were tested before, during, immediately after training and during the period off training (June, July, October 1989, April 1990). Their mechanical behaviour was investigated using firstly squat jumps performed without (SJ) or with low extra loads (20 kg, SJ20kg) and high extra loads (equivalent to body mass on the shoulders, SJbm) and secondly 15-30 s continuous jumping. These tests allowed the assessment of explosive dynamic strength production (SJ and SJ20kg), slow dynamic strength (SJbm) and maximal mechanical power (continuous jumping). The training adopted resulted in specific changes in neuromuscular performance; in fact all the variables studied showed a significant improvement (P < 0.01) from the beginning compared to the end of training. The range of improvement was between 55.4% (SJbm) and 12.5% (average power during 15-s continuous jumping). The enhancement of SJ had become significant by July. Surprisingly, even when no strength or jumping training was performed during the competition period (November-April), no deterioration in the neuromuscular performance was observed, there being no significant difference between the test values obtained in October 1989 and April 1990. It was concluded that the demanding competition programme of alpine skiers may provide a training stimulus adequate to maintain the neuromuscular improvement induced by training throughout the competition season.

Adult↗
PubMed1994

Cyclical behavior of genotype frequencies in a two-locus population under fluctuating haploid selection.

Numerical iterations have shown that periodic haploid two-locus selection with nonoverlapping generations can produce large-scale cyclical behavior with a period differing significantly from the environmental period. Among other types, we observed slowly damping oscillations with very long periods, stable T-cycles with a length containing several environmental periods, and chaotic-like dynamics. Possible biological implications are discussed.

Environment↗
PubMed2001

Reaction norms with bifurcations shaped by evolution.

Two versions of a model for the evolution of seasonal polyphenism investigate the evolution of reaction norm bifurcation and branching. The first version is without a specific submodel for morphological development and the second has an explicit developmental map. Version 1 is evolutionarily relatively unconstrained: (i) reaction norms are specified by matrices containing the probabilities of occurrence of environment-phenotype combinations, (ii) all conceivable reaction norm matrices are reachable through a sequence of mutations, and (iii) small as well as large mutational effects occur. This version is used to find the evolutionarily stable strategy favoured by the population ecology that is characterized by stabilizing viability selection with a cyclically fluctuating selection optimum. When the strength of selection is large and when the lag between initiation of development and selection on mature phenotype is not a multiple of half the period of the environmental cycle, a branching reaction norm evolves. In the second model version, branching reaction norms occur for certain parameter combinations of the developmental submodel, but the evolution of this pattern is often constrained. The evolutionary trajectory becomes trapped in a local selective optimum for the parameters of the developmental system. Substantial developmental noise evolves, but mutations that produce a selectively advantageous branching pattern do not occur from there.

Animals↗
PubMed2001

Divergent evolution of dispersal in a heterogeneous landscape.

The evolution of dispersal is investigated in a landscape of many patches with fluctuating carrying capacities and spatial heterogeneity in temporal fluctuations. Although asynchronous temporal fluctuations select for dispersal, spatial heterogeneity in the distribution of fluctuating environmental variables selects against it. We find evolutionary branching in dispersal rate leading to the evolutionarily stable coexistence of a high- and a low-dispersal phenotype. We study how the opposing forces of selection for and against dispersal change with the relative size and the environmental qualities of the source and sink habitats. Our results suggest that the evolution of dispersal dimorphism could be a first step towards speciation and local adaptation.

Animals↗
PubMed1993

Fluctuating asymmetry, sexual selection and canine teeth in primates.

Fluctuating asymmetry arises as small deviations from symmetry which can be expressed on either side of the body. Increases in fluctuating asymmetry can suggest genomic stress such as results from directional selection. It has been argued that epigamic structures and weapons should show high levels of fluctuating asymmetry because sexual selection is essentially directional in nature. We tested this prediction by examining the expression of fluctuating asymmetry in the upper canines of 21 species of Old World primates. We found, for males but not for females, that asymmetry was correlated with measures of sexual selection including canine dimorphism, canine size, mass dimorphism, and intra-male competition. However, there was no significant correlation with diet type and body mass, which are only weakly associated with sexual selection. Phylogenetic inertia did not account for the association between fluctuating asymmetry and sexual selection. We also found that species with high values of canine dimorphism and intra-male competition tended to have a negative correlation between asymmetry and mean canine height, and this latter effect was present in both males and females. The implications of these findings for sexual selection theory are discussed.

Animals↗
PubMed2025

Pervasive fitness trade-offs revealed by rapid adaptation to shifting population densities in large experimental populations of Drosophila melanogaster.

Trade-offs are an inherent feature of organismal biology that are expected play a fundamental role in the evolution of natural populations. Efforts to quantify trade-offs are largely confined to phenotypic measurements and the identification of negative genetic-correlations among fitness-relevant traits. Here, we use time-series genomic data collected during experimental evolution in large, genetically diverse populations of Drosophila melanogaster to directly measure the manifestation of trade-offs in response to fluctuating selection on ecological timescales. Specifically, we first conducted a lab-based selection experiment to quantify a genome-wide signal of antagonistic pleiotropy elicited in response to shifting population densities and associated with reproduction and stress tolerance selection. In doing so, we identified a putative role of two cosmopolitan inversions in these trade-offs. We then conducted an independent experiment to show that a simple manipulation of increasing population density under controlled lab-based conditions identified loci that are relevant to selection during population expansion and collapse in a complex, semi-natural setting. In concert, our results reveal how adaptation in complex, natural environments can be coarse-grained in such a manner to drive repeatable and predictable patterns of genomic variation, and further add credence to models positing a role of generic fitness trade-offs in the maintenance of variation in natural populations.

Drosophila melanogaster↗
PubMed1998

Rate variation of DNA sequence evolution in the Drosophila lineages.

Rate constancy of DNA sequence evolution was examined for three species of Drosophila, using two samples: the published sequences of eight genes from regions of the normal recombination rates and new data of the four AS-C (ac, sc, l'sc and ase) and ci genes. The AS-C and ci genes were chosen because these genes are located in the regions of very reduced recombination in Drosophila melanogaster and their locations remain unchanged throughout the entire lineages involved, yielding less effect of ancestral polymorphism in the study of rate constancy. The synonymous substitution pattern of the three lineages was found to be erratic in both samples. The dispersion index for replacement substitution was relatively high for the per, G6pd and ac genes. A significant heterogeneity was found in the number of synonymous substitutions in the three lineages between the two samples of genes with different recombination rates. This is partly due to a lack of the lineage effect in the D. melanogaster and Drosophila simulans lineages in the AS-C and ci genes in contrast to Akashi's observation of genes in regions of normal recombination. The higher codon bias in Drosophila yakuba as compared with D. melanogaster and D. simulans was observed in the four AS-C genes, which suggests change(s) in action of natural selection involved in codon usage on these genes. Fluctuating selection intensity may also be responsible for the observed locus-lineage interaction effects in synonymous substitution.

Animals↗
PubMed1994

Increased recombination frequencies resulting from directional selection for geotaxis in Drosophila.

Several classes of models have been suggested to explain how natural selection can favour non-zero recombination. Directional and fluctuating selection, abiotic and biotic, and selection against harmful mutations seem to be the most plausible factors, but little has been done to test the problem experimentally. Here we show that long-term selection for positive or negative geotaxis in Drosophila melanogaster results in a dramatic increase in recombination rates in different genomic regions. The total increment in recombination for the genome portion considered is 78 cM for geo+ and 66 cM for geo-. Selection for negative geotaxis did not result in recombination changes in chromosome 2 whereas selection in the opposite direction caused nearly a four-fold increase in the b-cn segment and a significant, albeit not as high, increase in the adjacent regions, al-b and cn-vg. In chromosomes X and 3, a significant increase in recombination was found in both selected lines. In total, the increment in exchange frequency in chromosome X (y-cv-ct-v-car) was from 72.6 per cent (the control level) to 124.7 and 110.3 per cent geo- and geo+, respectively, whereas for the studied portion of chromosome 3 (ru-h-cu-sr-e) we obtained, correspondingly, 60.8, 76.4 and 73.8 per cent. Thus, in general, selection for geotaxis resulted in increased recombination frequencies regardless of the direction of selection.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Longevity enhances selection of environmental sex determination.

Environmental sex determination (ESD) is a mechanism in which an individual develops as male or female largely in response to some environmental effect experienced early in life. Its forms range from sex determination by egg incubation temperature in reptiles to sex determination of photoperiod in amphipods. Previous theoretical work as suggested that ESD is favored by natural selection if the fitness consequences of the early environmental experience differ for males and females, so that an individual benefits by being male under some conditions and female under others. A drawback of ESD is that it enables climatic changes to influence the population sex ratio, and such fluctuations select against ESD. This study employed numerical analyses to investigate the balance between these two opposing forces. The negative impact of climatic fluctuations appears to depend greatly on species longevity: substantial between-year fluctuations are of little consequence in selecting against ESD in long-lived species because annual sex ratio fluctuations tend to cancel and thus alter the total population sex ratio only slightly. Thus, if a species is sufficiently long-lived, extreme ESD can be maintained despite only a weak advantage. This result offers one explanation for the failure to demonstrate an advantage for the extreme forms of ESD observed in reptiles.

Animals↗
PubMed2000

Consequences of cAMP and catalytic-subunit binding on the flexibility of the A-kinase regulatory subunit.

A combination of site-directed labeling and time-resolved fluorescence anisotropy was used to further elucidate the structure and underlying dynamic features of the type I regulatory (R(I)(alpha)) subunit of the cAMP-dependent protein kinase. Specifically, the consequences of cAMP and the catalytic (C)-subunit binding on the backbone flexibility around seven sites of cysteine substitution and fluorescein maleimide labeling (Thr(6)Cys, Leu(66)Cys, Ser(75)Cys, Ser(81)Cys, Ser(99)Cys, Ser(145)Cys, and Ser(373)Cys) in the R(I)(alpha) subunit were assessed. Focusing on the fast rotational correlation time, the results indicate that most of the interdomain segment connecting the dimerization/docking (D/D) and tandem cAMP-binding domains is probably weakly associated with the latter domain. Also, this segment becomes more tightly bound to the C subunit upon holoenzyme formation. The results also suggest that there is a short 'hinge' segment (around Leu(66)Cys) that could allow the structured interdomain/cAMP-binding and D/D domains to pivot about each other. Finally, cAMP binding dramatically reduces the backbone flexibility around only the two sites of cysteine substitution in the cAMP-binding domains, suggesting a selective structural stabilization caused by cAMP and a "tight" coupling of low-nanosecond fluctuations selectively within the tandem cAMP-binding domains.

Catalysis↗
PubMed2005

Evolution of genetic potential.

Organisms employ a multitude of strategies to cope with the dynamical environments in which they live. Homeostasis and physiological plasticity buffer changes within the lifetime of an organism, while stochastic developmental programs and hypermutability track changes on longer time-scales. An alternative long-term mechanism is "genetic potential"--a heightened sensitivity to the effects of mutation that facilitates rapid evolution to novel states. Using a transparent mathematical model, we illustrate the concept of genetic potential and show that as environmental variability decreases, the evolving population reaches three distinct steady state conditions: (1) organismal flexibility, (2) genetic potential, and (3) genetic robustness. As a specific example of this concept we examine fluctuating selection for hydrophobicity in a single amino acid. We see the same three stages, suggesting that environmental fluctuations can produce allele distributions that are distinct not only from those found under constant conditions, but also from the transient allele distributions that arise under isolated selective sweeps.

Journal Article↗