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Results for “oscillating allele frequency”

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At least 19 recordsLinked to original sources
PubMed2026

Seasonal fluctuations in fitness result in severe reductions in effective population size.

Genetic evidence for fluctuating selection has begun to accumulate for different species over the past few decades, especially for the Drosophila genus where studies have reported hundreds of loci undergoing putatively adaptive oscillations across successive seasons. However, most theoretical and simulation studies of fluctuating selection have relied on abstract or weakly parameterized models, making it difficult to assess their relevance for natural populations. In this study, we simulate multilocus seasonally fluctuating selection under a recently developed model and examine its effect on the variance effective population size (Ne ) at a genome-wide scale. By recapitulating genomic, demographic, and evolutionary parameters from natural Drosophila populations in our simulations, we were able to reproduce allele frequency oscillations reported in recent studies and show that these lead to ~50% genome-wide reductions in Ne . We also demonstrate that Ne reductions are well predicted by the maximum frequency amplitude among all adaptively fluctuating loci, and that the frequency amplitudes are largely determined by the number of adaptively fluctuating loci and the strength of their epistatic interactions. Our results demonstrate that fluctuating selection can substantially reduce effective population size and underscore the importance of temporally variable selection in shaping genome-wide patterns of variation beyond classical models.

Drosophila melanogaster↗
PubMed2026

Seasonal fluctuations in fitness result in severe reductions in effective population size.

Genetic evidence for fluctuating selection has begun to accumulate for different species over the past few decades, especially for the Drosophila genus where studies have reported hundreds of loci undergoing putatively adaptive oscillations across successive seasons. However, most theoretical and simulation studies of fluctuating selection have relied on abstract or weakly parameterized models, making it difficult to assess their relevance for natural populations. In this study, we simulate multilocus seasonally fluctuating selection acting on standing genetic variation under a recently developed model and examine its effect on the variance effective population size (Ne) at a genome-wide scale. By recapitulating genomic, demographic, and evolutionary parameters from natural Drosophila populations in our simulations, we were able to reproduce allele frequency oscillations reported in recent studies and show that these lead to ∼50% genome-wide reductions in Ne. We also demonstrate that Ne reductions are well predicted by the maximum frequency amplitude among all adaptively fluctuating loci, and that the frequency amplitudes are largely determined by the number of adaptively fluctuating loci and the strength of their epistatic interactions. Our results demonstrate that fluctuating selection can substantially reduce effective population size and underscore the importance of temporally variable selection in shaping genome-wide patterns of variation beyond classical models.

Drosophila melanogaster↗
PubMed2005

Selection in a cyclical environment: possible impact of phenotypic lag on Darwinian fitness.

We investigated the effect of generation time (as controlled by chemostat flow rate) and temporal variability in nutrient (arginine) availability on selection at a regulatory locus in Escherichia coli. We first determined the fitness conferred by argR(K12) (which regulates the arginine regulon) relative to argR(B) (a weak constitutive) in constant environments at several generation times across a range of concentrations of arginine. The relative fitness of argR(K12) with respect to argR(B) declines with longer generation times in the absence of arginine yet becomes independent of generation time in the presence of excess arginine. Control experiments show this differential response in selection is entirely attributable to transcriptional regulation by argR(K12). Temporal variability in the supply of arginine generates fluctuations in selection. A simple model, based on the assumption that relative fitness tracks changes in arginine availability instantaneously, captures many of the features of the oscillating allele frequencies and accurately predicts the direction and intensity of selection in environments where arginine concentrations fluctuate frequently or infrequently. However, the model fails to predict the direction and intensity of selection in environments that fluctuate at moderate frequencies. This suggests that phenotypic lag, wherein cellular physiology changes more slowly than the environment, may be influencing the outcome of competition in this experimental system.

Arginine↗
PubMed2026

Dissecting fluctuating selection: A unified population and quantitative genetics framework.

One of the longstanding debates in evolutionary biology is the effect of fluctuating selection on genetic changes in populations. However, the extent to which these periodic forces influence organisms at both genomic and phenotypic levels remains unclear. Despite the compelling evidence of fluctuating selection from recent studies, there is a disconnect between empirical and theoretical findings concerning the underlying mechanisms due to the limited evidence regarding the scale and processes that generate genome-wide oscillations. This study aims to elucidate how both genetic factors (e.g. heritability, number of causative loci) and ecological factors (e.g. season length, the difference in the phenotypic optima between seasons, population size dynamics) drive fluctuating selection and to identify the parameters that produce consistent oscillatory patterns. We developed a modeling framework integrating quantitative and population genetics to simulate a population under various selection regimes. We applied spectral analysis to detect periodicity, indicating cyclical selective environments. Our simulations highlight the conditions sustaining oscillations in allele frequencies over time. Spectral analysis successfully identifies the periodic patterns from allele frequency trajectories, even under highly complex selection regimes. Not only does our study clarify the conditions that yield oscillatory behaviors, but these parameters can also potentially be estimated in natural populations, providing a possibility of empirically testing these models.

Fluctuating selection↗
PubMed2026

Dissecting fluctuating selection: A unified population and quantitative genetics framework.

One of the longstanding debates in evolutionary biology is the effect of fluctuating selection on genetic changes in populations. However, the extent to which these periodic forces influence organisms at both genomic and phenotypic levels remains unclear. Despite the compelling evidence of fluctuating selection from recent studies, there is a disconnect between empirical and theoretical findings concerning the underlying mechanisms due to the limited evidence regarding the scale and processes that generate genome-wide oscillations. This study aims to elucidate how both genetic factors (e.g. heritability, number of causative loci) and ecological factors (e.g. season length, the difference in the phenotypic optima between seasons, population size dynamics) drive fluctuating selection and to identify the parameters that produce consistent oscillatory patterns. We developed a modeling framework integrating quantitative and population genetics to simulate a population under various selection regimes. We applied spectral analysis to detect periodicity, indicating cyclical selective environments. Our simulations highlight the conditions sustaining oscillations in allele frequencies over time. Spectral analysis successfully identifies the periodic patterns from allele frequency trajectories, even under highly complex selection regimes. Not only does our study clarify the conditions that yield oscillatory behaviors, but these parameters can also potentially be estimated in natural populations, providing a possibility of empirically testing these models.

Fluctuating selection↗
PubMed2003

Coevolution between hosts and parasites with partially overlapping geographic ranges.

Many host species interact with a specific parasite within only a fraction of their geographical range. Where host and parasite overlap geographically, selection may be reciprocal constituting a coevolutionary hot spot. Host evolution, however, may be driven primarily by selection imposed by alternative biotic or abiotic factors that occur outside such hot spots. To evaluate the importance of coevolutionary hot spots for host and parasite evolution, we analyse a spatially explicit genetic model for a host that overlaps with a parasite in only part of its geographical range. Our results show that there is a critical amount of overlap beyond which reciprocal selection leads to a coevolutionary response in the host. This critical amount of overlap depends upon the explicit spatial configuration of hot spots. When the amount of overlap exceeds this first critical level, host-parasite coevolution commonly generates stable allele frequency clines rather than oscillations. It is within this region that one of the primary predictions of the geographic mosaic theory is realized, and local maladaptation is prevalent in both species. Past a further threshold of overlap between the species oscillations do evolve, but allele frequencies in both species are spatially synchronous and local maladaptation is absent in both species. A consequence of such transitions between coevolutionary dynamics is that parasite adaptation is inversely proportional to the fraction of its host's range that it occupies. Hence, as the geographical range of a parasite increases, it becomes increasingly maladapted to the host. This suggests a novel mechanism through which the geographical range of parasites may be limited.

Animals↗
PubMed2005

Paternal leakage sustains the cytoplasmic polymorphism underlying gynodioecy but remains invasible by nuclear restorers.

Cytoplasmic male sterility (CMS) in plants often results in gynodioecious populations, composed of hermaphrodites and male-sterile females. All models of gynodioecy assume maternal inheritance of the cytoplasmic alleles and postulate a variety of negatively frequency-dependent mechanisms to maintain the cytoplasmic polymorphisms observed in many natural populations. However, in some plant species, mitochondria are transmitted at least occasionally by pollen, a process called paternal leakage. We show that even a small amount of paternal leakage is sufficient to sustain a permanent, stable cytoplasmic polymorphism. Because only hermaphrodites provide pollen in gynodioecious species, the effects of paternal leakage are biased and occur more often from the non-CMS male-fertile haplotype to the CMS male-sterile haplotype. We also show that a nuclear restorer disrupts the polymorphic cytoplasmic equilibrium, leading to fixation of both the CMS allele and the restorer. Although a dominant nuclear restorer fixes, it fixes much more slowly than in the standard CMS models. Although a stable cytonuclear polymorphism is possible with "matching alleles" nuclear restoration, oscillations to low frequencies present a risk of loss by drift. Paternal leakage enhances the stability of joint cytonuclear polymorphism by reducing the chance that a CMS allele is lost by drift.

Cell Nucleus↗
PubMed1975

A continuous selective model for an X-linked locus.

Neglecting age-structure, but taking into account matings with differential fertility in Mendelian reproduction, a continuous selective model is formulated for a single X-linked locus with an arbitrary number of alleles. Without restricting the mating system, differential equations are derived for the genotypic and allelic frequencies. Assuming random mating, no selection, and constant fertilities and mortalities, these differential equations are solved explicitly. For this case, in contrast to the corresponding phenomenon in the usual model with discrete, non-overlapping generation, the difference between the frequencies of any allele in males and females approaches zero without oscillation.

Age Factors↗
PubMed1978

Sex-linked genes in age-structured populations.

We study the progress towards equilibrium of the frequencies of sex-linked genes in elementary discrete time models of age-structured, overlapping generation populations. It is found that, if a finite upper age limit is assumed, the difference in the frequencies of an allele in males and females will oscillate as in the familiar non-overlapping generation models, although the oscillations may be irregular. Monotonic convergence of that difference, as found by Nagylaki (1975) in continuous-time overlapping generation models without age-structure, occurs in the models considered here only when there is no upper age limit and when there is "sufficient" overlap of generations.

Age Factors↗
PubMed2003

Further properties of Gavrilets' one-locus two-allele model of maternal selection.

I derive several properties of the model proposed by Gavrilets for maternal selection at a single diallelic locus. Most notably, (i) stable oscillations of genotype frequencies (i.e., cycling) can occur and (ii) in the special case in which maternal effects and standard viability selection act multiplicatively, maternal selection effectively acts on maternally derived alleles only.

Alleles↗
PubMed1993

[Heterogeneous selection in a subdivided population with unstable deme sizes].

The influence of small deme sizes oscillations in a one-locus two-allele model is considered. The dependence of frequency deviations from the fluctuation numbers is obtained. The new method of selection coefficients and migration matrix estimation from the deme numbers and the allele frequencies observations is found.

Alleles↗
PubMed1998

One-locus two-allele models with maternal (parental) selection.

I formulate and study a series of simple one-locus two-allele models for maternal (parental) selection. I show that maternal (parental) selection can result in simultaneous stability of equilibria of different types. Thus, in the presence of maternal (parental) selection the outcome of population evolution can significantly depend on initial conditions. With maternal selection, genetic variability can be maintained in the population even if none of the offspring of heterozygous mothers survive. I demonstrate that interactions of maternal and paternal selection can result in stable oscillations of genotype frequencies. A necessary condition for cycling is strong selection.

Alleles↗
PubMed2006

Prey evolution on the time scale of predator-prey dynamics revealed by allele-specific quantitative PCR.

Using rotifer-algal microcosms, we tracked rapid evolution resulting from temporally changing natural selection in ecological predator-prey dynamics. We previously demonstrated that predator-prey oscillations in rotifer-algal laboratory microcosms are qualitatively altered by the presence of genetic variation within the prey. In that study, changes in algal gene frequencies were inferred from their effects on population dynamics but not observed directly. Here, we document rapid prey evolution in this system by directly observing changes in Chlorella vulgaris genotype frequencies as the abundances of these algae and their consumer, Brachionus calyciflorus, change through time. We isolated a group of algal clones that we could distinguish by using microsatellite-DNA markers, and developed an allele-specific quantitative PCR technique (AsQ-PCR) to quantify the frequencies of pairs of clones in mixed culture. We showed that two of these genotypes exhibited a fitness tradeoff in which one was more resistant to predation (more digestion-resistant), and the other had faster population growth under limiting nitrogen concentrations. A fully specified mathematical model for the rotifer-algal population and evolutionary dynamics predicted that these two clones would undergo a single oscillation in clonal frequencies followed by asymptotic fixation of the more resistant clone, rather than the recurrent oscillations previously observed with other algal clones. We used AsQ-PCR to confirm this prediction: the superior competitor dominated initially, but as rotifer densities increased, the more predator-resistant clone predominated.

Alleles↗
PubMed1980

Oscillations of frequency in Batesian mimics, hawks and doves, and other simple frequency dependent polymorphisms.

It is customary to infer the properties of the internal equilibria produced by frequency dependent selection from the properties of the boundary equilibria (often called the "invasion" criterion). This paper demonstrates that there are some circumstances that there is a truly stable, unique, internal equilibrium. For two alleles with complete dominance, if phenotype fitness declines monotonically with increasing frequency, then the internal point of equal phenotype fitness is the unique internal equilibrium of the genes, and is not unstable; this criterion may also be met if the fitness of one phenotype increases with frequency. It must be truly stable, in the sense of not producing oscillations, if the decline of fitness is linear or convex upwards and no phenotype is lethal at any frequency; the hawk-dove game complies with both conditions, and at least the second condition is likely to be met in most of the models encountered in sociobiology. However, an equilibrium which induces damped oscillations, or perhaps even complex limit cycles, is possible if at least one phenotype can be lethal at high frequency, or if the decline in fitness is strongly curvilinear and concave upwards. One case of curvilinear frequency dependence, a dimorphic batesian mimic with a non-mimetic form, is examined in detail. Although oscillations about the recessive or Y-linked, this will only occur when selection coefficients are very large, and (except for Y-linkage) only if both sexes can be mimetic. As selection is density as well as frequency dependent, such conditions may be produced in the real world by large fluctuations in population size.

Adaptation, Biological↗
PubMed1997

Localized reversible frameshift mutation in an adhesin gene confers a phase-variable adherence phenotype in mycoplasma.

The variable adherence-associated (Vaa) antigen of Mycoplasma hominis is an abundant surface lipoprotein adhesin that may mediate important interactions of this wall-less prokaryotic pathogen with the human host. Extensive mutational variation of Vaa size, as well as sequence and antigenic divergence, has been described previously. Using a series of clonal isolates representing an isogenic lineage of variants oscillating in Vaa expression, Vaa is further shown in this study to undergo high-frequency phase variation in expression, which correlated precisely with the ability of M. hominis to adhere to cultured human cells. Although no DNA rearrangements or sequence differences in the 5' regions flanking vaa alleles were detected between Vaa+ and Vaa variants, intragenic vaa sequences from this lineage revealed an oscillating mutation involving a single nucleotide deletion/insertion in a short tract of adenine residues near the 5' end of the mature Vaa coding sequence, which created a translational frameshift resulting in either a complete Vaa ORF or an in-frame UAG stop codon immediately downstream of the poly-A tract. Evidence for the occurrence of this high-frequency frameshift mutation in vivo was obtained from analysis of PCR-generated vaa sequences amplified from the joint synovial fluid of a patient with M. hominis-associated arthritis, which indicated that Vaa phase variation occurs during M. hominis infection in the natural host. These results identify a distinctive frameshift mutator element in the vaa gene that governs M. hominis adherence and highlight the importance of mutational alteration of primary gene products on the mycoplasma surface as a means of generating and maintaining functional diversity in the host.

Adhesins, Bacterial↗
PubMed1994

The central complex of Drosophila melanogaster is involved in flight control: studies on mutants and mosaics of the gene ellipsoid body open.

Visual flight control is studied in three mutant alleles of the gene ellipsoid body open (ebo) of Drosophila melanogaster. In mutant ebo flies the central complex is disturbed to varying degrees. Defects range from a small opening in the ellipsoid body to the dissociation of the ring into two parts, a cleft in the fan-shaped body and hypoplasia in the protocerebral bridge. Other parts of the brain are not visibly affected. Flight behavior is normal with respect to the amplitude of the optomotor response and to the object response (single rotating stripe). A reduced amplitude in the small random oscillations of the torque trace (yaw torque activity), however, is found in all three alleles. In two of them the frequency of torque spikes is reduced. In the allele ebo678 the dynamics of the optomotor response is altered. Upon reversal of the direction of rotation mutant flies take longer than wild type to shift their yaw torque to the new response level (optomotor reversal time). Finally, these flies also behave abnormally in the flight simulator in which their yaw torque controls the angular velocity of the panorama. Many ebo678 flies fixate a single stripe less persistently than normal flies, some even trying to fly away from it (antifixation). In ebo678 gynandromorphs the four behavioral phenotypes ("yaw torque activity", "torque spike frequency", "on-target fixation" and "optomotor reversal time") are all highly correlated with the phenotype of the ellipsoid body. Yaw torque activity and torque spike frequency in addition are correlated with the phenotype of the thorax suggesting that these behavioral defects are in part caused by mutant influences on the ventral ganglion. The results support the hypothesis that the central complex is involved in the control of flight behavior.

Animals↗
PubMed1975

Polymorphisms in cyclically-varying environments.

We analysed both continuous and discrete two-allele models of cyclically-varying environments with an arbitrary degree of dominance. In continuous models, the gene frequency fluctuates with the period of the environmental oscillation. For the discrete case, the calculations were carried out to second order in selection. In contrast to the continuous models, and depending on the amount of dominance and the intitial gene frequency, fixation is possible as well as polymorphism.

Environment↗
PubMed1993

The interplay of light and the circadian clock. Independent dual regulation of clock-controlled gene ccg-2(eas).

Ambient light is the major agent mediating entrainment of circadian rhythms and is also a major factor influencing development and morphogenesis. We show that in Neurospora crassa the expression of clock-controlled gene 2 (ccg-2), a gene under the control of the circadian clock and allelic to the developmental gene easy wettable (eas), is regulated by light in wild-type strains. Light elicits a direct and important physiological effect on ccg-2(eas) expression as demonstrated using several mutant Neurospora strains. In white collar mutants (wc-1 and wc-2) that are "blind" to blue light, ccg-2(eas) mRNA shows no variation following illumination with saturating light. By contrast, ccg-2(eas) mRNA is photoinduced in clock-null strains such as frequency (bd;frq). The results in the clock mutants show that an intact circadian oscillator is not required for light induction of ccg-2(eas). Thus, ccg-2(eas) is subject to a dual regulation that involves separable regulation by light and circadian rhythm.

Alleles↗