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PubMed2006

Response of fluctuating and directional asymmetry to selection on wing shape in Drosophila melanogaster.

We tested whether directional selection on an index-based wing character in Drosophila melanogaster affected developmental stability and patterns of directional asymmetry. We selected for both an increase (up selection) and a decrease (down selection) of the index value on the left wing and compared patterns of fluctuating and directional asymmetry in the selection index and other wing traits across selection lines. Changes in fluctuating asymmetry across selection lines were predominantly small, but we observed a tendency for fluctuating asymmetry to decrease in the up-selected lines in both replicates. Because changes in fluctuating asymmetry depended on the direction of selection, and were not related to changes in trait size, these results fail to support existing hypotheses linking directional selection and developmental stability. Selection also produced a pattern of directional asymmetry that was similar in all selected lines whatever the direction of selection. This result may be interpreted as a release of genetic variance in directional asymmetry under selection.

Animals↗
PubMed1986

Directional selection and developmental stability: evidence from fluctuating asymmetry of dental characters in mice.

Developmental stability was assessed among lines of mice subjected to 11 generations of selection for increased (up line) and decreased (down line) widths of the first maxillary molar (M1), primarily to test the hypothesis that this stability would decline over time as a result of selection. Fluctuating asymmetry (FA) was used as an inverse measure of developmental stability, and was calculated for the M1 and a correlated character, the second mandibular molar (M2), in each generation. As measured by the regression of FA on generations, there was a statistically significant decline in stability only in the down selection line for the M2, and this trend did not differ significantly from that for the control line. The combined regressions obtained from pooling over all three lines were significantly different from zero in both molars, however, and this was taken to be evidence of a decline in stability due to increased homozygosity presumably generated by inbreeding during the selection experiment. The variation in FA among generations was greater for the selection lines than the control line for both molars, especially for the M2. The heritability of the M1 (and M2) was high, but there was no significant additive genetic variance for FA in either molar.

Analysis of Variance↗
PubMed1977

Heat stress, fluctuating asymmetry and prenatal selection in the laboratory rat.

Recent studies have demonstrated that stress may increase the fluctuating asymmetry of teeth and limbs in laboratory animals. The present study investigates the effects of heat on such parameters. Pregnant laboratory rats are exposed to temperatures of 33 degrees C during gestation. Increases in fluctuating asymmetry of dental dimensions as well as bone density are found for the pups of such females when compared to unstressed controls. A general increase in limb lengths is also reported for young of heat stressed animals. Prenatal selection with differential survival is suggested as a possible explanation for differences found between the experimental and control animals.

Animals↗
PubMed2005

The sound velocity in ideal liquid mixtures from thermal volume fluctuations.

The selection of the correct mixing rule for sound velocity in ideal liquid mixtures determines the interpretation of the sound velocity in real mixtures. This is especially important for the determination of apparent properties of solutes, such as their apparent compressibility. There are different approaches reported in the literature, and this article presents a new derivation of the mixing rule based on statistical mechanics. It is shown that the correlation of volume fluctuations between adjacent components has a crucial influence on the ideal mixing rule.

Journal Article↗
PubMed1980

Developmental stability opf Drosophila melanogaster under artificial and natural selection in constant and fluctuating environments.

Populations of Drosophila melanogaster in constant 25 degrees and fluctuating 20/29 degrees environments showed increases in developmental stability, indicated by decreases in bilateral asymmetry of sterno-pleural chaeta number. In both environments, rates of decrease in asymmetry were greater under natural selection (control lines) than under artificial stabilizing selection. Overall mean asymmetry was greater in the fluctuating environment.--There was no evidence that decreased asymmetry was due to heterozygosity, and the decline in asymmetry was not explained by the decline in chaeta number in the lines under natural selection. However, the decline was consistent with changes in total phenotypic variance and environmental variance.--The divergence between lines after 39 generations of selection was seen in differences in asymmetry and also in the genotype-environment interaction expressed in cross-culturing experiments.

Animals↗
PubMed2006

Maintenance of environmental homeostasis by biota, selected nonlocally by circulation and fluctuation mechanisms.

A simple abstract model is presented to show that a species with a favorable global effect on the whole biota (for example, by generating a moderate temperature range) can be selected through evolution. In the model, fluctuation in the growth rate among species leads to selection. The accompanying fluctuations in the quantity of resources, which return by circulation with a certain time lag, are likely to cause this selection. Different functions and various parameters are applied to the equations to monitor their effects on the whole system. In nature, producers satisfy the theoretical conditions of the model, implying the reality of the selection described by the mechanism presented here, during the history of the biota.

Biodiversity↗
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↗
PubMed2003

Gamma-frequency fluctuations of the membrane potential and response selectivity in visual cortical neurons.

Fluctuations at frequencies of 25-70 Hz is an inherent property of cortical activity. These rapid, gamma-range fluctuations are apparent in the local field potentials, in spiking of cells and cell groups, and in the membrane potential of neurons. To investigate stimulus dependence of the gamma-frequency fluctuations of the membrane potential, we have recorded intracellularly responses of cells in cat visual cortex to presentation of moving gratings. We found gamma-range fluctuations of the membrane potential in both simple and complex cells. The strength of the gamma-frequency fluctuations correlated with the stimulus optimality. Furthermore, the amplitude of the gamma-frequency fluctuations correlated with the phase of stimulus-imposed slow changes of the membrane potential. The combination of these features makes cortical neurons capable of encoding the slow changes in the visual world in a kind of amplitude modulation of the high frequency fluctuations. This assures reliable transformation of the membrane potential changes into spike responses without compromising the temporal resolution of visual information encoding in the low frequency range.

Action Potentials↗
PubMed2003

Selective excitation of native fluctuations during thermal unfolding simulations: horse heart cytochrome c as a case study.

The effect of temperature on the activation of native fluctuation motions during molecular dynamics unfolding simulations of horse heart cytochrome c has been studied. Essential dynamics analysis has been used to analyze the preferred directions of motion along the unfolding trajectories obtained by high temperature simulations. The results of this study have evidenced a clear correlation between the directions of the deformation motions that occur in the first stage of the unfolding process and few specific essential motions characterizing the 300 K dynamics of the protein. In particular, one of those collective motions, involved in the fluctuation of a loop region, is specifically excited in the thermal denaturation process, becoming progressively dominant during the first 500 ps of the unfolding simulations. As further evidence, the essential dynamics sampling performed along this collective motion has shown a tendency of the protein to promptly unfold. According to these results, the mechanism of thermal induced denaturation process involves the selective excitation of one or few specific equilibrium collective motions.

Animals↗
PubMed1990

Morphine-induced pupillary fluctuation: physiological evidence against selective action on the Edinger-Westphal nucleus.

In the rat, the predominant pupillary effect of morphine sulfate (30 mg/kg, i.p.) is mydriasis, interrupted periodically by miotic excursions. Using infrared video pupillometry, respirometry and EEG recording, we had previously reported that miotic excursions are always correlated with the onset of EEG bursting, while mydriatic excursions are preceded by respiratory slowing and correlated with EEG burst cessation. In the current study, we found that during morphine-induced EEG bursting and related miosis, delivery of an alerting stimulus to the rat caused an immediate conversion sequence composed of respiratory slowing, burst cessation and mydriatic excursion. We also simulated morphine-induced EEG bursting through non-opioid means by delivering kindling electrical stimuli to the amygdala. When the stimulus was given during morphine-induced mydriasis, the stimulus-induced bursting resulted in a miotic excursion identical to spontaneous morphine-induced miotic excursions. These results indicate 1) that the reticular activating system is involved in morphine-induced mydriatic excursions and 2) that EEG bursting is not simply correlated with morphine-induced miotic excursions, but causes them. Collectively, these results strengthen our hypothesis that the Edinger-Westphal nucleus is not the site in which the selective, receptor-mediated pupillary effects of morphine are initiated.

Amygdala↗
PubMed1991

The Desheathed Periphery of Aplysia Giant Neuron. Fine Structure and Measurement of [Ca2+]o Fluctuations with Calcium-selective Microelectrodes.

The visceral ganglion of Aplysia was mechanically desheathed after protease softening of the connective tissue to permit the positioning of ion-selective electrodes in the vicinity of the neuronal membrane. The effects of this treatment on satellite glia and neuronal cytology were observed by electron microscopy. The intracellular alterations were not suggestive of serious membrane damage but the cohesion between glial and neuronal membranes was affected-the glial processes appeared to retract from the trophospongium and in some cases the neuronal membrane was completely naked. The external calcium activity [Ca2+]o at the surface of identified giant neuron, R2, was measured using double-barrelled calcium-selective microelectrodes. A decrease of approximately 1 mM in [Ca2+]o could be recorded only during trains of action potentials induced by intracellular depolarizing current injection, and when the electrode was pushed firmly against the neuron surface. A recovery from this decrease in [Ca2+]o could sometimes, but not always, be observed during the phase of induced neuronal activity.

Journal Article↗
PubMed1993

Protein conformation monitored by energy-selective optical spectroscopy.

Fluctuations in the polypeptide chain lead to disorder in proteins and to a distribution in the parameters that regulate their functions. Using low temperature (to reduce the fluctuations) and narrow-band lasers (to select one substate among the many forms), high-resolution absorption and fluorescence spectra for chromophores in proteins can be obtained. These spectra reveal information on the kind and extent of disorder in proteins and allow for the determination of the vibrational energies of both ground and excited state molecules, true inhomogeneous spectral width, and kinetic studies of individual protein substates.

Lasers↗
PubMed1998

P-glycoprotein expression in Ehrlich ascites tumour cells after in vitro and in vivo selection with daunorubicin.

Fluctuation analysis experiments were performed to assess whether selection or induction determines expression of P-glycoprotein and resistance in the murine Ehrlich ascites tumour cell line (EHR2) after exposure to daunorubicin. Thirteen expanded populations of EHR2 cells were exposed to daunorubicin 7.5 x 10(-9) M or 10(-8) M for 2 weeks. Surviving clones were scored and propagated. Only clones exposed to daunorubicin 7.5 x 10(-9) M could be expanded for investigation. Drug resistance was assessed by the tetrazolium dye (MTT) cytotoxicity assay. Western blot was used for determination of P-glycoprotein. Compared with EHR2, the variant cells were 2.5- to 5.2-fold resistant to daunorubicin (mean 3.6-fold). P-glycoprotein was significantly increased in 11 of 25 clones (44%). Analysis of variance supported the hypothesis that spontaneous mutations conferred drug resistance in EHR2 cells exposed to daunorubicin 7.5 x 10(-9) M. At this level (5 log cell killing) of drug exposure, the mutation rate was estimated at 4.1 x 10(-6) per cell generation. In contrast, induction seemed to determine resistance in EHR2 cells in vitro exposed to daunorubicin 10(-8) M. The revertant EHR2/0.8/R was treated in vivo with daunorubicin for 24 h. After treatment, P-glycoprotein increased in EHR2/0.8/R (sevenfold) and the cell line developed resistance to daunorubicin (12-fold), suggesting that in EHR2/0.8/R the mdr1 gene was activated by induction. In conclusion, our study demonstrates that P-glycoprotein expression and daunorubicin resistance are primarily acquired by selection of spontaneously arising mutants. However, under certain conditions the mdr1 gene may be activated by induction.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Protein folding: binding of conformationally fluctuating building blocks via population selection.

Here we review different aspects of the protein folding literature. We present a broad range of observations, showing them to be consistent with a general hierarchical protein folding model. In such a model, local relatively stable, conformationally fluctuating building blocks bind through population selection, to yield the native state. The model includes several components: (1) the fluctuating building blocks that constitute local minima along the polypeptide chain, which even if unstable still possess higher population times than all alternate conformations; (2) the landscape around the bottom of the funnels; (3) the consideration that protein folding involves intramolecular recognition; (4) similar landscapes are observed for folding and for binding, and that (5) the landscape is dynamic, changing with the conditions. The model considers protein folding to be guided by native interactions. The reviewed literature includes the effects of changing the conditions, intermediates and kinetic traps, mutations, similar topologies, fragment complementation experiments, fragments and pathways, focusing on one specific well-studied example, that of the dihydrofolate reductase, chaperones, and chaperonines, in vivo vs. in vitro folding, still using the dihydrofolate example, amyloid formation, and molecular "disorder". These are consistent with the view that binding and folding are similar events, with the differences stemming from different stabilities and hence population times.

Models, Molecular↗
PubMed1976

Life-history tactics: a review of the ideas.

This review organizes ideas on the evolution of life histories. The key life-history traits are brood size, size of young, the age distribution of reproductive effort, the interaction of reproductive effort with adult mortality, and the variation in these traits among an individual's progeny. The general theoretical problem is to predict which combinations of traits will evolve in organisms living in specified circumstances. First consider single traits. Theorists have made the following predictions: (1) Where adult exceeds juvenile mortality, the organism should reproduce only once in its lifetime. Where juvenile exceeds adult mortality, the organism should reproduce several times. (2) Brood size should macimize the number of young surviving to maturity, summed over the lifetime of the parent. But when optimum brood-size unpredictably in time, smaller broods should be favored because they decrease the chances of total failure on a given attempt. (3) In expanding populations, selection should minimize age at maturity. In stable populations, when reproductive success depends on size, age, or social status, or when adult exceeds juvenile mortality, then maturation should be delayed, as it should be in declining populations. (4) Young should increase in size at birth with increased predation risk, and decrease in size with increased resource availability. Theorists have also predicted that only particular combinations of traits should occur in specified circumstances. (5) In growing populations, age at maturity should be minimized, reproductive effort concentrated early in life, and brood size increased. (6) One view holds that in stable environments, late maturity, broods, a few, large young, parental care, and small reproductive efforts should be favored (K-selection). In fluctuating environments, early maturity, many small young, reduced parental care, and large reproductive efforts should be favored (r-selection). (7) But another view holds that when juvenile mortality fluctuates more than adult mortality, the traits associated with stable and fluctuating environments should be reversed. We need experiments that test the assumptions and predictions reviewed here, more comprehensive theory that makes more readily falsifiable predictions, and examination of different definitions of fitness.

Age Factors↗
PubMed1982

Occupational mortality and morbidity in relation to selective turnover.

Because of the "healthy worker effect" most occupational cohorts, especially those of persons doing physically heavy work, are selected groups with regard to life expectancy. Health selection is also involved in turnover. Mortality and morbidity were studied on three different exposure levels, defined primarily according to physical demands: heavy level (iron foundries), medium level (manufacture of metal products), and light level (manufacture of electrical devices). The population comprised about 15,700 men who were employed in 1950-1976 in the three branches of the metal industry representing the different levels. The number of person-years of follow-up became about 215,800. During the period 1950-1978, there had occurred 1,407 deaths. Data for the mortality and disability analyses were obtained from the national death and disability registers. Occupational history, morbidity, and reasons for turnover were studied in a sample by means of questionnaire sent to 400 current and 600 former workers from each branch. In addition, a questionnaire concerning occupational history was sent to the next of kin of 450 dead persons. When the three cohorts were compared to the general male population of Finland, the standardized mortality ratio was 124 for the foundry workers, 92 for the metal product workers, and 107 for the electrical workers. The survival curves showed no great differences between the three exposure levels. However, the heavy level had the highest degree of mortality, and the medium level the lowest. Foundry workers showed less social selection than the two other cohorts. Metal product workers seemed to be socially and health selected. Economic fluctuations clearly regulated entries of new employees into the industries and thus introduced additional selective features.

Adolescent↗
PubMed1990

Theoretical study of near neutrality. I. Heterozygosity and rate of mutant substitution.

In order to clarify the nature of "near neutrality" in molecular evolution and polymorphism, extensive simulation studies were performed. Selection coefficients of new mutations are assumed to be small so that both random genetic drift and selection contribute to determining the behavior of mutants. The model also incorporates normally distributed spatial fluctuation of selection coefficients. If the system starts from "average neutrality," it will move to a better adapted state, and most new mutations will become "slightly deleterious." Monte Carlo simulations have indicated that such adaptation is attained, but that the rate of such "progress" is very low for weak selection. In general, the larger the population size, the more effective the selection becomes. Also, as selection becomes weaker, the behavior of the mutants approaches that of completely neutral genes. Thus, the weaker the selection, the smaller is the effect of population size on mutant dynamics. Increase of heterozygosity with population size is very pronounced for subdivided populations. The significance of these results is discussed in relation to various observed facts on molecular evolution and polymorphism, such as generation-time dependency and overdispersion of the molecular clock, or contrasting patterns of DNA and protein polymorphism among some closely related species.

Biological Evolution↗