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PubMed1999

[Environmental stress and genetic variation in animal populations].

The impact of environmental stress factors on genetic variation in animal populations is considered. It is tentatively concluded that genetical variability of populations generally increases in stressful environments. The exposure to stressful factors result in an increase of recombination and mutation rates. In quantitative traits, on which the review is focused, stress often leads to an increase in the genetic component of variation. Experiments on Drosophila demonstrated that the effect of stress on genetic variation is stress- and trait-specific. The possible role of stress factors in adaptation and evolution of populations is discussed.

Adaptation, Physiological↗
PubMed2005

Thermodynamical interpretation of evolutionary dynamics on a fitness landscape in an evolution reactor, II.

In our previous report [Aita, T., Morinaga, S., Hosimi, Y., 2004. Thermodynamical interpretation of evolutionary dynamics on a fitness landscape in an evolution reactor I. Bull. Math. Biol. 66, 1371-1403], an analogy between thermodynamics and adaptive walks on a Mt. Fuji-type fitness landscape in an artificial selection system was presented. Introducing the 'free fitness' as the sum of a fitness term and an entropy term and 'evolutionary force' as the gradient of free fitness on a fitness coordinate, we demonstrated that the adaptive walk (=evolution) is driven by the evolutionary force in the direction in which free fitness increases. In this report, we examine the effect of various modifications of the original model on the properties of the adaptive walk. The modifications were as follows: first, mutation distance d was distributed obeying binomial distribution; second, the selection process obeyed the natural selection protocol; third, ruggedness was introduced to the landscape according to the NK model; fourth, a noise was included in the fitness measurement. The effect of each modification was described in the same theoretical framework as the original model by introducing 'effective' quantities such as the effective mutation distance or the effective screening size.

Algorithms↗
PubMed2003

A quasispecies approach to viral evolution in the context of an adaptive immune system.

A deeper understanding of the mechanisms that determine viral evolution in the context of an adaptive immune system is vital for the development of efficient strategies to defeat viral infections. The problem of describing these mechanisms is discussed using the concept of quasispecies. Conditions for both an optimal immune response and for highest viral viability are derived from theoretical models and are supported by empirical data.

Animals↗
PubMed2001

Convergence in evolutionary programs with self-adaptation.

Evolutionary programs are capable of finding good solutions to difficult optimization problems. Previous analysis of their convergence properties has normally assumed the strategy parameters are kept constant, although in practice these parameters are dynamically altered. In this paper, we propose a modified version of the 1/5-success rule for self-adaptation in evolution strategies (ES). Formal proofs of the long-term behavior produced by our self-adaptation method are included. Both elitist and non-elitist ES variants are analyzed. Preliminary tests indicate an ES with our modified self-adaptation method compares favorably to both a non-adapted ES and a 1/5-success rule adapted ES.

Algorithms↗
PubMed2004

Endosymbiont phylogenesis in the dryophthoridae weevils: evidence for bacterial replacement.

Intracellular symbiosis is widespread in the insect world where it plays an important role in evolution and adaptation. The weevil family Dryophthoridae (Curculionoidea) is of particular interest in intracellular symbiosis evolution with regard to the great economical and ecological features of these invasive insects, and the potential for comparative studies across a wide range of host plants and environments. Here, we have analyzed the intracellular symbiotic bacteria of 19 Dryophthoridae species collected worldwide, representing a wide range of plant species and tissues. All except one (Sitophilus linearis) harbor symbiotic bacteria within specialized cells (the bacteriocytes) assembled as an organ, the bacteriome. Phylogenetic analysis of the 16S rDNA gene sequence of the Dryophthoridae endosymbionts revealed three endosymbiotic clades belonging to gamma3-Proteobacteria and characterized by different GC contents and evolutionary rate. The genus name Candidatus Nardonella was proposed for the ancestral clade infesting Dryophthoridae 100 MYA and represented by five of nine bacterial genera studied. For this clade showing low GC content (40.5% GC) and high evolutionary rate (0.128 substitutions/site per 100 Myr), a single infection and subsequent cospeciation of the host and the endosymbionts was observed. In the two other insect lineage endosymbionts, with relatively high GC content (53.4% and 53.8% GC), competition with ancestral pathogenic bacteria might have occurred, leading to endosymbiont replacement in present-day last insects.

Animals↗
PubMed1999

Evolution of haemoglobin function: molecular adaptations to environment.

1. Nearly 1000 mutations have been described for human haemoglobin (Hb), many of which result in subtle changes to the oxygen transport system. Similar changes have occurred over the course of animal evolution resulting in a diversity of functional attributes which appear to correlate the availability of oxygen in the environment with metabolic demand. 2. At an early stage in evolution, worm-like animals had large, polymeric aggregations of Hb subunits circulating through primitive circulatory systems and some possessed monomeric Hb in blood cells functioning as an oxygen store. 3. The circulating vertebrate red blood cell provides an environment allowing haem units to interact among themselves and with various organic phosphates to allow a responsive and highly regulated system of gas transport. During metazoan evolution the burden of physiological regulation has shifted from the cells to organ systems, as endothermy and aerial breathing permit a relatively constant environment. 4. An understanding of the adaptive possibilities of Hb has helped us to understand the ontogeny of oxygen transport and to interpret recently described functional properties of human embryonic haemoglobins.

Adaptation, Biological↗
PubMed2000

Body mass in lowland gorillas: a quantitative analysis.

Body proportions and tissue composition (e.g., relative contributions of muscle, skin, bone, and adipose to total body mass) were determined through dissection of four adult captive lowland gorillas. The relative contribution of bone varies little among the four animals (10.2-13.4%) despite considerable range in body weights (99.5-211 kg). In tissue composition, three animals have on average 37.3% muscle relative to body mass. Maximum estimates of body fat range between 19.4-44%. Differences in age, sex, and life history events partially explain the observed variation in body proportions and tissue composition among the four animals. Although gorillas are considered extremely sexually dimorphic in body weight and canine size, differences in tissue are not as dramatic as body mass differences suggest. This study found sex differences mostly in the upper body; males have relatively heavier forelimbs, including heavier deltoid, trunk-binding, and deep back muscles compared to the younger female. The old, obese female had one half the muscle tissue of the other three animals (16% vs. 37.3%), and twice the body fat (44%); forelimbs and upper body musculature were relatively well-developed to compensate for the restricted hip-joint movement due to arthritis. Data on the variation in tissue composition and body proportions in gorillas provide a basis for comparison with other hominoids, including humans. For example, compared to highly dimorphic orangutans, gorillas have more muscle, less adipose tissue, lighter forelimbs and heavier hindlimbs. Such analyses complement studies of the skeleton and contribute to our understanding of human evolution and adaptation.

Animals↗
PubMed2000

The role of genetic factors in the etiology of seasonality and seasonal affective disorder: an evolutionary approach.

The degree to which seasonal changes affect mood, energy, sleep, appetite, food preference, or the wish to socialize with other people has been called seasonality. Seasonal affective disorder (SAD), a condition where depressions in fall and winter alternate with non-depressed periods in spring and summer, is the most marked form of seasonality. Several lines of evidence suggest that genetic factors play an important role in the etiology of seasonality and SAD. Millions of years of evolution and adaptation have optimized human biochemical and physiological systems for function and survival under equatorial environmental conditions. Modern humans began their migration out of Africa only about 150 000 years ago. Little change in our 'equatorial' systems might have been expected over this relatively short evolutionary time-span. The author suggests that a genetic susceptibility to seasonal changes in mood and behavior is a genetic predisposition to an insufficient adaptation to temperate and high latitudes.

Biological Evolution↗
PubMed1983

Environmental adaptation of proteins: strategies for the conservation of critical functional and structural traits.

Comparative studies of lactate dehydrogenases (LDHs) and skeletal muscle actins from vertebrates adapted to widely different temperatures and hydrostatic pressures reveal major conservative trends in protein evolution and adaptation. For enzymes, ligand binding, as estimated by apparent Michaelis constant (Km) values, is strongly conserved at physiological temperatures, pressures, intracellular pH values and osmotic compositions of different organisms. The catalytic rate constants (kcat values) of enzyme homologues are highest for enzymes of low-body-temperature organisms, a trend that can be interpreted in terms of temperature compensation of metabolism. For skeletal muscle actins, the enthalpy and entropy changes accompanying the assembly of filamentous (F) actin from globular (G) actin are highest in high-body-temperature species and especially low in polar and deep-sea fishes. The thermal stability of G-actin is positively correlated with adaptation temperature, except in the case of actins of deep-sea fishes, which are also highly heat stable. Hydrophobic interactions between actin subunits may be of reduced importance in low-body-temperature animals and, especially, in deep-sea fishes. The differences in enthalpy and entropy changes during the G-to-F transformation favor a close conservation of the equilibrium constant for actin assembly under physiological conditions of temperature and pressure for different species. These adaptive patterns in enzymes and actin are likely to reflect changes in protein primary structure. The appropriate values for protein traits such as ligand binding abilities and catalytic rates are also shown to be established by the composition of the low molecular weight constituents of the cytosol. For example, the use of a combination of urea and methylamine solutes for osmoregulation by marine elasmobranchs is shown to be a mechanism which permits the conservation of key protein traits at high osmolarities. The methylamine solutes such as trimethylamine-N-oxide have effects on proteins opposite to those of urea, and at the approximately 2:1 concentration ratio of urea to methylamines, these counteracting effects are virtually complete. Regulation of hydrogen ion activity (pH) also is shown to play a major role in the conservation of critical protein traits. The importance of temperature-dependent pH in ectotherms is discussed in terms of stabilizing binding abilities and maintaining correct regulatory and structural sensitivities of proteins. The buffering capacity of tissues reflects the potential of the tissue for generating acidic end-products during anaerobic metabolism. Skeletal muscle, especially white locomotory muscle of fishes, is highly buffered relative to red locomotory muscle and heart muscle.(ABSTRACT TRUNCATED AT 400 WORDS)

Actins↗
PubMed2026

Selection favors cost-ordered adaptive mutational paths in a stress-magnitude-dependent manner.

Chronic exposure to stress requires adaptive strategies beyond canonical regulatory mechanisms. Stress varies, both qualitatively and quantitatively, across physiological niches and exerts distinct selection pressures on colonizing bacteria. Bacteria employ diverse defense strategies to withstand various stressful conditions, yet how they tailor their responses to different magnitudes of the same stressor remains poorly understood. We used multiple adaptive laboratory evolution experiments of Escherichia coli across varying paraquat concentrations and genetic backgrounds to dissect adaptive strategies at different levels of stress. Integrating multi-omic analyses with a tailored genome-scale metabolic model-based parametrized cost calculations, we identify two fundamentally distinct tolerance mechanisms. Under low-paraquat stress, blocking the polyamine transporter that is reported to be hijacked for paraquat influx suffices to maintain optimal growth. In contrast, higher stress levels activate an energetically demanding program involving enhanced detoxification and efflux. The transport flux regulation establishes a primary defense layer, upon which metabolic repair systems provide additional fitness advantages. The stress magnitude-dependent differential engagement of previously reported paraquat tolerance approaches offers insights into the principles governing dynamic bacterial adaptation.

Journal Article↗
PubMed2004

Ultrastructure of spermatozoa of Bullacta exarata (philippi) and its significance on reproductive evolution and physio-ecological adaptation.

The morphology and ultrastructure of Bullacta exarata spermatozoa observed by light and transmission electron microscopy are presented in this paper. The spermatozoa is composed of head with a simple acrosomal complex and an elongated nucleus, and tail with a midpiece, principal piece and an end piece. The midpiece consists of a mitochondrial ring, and the principal piece is composed of axoneme and lateral fin. The structure of B. exarata spermatozoa differs significantly from that of other gastropods, especially in the lateral fin and the principal piece, which was described scarcely before. A comparison is made between B. exarata and other gastropods, and its significance on reproductive evolution and physio-ecological adaptation is preliminarily discussed.

Animals↗
PubMed2004

Adaptation and constraint in the evolution of environmental sex determination.

When environments differentially influence male and female performance, environmental sex determination (ESD) might evolve. The conclusion from several previous theoretical models was that reaction norms for sex determination should have a single, sharp threshold, with only females being produced in some environments and only males in others. These reaction norms can be disadvantageous in fluctuating environments, however, because they lead to sex-ratio fluctuations. We analysed the evolution of ESD, looking for equilibrium strategies in unconstrained as well as constrained strategy spaces. We identified situations where a single-threshold reaction norm is not evolutionarily stable. In these cases, we found stable strategies in the form of complex reaction norms, showing an oscillatory pattern of sex determination with respect to variation in an environmental variable. Considering that constraints could prevent such phenotypes from being realized, we found that certain randomized reaction norms, with probabilistic sex determination for a range of environments, would achieve nearly the same fitness. We also investigated reaction norms constrained to have a single threshold and found that genetic polymorphism in the environmental threshold value could evolve, producing a similar effect as a randomized reaction norm. We argue that the appearance of genetic variation can be regarded as an alternative outcome when constraints prevent the evolution of a more complex or a randomized strategy.

Adaptation, Physiological↗
PubMed2026

Variations in carbapenem resistance associated with the VIM-1 metallo-β-lactamase across the Enterobacterales.

The VIM-1 metallo-β-lactamase enzyme, encoded within class 1 integrons, is found in Gram-negative clinical isolates worldwide and has been linked to outbreaks of bacterial pathogens in nosocomial settings. Six vim-1+ clinical isolates, from the genera Escherichia, Klebsiella and Enterobacter, were obtained from Kingston, Ontario, Canada. Whole-genome sequencing revealed that vim-1 was plasmid-borne in all strains and situated as the first gene in In916 or In110 integrons. Analysis of related plasmids suggested that these vim-1-containing plasmids are globally disseminated and have spread via horizontal gene transfer and autochthonous vertical spread within Ontario. Interestingly, the MICs of ertapenem and meropenem, two clinically relevant carbapenem antibiotics, against these six isolates varied more than tenfold, suggesting that the effects of VIM-1 are dependent on the genomic content of the host microbe. Introducing vim-1 into three common Enterobacterales laboratory strains was not sufficient to confer resistance to ertapenem and meropenem. Instead, adaptive laboratory evolution of the vim-1 + laboratory strains revealed that vim-1-mediated carbapenem resistance in these strains was dependent on epistatic interactions with ompC mutations, likely due to decreased outer membrane permeability to these antibiotics. Together, these results provide additional support for the role of gene epistasis in modulating the antimicrobial resistance phenotypes of acquired resistance genes, as well as previous results suggesting that the presence of a β-lactamase gene is insufficient to confer strong resistance to carbapenems without being paired with reduced outer membrane permeability.

beta-Lactamases↗
PubMed2000

Tibetan and Andean patterns of adaptation to high-altitude hypoxia.

Understanding the workings of the evolutionary process in contemporary humans requires linking the evolutionary history of traits with their current genetics and biology. Unusual environments provide natural experimental settings to investigate evolution and adaptation. The example of high-altitude hypoxia illustrates some of the progress and many of the remaining challenges for studies of evolution in contemporary populations. Current studies exemplify the frequently encountered problem of determining whether large, consistent population differences in mean values of a trait reflect genetic differences. In this review I describe 4 quantitative traits that provide evidence that indigenous populations of the Tibetan and Andean plateaus differ in their phenotypic adaptive responses to high-altitude hypoxia. These 4 traits are resting ventilation, hypoxic ventilatory response, oxygen saturation, and hemoglobin concentration. The Tibetan means of the first 2 traits were more than 0.5 standard deviation higher than the Aymara means, whereas the Tibetan means were more than 1 standard deviation lower than the Aymara means for the last 2 traits. Quantitative genetic analyses of within-population variance revealed significant genetic variance in all 4 traits in the Tibetan population but only in hypoxic ventilatory response and hemoglobin concentration in the Aymara population. A major gene for oxygen saturation was detected among the Tibetans. These findings are interpreted as indirect evidence of population genetic differences. It appears that the biological characteristics of sea-level humans did not constrain high-altitude colonists of the 2 plateaus to a single adaptive response. Instead, microevolutionary processes may have operated differently in the geographically separated Tibetan and Andean populations exposed to the same environmental stress. Knowledge of the genetic bases of these traits will be necessary to evaluate these inferences. Future research will likely be directed toward determining whether the population means reflect differences identified at the chromosomal level. Future research will also likely consider the biological pathways and environmental influences linking genotypes to phenotypes, the costs and benefits of the Tibetan and Andean patterns of adaptation, and the question of whether the observed phenotypes are indeed adaptations that enhance Darwinian fitness.

Adaptation, Physiological↗
PubMed2004

The evolution of premating isolation: local adaptation and natural and sexual selection against hybrids.

Although reinforcement is ostensibly driven by selection against hybrids, there are often other components in empirical cases and theoretical models of reinforcement that may contribute to premating isolation. One of these components is local adaptation of a trait used in mate choice. I use several different comparisons to assess the roles that local adaptation and selection against hybrids may play in reinforcement models. Both numerical simulations of exact recursion equations and analytical weak selection approximations are employed. I find that selection against hybrids may play a small role in driving preference evolution in a reinforcement model where the mating cue is separate from loci causing hybrid incompatibilities. When females have preferences directly for purebreds of their own population, however, selection against hybrids can play a large role in premating isolation evolution. I present some situations in which this type of selection is likely to exist. This work also illustrates shortfalls of using a weak selection approach to address questions about reinforcement.

Adaptation, Biological↗
PubMed1999

Inferring the fitness effects of DNA mutations from polymorphism and divergence data: statistical power to detect directional selection under stationarity and free recombination.

The fitness effects of classes of DNA mutations can be inferred from patterns of nucleotide variation. A number of studies have attributed differences in levels of polymorphism and divergence between silent and replacement mutations to the action of natural selection. Here, I investigate the statistical power to detect directional selection through contrasts of DNA variation among functional categories of mutations. A variety of statistical approaches are applied to DNA data simulated under Sawyer and Hartl's Poisson random field model. Under assumptions of free recombination and stationarity, comparisons that include both the frequency distributions of mutations segregating within populations and the numbers of mutations fixed between populations have substantial power to detect even very weak selection. Frequency distribution and divergence tests are applied to silent and replacement mutations among five alleles of each of eight Drosophila simulans genes. Putatively "preferred" silent mutations segregate at higher frequencies and are more often fixed between species than "unpreferred" silent changes, suggesting fitness differences among synonymous codons. Amino acid changes tend to be either rare polymorphisms or fixed differences, consistent with a combination of deleterious and adaptive protein evolution. In these data, a substantial fraction of both silent and replacement DNA mutations appear to affect fitness.

Adaptation, Biological↗
PubMed1999

Evolution of the rearfoot. A model of adaptation with evidence from the fossil record.

The evolution of the human foot presents an obfuscation: explanations for its occurrence and the exact nature of mechanisms of change are still not fully understood. This article outlines a model of adaptation from a primitive ape foot and presents this as a hypothesis. Evidence substantiating the hypothesis is then presented, which explains many of the large-scale features distinctive to the human foot. Further evidence is then presented that goes some way toward explaining the sequence of modification with first the lateral side becoming adapted for terrestrial function followed by the medial side. Paradoxically, this was hypothesized by Morton more than half a century ago in his "hypothetical prehuman foot," though it was not accepted favorably at the time.

Adaptation, Biological↗