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PubMed2003

Adaptive learning in arthropods: spider mites learn to distinguish food quality.

Many herbivorous arthropods have been shown to possess learning capabilities, yet fitness effects of learning are largely unknown. In this paper, we test whether two-spotted spider mites (Tetranychus urticae) learn to distinguish food quality in choice tests, and whether this results in fitness benefits. Food consisted of cucumber plants with one of three degrees of feeding damage: undamaged (no mites), mildly damaged (infested by a mite strain adapted to tomato) and heavily damaged (infested by a mite strain adapted to cucumber). Mites were subjected to one choice test in a greenhouse and three sequential choice tests on leaf disks. Thereafter, individual mite performance was measured as oviposition rate over four days. In the course of the three small-scale choice tests, preference shifted towards less damaged food. The performance tests showed that learning was adaptive: mites learned to prefer the food type that yielded the higher oviposition rate. Interestingly, innate preferences in the greenhouse tests were close to those shown after learning in the small-scale tests. Given that both strains of mites had not experienced cucumber for several years, we hypothesize that the preference in the greenhouse was due to avoidance of mite odours rather than odours of damaged plants. Through its effect on foraging behaviour, adaptive learning may promote the evolution of host plant specialization in herbivorous arthropods.

Adaptation, Physiological↗
PubMed2004

Comparative genomic structure of prokaryotes.

Recent advances in DNA-sequencing technologies have made available an enormous resource of data for the study of bacterial genomes. The broad sample of complete genomes currently available allows us to look at variation in the gross features and characteristics of genomes while the detail of the sequences reveal some of the mechanisms by which these genomes evolve. This review aims to describe bacterial genome structures according to current knowledge and proposed hypotheses. We also describe examples where mechanisms of genome evolution have acted in the adaptation of bacterial species to particular niches.

Bacteria↗
PubMed2004

Microbial adaptation and change: avian influenza.

The evolution of influenza is a continuing process involving viral and host factors. The increasing frequency of emergence of the highly pathogenic H5N1, H7N3 and H7N7 influenza viruses and the panzootic spread of H9N2 influenza virus, all of which can be potentially transmitted to humans, are of great concern to both veterinary and human public health officials. The question is how soon the next pandemic will emerge. A convergence of factors, including the population densities of poultry, pigs and humans, are likely factors affecting the evolution of the virus. Highly concentrated poultry and pig farming, in conjunction with traditional live animal or 'wet' markets, provide optimal conditions for increased mutation, reassortment and recombination of influenza viruses. Strategies to reduce the evolution of influenza and the emergence of pandemics include the separation of species, increased biosecurity, the development of new vaccine strategies and better basic knowledge of the virus. More effective co-operation between scientists and veterinary and public health officials is required to achieve these goals.

Animals↗
PubMed1997

Evolution of high mutation rates in experimental populations of E. coli.

Most mutations are likely to be deleterious, and so the spontaneous mutation rate is generally held at a very low value. Nonetheless, evolutionary theory predicts that high mutation rates can evolve under certain circumstances. Empirical observations have previously been limited to short-term studies of the fates of mutator strains deliberately introduced into laboratory populations of Escherichia coli, and to the effects of intense selective events on mutator frequencies in E. coli. Here we report the rise of spontaneously originated mutators in populations of E. coli undergoing long-term adaptation to a new environment. Our results corroborate computer simulations of mutator evolution in adapting clonal populations, and may help to explain observations that associate high mutation rates with emerging pathogens and with certain cancers.

Adaptation, Physiological↗
PubMedDate not supplied

[Philosophical aspects of the theory of adaptation].

This paper discusses the general concepts of the problem of adaptation from the dialectic point of view which, according to F. Engels, is the most important pattern of thinking in natural sciences. Dialectics provides an analog and therefore a method for interpreting developmental processes, universal relationships in nature, transition from one area of research to another. From the point of view of dialectic laws adaptation acts as a contradictory process of habituation to various environments. The contradictory pattern of the adaptive process and its result is very distinct in terms of heredity and variability. A logical enlargement of the concept of adaptation is the transition to the study of homeostasis which is assumed to be its mechanism, a property which has developed in the course of evolution and fixed in heredity. This adaptive property is contradictory in its essence because homeostasis is a unity of stability and instability, a fluctuating constancy. In addition to the law of constancy of the inner melieu, there is a law of homeostatic deviations. This concept can be understood through an analysis of the system theory that includes a continuous variation and conservation of structure which indicates its ordered oscillation, that is, its rhythmicity. This clarifies the relationship between homeostasis and biological rhythmicity as a method of maintaining the former. Thus, a consistent analysis of the problem of adaptation can help identify transition from one area of research to another, specifically to the study of oscillatory processes in living systems, including such oscillatory processes that have characteristics of universality and necessity. Such processes are biological rhythms with a period of about 24 hours, that is, circadian rhythms.

Adaptation, Biological↗
PubMed1995

Thermoreduction, a hypothesis for the origin of prokaryotes.

All thermophiles discovered so far are prokaryotes (Bacteria or Archaea). Furthermore, reconstructions of rRNA phylogenies suggest that the progenitor of all prokaryotes was a thermophile. These data are usually interpreted as supporting the hypothesis that all present day organisms, including eukaryotes, originated from hyperthermophiles. However, this scenario is difficult to reconcile with the RNA world theory, considering the instability of RNA at very high temperatures, and it is also contradicted by the finding of sophisticated devices for thermophilic adaptation in present day hyperthermophiles. Accordingly, I propose here 2 new hypotheses to explain the correlation between the procaryotic phenotype and thermophilic life without reference to a putative hot origin of life. Firstly, eukaryotes would be unable to live in thermophilic biotopes because of the susceptibility of their mRNA to degradation at high temperature. In prokaryotes, the absence of a nuclear membrane allows these organisms to bypass the problem of mRNA heat-induced hydrolysis by coupling transcription and translation. As a corollary of this first hypothesis, I also suggest that today prokaryotes might have originated from mesophilic ancestors via reductive evolution, in the process of adaptation to thermophily.

Biological Evolution↗
PubMed1997

The adaptational system as a dynamical feedback system.

The characteristics of biological systems of adaptation are developed from the principle that the manifestations of life are modified by and must conform with their environment in order to enable organismic persistence. The two roles of the environment, termed "modifying" and "adaptive", give rise to the distinction of three elementary and sequentially coupled subsystems characterizing the adaptational system: the modifying system, comparator system, and state regulation system. The third system determines which state alterations are required for adaptation of manifestations (responses) to the demands of the adaptive environment. Adaptational valuation is introduced as a measure of adaptedness of response to adaptive environment. The dynamical aspect of adaptation is shown to be completely described by the timing of feedback. Discrete and continuous forms of adaptation can thus be treated on the same conceptional basis. All steps of the generic system formulation are illustrated with the help of a simple model with additive effects and linear state regulation. The system representation is used to demonstrate how basic intuitive conceptions, such as adaptational lag or adaptational capacity, can be made amenable to precise analysis. Another demonstration concerns recognition of adaptational clues resulting from the distinction between the two environmental classes, modifying and adaptive. Among these clues are challenges of low correlation between the two classes to adaptational systems and the specification of questions of the evolution of phenotypic plasticity.

Adaptation, Biological↗
PubMed2005

Why do snails have hairs? A Bayesian inference of character evolution.

BACKGROUND: Costly structures need to represent an adaptive advantage in order to be maintained over evolutionary times. Contrary to many other conspicuous shell ornamentations of gastropods, the haired shells of several Stylommatophoran land snails still lack a convincing adaptive explanation. In the present study, we analysed the correlation between the presence/absence of hairs and habitat conditions in the genus Trochulus in a Bayesian framework of character evolution. RESULTS: Haired shells appeared to be the ancestral character state, a feature most probably lost three times independently. These losses were correlated with a shift from humid to dry habitats, indicating an adaptive function of hairs in moist environments. It had been previously hypothesised that these costly protein structures of the outer shell layer facilitate the locomotion in moist habitats. Our experiments, on the contrary, showed an increased adherence of haired shells to wet surfaces. CONCLUSION: We propose the hypothesis that the possession of hairs facilitates the adherence of the snails to their herbaceous food plants during foraging when humidity levels are high. The absence of hairs in some Trochulus species could thus be explained as a loss of the potential adaptive function linked to habitat shifts.

Adaptation, Biological↗
PubMed2006

Adaptive response of a gene network to environmental changes by fitness-induced attractor selection.

Cells switch between various stable genetic programs (attractors) to accommodate environmental conditions. Signal transduction machineries efficiently convey environmental changes to the gene regulation apparatus in order to express the appropriate genetic program. However, since the number of environmental conditions is much larger than that of available genetic programs so that the cell may utilize the same genetic program for a large set of conditions, it may not have evolved a signaling pathway for every environmental condition, notably those that are rarely encountered. Here we show that in the absence of signal transduction, switching to the appropriate attractor state expressing the genes that afford adaptation to the external condition can occur. In a synthetic bistable gene switch in Escherichia coli in which mutually inhibitory operons govern the expression of two genes required in two alternative nutritional environments, cells reliably selected the "adaptive attractor" driven by gene expression noise. A mathematical model suggests that the "non-adaptive attractor" is avoided because in unfavorable conditions, cellular activity is lower, which suppresses mRNA metabolism, leading to larger fluctuations in gene expression. This, in turn, renders the non-adaptive state less stable. Although attractor selection is not as efficient as signal transduction via a dedicated cascade, it is simple and robust, and may represent a primordial mechanism for adaptive responses that preceded the evolution of signaling cascades for the frequently encountered environmental changes.

Adaptation, Biological↗
PubMed1994

Evolution. How does increased fitness evolve?

Populations of bacteria exposed to a new environment have undergone adaptive evolutionary change over 10,000 generations. These populations provide a testing ground for alternative models of long-term evolution.

Adaptation, Biological↗
PubMed1997

Adaptations in scale insects.

Many unusual features of scale insects (Hemiptera: Coccoidea) can be explained as historical legacy. Developmental specializations in ancestral coccoids resulted in a neotenous adult female and a drastic metamorphosis of the male. Subsequent evolution led to numerous, often convergently derived, adaptations to parasitic life on higher plants. The sedentary lifestyle of female scale insects has favored the evolution of appendage reduction or loss, gross changes in body shape, and protective wax secretions, tests, and other scale covers. Morphological peculiarities of adult males relate to flight or to mating with concealed females. Scale insects have diverse egg-protecting methods, a range of chromosome behaviors (including several methods of sex determination), marked sexual dimorphism [even sometimes in first-instar nymphs (crawlers)], and more rarely sexual dichronism. Crawlers have evolved as the main agents of dispersal. The biotic interactions of scale insects include diverse endosymbioses with microorganisms, sometimes morphological and behavioral adaptations for obligate association with ants, and often highly specific host-plant associations that may lead to demic adaptation or the evolution of complex galls.

Journal Article↗
PubMed2003

[Preface to special issue: "Molecular mechanism of the adaptation of terrestrial plants to gravity environment on Earth"].

Organisms borne in the primitive sea about 30 million years ago had evolved in water without a large influence of gravity on earth. About 4 million years ago, the first terrestrial organisms, plants appeared on the land from the sea. The terrestrial plants have adapted to and evolved on the land environment so that they can extend their roots downward in soil and their shoots upward against 1 g gravity. At least two functions that were acquired during the process of evolution helped the terrestrial plants to adapt to gravity environment on earth. One is gravitropism. The other is the reinforcement of the cell wall, particularly the secondary cell wall. In the present feature articles, the molecular mechanism of the adaptation of terrestrial plants to gravity environment on earth will be reviewed, paying special attention to the mechanism of the genetic control of the signaling of gravity stimulus in gravitropism, automorphogenesis, genes involved in auxin transport, gravity effect on cell wall properties and gravimorphogenesis in terrestrial plants.

Adaptation, Biological↗
PubMed1997

The Frog in Space (FRIS) experiment onboard Space Station Mir: final report and follow-on studies.

The "Frog in Space" (FRIS) experiment marked a major step for Japanese space life science, on the occasion of the first space flight of a Japanese cosmonaut. At the core of FRIS were six Japanese tree frogs, Hyla japonica, flown on Space Station Mir for 8 days in 1990. The behavior of these frogs was observed and recorded under microgravity. The frogs took up a "parachuting" posture when drifting in a free volume on Mir. When perched on surfaces, they typically sat with their heads bent backward. Such a peculiar posture, after long exposure to microgravity, is discussed in light of motion sickness in amphibians. Histological examinations and other studies were made on the specimens upon recovery. Some organs, such as the liver and the vertebra, showed changes as a result of space flight; others were unaffected. Studies that followed FRIS have been conducted to prepare for a second FRIS on the International Space Station. Interspecific diversity in the behavioral reactions of anurans to changes in acceleration is the major focus of these investigations. The ultimate goal of this research is to better understand how organisms have adapted to gravity through their evolution on earth.

Acceleration↗