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PubMed2005

Population variability in biological adaptive responses to DNA damage and the shapes of carcinogen dose-response curves.

Carcinogen dose-response curves for both ionizing radiation and chemicals are typically assumed to be linear at environmentally relevant doses. This assumption is used to ensure protection of the public health in the absence of relevant dose-response data. A theoretical justification for the assumption has been provided by the argument that low dose linearity is expected when an exogenous agent adds to an ongoing endogenous process. Here, we use computational modeling to evaluate (1) how two biological adaptive processes, induction of DNA repair and cell cycle checkpoint control, may affect the shapes of dose-response curves for DNA-damaging carcinogens and (2) how the resulting dose-response behaviors may vary within a population. Each model incorporating an adaptive process was capable of generating not only monotonic dose-responses but also nonmonotonic (J-shaped) and threshold responses. Monte Carlo analysis suggested that all these dose-response behaviors could coexist within a population, as the spectrum of qualitative differences arose from quantitative changes in parameter values. While this analysis is largely theoretical, it suggests that (a) accurate prediction of the qualitative form of the dose-response requires a quantitative understanding of the mechanism, (b) significant uncertainty is associated with human health risk prediction in the absence of such quantitative understanding and (c) a stronger experimental and regulatory focus on biological mechanisms and interindividual variability would allow flexibility in regulatory treatment of environmental carcinogens without compromising human health.

Adaptation, Physiological↗
PubMed2000

Obesity: a disease or a biological adaptation?

The increase in obesity prevalence is problematic as this condition is associated with health complications such as diabetes and cardiovascular diseases, more particularly when the excess body fat is stored in the deep abdominal region. On the other hand, obesity facilitates the maintenance of body homeostasis probably because of an increased hormonal gradient which favours the regulation of energy balance, to give but one example. The regulation potential of excess body fat is particularly apparent in the reduced-obese state where a reduction of energy expenditure, fat oxidation and some immune system markers, as well as an increase in appetite, stress vulnerability and circulating and adipose tissue organochlorines have been observed. These constitute another category of risk factors which can certainly favour the accumulation of body fat to reestablish body homeostasis on other fronts. Under such conditions, obesity is perceived by the physiologist as a necessary biological adaptation rather than a disease. For health professionals, this emphasizes the importance to seek a reasonable compromise between the favourable reduction of risk to develop metabolic complications by body weight loss and the physiological vulnerability which is also generated by such an intervention.

Adaptation, Physiological↗
PubMed2003

Testing evolutionary hypotheses about human biological adaptation using cross-cultural comparison.

Physiological data from a range of human populations living in different environments can provide valuable information for testing evolutionary hypotheses about human adaptation. By taking into account the effects of population history, phylogenetic comparative methods can help us determine whether variation results from selection due to particular environmental variables. These selective forces could even be due to cultural traits-which means that gene-culture co-evolution may be occurring. In this paper, we outline two examples of the use of these approaches to test adaptive hypotheses that explain global variation in two physiological traits: the first is lactose digestion capacity in adults, and the second is population sex-ratio at birth. We show that lower than average sex ratio at birth is associated with high fertility, and argue that global variation in sex ratio at birth has evolved as a response to the high physiological costs of producing boys in high fertility populations.

Adaptation, Physiological↗
PubMed1989

Modeling adaptive biological systems.

During the evolution of many systems found in nature, both the system composition and the interactions between components will vary. Equating the dimension with the number of different components, a system which adds or deletes components belongs to a class of dynamical systems with a finite dimensional phase space of variable dimension. We present two models of biochemical systems with a variable phase space, a model of autocatalytic reaction networks in the prebiotic soup and a model of the idiotypic network of the immune system. Each model contains characteristic meta-dynamical rules for constructing equations of motion from component properties. The simulation of each model occurs on two levels. On one level, the equations of motion are integrated to determine the state of each component. On a second level, algorithms which approximate physical processes in the real system are employed to change the equations of motion. Models with meta-dynamical rules possess several advantages for the study of evolving systems. First, there are no explicit fitness functions to determine how the components of the model rank in terms of survivability. The success of any component is a function of its relationship to the rest of the system. A second advantage is that since the phase space representation of the system is always finite but continually changing, we can explore a potentially infinite phase space which would otherwise be inaccessible with finite computer resources. Third, the enlarged capacity of systems with meta-dynamics for variation allows us to conduct true evolution experiments. The modeling methods presented here can be applied to many real biological systems. In the two studies we present, we are investigating two apparent properties of adaptive networks. With the simulation of the prebiotic soup, we are most interested in how a chemical reaction network might emerge from an initial state of relative disorder. With the study of the immune system, we study the self-regulation of the network including its ability to distinguish between species which are part of the network and those which are not.

Adaptation, Biological↗
PubMed2005

Adaptive biological trends in the European upper palaeolithic: the case of the Sunghir remains.

Sunghir is one of the most important Upper Palaeolithic sites in the world because of its most Northern location, the extraordinary richness of the artifacts, and the state of human bone preservation. The skeletal finds give evidence for the study both of adult and subadult body builds in the group. For the reconstruction of patterns of postcranial morphology, total measurements of bones and X-ray observations have been used. We have determined the basic structural traits typical for Sunghirians: small corticalisation of adult postcranial skeletons; large volume of the bone marrow cavity relative to the general size; quick tempo of attainment in early ontogenesis of large adult size combined with late synostoses ensuring prolonged linear growth; macroskelia combined with extreme andromorphy in the shoulder belt structure; capacious chest. The above traits can be interpreted in terms of adaptation to such formative factors as low temperature stress, deficit of atmospheric oxygen, high protein nutrition, and mechanical loads.

Adaptation, Biological↗
PubMed1976

[Altitude adaptation. Biological problems in the context of the environment].

The following part of the description of adaptation to high altitude describes the geographical specifities of the relevant regions of the world. There are several factors which require an adaptive answer, such as hypoxia, temperature, terrain, nutrition etc. The terms of genetically determined and of individual adaptation are discussed, with special consideration of a duration of settlement in the main altitude regions of about ten thousand years, as well as the principles of adaptation in general, including the phenomenon of maladaptation. The problem of adaptation of animals to high altitude is reviewed in short especially in regard to mammals. The differential fertility proves to be most important in the survival of a species in high altitude as well as the individual adaptability, is the fitness which makes high altitude tolerable to newcomers.

Acclimatization↗
PubMedDate not supplied

Biological adaptation and social behaviour.

In 1930, both Fisher and Wright identified Darwin's initial concept of adaptive evolution in the light of the genetical theory with intergenerational variation in allelic frequencies brought about by the action of natural selection through differential reproduction. They emphasized that selection only works at the level of the individual and that its only consequence is to increase fitness. One genetical evolution not easy to explain on these bases was that of social behaviour because any altruistic gene disadvantageous for its carriers in an antisocial environment would have been opposed by selection. In the 1950s, ethologists focusing on what appeared to be evolved collective behaviours, hypothesized that selection could operate at group level. Though the controversy between group selectionists and evolutionary geneticists ended by the rejection of the evolutionary role of group selection, it has remained a subject of investigation until now. Kin selection, proposed by Hamilton, offered a solution to the problem of the evolution of altruism and gave the impetus to the trend of adaptive explanations of basic behaviours, which was to become the core of human sociobiology. The intrusion of behaviour into the process of adaptive evolution was an invitation to investigate culture as an evolutive process. The first sociobiological interpretations of culture as a derivative of genetic processes were followed by other ideas in which culture, though channelled by evolved predispositions, was essentially free from biological determinism. It is concluded that as we have come to better understand human adaptation, its complexities have been further revealed, a development already implicit in Darwin's notion.

Adaptation, Physiological↗
PubMed2004

Biological adaptive control model: a mechanical analogue of multi-factorial bone density adaptation.

The mechanism of how bone adapts to every day demands needs to be better understood to gain insight into situations in which the musculoskeletal system is perturbed. This paper offers a novel multi-factorial mathematical model of bone density adaptation which combines previous single-factor models in a single adaptation system as a means of gaining this insight. Unique aspects of the model include provision for interaction between factors and an estimation of the relative contribution of each factor. This interacting system is considered analogous to a Newtonian mechanical system and the governing response equation is derived as a linear version of the adaptation process. The transient solution to sudden environmental change is found to be exponential or oscillatory depending on the balance between cellular activation and deactivation frequencies.

Adaptation, Physiological↗
PubMed2002

Biological adaptabilities and quantum entropies.

The entropy-based theory of adaptability set forth by Michael Conrad in the early 1970s continued to appear in his work for over two decades, and was the subject of the only book he published in his lifetime. He applied this theory to a host of subjects ranging from enzyme dynamics to sociology. This paper reviews the formalism of adaptability theory, clarifying some of its mathematical and interpretive difficulties. The theory frames the computational tradeoff principle, a thesis that was the most frequently recurring claim in his work. The formulation of adaptability theory presented here allows the introduction of quantum entropy functions into the theory, revealing an interesting relationship between adaptability and another one of Conrad's deep preoccupations, the role of quantum processes in life.

Adaptation, Physiological↗
PubMed2003

The rotator cuff: biological adaptations to its environment.

The rotator cuff is a common source of shoulder pain in individuals who rely on overhead activities for work and sport. As diagnostic and treatment measures continue to advance, it is important for the physician to retain a knowledge of the anatomy and biological properties of the rotator cuff in its surroundings. The collagen composition, proteoglycan and glycosaminoglycan content, and cellular activity of the rotator cuff reflect its mechanical function. Also, the rotator cuff maintains fibrocartilagenous properties as it is under compression in its normal state. While many of these characteristics appear to be adaptive and occur in the healthy rotator cuff, some may predispose the tendon complex to pathology.

Adaptation, Physiological↗
PubMed2003

Intracellular parasitism: cell biological adaptations of parasitic protozoa to a life inside cells.

Several protozoan parasites evade the host's immune defence because most of their development takes place inside specific host cells. Only a few of these protozoa live within the host cell cytosol. Most parasites are sequestered within membrane-bound compartments, collectively called 'vacuoles'. Recent advances in the cell biology of intracellular parasites have revealed fundamental differences in the strategies whereby such organisms gain entry into their respective host cells. These differences have important implications for host-parasite interaction and for nutrient acquisition by the parasite. Leishmania spp. take advantage of the phagocytic properties of their host cells and presumably contribute little to the uptake process. In contrast, apicomplexan parasites have developed highly specialised organelles, called micronemes and rhoptries, to actively invade a variety of nucleated cells and, in the case of Plasmodium falciparum, human erythrocytes. Following invasion, parasites use a multitude of strategies to protect themselves from the defence mechanisms of the parasitized cells. In addition, they induce novel pathways within the infected cell that allow a most efficient nutrient acquisition both from the host cell cytoplasm and from the extracellular environment. Parasite-induced changes of host cells are most apparent in erythrocytes infected with Plasmodium spp. Mammalian erythrocytes are deficient in de novo protein and lipid biosynthesis and, consequently, pathways which allow the transport of macromolecules and small solutes are established by metabolic activities of the parasite. Research into the cell biology of intracellular parasitism has identified fascinating phenomena some of which we are beginning to understand at a molecular level. They are fascinating because they allow insights into a very intimate interaction between two eukaryotic cells of entirely different phylogenetic origins.

Journal Article↗
PubMed1995

Biological adaptation of the myocardium to chronic mechanical overload. Molecular determinants of the autonomic nervous system.

Cardiac hypertrophy due to chronic mechanical overload is the physiological reaction of the heart to a disease, but is not a disease itself. The hypertrophied heart is both quantitatively and qualitatively modified, and these changes allow the heart to produce normal active tension at a low cost in terms of heat production. The biological cascade which finally leads to hypertrophy includes a trigger which is likely to be mechanical stretch, the phosphoinisitol pathway and a target at the level of DNA. Most of the physiological alterations observed during cardiac overload include changes in systolic and diastolic function and arrhythmias. The components of the autonomous nervous system are also greatly modified and their regulation is a rather complex issue. Future research to elucidate these mechanisms centres on the regulation process and the possibilities offered by gene transfer.

Adaptation, Physiological↗
PubMed2003

A transmural pressure gradient induces mechanical and biological adaptive responses in endothelial cells.

A sudden increase in the transmural pressure gradient across endothelial monolayers reduces hydraulic conductivity (L(p)), a phenomenon known as the sealing effect. To further characterize this endothelial adaptive response, we measured bovine aortic endothelial cell (BAEC) permeability to albumin and 70-kDa dextran, L(p), and the solvent-drag reflection coefficients (sigma) during the sealing process. The diffusional permeability coefficients for albumin (1.33 +/- 0.18 x 10(-6) cm/s) and dextran (0.60 +/- 0.16 x 10(-6) cm/s) were measured before pressure application. The effective permeabilities (measured when solvent drag contributes to solute transport) of albumin and dextran (P(ealb) and P(edex)) were measured after the application of a 10 cmH(2)O pressure gradient; during the first 2 h of pressure application, P(ealb), P(edex), and L(p) were significantly reduced by 2.0 +/- 0.3-, 2.1 +/- 0.3-, and 3.7 +/- 0.3-fold, respectively. Immunostaining of the tight junction (TJ) protein zonula occludens-1 (ZO-1) was significantly increased at cell-cell contacts after the application of transmural pressure. Cytochalasin D treatment significantly elevated transport but did not inhibit the adaptive response, whereas colchicine treatment had no effect on diffusive permeability but inhibited the adaptive response. Neither cytoskeletal inhibitor altered sigma despite significantly elevating both L(p) and effective permeability. Our data suggest that BAECs actively adapt to elevated transmural pressure by mobilizing ZO-1 to intercellular junctions via microtubules. A mechanical (passive) component of the sealing effect appears to reduce the size of a small pore system that allows the transport of water but not dextran or albumin. Furthermore, the structures of the TJ determine transport rates but do not define the selectivity of the monolayer to solutes (sigma).

Animals↗
PubMed1988

Membrane fluidity in Bacillus subtilis. Physical change and biological adaptation.

The thermotropic behaviour of membrane phospholipids was estimated in intact cells of Bacillus subtilis. Membrane fluidity (microviscosity) of intact cells depended markedly on the ambient temperature - increase in cultivation temperature led to an increase in membrane fluidity. Estimated as anisotropy of 1,6-diphenyl-1,3,5-hexatriene fluorescence, a 30% difference was observed when cells cultivated at 20 and 40 degrees C were compared. This lack of rigorous homeostatic control of bulk-phase lipid fluidity prompted the reevaluation of the physiological significance of the "homeoviscous adaptation" in B. subtilis.

Adaptation, Physiological↗
PubMed2004

Evolutionary biology: adaptive developmental plasticity in snakes.

The morphology of organisms is generally well matched to their environment, presumably because expression of their genes is tailored either at the population or the individual level to suit local conditions: for example, snake populations that persistently encounter large prey may accumulate gene mutations that specify a large head size, or head growth may be increased in individual snakes to meet local demands (adaptive developmental plasticity). Here we test the relative contributions of genetics and environment to the jaw sizes of two tiger snake populations: one that consumes small prey on the mainland, and an island population that relies on larger prey and has a larger jaw size. Although the idea of adaptive plasticity in response to environmental pressures is controversial, we find that both factors influence the difference in jaw size between the two populations, and the influence of developmental plasticity is greater in the island population.

Adaptation, Physiological↗