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PubMed2004

Evolution of Hsp90 expression in Tetrahymena thermophila (Protozoa, Ciliata) populations exposed to thermally variable environments.

Evolutionary consequences of thermally varying environments were studied in the ciliated protozoan Tetrahymena thermophila. Replicated lines were propagated for 60 days, a maximum of 500 generations, in stable, slowly fluctuating (red spectrum), and rapidly fluctuating (blue spectrum) temperatures. The red and blue fluctuations had a dominant period length of 15 days and two hours, respectively. The mean temperature of all time series was 25 degrees C and the fluctuating temperatures had the same minimum (10 degrees C), maximum (40 degrees C), and variance. During the experiment, population sizes and biomasses were monitored at three-day intervals. After the experiment, carrying capacity and maximum growth rate were measured at low (15 degrees C), intermediate (25 degrees C), and high (35 degrees C) temperatures for each experimental line. Physiological changes in the lines were assessed by measuring the expression of stress-induced heat shock protein Hsp90 at 25 degrees C, 35 degrees C, and 39 degrees C. Population sizes and biomasses showed no differences between stable, blue, or red temperature treatments during the experiment. Also, after the experiment, mean carrying capacities and maximum growth rates were comparable in the stable, blue, and red temperature treatments. The expression of Hsp90 was higher in lines from the blue environment than in lines from the stable environment. Lines from the red environment had an intermediate level of Hsp90 expression. This supports the hypothesis that inducible thermotolerance and expression of canalizing genes can evolve in response to rapidly varying environments. Furthermore, we found correlative evidence of benefits and disadvantages of high Hsp90 expression. Lines with high expression of Hsp90 had an increased growth rate at the highest temperature when food resources were not limiting growth. At low and intermediate temperatures the same lines had the lowest carrying capacities.

Analysis of Variance↗
PubMed2002

A lotka-volterra model of coexistence between a sexual population and multiple asexual clones.

At carrying capacity, small advantages in competitive ability can compensate a sexual population for its two-fold disadvantage in growth capacity when facing invasion by asexual mutants. In this paper, we develop a generic analytical model to consider the ecology of a sexual population comprising equal numbers of males and females, competing for shared prey resources with multiple female-only clones. We assume that the clones arise from the sexual population and are distinguished from it only by having narrower resource niches and twice the growth capacity. For sexual populations, at density-dependent carrying capacity, intra-specific competition between clonal individuals prevents them from realizing their two-fold advantage in intrinsic growth. This prediction leads to three novel outcomes: (i) a sexual population can coexist with any number of clones, provided their combined competitive impact remains less than the impact of the clones on each other; (ii) a sexual species can immediately exclude asexual invaders if it is a fast growing and strong competitor of shared resources and also has refuge in an abundant alternative resource; (iii) the rate of accumulation of clones in a sexual population will be slowed by intra and inter-specific competition amongst the clones themselves, in addition to the competitive impact from the original sexual population.

Animals↗
PubMed2004

Oxygen-carrying blood substitutes: a microvascular perspective.

Development of a viable blood substitute began by focusing on recreating the oxygen-carrying capacity of blood, leading to the recognition that haemoglobin (Hb) is presently unequalled for this function. However, as human Hb is the only realistic source of this protein, the production of a blood substitute that solves transfusional blood availability problems and shortages must introduce a multiplying factor between supply of natural blood and blood substitute, while maintaining equivalency of function/efficacy. In other words, a unit of blood should produce several units of equivalent blood substitute. This expansion is now possible because of new understanding of how blood delivers oxygen in the microcirculation and the consequences of reducing oxygen-carrying capacity in haemorrhage. This information is used to provide improved resuscitation capacity and maintenance of tissue metabolism by tailoring the properties of a blood substitute to the task of maintaining microvascular function, rather than oxygen delivery capacity. Resuscitation in an organism that is haemorrhaging requires maintenance perfusion, a process directly linked to the maintenance of adequate levels of shear stress on the endothelium, induced by either increased blood/plasma viscosity or increased blood flow velocity in the microcirculation. This process must also be intimately coupled with the requirement that no portion of the tissue is anoxic. This disparate set of requirements can be satisfied with high viscosity Hb solutions that have high affinity for oxygen, a combination of properties that causes the microcirculation to remain functional, and a requirement that supersedes restoration of oxygen-carrying capacity in the treatment of haemorrhage.

Animals↗
PubMed2005

Global production increased by spatial heterogeneity in a population dynamics model.

Spatial and temporal heterogeneity are often described as important factors having a strong impact on biodiversity. The effect of heterogeneity is in most cases analyzed by the response of biotic interactions such as competition of predation. It may also modify intrinsic population properties such as growth rate. Most of the studies are theoretic since it is often difficult to manipulate spatial heterogeneity in practice. Despite the large number of studies dealing with this topics, it is still difficult to understand how the heterogeneity affects populations dynamics. On the basis of a very simple model, this paper aims to explicitly provide a simple mechanism which can explain why spatial heterogeneity may be a favorable factor for production. We consider a two patch model and a logistic growth is assumed on each patch. A general condition on the migration rates and the local subpopulation growth rates is provided under which the total carrying capacity is higher than the sum of the local carrying capacities, which is not intuitive. As we illustrate, this result is robust under stochastic perturbations.

Models, Theoretical↗
PubMed2000

The ecological cost of sex.

Why sex prevails in nature remains one of the great puzzles of evolution. Sexual reproduction has an immediate cost relative to asexual reproduction, as males only express their contribution to population growth through females. With no males to sustain, an asexual mutant can double its relative representation in the population in successive generations. This is the widely accepted 'twofold cost of males'. Many studies have attempted to explain how sex can recoup this cost from fitness benefits associated with the recombination of parental genotypes, but these require complex biological environments that cycle over evolutionary timescales. In contrast, we have considered the ecological dynamics that govern asexual invasion. Here we show the existence of a threshold growth rate for the sexual population, above which the invasion is halted by intraspecific competition. The asexual population then exerts a weaker inhibitory effect on the carrying capacity of the sexual population than on its own carrying capacity. The stable outcome of this is coexistence on a depleted resource base. Under these ecological circumstances, longer-term benefits of sex may eventually drive out the asexual competitor.

Animals↗
PubMed1981

Development of a perfluorochemical whole blood substitute (Fluosol-DA, 20%)--an overview of clinical studies with 185 patients.

Fluosol-DA, 20%, a perfluorochemical whole blood substitute, was infused during Phase II and Phase III clinical trials at 24 medical institutions in Japan to 185 patients for replacement of blood lost during surgery or for improvement of cerebral circulation. Its active ingredients (perfluorodecalin, perfluorotripropylamine, hydroxyethyl starch and Krebs-Ringer bicarbonate solution) give this biologically inert emulsion not only plasma-expanding properties but also a high oxygen-carrying capacity (7.2 vol.% at 37 degrees C; the oxygen carrying capacity of red blood cells is 17 to 20 vol.%). Doses given to the patients ranged from 6 to 25 ml/kg body weight. With regard to arterial blood oxygen tension, arterial blood oxygen content, blood oxygen transport, oxygen consumption, and acid-base balance, beneficial effects were generally observed after infusion of the emulsion following blood loss especially when the fractional concentration of oxygen in inspired gas (FiO2) was kept higher than 0.5. The emulsion also manifested beneficial plasma-expander effects on hemodynamics (blood pressure, pulse rate, and central venous pressure). In no case was there any anaphylactoid or other untoward reaction observed or reported during or after infusion of the emulsion. Although a slight prolongation of bleeding time (Duke) was found, the surgeons never experienced and hemorrhagic tendencies during or after their operations. Slight and transient elevations of SGOT were found but SGPT and alkaline phosphatase levels remained normal. All other hematological and biochemical parameters measured in blood, serum and urine remained within normal ranges.

Blood Gas Analysis↗
PubMed2006

Molecular diversity after a range expansion in heterogeneous environments.

Recent range expansions have probably occurred in many species, as they often happen after speciation events, after ice ages, or after the introduction of invasive species. While it has been shown that range expansions lead to patterns of molecular diversity distinct from those of a pure demographic expansion, the fact that many species do live in heterogeneous environments has not been taken into account. We develop here a model of range expansion with a spatial heterogeneity of the environment, which is modeled as a gamma distribution of the carrying capacities of the demes. By allowing temporal variation of these carrying capacities, our model becomes a new metapopulation model linking ecological parameters to molecular diversity. We show by extensive simulations that environmental heterogeneity induces a loss of genetic diversity within demes and increases the degree of population differentiation. We find that metapopulations with low average densities are much more affected by environmental heterogeneity than metapopulations with high average densities, which are relatively insensitive to spatial and temporal variations of the environment. Spatial heterogeneity is shown to have a larger impact on genetic diversity than temporal heterogeneity. Overall, temporal heterogeneity and local extinctions are not found to leave any specific signature on molecular diversity that cannot be produced by spatial heterogeneity.

Computer Simulation↗
PubMed2006

Importance of hemoglobin concentration to exercise: acute manipulations.

An acute reduction of blood hemoglobin concentration ([Hb]), even when the circulating blood volume is maintained, results in lower (.)V(O(2)(max) and endurance performance, due to the reduction of the oxygen carrying capacity of blood. Conversely, an increase of [Hb] is associated with enhanced (.)V(O(2)(max) and endurance capacity, that is also proportional to the increase in the oxygen carrying capacity of blood. The effects on endurance capacity appear more pronounced and prolonged than on (.)V(O(2)(max). During submaximal exercise, there is a tight coupling between O(2) demand and O(2) delivery, such that if [Hb] is acutely decreased muscle blood flow is increased proportionally and vice versa. During maximal exercise with either a small or a large muscle mass, neither peak cardiac output nor peak leg blood flow are affected by reduced [Hb]. An acute increase of [Hb] has no effect on maximal exercise capacity or (.)V(O(2)(max) during exercise in acute hypoxia. Likewise, reducing [Hb] in altitude-acclimatized humans to pre-acclimatization values has no effect on (.)V(O(2)(max) during exercise in hypoxia.

Altitude↗
PubMedDate not supplied

Elevated levels of methaemoglobin in Tanzanian children with severe and uncomplicated malaria.

Elevated levels of methaemoglobin, the ferric form of haemoglobin incapable of oxygen transport, have been previously found during Plasmodium vivax infections and in acidotic infants. We measured methaemoglobin in the following 5 groups of children with P. falciparum malaria admitted to Muhimbili Medical Centre, Dar es Salaam, Tanzania. (i) Cerebral malaria (CM) with unrousable coma (n = 50), including 32 with complete recovery (CMCR) and 18 with death or neurological sequelae (CMDS); (ii) malaria with severe anaemia but without severe respiratory distress (SA; n = 6); (iii) uncomplicated malaria (UM; n = 37); (iv) asymptomatic parasitaemia (AP; n = 5); and (v) healthy controls (HC; n = 34). Mean methaemoglobin levels were elevated in all groups with malaria, forming up to 16.4% of circulating haemoglobin. The degree of methaemoglobinaemia correlated with disease severity and severity of anaemia. Mean methaemoglobin levels in children with AP, UM, SA, CMCR and CMDS were 3.3%, 4.1%, 5.6%, 4.7% and 5.8% respectively; the mean levels in those with clinical disease were significantly higher than those in healthy controls (2.0%). Methaemoglobinaemia > 10% was found in 5.4%, 16.7%, 12.5%, and 22.2% of those with UM, SA, CMCR and CMDS, respectively. In the presence of parasite sequestration, impaired tissue perfusion, and a reduction in oxygen carrying capacity of blood due to anaemia, a further reduction in oxygen carrying capacity from even a modest concentration of methaemoglobin is likely to exacerbate tissue hypoxia, perhaps critically so in a minority of anaemic and acidotic patients with severe falciparum malaria.

Antimalarials↗
PubMed2005

Competitive suppression in mixed-clone parasite cultures.

Mixed-genotype infections occur frequently in natural populations. Parasite genotypes are expected to interact within a host: competing for shared nutrients and being affected by the host's immune response to each other. Theoretically, competing parasites can be expected to exhibit increased rates of replication. Here, we investigate whether interactions between clones of Theileria annulata, a protozoan parasite of cattle, affect clones' replication rates in mixed cultures in vitro. Intrinsic replication rates and carrying capacities estimated from single-clone control cultures were used to predict replication rates of mixed cultures under different competitive assumptions. Mixed-culture dynamics deviated significantly from expectations in five out of six different clone combinations tested. Contrary to expectation, mixed cultures often replicated more slowly than predicted from single-clone control cultures. Competition coefficients were calculated from the mixed-culture data and a competitive hierarchy of clones determined. The results suggest that inherent competitive ability may be greater in clones with lower carrying capacities-those clones which would otherwise be excluded in a genetically diverse environment. Moreover, significant negative deviations from expected replication rates corresponded with successful out-competing of a higher carrying capacity clone by a lower carrying capacity clone.

Animals↗
PubMed2000

Comparing risk factors for population extinction.

Extinction risk of natural populations of animals and plants is enhanced by many different processes, including habitat size reduction and toxic chemical exposure. We develop a method to evaluate different risk factors in terms of the decrease in the mean extinction time. We choose a population model with logistic growth, environmental and demographic stochasticities with three parameters (intrinsic growth rate r, carrying capacity K, and environmental noise sigma(2)(e)). The reduction in the habitat size decreases carrying capacity K only, whilst toxic chemical exposure decreases survivorship (or fertility) and in effect reduces both r and K. We derived a formula for the reduction in habitat size that decrease the mean extinction time by the same magnitude as a given level of toxic chemical exposure. In a large population (large K) or in a slowly growing population (small r), a small decrease in survivorship can cause the extinction risk increase corresponding to a significant reduction in the habitat size. This conclusion depends also on the nonlinearity of dose-effect relationship. To illustrate the method, we analyse a freshwater fish, Japanese crucian carp (Carassius auratus subsp.) in Lake Biwa.

Animals↗
PubMed1999

Haemoglobin H+ equilibria in lamprey (Lampetra fluviatilis) and hagfish (Myxine glutinosa)

Agnathans, comprising lamprey and hagfish species, have been reported to be practically devoid of HCO3-/Cl- exchange across the red blood cell membrane. This suggests that the capacity of their haemoglobin (Hb) to remove H+ is essential for obtaining a high CO2-carrying capacity in the blood. Hydrogen ion titrations were performed on oxygenated and deoxygenated composite Hbs from river lamprey and from Atlantic hagfish at 15 degrees C and an ionic strength of 0.1 (0.1 mol l-1 KCl). Lamprey Hb was characterised by very low buffer values when the degree of oxygenation was constant, whereas the fixed-acid Haldane effect was large (uptake of approximately 0.9 H+ per monomer upon deoxygenation). Hagfish Hb, in contrast, had large buffer values and a moderate fixed-acid Haldane effect. In deoxygenated Hb, the low buffer values in lamprey correlated with the presence of only 1-1.5 titratable 'neutral' groups (normally histidines and &agr; -amino groups) per monomer, whereas there were 4-5 titratable 'neutral' groups per monomer in hagfish. The large differences in Hb/H+ equilibria between the two species reflect the early evolutionary divergence between lampreys and hagfish. With respect to CO2 transport, the special Hb/H+ equilibria and the high red blood cell pH in lamprey ensure a high concentration of free HCO3- inside the red cells in venous blood, which compensates for the absence of a shift of HCO3- to the plasma. The Hb/H+ equilibria in hagfish are less effective in ensuring a high CO2-carrying capacity given the virtual absence of a red blood cell HCO3-/Cl- exchange, and other adaptations may be involved.

Journal Article↗
PubMed1994

Host-host-pathogen models and microbial pest control: the effect of host self regulation.

A model has been investigated of the dynamics of the interaction between two hosts that are both attacked by a common pathogen with free-living infective stages, where the hosts are also subject to self-regulation. If either host interacted with the pathogen alone, two types of dynamics would be possible: an uninfected state where the host settles at its carrying capacity, and an infected state where the host settles at, or cycles around, a density lower than the carrying capacity. The three possible combination of two hosts have been investigated: uninfected-uninfected (both hosts uninfected if alone with the pathogen), infected-uninfected and infected-infected. A range of dynamics is generated, depending on parameter values, including infected co-existence of the two hosts (arrived at by a variety of routes), uninfected co-existence of the two hosts, exclusion of one host by the other which remains in an infected state, and a number of outcomes contingent on the initial densities in the system. Free-living infective stages make uninfected co-existence more likely and introduce additional contingency into the dynamics. The implications for microbial pest control are into the dynamics. The implications for microbial pest control are markedly different from those derived from related models without host self-regulation. There appears to be little chance of a non-target host undermining pest control, relatively little chance of the non-target enhancing pest control and a small but non-negligible threat to non-targets when parameter values are appropriate. The application of the results is commended but great caution is urged.

Animals↗
PubMed2004

Analysis of a predator-prey system with predator switching.

In this paper, we consider an interaction of prey and predator species where prey species have the ability of group defence. Thresholds, equilibria and stabilities are determined for the system of ordinary differential equations. Taking carrying capacity as a bifurcation parameter, it is shown that a Hopf bifurcation can occur implying that if the carrying capacity is made sufficiently large by enrichment of the environment, the model predicts the eventual extinction of the predator providing strong support for the so-called 'paradox of enrichment'.

Animals↗
PubMed2004

Unique tryptic peptides specific for bovine and human hemoglobin in the detection and confirmation of hemoglobin-based oxygen carriers.

Hemoglobin-based oxygen carriers (HBOCs) of bovine hemoglobin (Hb) or human Hb origin were developed for replacement or augmentation of blood during transfusion and have the potential to increase oxygen-carrying capacity of circulating blood and thus improve tissue oxygen delivery. Due to their potential for increasing oxygen-carrying capacity of circulating blood, they are excellent candidates for abuse in human and equine athletes. To deter athletes from blood doping with HBOCs such as Hemopure and Oxyglobin (OXY), a method for detection, confirmation, quantification, and distinguishing of HBOCs from native hemoglobin in test samples is needed. The purpose of this study was to identify unique peptides specific for bovine Hb and human Hb that are useful in the detection and confirmation of HBOCs in test samples. The LC-MS chromatographic peak profiles of tryptic digests from OXY, bovine Hb, human Hb, and equine Hb were compared, and unique tryptic peptides specific for bovine Hb, human Hb, and equine Hb were identified. The peptides specific for bovine Hb and OXY are related to bovine Hb alpha chain residues 69-90 and beta chain residues 40-58. The peptides specific for human Hb are related to human Hb alpha chain residues 63-91 and beta chain residues 42-60 and 68-83. The amino acid sequences of these unique tryptic peptides were confirmed by their characteristic MS/MS spectra. MS/MS spectra, b-ion series and y-ion series, and LC retention time of the tryptic peptides are essential pieces of information for the unequivocal identification, detection, and confirmation of HBOCs. The results of this study provide useful and defensible data on identification, detection, and confirmation of HBOCs of bovine Hb or human Hb origin. In addition, in-ESI-source fragmentation of tryptic peptides was observed in this study. The fragmentation was undesired since it decreased intensities of the trypic peptide ions, but it was helpful to elucidating sequences of the tryptic peptides thanks to the fragment peptide ions produced from the fragmentation.

Amino Acid Sequence↗
PubMed1987

Cardiorespiratory effects of exchange transfusions with synthetic erythrocytes in rats.

Synthetic erythrocytes (SE) can maintain life with near-normal hemodynamics in rats with hematocrits (Hct) 45% below the lethal levels, as shown when we exchanged virtually all their blood. We compared cardiorespiratory variables between the SE and control animals, which were hemodiluted with 7% albumin, at the 78% exchange level. In addition, SE animals at 92% exchange were compared with the 78% exchange and baseline levels. All our control rats died at Hct above 5% with corresponding oxygen-carrying capacity of 2.65 ml/dl. All SE rats survived, having a final Hct of 2.96% with an oxygen-carrying capacity of 7.05 ml/dl. SE animals maintained normal BP and marginally increased cardiac output, while control animals did not. Vascular resistance of control animals at 78% exchange was reduced to 30%, while in SE animals at 92% exchange, vascular resistance was lowered to 80% of baseline values.

Animals↗
PubMed2002

Industrial estate planning and management in India--an integrated approach towards industrial ecology.

Industrial estates (IE) are today perceived as an integral part of development strategies of many countries worldwide. The environmental impacts from a concentration of large number of industries in a small area or unplanned IE, can pose a serious threat to both local and global sustainable development initiatives. The formation of ecologically balanced industrial systems can result in numerous environmental and economic benefits. This paper examines the relevance of industrial symbiosis and carrying capacity concepts and proposes an integrated approach towards IE planning in India based on grouping combinations of industries based on carrying capacity, formation of green industrial townships, development of environmental impact assessment guidelines for IE and implementation of environmental management systems.

Conservation of Natural Resources↗
PubMed1988

Hemodynamic effects of exchange transfusions with liposome-encapsulated hemoglobin.

The ability of liposome-encapsulated hemoglobin (LEH) to sustain life in rats at hematocrits 45% below lethal levels was demonstrated by virtually total exchange transfusions. All control animals (transfused with 7% albumin in Erilyte) died at a mean hematocrit of 5.35%, with corresponding oxygen-carrying capacity of 2.65 ml/100 ml. All LEH animals survived with a final RBC hematocrit of 2.96% and an oxygen-carrying capacity of 7.05 ml/100 ml. LEH animals maintained normal blood pressures and essentially normal cardiac output, while control animals failed to do so. Systemic vascular resistance of control animals at 78% exchange was reduced to 33% of baseline, while of LEH animals at 92% exchange, to 80% of baseline. In-vitro measurements were made of LEH and RBC suspension viscosity as a function of shear rate, suspension concentration, and lipid membrane composition. The viscous behavior of the LEH suspensions was non-Newtonian and nearly the same as suspensions of natural RBC prepared similarly, though LEH suspensions had slightly higher viscosity.

Animals↗