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At least 199 records · Page 11Linked to original sources
PubMed2005

Local adaptation and enhanced virulence of Nosema granulosis artificially introduced into novel populations of its crustacean host, Gammarus duebeni.

Local adaptation theory predicts that, on average, most parasite species should be locally adapted to their hosts (more suited to hosts from local than distant populations). Local adaptation has been studied for many horizontally transmitted parasites, however, vertically transmitted parasites have received little attention. Here we present the first study of local adaptation in an animal/parasite system where the parasite is vertically transmitted. We investigate local adaptation and patterns of virulence in a crustacean host infected with the vertically transmitted microsporidian Nosema granulosis. Nosema granulosis is vertically transmitted to successive generations of its crustacean host, Gammarus duebeni and infects up to 46% of adult females in natural populations. We investigate local adaptation using artificial horizontal infection of different host populations in the UK. Parasites were artificially inoculated from a donor population into recipient hosts from the sympatric population and into hosts from three allopatric populations in the UK. The parasite was successfully established in hosts from all populations regardless of location, infecting 45% of the recipients. Nosema granulosis was vertically (transovarially) transmitted to 39% of the offspring of artificially infected females. Parasite burden (intensity of infection) in developing embryos differed significantly between host populations and was an order of magnitude higher in the sympatric population, suggesting some degree of host population specificity with the parasite adapted to its local host population. In contrast with natural infections, artificial infection with the parasite resulted in substantial virulence, with reduced host fecundity (24%) and survival (44%) of infected hosts from all the populations regardless of location. We discuss our findings in relation to theories of local adaptation and parasite-host coevolution.

Adaptation, Physiological↗
PubMedDate not supplied

Spike-frequency adaptation of a generalized leaky integrate-and-fire model neuron.

Although spike-frequency adaptation is a commonly observed property of neurons, its functional implications are still poorly understood. In this work, using a leaky integrate-and-fire neural model that includes a Ca2+-activated K+ current (IAHP), we develop a quantitative theory of adaptation temporal dynamics and compare our results with recent in vivo intracellular recordings from pyramidal cells in the cat visual cortex. Experimentally testable relations between the degree and the time constant of spike-frequency adaptation are predicted. We also contrast the IAHP model with an alternative adaptation model based on a dynamical firing threshold. Possible roles of adaptation in temporal computation are explored, as a a time-delayed neuronal self-inhibition mechanism. Our results include the following: (1) given the same firing rate, the variability of interspike intervals (ISIs) is either reduced or enhanced by adaptation, depending on whether the IAHP dynamics is fast or slow compared with the mean ISI in the output spike train; (2) when the inputs are Poisson-distributed (uncorrelated), adaptation generates temporal anticorrelation between ISIs, we suggest that measurement of this negative correlation provides a probe to assess the strength of IAHP in vivo; (3) the forward masking effect produced by the slow dynamics of IAHP is nonlinear and effective at selecting the strongest input among competing sources of input signals.

Action Potentials↗
PubMed2006

Hot limpets: predicting body temperature in a conductance-mediated thermal system.

Living at the interface between the marine and terrestrial environments, intertidal organisms may serve as a bellwether for environmental change and a test of our ability to predict its biological consequences. However, current models do not allow us to predict the body temperature of intertidal organisms whose heat budgets are strongly affected by conduction to and from the substratum. Here, we propose a simple heat-budget model of one such animal, the limpet Lottia gigantea, and test the model against measurements made in the field. Working solely from easily measured physical and meteorological inputs, the model predicts the daily maximal body temperatures of live limpets within a fraction of a degree, suggesting that it may be a useful tool for exploring the thermal biology of limpets and for predicting effects of climate change. The model can easily be adapted to predict the temperatures of chitons, acorn barnacles, keyhole limpets, and encrusting animals and plants.

Acclimatization↗
PubMed1992

Design of intramedullary prostheses to prevent bone loss: predictions based on damage-stimulated remodelling.

The adaptation of bone around intramedullary fixated prostheses, such as the femoral component of the hip joint or the radial component of the elbow joint, is well documented in follow-up studies. Bone adaptation takes the form of proximal bone atrophy accompanied, in some cases, by distal bone hypertrophy. A mechanistic model has been formulated to predict bone adaptation based on the concept that the continuous processes of damage and repair regulate bone adaptation. We apply the model to investigate the significance of two features of intramedullary prosthesis design on bone adaptation: prosthesis Young's modulus and the presence of a prosthesis collar. Results, as well, as indicating some characteristics of accumulative-damage stimulated bone adaptation, predict that a low Young's modules stem will very much reduce the extent of bone loss whereas the presence of a collar will have no significant effect. The results predict that a collarless low stiffness prosthesis is one possible approach for improving the secondary stability of intramedullary-fixated orthopaedic implants.

Adaptation, Physiological↗
PubMed1981

Adaptive Behavior Scale, Part Two: predictive efficiency of severity and frequency scores.

Severity and frequency of occurrence methods of scoring the Adaptive Behavior Scale, Part Two, were compared using ratings for seven groups of mentally retarded persons. Comparisons involved separately correlating the two methods with independently obtained clinical impressions of symptomatology. The severity scoring system predicted approximately 11 percent more of the variance in the criterion than did frequency scores. These results provide considerable construct and predictive validity for the severity scoring system.

Adolescent↗
PubMed1976

Computer assisted prescribing of drugs.

Computer programs for drug dosage adjustment may be fixed, adaptive or empirical. The aminoglycoside antibiotic dosage requirements of individual patients are relatively predictable, and it seems to be adequate to assume that volume of distribution is a fixed proportion of body weight and that renal clearance is a fixed proportion of creatinine clearance. This approach has been less successful with digoxin because patient compliance, the proportion absorbed and liver clearance are not yet predictable. Accordingly, adaptive programs have been developed which use feedback from drug concentration measurements to predict the future dosage needs of the patient. When individual needs are known for a large patient group it becomes possible to predict the dosage requirements of a new patient from the same population by empirical methods. Computer programs for dosage adjustment will not be widely used until their scope is increased and objective evidence of clinical benefit is obtained.

Bayes Theorem↗
PubMed2004

Multigrid approach to predictive wave-front reconstruction in adaptive optical systems.

A computationally efficient approach, based on the principles of multigrid methods, to predictive wave-front reconstruction in adaptive optical systems is described. Local predictive estimators are computed by use of recursive least squares on multiple grids. Each grid is increasingly coarse, allowing for temporal prediction of the behavior of both high- and low-spatial-frequency aberrations. Example numerical simulation results are given, showing that implementing the recursive least-squares algorithm for predictive estimation in a multigrid fashion greatly accelerates convergence to the steady-state optimal estimator condition. By implementation of the multigrid predictive reconstructor in parallel, the computational cost of implementing a predictive wave-front reconstruction scheme that uses recursive least squares for each processor at each cycle can be reduced from [symbol: see text](m2) to [symbol: see text](2m), where m is the number of actuators.

Journal Article↗
PubMed2001

Prism adaptation response is useful for predicting surgical outcome in selected types of intermittent exotropia.

PURPOSE: To evaluate the prevalence of prism adaptation response in Japanese patients with intermittent exotropia (X [T]) using the prism adaptation test and to assess whether patients with selected types of X [T] benefit from surgical outcome to which prism adaptation response may contribute. METHODS: In a prospective study, 128 consecutive patients with X [T] between 1990 and 1995 were enrolled. The prism adaptation test was conducted by neutralizing the angle of deviation for 2 to 3 hours. Patients who showed an increase in exodeviation by 10triangle up or more with the prism adaptation test were defined as having a prism adaptation response. For classification of the pattern of X [T], we chose a value of 15triangle up as the difference between the distance and near measurements. RESULTS: The percentage of patients in whom the prism adaptation response was observed at near fixation was significantly larger than those at distance fixation [35 (27%) patients versus 10 (8%) patients, P <.05]. Of 35 patients shown to have a prism adaptation response at near fixation, 21 patients (83%) had the basic type of exotropia. Fourteen patients (17%) with the basic type were changed to convergence insufficiency type because of an increase in near deviation and were defined as pseudo basic type. Patients with pseudo basic type had a significantly better surgical outcome compared with that of true basic type, whereas in the convergence insufficiency type, no definite tendency was found between the two subtypes, true and pseudo types. CONCLUSION: Patients with the pseudo basic type of X [T] in whom a prism adaptation response was demonstrated had a more favorable surgical outcome.

Adaptation, Ocular↗
PubMed2000

Sperm competition games played by dimorphic male beetles: fertilization gains with equal mating access.

Alternative mating tactics can generate asymmetry in the sperm competition risk between males within species. Theory predicts that adaptations to sperm competition should arise in males facing the greater risk. This prediction is met in the dung beetle Onthophagus binodis where minor males which sneak copulations have a greater expenditure on the ejaculate. In its congener Onthophagus taurus there is a reduced asymmetry in sperm competition risk such that both tactics have equal ejaculate expenditure. We used the irradiated male technique to test whether adaptations to sperm competition in minor males result in higher paternity. We found that for both species, on average, each of two males gained equal numbers of fertilizations, confirming the assumption that sperm compete in a raffle. There were no differences in the sperm competition success of major and minor males in O. taurus as predicted from their equal expenditure on their ejaculate. Contrary to expectations, there were also no differences in fertilization success between the male tactics in O. binodis. Thus, in O. binodis minor males must expend more on their ejaculate in order to obtain the same fertilization gains as major males.

Animals↗
PubMed1993

Rethinking Oedipus: an evolutionary perspective of incest avoidance.

The author presents a biological hypothesis of incest avoidance. Pertinent literature from evolutionary biology, ethology, anthropology, and clinical research is reviewed. Secure early bonding to immediate kin predicts later adaptive kin-directed behaviors, including preferential altruism (kin selection) and incest avoidance. Impaired bonding predicts aberrant kin-directed behavior, including diminished altruism, neglect, and an increased incidence of incest. Failed bonding predicts the highest frequency of incest. Secure bonding to kin may function to establish adaptive kin-directed behaviors, including incest avoidance. Bonding is conceived of as the developmental foundation of a form of social attraction, here called "familial attraction," which is evolutionarily distinct from sexual attraction.

Altruism↗
PubMed1995

The role of maternal factors in the adaptation of children with craniofacial disfigurement.

This study hypothesized that maternal adjustment, perceptions, and social support would better predict child adaptation to craniofacial disfigurement than medical severity. Mothers of 77 children (ages 6-12) completed the Child Behavior Checklist, Beck Depression Inventory, Spielberger Trait Anxiety Scale, Social Support Questionnaire Revised, and Parenting Stress Index. Medical severity was assessed by the number of operations (craniofacial and other), comorbid medical conditions, and the Hay Attractiveness Scale. The children and mothers in our sample resembled a normal population in terms of their psychological functioning and quality of the mother-child relationships. Maternal adjustment and maternal perceptions of the mother-child relationship were more potent predictors of children's emotional adjustment than either medical severity or maternal social support.

Adaptation, Psychological↗
PubMed2000

Sexual expression following spinal cord injury.

Sexual adjustment, defined within this study as post-injury sexual views of the self, among 109 men and 86 women with spinal cord injury (SCI) was explored through cognitive adaptation theory [30]. It was predicted that cognitive adaptation constructs (i.e., personal control, optimism, meaning, and self-esteem) and sexual self-esteem would be predictive of sexual adjustment. It was also hypothesized that sexual self-esteem would be predictive of sexual adjustment over and above cognitive adaptation constructs. A series of hierarchical regression models were performed with results being consistent with proposed hypotheses. Implications for rehabilitation professionals are discussed and clinical suggestions are provided.

Journal Article↗
PubMedDate not supplied

Handicap-related problems in mothers of children with physical impairments.

An inventory was developed for the measurement of handicap-related problems experienced by mothers of children with chronic physical conditions and an initial evaluation of its psychometric properties was completed in a sample of 119 mothers of children with physical or sensory impairments. Principal component analysis of the Handicap-related Problems for Parents Inventory (HPPI) yielded three subscales, which accounted for 54% of the total variance. The HPPI demonstrated excellent internal consistency for each scale and total score. It also generally had good test-retest reliability over 6-, 12-, and 18-month periods. There was minimal covariation between HPPI scores and demographic status. Concurrent validity was demonstrated by significant correlations between appropriate HPPI scales and measures of daily stress and the child's physical condition or disability status. Support for its construct validity was obtained when expected convergent and discriminant relationships were confirmed between HPPI scales and measures of maternal adaptation, maternal social support, and child behavior problems. Among other results, HPPI scores predicted maternal adaptation 18 months later. The potential uses of the HPPI in research and intervention with mothers of children with chronic physical conditions were discussed.

Adaptation, Psychological↗
PubMedDate not supplied

Thermoregulatory consequences of cardiovascular impairment during NMR imaging in warm/humid environments.

A simple model of physiological thermoregulation, previously adapted to predict the thermoregulatory consequences of exposure to the nuclear magnetic resonance (NMR) imaging environment, has been further adapted to simulate impaired cardiovascular function. Restrictions on the rate of skin blood flow (SkBF), ranging from 0 to 89% of normal, were studied. Predictions of physiological heat loss responses in real time were generated as a function of ambient temperature (Ta), relative humidity (RH) and rate of whole-body radiofrequency (RF) energy deposition (SAR). Under conditions that are desirable in the clinic (Ta = 20 degrees C, 50% RH, still air), moderate restrictions (up to 67%) of SkBF yield tolerable increases in core temperature (delta Tco less than or equal to 1 degree C) during NMR exposures (SAR less than or equal to 4 W/kg) of 40 min or less. Increased Ta and RH exacerbate the thermal stress imposed by absorbed RF energy; severely impaired SkBF encourages short NMR exposures (e.g., 20 min or less) at SARs less than or equal to 3 W/kg. In warm/humid environments, sweating is predicted to be profuse and evaporative cooling curtailed, yielding a state of extreme thermal discomfort. Added insulation (e.g., a blanket) is discouraged. Some guidelines, incorporating SkBF restrictions, Ta, RH, and insulation, are offered for the prediction of tolerable NMR exposure conditions.

Body Temperature Regulation↗
PubMed1997

Relationship of family schema to family adaptation to brain injury.

The relationship between family schema and family adaptation to brain injury was investigated. Participants were 87 primary caregivers of persons with brain injuries in Wisconsin who are part of a comprehensive, longitudinal study of family adaptation to having a member with a brain injury. Stepwise multiple regression of variables measuring family schema on family adaptation indicated that manageability and meaningfulness were predictive of family adaptation. Thus the hypothesis that family adaptation can be predicted from variables measuring family schema was supported. Family intervention and research implications are discussed.

Adaptation, Psychological↗
PubMed1995

A model of excitation and adaptation in bacterial chemotaxis.

We present a model of the chemotactic mechanism of Escherichia coli that exhibits both initial excitation and eventual complete adaptation to any and all levels of stimulus ("exact" adaptation). In setting up the reaction network, we use only known interactions and experimentally determined cytosolic concentrations. Whenever possible, rate coefficients are first assigned experimentally measured values; second, we permit some variation in these rate coefficients by using a multiple-well optimization technique and incremental adjustment to obtain values that are sufficient to engender initial response to stimuli (excitation) and an eventual return of behavior to baseline (adaptation). The predictions of the model are similar to the observed behavior of wild-type bacteria in regard to the time scale of excitation in the presence of both attractant and repellent. The model predicts a weaker response to attractant than that observed experimentally, and the time scale of adaptation does not depend as strongly upon stimulant concentration as does that for wild-type bacteria. The mechanism responsible for long-term adaptation is local rather than global: on addition of a repellent or attractant, the receptor types not sensitive to that attractant or repellent do not change their average methylation level in the long term, although transient changes do occur. By carrying out a phenomenological simulation of bacterial chemotaxis, we find that the model is insufficiently sensitive to effect taxis in a gradient of attractant. However, by arbitrarily increasing the sensitivity of the motor to the tumble effector (phosphorylated CheY), we can obtain chemotactic behavior.

Adaptation, Biological↗
PubMed2004

A mathematical analysis for the cardiovascular control adaptations in chronic renal failure.

A model of baroreflex control of blood pressure (BP) is proposed in terms of a delay differential equation and this is used to predict the adaptation of short-term cardiovascular control in chronic renal failure (CRF) patients. Cardiac pump dynamics are explored by means of plots of blood flow vs. mean BP. The parameters of the model were determined from available data and from a sensitivity analysis. The model predicts stable and unstable equilibria close to the steady BP. It is shown that the unstable equilibrium point generates a quasiperiodic solution with two main harmonics for healthy subjects. We also show that the parameters for CRF patients predict solutions whose spectra exhibit a small high frequency component. This is due to the coalescence of the equilibrium points. The heart rate variability (HRV) time series and power spectra from healthy volunteers and CRF patients were compared with the model predictions. As an adequate measure of the sympathovagal balance we use the LF/HF index obtained from the power spectrum. The model allows the interpretation of the variability of the LF/HF index in terms of a specific set of cardiovascular parameters which are known to change from healthy to CRF patients. Comparisons of the changes in the LF/HF index predicted by the model are in agreement with actual observations for both the healthy and the CRF patients. These results show that the cardiac pump has a more restricted response in CRF patients. The model quantifies the cardiovascular adaptations to the CRF condition in terms of increased peripheral resistance and baroreflex delay and decreased arterial compliance, cardiac period, and stroke volume.

Adaptation, Physiological↗
PubMed1994

A model of calcium dynamics in cardiac myocytes based on the kinetics of ryanodine-sensitive calcium channels.

The ryanodine-sensitive calcium channels are pivotal to signal transduction and cell function in many cell types, including cardiac myocytes. In this paper a kinetic model is proposed for these channels. In the model there are two Ca regulatory sites on the channel protein, one positive and the other negative. Cytoplasmic Ca binds to these regulatory sites independently It is assumed that the binding of Ca to the positive site is a much faster process than binding to the negative site. At steady state, the channel opening as a function of the Ca concentration is a bell-shaped curve. The model predicts the adaptation of channels to constant Ca stimulus. When this model is applied to cardiac myocytes, it predicts excitability with respect to Ca perturbations, smoothly graded responses, and Ca oscillations in certain pathological circumstances. In a spatially distributed system, traveling Ca waves in individual myocytes exist under certain conditions. This model can also be applied to other systems where the ryanodine-sensitive channels have been identified.

Adaptation, Physiological↗