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PubMed1996

Contrast discrimination at high contrasts reveals the influence of local light adaptation on contrast processing.

Previous measurements of contrast discrimination threshold, delta C, as a function of pedestal contrast, C, for sine-wave gratings have shown a power law relationship between delta C and C at suprathreshold levels of C. However, these studies have rarely used contrasts greater than 50%. Whittle (1986), using incremental and decremental patches, found that delta C increased with C only up to about 50%. At higher contrasts it decreased. Since a periodic stimulus can be considered to be composed of increments and decrements, we thought we might find such an inverse U-shaped function for gratings if we used contrasts up to 100%. We tested this for both sine-wave and square-wave stimuli at spatial frequencies from 0.0625 to 8.0 c/deg. We found that for frequencies up to 0.5 c/deg, delta C in nearly all cases 'dipped down' after about C = 50% contrast. At 4.0 and 8.0 c/deg, however, no dip-down occurred. Additional experiments showed that the dip-down was unlikely to be due to cortical long-term adaptation and most likely an effect of localized light adaptation to the dark bars. We argue that the absence of dip-down at high spatial frequencies was mainly due to the attenuation of contrast by the optics of the eye. As for the results of Whittle (1986), a Weber's Law in W = (Lmax-Lmin)/Lmin describes the inverse U-shaped contrast discrimination function well. Two other contrast expressions also linearize the data on log-log plots. We show how some familiar notions about the physiological operation of localized light adaptation can easily account for the form of the contrast discrimination function. Finally we estimate the number of discriminable steps in contrast from detection threshold to maximum contrast for the various spatial frequencies tested.

Adaptation, Ocular↗
PubMed1996

Hypothermic general cold adaptation induced by local cold acclimation.

To study relationships between local cold adaptation of the lower limbs and general cold adaptation, eight subjects were submitted both to a cold foot test (CFT, 5 degrees C water immersion, 5 min) and to a whole-body standard cold air test (SCAT, 1 degree C, 2 h, nude at rest) before and after a local cold acclimation (LCA) of the lower limbs effected by repeated cold water immersions. The LCA induced a local cold adaptation confirmed by higher skin temperatures of the lower limbs during CFT and a hypothermic insulative general cold adaptation (decreased rectal temperature and mean skin temperature P < 0.05) without a change either in metabolic heat production or in lower limb skin temperatures during SCAT after LCA. It was concluded that local cold adaptation was related to the habituation process confirmed by decreased plasma concentrations of noradrenaline (NA) during LCA (P < 0.05). However, the hypothermic insulative general cold adaptation was unrelated either to local cold adaptation or to the habituation process, because an increased NA during SCAT after LCA (P < 0.05) was observed but was rather related to a "T3 polar syndrome" occurring during LCA.

Acclimatization↗
PubMed1992

General and local cold adaptation after a ski journey in a severe arctic environment.

It is hypothesized that some of the variability in the conclusions of several human cold adaptation studies could be explained if not only were the changes in core and shell temperatures taken into account, before and after cold adaptation, but also the absolute temperatures and metabolic rate in both thermally neutral environments and in the cold. Such an approach was used in a group of volunteers before and after a ski journey (3 weeks at -20 to -30 degrees C) across Greenland. Eight subjects were submitted to cold tests (Tdb = 1 degree C, r.h. = 40%, wind speed = 0.8 m.s-1) for 2 hours. Thermoregulatory changes were also monitored in a neutral environment (Tdb = 30 degrees C). In the neutral environment, the arctic journey increased metabolic rate (11.2%; P less than 0.05) and mean skin temperature [Tsk: 33.5 (SEM 0.2) degrees C vs 32.9 (SEM 0.2) degrees C, P less than 0.05]. During the cold test, the arctic journey was associated with a lower final rectal temperature [36.8 (SEM 0.2) degrees C vs 37.3 (SEM 0.2) degrees C, P less than 0.01], a lower final Tsk [20.7 (SEM 0.4) degrees C vs 21.2 (SEM 0.3) degrees C, P less than 0.01] with no change in metabolic heat production. These observations are indicative of an hypothermic insulative isometabolic general cold adaptation, which was associated with a local cold adaptation of the extremities, as shown by warmer foot temperatures [12.3 (SEM 0.9) degrees C vs 9.8 (SEM 0.9) degrees C, P less than 0.001].

Adaptation, Physiological↗
PubMed2025

Experimental Validation of Genome-Environment Associations in Arabidopsis.

Identifying the genetic basis of local adaptation is a key goal in evolutionary biology. Allele frequency clines along environmental gradients, known as genotype-environment associations (GEA), are often used to detect potential loci causing local adaptation but are rarely followed by experimental validation. Here, we tested loci identified in three moisture-related GEA studies on Arabidopsis. We studied 42 GEA-identified genes using t-DNA knockout lines under drought and tested effects on flowering time, an adaptive trait, and genotype-by-environment (GxE) interactions for performance and fitness. In total, 16/42 genes had significant effects on traits involved in local adaptation or performance responses to the environment. We found that wrky38 mutants had significant GxE effects for fitness; lsd1 plants had a significant GxE effect for flowering time, and 11 genes showed flowering time effects with no drought interaction. However, most GEA candidates did not exhibit GxE. In the follow-up experiments, wrky38 caused decreased stomatal conductance and specific leaf area under drought, indicating potentially adaptive drought avoidance. Additionally, GEA identified natural putative LoF variants of WRKY38 associated with dry environments, as well as alleles associated with variation in LSD1 expression. While only a few GEA-identified genes were validated for GxE interactions for fitness, we likely overlooked some genes because experiments might not well represent natural environments and t-DNA insertions might not well represent natural alleles. Nevertheless, GEAs apparently identified some genes contributing to local adaptation. GEA and follow-up experiments are straightforward to implement in model systems and demonstrate prospects for GEA discovery of new local adaptations.

Arabidopsis↗
PubMed2001

Synchronization of single-side locally averaged adaptive coupling and its application to shock capturing.

We propose a single-sided locally averaged adaptive coupling scheme for the synchronization of spatially extended systems. Coupling and synchronization are analyzed from the viewpoint of image filter construction and numerical dissipation. Single-sided locally averaged coupling is introduced based on the resolution argument of control process. Control sensors are adaptively selected and automatically adjusted according to the magnitude of local oscillations. We demonstrate that the present scheme can effectively suppress and control spatiotemporal oscillations and, thus, provide a powerful approach for shock capturing. Both the Navier-Stokes equation and Burgers' equation are used to illustrate the idea.

Journal Article↗
PubMed2003

The importance of clinical practice guidelines (CPGs) for the quality and development of supportive care in Central and Eastern European (CEE) countries.

Supportive care CPGs are intended to improve the quality of supportive care received by cancer patients. They hold potential benefits for health-care professionals, health-care organizations and patients. In order to provide an effective influence of CPGs on supportive care development in CEE countries their validity and successful implementation in clinical practice must be ensured. This would involve several important steps: (1) achievement of a consensus across Europe about what constitutes supportive care in cancer; (2) identification of supportive care priorities in CEE countries to be covered by the guidelines; and (3) searching existing CPGs relevant to previously identified priorities. Valid international CPGs could then be translated and adapted to local resources and circumstances in CEE countries and used to prepare national supportive care CPGs which could assist in the development of national supportive care standards. Skills, expertise and additional investment are required for local adaptation, dissemination and implementation of international supportive care CPGs.

Clinical Competence↗
PubMed1996

Predatory behavior of jumping spiders.

Salticids, the largest family of spiders, have unique eyes, acute vision, and elaborate vision-mediated predatory behavior, which is more pronounced than in any other spider group. Diverse predatory strategies have evolved, including araneophagy, aggressive mimicry, myrmicophagy, and prey-specific prey-catching behavior. Salticids are also distinctive for development of behavioral flexibility, including conditional predatory strategies, the use of trial-and-error to solve predatory problems, and the undertaking of detours to reach prey. Predatory behavior of araneophagic salticids has undergone local adaptation to local prey, and there is evidence of predator-prey coevolution. Trade-offs between mating and predatory strategies appear to be important in ant-mimicking and araneophagic species.

Journal Article↗
PubMed2005

Population genetic structure and tolerance to dioxin-like compounds of a migratory marine fish (Menidia menidia) at polychlorinated biphenyl-contaminated and reference sites.

The present study was conducted to evaluate evidence of genetic adaptation to local contaminants in populations of the migratory marine fish Menidia menidia residing seasonally in reference sites or an industrial harbor contaminated with dioxin-like compounds (DLCs). For this purpose, we compared DLC sensitivity and genetic patterns of populations sampled from sites both inside and outside New Bedford Harbor (NBH; MA, USA), a U.S. Environmental Protection Agency Superfund site with extreme polychlorinated biphenyl (PCB) contamination. Offspring of M. menidia collected from NBH were significantly less sensitive regarding embryonic exposure to the dioxin-like PCB congener 3,3',4,4',5-pentachlorobiphenyl (PCB 126) than offspring of M. menidia from a reference site. Analysis of 10 polymorphic enzymatic loci indicated little genetic differentiation among populations in the study area. However, genotype frequencies of juveniles from both NBH and an adjacent site in Massachusetts exhibited significant deviations from Hardy-Weinberg equilibrium expectations at one locus, phosphoglucomutase (PGM*). Genetic analysis of survivors of embryonic laboratory exposure to PCB 126 indicated that genotypes at PGM* were related to survivorship. Although a relationship was identified between DLC tolerance and PGM* genotype, regional mixing of M. menidia populations during migration and absence of multigeneration exposure at contaminated sites may limit localized adaptation.

Adaptation, Physiological↗
PubMed1993

Evaluation of the home-based maternal record: a WHO collaborative study.

Thirteen centres in eight countries (Egypt, India, Pakistan, Philippines, Senegal, Sri Lanka, Democratic Yemen and Zambia) participated in the WHO collaborative study to evaluate the home-based maternal record (HBMR). The evaluation showed that use of the HBMR had a favourable impact on utilization of health care services and continuity of the health care of women during their reproductive period. When adapted to local risk conditions, their cut-off points and the available resources, the HBMR succeeded in promoting self-care by mothers and their families and in enhancing the timely identification of at-risk cases that needed referral and special care. The introduction of the HBMR increased the diagnosis and referral of at-risk pregnant women and newborn infants, improved family planning and health education, led to an increase in tetanus toxoid immunization, and provided a means of collecting health information in the community. The HBMR was liked by mothers, community health workers and other health care personnel because, by using it, the mothers became more involved in looking after their own health and that of their babies. Apart from local adaptation of the HBMR, the training and involvement of health personnel (including those at the second and tertiary levels) from the start of the HBMR scheme influenced its success in promoting maternal and child health care. It also improved the collection of community-based data and the linking of referral networks.

Continuity of Patient Care↗
PubMed1977

The interplay between peripheral and central factors in the adaptive response to exercise and training.

(1) Local adaptation of skeletal muscles (fibers) only occurs in the extremity involved in the training. (2) Work performance and maximal oxygen uptake were significantly increased only in the trained leg, and the "transfer" to the untrained leg was very small. (3) The classical sign of a training effect with a lowered submaximal heart rate response could only be elicited when exercising the trained leg. Lactate concentration and release of lactate were also lower when the trained leg performed the exercise. (4) The present results suggest that the local adaptation of skeletal muscle to training is of primary importance for enhancing work capacity and oxygen uptake. (5) The results also indicate that there may exist a peripheral factor in the regulation of the heart rate response during exercise. Moreover, the data favor the hypothesis of a chemical receptor playing a role in such a peripheral control system.

Adaptation, Physiological↗
PubMed2006

Proximate mechanisms causing morphological variation in a turban snail among different shores.

In many benthic organisms with a planktonic larval stage, local populations have different morphology. Such difference may arise from some of the following proximate mechanisms. "Local recruitment (LR)": no larvae move between local populations, and segregated populations possess alleles coding for locally adaptive morphology. "Intragenerational selection (IS)": larvae move between local populations, and individuals with alleles for locally adaptive morphology survive after recruitment. "Phenotypic plasticity (PP)": larvae move between local populations and show phenotypic plasticity to adapt to a locality after recruitment. We examined which mechanism explains our finding that a planktonic developer Turbo coronatus coronatus (Gastropoda) had significantly longer spines on its shell on more exposed shores at scales of < 2 km. Experiments at Ishigaki Island, Okinawa, Japan, showed the following results. (a) Shorter- and longer-spined populations occurring within 2 km showed non-significant low psi(ST) values (-0.0040 to 0.00095) for the mitochondrial DNA COI region. This suggests no segregation of the local populations, supporting the mechanisms IS and PP. (b) T. c. coronatus generated significantly longer spines 70 days after being transplanted to the habitat of a longer-spined population, supporting IS and PP. (c) Individuals caged in the sea for 79 days generated longer spines than individuals in the laboratory, supporting PP. In conclusion, shore-specific morphology of T. c. coronatus arises most likely from phenotypic plasticity and possibly from intragenerational selection.

Animals↗
PubMed2000

Spatial and temporal properties of light adaptation in the rod system.

Little is known about the mechanism that regulates the sensitivity of rod system at its normal operating light levels. Two experiments are reported in this paper. First, we searched for nonlinear distortion products in rod vision that could be generated from any local adaptation process, using a sensitive experimental procedure that has demonstrated local adaptation in cone vision. No local adaptation was evident in the rod system, even at near saturating light levels. Second, to investigate the dynamics of light adaptation in the rod system we presented a uniform flickering background, sinusoidally modulated in time, and measured increment thresholds for brief test flashes that were superimposed on this background at different times during the sinusoidal flicker cycle. At frequencies less than 5-6 Hz, the rod increment threshold follows the background modulation, with a slight phase advance. When the background is modulated faster than 5-6 Hz, the increment threshold remains the same regardless of when the test flash occurred during the background cycle. Thus the rod system sensitivity, unlike that of the cone system, can only change slowly, and is set by a space-integrated signal rather than independently for different rods.

Adaptation, Ocular↗
PubMed2002

Plasticity of the vertical VOR: a system identification approach to localizing the adaptive sites.

The vestibulo-ocular reflex (VOR) stabilizes the visual image on the retina during head movement by counter-rotating the eyes in the head. The VOR is under adaptive control and has been extensively used to investigate sensorimotor transformations and motor learning. The cerebellar flocculus (FL) is intimately involved in VOR motor control and learning, because its sole output, the Purkinje cell firing pattern, modulates during visual-vestibular interaction paradigms that induce motor learning, and flocculectomy impairs the ability to modify the VOR. However, the role of the FL in VOR motor learning and the possibility of another neuronal site responsible for learning have been controversial. Currently, we performed single unit recordings of FL Purkinje cells during adaptation of the vertical (V) VOR in squirrel monkeys and used a system identification approach to localize the adaptable neuronal sites responsible for VVOR motor learning. We demonstrated that there are multiple adaptive sites: one upstream or in the FL, another in the non-FL pathway; change in the former site is in the wrong direction to cause the observed VVOR gain change, whereas that in the latter site is in the correct direction. The possibility that FL Purkinje cells convey an error signal to their target neurons that can be used to aid learning is discussed.

Adaptation, Physiological↗
PubMed2004

Allee effects, immigration, and the evolution of species' niches.

Theoretical studies of adaptation to sink environments (with conditions outside the niche requirements of a species) have shown that immigration from source habitats can either facilitate or inhibit local adaptation. Here, we examine the influence of immigration on the evolution of local adaptation, given an Allee effect (i.e., at low densities, absolute fitness increases with population density). We consider a deterministic model for evolution at a haploid locus, and a stochastic individual-based model for evolution of a quantitative trait, and several kinds of Allee effects. We demonstrate that increased immigration can greatly facilitate adaptive evolution in the sink; with greater immigration, local population sizes rise, and because of the Allee effect, there is a positive indirect effect of immigration on local fitness. This makes it easier for alleles of modest effect to be captured by natural selection, transforming the sink into a locally adapted population that can persist without immigration.

Adaptation, Biological↗
PubMed2026

Rapid and exceptionally small-scale adaptation of the alpine plant Cardamine resedifolia to mining-contaminated soils in multi-stress condition.

The mechanisms by which plants tolerate soil contamination have been studied in details in controlled laboratory conditions, but they still remain largely unexplored in natural conditions where mixtures of contaminants are present in soils and their effects might interact with other environmental variables. This is especially true in high-altitude alpine environments, where abiotic stress is naturally heightened, but which so far have received little attention in environmental pollution studies. As we were interested in the tolerance mechanisms at play on very fine spatiotemporal scales for alpine plants growing under multi-stress conditions, we chose Cardamine resedifolia as our biological model. This plant is indeed frequently found in areas contaminated by Trace Metals and Metalloids and Polycyclic Aromatic Hydrocarbons in high elevation. We studied populations from former copper, silver-lead, and coal mines in alpine environments, along with populations growing on nearby reference soils. We measured genetic variability within populations as well as genetic differentiation between them, and tested for local adaptation to soil contamination using reciprocal transplants. Population pairs showing signs of local adaptation were then examined using genome scans to identify genes potentially under selection. We found high levels of genetic differentiation between populations growing on contaminated and reference soils a few dozen meters apart. In most cases local adaptation was detected, especially in former copper mines. Genome scans identified genes involved in metal stress management as potentially being under selection. This study provides evidence for rapid adaptation to human-induced pollution in alpine plants at remarkably small spatial scales. It offers new insights into the short-term ecological and evolutionary consequences of mining activities in alpine ecosystems, particularly in relation to substrate-driven differentiation.

Alpine plants↗
PubMed2005

Maternal effects provide phenotypic adaptation to local environmental conditions.

In outcrossing plants, seed dispersal distance is often less than pollen movement. If the scale of environmental heterogeneity within a population is greater than typical seed dispersal distances but less than pollen movement, an individual's environment will be similar to that of its mother but not necessarily its father. Under these conditions, environmental maternal effects may evolve as a source of adaptive plasticity between generations, enhancing offspring fitness in the environment that they are likely to experience. This idea is illustrated using Campanula americana, an herb that grows in understory and light-gap habitats. Estimates of seed dispersal suggest that offspring typically experience the same light environment as their mother. In a field experiment testing the effect of open vs understory maternal light environments, maternal light directly influenced offspring germination rate and season, and indirectly affected germination season by altering maternal flowering time. Results to date indicate that these maternal effects are adaptive; further experimental tests are ongoing. Evaluating maternal environmental effects in an ecological context demonstrates that they may provide phenotypic adaptation to local environmental conditions.

Adaptation, Physiological↗
PubMed2005

Disturbance induces the contrasting evolution of reinforcement and dispersiveness in directed and random movers.

Spatial models commonly assume that dispersal rates are constant across individuals and environments and that movement directions are unbiased. These random-movement assumptions are inadequate to capture the range of dispersal behaviors revealed in diverse case studies. We examine an alternative assumption of directed movement, in which dispersal is a conditional and directional response by individuals to varying environmental conditions. Specifically, we assume individuals bias their movements to climb spatial fitness gradients. We compare the consequences of random and directed movement for local adaptation, the evolution of dispersal, and the reinforcement process. The implications of each movement strategy depend on the nature of environmental disturbance, and we examine the outcomes for undisturbed environments and with uncorrelated and autocorrelated disturbances. Both movement strategies offer advantages over sedentary life histories by allowing colonization of suitable habitats. However, random movement eventually becomes costly in stable environments because it inhibits local adaptation. In contrast, directed movement accelerates local adaptation. In disturbed environments, random movement offers bet-spreading advantages by distributing offspring across habitats. Despite being a more targeted strategy, an intermediate amount of directed movement provides similar bet-spreading benefits. These fitness consequences have implications for the evolution of dispersal. Dispersiveness is lost by random movers in undisturbed environments, is maintained in polymorphism with infrequent disturbances, and evolves when disturbances are uncorrelated. Directed movement becomes selectively neutral in the absence of disturbance, evolves when disturbances are autocorrelated, and is maintained in polymorphism with uncorrelated disturbances. Disturbance also determines the outcome of the reinforcement process for each strategy. For example, directed movers show no progress toward reinforcement in undisturbed environments, evolve random mating with uncorrelated disturbances, and can evolve assortative mating in infrequently disturbed environments.

Animals↗