[Local adaptation].
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Adaptation, Ocular↗
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Local adaptation to intermittent light as a function of frequency and eccentricity.
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Adaptation, Ocular↗
[Utilization of color stimuli in the study of early local adaptation (preliminary note)].
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Adaptation, Ocular↗
[Vaccination of health personnel against hepatitis B. Local adaptation based on recommendations by the National Board of Health and Welfare].
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Health Personnel↗
Towards a molecular characterization of adaptation in local populations.
Adaptation of local populations to their environment is central to our understanding of biodiversity and processes of speciation; nevertheless, the genetic changes that are required for such local adaptations are understood poorly. Recent studies have shown that multilocus scans that compare different populations for several loci can identify genomic regions carrying a mutation that results in a local adaptation.
Adaptation, Biological↗
Adaptive divergence vs. environmental plasticity: tracing local genetic adaptation of metamorphosis traits in salamanders.
In order to assess the significance of local adaptation relative to environmental plasticity on the evolution of life history traits, we analysed the possible genetic basis of differences between pond- and stream-breeding fire salamanders (Salamandra salamandra) in Germany. These salamanders typically deposit their larvae in small streams, where they grow until they are sufficiently large to metamorphose. However, some populations in Western Germany use ponds as larval habitat. Because habitat quality of streams differs from that of ponds one expects life history differences in the pond animals, which may result either from a plastic response or through genetic differentiation (i.e. local adaptation). Using a phylogeographical analysis of mitochondrial D-loop sequences, we show that both stream and pond populations in Western Germany are derived from a single lineage that recolonized following the last glaciation. This finding suggests that pond breeding originated very recently. Our studies of habitat quality and metamorphic behaviour of larvae in natural ponds and streams disclosed that pond larvae experience a significantly reduced food supply and greater risk of drying than do stream larvae. Pond larvae metamorphose earlier at the cost of reduced mass. Common-environment experiments with pond and stream larvae show that metamorphic behaviour of pond larvae under limited-food conditions is determined genetically and is not simply a plastic response to the differing habitat conditions. These results show that phenotypic plasticity is less important than local adaptation in explaining differences in ecological diversification within this species and suggests the possibility of rapid evolution of genetic adaptations when new habitats are exploited.
Adaptation, Physiological↗
Psychophysical signatures associated with magnocellular and parvocellular pathway contrast gain.
Physiological data have revealed characteristic contrast gain and temporal integration signatures of the magnocellular (MC) and the parvocellular (PC) pathways. The goal in this study was to find psychophysical correlates of these signatures. Psychophysical forced-choice, luminance pedestal discrimination data were collected with a stimulus-surround display. A 2.05 degrees four-square stimulus array was varied from 73 to 182 trolands (Td) in a larger 115-Td surround. When the stimulus array was pulsed briefly, discrimination thresholds showed a minimum at the surround retinal illuminance, increasing in a V shape when the stimulus array was incremental or decremental to the surround. When the stimulus array was presented continuously as a steady pedestal within the constant 115-Td surround, discrimination thresholds increased monotonically with stimulus array retinal illuminance, obeying a slope of unity. Exposure duration variation showed temporal summation to extend to longer durations for the pulse increments and decrements than for the steady pedestal condition. Discrimination thresholds for pulsed medium-sized contrast steps showed the contrast pedestal paradigm showed the temporal signature of the MC pathway. Discrimination thresholds for small pedestal steps of the stimulus array from a steady pedestal showed the contrast gain signature of the MC pathway. The data suggested a difference in the spatiotemporal control of adaptation of the two pathways: The MC pathway adapted locally to the stimulus array, while the PC pathways showed little evidence of local adaptation. The experiments show that characteristic signatures of MC- and PC-pathway processing can be demonstrated by use of psychophysical procedures.
Adaptation, Physiological↗
Adapting a national guideline for local use: a comparative case study in a US and an Israeli health maintenance organization.
OBJECTIVES: We compared the way a US and an Israeli health maintenance organization (HMO) used the Fifth Report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (the JNC-V) in developing a hypertension guideline. METHODS: Comparative case study. We describe and contrast the two HMOs, the social contexts in which they function, their motivations for creating a local guideline and their guideline development processes. We then compare the two HMO guidelines with each other and with the JNC-V. Based on this analysis, we offer provisional answers to some key concerns raised by local adaptations of national or international guidelines. These include whether adaptations will reflect local cost-containment concerns in ways that could threaten quality of care, whether guidelines constitute a threat to physician autonomy and the relationship between local adaptations and the evolution of national or international guidelines. RESULTS: The HMO guidelines differed substantially, and in similar ways, from the JNC-V in format, coverage and emphasis of topics. They differed from it minimally, but also in similar ways, in the content of their recommendations. Each HMO guideline 'improvised' on the JNC-V in ways that differed to reflect local needs and objectives but did not significantly distort the original. Quality of care considerations appeared to predominate over cost considerations, and we found no evidence that guidelines threatened physician autonomy. CONCLUSIONS: Local adaptations may function as part of the iterative process through which national or international guidelines evolve in ways more suitable for potential local use.
Evidence-Based Medicine↗
Host range and local parasite adaptation.
Parasites may be expected to become locally adapted to their hosts. However, while many empirical studies have demonstrated local parasite adaptation, others have failed to demonstrate it, or have shown local parasite maladaptation. Researchers have suggested that gene flow can swamp local parasite-host dynamics and produce local adaptation only at certain geographical scales; others have argued that evolutionary lags can account for both null and maladaptive results. In this paper, we use item response theory (IRT) to test whether host range influences the likelihood of parasites locally adapting to their hosts. We collated 32 independent experiments testing for local adaptation, where parasites could be assigned as having either broad or narrow host ranges (BHR and NHR, respectively). Twenty-five tests based on BHR parasites had a significantly lower average effect size than seven NHR tests, indicating that studies based on BHR parasites are less likely to demonstrate local parasite adaptation. We argue that this may relate to evolutionary lags during diffuse coevolution of BHR parasites with their hosts, rather than differences in experimental approaches or other confounds between BHR and NHR studies.
Adaptation, Physiological↗
Facilitatory and inhibitory after-effect of spatially localized grating adaptation.
Aftereffects of spatially localized grating adaptation were measured for different locations of the adaptation grating relative to test grating. When the adaptation grating was located on or near the retinal area occupied by the test grating, contrast sensitivity was markedly reduced. When the adaptation grating was spatially separated from the test grating, contrast sensitivity was significantly increased. This aftereffect of spatially localized grating adaptation suggests that spatial-frequency-selective detectors are not spatially independent, but tonically inhibited by spatially contiguous mechanisms. Thus the adaptation of these mechanisms might cause an increase in contrast sensitivity of detectors subserving the test grating.
Adaptation, Ocular↗
Effect of localized grating adaptation as a function of separation along the length axis between test and adaptation areas.
Aftereffect following adaptation to localized gratings was measured as a function of the separation along the length axis between test and adaptation gratings. When the adaptation gratings were located on or near the retinal area occupied by the test grating, contrast sensitivity greatly decreased. When the adaptation gratings were spatially separated from the test grating, contrast sensitivity significantly increased. This property is similar to that which was observed in our previous study, in which the adaptation gratings were displaced from a test grating along the modulation axis. The facilitatory aftereffect of the grating adaptation can be accounted for by assuming that there may exist two mechanisms involved in the adaptation process; one is a center mechanism responsible for the detection of a test pattern, its adaptation producing a reduction in responsiveness; the other is a surround mechanism which tonically inhibits the center mechanism, its adaptation resulting in an increase in the sensitivity of the center mechanism by releasing the tonic inhibition. The spatial property of the adaptation effect may reflect the nature of spatial integration process of the center and surround mechanism.
Adaptation, Ocular↗
Parasite adaptation to locally common host genotypes.
According to the Red Queen hypothesis--which states that interactions among species (such as hosts and parasites) lead to constant natural selection for adaptation and counter-adaptation--the disproportionate evolutionary success of parasites on common host genotypes leads to correlated selection for sexual reproduction and local adaptation by the parasite population. Here we determined whether local adaptation is due to disproportionate infection of common host genotypes, and, if so, whether infection of common host genotypes is due to commonness per se, or some other aspect of these genotypes. In a reciprocal cross-inoculation experiment parasites occupying the same geographical area (sympatric) infected locally common host genotypes significantly more often than rare host genotypes, whereas parasites occupying separate geographical areas (allopatric) showed no such significant difference. A mixed source of parasites (containing F1 hybrids) also showed no difference in infection between rare and common host genotypes. These results show that local adaptation results from parasite tracking of locally common host genotypes, and, as such, a necessary condition of the Red Queen hypothesis is met.
Adaptation, Physiological↗
Why do bacterial plasmids carry some genes and not others?
Previous explanations of why bacterial genes for certain "optional" traits tend to occur on plasmids rather than chromosomes are based on an outdated misunderstanding of natural selection. They also fail to explain why certain characters that are ubiquitous in some bacterial species tend to occur on plasmids. This paper shows that all major classes of traits usually associated with plasmids rather than chromosomes confer adaptations to locally restricted conditions. A new "local adaptation" model of plasmid evolution, based on simultaneous application of modern selection theory at the levels of gene, plasmid, cell, and clone reproduction, shows that genes coding local adaptations will reproduce more successfully when on plasmids than when on chromosomes, due to plasmids' greater horizontal mobility.
Adaptation, Physiological↗
Fine-scale genetically based differentiation of life-history traits in the perennial shrub Lupinus arboreus.
Across large spatial scales, plants often exhibit genetically based differentiation in traits that allow adaptation to local sites. At smaller spatial scales, sharp boundaries between edaphic conditions also can create strong gradients in selection that counteract gene flow and result in local adaptation. Few studies, however, have examined the degree to which continuous populations of perennial plants exhibit genetically based differentiation in life-history traits over small spatial scales. We quantified the degree of genetically based differentiation in adaptive traits among bush lupine (Lupinus arboreus) from nearby dune and grassland sites (sites separated by < 0.75 km) that formed part of a larger continuous population of L. arboreus. We also investigated the spatial genetic structure of bush lupine by examining how genetic structure differed between seeds and juvenile plants that were less than two years old. We calculated F-statistics from gel electrophoresis of 10 polymorphic loci. We then used these values to infer levels of gene flow. To examine differentiation in adaptive traits, we created full-sibling/half-sibling families of lupine within each area and established reciprocal common gardens at each site. Across two years, we measured canopy volume, flowering time, seed set, and mortality of progeny planted in each garden. Spatial genetic structure among seeds was virtually nonexistent (F(ST) = 0.002), suggesting that gene flow between the three areas could be quite high. However, genetic structure increased 20-fold among juvenile plants (F(ST) = 0.041). We found strong evidence for fine-scale genetically based differentiation and local adaptation in adaptive traits such as plant size, flowering phenology, fecundity, and mortality. Thus, it is likely that strong but differing selection regimes within each area drive spatial differentiation in lupine life-history traits.
Adaptation, Physiological↗
The population ecology of contemporary adaptations: what empirical studies reveal about the conditions that promote adaptive evolution.
Under what conditions might organisms be capable of rapid adaptive evolution? We reviewed published studies documenting contemporary adaptations in natural populations and looked for general patterns in the population ecological causes. We found that studies of contemporary adaptation fall into two general settings: (1) colonization of new environments that established newly adapted populations, and (2) local adaptations within the context of a heterogeneous environments and metapopulation structure. Local ecological processes associated with colonizations and introductions included exposure to: (1) a novel host or food resource; (2) a new biophysical environment; (3) a new predator community; and (4) a new coexisting competitor. The new environments that were colonized often had depauperate communities, sometimes because of anthropogenic disturbance. Local adaptation in heterogeneous environments was also often associated with recent anthropogenic changes, such as insecticide and herbicide resistance, or industrial melanism. A common feature of many examples is the combination of directional selection with at least a short-term opportunity for population growth. We suggest that such opportunities for population growth may be a key factor that promotes rapid evolution, since directional selection might otherwise be expected to cause population decline and create the potential for local extinction, which is an ever-present alternative to local adaptation. We also address the large discrepancy between the rate of evolution observed in contemporary studies and the apparent rate of evolution seen in the fossil record.
Adaptation, Biological↗
Genetically diverse populations hold the keys to climatic adaptation in the Western barn owl (Tyto alba).
Although local adaptation influences species distributions, its role in driving evolutionary resilience under climate change remains unclear. Current predictive models focus on genetic adaptation to present climates, providing limited insight into future adaptive capacity. We hypothesise that historical responses to climatic shifts can reveal candidate loci for local adaptation in the future. Combining ecological niche modelling and genomic analyses, we investigate spatiotemporal patterns and mechanisms of local adaptation of the Western Palearctic barn owl (Tyto alba). Ecological modelling reveals that barn owls now occupy a broader climatic niche than during the Last Glacial Maximum. Genomic analyses indicate ongoing adaptation, with regions under selection linked to environmental factors across all populations. We find that local adaptation drives evolutionary changes across populations, enabling colonisation of new habitats and shaping responses to climate change in resident populations. We show that standing genetic diversity plays a crucial role in adaptation to past, present, and future environmental shifts.
Animals↗
Effect of saccadic adaptation on localization of visual targets.
Objects flashed briefly around the time of a saccadic eye movement are grossly mislocalized by human subjects, so they appear to be compressed toward the endpoint of the saccade. In this study, we investigate spatial localization during saccadic adaptation to examine whether the focus of compression tends toward the intended saccadic target or at the endpoint of the actual (adapted) movement. We report two major results. First, that peri-saccadic focus of the compression did not occur at the site of the initial saccadic target, but tended toward the actual landing site of the saccade. Second, and more surprisingly, we observed a large long-term perceptual distortion of space, lasting for hundreds of milliseconds. This distortion did not occur over the whole visual field but was limited to a local region of visual space around the saccade target, suggesting that saccadic adaptation induces a visuo-topic remapping of space. The results imply that the mechanisms controlling saccadic adaptation also affect perception of space and point to a strong perceptual plasticity coordinated with the well-documented plasticity of the motor system.
Adaptation, Physiological↗
A simple model of unbounded evolutionary versatility as a largest-scale trend in organismal evolution.
The idea that there are any large-scale trends in the evolution of biological organisms is highly controversial. It is commonly believed, for example, that there is a large-scale trend in evolution towards increasing complexity, but empirical and theoretical arguments undermine this belief. Natural selection results in organisms that are well adapted to their local environments, but it is not clear how local adaptation can produce a global trend. In this paper, I present a simple computational model, in which local adaptation to a randomly changing environment results in a global trend towards increasing evolutionary versatility. In this model, for evolutionary versatility to increase without bound, the environment must be highly dynamic. The model also shows that unbounded evolutionary versatility implies an accelerating evolutionary pace. I believe that unbounded increase in evolutionary versatility is a large-scale trend in evolution. I discuss some of the testable predictions about organismal evolution that are suggested by the model.
Biological Evolution↗