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PubMed2006

Local maladaptation in the soft scale insect Saissetia coffeae (Hemiptera: Coccidae).

Local adaptation has often been documented in herbivorous insects. The potential for local maladaptation in phytophagous insects, however, has not been widely considered. I performed a two-generation reciprocal cross-transplant experiment with the generalist soft scale insect Saissetia coffeae (Hemiptera: Coccidae) on two common species of host plants in rain forest habitat in Costa Rica. In this system, S. coffeae showed significant local maladaptation at the level of the host species. Lineages originally collected from Witheringia enjoyed a strong advantage over those collected from Lomariopsis when both sets of lineages were placed on Lomariopsis; however, when both sets of lineages were raised on Witheringia, their fitnesses were statistically indistinguishable. While some aspects of the biology of S. coffeae may impair its ability to adapt to local selection pressures, scale insects are often locally adapted on fine spatial scales, and local maladaptation is therefore especially surprising. Other documented cases of local maladaptation in parasites appear to be due to evolution on the part of the host. The possibility that hosts or natural enemies may place local genotypes at a disadvantage, producing a pattern of local maladaptation, is one that deserves more consideration in the context of plant-insect interactions.

Adaptation, Physiological↗
PubMed2006

Spatial and temporal variations in local transmission of Schistosoma haematobium in Msambweni, Kenya.

As part of an extensive study of the eco-epidemiology of urinary schistosomiasis along the southern coast of Kenya, spatial and temporal transmission patterns were associated with various ponds infested with Bulinus snails. The household-level spatial pattern of infection for children of various age groups in 2000 was contrasted with historical data from 1984. Significant local clustering of high and low infection levels among school age children was detected, and the spatial extent of clusters and their direction from specific water sources were measured. High infection levels were clustered around ponds known to contain Bulinus nasutus snails that shed Schistosoma haematobium cercariae, and low infection levels were concentrated near a river where intermediate host snails were rarely found. The spatial patterns of infection varied between 2000 and 1984 and between age groups. High levels of infection were clustered around different transmission foci in the two study periods, and, for younger children in 2000, were clustered nearer to the transmission foci than for the older children. Simultaneous consideration of the effects of different foci on transmission will allow for targeted application of control measures aimed at interrupting S. haematobium transmission at a local level.

Adolescent↗
PubMed2003

Direct visualization of Ras proteins in spatially distinct cell surface microdomains.

Localization of signaling complexes to specific microdomains coordinates signal transduction at the plasma membrane. Using immunogold electron microscopy of plasma membrane sheets coupled with spatial point pattern analysis, we have visualized morphologically featureless microdomains, including lipid rafts, in situ and at high resolution. We find that an inner-plasma membrane lipid raft marker displays cholesterol-dependent clustering in microdomains with a mean diameter of 44 nm that occupy 35% of the cell surface. Cross-linking an outer-leaflet raft protein results in the redistribution of inner leaflet rafts, but they retain their modular structure. Analysis of Ras microlocalization shows that inactive H-ras is distributed between lipid rafts and a cholesterol-independent microdomain. Conversely, activated H-ras and K-ras reside predominantly in nonoverlapping, cholesterol-independent microdomains. Galectin-1 stabilizes the association of activated H-ras with these nonraft microdomains, whereas K-ras clustering is supported by farnesylation, but not geranylgeranylation. These results illustrate that the inner plasma membrane comprises a complex mosaic of discrete microdomains. Differential spatial localization within this framework can likely account for the distinct signal outputs from the highly homologous Ras proteins.

Animals↗
PubMed2000

Twist localizes three-dimensional patterns

A mechanism for the localization of spatially periodic, self-organized patterns in anisotropic media which requires systems extended in all three spatial dimensions is presented: When the anisotropy axis is twisted, the pattern becomes localized in planes parallel to the anisotropy axis. An analytical description of the effect is developed, and used to interpret recent experiments in the high-frequency regime of electroconvection by Bohatsch and Stannarius [Phys. Rev. E 60, 5591 (1999)]. The localization width is found to be of the order of magnitude of the geometrical average of the pattern wavelength and the inverse twist.

Journal Article↗
PubMed2006

Spatial patterns of labile forms of phosphorus in a subtropical wetland.

Phosphorus (P) has been identified as the key constituent defining wetland productivity, structure, and function. Our goal was to investigate the spatial patterns of total P and three labile forms of P (labile organic, inorganic, and microbial biomass P) across a subtropical wetland located in east-central Florida, the Blue Cypress Marsh Conservation Area (BCMCA), and link spatial patterns to ecosystem processes. The wetland received a continual input of nutrients primarily from the south and intermittently from the west and east, respectively, which ceased in the mid-1990s. Since then the marsh system has been undergoing natural succession. We used (i) ordinary kriging to characterize the spatial patterns of total P and labile P forms across the wetland, (ii) local, moving spatial correlations to investigate relationships between total P and labile P forms, and (iii) a clustering technique to link the identified spatial patterns to biogeochemical processes. The spatially explicit analyses revealed patterns of total P and labile P forms as well as changing relationships between variables across the marsh. We were able to distinguish P-enriched areas from unaffected ("natural") areas and intermediate zones that are currently undergoing change as P is mobilized and translocated. We also identified areas that are at risk, showing a shift toward a more P-enriched status. Our results improve our understanding of P and its labile components within a spatially explicit context.

Ecosystem↗
PubMed1987

The local redshift-distance relation and spatial uniformity.

Regrettably, the review of the redshift-distance relation in the review by Salpeter and Hoffman [Salpeter, E. E. & Hoffman, G. L., Jr. (1986) Proc. Natl. Acad. Sci. USA 83, 3056-3063], appears flawed. In particular, the logically inconclusive and uncertain hypothesis of local extragalactic spatial uniformity is used in an essential way. Moreover, even in conjunction with this hypothesis, the Lundmark law fits more closely than the Hubble law, on the basis of the data and criteria of Salpeter and Hoffman, when a rough approximation involved in the estimation of the galaxy luminosity function is eliminated. Specifically, the assumption that all galaxies in the redshift range 500-1700 km.s(-1) are effectively at the redshift 1100 km.s(-1) is made; when this assumption is replaced by a statistically optimal procedure that uses the precise redshifts, the relative fit of the two laws is reversed.

Journal Article↗
PubMed2004

Differential expression profiles of growth-related genes in the elongation zone of maize primary roots.

Growth in the apical elongation zone of plant roots is central to the development of functional root systems. Rates of root segmental elongation change from accelerating to decelerating as cell development proceeds from newly formed to fully elongated status. One of the primary variables regulating these changes in elongation rates is the extensibility of the elongating cell walls. To help decipher the complex molecular mechanisms involved in spatially variable root growth, we performed a gene identification study along primary root tips of maize (Zea mays) seedlings using suppression subtractive hybridization (SSH) and candidate gene approaches. Using SSH we isolated 150 non-redundant cDNA clones representing root growth-related genes (RGGs) that were preferentially expressed in the elongation zone. Differential expression patterns were revealed by Northern blot analysis for 41 of the identified genes and several candidate genes. Many of the genes have not been previously reported to be involved in root growth processes in maize. Genes were classified into groups based on the predicted function of the encoded proteins: cell wall metabolism, cytoskeleton, general metabolism, signaling and unknown. In-situ hybridization performed for two selected genes, confirmed the spatial distribution of expression shown by Northern blots and revealed subtle differences in tissue localization. Interestingly, spatial profiles of expression for some cell wall related genes appeared to correlate with the profile of accelerating root elongation and changed appropriately under growth-inhibitory water deficit.

DNA, Complementary↗
PubMed1978

1H nuclear-magnetic-resonance studies of the molecular conformation of monomeric glucagon in aqueous solution.

Dilute aqueous solutions of glucagon were investigated by high-resolution 1H nuclear magnetic resonance at 360 MHZ. Monomeric glucagon was found to adopt predominantly an extended flexible conformation which contains, however, a local non-random spatial structure involving the fragment--Phe-22--Val-23--Gln-24--Trp-25--. This local conformation is preserved in the partial sequence 22--26 and could thus be characterized in detail. Two interesting conclusions resulted from these experiments. One is that the local spatial structure in the fragment 22--25 of glucagon is identical to that observed in the fragment 20--23 of the human parathyroid hormone. Secondly, the backbone conformation in the C-terminal fragment of glucagon in solution must be different from the alpha-helical structure observed in single crystals of glucagon. These new structural data are analyzed with regard to relationships with glucagon binding to the target cells.

Glucagon↗
PubMedDate not supplied

In vivo 1H-NMR procedure to determine several rat cerebral metabolite levels simultaneously, undisturbed by water and lipid signals.

Methods developed for in vivo 1H-NMR spectroscopy are evaluated and applied using conscious rats. Good quality 1H-spectra of the brain are obtained using a surface coil and a spin echo pulse sequence with the binomial 1-1 and 2-2 water suppression pulses. However, comparing spectra from various rats with each other the water and lipid signals, which cause spectral overlap problems, may differ while the other spectral peaks agree well. Spatially one- and two-dimensional 1H spectroscopic imaging of the rat brain shows that the former signals stem from distinct spatial regions localized close to the rf coil. From a spectroscopic image, a spectrum over a limited spatial region is constructed in which the water signals are strongly reduced, the lipid signals are eliminated and lactic acid can be observed clearly simultaneously with other metabolites.

Animals↗
PubMed1985

Capabilities of monkey cortical cells in spatial-resolution tasks.

The performance of individual neurons in monkey striate cortex has been examined in three spatial-resolution tasks by making microelectrode recordings from single cells in anaesthetized, paralyzed animals. The statistical reliability of responses from cells was used to estimate threshold levels of performance. For each task (resolution acuity for high-contrast gratings, discrimination of gratings varying in spatial frequency, and localization ability, i.e., discrimination of spatial phase), performance approaching psychophysical thresholds was obtained from single cortical cells. The receptive-field organization underlying localization performance was examined in detail by the use of a linear model that relates localization ability to the sensitivity of the receptive field to luminance contrast. Calculations from this model agree well with direct measurements of localization performance and are comparable with psychophysical measurements of hyperacuity. Though it has been suggested that cells with nonoriented receptive fields in cortical layer IVc beta may be responsible for recovering fine-grain spatial information, our calculations indicate that these cells are poorer at localization than many other cells in the cortex.

Animals↗
PubMed2004

Blink and shrink: the effect of the attentional blink on spatial processing.

The detection or discrimination of the second of 2 targets in a rapid serial visual presentation (RSVP) task is often temporarily impaired-a phenomenon termed the attentional blink. This study demonstrated that the attentional blink also affects localization performance. Spatial cues pointed out the possible target positions in a subsequent visual search display. When cues were presented inside an attentional blink (as induced by an RSVP task), the observers' capacity to use them was reduced. This effect was not due to attention being highly focused, to general task switching costs, or to complete unawareness of the cues. Instead, the blink induced a systematic localization bias toward the fovea, reflecting what appears to be spatial compression.

Adolescent↗
PubMed1997

Spatio-temporal boundary formation: the role of local motion signals in boundary perception.

Spatio-temporal boundary formation (SBF) refers to a perceptual process responsible for perception of moving, bounded surfaces from sequential changes in spatially separated local elements. Previous research has indicated that this process produces perception of global form, continuous boundaries and global motion from spatially and temporally sparse element changes. In the present paper, we sought to distinguish between two classes of models for SBF: form-precedes-motion and motion-precedes-form models. Experiment 1 tested the effects of the addition of spurious motion signals, a manipulation that should affect a motion-precedes-form computation but not a form-precedes-motion computation. Shape identification in a 10-alternative forced-choice procedure was disrupted by this manipulation, supporting the former class of models. A particular computational scheme, edge orientation from motion (EOFM) instantiating a motion-precedes-form model is described and tested in Experiment 2. The EOFM model should be disrupted when initiating element changes occur in a certain type of sequential order, relative to randomly arranged changes. Sequential changes markedly disrupted performance, supporting this EOFM approach. The results favor motion-precedes-form models of SBF and are consistent with the particular computational scheme proposed.

Form Perception↗
PubMed2004

Real-time ozone mapping using a regression-interpolation hybrid approach, applied to Tucson, Arizona.

Real-time ozone (O3) maps, intended for public access and mass media, are generated from spatially interpolating (i.e., kriging) sparse monitoring data and are typically characterized by over-smoothed surfaces that inadequately represent local-scale spatial patterns (e.g., averaged over 1 km2). In this paper, a hybrid regression-interpolation methodology is developed to enhance the representation of local-scale spatiotemporal patterns with an application to Tucson, Arizona. The mapping of local patterns is enhanced with pre-interpolation regression modeling of local-scale deviation-from-mean variability, preserving variation in the monitor data that is ubiquitous across the modeling domain (i.e., the areal mean). The model is trained on several years of deviation-from-mean hourly O3 data, and predictor variables are developed using theoretically and empirically derived proxy regression variables. The regression model explains a significant proportion of the variation in the data (r2 = 0.54), with an average error of 7.1 ppb. When augmented with the areal mean, the r2 of the pre-interpolation model increases to 0.847. Model residuals are then spatially interpolated to the extents of the modeling domain. Final concentration estimate maps are the summation of areal mean, regression, and spatially interpolated surfaces, preserving absolute values at monitor locations.

Air Pollutants↗
PubMed2004

Power-law spatial correlations in arrays of locally coupled lasers.

We investigate correlations of the intensity fluctuations of two-dimensional arrays of nonidentical, locally coupled lasers, numerically and experimentally. We find evidence of a power-law dependence of spatial correlations as a function of laser pair distance (or coupling strength) near the phase-locking threshold.

Journal Article↗
PubMed2005

Spatially correlated disturbances in a locally dispersing population model.

The basic contact process in continuous time is studied, where instead of single occupied sites becoming empty independently, larger-scale disturbance events simultaneously remove the population from contiguous blocks of sites. Stochastic spatial simulations and pair approximations were used to investigate the model. Increasing the spatial scale of disturbance events increases spatial clustering of the population and variability in growth rates within localized regions, reduces the effective overall population density, and increases the critical reproductive rate necessary for the population to persist. Pair approximations yield a closed-form analytic expression for equilibrium population density and the critical value necessary for persistence.

Animals↗
PubMed2006

Spatial relational memory in 9-month-old macaque monkeys.

This experiment assesses spatial and nonspatial relational memory in freely moving 9-mo-old and adult (11-13-yr-old) macaque monkeys (Macaca mulatta). We tested the use of proximal landmarks, two different objects placed at the center of an open-field arena, as conditional cues allowing monkeys to predict the location of food rewards hidden in one of two sets of three distinct locations. Monkeys were tested in two different conditions: (1) when local visual cues marked the two sets of potentially baited locations, so that monkeys could use both local and spatial information to discriminate these locations from never-baited locations; and (2) when no local visual cues marked the two sets of potentially baited locations, so that monkeys had to rely on a spatial relational representation of the environment to discriminate these locations. No 9-mo-old or adult monkey associated the presence of the proximal landmarks, at the center of the arena, with the presence of food in one set of three distinct locations. All monkeys, however, discriminated the potentially baited locations in the presence of local visual cues, thus providing evidence of visual discrimination learning. More importantly, all 9-mo-old monkeys tested discriminated the potentially baited locations in absence of the local visual cues, thus exhibiting evidence of spatial relational learning. These findings indicate that spatial memory processes characterized by a relational representation of the environment are present as early as 9 mo of age in macaque monkeys.

Age Factors↗
PubMed1997

Working memory: a view from neuroimaging.

We have used neuroimaging techniques, mainly positron emission tomography (PET), to study cognitively driven issues about working memory. Two kinds of experiments are described. In the first kind, we employ standard subtraction logic to uncover the basic components of working memory. These studies indicate that: (a) there are different working-memory systems for spatial, object, and verbal information (with the spatial system localized more in the right hemisphere, and the verbal system more in the left hemisphere); (b) within at least the spatial and verbal systems, separable components seem to be responsible for the passive storage of information and the active maintenance of information (with the storage component being localized more in the back of the brain, and the maintenance component in the front); and (c) there may be separate components responsible for processing the contents of working memory (localized in prefrontal cortex). In our second kind of experiment we have focused on verbal working memory and incrementally varied one task parameter-memory load-in an effort to obtain a more fine-grained analysis of the system's operations. The results indicate that all relevant components of the system show some increase in activity with increasing memory load (e.g., the frontal regions responsible for verbal rehearsal show incremental increases in activation with increasing memory load). In contrast, brain regions that are not part of the working-memory system show no effect of memory load. Furthermore, the time courses of activation may differ for regions that are sensitive to load versus those that are not. Taken together, our results provide support for certain cognitive models of working memory (e.g., Baddeley, 1992) and also suggest some distinctions that these models have not emphasized. And more fundamentally, the results provide a neural base for cognitive models of working memory.

Brain↗
PubMedDate not supplied

Glucose treatment attenuates spatial learning and memory deficits of aged rats on tests of hippocampal function.

Groups of old and young rats were administered three tests of spatial learning and memory that are known to be sensitive to hippocampal dysfunction: the radial arm maze (RAM), spatial non-matching-to-sample (SNMTS), and a spatial vs. local cue-preference task. Old rats performed worse than young rats on the RAM and SNMTS tasks; on the cue-preference task, young rats were biased to use spatial cues, whereas old rats exhibited strong preferences for distinct, local cues. Peripheral injections of glucose (100 mg/kg) improved performance by old rats on the RAM and SNMTS, which correlated with measures of glucose metabolism. Glucose treatment did not affect old rats performance on the cue-preference task. There was evidence that glucose-treatment improved performance of young rats in the RAM test, but not the other tests. The results extend the range of tasks on which glucose-induced cognitive enhancement has been demonstrated in aged rats, and provides further evidence that memory loss resulting from hippocampal dysfunction is especially amenable to glucose treatment.

Aging↗