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The method proposed by Hardwick and Wood (1972) for relating genotype-environment interactions to measures of environmental variables is extended and two examples are discussed.
This study was undertaken to investigate the significance of social, environmental, and biological variables in relation to caries status in a group of young children, and to determine whether incorporating data on social and environmental variables into a multivariate model could improve the accuracy of a screening approach that relies solely on quantifying levels of salivary Streptococcus mutans. Data regarding fluoride status and sociodemographic characteristics were collected from the dental records of 89 children who ranged in age from 10-71 months, and who had been screened previously for S. mutans. Multivariate analyses (logit) revealed that the probability of having clinically or radiographically detectable caries was associated with 1) higher levels of salivary S. mutans, 2) residing in a single-parent household, 3) having suboptimal levels of fluoride in the drinking water and 4) not being covered by a dental insurance plan. The findings attest to the importance of considering social and environmental factors, in addition to biological variables, when evaluating caries status in young children.
Two types of time scales--10-day intervals (D) and phenological phases (P)--were applied to environmental variables for the development of statistical regression models relating to the southwest pampa region of Argentina, with the aim of detecting the effects of weather on wheat yields for the period 1977-1999. The parameters were grouped as meteorological and processed variables and indices. The processed variables used were total soil water availability (SWA) and the ratio of actual evapotranspiration to potential evapotranspiration (alpha), obtained from a water-balance model in which the moisture anomaly index (Z) and the Palmer drought severity index (PDSI) were calculated according to Palmer's model. For these parameters it was possible to establish the times of year and the phenological phases with the best correlation to grain yield. The regression equation for meteorological variables on a 10-day scale provides one of the best fits. Using mixed parameters, the two models, D and P, give rise to a standard error of estimate of approximately 200 kg ha(-1). Truncated models perform better on a P scale than on a D scale. The use of phenological stages improved yield assessment, particularly for those years with extreme meteorological conditions. The optimum models were tested and root-mean-square errors (RMSE) of 440 kg ha(-1) and 470 kg ha(-1) were obtained for P and D scales respectively.
A risk index based on a variety of reproductive, perinatal and environmental variables was used to attempt to predict the developmental outcome of very low birthweight infants (birthweights under 1501 grams). Forty-one preterm infants and a demographically matched group of 42 fullterm infants were studied. The McCarthy Scales of Children's Abilities was administered to the children at 5 years of age. In general, the preterm children were delayed in the perceptual, memory, and motor abilities in comparison with the fullterm children. There were no significant differences between the AGA (appropriate for gestational age) and SGA (small for gestational age) preterm groups. Multiple regression and discriminant function measures were used to examine the overall relationship between the earlier measures and later development and to assess the risk for an individual child. The risk index was able to account for typically 30-40% of the variance associated with the 5 year scores and the prediction of an individual child's development was accurate for approximately 85% of the time. Severity of illness during the perinatal period, independently of social class and infant tests scores were the best predictors of outcome. This study demonstrates that developmental outcome can be predicted with a high degree of accuracy and a relatively simple system.
A discrete-time Markov chain model, a continuous-time Markov chain model, and a stochastic differential equation model are compared for a population experiencing demographic and environmental variability. It is assumed that the environment produces random changes in the per capita birth and death rates, which are independent from the inherent random (demographic) variations in the number of births and deaths for any time interval. An existence and uniqueness result is proved for the stochastic differential equation system. Similarities between the models are demonstrated analytically and computational results are provided to show that estimated persistence times for the three stochastic models are generally in good agreement when the models satisfy certain consistency conditions.
The present study evaluated a measure of perceived physical environments that may influence physical activity. Forty-three self-report items were used to assess environmental variables at homes, in neighborhoods, or on frequently traveled routes. The presence of facilitators of (e.g., equipment, programs, attractive surroundings) and barriers to (e.g., high crime) physical activity was assessed. In 110 college students, test-retest reliabilities were .89 for the home equipment scale, .68 for the neighborhood scale, and .80 for the convenient facilities scale. Home equipment and convenient facilities scales were correlated with self-reported physical activity. In multiple regression analyses, the only significant association, after adjusting for neighborhood socioeconomic status, was home equipment with strength exercise. Further research is needed to identify other environmental characteristics that may influence physical activity.
Statistical analyses of the relationships between the patterns of distribution of plants with C4 photosynthesis and Crassulacean acid metabolism (CAM) have revealed a variety of correlations with environmental variables. The worldwide abundance of C4 grasses, relative to C3 grasses, is highly positively correlated with growing season temperature. However, microscale analyses have revealed that C4 grasses are more abundant than C3 grasses in habitats with high levels of solar irradiance and low moisture availability. There are numerous exceptions to these generalizations. C4 dicots generally are more abundant in habitats characterized by high rates of evaporation. Species possessing CAM occur in habitats having low levels of soil moisture store. In the Cactaceae such habitats also have very high potential rates of evaporation and the CAM pathway is the primary mechanism of the uptake of atmospheric CO2. In contrast many species of the Crassulaceae grow in habitats with lower potential rates of evaporation and the CAM pathway is less important or not used at all in the uptake of atmospheric CO2.
The regular fall-winter onset of seasonal affective disorder is believed to be related to seasonal changes in the environment. However, the high correlation among various environmental variables has made it difficult to distinguish which ones may play a causal role. Photoperiod should explain variations in onset risk across both latitude and day of the year because it varies as a function of only these 2 factors. In Study 1, the authors found this to be the case using data from 5 locations. Environmental factors that vary from year to year should explain variations in onset risk across both time of year and actual year. In Study 2, the authors examined data from 7 years at 1 location and failed to find evidence of this effect for daily hours of sunshine, mean daily temperature, and total daily radiation. Findings support photoperiod as being related to the onset of seasonal affective disorder.
The need to define the geographical distribution of Phlebotomus orientalis results from its importance as the dominant vector of kala azar (visceral Iceishmaniasis) in Sudan. Recent epidermics of this disease in southern and eastern Sudan caused an estimated 100000 deaths and have renewed the impetus for defining the ecological boundaries of the vector. This information is an essential prerequisite to the production of a risk map for kala azar. This study uses data on the presence and absence of P. orientalis from 44 collecting sites across the central belt of Sudan. A logistic regression model was used to estimate the probability of the presence of P. orientalis at each collecting site as a function of climatic and environmental variables (rainfall; temperature; altitude; soil type and the satellite-derived environmental proxies - Normalized Difference Vegetation Index and Land Surface Temperature). The logistic regression model indicates mean annual maximum daily temperature and soil type as the most important ecological determinants of P. orientalis distribution. An initial risk map was created in a raster-based geographical information system which delineates the area where P. orientalis may occur. This map was then refined using a mask layer indicating the known rainfall-based boundaries of the distribution of Acacia-Balanites woodland - a woodland type known to be associated with the distribution of this vector. The predictive performance of the risk map is discussed.
The immature stages of Ochlerotatus albifasciatus develop in temporary pools. The present study aims at evaluating the seasonal dynamics of the aquatic stages of this mosquito, also analyzing the relationship among their presence and breeding success to some relevant climatic and environmental variables in the ephemeral rain pools of an urban park. Nineteen cohorts of O. albifasciatus that developed synchronously after rain events were recorded in all seasons. The proportions of mosquito-positive pools were significantly higher during the fall-winter period than in the spring-summer months (p < 0.001). The presence of this mosquito species was positively related to the amount of rain (p < 0.001), whereas negatively correlated to air temperature (p < 0.05) within a 5.2 to 29.7 degrees C range. The distribution of the number of cohorts per pool throughout the year was grouped (variance/mean: 3.96), indicating that these habitats were not equally suitable as breeding sites. The immature stages of O. albifasciatus were detected in pools belonging to all of the categories of surface area, depth, duration, vegetation cover, and insolation. However, the proportion of pools where immature mosquitoes were detected was positively and significantly related to surface, depth, duration, and vegetation cover. On the other hand, the proportion of mosquito-positive pools was higher at an intermediate insolation degree. Our results suggest that although preimaginal stages were present in all seasons, high temperatures may be unfavorable to larval development, and substrate vegetation may regulate water temperature. The positive relationship between the proportion of mosquito-positive pools and pool size and duration might reflect a strategy of O. albifasciatus to accomplish immature development.
Dispersal is a critical process in ecology. It is an important biological driver of, for example, invasions, metapopulation dynamics, spatial pattern formation and pathogen movement. Much is known about the effect of environmental variability, including turbulence, on dispersal of diaspores. Here, we document experimentally the strong but under-explored influence of turbulence on the initiation of dispersal. Flower heads of two thistle species (Carduus nutans and Carduus acanthoides) with ripe seeds were exposed to series of laminar and turbulent air flows of increasing velocity in a wind tunnel. Seed release increased with wind speeds for both laminar and turbulent flows for both species. However, far more seeds were released, at significantly lower wind speeds, during turbulent flows. These results strongly suggest a need for more quantitative studies of abscission in the field, as well as dispersal models that incorporate variability in the diaspore release phase.
Naegleria gruberi amebae normally transform into biflagellated cells. When subjected to high temperatures during flagellate differentiation, populations develop an average of 4-5 flagella/flagellate. Attempts to maximize this phenomenon by altering cellular and environmental variables revealed that: (a) few Naegleria isolates become multiflagellated: strain NB-1 gives the greatest response to heat shocks; (b) temperature is the most critical variable: highest numbers of flagella are obtained only if cells are temperature-shocked at precisely 38.2 +/- 0.1 C, then returned to 19-22 C to complete differentiation; (c) although pH alone does not affect numbers of flagella, a pH optimum of 5.5-7.0 exists for temperature-shocked cells; and (d) single cells in microdrops become multiflagellated, but the population response is density-dependent. Optimal conditions are described for growing, washing, and transforming amebae to generate reproducibly highest numbers of flagella.
Six bivalve mollusk species were sampled for genetic variability at two enzyme synthesizing loci. The effective number of alleles and absolute number of alleles decreased with depth of burial within the sediment, intertidally, and with depth of water, subtidally. It is proposed that environmental variability regulates genetic variability at these two loci.
Because of the increasing emphasis placed upon land application as a means of wastewater disposal, it is important to evaluate the influences of different factors upon virus survival in soil. The objective of this study was to measure the effects of various environmental variables on virus persistence. Test samples of soil were placed in vials, and the soil was wetted with suspensions of virus in either distilled water, unchlorinated secondary sewage effluent, or mixtures of effluent and water. The viruses used were coxsackieviruses A9 and B3, echovirus 1, poliovirus 2, rotavirus SA11, and bacteriophages T2 and MS2. The rate of virus inactivation was evaluated statistically with regard to conditions under which the vials were incubated and to the soil characteristics. The factors that were found to influence virus survival were temperature, soil moisture content, presence of aerobic microorganisms, degree of virus adsorption to the soil, soil levels of resin-extractable phosphorus, exchangeable aluminium, and soil pH. Overall, temperature and virus adsorption to soil appeared to be the most important factors affecting virus survival.
This comparative analysis of clinical laboratories was intended to develop a more quantitative understanding of environmental, structural, and process variables and their relationships to the quality of laboratory services. The quality of laboratory services was defined as analytic capability demonstrated on proficiency-test specimens of the College of American Pathologists. Independent variables describing the laboratory environment, as well as structural and process aspects of management, were obtained from management reports, staffing records, and workload reports. Although correlations between the eight proficiency testing indices and the independent variables were generally low, a number of significant correlates were evident in three areas: bacteriology, parasitology, and qualitative hematology. Environmental variables describing organizational size were related to proficiency, as were variables dealing with accreditation by the College of American Pathologists and time accredited by the College of American Pathologists. The education and experience of personnel and the percentage of specialized supervisors were related to proficiency-testing success in bacteriology and parasitology. Empirical evidence suggests that the size of the laboratory indirectly affects proficiency in these three tested areas. Presumably, this relationship is mediated through specialization of work and reinforcement of learning. Few significant correlates were evident in the five remaining areas tested: chemistry, quantitative hematology, blood bank, immunology, and syphilis serology. Despite the concentration of personnel resources and other assets in larger laboratories, size appeared to have no effect on proficiency-testing performance in these five areas.
We tested the influence of the apolipoprotein E (apoE) polymorphism on the intrapair differences in the levels of plasma cholesterol, plasma triglycerides, low density lipoprotein-cholesterol, apoB and apoE in monozygotic (MZ) twins, and estimated whether or not there was a interaction between the apoE polymorphism and environmental factors. In 65 MZ twin pairs, the intrapair differences in the measured lipoprotein parameters were similar in the different apoE phenotype classes. This indicates that the effect of the apoE polymorphism is not influenced by environmental variability between the MZ pair members and accordingly identifies the APOE gene as a "level" gene.
In their 1990 paper Optimal reproductive efforts and the timing of reproduction of annual plants in randomly varying environments, Amir and Cohen considered stochastic environments consisting of i.i.d. sequences in an optimal allocation discrete-time model. We suppose here that the sequence of environmental factors is more generally described by a Markov chain. Moreover, we discuss the connection between the time interval of the discrete-time dynamic model and the ability of the plant to rebuild completely its vegetative body (from reserves). We formulate a stochastic optimization problem covering the so-called linear and logarithmic fitness (corresponding to variation within and between years), which yields optimal strategies. For "linear maximizers'', we analyse how optimal strategies depend upon the environmental variability type: constant, random stationary, random i.i.d., random monotonous. We provide general patterns in terms of targets and thresholds, including both determinate and indeterminate growth. We also provide a partial result on the comparison between ;"linear maximizers'' and "log maximizers''. Numerical simulations are provided, allowing to give a hint at the effect of different mathematical assumptions.
Significant heterogeneity in the distribution of within pair variances of serum total cholesterol, HDL cholesterol, non HDL cholesterol and triglyceride levels has been found in one or both of two samples of MZ twins. We have found some support for the observation of Magnus et al. (1981) that M- pairs have greater environmental variability in cholesterol levels than M+ pairs and weaker evidence that Jka+ pairs are more variable than Jka- pairs. However, these effects appear to be more striking on triglyceride levels. The low power of the variance ratio test is advanced as a possible reason for the inconsistencies in these findings.