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PubMed2005

Spouse selection and environmental effects on spouse correlation in lung function measures.

PURPOSE: Concordance between spouses may be due to partner selection factors and/or the effects of marriage/environment. The extent to which partner selection factors contribute to spouse concordance has important implications for heritability studies. The aim of this study was to examine the magnitude of spouse correlation in lung function measures and its relationship to duration of marriage. METHODS: Cross-sectional and longitudinal data collected over the period 1969 to 1995 for 2615 couples from the Busselton Health Study have been analyzed using the program FISHER. RESULTS: Unadjusted correlations were around 0.45 for forced expiratory volume in 1 second (FEV1) and 0.25 for FEV1/FVC (forced vital capacity) and were reduced to 0.05 and 0.10, respectively, after adjustment for age, height, and smoking. No trend with marriage duration was apparent in both cross-sectional and longitudinal analyses but there was a significant downward trend in the correlations with age at marriage. CONCLUSIONS: The findings indicate that observed correlations in lung function measures are mostly due to partner selection factors and that partner selection factors have greater influence for couples that marry at younger ages. Family studies that aim to identify and separate genetic from other influences on lung function measures should not regard the mother-father correlation as due to common environment effects.

Adult↗
PubMed1993

Long-term environmental trends: selection of sampling locations in a reactor-aquatic cooling system.

The study objective was to determine whether environmental radionuclide accumulations were occurring in an aquatic system with a 13-y history of supplying a power plant with reactor-cooling water as well as receiving plant discharge. The aquatic system consisted of the following: 1) a reactor-cooling lake; 2) a secondary lake approximately 8 km downstream; and 3) a small stream that interfaced with the two lakes. Gamma-emitting radionuclides were identified and quantified in samples of benthic sediments obtained from representative areas of the aquatic system. This study demonstrated that in a reactor-aquatic cooling system, the component of the aquatic system most likely to experience radionuclide accumulation will not necessarily be the reactor-cooling lake, but will be that component of the aquatic system whose benthic sediments contain the highest concentrations of organic matter. Further, it was shown that the quantity of oxidizable organic matter present in a sediment is a good predictor or marker for potential sites of radionuclide accumulation (i.e., 60Co and 137Cs).

Cesium Radioisotopes↗
PubMed1993

Available lambda B cell repertoire in the mouse: evidence of positive selection by environmental factors.

We have recently shown that, from two BALB/c mice treated with rabbit anti-C lambda 2/C lambda 3 antibodies coupled to lipopolysaccharide, variable heavy chain (VH) family repertoires associated with lambda 2 or lambda 3 light chains can differ from one lambda subtype to another and from one individual mouse to another. Indeed, 4 out of 6 lambda 2 (VxJ2) hybridomas from one mouse preferentially expressed the VH10 family while 3 out of 8 lambda 2 (V2J2) and 5 out of 8 lambda 2 (VxJ2) hybridomas from a second mouse preferentially expressed the S107 and VGAM3.8 VH families, respectively. In this report, we describe the structural basis of such preferential pairings by sequence analysis of the 12 lambda 2 hybridomas. The sequence comparison of their VH regions show that each preferential association of a VH family to one V lambda region is restricted to the use of a single member or very closely related members inside a VH family and that a great variability of CDR3 of heavy chain is observed. We, therefore, suggest that environmental factors can modify the available lambda B cell repertoire through a positive selection of particular VH/V lambda pairings. Moreover, our data support that this selection does not require clonal expansion and punctual somatic mutation.

Amino Acid Sequence↗
PubMedDate not supplied

Mutagenicity studies on complex environmental mixtures: selection of solvent system for extraction.

The mutagenic activities in the Salmonella/microsome assay of dichloromethane (DCM) and acetone extracts of complex environmental mixtures were compared. The particulate samples used in the IPCS collaborative study were Soxhlet-extracted twice with DCM followed by a third extraction with acetone. Compared with the mutagenic activity of the first extract, the third (acetone) extract of the urban particulate matter showed a relatively high mutagenic activity. In contrast to this the third extract of the diesel particulate matter contributed very little additional mutagenic activity. Furthermore, 10 filter samples of air particulates from a suburban airport area were collected for comparison of the extraction efficiency of DCM and acetone. Each sample was divided into two samples of identical size followed by extraction with acetone and DCM, respectively. No clear difference in the mutagenic activity of these extracts was observed in strains TA98 and TA98NR. It is concluded that for ambient air particulates (but not emission samples) acetone may extract some mutagenic compounds which are not extracted by DCM. The amount of these additional extractable compounds seems to depend on the composition of the sample. As DCM extracts are better suited for further fractionation and chemical analysis DCM is considered to be the best choice for a general solvent system for extraction of complex environmental mixtures.

Acetone↗
PubMed1989

Longevity enhances selection of environmental sex determination.

Environmental sex determination (ESD) is a mechanism in which an individual develops as male or female largely in response to some environmental effect experienced early in life. Its forms range from sex determination by egg incubation temperature in reptiles to sex determination of photoperiod in amphipods. Previous theoretical work as suggested that ESD is favored by natural selection if the fitness consequences of the early environmental experience differ for males and females, so that an individual benefits by being male under some conditions and female under others. A drawback of ESD is that it enables climatic changes to influence the population sex ratio, and such fluctuations select against ESD. This study employed numerical analyses to investigate the balance between these two opposing forces. The negative impact of climatic fluctuations appears to depend greatly on species longevity: substantial between-year fluctuations are of little consequence in selecting against ESD in long-lived species because annual sex ratio fluctuations tend to cancel and thus alter the total population sex ratio only slightly. Thus, if a species is sufficiently long-lived, extreme ESD can be maintained despite only a weak advantage. This result offers one explanation for the failure to demonstrate an advantage for the extreme forms of ESD observed in reptiles.

Animals↗
PubMed1975

Determination of the environmental sensitivity of selection lines by the selection environment.

The parents chosen to continue 10 independent selection lines of Schizophyllum commune over eight successive generations of selection, along with unselected controls, have been retrospectively examined for their response to growth at 15 degrees, 20 degrees, 25 degrees, 30 degrees and 35 degrees C. The regression of rate of growth on temperature was essentially linear over the range 15 degrees to 30 degrees C for all lines in all generations as was also the regression of rate of growth on various biological assessments of the environments over the whole temperature range. Either regression, therefore, provided linear regression coefficients which adequately accounted for the relative sensitivities of the lines to temperature in each generation of selection. These measures of environmental sensitivity confirmed our earlier report that selection for high mean performance in a good environment or for low mean performance in a poor environment leads to selections that are more sensitive to environmental variation than selections for high mean performance in a poor environment or for low mean performance in a good environment. These differences in sensitivity emerge as correlated responses during selection and the magnitude of these correlated responses is higher in the good environment than in the poor environment irrespective of the direction of selection. The environmental sensitivity of selection lines can be modified in either direction as required by either selecting for sensitivity simultaneously with the selection for mean performance or by selecting for mean performance in an above or below average environment. The quality of environments in which artificial selection is usually carried out is likely to have led to high selections with maximum environmental sensitivity and low selections with minimum sensitivity.

Environment↗
PubMed1973

Ecological genetics and natural selection in molluscs.

Polymorphic snails of the genus Cepaea have been widely used for research in ecological genetics. Natural selection by selective predation is important in controlling morph frequencies in some populations of C. nemoralis in England. The importance of environmental selection in affecting other patterns of local genetic differentiation of population structure (area effects) is a matter of controversy. Some authors emphasize divergent evolution of whole gene pools between area effects, while others feel that climatic selection acting on individual loci is important. Analysis of 500,000 C. nemoralis snails from throughout Europe shows that there is a strong positive association between gene frequencies at the shell color locus and mean summer temperature, but that no climatic correlations are obvious at other loci. Another species, C. vindobonensis, which has a much simpler system of polymorphism than does C. nemoralis, was investigated in Yugoslavia, in a region where there is known to be intense microclimatic differentiation because of the accumulation of cold air in frost hollows. There was a striking tendency for snails with lightly pigmented shell bands to be found in places with a warm microclimate. Physiological and behavioral experiments demonstrate that this is due primarily to differential energy absorption from sunshine by the different shell phenotypes. As in C. nemoralis, other C. vindobonensis phenotypes show no detectable association with the environment. It is possible that genes whose frequencies cannot be related to environmental selection may have evolved strong linkage interactions with other genes in the population's gene pool. Selection by the ecological environment and the genetic environment may therefore both be important in controlling the genetic structure of snail populations.

Animals↗
PubMed2002

The evolution of trade-offs: testing predictions on response to selection and environmental variation.

The concept of phenotypic trade-offs is a central element in evolutionary theory. In general, phenotypic models assume a fixed trade-off function, whereas quantitative genetic theory predicts that the trade-off function will change as a result of selection. For a linear trade-off function selection will readily change the intercept but will have to be relatively stronger to change the slope. We test these predictions by examining the trade-off between fecundity and flight capability, as measured by dorso-longitudinal muscle mass, in four different populations of the sand cricket, Gryllus firmus. Three populations were recently derived from the wild, and the fourth had been in the laboratory for 19 years. We hypothesized that the laboratory population had most likely undergone more and different selection from the three wild populations and therefore should differ from these in respect to both slope and intercept. Because of geographic variation in selection, we predicted a general difference in intercept among the four populations. We further tested the hypothesis that this intercept will be correlated with proportion macropterous and that this relationship will itself vary with environmental conditions experienced during both the nymphal and adult period. Observed variation in the phenotypic trade-off was consistent with the predictions of the quantitative genetic model. These results point to the importance of modeling trade-offs as dynamic rather than static relationships. We discuss how phenotypic models can incorporate such variation. The phenotypic trade-off between fecundity and dorso-longitudinal muscle mass is determined in part by variation in body size, illustrating the necessity of considering trade-offs to be multi factorial rather than simply bivariate relationships.

Animals↗
PubMed2000

Dualism and conflicts in understanding speciation.

Speciation is a central but elusive issue in evolutionary biology. Over the past sixty years, the subject has been studied within a framework conceived by Ernst Mayr and Theodosius Dobzhansky and subsequently developed further by numerous other workers. In this "isolation" theory, the evolution of reproductive isolation is a key element of speciation; natural selection is given only secondary importance while gene flow is considered prohibitive to the process. In this paper, I argue that certain elements in this approach have produced confusion and irreconcilability among students of speciation. The more prominent debates in speciation (i.e., the species definition, sympatry/allopatry, and the role of reinforcement) all derive from an inherent conflict between the "isolation" theory and Darwin's "selection" view on species and speciation (in which disruptive selection is crucial). New data, mainly from field ecology, molecular population genetics, laboratory studies with Drosophila and computer analysis, all suggest that the isolation theory may no longer be the most desirable vantage point from which to explore speciation. Instead, environmental selection in large populations, often unimpeded by ongoing gene flow, appears to be the decisive element. The traditional preoccupation with reproductive isolation has created gaps in our knowledge of several crucial issues, mainly regarding the role of environmental selection and its connection with mate selection.

Animals↗
PubMed2006

Confounder selection in environmental epidemiology: assessment of health effects of prenatal mercury exposure.

PURPOSE: The purpose of the study is to compare different approaches to the identification of confounders needed for analyzing observational data. Whereas standard analysis usually is conducted as if the confounders were known a priori, selection uncertainty also must be taken into account. METHODS: Confounders were selected by using backward elimination (BE), change in estimate (CIE) method, Akaike information criterion, Bayesian information criterion (BIC), and an empirical approach using a priori information. A modified ridge regression estimator, which shrinks effects of confounders toward zero, also was considered. For each criterion, uncertainty in the estimated exposure effect was assessed by using bootstrap simulations for which confounders were selected in each sample. These methods were illustrated by using data for mercury neurotoxicity in Faroe Islands children. Point estimates and standard errors of mercury effects on confounder-sensitive neurobehavioral outcomes were calculated for each selection procedure. RESULTS: The full model and the empirical a priori model showed approximately the same precision, and these methods were (slightly) inferior to only modified ridge regression. Lower precisions were obtained by using BE with a low cutoff level, BIC, and CIE. CONCLUSIONS: Standard analysis ignores model selection uncertainty and is likely to yield overoptimistic inferences. Thus, the traditional BE procedure with p = 5% should be avoided. If data-dependent procedures are required for confounder identification, we recommend that inferences be based on bootstrap statistics to describe the selection process.

Animals↗
PubMed2005

Is more choice always desirable? Evidence and arguments from leks, food selection, and environmental enrichment.

Recent studies on humans show that too much choice can make subjects less likely to choose any item. I consider general adaptive and non-adaptive explanations of why such choice aversion, or its converse, might occur in animals. There are three questions: is more choice always preferred, does it ever lead to less consumption (or a lower probability of consumption), and may it result in worse items being selected ? A preference for choice is one of the main explanations for lek formation and I draw attention to previously unrecognised parallels with models of human shopping behaviour. There is indeed evidence of female preference for larger leks, although much of the observational data are open to other interpretations. Unfortunately nobody has looked for choice aversion where it is most to be expected, in leks larger than normally occur. Evidence that too much choice of males confuses females is strongest in acoustically advertising frogs, but the widespread decrease of mating skew in larger leks might also have this explanation. A model reanalyses data on skew in black grouse Tetrao tetrix and suggests that considering only a random subset of a large lek may increase the chances of selecting the better males: larger leks are more likely to include better males, but these are less likely to be selected. These opposing effects may lead to an optimum lek size, but only with a sufficient decline in choice accuracy with size. With food choice, very few studies have avoided confounding choice with food quality, by manipulating only flavour. The widespread phenomena of stimulus-specific satiety and novelty seeking imply that monotonous diets are aversive, but no studies test whether animals choose sites where they know food diversity to be greater. Operant experiments that demonstrate mild preferences for free choice concern choice about the means to get food rather than the food itself. In some insect species even moderate choice of diet can be deleterious, and studies on search images and the confusion effect may be evidence of this in vertebrates. Environmental enrichment of captive animals often relies on increasing the options available, but it need not be the choice itself that is beneficial. I consider briefly further areas in biology where choice preference or aversion are potentially important.

Adaptation, Biological↗
PubMed2004

Selection and dispersal in a multispecies oak hybrid zone.

The four western North American red oak species (Quercus wislizeni, Q. parvula, Q. agrifolia, and Q. kelloggii) are known to produce hybrid products in all interspecific combinations. However, it is unknown whether hybrids are transitory resulting from interspecific gene flow or whether they are maintained through extrinsic selection. Here, we examine cryptic hybrid structure in Q. wislizeni through a broad region including contact and isolation from three other western North American red oaks using amplified fragment length polymorphism molecular markers. All four species were simultaneously detected in the genetic background of individuals morphologically assigned to Q. wislizeni, although the contribution of Q. kelloggii was minor. In some cases, introgression was detected well outside the region of sympatry with one of the parental species. Molecular structure at the individual level indicated this was due to long-distance pollen dispersal and not to local extinction of parental species. Species admixture proportions were correlated with climatic variables and greater proportions of Q. agrifolia and Q. parvula were present in the genetic background of Q. wislizeni in sites with cooler and more humid summers, corresponding with habitat preferences of the parental species. Partial Mantel tests indicated that climate was more important than distance from pollen source in this association. Despite high levels of introgression, species integrity was maintained in some populations in close proximity to the other species, providing further support to environmental selection in determining population genetic structure. Thus, the contribution of species mixtures to population genetic structure varies across the landscape according to availability of pollen, but more importantly to varying environmental selection pressures that produce a complex pattern of hybrid and pure gene pools.

California↗
PubMed2006

Associations between environmental stress, selection history, and quantitative genetic variation in Drosophila melanogaster.

Stressful environments may increase quantitative genetic variation in populations by promoting the expression of genetic variation that has not previously been eliminated or canalized by natural selection. This "selection history" hypothesis predicts that novel stressors will increase quantitative genetic variation, and that the magnitude of this effect will decrease following continued stress exposure. We tested these predictions using Drosophila melanogaster and sternopleural bristle number as a model system. In particular, we examined the effect of high temperature stress (31 degrees Celsius) on quantitative genetic variation before and after our study population had been reared at 31 degrees Celsius for 15 generations. High temperature stress was found to increase both additive genetic variance and heritability, but contrary to the selection history hypothesis prediction, the magnitude of this effect significantly increased after the study population had been reared for 15 generations under high temperature stress. These results demonstrate that high temperature stress increases quantitative genetic variation for bristle number, but do not support the selection history hypothesis as an explanation for this effect.

Adaptation, Biological↗
PubMed1992

Association of selected social, environmental and constitutional factors to blood lead levels in men aged 55-75 years.

Blood lead (B-Pb) levels were determined in 1802 out of 1856 non-occupationally exposed men aged 55-75 years living in the Rome area who participated, between 1989 and 1990, in an epidemiological survey for coronary heart disease (New Risk Factors Project). The median B-Pb level was 113 micrograms/l (10th-90th centiles: 74-180 micrograms/l) and only 0.7 per cent (n = 14) of the subjects had B-Pb values higher than 300 micrograms/l. B-Pb levels were significantly and positively associated to alcohol consumption. Moderate and heavy drinkers had median B-Pb level of 143 micrograms/l (10th-90th centiles: 92-233) and 165 micrograms/l (10th-90th centiles: 102-285) respectively, whereas non-drinkers had a median B-Pb level of 96 micrograms/l (10th-90th centiles: 66-143). The influence of smoking habits was less relevant. Subjects who never smoked and subjects smoking more than 20 cigarettes daily had median B-Pb levels of 103 and 133 micrograms/l, respectively. Individuals classified as habitual car-drivers had slightly higher Pb levels than non-drivers. Subjects classified as manual workers had higher B-Pb levels in comparison with non-manual workers and retired subjects. B-Pb levels were directly related to HDL-cholesterol (HDL-C, r = 0.2252) and gamma-glutamyltransferase (gamma-GT, r = 0.2207) serum levels. The alleged alcohol consumption was more related to B-Pb level (r = 0.3848) than to serum level of HDL-C (r = 0.2474) or gamma-GT (r = 0.2469). A significant correlation (r = 0.2409) also existed between B-Pb and blood cadmium levels (B-Cd). Subjects with a low Gaensler ratio, an index of respiratory function, had higher B-Pb levels. In multiple regression analyses alcohol intake was the most important predictor of B-Pb level, explaining more (14.27%) of the total variance than did B-Cd (4.98%), HDL-C (1.89%), driving habits (1.46%), gamma-GT (1.09%), skinfold thickness (0.96%), and Gaensler index (0.38%). The risk ratio of having B-Pb level higher than 180 micrograms/l (90th centile of B-Pb distribution in our subjects) was 5.3 (95% CI: 2.7-10.4) for drinkers versus non-drinkers and 1.9 (95% CI: 1.2-3.1) for current smokers versus subjects who had never smoked. B-Pb was, at least in our subjects, a more specific and sensitive objective index of alcohol consumption than gamma-GT and HDL-C.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗
PubMed2002

Environmental salinity selectively modifies the outer-ring deiodinating activity of liver, kidney and gill in the rainbow trout.

We here analyzed the effect of a mild hyperosmotic challenge on the activities of deiodinases type I (D1) and II (D2) in the trout liver, and D1 in kidney and gill, two organs involved in osmoregulation. FW-adapted immature rainbow trout were transferred to 5 per thousand SW and killed 0.5, 1, 2, 4, 8 12, 24 and 48 h post-transfer (PT). Fish maintained in FW served as controls. Hepatic, renal and branchial D1 and hepatic D2 activities were assessed as well as circulating levels of T(3), T(4) and cortisol. Hyperosmotic challenge elicited significant and sustained decreases in kidney D1 and liver D2 activities at 8 h PT, which returned to control values at 48 h PT. In contrast, liver and gill D1 activities exhibited no significant change throughout the study. Also, significant increases in circulating T(4) at 2-4 and 48 h PT were observed. Circulating T(3) remained unmodified until 24-48 h PT, when it rose sharply. Simultaneously, cortisol showed a trend towards increase during the initial 4 h PT, which attained significance at 48 h PT. The present findings demonstrate that a mild hypertonic challenge is sufficient to elicit responses in the trout thyroidal axis. Hormonal changes in the circulatory compartment are in accordance with those previously described for migratory salmonids. A novel aspect of our findings is the organ-specific differential response exhibited by ORD-enzymes when trout are exposed to a mildly different osmotic environment. Our findings further establish the uniqueness of fish thyroid physiology, and can be of value in further understanding the evolutionary aspects of this ORD family of deiodinases.

Animals↗