The Effect of Heterogeneous Environments and a Competitor on Genetic Variation in Drosophila

1978 ◽  
Vol 112 (987) ◽  
pp. 935-947 ◽  
Author(s):  
Jeffrey R. Powell ◽  
Harry Wistrand
Keyword(s):  
Genetic Variation ◽  
Heterogeneous Environments

GENETIC LOADS IN HETEROGENEOUS ENVIRONMENTS

Genetics ◽  
1975 ◽  
Vol 80 (3) ◽  
pp. 621-635
Author(s):  
Charles E Taylor
Keyword(s):  
Population Structure ◽  
Genetic Variation ◽  
Gene Frequency ◽  
Phase Plane ◽  
Genetic Load ◽  
Sufficient Conditions ◽  
Heterogeneous Environments ◽  
Niche Space ◽  
Necessary And Sufficient ◽  
Existence Of Equilibria

ABSTRACT A model of population structure in heterogeneous environments is described with attention focused on genetic variation at a single locus. The existence of equilibria at which there is no genetic load is examined.—The absolute fitness of any genotype is regarded as a function of location in the niche space and the population density at that location. It is assumed that each organism chooses to live in that habitat in which it is most fit ("optimal habitat selection").—Equilibria at which there is no segregational load ("loadless equilibria") may exist. Necessary and sufficient conditions for the existence of such equilibria are very weak. If there is a sufficient amount of dominance or area in which the alleles are selectively neutral, then there exist equilibria without segregational loads. In the N, p phase plane defined by population size, N, and gene frequency, p, these equilibria generally consist of a line segment which is parallel to the p axis. These equilibria are frequently stable.

scholarly journals Genetic variation in varying environments

1981 ◽  
Vol 37 (1) ◽  
pp. 79-93 ◽  
Author(s):  
Trudy F. C. Mackay
Keyword(s):  
Body Weight ◽  
Genetic Variation ◽  
Spatial Heterogeneity ◽  
Temporal Variation ◽  
Genetic Variance ◽  
Environmental Variability ◽  
Additive Genetic Variance ◽  
Environmental Variation ◽  
Heterogeneous Environments ◽  
Varying Environments

SUMMARYIn order to assess the relationship between genetic and environmental variability, a large natural population of Drosophila melanogaster was replicated as eight subpopulations, which were subjected to four different patterns of environmental variation. The environmental variable imposed was presence of 15% ethanol in the culture medium. Experimental treatments of the populations were intended to simulate constant environmental conditions, spatial heterogeneity in the environment, and two patterns of temporal environmental variation with different periodicity (long- and short-term temporal variation). Additive genetic and phenotypic variation in sternopleural and abdominal chaeta number, and body weight, were estimated in two successive years, and measurements were taken of the genotype–environment correlation of body weight and sternopleural bristle score with medium type.Additive genetic variance of sternopleural chaeta number and of body weight was significantly greater in the three populations experiencing environmental heterogeneity than in the control population, but additive genetic variance of abdominal bristle score was not clearly affected by exposing populations to varying environments. Temporal environmental variation was equally, if not more, efficient in promoting the maintenance of genetic variation than spatial heterogeneity, but the cycle length of the temporal variation was of no consequence. Specific genotype–environment interactions were not present, therefore adaptation to heterogeneous environments is by selection of heterozygosity per se, rather than by differential survival of genotypes in the alternate niches.

Adaptation of Pinuscontorta populations to heterogeneous environments in northern Idaho

1983 ◽  
Vol 13 (3) ◽  
pp. 405-411 ◽  
Author(s):  
G. E. Rehfeldt
Keyword(s):  
Genetic Variation ◽  
Multiple Regression ◽  
Regression Models ◽  
Leaf Length ◽  
Seed Source ◽  
Freezing Injury ◽  
Quadratic Model ◽  
Heterogeneous Environments ◽  
Multiple Regression Models ◽  
Northern Idaho

Genetic variation among 28 lodgepole pine (Pinuscontorta Dougl.) populations from northern Idaho was studied in three contrasting environments. Populations were located within 55 km of the Priest River Experimental Forest where 4-year-old seedlings were compared in environments at 750, 1200, and 1500 m elevation. Statistical analyses of six variables (4-year height, leaf length, freezing injury, multiple whorls, lammas growth, and adjusted height) detected differentiation among populations. Multiple regression models related adaptive differentiation to geographic and ecologic characteristics of the seed source. Elevation of the seed source, represented in a quadratic model, accounted for as much as 86% of the variance among populations. Results were used to estimate the limits and consequences of elevational transfers of seed.

scholarly journals Cryptic microgeographic variation in responses of larval Atlantic cod to warmer temperatures

2021 ◽  
Author(s):  
Rebekah A. Oomen ◽  
Elisabeth Juliussen ◽  
Esben M. Olsen ◽  
Halvor Knutsen ◽  
Sissel Jentoft ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Gadus Morhua ◽  
Atlantic Cod ◽  
Common Garden ◽  
Reaction Norm ◽  
Heterogeneous Environments ◽  
Growth And Survival ◽  
Cryptic Genetic Variation ◽  
Thermal Plasticity ◽  
Microgeographic Variation

AbstractAlthough temperature is known to drive species dynamics and distributions, our understanding of the extent to which thermal plasticity varies within species is poor. Differences in plasticity can arise through local adaptation to heterogeneous environments, hybridization, and the release of cryptic genetic variation in novel environments. Here, wild Atlantic cod (Gadus morhua) from contrasting environments inside and outside of a fjord system in southern Norway spawned freely in a semi-natural laboratory environment, generating pure crosses and reciprocal hybrids. A common-garden rearing experiment of the larvae at 6°C, 9.5°C, and 13°C revealed cryptic genetic variation in thermal responses of growth and survival at warmer temperatures. Variation in growth plasticity was greatest from 9.5°C to 13°C, the latter of which exceeds temperatures currently typical of larvae in their native environments. In contrast to our prediction of intermediate hybrid responses consistent with additive genetic effects, one reciprocal hybrid cross showed a 4% increase in size at the highest temperature, whereas most crosses exhibited 4-12% reductions in size. All crosses experienced severe (76-93%) reductions in survival from 9.5°C to 13°C. Variation in survival plasticity suggests a genetically variable basis for the severity with which survival declines with increasing temperature and the potential for an adaptive response to warming. Notably, we demonstrate the potential for hybridization between coexisting ‘fjord’ and ‘North Sea’ ecotypes that naturally inhabit the inner and outer fjord environments at contrasting frequencies. Yet, ecotype explained a minor (3-10%) component of growth reaction norm variation, suggesting it is insufficient for describing important biological variation. Current broad-scale management and lack of coastal monitoring impede the development of strategies to maintain the potential for adaptation to warming temperatures in systems with such phenotypic complexity resulting from cryptic genetic variation, coexisting ecotypes, and gene flow.

scholarly journals Effect of migration and environmental heterogeneity on the maintenance of quantitative variation: a simulation study

2017 ◽  
Author(s):  
Tegan Krista McDonald ◽  
Sam Yeaman
Keyword(s):  
Genetic Variation ◽  
Habitat Fragmentation ◽  
Environmental Heterogeneity ◽  
Mutation Rates ◽  
Stabilizing Selection ◽  
Heterogeneous Environments ◽  
Migration Rates ◽  
Theoretical Predictions ◽  
And Migration ◽  
General Explanation

AbstractThe paradox of high genetic variation observed in traits under stabilizing selection is a longstanding problem in evolutionary theory, as mutation rates are 10-100 times too low to explain observed levels of standing genetic variation under classic models of mutation-selection balance. Here, we use individual-based simulations to explore the effect of various types of environmental heterogeneity on the maintenance of genetic variation (VA) for a quantitative trait under stabilizing selection. We find that VA is maximized at intermediate migration rates in spatially heterogeneous environments, and that the observed patterns are robust to changes in population size. Spatial environmental heterogeneity increased variation by as much as 10-fold over mutation-selection-balance alone, whereas pure temporal environmental heterogeneity increased variance by only 45% at max. Our results show that some combinations of spatial heterogeneity and migration can maintain considerably more variation than mutation-selection balance, potentially reconciling the discrepancy between theoretical predictions and empirical observations. However, given the narrow regions of parameter space required for this effect, this is unlikely to provide a general explanation for the maintenance of variation. Nonetheless, our results suggest that habitat fragmentation may affect the maintenance of VA and thereby reduce the adaptive capacity of populations.

scholarly journals Extreme climatic events but not environmental heterogeneity shape within-population genetic variation in maritime pine

2021 ◽  
Author(s):  
Juliette Archambeau ◽  
Marta Benito Garzón ◽  
Marina de Miguel Vega ◽  
Benjamin Brachi ◽  
Frédéric Barraquand ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Population Genetic ◽  
Environmental Heterogeneity ◽  
Maritime Pine ◽  
Heterogeneous Environments ◽  
Evolutionary Forces ◽  
Common Gardens ◽  
Quantitative Genetic ◽  
Population Genetic Variation

AbstractHow evolutionary forces interact to maintain quantitative genetic variation within populations has been a matter of extensive theoretical debates. While mutation and migration increase genetic variation, natural selection and genetic drift are expected to deplete it. To date, levels of genetic variation observed in natural populations are hard to predict without accounting for other processes, such as balancing selection in heterogeneous environments. We aimed to empirically test three hypotheses: (i) admixed populations have higher quantitative genetic variation due to introgression from other gene pools, (ii) quantitative genetic variation is lower in populations from harsher environments (i.e. experiencing stronger selection), and (iii) quantitative genetic variation is higher in populations from spatially heterogeneous environments. We used phenotypic measurements of five growth, phenological and functional traits from three clonal common gardens, consisting of 523 clones from 33 populations of maritime pine (Pinus pinaster Aiton). Populations from harsher climates (mainly colder areas) showed lower genetic variation for height in the three common gardens. Surprisingly, we did not find any association between within-population genetic variation and environmental heterogeneity or population admixture for any trait. Our results suggest a predominant role of natural selection in driving within-population genetic variation, and therefore indirectly their adaptive potential.

scholarly journals Gene Flow and Genetic Variation Explain Signatures of Selection across a Climate Gradient in Two Riparian Species

Genes ◽  
2019 ◽  
Vol 10 (8) ◽  
pp. 579 ◽  
Author(s):  
Hopley ◽  
Byrne
Keyword(s):  
Genetic Variation ◽  
Gene Flow ◽  
Environmental Gradients ◽  
Genetic Connectivity ◽  
Heterogeneous Environments ◽  
Climate Gradients ◽  
Climate Gradient ◽  
Riparian Species ◽  
High Gene ◽  
Signatures Of Selection

Many species occur across environmental gradients and it is expected that these species will exhibit some signals of adaptation as heterogeneous environments and localized gene flow may facilitate local adaptation. While riparian zones can cross climate gradients, many of which are being impacted by climate change, they also create microclimates for the vegetation, reducing environmental heterogeneity. Species with differing distributions in these environments provide an opportunity to investigate the importance of genetic connectivity in influencing signals of adaptation over relatively short geographical distance. Association analysis with genomic data was used to compare signals of selection to climate variables in two species that have differing distributions along a river traversing a climate gradient. Results demonstrate links between connectivity, standing genetic variation, and the development of signals of selection. In the restricted species, the combination of high gene flow in the middle and lower catchment and occurrence in a microclimate created along riverbanks likely mitigated the development of selection to most climatic variables. In contrast the more widely distributed species with low gene flow showed a stronger signal of selection. Together these results strengthen our knowledge of the drivers and scale of adaptation and reinforce the importance of connectivity across a landscape to maintain adaptive potential of plant species.

Adaptation of Picea engelmannii populations to the heterogeneous environments of the Intermountain West

1994 ◽  
Vol 72 (8) ◽  
pp. 1197-1208 ◽  
Author(s):  
Gerald E. Rehfeldt
Keyword(s):  
Genetic Variation ◽  
Regression Models ◽  
Cold Hardiness ◽  
Ecological Genetics ◽  
Picea Engelmannii ◽  
Heterogeneous Environments ◽  
Intermountain West ◽  
Morphometric Characters ◽  
Blue Spruce ◽  
Engelmann Spruce

Seedlings from 104 natural populations of Engelmann spruce (Picea engelmannii) and 10 blue spruce (Picea pungens) populations from the Intermountain West, U.S.A., were compared in common gardens. Comparisons involved 16 characters that described growth, development, and cold hardiness plus nine monoterpenes. Canonical discriminant analyses detected one population of blue spruce that had been misidentified, readily separated populations of blue and Engelmann spruce, suggested that three Southwest populations differed markedly from Intermountain populations of Engelmann spruce, but identified no Intermountain populations that reflected introgression with blue spruce. Genetic differences were detected among populations of Engelmann spruce for 16 of the morphometric characters, and multiple regression models accounted for as much as 70% of the variance among populations. The regressions described genetic variation occurring along clines that were dominated by elevational and latitudinal effects. The slope of the clines, however, was relatively gentle; populations located within the same physiographic province must be separated by at least 420 m in elevation before genetic differentiation becomes a reasonable possibility. By providing a means for assessing the degree by which similar genotypes recur across the landscape, the regression models have direct practical application in programs ranging from land management to conservation biology. Key words: population differentiation, genetic variation, ecological genetics.

scholarly journals GENETIC VARIATION IN HETEROGENEOUS ENVIRONMENTS

Genetics ◽  
1976 ◽  
Vol 83 (4) ◽  
pp. 887-894
Author(s):  
Charles E Taylor
Keyword(s):  
Population Structure ◽  
Genetic Variation ◽  
Habitat Selection ◽  
Population Density ◽  
Genetic Polymorphisms ◽  
Sufficient Conditions ◽  
Adaptive Significance ◽  
The Other ◽  
Heterogeneous Environments ◽  
Niche Space

ABSTRACT A model of population structure in heterogeneous environments is described and conditions sufficient for maintaining a polymorphism are derived. The absolute fitness of any genotype is regarded as a function of location in the niche space and the population density at that location. Two modes of habitat selection are examined: (1) organisms are distributed uniformly over the environment; and (2) each organism selects to occupy that habitat in which it is most fit ("optimal habitant selection").—Sufficient conditions for maintenance of genetic polymorphisms are derived for both models. In populations which do not practice habitat selection heterozygote superiority averaged over the environment is sufficient to guarantee the existence of polymorphisms. Comparable conditions for populations which practice optimal habitat selection are much less restrictive. If the heterozygotes are superior to one homozygote in any one part of the niche and to the other homozygote in any other part of the niche then a polymorphism will be defined.—A positive correlation between genetic and environmental variation follows from the model with habitat selection, but not from the other. The adaptive significance of polymorphisms thus depends on how animals behave.

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