scholarly journals Limits to adaptation along environmental gradients

2014 ◽  
Author(s):  
Jitka Polechová ◽  
Nick Barton
Keyword(s):  
Gene Flow ◽  
Genetic Drift ◽  
Environmental Gradients ◽  
Single Species ◽  
Local Conditions ◽  
Deterministic Theory ◽  
Range Margin ◽  
Abrupt Changes ◽  
Analytical Tools ◽  
Range Fragmentation

Why do species not adapt to ever-wider ranges of conditions, gradually expanding their ecological niche and geographic range? Gene flow across environments has two conflicting effects: while it increases genetic variation, which is a prerequisite for adaptation, gene flow may swamp adaptation to local conditions. In 1956, Haldane proposed that when the environment varies across space, ?swamping? by gene flow creates a positive feedback between low population size and maladaptation, leading to a sharp range margin. Yet, current deterministic theory shows that when variance can evolve, there is no such limit. Using simple analytical tools and simulations, we show that genetic drift can generate a sharp margin to a species' range, by reducing genetic variance below the level needed for adaptation to spatially variable conditions. Aided by separation of ecological and evolutionary time scales, the identified effective dimensionless parameters reveal a simple threshold that predicts when adaptation at the range margin fails. Two observable parameters determine the threshold: i) the effective environmental gradient, which can be measured by the loss of fitness due to dispersal to a different environment, and ii) the efficacy of selection relative to genetic drift. The theory predicts sharp range margins even in the absence of abrupt changes in the environment. Furthermore, it implies that gradual worsening of conditions across a species' habitat may lead to a sudden range fragmentation, when adaptation to a wide span of conditions within a single species becomes impossible.

scholarly journals Limits to adaptation along environmental gradients

2015 ◽  
Vol 112 (20) ◽  
pp. 6401-6406 ◽  
Author(s):  
Jitka Polechová ◽  
Nicholas H. Barton
Keyword(s):  
Gene Flow ◽  
Genetic Drift ◽  
Environmental Gradients ◽  
Single Species ◽  
Local Conditions ◽  
Deterministic Theory ◽  
Range Margin ◽  
Abrupt Changes ◽  
Analytical Tools ◽  
Range Fragmentation

Why do species not adapt to ever-wider ranges of conditions, gradually expanding their ecological niche and geographic range? Gene flow across environments has two conflicting effects: although it increases genetic variation, which is a prerequisite for adaptation, gene flow may swamp adaptation to local conditions. In 1956, Haldane proposed that, when the environment varies across space, “swamping” by gene flow creates a positive feedback between low population size and maladaptation, leading to a sharp range margin. However, current deterministic theory shows that, when variance can evolve, there is no such limit. Using simple analytical tools and simulations, we show that genetic drift can generate a sharp margin to a species’ range, by reducing genetic variance below the level needed for adaptation to spatially variable conditions. Aided by separation of ecological and evolutionary timescales, the identified effective dimensionless parameters reveal a simple threshold that predicts when adaptation at the range margin fails. Two observable parameters determine the threshold: (i) the effective environmental gradient, which can be measured by the loss of fitness due to dispersal to a different environment; and (ii) the efficacy of selection relative to genetic drift. The theory predicts sharp range margins even in the absence of abrupt changes in the environment. Furthermore, it implies that gradual worsening of conditions across a species’ habitat may lead to a sudden range fragmentation, when adaptation to a wide span of conditions within a single species becomes impossible.

scholarly journals Pervasive Genomic Signatures of Local Adaptation to Altitude Across Highland Specialist Andean Hummingbird Populations

2021 ◽  
Author(s):  
Marisa C W Lim ◽  
Ke Bi ◽  
Christopher C Witt ◽  
Catherine H Graham ◽  
Liliana M Dávalos
Keyword(s):  
Gene Flow ◽  
Local Adaptation ◽  
Genetic Drift ◽  
Population Genetic ◽  
Environmental Gradients ◽  
Functional Differentiation ◽  
High Elevation ◽  
Nucleotide Polymorphisms ◽  
Peruvian Andes ◽  
Tropical Mountains

Abstract Populations along steep environmental gradients are subject to differentiating selection that can result in local adaptation, despite countervailing gene flow, and genetic drift. In montane systems, where species are often restricted to narrow ranges of elevation, it is unclear whether the selection is strong enough to influence functional differentiation of subpopulations differing by a few hundred meters in elevation. We used targeted capture of 12 501 exons from across the genome, including 271 genes previously implicated in altitude adaptation, to test for adaptation to local elevations for 2 highland hummingbird species, Coeligena violifer (n = 62) and Colibri coruscans (n = 101). For each species, we described population genetic structure across the complex geography of the Peruvian Andes and, while accounting for this structure, we tested whether elevational allele frequency clines in single nucleotide polymorphisms (SNPs) showed evidence for local adaptation to elevation. Although the 2 species exhibited contrasting population genetic structures, we found signatures of clinal genetic variation with shifts in elevation in both. The genes with SNP-elevation associations included candidate genes previously discovered for high-elevation adaptation as well as others not previously identified, with cellular functions related to hypoxia response, energy metabolism, and immune function, among others. Despite the homogenizing effects of gene flow and genetic drift, natural selection on parts of the genome evidently optimizes elevation-specific cellular function even within elevation range-restricted montane populations. Consequently, our results suggest local adaptation occurring in narrow elevation bands in tropical mountains, such as the Andes, may effectively make them “taller” biogeographic barriers.

scholarly journals The costs and benefits of dispersal in small populations

2021 ◽  
Author(s):  
Jitka Polechova
Keyword(s):  
Gene Flow ◽  
Genetic Drift ◽  
Environmental Gradients ◽  
Strong Increase ◽  
Small Populations ◽  
Marginal Populations ◽  
Neighbourhood Size ◽  
Mean Fitness ◽  
Varying Environments

Dispersal has three major effects on adaptation. First, the gene flow mixes alleles adapted to different environments, potentially hindering (swamping) adaptation. Second, it inflates genetic variance: this aids adaptation to spatially (and temporally) varying environments but if selection is hard, it lowers the mean fitness of the population. Third, neighbourhood size, which determines how weak genetic drift is, increases with dispersal -- when genetic drift is strong, increase of neighbourhood size with dispersal aids adaptation. In this note I focus on the role of dispersal in environments which change smoothly across space, and when local populations are quite small such that genetic drift has a significant effect. Using individual-based simulations, I show that in small populations, even leptokurtic dispersal benefits adaptation, by reducing the power of genetic drift. This has implications for management of small marginal populations: increased gene flow appears beneficial as long as adaptations involves a quantitative, rather than a discrete, trait. However, heavily leptokurtic dispersal will swamp continuous adaptation along steep environmental gradients so that only patches of locally adapted subpopulations remain.

scholarly journals Effects of Genetic Drift and Gene Flow on the Selective Maintenance of Genetic Variation

Genetics ◽  
2013 ◽  
Vol 194 (1) ◽  
pp. 235-244 ◽  
Author(s):  
Bastiaan Star ◽  
Hamish G. Spencer
Keyword(s):  
Genetic Variation ◽  
Gene Flow ◽  
Genetic Drift ◽  
Selective Maintenance

scholarly journals Environmental variation mediates the prevalence and co-occurrence of parasites in the common lizard, Zootoca vivipara

BMC Ecology ◽  
2019 ◽  
Vol 19 (1) ◽  
Author(s):  
Qiang Wu ◽  
Murielle Richard ◽  
Alexis Rutschmann ◽  
Donald B. Miles ◽  
Jean Clobert
Keyword(s):  
Environmental Factors ◽  
Human Disturbance ◽  
Vegetation Cover ◽  
Structural Equation ◽  
Environmental Gradients ◽  
Parasite Load ◽  
Single Species ◽  
Common Lizard ◽  
Zootoca Vivipara ◽  
The Common

Abstract Background Hosts and their parasites are under reciprocal selection, leading to coevolution. However, parasites depend not only on a host, but also on the host’s environment. In addition, a single host species is rarely infested by a single species of parasite and often supports multiple species (i.e., multi-infestation). Although the arms race between a parasite and its host has been well studied, few data are available on how environmental conditions may influence the process leading to multiple infestations. In this study, we examine whether: (1) environmental factors including altitude, temperature, vegetation cover, human disturbance, and grazing by livestock affect the prevalence of two types of ectoparasites, mites and ticks, on their host (the common lizard, Zootoca vivipara) and (2) competition is evident between mites and ticks. Results We found the probability of mite infestation increased with altitude and vegetation cover, but decreased with human disturbance and presence of livestock. In contrast, the probability of tick infestation was inversely associated with the same factors. Individuals with low body condition and males had higher mite loads. However, this pattern was not evident for tick loads. The results from a structural equation model revealed that mites and ticks indirectly and negatively affected each other’s infestation probability through an interaction involving the environmental context. We detected a direct negative association between mites and ticks only when considering estimates of parasite load. This suggests that both mites and ticks could attach to the same host, but once they start to accumulate, only one of them takes advantage. Conclusion The environment of hosts has a strong effect on infestation probabilities and parasite loads of mites and ticks. Autecological differences between mites and ticks, as indicated by their opposing patterns along environmental gradients, may explain the pattern of weak contemporary interspecific competition. Our findings emphasize the importance of including environmental factors and the natural history of each parasite species in studies of host–parasite coevolution.

scholarly journals Ecological Divergence of a Novel Group of Chloroflexus Strains along a Geothermal Gradient

2012 ◽  
Vol 79 (4) ◽  
pp. 1353-1358 ◽  
Author(s):  
Michael L. Weltzer ◽  
Scott R. Miller
Keyword(s):  
16S Rrna ◽  
Carbon Fixation ◽  
Hot Spring ◽  
Environmental Gradients ◽  
Geothermal Gradient ◽  
Geothermal Systems ◽  
Local Conditions ◽  
Content Type ◽  
Thermal Niche ◽  
Coa Reductase

ABSTRACTEnvironmental gradients are expected to promote the diversification and coexistence of ecological specialists adapted to local conditions. Consistent with this view, genera of phototrophic microorganisms in alkaline geothermal systems generally appear to consist of anciently divergent populations which have specialized on different temperature habitats. At White Creek (Lower Geyser Basin, Yellowstone National Park), however, a novel, 16S rRNA-defined lineage of the filamentous anoxygenic phototrophChloroflexus(OTU 10, phylumChloroflexi) occupies a much wider thermal niche than other 16S rRNA-defined groups of phototrophic bacteria. This suggests thatChloroflexusOTU 10 is either an ecological generalist or, alternatively, a group of cryptic thermal specialists which have recently diverged. To distinguish between these alternatives, we first isolated laboratory strains ofChloroflexusOTU 10 from along the White Creek temperature gradient. These strains are identical for partial gene sequences encoding the 16S rRNA and malonyl coenzyme A (CoA) reductase. However, strains isolated from upstream and downstream samples could be distinguished based on sequence variation atpcs, which encodes the propionyl-CoA synthase of the 3-hydroxypropionate pathway of carbon fixation used by the genusChloroflexus. We next demonstrated that strains have diverged in temperature range for growth. Specifically, we obtained evidence for a positive correlation between thermal niche breadth and temperature optimum, with strains isolated from lower temperatures exhibiting greater thermal specialization than the most thermotolerant strain. The study has implications for our understanding of both the process of niche diversification of microorganisms and how diversity is organized in these hot spring communities.

scholarly journals Contrasting signatures of genomic divergence during sympatric speciation

Nature ◽  
2020 ◽  
Vol 588 (7836) ◽  
pp. 106-111 ◽  
Author(s):  
Andreas F. Kautt ◽  
Claudius F. Kratochwil ◽  
Alexander Nater ◽  
Gonzalo Machado-Schiaffino ◽  
Melisa Olave ◽  
...  
Keyword(s):  
Gene Flow ◽  
Genetic Architecture ◽  
Single Species ◽  
Sympatric Speciation ◽  
Ecological Performance ◽  
Genome Wide ◽  
Genomic Divergence ◽  
Empirical Tests ◽  
Selected Traits ◽  
Stable Genome

AbstractThe transition from ‘well-marked varieties’ of a single species into ‘well-defined species’—especially in the absence of geographic barriers to gene flow (sympatric speciation)—has puzzled evolutionary biologists ever since Darwin1,2. Gene flow counteracts the buildup of genome-wide differentiation, which is a hallmark of speciation and increases the likelihood of the evolution of irreversible reproductive barriers (incompatibilities) that complete the speciation process3. Theory predicts that the genetic architecture of divergently selected traits can influence whether sympatric speciation occurs4, but empirical tests of this theory are scant because comprehensive data are difficult to collect and synthesize across species, owing to their unique biologies and evolutionary histories5. Here, within a young species complex of neotropical cichlid fishes (Amphilophus spp.), we analysed genomic divergence among populations and species. By generating a new genome assembly and re-sequencing 453 genomes, we uncovered the genetic architecture of traits that have been suggested to be important for divergence. Species that differ in monogenic or oligogenic traits that affect ecological performance and/or mate choice show remarkably localized genomic differentiation. By contrast, differentiation among species that have diverged in polygenic traits is genomically widespread and much higher overall, consistent with the evolution of effective and stable genome-wide barriers to gene flow. Thus, we conclude that simple trait architectures are not always as conducive to speciation with gene flow as previously suggested, whereas polygenic architectures can promote rapid and stable speciation in sympatry.

scholarly journals Gene Flow Limits Adaptation along Steep Environmental Gradients

2020 ◽  
Vol 195 (3) ◽  
pp. E67-E86 ◽  
Author(s):  
Judith C. Bachmann ◽  
Alexandra Jansen van Rensburg ◽  
Maria Cortazar-Chinarro ◽  
Anssi Laurila ◽  
Josh Van Buskirk
Keyword(s):  
Gene Flow ◽  
Environmental Gradients

scholarly journals Cooperation mitigates diversity loss in a spatially expanding microbial population

2019 ◽  
Vol 116 (47) ◽  
pp. 23582-23587 ◽  
Author(s):  
Saurabh R. Gandhi ◽  
Kirill S. Korolev ◽  
Jeff Gore
Keyword(s):  
Genetic Drift ◽  
Founder Effect ◽  
Microbial Population ◽  
Growth Dynamics ◽  
Low Density ◽  
Drastic Reduction ◽  
Diversity Loss ◽  
Abrupt Changes ◽  
Expanding Population ◽  
Serial Founder Effect

The evolution and potentially even the survival of a spatially expanding population depends on its genetic diversity, which can decrease rapidly due to a serial founder effect. The strength of the founder effect is predicted to depend strongly on the details of the growth dynamics. Here, we probe this dependence experimentally using a single microbial species, Saccharomyces cerevisiae, expanding in multiple environments that induce varying levels of cooperativity during growth. We observe a drastic reduction in diversity during expansions when yeast grows noncooperatively on simple sugars, but almost no loss of diversity when cooperation is required to digest complex metabolites. These results are consistent with theoretical expectations: When cells grow independently from each other, the expansion proceeds as a pulled wave driven by growth at the low-density tip of the expansion front. Such populations lose diversity rapidly because of the strong genetic drift at the expansion edge. In contrast, diversity loss is substantially reduced in pushed waves that arise due to cooperative growth. In such expansions, the low-density tip of the front grows much more slowly and is often reseeded from the genetically diverse population core. Additionally, in both pulled and pushed expansions, we observe a few instances of abrupt changes in allele fractions due to rare fluctuations of the expansion front and show how to distinguish such rapid genetic drift from selective sweeps.

scholarly journals Evaluation of genetic isolation within an island flora reveals unusually widespread local adaptation and supports sympatric speciation

2014 ◽  
Vol 369 (1648) ◽  
pp. 20130342 ◽  
Author(s):  
Alexander S. T. Papadopulos ◽  
Maria Kaye ◽  
Céline Devaux ◽  
Helen Hipperson ◽  
Jackie Lighten ◽  
...  
Keyword(s):  
Gene Flow ◽  
Local Adaptation ◽  
Plant Species ◽  
Environmental Gradients ◽  
Isolation By Distance ◽  
Model Averaging ◽  
Dispersal Limitation ◽  
Population Divergence ◽  
Environmental Pressures ◽  
Isolation By Environment

It is now recognized that speciation can proceed even when divergent natural selection is opposed by gene flow. Understanding the extent to which environmental gradients and geographical distance can limit gene flow within species can shed light on the relative roles of selection and dispersal limitation during the early stages of population divergence and speciation. On the remote Lord Howe Island (Australia), ecological speciation with gene flow is thought to have taken place in several plant genera. The aim of this study was to establish the contributions of isolation by environment (IBE) and isolation by community (IBC) to the genetic structure of 19 plant species, from a number of distantly related families, which have been subjected to similar environmental pressures over comparable time scales. We applied an individual-based, multivariate, model averaging approach to quantify IBE and IBC, while controlling for isolation by distance (IBD). Our analyses demonstrated that all species experienced some degree of ecologically driven isolation, whereas only 12 of 19 species were subjected to IBD. The prevalence of IBE within these plant species indicates that divergent selection in plants frequently produces local adaptation and supports hypotheses that ecological divergence can drive speciation in sympatry.

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