Interspecific Competition, Environmental Gradients, Gene Flow, and the Coevolution of Species' Borders

2000 ◽  
Vol 155 (5) ◽  
pp. 583-605 ◽  
Author(s):  
Ted J. Case ◽  
Mark L. Taper
Keyword(s):  
Gene Flow ◽  
Interspecific Competition ◽  
Environmental Gradients ◽  
Species Borders

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 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.

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 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.

Molecular genetic variation in a widespread forest tree species Eucalyptus obliqua (Myrtaceae) on the island of Tasmania

2011 ◽  
Vol 59 (3) ◽  
pp. 226 ◽  
Author(s):  
Justin A. Bloomfield ◽  
Paul Nevill ◽  
Brad M. Potts ◽  
René E. Vaillancourt ◽  
Dorothy A. Steane
Keyword(s):  
Genetic Variation ◽  
Gene Flow ◽  
Environmental Gradients ◽  
Molecular Genetic ◽  
Continuous Distribution ◽  
Main Mode ◽  
Chloroplast Microsatellite ◽  
Eastern Australia ◽  
Nuclear Microsatellite ◽  
Microsatellite Diversity

Eucalyptus obliqua L’Hér. is widespread across south-eastern Australia. On the island of Tasmania it has a more-or-less continuous distribution across its range and it dominates much of the wet sclerophyll forest managed for forestry purposes. To understand better the distribution of genetic variation in these native forests we examined nuclear microsatellite diversity in 432 mature individuals from 20 populations of E. obliqua across Tasmania, including populations from each end of three locally steep environmental gradients. In addition, chloroplast microsatellite loci were assessed in 297 individuals across 31 populations. Nuclear microsatellite diversity values in E. obliqua were high (average HE = 0.80) and inbreeding coefficients low (average F = 0.02) within these populations. The degree of differentiation between populations was very low (FST = 0.015). No significant microsatellite differentiation could be found across three locally steep environmental gradients, even though there is significant genetic differentiation in quantitative traits. This suggests that the observed quantitative variation is maintained by natural selection. Population differentiation based on chloroplast haplotypes was high (GST = 0.69) compared with that based on nuclear microsatellites, suggesting that pollen-mediated gene flow is >150 times the level of seed-mediated gene flow in this animal-pollinated species; hence, pollen is likely to be the main mode of gene flow countering selection along local environmental gradients. Implications of these results for silvicultural practices are discussed.

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