scholarly journals The limits to parapatric speciation 3: Evolution of strong reproductive isolation in presence of gene flow despite limited ecological differentiation

2020 ◽  
Author(s):  
Alexandre Blanckaert ◽  
Claudia Bank ◽  
Joachim Hermisson
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Local Adaptation ◽  
Maximum Amount ◽  
Genetic Barrier ◽  
Incipient Species ◽  
Postzygotic Reproductive Isolation ◽  
Minimal Configuration ◽  
Parapatric Speciation ◽  
Two Populations

AbstractGene flow tends to impede the accumulation of genetic divergence. Here, we determine the limits for the evolution of postzygotic reproductive isolation in a model of two populations that are connected by gene flow. We consider two selective mechanisms for the creation and maintenance of a genetic barrier: local adaptation leads to divergence among incipient species due to selection against migrants, and Dobzhansky-Muller incompatibilities (DMIs) reinforce the genetic barrier through selection against hybrids. In particular, we are interested in the maximum strength of the barrier under a limited amount of local adaptation, a challenge that may initially face many incipient species. We first confirm that with classical two-locus DMIs, the maximum amount of local adaptation is indeed a limit to the strength of a genetic barrier. However, with three or more loci and cryptic epistasis, this limit holds no longer. In particular, we identify a minimal configuration of three epistatically interacting mutations that is sufficient to confer strong reproductive isolation.

scholarly journals The limits to parapatric speciation 3: evolution of strong reproductive isolation in presence of gene flow despite limited ecological differentiation

2020 ◽  
Vol 375 (1806) ◽  
pp. 20190532 ◽  
Author(s):  
Alexandre Blanckaert ◽  
Claudia Bank ◽  
Joachim Hermisson
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Local Adaptation ◽  
Theme Issue ◽  
Genetic Barrier ◽  
Incipient Species ◽  
Postzygotic Reproductive Isolation ◽  
Minimal Configuration ◽  
Parapatric Speciation ◽  
Two Populations

Gene flow tends to impede the accumulation of genetic divergence. Here, we determine the limits for the evolution of postzygotic reproductive isolation in a model of two populations that are connected by gene flow. We consider two selective mechanisms for the creation and maintenance of a genetic barrier: local adaptation leads to divergence among incipient species due to selection against migrants, and Dobzhansky–Muller incompatibilities (DMIs) reinforce the genetic barrier through selection against hybrids. In particular, we are interested in the maximum strength of the barrier under a limited amount of local adaptation, a challenge that many incipient species may initially face. We first confirm that with classical two-locus DMIs, the maximum amount of local adaptation is indeed a limit to the strength of a genetic barrier. However, with three or more loci and cryptic epistasis, this limit holds no longer. In particular, we identify a minimal configuration of three epistatically interacting mutations that is sufficient to confer strong reproductive isolation. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.

scholarly journals The impact of global selection on local adaptation and reproductive isolation

2019 ◽  
Author(s):  
Gertjan Bisschop ◽  
Derek Setter ◽  
Marina Rafajlović ◽  
Stuart J.E. Baird ◽  
Konrad Lohse
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Local Adaptation ◽  
Genetic Load ◽  
Divergent Selection ◽  
Mutation Process ◽  
Genome Wide ◽  
The Impact ◽  
Two Populations ◽  
Global Selection

AbstractDespite the homogenising effect of strong gene flow between two populations, adaptation under symmetric divergent selection pressures results in partial reproductive isolation: adaptive substitutions act as local barriers to gene flow, and if divergent selection continues unimpeded, this will result in complete reproductive isolation of the two populations, i.e. speciation. However, a key issue in framing the process of speciation as a tension between local adaptation and the homogenising force of gene flow is that the mutation process is blind to changes in the environment and therefore tends to limit adaptation. Here we investigate how globally beneficial mutations (GBMs) affect divergent local adaptation and reproductive isolation. When phenotypic divergence is finite, we show that the presence of GBMs limits local adaptation, generating a persistent genetic load at the loci which contribute to the trait under divergent selection and reducing genome-wide divergence. Furthermore, we show that while GBMs cannot prohibit the process of continuous differentiation, they induce a substantial delay in the genome-wide shutdown of gene flow.

scholarly journals The impact of global selection on local adaptation and reproductive isolation

2020 ◽  
Vol 375 (1806) ◽  
pp. 20190531 ◽  
Author(s):  
Gertjan Bisschop ◽  
Derek Setter ◽  
Marina Rafajlović ◽  
Stuart J. E. Baird ◽  
Konrad Lohse
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Local Adaptation ◽  
Genetic Load ◽  
Divergent Selection ◽  
Mutation Process ◽  
Genome Wide ◽  
The Impact ◽  
Two Populations ◽  
Global Selection

Despite the homogenizing effect of strong gene flow between two populations, adaptation under symmetric divergent selection pressures results in partial reproductive isolation: adaptive substitutions act as local barriers to gene flow, and if divergent selection continues unimpeded, this will result in complete reproductive isolation of the two populations, i.e. speciation. However, a key issue in framing the process of speciation as a tension between local adaptation and the homogenizing force of gene flow is that the mutation process is blind to changes in the environment and therefore tends to limit adaptation. Here we investigate how globally beneficial mutations (GBMs) affect divergent local adaptation and reproductive isolation. When phenotypic divergence is finite, we show that the presence of GBMs limits local adaptation, generating a persistent genetic load at the loci that contribute to the trait under divergent selection and reducing genome-wide divergence. Furthermore, we show that while GBMs cannot prohibit the process of continuous differentiation, they induce a substantial delay in the genome-wide shutdown of gene flow. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.

scholarly journals The Limits to Parapatric Speciation II: Strengthening a Preexisting Genetic Barrier to Gene Flow in Parapatry

2018 ◽  
Author(s):  
Alexandre Blanckaert ◽  
Joachim Hermisson
Keyword(s):  
New Species ◽  
Gene Flow ◽  
Genetic Barrier ◽  
New Mutation ◽  
Genetic Incompatibility ◽  
Complex Process ◽  
Parapatric Speciation ◽  
The Impact ◽  
New Mutations

AbstractParapatric speciation has recently received a lot of attention. By encompassing the whole continuum between allopatric and sympatric scenarios, it includes many potential scenarios for the evolution of new species. Building upon previous work, we investigate how a genetic barrier to gene flow, that relies on a single postzygotic genetic incompatibility, may further evolve. We consider a continent island model with three loci involved in pairwise Dobzhansky-Muller incompatibilities (DMIs). Using a deterministic and analytic approach, we derive the conditions for invasion of a new mutation and its consequences on an already existing genetic barrier to gene flow. We focus on quantifying the impact of the epistasis generated by the new mutation on the genetic barrier. We show that the accumulation of genetic incompatibilities in the presence of gene flow is a complex process, where new mutations can either strengthen or destroy a preexisting barrier. In particular, preexisting polymorphism and incompatibilities do not always facilitate the growth of the genetic barrier by accumulation of further barrier genes. Migration may disrupt the snowball effect (the accelerating rate of DMI accumulation in allopatry) because incompatibilities are directly tested by selection. Our results also show an ambiguous role of gene flow, which can either impede or facilitate the strengthening of the genetic barrier. Overall, our results illustrate how the inclusion of gene flow renders the building of a genetic barrier difficult to analyze.

scholarly journals Establishment of locally adapted mutations under divergent selection

2018 ◽  
Author(s):  
Matteo Tomasini ◽  
Stephan Peischl
Keyword(s):  
Gene Flow ◽  
Local Adaptation ◽  
Migration Rate ◽  
Analytical Approximation ◽  
Multitype Branching Process ◽  
Process Framework ◽  
Establishment Probability ◽  
Two Populations ◽  
Closed Form Approximation

AbstractWe study the establishment probabilities of locally adapted mutations using a multitype branching process framework. We find a surprisingly simple and intuitive analytical approximation for the establishment probabilities in a symmetric two-deme model under the assumption of weak (positive) selection. This is the first analytical closed-form approximation for arbitrary migration rate to appear in the literature. We find that the establishment probability lies between the weak and the strong migration limits if we condition the origin of the mutation to the deme where it is advantageous. This is not the case when we condition the mutation to first occur in a deme where it is disadvantageous. In this case we find that an intermediate migration rate maximizes the probability of establishment. We extend our results to the cases of multiple demes, two demes with asymmetric rates of gene flow, and asymmetric carrying capacities. The latter case allows us to illustrate how density regulation can affect establishment probabilities. Finally we use our results to investigate the role of gene flow on the rate of local adaptation and identify cases in which intermediate amounts of gene flow facilitate the rate of local adaptation as compared to two populations without gene flow.

scholarly journals PARALLEL EVOLUTION OF LOCAL ADAPTATION AND REPRODUCTIVE ISOLATION IN THE FACE OF GENE FLOW

Evolution ◽  
2013 ◽  
Vol 68 (4) ◽  
pp. 935-949 ◽  
Author(s):  
Roger K. Butlin ◽  
Maria Saura ◽  
Grégory Charrier ◽  
Benjamin Jackson ◽  
Carl André ◽  
...  
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Local Adaptation ◽  
Parallel Evolution ◽  
The Face

scholarly journals No evidence for extrinsic post-zygotic isolation in a wild Saccharomyces yeast system

2017 ◽  
Vol 13 (6) ◽  
pp. 20170197 ◽  
Author(s):  
Guillaume Charron ◽  
Christian R. Landry
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Yeast Species ◽  
Reproductive Barriers ◽  
Partial Dominance ◽  
Saccharomyces Paradoxus ◽  
Incipient Species ◽  
Speciation Process ◽  
Saccharomyces Yeast

Although microorganisms account for the largest fraction of Earth's biodiversity, we know little about how their reproductive barriers evolve. Sexual microorganisms such as Saccharomyces yeasts rapidly develop strong intrinsic post-zygotic isolation, but the role of extrinsic isolation in the early speciation process remains to be investigated. We measured the growth of F 1 hybrids between two incipient species of Saccharomyces paradoxus to assess the presence of extrinsic post-zygotic isolation across 32 environments. More than 80% of hybrids showed either partial dominance of the best parent or over-dominance for growth, revealing no fitness defects in F 1 hybrids. Extrinsic reproductive isolation therefore likely plays little role in limiting gene flow between incipient yeast species and is not a requirement for speciation.

scholarly journals The evolution of reproductive isolation in Daphnia

2019 ◽  
Vol 19 (1) ◽  
Author(s):  
Tiffany A. Chin ◽  
Carla E. Cáceres ◽  
Melania E. Cristescu
Keyword(s):  
Gene Flow ◽  
Reproductive Isolation ◽  
Daphnia Pulex ◽  
Early Stages ◽  
Relative Contribution ◽  
Prezygotic Barriers ◽  
Ecological Barriers ◽  
Species Formation ◽  
Complex Process ◽  
Postzygotic Reproductive Isolation

Abstract Background The process by which populations evolve to become new species involves the emergence of various reproductive isolating barriers (RIB). Despite major advancements in understanding this complex process, very little is known about the order in which RIBs evolve or their relative contribution to the total restriction of gene flow during various stages of speciation. This is mainly due to the difficulties of studying reproductive isolation during the early stages of species formation. This study examines ecological and non-ecological RIB within and between Daphnia pulex and Daphnia pulicaria, two recently diverged species that inhabit distinct habitats and exhibit an unusual level of intraspecific genetic subdivision. Results We find that while ecological prezygotic barriers are close to completion, none of the non-ecological barriers can restrict gene flow between D. pulex and D. pulicaria completely when acting alone. Surprisingly, we also identified high levels of postzygotic reproductive isolation in ‘conspecific’ interpopulation crosses of D. pulex. Conclusions While the ecological prezygotic barriers are prevalent during the mature stages of speciation, non-ecological barriers likely dominated the early stages of speciation. This finding indicates the importance of studying the very early stages of speciation and suggests the contribution of postzygotic isolation in initiating the process of speciation.

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