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Ole Seehausen - One of the best experts on this subject based on the ideXlab platform.
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admixture between old lineages facilitated contemporary Ecological Speciation in lake constance stickleback
Nature Communications, 2019Co-Authors: David Alexander Marques, Kay Lucek, Ole Seehausen, Vitor C Sousa, Laurent ExcoffierAbstract:Ecological Speciation can sometimes rapidly generate reproductively isolated populations coexisting in sympatry, but the origin of genetic variation permitting this is rarely known. We previously explored the genomics of very recent Ecological Speciation into lake and stream ecotypes in stickleback from Lake Constance. Here, we reconstruct the origin of alleles underlying Ecological Speciation by combining demographic modelling on genome-wide single nucleotide polymorphisms, phenotypic data and mitochondrial sequence data in the wider European biogeographical context. We find that parallel differentiation between lake and stream ecotypes across replicate lake-stream ecotones resulted from recent secondary contact and admixture between old East and West European lineages. Unexpectedly, West European alleles that introgressed across the hybrid zone at the western end of the lake, were recruited to genomic islands of differentiation between ecotypes at the eastern end of the lake. Our results highlight an overlooked outcome of secondary contact: Ecological Speciation facilitated by admixture variation. Ecological Speciation can proceed rapidly, but the origin of genetic variation facilitating it has remained elusive. Here, the authors show that secondary contact and introgression between deeply diverged lineages of stickleback fish facilitated rapid Ecological Speciation into lake and stream ecotypes in Lake Constance.
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repeated and predictable patterns of ecotypic differentiation during a biological invasion lake stream divergence in parapatric swiss stickleback
Journal of Evolutionary Biology, 2013Co-Authors: Kay Lucek, Ole Seehausen, Denis Roy, Arjun SivasundarAbstract:The relative importance of Ecological selection and geographical isolation in promoting and constraining genetic and phenotypic differentiation among populations is not always obvious. Interacting with divergent selection, restricted opportunity for gene flow may in some cases be as much a cause as a consequence of adaptation, with the latter being a hallmark of Ecological Speciation. Ecological Speciation is well studied in parts of the native range of the three-spined stickleback. Here, we study this process in a recently invaded part of its range. Switzerland was colonized within the past 140 years from at least three different colonization events involving different stickleback lineages. They now occupy diverse habitats, ranging from small streams to the pelagic zone of large lakes. We use replicated systems of parapatric lake and stream populations, some of which trace their origins to different invasive lineages, to ask (i) whether phenotypic divergence occurred among populations inhabiting distinct habitats, (ii) whether trajectories of phenotypic divergence follow predictable parallel patterns and (iii) whether gene flow constrains divergent adaptation or vice versa. We find consistent phenotypic divergence between populations occupying distinct habitats. This involves parallel evolution in several traits with known Ecological relevance in independent evolutionary lineages. Adaptive divergence supersedes homogenizing gene flow even at a small spatial scale. We find evidence that adaptive phenotypic divergence places constraints on gene flow over and above that imposed by geographical distance, signalling the early onset of Ecological Speciation.
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sexual dimorphism dominates divergent host plant use in stick insect trophic morphology
BMC Evolutionary Biology, 2013Co-Authors: Denis Roy, Ole Seehausen, Patrik NosilAbstract:Background: Clear examples of Ecological Speciation exist, often involving divergence in trophic morphology. However, substantial variation also exists in how far the Ecological Speciation process proceeds, potentially linked to the number of Ecological axes, traits, or genes subject to divergent selection. In addition, recent studies highlight how differentiation might occur between the sexes, rather than between populations. We examine variation in trophic morphology in two host-plant ecotypes of walking-stick insects (Timema cristinae), known to have diverged in morphological traits related to crypsis and predator avoidance, and to have reached an intermediate point in the Ecological Speciation process. Here we test how host plant use, sex, and rearing environment affect variation in trophic morphology in this species using traditional multivariate, novel kernel density based and Bayesian morphometric analyses. Results: Contrary to expectations, we find limited host-associated divergence in mandible shape. Instead, the main predictor of shape variation is sex, with secondary roles of population of origin and rearing environment. Conclusion: Our results show that trophic morphology does not strongly contribute to host-adapted ecotype divergence in T. cristinae and that traits can respond to complex selection regimes by diverging along different intraspecific lines, thereby impeding progress toward Speciation.
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the role of parasitism in adaptive radiations when might parasites promote and when might they constrain Ecological Speciation
International Journal of Ecology, 2012Co-Authors: Anssi Karvonen, Ole SeehausenAbstract:Research on Speciation and adaptive radiation has flourished during the past decades, yet factors underlying initiation of reproductive isolation often remain unknown. Parasites represent important selective agents and have received renewed attention in Speciation research. We review the literature on parasite-mediated divergent selection in context of Ecological Speciation and present empirical evidence for three nonexclusive mechanisms by which parasites might facilitate Speciation: reduced viability or fecundity of immigrants and hybrids, assortative mating as a pleiotropic by-product of host adaptation, and Ecologically-based sexual selection. We emphasise the lack of research on Speciation continuums, which is why no study has yet made a convincing case for parasite driven divergent evolution to initiate the emergence of reproductive isolation. We also point interest towards selection imposed by single versus multiple parasite species, conceptually linking this to strength and multifariousness of selection. Moreover, we discuss how parasites, by manipulating behaviour or impairing sensory abilities of hosts, may change the form of selection that underlies Speciation. We conclude that future studies should consider host populations at variable stages of the Speciation process, and explore recurrent patterns of parasitism and resistance that could pinpoint the role of parasites in imposing the divergent selection that initiates Ecological Speciation.
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thermal adaptation and Ecological Speciation
Molecular Ecology, 2012Co-Authors: Irene Keller, Ole SeehausenAbstract:Ecological Speciation is defined as the emergence of reproductive isolation as a direct or indirect consequence of divergent Ecological adaptation. Several empirical examples of Ecological Speciation have been reported in the literature which very often involve adaptation to biotic resources. In this review, we investigate whether adaptation to different thermal habitats could also promote Speciation and try to assess the importance of such processes in nature. Our survey of the literature identified 16 animal and plant systems where divergent thermal adaptation may underlie (partial) reproductive isolation between populations or may allow the stable coexistence of sibling taxa. In many of the systems, the differentially adapted populations have a parapatric distribution along an environmental gradient. Isolation often involves extrinsic selection against locally maladapted parental or hybrid genotypes, and additional pre- or postzygotic barriers may be important. Together, the identified examples strongly suggest that divergent selection between thermal environments is often strong enough to maintain a bimodal genotype distribution upon secondary contact. What is less clear from the available data is whether it can also be strong enough to allow Ecological Speciation in the face of gene flow through reinforcement-like processes. It is possible that intrinsic features of thermal gradients or the genetic basis of thermal adaptation make such reinforcement-like processes unlikely but it is equally possible that pertinent systems are understudied. Overall, our literature survey highlights (once again) the dearth of studies that investigate similar incipient species along the continuum from initial divergence to full reproductive isolation and studies that investigate all possible reproductive barriers in a given system.
Andrew P Hendry - One of the best experts on this subject based on the ideXlab platform.
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the consequences of phenotypic plasticity for Ecological Speciation
Journal of Evolutionary Biology, 2011Co-Authors: Xavier Thibertplante, Andrew P HendryAbstract:We use an individual-based numerical simulation to study the effects of phenotypic plasticity on Ecological Speciation. We find that adaptive plasticity evolves readily in the presence of dispersal between populations from different Ecological environments. This plasticity promotes the colonization of new environments but reduces genetic divergence between them. We also find that the evolution of plasticity can either enhance or degrade the potential for divergent selection to form reproductive barriers. Of particular importance here is the timing of plasticity in relation to the timing of dispersal. If plasticity is expressed after dispersal, reproductive barriers are generally weaker because plasticity allows migrants to be better suited for their new environment. If plasticity is expressed before dispersal, reproductive barriers are either unaffected or enhanced. Among the potential reproductive barriers we considered, natural selection against migrants was the most important, primarily because it was the earliest-acting barrier. Accordingly, plasticity had a much greater effect on natural selection against migrants than on sexual selection against migrants or on natural and sexual selection against hybrids. In general, phenotypic plasticity can strongly alter the process of Ecological Speciation and should be considered when studying the evolution of reproductive barriers.
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when can Ecological Speciation be detected with neutral loci
Molecular Ecology, 2010Co-Authors: Xavier Thibertplante, Andrew P HendryAbstract:It is not yet clear under what conditions empirical studies can reliably detect progress toward Ecological Speciation through the analysis of allelic variation at neutral loci. We use a simulation ...
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Ecological Speciation or the lack thereof this perspective is based on the author s j c stevenson memorial lecture delivered at the canadian conference for fisheries research in halifax nova scotia january 2008
Canadian Journal of Fisheries and Aquatic Sciences, 2009Co-Authors: Andrew P HendryAbstract:Ecological Speciation occurs when adaptation to different environments or resources causes the evolution of reproductive isolation. This process is now thought to be very important in the evolution...
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Ecological Speciation or the lack thereof this perspective is based on the author s j c stevenson memorial lecture delivered at the canadian conference for fisheries research in halifax nova scotia january 2008
Canadian Journal of Fisheries and Aquatic Sciences, 2009Co-Authors: Andrew P HendryAbstract:Ecological Speciation occurs when adaptation to different environments or resources causes the evolution of re- productive isolation. This process is now thought to be very important in the evolution of biological diversity. Indeed, sup- port for Ecological Speciation is so often asserted in the literature that one can get the impression of ubiquity. Eager to ride on the coattails of this exciting work, my own research has investigated Ecological Speciation in guppies, sticklebacks, and Darwin's finches. Much to my initial dismay, I failed to find simple and strong signatures of Ecological Speciation in the first two of these systems. Setting aside the possibility of personal incompetence, my apparent deviation from ubiquity might simply reflect an existing literature bias. This bias seems obvious in retrospect given that essentially all published studies of Ecological Speciation purport to be confirmatory, whereas many cases of divergent selection and adaptive diver- gence are associated with only weak to modest levels of reproductive isolation. In short, different populations can be ar- rayed along a continuum from panmixia to complete reproductive isolation. Variation along this continuum might profitably be used for studying factors, outlined herein, that can promote or constrain ''progress'' toward Ecological specia- tion. Resume´ : La Speciation ecologique se produit lorsqu'une adaptation a des ressources ou des milieux differents entraoˆne l'evolution d'un isolement reproductif. On croit actuellement que ce processus est tres important dans l'evolution de la di- versitebiologique. En fait, la Speciation ecologique est si souvent invoquee dans la litterature qu'on a l'impression qu'elle est ubiquiste. Dans la foulee de cette recherche interessante, mes travaux personnels ont examinela Speciation ecologique chez les guppys, les epinoches et les pinsons de Darwin. Au depart, il m'a eteimpossible, a mon desarroi, de trouver des signatures simples et prononcees de Speciation ecologique dans les deux premiers de ces systemes. Excluant la possibilite ´ de mon incompetence personnelle, mon incapaciteatrouver l'ubiquitedu phenomene peut etre due a une distorsion de la litterature actuelle. Retrospectivement, cette distorsion paraoˆ tevidente parce qu'essentiellement toutes les etudes publiees sur la Speciation ecologique pretendent avoir un caractere confirmatif, alors que plusieurs cas de selection divergente et de divergence adaptative sont associes avec seulement des niveaux faibles a modestes d'isolement reproductif. Bref, les dif- ferentes populations peuvent etre placees sur un continuum qui va de la panmixie al'isolement reproductif complet. La variation le long de ce gradient peut etre utilisee avec profit pour etudier facteurs, enumeres ici, qui peuvent favoriser ou restreindre la « progression » vers la Speciation ecologique. (Traduit par la Redaction)
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variable progress toward Ecological Speciation in parapatry stickleback across eight lake stream transitions
Evolution, 2009Co-Authors: Daniel Berner, Annecatherine Grandchamp, Andrew P HendryAbstract:Divergent selection between contrasting habitats can sometimes drive adaptive divergence and the evolution of reproductive isolation in the face of initially high gene flow. "Progress" along this Ecological Speciation pathway can range from minimal divergence to full Speciation. We examine this variation for threespine stickleback fish that evolved independently across eight lake-stream habitat transitions. By quantifying stickleback diets, we show that lake-stream transitions usually coincide with limnetic-benthic ecotones. By measuring genetically based phenotypes, we show that these ecotones often generate adaptive divergence in foraging morphology. By analyzing neutral genetic markers (microsatellites), we show that adaptive divergence is often associated with the presence of two populations maintaining at least partial reproductive isolation in parapatry. Coalescent-based simulations further suggest that these populations have diverged with gene flow within a few thousand generations, although we cannot rule out the possibility of phases of allopatric divergence. Finally, we find striking variation among the eight lake-stream transitions in progress toward Ecological Speciation. This variation allows us to hypothesize that progress is generally promoted by strong divergent selection and limited dispersal across the habitat transitions. Our study thus makes a case for Ecological Speciation in a parapatric context, while also highlighting variation in the outcome.
Dolph Schluter - One of the best experts on this subject based on the ideXlab platform.
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parallel changes in gut microbiome composition and function during colonization local adaptation and Ecological Speciation
Proceedings of The Royal Society B: Biological Sciences, 2019Co-Authors: Diana J Rennison, Seth M Rudman, Dolph SchluterAbstract:The processes of local adaptation and Ecological Speciation are often strongly shaped by biotic interactions such as competition and predation. One of the strongest lines of evidence that biotic interactions drive evolution comes from the repeated divergence of lineages in association with repeated changes in the community of interacting species. Yet relatively little is known about the repeatability of changes in gut microbial communities and their role in adaptation and divergence of host populations in nature. Here we use three cases of rapid, parallel adaptation and Speciation in freshwater threespine stickleback to test for parallel changes in associated gut microbiomes. We find that features of the gut microbial communities have shifted repeatedly in the same direction in association with parallel divergence and Speciation of stickleback hosts. These results suggest that changes to gut microbiomes can occur rapidly and predictably in conjunction with host evolution, and that host-microbe interactions might play an important role in host adaptation and diversification.
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parallel changes in gut microbiome composition and function during colonization local adaptation and Ecological Speciation
Proceedings of The Royal Society B: Biological Sciences, 2019Co-Authors: Diana J Rennison, Seth M Rudman, Dolph SchluterAbstract:The processes of local adaptation and Ecological Speciation are often strongly shaped by biotic interactions such as competition and predation. One of the strongest lines of evidence that biotic in...
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advances in Ecological Speciation an integrative approach
Molecular Ecology, 2014Co-Authors: Juan Galindo, Rui Faria, Sebastien Renaut, Catarina Pinho, Jose Meloferreira, Martim Melo, Felicity C Jones, Walter Salzburger, Dolph SchluterAbstract:The role of natural selection in promoting reproductive isolation has received substantial renewed interest within the last two decades. As a consequence, the study of Ecological Speciation has become an extremely productive research area in modern evolutionary biology. Recent innovations in sequencing technologies offer an unprecedented opportunity to study the mechanisms involved in Ecological Speciation. Genome scans provide significant insights but have some important limitations; efforts are needed to integrate them with other approaches to make full use of the sequencing data deluge. An international conference 'Advances in Ecological Speciation' organized by the University of Porto (Portugal) aimed to review current progress in Ecological Speciation. Using some of the examples presented at the conference, we highlight the benefits of integrating Ecological and genomic data and discuss different mechanisms of parallel evolution. Finally, future avenues of research are suggested to advance our knowledge concerning the role of natural selection in the establishment of reproductive isolation during Ecological Speciation.
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genetics and Ecological Speciation
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Dolph Schluter, Gina L ConteAbstract:Species originate frequently by natural selection. A general mechanism by which this occurs is Ecological Speciation, defined as the evolution of reproductive isolation between populations as a result of Ecologically-based divergent natural selection. The alternative mechanism is mutation-order Speciation in which populations fix different mutations as they adapt to similar selection pressures. Although numerous cases now indicate the importance of Ecological Speciation in nature, very little is known about the genetics of the process. Here, we summarize the genetics of premating and postzygotic isolation and the role of standing genetic variation in Ecological Speciation. We discuss the role of selection from standing genetic variation in threespine stickleback (Gasterosteus aculeatus), a complex of species whose ancestral marine form repeatedly colonized and adapted to freshwater environments. We propose that Ecological Speciation has occurred multiple times in parallel in this group via a "transporter" process in which selection in freshwater environments repeatedly acts on standing genetic variation that is maintained in marine populations by export of freshwater-adapted alleles from elsewhere in the range. Selection from standing genetic variation is likely to play a large role in Ecological Speciation, which may partly account for its rapidity.
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evidence for Ecological Speciation and its alternative
Science, 2009Co-Authors: Dolph SchluterAbstract:Natural selection commonly drives the origin of species, as Darwin initially claimed. Mechanisms of Speciation by selection fall into two broad categories: Ecological and mutation-order. Under Ecological Speciation, divergence is driven by divergent natural selection between environments, whereas under mutation-order Speciation, divergence occurs when different mutations arise and are fixed in separate populations adapting to similar selection pressures. Tests of parallel evolution of reproductive isolation, trait-based assortative mating, and reproductive isolation by active selection have demonstrated that Ecological Speciation is a common means by which new species arise. Evidence for mutation-order Speciation by natural selection is more limited and has been best documented by instances of reproductive isolation resulting from intragenomic conflict. However, we still have not identified all aspects of selection, and identifying the underlying genes for reproductive isolation remains challenging.
Louis Bernatchez - One of the best experts on this subject based on the ideXlab platform.
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holobionts and Ecological Speciation the intestinal microbiota of lake whitefish species pairs
Microbiome, 2018Co-Authors: Maelle Sevellec, Nicolas Derome, Louis BernatchezAbstract:It is well established that symbionts have considerable impact on their host, yet the investigation of the possible role of the holobiont in the host’s Speciation process is still in its infancy. In this study, we compared the intestinal microbiota among five sympatric pairs of dwarf (limnetic) and normal (benthic) lake whitefish Coregonus clupeaformis representing a continuum in the early stage of Ecological Speciation. We sequenced the 16s rRNA gene V3-V4 regions of the intestinal microbiota present in a total of 108 wild sympatric dwarf and normal whitefish as well as the water bacterial community from five lakes to (i) test for differences between the whitefish intestinal microbiota and the water bacterial community and (ii) test for parallelism in the intestinal microbiota of dwarf and normal whitefish. The water bacterial community was distinct from the intestinal microbiota, indicating that intestinal microbiota did not reflect the environment, but rather the intrinsic properties of the host microbiota. Our results revealed a strong influence of the host (dwarf or normal) on the intestinal microbiota with pronounced conservation of the core intestinal microbiota (mean ~ 44% of shared genera). However, no clear evidence for parallelism was observed, whereby non-parallel differences between dwarf and normal whitefish were observed in three of the lakes while similar taxonomic composition was observed for the two other species pairs. This absence of parallelism across dwarf vs. normal whitefish microbiota highlighted the complexity of the holobiont and suggests that the direction of selection could be different between the host and its microbiota.
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snp signatures of selection on standing genetic variation and their association with adaptive phenotypes along gradients of Ecological Speciation in lake whitefish species pairs coregonus spp
Molecular Ecology, 2011Co-Authors: Sean M Rogers, Sebastien Renaut, Nicolas Derome, Arne W Nolte, Louis BernatchezAbstract:As populations adapt to novel environments, divergent selection will promote heterogeneous genomic differentiation via reductions in gene flow for loci underlying adaptive traits. Using a data set of over 100 SNP markers, genome scans were performed to investigate the effect of natural selection maintaining differentiation in five lakes harbouring sympatric pairs of normal and dwarf lake whitefish (Coregonus clupeaformis). A variable proportion of SNPs (between 0% and 12%) was identified as outliers, which corroborated the predicted intensity of competitive interactions unique to each lake. Moreover, strong reduction in heterozygosity was typically observed for outlier loci in dwarf but not in normal whitefish, indicating that directional selection has been acting on standing genetic variation more intensively in dwarf whitefish. SNP associations in backcross hybrid progeny identified 16 genes exhibiting genotype-phenotype associations for four adaptive traits (growth, swimming activity, gill rakers and condition factor). However, neither simple relationship between elevated levels of genetic differentiation with adaptive phenotype nor conspicuous genetic signatures for parallelism at outlier loci were detected, which underscores the importance of independent evolution among lakes. The integration of phenotypic, transcriptomic and functional genomic information identified two candidate genes (sodium potassium ATPase and triosephosphate isomerase) involved in the recent Ecological divergence of lake whitefish. Finally, the identification of several markers under divergent selection suggests that many genes, in an environment-specific manner, are recruited by selection and ultimately contributed to the repeated Ecological Speciation of a dwarf phenotype.
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the genetic architecture of Ecological Speciation and the association with signatures of selection in natural lake whitefish coregonus sp salmonidae species pairs
Molecular Biology and Evolution, 2007Co-Authors: Sean M Rogers, Louis BernatchezAbstract:Adaptive evolutionary change is contingent on variation and selection; thus, understanding adaptive divergence and ultimately Speciation requires information on both the genetic basis of adaptive traits as well as an understanding of the role of divergent natural selection on those traits. The lake whitefish (Coregonus clupeaformis) consists of several sympatric "dwarf" (limnetic) and normal (benthic) species pairs that co-inhabit northern postglacial lakes. These young species pairs have evolved independently and display parallelism in life history, behavioral, and morphological divergence associated with the use of distinct trophic resources. We identified phenotype-environment associations and determined the genetic architecture and the role of selection modulating population genetic divergence in sympatric dwarf and normal lake whitefish. The genetic architecture of 9 adaptive traits was analyzed in 2 hybrid backcrosses individually phenotyped throughout their life history. Significant quantitative trait loci (QTL) were associated with swimming behavior (habitat selection and predator avoidance), growth rate, morphology (condition factor and gill rakers), and life history (onset of maturity and fecundity). Genome scans among 4 natural sympatric pairs, using loci segregating in the map, revealed a signature of selection for 24 loci. Loci exhibiting a signature of selection were associated with QTL relative to other regions of the genome more often than expected by chance alone. Two parallel QTL outliers for growth and condition factor exhibited segregation distortion in both mapping families, supporting the hypothesis that adaptive divergence contributing to parallel reductions of gene flow among natural populations may cause genetic incompatibilities. Overall, these findings offer evidence that the genetic architecture of Ecological Speciation is associated with signatures of selection in nature, providing strong support for the hypothesis that divergent natural selection is currently maintaining adaptive differentiation and promoting Ecological Speciation in lake whitefish species pairs.
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correlated trophic specialization and genetic divergence in sympatric lake whitefish ecotypes coregonus clupeaformis support for the Ecological Speciation hypothesis
Evolution, 1999Co-Authors: Guoqing Lu, Louis BernatchezAbstract:: There is ample empirical evidence that phenotypic diversification in an adaptive radiation is the outcome of divergent natural selection related to differential resource use. In contrast, the role of Ecological forces in favoring and maintaining reproductive isolation in nature remains poorly understood. If the same forces driving phenotypic divergence are also responsible for Speciation, one would predict a correlation between the extent of trophic specialization (reflecting variable intensity of divergent natural selection) and that of reproductive isolation being reached in a given environment. We tested this hypothesis by comparing the extent of morphological and genetic differentiation between sympatric dwarf and normal whitefish ecotypes (Coregonus sp.) from six lakes of the St. John River basin (eastern Canada and northern Maine). Eight meristic variables, 19 morphometric variables, and six microsatellite loci were used to quantify morphological and genetic differentiation, respectively. Dwarf and normal ecotypes in each lake differed primarily by traits related to trophic specialization, but the extent of differentiation varied among lakes. Significant but variable genetic divergence between ecotypes within lakes was also observed. A negative correlation was observed between the extent of gene flow between ecotypes within a lake and that of their morphological differentiation in trophic-related traits. The extent of reproductive isolation reached between dwarf and normal whitefish ecotypes appears to be driven by the potential for occupying distinct trophic niches and, thus, by the same selective forces driving tropic specialization in each lake. These results therefore support the hypothesis of Ecological Speciation.
Sean M Rogers - One of the best experts on this subject based on the ideXlab platform.
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snp signatures of selection on standing genetic variation and their association with adaptive phenotypes along gradients of Ecological Speciation in lake whitefish species pairs coregonus spp
Molecular Ecology, 2011Co-Authors: Sean M Rogers, Sebastien Renaut, Nicolas Derome, Arne W Nolte, Louis BernatchezAbstract:As populations adapt to novel environments, divergent selection will promote heterogeneous genomic differentiation via reductions in gene flow for loci underlying adaptive traits. Using a data set of over 100 SNP markers, genome scans were performed to investigate the effect of natural selection maintaining differentiation in five lakes harbouring sympatric pairs of normal and dwarf lake whitefish (Coregonus clupeaformis). A variable proportion of SNPs (between 0% and 12%) was identified as outliers, which corroborated the predicted intensity of competitive interactions unique to each lake. Moreover, strong reduction in heterozygosity was typically observed for outlier loci in dwarf but not in normal whitefish, indicating that directional selection has been acting on standing genetic variation more intensively in dwarf whitefish. SNP associations in backcross hybrid progeny identified 16 genes exhibiting genotype-phenotype associations for four adaptive traits (growth, swimming activity, gill rakers and condition factor). However, neither simple relationship between elevated levels of genetic differentiation with adaptive phenotype nor conspicuous genetic signatures for parallelism at outlier loci were detected, which underscores the importance of independent evolution among lakes. The integration of phenotypic, transcriptomic and functional genomic information identified two candidate genes (sodium potassium ATPase and triosephosphate isomerase) involved in the recent Ecological divergence of lake whitefish. Finally, the identification of several markers under divergent selection suggests that many genes, in an environment-specific manner, are recruited by selection and ultimately contributed to the repeated Ecological Speciation of a dwarf phenotype.
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The role of gene expression in Ecological Speciation
Annals of the New York Academy of Sciences, 2010Co-Authors: Scott A. Pavey, Hélène Collin, Patrik Nosil, Sean M RogersAbstract:Ecological Speciation is the process by which barriers to gene flow between populations evolve due to adaptive divergence via natural selection. A relatively unexplored area in Ecological Speciation is the role of gene expression. Gene expression may be associated with Ecologically important phenotypes not evident from morphology and play a role during colonization of new environments. Here we review two potential roles of gene expression in Ecological Speciation: (1) its indirect role in facilitating population persistence and (2) its direct role in contributing to genetically based reproductive isolation. We find indirect evidence that gene expression facilitates population persistence, but direct tests are lacking. We also find clear examples of gene expression having effects on phenotypic traits and adaptive genetic divergence, but links to the evolution of reproductive isolation itself remain indirect. Gene expression during adaptive divergence seems to often involve complex genetic architectures controlled by gene networks, regulatory regions, and "eQTL hotspots." Nonetheless, we review how approaches for isolating the functional mutations contributing to adaptive divergence are proving to be successful. The study of gene expression has promise for increasing our understanding Ecological Speciation, particularly when integrative approaches are applied.
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the genetic architecture of Ecological Speciation and the association with signatures of selection in natural lake whitefish coregonus sp salmonidae species pairs
Molecular Biology and Evolution, 2007Co-Authors: Sean M Rogers, Louis BernatchezAbstract:Adaptive evolutionary change is contingent on variation and selection; thus, understanding adaptive divergence and ultimately Speciation requires information on both the genetic basis of adaptive traits as well as an understanding of the role of divergent natural selection on those traits. The lake whitefish (Coregonus clupeaformis) consists of several sympatric "dwarf" (limnetic) and normal (benthic) species pairs that co-inhabit northern postglacial lakes. These young species pairs have evolved independently and display parallelism in life history, behavioral, and morphological divergence associated with the use of distinct trophic resources. We identified phenotype-environment associations and determined the genetic architecture and the role of selection modulating population genetic divergence in sympatric dwarf and normal lake whitefish. The genetic architecture of 9 adaptive traits was analyzed in 2 hybrid backcrosses individually phenotyped throughout their life history. Significant quantitative trait loci (QTL) were associated with swimming behavior (habitat selection and predator avoidance), growth rate, morphology (condition factor and gill rakers), and life history (onset of maturity and fecundity). Genome scans among 4 natural sympatric pairs, using loci segregating in the map, revealed a signature of selection for 24 loci. Loci exhibiting a signature of selection were associated with QTL relative to other regions of the genome more often than expected by chance alone. Two parallel QTL outliers for growth and condition factor exhibited segregation distortion in both mapping families, supporting the hypothesis that adaptive divergence contributing to parallel reductions of gene flow among natural populations may cause genetic incompatibilities. Overall, these findings offer evidence that the genetic architecture of Ecological Speciation is associated with signatures of selection in nature, providing strong support for the hypothesis that divergent natural selection is currently maintaining adaptive differentiation and promoting Ecological Speciation in lake whitefish species pairs.
