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67 results for “Speciation: genetics”
Loss of ecologically important genetic variation in late generation hybrids reveals links between adaptation and speciation
Adaptation to contrasting environments occurs when advantageous alleles accumulate in each population, but it remains largely unknown whether these same advantageous alleles create genetic incompatibilities that can cause intrinsic reproductive isolation leading to speciation. Identifying alleles that underlie both adaptation and reproductive isolation is further complicated by factors such as dominance and genetic interactions among loci, which can affect both processes differently and obscure potential links between adaptation and speciation. Here, we use a combination of field and glasshouse experiments to explore the connection between adaptation and speciation while accounting for dominance and genetic interactions. We created a hybrid population with equal contributions from four contrasting ecotypes of Senecio lautus (Asteraceae), which produced hybrid genomes both before (F1 hybrid generation) and after (F4 hybrid generation) recombination among the parental ecotypes. In the glasshouse, plants in the second generation (F2 hybrid generation) showed reduced fitness as a loss of fertility, but fertility was recovered in subsequent generations suggesting that genetic variation underlying fertility reduction was lost in subsequent generations. To quantify the effects of losing genetic variation at the F2 generation on the fitness of later generation hybrids, we used a reciprocal transplant to test for fitness differences between parental ecotypes, and F1 and F4 hybrids in all four parental habitats. Compared to the parental ecotypes and F1 hybrids, variance in F4 hybrid fitness was lower, and lowest in habitats that showed stronger native-ecotype advantage, suggesting that stronger natural selection for the native ecotype reduced fitness variation in the F4 hybrids. Fitness trade-offs that were present in the parental ecotypes and F1 hybrids were absent in the F4 hybrid. Together, these results suggest that the genetic variation lost after the F2 generation was likely associated with both adaptation and intrinsic reproductive isolation among populations adapted to contrasting environments.
Limited genetic parallelism underlies recent, repeated incipient speciation in geographically proximate populations of an Arctic fish (Salvelinus alpinus)
<p>The genetic underpinnings of incipient speciation, including the genomic mechanisms which contribute to morphological and ecological differentiation and reproductive isolation, remain poorly understood. The repeated evolution of consistently, phenotypically distinct morphs of Arctic Charr (<i>Salvelinus alpinus</i>) within the Quaternary period offer an ideal model to study the repeatability of evolution at the genomic level. Sympatric morphs of Arctic Charr are found across this species' circumpolar distribution. However, the specific genetic mechanisms driving this morph differentiation are largely unknown despite the cultural and economic importance of the anadromous morph. We used a newly designed 87k SNP chip to investigate the character and consistency of the genomic differences among sympatric morphs within three recently deglaciated and geographically proximate lakes in Labrador, Canada. We found genetically distinct small and large morph Arctic Charr in all three lakes consistent with resident and anadromous morphs, respectively. A degree of reproductive isolation among sympatric morphs is likely given genome-wide distributions of outlier SNPs and high genome-wide <i>F</i><sub>ST</sub>s. Across all lakes, outlier SNPs were largely non-overlapping suggesting a lack of genetic parallelism driving morph differentiation. Alternatively, several genes and paralogous copies of the same gene consistently differentiated morphs across multiple lakes suggesting their importance to the manifestation of morphs. Our results confirm the utility of Arctic Charr as a model for investigating the predictability of evolution and support the importance of both genetic parallelism and non-parallelism to the incipient speciation of Arctic Charr morphs.</p>
Data from: Selection on a genetic polymorphism counteracts ecological speciation in a stick insect
The interplay between selection and aspects of the genetic architecture of traits (such as linkage, dominance, and epistasis) can either drive or constrain speciation. Despite accumulating evidence that speciation can progress to "intermediate" stages—with populations evolving only partial reproductive isolation—studies describing selective mechanisms that impose constraints on speciation are more rare than those describing drivers. The stick insect Timema cristinae provides an example of a system in which partial reproductive isolation has evolved between populations adapted to different host plant environments, in part due to divergent selection acting on a pattern polymorphism. Here, we demonstrate how selection on a green/melanistic color polymorphism counteracts speciation in this system. Specifically, divergent selection between hosts does not occur on color phenotypes because melanistic T. cristinae are cryptic on the stems of both host species, are resistant to a fungal pathogen, and have a mating advantage. Using genetic crosses and genome-wide association mapping, we quantify the genetic architecture of both the pattern and color polymorphism, illustrating their simple genetic control. We use these empirical results to develop an individual-based model that shows how the melanistic phenotype acts as a "genetic bridge" that increases gene flow between populations living on different hosts. Our results demonstrate how variation in the nature of selection acting on traits, and aspects of trait genetic architecture, can impose constraints on both local adaptation and speciation.
Fig. 3 in Genetic Differentiation Of Ukrainian Populations Of Eusomus Ovulum (Coleoptera, Curculionidae): Evidence Of Multiple Hybrid Speciation
Fig. 3. Polyclonal structure of studied Eusomus ovlulum samples inUkraine.
Fig. 2 in Genetic Differentiation Of Ukrainian Populations Of Eusomus Ovulum (Coleoptera, Curculionidae): Evidence Of Multiple Hybrid Speciation
Fig. 2. The electrophoretic spectra of the esterases in the Eusomus ovulum specimens.
Fig. 1 in Genetic Differentiation Of Ukrainian Populations Of Eusomus Ovulum (Coleoptera, Curculionidae): Evidence Of Multiple Hybrid Speciation
Fig. 1. Geographic localization of Eusomus ovulum samples.
Genome-wide SNP analysis elucidates the evolution of Prunus takesimensis in Ulleung Island: Genetic consequences of anagenetic speciation
<p>Of two major speciation modes of endemic plants on oceanic islands, cladogenesis and anagenesis, the latter has been recently emphasized as an effective mechanism for increasing plant diversity in isolated, ecologically homogeneous insular setting. As a single flowering cherry occurring on Ulleung Island in East Sea, <i>Prunus takesimensis</i> Nakai has been presumed as derived through anagenetic speciation on the Island. Based on morphological similarities, <i>P. sargentii </i>distributed in adjacent continental areas and islands has been suggested as its purported continental progenitor.<i> </i>However, the overall genetic complexity and resultant non-monophylies of closely related flowering cherries have hindered determining their phylogenetic relationships as well as establishing concrete continental progenitor and insular derivative relationship. Based on extensive sampling of wild flowering cherries including <i>P. takesimensis</i> and<i> P. sargentii</i> from Ulleung Island and its adjacent areas, this study inferred the origin and evolution of <i>P. takesimensis</i> using multiple different molecular markers. As the result of phylogeny and population genetic structure analyses based on SNPs detected by MIG-Seq and complementary cpDNA haplotypes, we could provide the extensive and convincing evidence for (1) the monophyly of<i> P. takesimensis</i>,<i> </i>(2) clear genetic differentiation between <i>P. takesimensis</i> (insular derivative) and <i>P. sargentii</i> (continental progenitor), (3) the geographic origin of <i>P. takesimensis</i> via single introduction from source population of <i>P. sargentii</i> in Korean Peninsula, (4) no significant genetic reduction in anagenetically derived insular species <i>P. takesimsnsis</i> compared to continental progenitor <i>P. sargentii</i>, (5) no strong population genetic structuring or geographical patters in the insular derived species, and (6) Mig-seq method as an effective tool to unravel complex evolutionary history of plant groups.</p>
Integrating top-down and bottom-up approaches to understand the genetic architecture of speciation across a monkeyflower hybrid zone
<p><span>Understanding the phenotypic and genetic architecture of reproductive isolation is a longstanding goal of speciation research. In several systems, large-effect loci contributing to barrier phenotypes have been characterized, but such causal connections are rarely known for more complex genetic architectures. In this study, we combine 'top-down' and 'bottom-up' approaches with demographic modeling toward an integrated understanding of speciation across a monkeyflower hybrid zone. Previous work suggests that pollinator visitation acts as a primary barrier to gene flow between two divergent red- and yellow-flowered ecotypes of <em>Mimulus</em> <em>aurantiacus</em>. Several candidate isolating traits and anonymous SNP loci under divergent selection have been identified, but their genomic positions remain unknown. Here, we report findings from demographic analyses that indicate this hybrid zone formed by secondary contact, but that subsequent gene flow was restricted by widespread barrier loci across the genome. Using a novel, geographic cline-based genome scan, we demonstrate that candidate barrier loci are broadly distributed across the genome, rather than mapping to one or a few 'islands of speciation.' Quantitative trait locus (QTL) mapping reveals that most floral traits are polygenic, with little evidence that QTL co-localize, indicating that most traits are genetically independent. Finally, we find little evidence that QTL and candidate barrier loci overlap, suggesting that some loci contribute to other forms of reproductive isolation. Our findings highlight the challenges of understanding the genetic architecture of reproductive isolation and reveal that barriers to gene flow aside from pollinator isolation may play an important role in this system.</span></p>
The population genetics of speciation by cascade reinforcement
<p>Species interactions drive diverse evolutionary outcomes. Speciation by cascade reinforcement represents one example of how species interactions can contribute to the proliferation of species. This process occurs when the divergence of mating traits in response to selection against interspecific hybridization incidentally leads to reproductive isolation among populations of the same species. Here, we investigated the population genetic outcomes of cascade reinforcement in North American chorus frogs (Hylidae: <em>Pseudacris</em>). Specifically, we estimated the frequency of hybridization among three taxa, assessed genetic structure within the focal species, <em>P. feriarum</em>, and ascertained the directionality of gene flow within <em>P. feriarum</em> across replicated contact zones via coalescent modeling. Through field observations and preliminary experimental crosses, we assessed whether hybridization is possible under natural and laboratory conditions. We found that hybridization occurs among <em>P. feriarum</em> and two conspecifics at a low rate in multiple contact zones and that gene flow within the former species is unidirectional from allopatry into sympatry with these other species in three of four contact zones studied. We found evidence of substantial genetic structuring within <em>P. feriarum</em> including a divergent western allopatric cluster, a behaviorally-distinct sympatric South Carolina cluster, and several genetically-overlapping clusters from the remainder of the distribution. Furthermore, we found sub-structuring between reinforced and non-reinforced populations in the two most intensely-sampled contact zones. Our literature review indicated that <em>P. feriarum</em> hybridizes with at least five heterospecifics at the periphery of its range providing a mechanism for further intraspecific diversification. This work strengthens the evidence for cascade reinforcement in this clade, revealing the geographic and genetic landscape upon which this process can contribute to the proliferation of species. </p>
Data from: Genetic, phenotypic and ecological differentiation suggests incipient speciation in two Charadrius plovers along the Chinese coast
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Integrating top-down and bottom-up approaches to understand the genetic architecture of speciation across a monkeyflower hybrid zone
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Limited genetic parallelism underlies recent, repeated incipient speciation in geographically proximate populations of an Arctic fish (Salvelinus alpinus)
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Data from: Parallel genetic evolution and speciation from standing variation
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Data from: Selection on a genetic polymorphism counteracts ecological speciation in a stick insect
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The population genetics of speciation by cascade reinforcement
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Loss of ecologically important genetic variation in late generation hybrids reveals links between adaptation and speciation
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Genome-wide SNP analysis elucidates the evolution of Prunus takesimensis in Ulleung Island: Genetic consequences of anagenetic speciation
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Data from: Ecological speciation in sympatric palms: 3. genetic map reveals genomic islands underlying species divergence in Howea
Although it is now widely accepted that speciation can occur in the face of continuous gene flow, with little or no spatial separation, the mechanisms and genomic architectures that permit such divergence are still debated. Here, we examined speciation in the face of gene flow in the Howea palms of Lord Howe Island, Australia. We built a genetic map using a novel method applicable to long-lived tree species, combining it with double digest restriction-site associated DNA sequencing of multiple individuals. Based upon various metrics, we detected 46 highly differentiated regions throughout the genome, some of which contained genes with functions that are particularly relevant to the speciation scenario for Howea, specifically salt and drought tolerance.
Data from: Are sympatrically speciating Midas cichlid fish special? Patterns of morphological and genetic variation in the closely related species Archocentrus centrarchus
Established empirical cases of sympatric speciation are scarce, although there is an increasing consensus that sympatric speciation might be more common than previously thought. Midas cichlid fish are one of the few substantiated cases of sympatric speciation, and they formed repeated radiations in crater lakes. In contrast, in the same environment, such radiation patterns have not been observed in other species of cichlids and other families of fish. We analyze morphological and genetic variation in a cichlid species (Archocentrus centrarchus) that co-inhabits several crater lakes with the Midas species complex. In particular, we analyze variation in body and pharyngeal jaw shape (two ecologically important traits in sympatrically divergent Midas cichlids) and relate that to genetic variation in mitochondrial control region and microsatellites. Using these four datasets, we analyze variation between and within two Nicaraguan lakes: a crater lake where multiple Midas cichlids have been described and a lake where the source population lives. We do not observe any within-lake clustering consistent across morphological traits and genetic markers, suggesting the absence of sympatric divergence in A. centrarchus. Genetic differentiation between lakes was low and morphological divergence absent. Such morphological similarity between lakes is found not only in average morphology, but also when analyzing covariation between traits and degree of morphospace occupation. A combined analysis of the mitochondrial control region in A. centrarchus and Midas cichlids suggests that a difference between lineages in the timing of crater lake colonization cannot be invoked as an explanation for the difference in their levels of diversification. In light of our results, A. centrarchus represents the ideal candidate to study the genomic differences between these two lineages that might explain why some lineages are more likely to speciate and diverge in sympatry than others.
Data from: Timeframes of speciation, reticulation, and hybridization in the Bulldog bat explained through phylogenetic analyses of all genetic transmission elements
Phylogenetic comparisons of the different mammalian genetic transmission elements (mtDNA, X-, Y-, and autosomal DNA) is a powerful approach for understanding the process of speciation in nature. Through such comparisons the unique inheritance pathways of each genetic element and gender-biased processes can link genomic structure to the evolutionary process, especially among lineages which have recently diversified, in which genetic isolation may be incomplete. Bulldog bats of the genus Noctilio are an exemplar lineage, being a young clade, widely distributed, and exhibiting unique feeding ecologies. In addition, currently recognized species are paraphyletic with respect to the mtDNA gene tree and contain morphologically identifiable clades that exhibit mtDNA divergences as great as among many species. To test taxonomic hypotheses and understand the contribution of hybridization to the extant distribution of genetic diversity in Noctilio, we used phylogenetic, coalescent stochastic modeling, and divergence time estimates using sequence data from cytochrome-b, cytochrome c oxidase-I, zinc finger Y, and zinc finger X, as well as evolutionary reconstructions based on amplified fragment length polymorphisms (AFLP) data. No evidence of ongoing hybridization between the two currently recognized species was identified. However, signatures of an ancient mtDNA capture were recovered in which an mtDNA lineage of one species was captured early in the noctilionid radiation. Among subspecific mtDNA clades, which were generally coincident with morphology and statistically definable as species, signatures of ongoing hybridization were observed in sex chromosome sequences and AFLP. Divergence dating of genetic elements corroborates the diversification of extant Noctilio beginning about three million years ago, with ongoing hybridization between mitochondrial lineages separated by 2.5 million years. The time-frame of species' divergence within Noctilio supports the hypothesis that shifts in the dietary strategies of gleaning insects (N. albiventris) or fish (N. leporinus) are among the most rapid instances of dietary evolution observed in mammals. This study illustrates the complex evolutionary dynamics shaping gene pools in nature, how comparisons of genetic elements can serve for understanding species boundaries, and the complex considerations for accurate taxonomic assignment.
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