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1.
New Phytol ; 226(2): 326-344, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31951018

RESUMO

Two major developments have made it possible to use examples of ecological radiations as model systems to understand evolution and ecology. First, the integration of quantitative genetics with ecological experiments allows detailed connections to be made between genotype, phenotype, and fitness in the field. Second, dramatic advances in molecular genetics have created new possibilities for integrating field and laboratory experiments with detailed genetic sequencing. Combining these approaches allows evolutionary biologists to better study the interplay between genotype, phenotype, and fitness to explore a wide range of evolutionary processes. Here, we present the genus Senecio (Asteraceae) as an excellent system to integrate these developments, and to address fundamental questions in ecology and evolution. Senecio is one of the largest and most phenotypically diverse genera of flowering plants, containing species ranging from woody perennials to herbaceous annuals. These Senecio species exhibit many growth habits, life histories, and morphologies, and they occupy a multitude of environments. Common within the genus are species that have hybridized naturally, undergone polyploidization, and colonized diverse environments, often through rapid phenotypic divergence and adaptive radiation. These diverse experimental attributes make Senecio an attractive model system in which to address a broad range of questions in evolution and ecology.

2.
Nat Commun ; 10(1): 5230, 2019 11 19.
Artigo em Inglês | MEDLINE | ID: mdl-31745089

RESUMO

The Hengduan Mountains (HDM) biodiversity hotspot exhibits exceptional alpine plant diversity. Here, we investigate factors driving intraspecific divergence within a HDM alpine species Salix brachista (Cushion willow), a common component of subnival assemblages. We produce a high-quality genome assembly for this species and characterize its genetic diversity, population structure and pattern of evolution by resequencing individuals collected across its distribution. We detect population divergence that has been shaped by a landscape of isolated sky island-like habitats displaying strong environmental heterogeneity across elevational gradients, combined with population size fluctuations that have occurred since approximately the late Miocene. These factors are likely important drivers of intraspecific divergence within Cushion willow and possibly other alpine plants with a similar distribution. Since intraspecific divergence is often the first step toward speciation, the same factors can be important contributors to the high alpine species diversity in the HDM.

3.
Ecol Evol ; 9(13): 7528-7548, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31346420

RESUMO

Determining the factors promoting speciation is a major task in ecological and evolutionary research and can be aided by phylogeographic analysis. The Qinling-Daba Mountains (QDM) located in central China form an important geographic barrier between southern subtropical and northern temperate regions, and exhibit complex topography, climatic, and ecological diversity. Surprisingly, few phylogeographic analyses and studies of plant speciation in this region have been conducted. To address this issue, we investigated the genetic divergence and evolutionary histories of three closely related tree peony species (Paeonia qiui, P. jishanensis, and P. rockii) endemic to the QDM. Forty populations of the three tree peony species were genotyped using 22 nuclear simple sequence repeat markers (nSSRs) and three chloroplast DNA sequences to assess genetic structure and phylogenetic relationships, supplemented by morphological characterization and ecological niche modeling (ENM). Morphological and molecular genetic analyses showed the three species to be clearly differentiated from each other. In addition, coalescent analyses using DIYABC conducted on nSSR variation indicated that the species diverged from each other in the late Pleistocene, while ecological niche modeling (ENM) suggested they occupied a larger area during the Last Glacial Maximum (LGM) than at present. The combined genetic evidence from nuclear and chloroplast DNA and the results of ENM indicate that each species persisted through the late Pleistocene in multiple refugia in the Qinling, Daba, and Taihang Mountains with divergence favored by restricted gene flow caused by geographic isolation, ecological divergence, and limited pollen and seed dispersal. Our study contributes to a growing understanding of the origin and population structure of tree peonies and provides insights into the high level of plant endemism present in the Qinling-Daba Mountains of Central China.

4.
Commun Biol ; 2: 213, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31240251

RESUMO

Introgression may act as an important source of new genetic variation to facilitate the adaptation of organisms to new environments, yet how introgression might enable tree species to adapt to higher latitudes and elevations remains unclear. Applying whole-transcriptome sequencing and population genetic analyses, we present an example of ancient introgression from a cypress species (Cupressus gigantea) that occurs at higher latitude and elevation on the Qinghai-Tibet Plateau into a related species (C. duclouxiana), which has likely aided the latter species to extend its range by colonizing cooler and drier mountain habitats during postglacial periods. We show that 16 introgressed candidate adaptive loci could have played pivotal roles in response to diverse stresses experienced in a high-elevation environment. Our findings provide new insights into the evolutionary history of Qinghai-Tibet Plateau plants and the importance of introgression in the adaptation of species to climate change.

5.
AoB Plants ; 11(1): ply078, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30740200

RESUMO

A new homoploid hybrid lineage needs to establish a degree of reproductive isolation from its parent species if it is to persist as an independent entity, but the role hybridization plays in this process is known in only a handful of cases. The homoploid hybrid ragwort species, Senecio squalidus (Oxford ragwort), originated following the introduction of hybrid plants to the UK approximately 320 years ago. The source of the hybrid plants was from a naturally occurring hybrid zone between S. aethnensis and S. chrysanthemifolius on Mount Etna, Sicily. Previous studies of the parent species found evidence for multiple incompatibility loci causing transmission ratio distortion of genetic markers in their hybrid progeny. This study closes the hybridization triangle by reporting a genetic mapping analysis of the remaining two paired cross combinations between S. squalidus and its parents. Genetic maps produced from F2 mapping families were generally collinear but with half of the linkage groups showing evidence of genomic reorganization between genetic maps. The new maps produced from crosses between S. squalidus and each parent showed multiple incompatibility loci distributed across the genome, some of which co-locate with previously reported incompatibility loci between the parents. These findings suggest that this young homoploid hybrid species has inherited a unique combination of genomic rearrangements and incompatibilities from its parents that contribute to its reproductive isolation.

6.
Mol Ecol ; 27(23): 4875-4887, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30357974

RESUMO

An increasing number of species are thought to have originated by homoploid hybrid speciation (HHS), but in only a handful of cases are details of the process known. A previous study indicated that Picea purpurea, a conifer in the Qinghai-Tibet Plateau (QTP), originated through HHS from P. likiangensis and P. wilsonii. To investigate this origin in more detail, we analysed transcriptome data for 114 individuals collected from 34 populations of the three Picea species from their core distributions in the QTP. Phylogenetic, principal component and admixture analyses of nuclear SNPs showed the species to be delimited genetically and that P. purpurea was admixed with approximately 60% of its ancestry derived from P. wilsonii and 40% from P. likiangensis. Coalescent simulations revealed the best-fitting model of origin involved formation of an intermediate hybrid lineage between P. likiangensis and P. wilsonii approximately 6 million years ago (mya), which backcrossed to P. wilsonii to form P. purpurea approximately one mya. The intermediate hybrid lineage no longer exists and is referred to as a "ghost" lineage. Our study emphasizes the power of population genomic analysis combined with coalescent analysis for reconstructing the stages involved in the origin of a homoploid hybrid species over an extended period. In contrast to other studies, we show that these stages can in some instances span a relatively long period of evolutionary time.


Assuntos
Genética Populacional , Hibridização Genética , Filogenia , Picea/classificação , DNA de Plantas/genética , Especiação Genética , Metagenômica , Modelos Genéticos , Picea/genética , Polimorfismo de Nucleotídeo Único , Tibet , Transcriptoma
7.
Evolution ; 72(12): 2669-2681, 2018 12.
Artigo em Inglês | MEDLINE | ID: mdl-30315582

RESUMO

The role of reticulation in the rapid diversification of organisms is attracting greater attention in evolutionary biology. Evidence of genetic exchange between diverging taxa is reported frequently, although most studies fail to show how hybridization and introgression contribute to the adaptation and differentiation of introgressed taxa. Here, we report a population genomics approach to test the role of hybridization and introgression in the evolution of the Picea likiangensis species complex, which comprises four taxa occurring in the biodiversity hotspot of the Hengduan-Himalayan mountains. Based on 84,793 SNPs detected in transcriptomes of 82 trees collected from 35 localities, we identified 18 hybrids (including backcrosses) distributed within the range boundaries of the four taxa. Coalescent simulations, for each pair of taxa and for all taxa taken together, rejected several tree-like divergence models and supported instead a reticulate evolution model with secondary contacts occurring during Pleistocene glacial cycles after initial divergence in the late Pliocene. Significant gene flow occurred among some taxa after secondary contact according to an analysis based on modified ABBA-BABA statistics that accommodated a rapid diversification scenario. A novel finding was that introgression between certain taxa can contribute to increasing divergence (and possibly reproductive isolation) between those taxa and other taxa within a complex at some loci. These results illuminate the reticulate nature of evolution within the P. likiangensis complex and highlight the value of population genomic data in detecting the effects of introgression in the rapid diversification of related taxa.


Assuntos
Evolução Biológica , Variação Genética , Genômica/métodos , Picea/genética , Biodiversidade , Análise por Conglomerados , Genoma de Planta , RNA de Plantas , Análise de Sequência de RNA
8.
Mol Ecol ; 27(14): 2943-2955, 2018 07.
Artigo em Inglês | MEDLINE | ID: mdl-29862594

RESUMO

The halophyte model plant Eutrema salsugineum (Brassicaceae) disjunctly occurs in temperate to subarctic Asia and North America. This vast, yet extremely discontinuous distribution constitutes an ideal system to examine long-distance dispersal and the ensuing accumulation of deleterious mutations as expected in expanding populations of selfing plants. In this study, we resequenced individuals from 23 populations across the range of E. salsugineum. Our population genomic data indicate that E. salsugineum migrated "out of the Altai region" at least three times to colonize northern China, northeast Russia and western China. It then expanded its distribution into North America independently from northeast Russia and northern China, respectively. The species colonized northern China around 33.7 thousand years ago (kya) and underwent a considerable expansion in range size approximately 7-8 kya. The western China lineage is likely a hybrid derivative of the northern China and Altai lineages, originating approximately 25-30 kya. Deleterious alleles accumulated in a stepwise manner from (a) Altai to northern China and North America and (b) Altai to northeast Russia and North America. In summary, E. salsugineum dispersed from Asia to North America and deleterious mutations accumulated in a stepwise manner during the expansion of the species' distribution.


Assuntos
Brassicaceae/genética , Genética Populacional , Tolerância ao Sal/genética , Plantas Tolerantes a Sal/genética , Alelos , Ásia , Brassicaceae/crescimento & desenvolvimento , China , Regulação da Expressão Gênica de Plantas , Carga Genética , América do Norte , Filogenia , Federação Russa , Plantas Tolerantes a Sal/crescimento & desenvolvimento
9.
Proc Natl Acad Sci U S A ; 115(2): E236-E243, 2018 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-29279400

RESUMO

How genome divergence eventually leads to speciation is a topic of prime evolutionary interest. Genomic islands of elevated divergence are frequently reported between diverging lineages, and their size is expected to increase with time and gene flow under the speciation-with-gene-flow model. However, such islands can also result from divergent sorting of ancient polymorphisms, recent ecological selection regardless of gene flow, and/or recurrent background selection and selective sweeps in low-recombination regions. It is challenging to disentangle these nonexclusive alternatives, but here we attempt to do this in an analysis of what drove genomic divergence between four lineages comprising a species complex of desert poplar trees. Within this complex we found that two morphologically delimited species, Populus euphratica and Populus pruinosa, were paraphyletic while the four lineages exhibited contrasting levels of gene flow and divergence times, providing a good system for testing hypotheses on the origin of divergence islands. We show that the size and number of genomic islands that distinguish lineages are not associated with either rate of recent gene flow or time of divergence. Instead, they are most likely derived from divergent sorting of ancient polymorphisms and divergence hitchhiking. We found that highly diverged genes under lineage-specific selection and putatively involved in ecological and morphological divergence occur both within and outside these islands. Our results highlight the need to incorporate demography, absolute divergence measurement, and gene flow rate to explain the formation of genomic islands and to identify potential genomic regions involved in speciation.


Assuntos
Evolução Biológica , Especiação Genética , Ilhas Genômicas , Polimorfismo Genético , Populus/genética , Mapeamento Cromossômico , Cromossomos de Plantas/genética , Genoma de Planta
10.
Mol Ecol ; 26(11): 3037-3049, 2017 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-28295838

RESUMO

Reconstructing the origin of a polyploid species is particularly challenging when an ancestor has become extinct. Under such circumstances, the extinct donor of a genome found in the polyploid may be treated as a 'ghost' species in that its prior existence is recognized through the presence of its genome in the polyploid. In this study, we aimed to determine the polyploid origin of Oxyria sinensis (2n = 40) for which only one congeneric species is known, that is diploid O. digyna (2n = 14). Genomic in situ hybridization (GISH), transcriptome, phylogenetic and demographic analyses, and ecological niche modelling were conducted for this purpose. GISH revealed that O. sinensis comprised 14 chromosomes from O. digyna and 26 chromosomes from an unknown ancestor. Transcriptome analysis indicated that following divergence from O. digyna, involving genome duplication around 12 million years ago (Ma), a second genome duplication occurred approximately 6 Ma to give rise to O. sinensis. Oxyria sinensis was shown to contain homologous gene sequences divergent from those present in O. digyna in addition to a set that clustered with those in O. digyna. Coalescent simulations indicated that O. sinensis expanded its distribution approximately 6-7 Ma, possibly following the second polyploidization event, whereas O. digyna expanded its range much later. It was also indicated that the distributions of both species contracted and re-expanded during the Pleistocene climatic oscillations. Ecological niche modelling similarly suggested that both species experienced changes in their distributional ranges in response to Quaternary climatic changes. The extinction of the unknown 'ghost' tetraploid species implicated in the origin of O. sinensis could have resulted from superior adaptation of O. sinensis to repeated climatic changes in the region where it now occurs.


Assuntos
Evolução Biológica , Genoma de Planta , Filogenia , Polygonaceae/genética , Poliploidia , Diploide , Ecossistema , Hibridização In Situ , Transcriptoma
12.
J Hered ; 107(5): 445-54, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27217580

RESUMO

The contribution of gene expression modulation to phenotypic evolution is of major importance to an understanding of the origin of divergent or convergent phenotypes during and following polyploid speciation. Here, we analyzed genome-wide gene expression in 2 subspecies of the allotetraploid species, Senecio mohavensis A. Gray, and its diploid parents S. flavus (Decne.) Sch. Bip. and S. glaucus L. The tetraploid is morphologically much more similar to S. flavus, leading to earlier confusion over its taxonomic status. By means of an analysis of transcriptomes of all 3 species, we show that gene expression divergence between the parent species is relatively low (ca. 14% of loci), whereas there is significant unequal expression between ca. 20-25% of the parental homoeologues (gene copies) in the tetraploid. The majority of the expression bias in the tetraploid is in favor of S. flavus homoeologues (ca. 65% of the differentially expressed loci), and overall expression of this parental species subgenome is higher than that of the S. glaucus subgenome. To determine whether absence of expression of a particular S. glaucus homoeologue in the allotetraploid could be due to loss of DNA, we carried out a PCR-based assay and confirmed that in 3 out of 10 loci the S. glaucus homoeologue appeared absent. Our results suggest that biased gene expression is one cause of the allotetraploid S. mohavensis being more similar in morphology to one of its parent, S. flavus, and that such bias could result, in part, from loss of S. glaucus homoeologues at some loci in the allotetraploid.


Assuntos
Evolução Biológica , Regulação da Expressão Gênica de Plantas , Estudos de Associação Genética , Variação Genética , Fenótipo , Poliploidia , Biologia Computacional/métodos , Deleção de Genes , Perfilação da Expressão Gênica , Anotação de Sequência Molecular , Análise de Sequência de DNA
13.
AoB Plants ; 82016.
Artigo em Inglês | MEDLINE | ID: mdl-27083198

RESUMO

Knowledge of the genetic basis of phenotypic divergence between species and how such divergence is caused and maintained is crucial to an understanding of speciation and the generation of biodiversity. The hybrid zone between Senecio aethnensis and S. chrysanthemifolius on Mount Etna, Sicily, provides a well-studied example of species divergence in response to conditions at different elevations, despite hybridization and gene flow. Here, we investigate the genetic architecture of divergence between these two species using a combination of quantitative trait locus (QTL) mapping and genetic differentiation measures based on genetic marker analysis. A QTL architecture characterized by physical QTL clustering, epistatic interactions between QTLs, and pleiotropy was identified, and is consistent with the presence of divergent QTL complexes resistant to gene flow. A role for divergent selection between species was indicated by significant negative associations between levels of interspecific genetic differentiation at mapped marker gene loci and map distance from QTLs and hybrid incompatibility loci. Within-species selection contributing to interspecific differentiation was evidenced by negative associations between interspecific genetic differentiation and genetic diversity within species. These results show that the two Senecio species, while subject to gene flow, maintain divergent genomic regions consistent with local selection within species and selection against hybrids between species which, in turn, contribute to the maintenance of their distinct phenotypic differences.

14.
New Phytol ; 209(1): 343-53, 2016 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-26197783

RESUMO

Many plant species comprising the present-day Arctic flora are thought to have originated in the high mountains of North America and Eurasia, migrated northwards as global temperatures fell during the late Tertiary period, and thereafter attained a circumarctic distribution. However, supporting evidence for this hypothesis that provides a temporal framework for the origin, spread and initial attainment of a circumarctic distribution by an arctic plant is currently lacking. Here we examined the origin and initial formation of a circumarctic distribution of the arctic mountain sorrel (Oxyria digyna) by conducting a phylogeographic analysis of plastid and nuclear gene DNA variation. We provide evidence for an origin of this species in the Qinghai-Tibet Plateau of southwestern China, followed by migration into Russia c. 11 million yr ago (Ma), eastwards into North America by c. 4 Ma, and westwards into Western Europe by c. 1.96 Ma. Thereafter, the species attained a circumarctic distribution by colonizing Greenland from both sides of the Atlantic Ocean. Following the arrival of the species in North America and Europe, population sizes appear to have increased and then stabilized there over the last 1 million yr. However, in Greenland a marked reduction followed by an expansion in population size is indicated to have occurred during the Pleistocene.


Assuntos
Polygonaceae/genética , Regiões Árticas , Oceano Atlântico , Sequência de Bases , China , Europa (Continente) , Variação Genética , Groenlândia , Dados de Sequência Molecular , América do Norte , Filogeografia , Plastídeos/genética , Federação Russa , Análise de Sequência de DNA , Tibet
16.
Philos Trans R Soc Lond B Biol Sci ; 369(1648)2014 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-24958920

RESUMO

Altitudinal gradients are characterized by steep changes of the physical and biotic environment that present challenges to plant adaptation throughout large parts of the world. Hybrid zones may form where related species inhabit different neighbouring altitudes and can facilitate interspecific gene flow and potentially the breakdown of species barriers. Studies of such hybrid zones can reveal much about the genetic basis of adaptation to environmental differences stemming from changes in altitude and the maintenance of species divergence in the face of gene flow. Furthermore, owing to recombination and transgressive effects, such hybrid zones can be sources of evolutionary novelty. We document plant hybrid zones associated with altitudinal gradients and emphasize similarities and differences in their structure. We then focus on recent studies of a hybrid zone between two Senecio species that occur at high and low altitude on Mount Etna, Sicily, showing how adaptation to local environments and intrinsic selection against hybrids act to maintain it. Finally, we consider the potential of altitudinal hybrid zones for generating evolutionary novelty through adaptive introgression and hybrid speciation. Examples of homoploid hybrid species of Senecio and Pinus that originated from altitudinal hybrid zones are discussed.


Assuntos
Adaptação Biológica/genética , Altitude , Evolução Biológica , Hibridização Genética/genética , Dispersão Vegetal/genética , Senécio/genética , Sicília
17.
Mol Ecol ; 23(12): 3013-27, 2014 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24805369

RESUMO

Despite the well-known effects that Quaternary climate oscillations had on shaping intraspecific diversity, their role in driving homoploid hybrid speciation is less clear. Here, we examine their importance in the putative homoploid hybrid origin and evolution of Ostryopsis intermedia, a diploid species occurring in the Qinghai-Tibet Plateau (QTP), a biodiversity hotspot. We investigated interspecific relationships between this species and its only other congeners, O. davidiana and O. nobilis, based on four sets of nuclear and chloroplast population genetic data and tested alternative speciation hypotheses. All nuclear data distinguished the three species clearly and supported a close relationship between O. intermedia and the disjunctly distributed O. davidiana. Chloroplast DNA sequence variation identified two tentative lineages, which distinguished O. intermedia from O. davidiana; however, both were present in O. nobilis. Admixture analyses of genetic polymorphisms at 20 SSR loci and sequence variation at 11 nuclear loci and approximate Bayesian computation (ABC) tests supported the hypothesis that O. intermedia originated by homoploid hybrid speciation from O. davidiana and O. nobilis. We further estimated that O. davidiana and O. nobilis diverged 6-11 Ma, while O. intermedia originated 0.5-1.2 Ma when O. davidiana is believed to have migrated southward, contacted and hybridized with O. nobilis possibly during the largest Quaternary glaciation that occurred in this region. Our findings highlight the importance of Quaternary climate change in the QTP in causing hybrid speciation in this important biodiversity hotspot.


Assuntos
Betulaceae/classificação , Mudança Climática , Evolução Molecular , Especiação Genética , Teorema de Bayes , Betulaceae/genética , DNA de Cloroplastos/genética , DNA de Plantas/genética , DNA Espaçador Ribossômico/genética , Diploide , Ecossistema , Genética Populacional , Hibridização Genética , Repetições de Microssatélites , Modelos Genéticos , Filogenia , Análise de Sequência de DNA
18.
Ecol Evol ; 4(7): 1019-29, 2014 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-24772279

RESUMO

Because of introgressive hybridization, closely related species can be more similar to each other in areas of range overlap (parapatry or sympatry) than in areas where they are geographically isolated from each other (allopatry). Here, we report the reverse situation based on nuclear genetic divergence between two fir species, Abies chensiensis and Abies fargesii, in China, at sites where they are parapatric relative to where they are allopatric. We examined genetic divergence across 126 amplified fragment length polymorphism (AFLP) markers in a set of 172 individuals sampled from both allopatric and parapatric populations of the two species. Our analyses demonstrated that AFLP divergence was much greater between the species when comparisons were made between parapatric populations than between allopatric populations. We suggest that selection in parapatry may have largely contributed to this increased divergence.

19.
New Phytol ; 201(3): 1031-44, 2014 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-24400906

RESUMO

Quaternary climatic oscillations greatly influenced the distribution and pattern of biodiversity in the Northern Hemisphere. Here we examine how such oscillations in South East Asia may have affected the demographic and evolutionary history of a polyploid plant complex associated with semi-dry habitats. We analyzed plastid and nuclear ribosomal DNA (rDNA) internal transcribed spacer (ITS) sequence variation within the Chrysanthemum indicum complex (Asteraceae), which comprises diploid and polyploid plants distributed throughout China. In total, 368 individuals from 47 populations across the geographical range of the complex were analyzed. We show that the relatively widespread tetraploid form of C. indicum expanded its range southward in the Pleistocene, possibly during the most recent or previous glacial period when conditions became drier and forests retreated in southern China. In marked contrast, diploid and other polyploid members of the complex failed to expand their ranges at these times or have since undergone range contractions in contrast to tetraploid C. indicum. We conclude that hybridization and gene flow between taxa occurred frequently during the evolutionary history of the complex, causing considerable sharing of chlorotypes and ITS types. Nevertheless, taxa within ploidy levels could be largely distinguished according to chlorotype and/or ITS type.


Assuntos
Evolução Biológica , Chrysanthemum/genética , Mudança Climática , Geografia , Poliploidia , China , DNA Espaçador Ribossômico/genética , Variação Genética , Dados de Sequência Molecular , Filogenia , Tamanho da Amostra , Fatores de Tempo
20.
Mol Ecol ; 23(2): 343-59, 2014 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26010556

RESUMO

Hybridization and introgression can play an important role in speciation. Here, we examine their roles in the origin and evolution of Picea purpurea, a diploid spruce species occurring on the Qinghai-Tibet Plateau (QTP). Phylogenetic relationships and ecological differences between this species and its relatives, P. schrenkiana, P. likiangensis and P. wilsonii, are unclear. To clarify them, we surveyed sequence variation within and between them for 11 nuclear loci, three chloroplast (cp) and two mitochondrial (mt) DNA fragments, and examined their ecological requirements using ecological niche modelling. Initial analyses based on 11 nuclear loci rejected a close relationship between P. schrenkiana and P. purpurea. BP&P tests and ecological niche modelling indicated substantial divergence between the remaining three species and supported the species status of P. purpurea, which contained many private alleles as expected for a well-established species. Sequence variation for cpDNA and mtDNA suggested a close relationship between P. purpurea and P. wilsonii, while variation at the nuclear se1364 gene suggested P. purpurea was more closely related to P. likiangensis. Analyses of genetic divergence, Bayesian clustering and model comparison using approximate Bayesian computation (ABC) of nuclear (nr) DNA variation all supported the hypothesis that P. purpurea originated by homoploid hybrid speciation from P. wilsonii and P. likiangensis. The ABC analysis dated the origin of P. purpurea at the Pleistocene, and the estimated hybrid parameter indicated that 69% of its nuclear composition was contributed by P. likiangensis and 31% by P. wilsonii. Our results further suggested that during or immediately following its formation, P. purpurea was subject to organelle DNA introgression from P. wilsonii such that it came to possess both mtDNA and cpDNA of P. wilsonii. The estimated parameters indicated that following its origin, P. purpurea underwent an expansion during/after the largest Pleistocene glaciation recorded for the QTP.


Assuntos
Evolução Biológica , Hibridização Genética , Filogenia , Picea/classificação , Teorema de Bayes , Núcleo Celular/genética , DNA de Cloroplastos/genética , DNA Mitocondrial/genética , DNA de Plantas/genética , Ecossistema , Ligação Genética , Variação Genética , Genética Populacional , Genótipo , Modelos Genéticos , Dados de Sequência Molecular , Picea/genética , Análise de Sequência de DNA , Tibet
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