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Wessinger CA, Katzer AM, Hime PM, Rausher MD, Kelly JK, Hileman LC. A few essential genetic loci distinguish Penstemon species with flowers adapted to pollination by bees or hummingbirds. PLoS Biol 2023; 21:e3002294. [PMID: 37769035 PMCID: PMC10538765 DOI: 10.1371/journal.pbio.3002294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Accepted: 08/11/2023] [Indexed: 09/30/2023] Open
Abstract
In the formation of species, adaptation by natural selection generates distinct combinations of traits that function well together. The maintenance of adaptive trait combinations in the face of gene flow depends on the strength and nature of selection acting on the underlying genetic loci. Floral pollination syndromes exemplify the evolution of trait combinations adaptive for particular pollinators. The North American wildflower genus Penstemon displays remarkable floral syndrome convergence, with at least 20 separate lineages that have evolved from ancestral bee pollination syndrome (wide blue-purple flowers that present a landing platform for bees and small amounts of nectar) to hummingbird pollination syndrome (bright red narrowly tubular flowers offering copious nectar). Related taxa that differ in floral syndrome offer an attractive opportunity to examine the genomic basis of complex trait divergence. In this study, we characterized genomic divergence among 229 individuals from a Penstemon species complex that includes both bee and hummingbird floral syndromes. Field plants are easily classified into species based on phenotypic differences and hybrids displaying intermediate floral syndromes are rare. Despite unambiguous phenotypic differences, genome-wide differentiation between species is minimal. Hummingbird-adapted populations are more genetically similar to nearby bee-adapted populations than to geographically distant hummingbird-adapted populations, in terms of genome-wide dXY. However, a small number of genetic loci are strongly differentiated between species. These approximately 20 "species-diagnostic loci," which appear to have nearly fixed differences between pollination syndromes, are sprinkled throughout the genome in high recombination regions. Several map closely to previously established floral trait quantitative trait loci (QTLs). The striking difference between the diagnostic loci and the genome as whole suggests strong selection to maintain distinct combinations of traits, but with sufficient gene flow to homogenize the genomic background. A surprisingly small number of alleles confer phenotypic differences that form the basis of species identity in this species complex.
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Affiliation(s)
- Carolyn A. Wessinger
- Department of Biological Sciences, University of South Carolina, Columbia, South Carolina, United States of America
| | - Amanda M. Katzer
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas, United States of America
| | - Paul M. Hime
- Biodiversity Institute and Natural History Museum, University of Kansas, Lawrence, Kansas, United States of America
| | - Mark D. Rausher
- Department of Biology, Duke University, Durham, North Carolina, United States of America
| | - John K. Kelly
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas, United States of America
| | - Lena C. Hileman
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas, United States of America
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2
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Zalmat AS, Sotola VA, Nice CC, Martin NH. Genetic structure in Louisiana Iris species reveals patterns of recent and historical admixture. AMERICAN JOURNAL OF BOTANY 2021; 108:2257-2268. [PMID: 34618352 DOI: 10.1002/ajb2.1758] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 08/10/2021] [Accepted: 08/18/2021] [Indexed: 06/13/2023]
Abstract
PREMISE When divergent lineages come into secondary contact, reproductive isolation may be incomplete, thus providing an opportunity to investigate how speciation is manifested in the genome. The Louisiana Irises (Iris, series Hexagonae) comprise a group of three or more ecologically and reproductively divergent lineages that can produce hybrids where they come into contact. We estimated standing genetic variation to understand the current distribution of population structure in the Louisiana Irises. METHODS We used genotyping-by-sequencing techniques to sample the genomes of Louisiana Iris species across their ranges. We sampled 20 populations (n = 632 individuals) across 11,249 loci and used Entropy and PCA models to assess population genetic data. RESULTS We discovered evidence for interspecific gene flow in parts of the range. Our analysis revealed patterns of population structure at odds with widely accepted nominal taxonomy. We discovered undescribed hybrid populations, designated as belonging to the I. brevicaulis lineage. Iris nelsonii shared significant ancestry with only one of the purported parent species, I. fulva, evidence inconsistent with a hybrid origin. CONCLUSIONS This study provides several key findings important to the investigation of standing genetic variation in the Louisiana Iris species complex. Compared to the other nominal species, I. brevicaulis contains a large amount of genetic diversity. In addition, we discovered a previously unknown hybrid zone between I. brevicaulis and I. hexagona along the Texas coast. Finally, our results do not support the long-standing hypothesis that I. nelsonii has mixed ancestry from three parental taxa.
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Affiliation(s)
- Alexander S Zalmat
- Department of Biology, Texas State University, San Marcos, Texas, 78666-0202, USA
| | - V Alex Sotola
- Department of Genetics, University of Georgia, Athens, Georgia, 30602-7223, USA
| | - Chris C Nice
- Department of Biology, Texas State University, San Marcos, Texas, 78666-0202, USA
| | - Noland H Martin
- Department of Biology, Texas State University, San Marcos, Texas, 78666-0202, USA
- Director of the Population and Conservation Biology Program, Department of Biology, Texas State University, San Marcos, Texas, 78666-0202, USA
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3
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Kay KM, Surget-Groba Y. The genetic basis of floral mechanical isolation between two hummingbird-pollinated Neotropical understorey herbs. Mol Ecol 2021; 31:4351-4363. [PMID: 34487383 DOI: 10.1111/mec.16165] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 07/29/2021] [Accepted: 08/31/2021] [Indexed: 12/29/2022]
Abstract
Floral divergence can contribute to reproductive isolation among plant lineages, and thus provides an opportunity to study the genetics of speciation, including the number, effect size, mode of action and interactions of quantitative trait loci (QTL). Moreover, flowers represent suites of functionally interrelated traits, but it is unclear to what extent the phenotypic integration of the flower is underlain by a shared genetic architecture, which could facilitate or constrain correlated evolution of floral traits. Here, we examine the genetic architecture of floral morphological traits involved in an evolutionary switch from bill to forehead pollen placement between two species of hummingbird-pollinated Neotropical understorey herbs that are reproductively isolated by these floral differences. For the majority of traits, we find multiple QTL of relatively small effect spread throughout the genome. We also find substantial colocalization and alignment of effects of QTL underlying different floral traits that function together to promote outcrossing and reduce heterospecific pollen transfer. Our results are consistent with adaptive pleiotropy or linkage of many co-adapted genes, either of which could have facilitated a response to correlated selection and helped to stabilize divergent phenotypes in the face of low levels of hybridization. Moreover, our results indicate that floral mechanical isolation can be consistent with an infinitesimal model of adaptation.
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Affiliation(s)
- Kathleen M Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, USA
| | - Yann Surget-Groba
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA, USA.,Département de Biologie, Université du Québec en Outaouais, Ripon, QC, Canada
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4
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Edwards MB, Choi GPT, Derieg NJ, Min Y, Diana AC, Hodges SA, Mahadevan L, Kramer EM, Ballerini ES. Genetic architecture of floral traits in bee- and hummingbird-pollinated sister species of Aquilegia (columbine). Evolution 2021; 75:2197-2216. [PMID: 34270789 DOI: 10.1111/evo.14313] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 06/21/2021] [Accepted: 06/25/2021] [Indexed: 01/24/2023]
Abstract
Interactions with animal pollinators have helped shape the stunning diversity of flower morphologies across the angiosperms. A common evolutionary consequence of these interactions is that some flowers have converged on suites of traits, or pollination syndromes, that attract and reward specific pollinator groups. Determining the genetic basis of these floral pollination syndromes can help us understand the processes that contributed to the diversification of the angiosperms. Here, we characterize the genetic architecture of a bee-to-hummingbird pollination shift in Aquilegia (columbine) using QTL mapping of 17 floral traits encompassing color, nectar composition, and organ morphology. In this system, we find that the genetic architectures underlying differences in floral color are quite complex, and we identify several likely candidate genes involved in anthocyanin and carotenoid floral pigmentation. Most morphological and nectar traits also have complex genetic underpinnings; however, one of the key floral morphological phenotypes, nectar spur curvature, is shaped by a single locus of large effect.
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Affiliation(s)
- Molly B Edwards
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138
| | - Gary P T Choi
- Department of Mathematics, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02142
| | - Nathan J Derieg
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138
| | - Ya Min
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138
| | - Angie C Diana
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138
| | - Scott A Hodges
- Department of Ecology, Evolutionary, and Marine Biology, University of California Santa Barbara, Santa Babara, California, 93106
| | - L Mahadevan
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138.,School of Engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, 02138.,Department of Physics, Harvard University, Cambridge, Massachusetts, 02138
| | - Elena M Kramer
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, 02138
| | - Evangeline S Ballerini
- Department of Ecology, Evolutionary, and Marine Biology, University of California Santa Barbara, Santa Babara, California, 93106.,Dept. of Biological Sciences, California State University Sacramento, Sacramento, California, 95819
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5
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Thompson KA, Urquhart-Cronish M, Whitney KD, Rieseberg LH, Schluter D. Patterns, Predictors, and Consequences of Dominance in Hybrids. Am Nat 2021; 197:E72-E88. [PMID: 33625966 DOI: 10.1086/712603] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AbstractCompared to those of their parents, are the traits of first-generation (F1) hybrids typically intermediate, biased toward one parent, or mismatched for alternative parental phenotypes? To address this empirical gap, we compiled data from 233 crosses in which traits were measured in a common environment for two parent taxa and their F1 hybrids. We find that individual traits in F1s are halfway between the parental midpoint and one parental value. Considering pairs of traits together, a hybrid's bivariate phenotype tends to resemble one parent (parent bias) about 50% more than the other, while also exhibiting a similar magnitude of mismatch due to different traits having dominance in conflicting directions. Using data from an experimental field planting of recombinant hybrid sunflowers, we illustrate that parent bias improves fitness, whereas mismatch reduces fitness. Our study has three major conclusions. First, hybrids are not phenotypically intermediate but rather exhibit substantial mismatch. Second, dominance is likely determined by the idiosyncratic evolutionary trajectories of individual traits and populations. Finally, selection against hybrids likely results from selection against both intermediate and mismatched phenotypes.
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6
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Genetic architecture of quantitative flower and leaf traits in a pair of sympatric sister species of Primulina. Heredity (Edinb) 2018; 122:864-876. [PMID: 30518967 DOI: 10.1038/s41437-018-0170-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Revised: 11/19/2018] [Accepted: 11/19/2018] [Indexed: 01/10/2023] Open
Abstract
Flowers and leaves each represent suites of functionally interrelated traits that are often involved in species divergence and local adaptation. However, a major unresolved issue is how the individual component traits that make up a complex trait such as a flower evolve in a coordinated fashion to retain a high degree of functionality. We use a quantitative trait loci (QTL) approach to elucidate the genetic architecture of divergence in flower and leaf traits between the sister species Primulina depressa and Primulina danxiaensis, which grow sympatrically but in contrasting microhabitats. We found that flower traits were controlled by multiple QTL of small effect, while leaf physiological and morphological traits tended to be controlled by QTL of larger effect. The observed floral integration, manifested by a high degree overlap in both individual trait QTL and QTL for principal component scores (PCA QTL), may have been critical for evolutionary divergence of floral morphology in relation to their pollinators. This overlap suggests that direct selection on only one or a few of the component traits could have caused substantial divergence in other floral traits due to genetic correlations, while the low QTL overlap between floral and vegetative traits suggests that these trait suites are genetically unlinked and can evolve independently in response to different selective pressures corresponding to their distinct functions.
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7
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Sung C, Bell KL, Nice CC, Martin NH. Integrating Bayesian genomic cline analyses and association mapping of morphological and ecological traits to dissect reproductive isolation and introgression in a Louisiana Iris hybrid zone. Mol Ecol 2018; 27:959-978. [DOI: 10.1111/mec.14481] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Accepted: 12/14/2017] [Indexed: 01/01/2023]
Affiliation(s)
- Cheng‐Jung Sung
- Population and Conservation Biology Program Department of Biology Texas State University San Marcos TX USA
| | - Katherine L. Bell
- Population and Conservation Biology Program Department of Biology Texas State University San Marcos TX USA
| | - Chris C. Nice
- Population and Conservation Biology Program Department of Biology Texas State University San Marcos TX USA
| | - Noland H. Martin
- Population and Conservation Biology Program Department of Biology Texas State University San Marcos TX USA
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8
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Moyers BT, Owens GL, Baute GJ, Rieseberg LH. The genetic architecture of UV floral patterning in sunflower. ANNALS OF BOTANY 2017; 120:39-50. [PMID: 28459939 PMCID: PMC5737206 DOI: 10.1093/aob/mcx038] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Accepted: 03/14/2017] [Indexed: 06/07/2023]
Abstract
Background and Aims The patterning of floral ultraviolet (UV) pigmentation varies both intra- and interspecifically in sunflowers and many other plant species, impacts pollinator attraction, and can be critical to reproductive success and crop yields. However, the genetic basis for variation in UV patterning is largely unknown. This study examines the genetic architecture for proportional and absolute size of the UV bullseye in Helianthus argophyllus , a close relative of the domesticated sunflower. Methods A camera modified to capture UV light (320-380 nm) was used to phenotype floral UV patterning in an F 2 mapping population, then quantitative trait loci (QTL) were identified using genotyping-by-sequencing and linkage mapping. The ability of these QTL to predict the UV patterning of natural population individuals was also assessed. Key Results Proportional UV pigmentation is additively controlled by six moderate effect QTL that are predictive of this phenotype in natural populations. In contrast, UV bullseye size is controlled by a single large effect QTL that also controls flowerhead size and co-localizes with a major flowering time QTL in Helianthus . Conclusions The co-localization of the UV bullseye size QTL, flowerhead size QTL and a previously known flowering time QTL may indicate a single highly pleiotropic locus or several closely linked loci, which could inhibit UV bullseye size from responding to selection without change in correlated characters. The genetic architecture of proportional UV pigmentation is relatively simple and different from that of UV bullseye size, and so should be able to respond to natural or artificial selection independently.
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Affiliation(s)
- Brook T. Moyers
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Room 3529-6270 University Blvd, Vancouver, BC V6T 1Z4, Canada
- Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523, USA
| | - Gregory L. Owens
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Room 3529-6270 University Blvd, Vancouver, BC V6T 1Z4, Canada
| | - Gregory J. Baute
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Room 3529-6270 University Blvd, Vancouver, BC V6T 1Z4, Canada
| | - Loren H. Rieseberg
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Room 3529-6270 University Blvd, Vancouver, BC V6T 1Z4, Canada
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9
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Amrad A, Moser M, Mandel T, de Vries M, Schuurink RC, Freitas L, Kuhlemeier C. Gain and Loss of Floral Scent Production through Changes in Structural Genes during Pollinator-Mediated Speciation. Curr Biol 2016; 26:3303-3312. [PMID: 27916524 DOI: 10.1016/j.cub.2016.10.023] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2016] [Revised: 10/06/2016] [Accepted: 10/12/2016] [Indexed: 10/20/2022]
Abstract
The interactions of plants with their pollinators are thought to be a driving force in the evolution of angiosperms. Adaptation to a new pollinator involves coordinated changes in multiple floral traits controlled by multiple genes. Surprisingly, such complex genetic shifts have happened numerous times during evolution. Here we report on the genetic basis of the changes in one such trait, floral scent emission, in the genus Petunia (Solanaceae). The increase in the quantity and complexity of the volatiles during the shift from bee to hawkmoth pollination was due to de novo expression of the genes encoding benzoic acid/salicylic acid carboxyl methyltransferase (BSMT) and benzoyl-CoA:benzylalcohol/2-phenylethanol benzoyltransferase (BPBT) together with moderately increased transcript levels for most enzymes of the phenylpropanoid/benzenoid pathway. Loss of cinnamate-CoA ligase (CNL) function as well as a reduction in the expression of the MYB transcription factor ODO1 explain the loss of scent during the transition from moth to hummingbird pollination. The CNL gene in the hummingbird-adapted species is inactive due to a stop codon, but also appears to have undergone further degradation over time. Therefore, we propose that loss of scent happened relatively early in the transition toward hummingbird pollination, and probably preceded the loss of UV-absorbing flavonols. The discovery that CNL is also involved in the loss of scent during the transition from outcrossing to selfing in Capsella (Brassicaceae) (see the accompanying paper) raises interesting questions about the possible causes of deep evolutionary conservation of the targets of evolutionary change.
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Affiliation(s)
- Avichai Amrad
- Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland
| | - Michel Moser
- Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland
| | - Therese Mandel
- Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland
| | - Michel de Vries
- Swammerdam Institute for Life Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands
| | - Robert C Schuurink
- Swammerdam Institute for Life Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, the Netherlands
| | - Loreta Freitas
- Laboratory of Molecular Evolution, Department of Genetics, Universidade Federal do Rio Grande do Sul, P.O. Box 15053, Avenida Bento Goncalves, 9500 Porto Alegre, Brazil
| | - Cris Kuhlemeier
- Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland.
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10
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Brennan AC, Hiscock SJ, Abbott RJ. Genomic architecture of phenotypic divergence between two hybridizing plant species along an elevational gradient. AOB PLANTS 2016; 8:plw022. [PMID: 27083198 PMCID: PMC4887755 DOI: 10.1093/aobpla/plw022] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Accepted: 03/19/2016] [Indexed: 05/03/2023]
Abstract
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.
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Affiliation(s)
- Adrian C Brennan
- School of Biology, University of St Andrews, Harold Mitchell Building, St Andrews, Fife KY16 9TH, UK Estación Biológica de Doñana (EBD-CSIC), Avenida Américo Vespucio s/n, 41092 Sevilla, Spain Present address: School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK
| | - Simon J Hiscock
- School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK
| | - Richard J Abbott
- School of Biology, University of St Andrews, Harold Mitchell Building, St Andrews, Fife KY16 9TH, UK
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11
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MYB-FL controls gain and loss of floral UV absorbance, a key trait affecting pollinator preference and reproductive isolation. Nat Genet 2015; 48:159-66. [PMID: 26656847 DOI: 10.1038/ng.3462] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 11/12/2015] [Indexed: 01/26/2023]
Abstract
Adaptations to new pollinators involve multiple floral traits, each requiring coordinated changes in multiple genes. Despite this genetic complexity, shifts in pollination syndromes have happened frequently during angiosperm evolution. Here we study the genetic basis of floral UV absorbance, a key trait for attracting nocturnal pollinators. In Petunia, mutations in a single gene, MYB-FL, explain two transitions in UV absorbance. A gain of UV absorbance in the transition from bee to moth pollination was determined by a cis-regulatory mutation, whereas a frameshift mutation caused subsequent loss of UV absorbance during the transition from moth to hummingbird pollination. The functional differences in MYB-FL provide insight into the process of speciation and clarify phylogenetic relationships between nascent species.
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12
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Hamlin JAP, Arnold ML. Neutral and Selective Processes Drive Population Differentiation for Iris hexagona. J Hered 2015; 106:628-36. [PMID: 26163584 DOI: 10.1093/jhered/esv045] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2015] [Accepted: 06/11/2015] [Indexed: 11/15/2022] Open
Abstract
Gene flow among widespread populations can be reduced by geographical distance or by divergent selection resulting from local adaptation. In this study, we tested for the divergence of phenotypes and genotypes among 8 populations of Iris hexagona. Using a genotyping-by-sequencing approach, we generated a panel of 750 single nucleotide polymorphisms (SNPs) and used population genetic analyses to determine what may affect patterns of divergence across I. hexagona populations. Specifically, genetic differentiation was compared between populations at neutral and nonneutral SNPs and detected significant differences between the 2 types of markers. We then asked whether loci with the strongest degree of population genetic differentiation were also the loci with the strongest association to morphology or climate differences, allowing us to test if pollinators or climate drive population differentiation or some combination of both. We found 2 markers that were associated with morphology and 1 marker associated with 2 of the environmental variables, which were also identified in the outlier analysis. We then show that the SNPs putatively under selection were positively correlated with both geographic distance and phenotypic distance, albeit weakly to phenotypic distance. Moreover, neutral SNPs were only correlated with geographic distance and thus isolation-by-distance was observed for neutral SNPs. Our data suggest that both deterministic and neutral processes have contributed to the evolutionary trajectory of I. hexagona populations.
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Affiliation(s)
- Jennafer A P Hamlin
- From the Department of Genetics, University of Georgia, 120 East Green St., Davison Life Sciences Building, Athens, GA (Arnold) and the Department of Biology, Indiana University, Bloomington, IN 47405, USA (Hamlin).
| | - Michael L Arnold
- From the Department of Genetics, University of Georgia, 120 East Green St., Davison Life Sciences Building, Athens, GA (Arnold) and the Department of Biology, Indiana University, Bloomington, IN 47405, USA (Hamlin)
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13
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Wessinger CA, Hileman LC, Rausher MD. Identification of major quantitative trait loci underlying floral pollination syndrome divergence in Penstemon. Philos Trans R Soc Lond B Biol Sci 2015; 369:rstb.2013.0349. [PMID: 24958923 DOI: 10.1098/rstb.2013.0349] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Distinct floral pollination syndromes have emerged multiple times during the diversification of flowering plants. For example, in western North America, a hummingbird pollination syndrome has evolved more than 100 times, generally from within insect-pollinated lineages. The hummingbird syndrome is characterized by a suite of floral traits that attracts and facilitates pollen movement by hummingbirds, while at the same time discourages bee visitation. These floral traits generally include large nectar volume, red flower colour, elongated and narrow corolla tubes and reproductive organs that are exerted from the corolla. A handful of studies have examined the genetic architecture of hummingbird pollination syndrome evolution. These studies find that mutations of relatively large effect often explain increased nectar volume and transition to red flower colour. In addition, they suggest that adaptive suites of floral traits may often exhibit a high degree of genetic linkage, which could facilitate their fixation during pollination syndrome evolution. Here, we explore these emerging generalities by investigating the genetic basis of floral pollination syndrome divergence between two related Penstemon species with different pollination syndromes--bee-pollinated P. neomexicanus and closely related hummingbird-pollinated P. barbatus. In an F2 mapping population derived from a cross between these two species, we characterized the effect size of genetic loci underlying floral trait divergence associated with the transition to bird pollination, as well as correlation structure of floral trait variation. We find the effect sizes of quantitative trait loci for adaptive floral traits are in line with patterns observed in previous studies, and find strong evidence that suites of floral traits are genetically linked. This linkage may be due to genetic proximity or pleiotropic effects of single causative loci. Interestingly, our data suggest that the evolution of floral traits critical for hummingbird pollination was not constrained by negative pleiotropy at loci that show co-localization for multiple traits.
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Affiliation(s)
- Carolyn A Wessinger
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA
| | - Lena C Hileman
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045, USA
| | - Mark D Rausher
- Department of Biology, Duke University, Durham, NC 27708, USA
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14
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Comeault AA, Soria-Carrasco V, Gompert Z, Farkas TE, Buerkle CA, Parchman TL, Nosil P. Genome-Wide Association Mapping of Phenotypic Traits Subject to a Range of Intensities of Natural Selection in Timema cristinae. Am Nat 2014; 183:711-27. [DOI: 10.1086/675497] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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15
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Hamlin JAP, Arnold ML. Determining population structure and hybridization for two iris species. Ecol Evol 2014; 4:743-55. [PMID: 24683457 PMCID: PMC3967900 DOI: 10.1002/ece3.964] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Revised: 12/20/2013] [Accepted: 01/08/2014] [Indexed: 12/24/2022] Open
Abstract
Identifying processes that promote or limit gene flow can help define the ecological and evolutionary history of a species. Furthermore, defining those factors that make up “species boundaries” can provide a definition of the independent evolutionary trajectories of related taxa. For many species, the historic processes that account for their distribution of genetic variation remain unresolved. In this study, we examine the geographic distribution of genetic diversity for two species of Louisiana Irises, Iris brevicaulis and Iris fulva. Specifically, we asked how populations are structured and if population structure coincides with potential barriers to gene flow. We also asked whether there is evidence of hybridization between these two species outside Louisiana hybrid zones. We used a genotyping-by-sequencing approach and sampled a large number of single nucleotide polymorphisms across these species' genomes. Two different population assignment methods were used to resolve population structure in I. brevicaulis; however, there was considerably less population structure in I. fulva. We used a species tree approach to infer phylogenies both within and between populations and species. For I. brevicaulis, the geography of the collection locality was reflected in the phylogeny. The I. fulva phylogeny reflected much less structure than detected for I. brevicaulis. Lastly, combining both species into a phylogenetic analysis resolved two of six populations of I. brevicaulis that shared alleles with I. fulva. Taken together, our results suggest major differences in the level and pattern of connectivity among populations of these two Louisiana Iris species.
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Affiliation(s)
- Jennafer A P Hamlin
- Correspondence Jennafer A. P. Hamlin, Department of Genetics, University of Georgia, 120 East Green St. Davison Life Sciences Building, Athens, GA. Tel: 706 410 7529; Fax: 706 542 3910; E-mail:
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Brothers AN, Barb JG, Ballerini ES, Drury DW, Knapp SJ, Arnold ML. Genetic Architecture of Floral Traits in Iris hexagona and Iris fulva. J Hered 2013; 104:853-61. [DOI: 10.1093/jhered/est059] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
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Yuan YW, Byers KJRP, Bradshaw HD. The genetic control of flower-pollinator specificity. CURRENT OPINION IN PLANT BIOLOGY 2013; 16:422-8. [PMID: 23763819 PMCID: PMC3748206 DOI: 10.1016/j.pbi.2013.05.004] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2013] [Revised: 05/15/2013] [Accepted: 05/17/2013] [Indexed: 05/16/2023]
Abstract
The ca. 275,000 species of flowering plants are the result of a recent adaptive radiation driven largely by the coevolution between plants and their animal pollinators. Identification of genes and mutations responsible for floral trait variation underlying pollinator specificity is crucial to understanding how pollinator shifts occur between closely related species. Petunia, Mimulus, and Antirrhinum have provided a high standard of experimental evidence to establish causal links from genes to floral traits to pollinator responses. In all three systems, MYB transcription factors seem to play a prominent role in the diversification of pollinator-associated floral traits.
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Affiliation(s)
- Yao-Wu Yuan
- Department of Biology, University of Washington, Seattle, WA 98195, United States
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Nakazato T, Rieseberg LH, Wood TE. The genetic basis of speciation in the Giliopsis lineage of Ipomopsis (Polemoniaceae). Heredity (Edinb) 2013; 111:227-37. [PMID: 23652565 DOI: 10.1038/hdy.2013.41] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2012] [Revised: 03/27/2013] [Accepted: 04/02/2013] [Indexed: 12/29/2022] Open
Abstract
One of the most powerful drivers of speciation in plants is pollinator-mediated disruptive selection, which leads to the divergence of floral traits adapted to the morphology and behavior of different pollinators. Despite the widespread importance of this speciation mechanism, its genetic basis has been explored in only a few groups. Here, we characterize the genetic basis of pollinator-mediated divergence of two species in genus Ipomopsis, I. guttata and I. tenuifolia, using quantitative trait locus (QTL) analyses of floral traits and other variable phenotypes. We detected one to six QTLs per trait, with each QTL generally explaining small to modest amounts of the phenotypic variance of a backcross hybrid population. In contrast, flowering time and anthocyanin abundance (a metric of color variation) were controlled by a few QTLs of relatively large effect. QTLs were strongly clustered within linkage groups, with 26 of 37 QTLs localized to six marker-interval 'hotspots,' all of which harbored pleiotropic QTLs. In contrast to other studies that have examined the genetic basis of pollinator shifts, our results indicate that, in general, mutations of small to modest effect on phenotype were involved. Thus, the evolutionary transition between the distinct pollination modes of I. guttata and I. tenuifolia likely proceeded incrementally, rather than saltationally.
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Affiliation(s)
- T Nakazato
- Department of Biological Sciences, University of Memphis, Memphis, TN, USA
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Abstract
Flowers exhibit amazing morphological diversity in many traits, including their size. In addition to interspecific flower size differences, many species maintain significant variation in flower size within and among populations. Flower size variation can contribute to reproductive isolation of species and thus has clear evolutionary consequences. In this review we integrate information on flower size variation from both evolutionary and developmental biology perspectives. We examine the role of flower size in the context of mating system evolution. In addition, we describe what is currently known about the genetic basis of flower size based on quantitative trait locus (QTL) mapping in several different plant species and molecular genetic studies in model plants, primarily Arabidopsis thaliana. Work in Arabidopsis suggests that many independent pathways regulate floral organ growth via effects on cell proliferation and/or cell expansion.
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Affiliation(s)
- Beth A Krizek
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA.
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Taylor SJ, Rojas LD, Ho SW, Martin NH. Genomic collinearity and the genetic architecture of floral differences between the homoploid hybrid species Iris nelsonii and one of its progenitors, Iris hexagona. Heredity (Edinb) 2012; 110:63-70. [PMID: 23047202 DOI: 10.1038/hdy.2012.62] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Hybrid speciation represents a relatively rapid form of diversification. Early models of homoploid hybrid speciation suggested that reproductive isolation between the hybrid species and progenitors primarily resulted from karyotypic differences between the species. However, genic incompatibilities and ecological divergence may also be responsible for isolation. Iris nelsonii is an example of a homoploid hybrid species that is likely isolated from its progenitors primarily by strong prezygotic isolation, including habitat divergence, floral isolation and post-pollination prezygotic barriers. Here, we used linkage mapping and quantitative trait locus (QTL) mapping approaches to investigate genomic collinearity and the genetic architecture of floral differences between I. nelsonii and one of its progenitor species I. hexagona. The linkage map produced from this cross is highly collinear with another linkage map produced between I. fulva and I. brevicaulis (the two other species shown to have contributed to the genomic makeup of I. nelsonii), suggesting that karyotypic differences do not contribute substantially to isolation in this homoploid hybrid species. Similar to other studies of the genetic architecture of floral characteristics, at least one QTL was found that explained >20% variance in each color trait, while minor QTLs were detected for each morphological trait. These QTLs will serve as hypotheses for regions under selection by pollinators.
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Affiliation(s)
- S J Taylor
- Department of Biology, Texas State University-San Marcos, San Marcos, TX 78666, USA.
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References. Mol Ecol 2012. [DOI: 10.1002/9780470979365.refs] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Brock MT, Kover PX, Weinig C. Natural variation in GA1 associates with floral morphology in Arabidopsis thaliana. THE NEW PHYTOLOGIST 2012; 195:58-70. [PMID: 22510148 DOI: 10.1111/j.1469-8137.2012.04145.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
• The genetic architecture of floral traits is evolutionarily important due to the fitness consequences of quantitative variation in floral morphology. Yet, little is known about the genes underlying these traits in natural populations. Using Arabidopsis thaliana, we examine molecular variation at GIBBERELLIC ACID REQUIRING 1 (GA1) and test for associations with floral morphology. • We examined full-length sequence in 32 accessions and describe two haplotypes (comprising four nonsynonymous polymorphisms) in GA1 that segregate at intermediate frequencies. In 133 A. thaliana accessions, we test for genotype-phenotype associations and corroborate these findings in segregating progenies. • The two common GA1 haplotypes were associated with the length of petals, stamens, and to a lesser extent style-stigma length. Associations were confirmed in a segregating progeny developed from 19 accessions. We find analogous results in recombinant inbred lines of the Bayreuth × Shahdara cross, which differ only at one of 4 SNPs, suggesting that this SNP may contribute to the observed association. • Assuming GA1 causally affects floral organ size, it is interesting that adjacent petal and stamen whorls are most strongly affected. This pattern suggests that GA1 could contribute to the greater strength of petal-stamen correlations relative to other floral-length correlations observed in some Brassicaceous species.
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Affiliation(s)
- Marcus T Brock
- Department of Botany, University of Wyoming, Laramie, WY 82071, USA.
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Ballerini ES, Brothers AN, Tang S, Knapp SJ, Bouck A, Taylor SJ, Arnold ML, Martin NH. QTL mapping reveals the genetic architecture of loci affecting pre- and post-zygotic isolating barriers in Louisiana Iris. BMC PLANT BIOLOGY 2012; 12:91. [PMID: 22702308 PMCID: PMC3490880 DOI: 10.1186/1471-2229-12-91] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 05/18/2012] [Indexed: 06/01/2023]
Abstract
BACKGROUND Hybridization among Louisiana Irises has been well established and the genetic architecture of reproductive isolation is known to affect the potential for and the directionality of introgression between taxa. Here we use co-dominant markers to identify regions where QTL are located both within and between backcross maps to compare the genetic architecture of reproductive isolation and fitness traits across treatments and years. RESULTS QTL mapping was used to elucidate the genetic architecture of reproductive isolation between Iris fulva and Iris brevicaulis. Homologous co-dominant EST-SSR markers scored in two backcross populations between I. fulva and I. brevicaulis were used to generate genetic linkage maps. These were used as the framework for mapping QTL associated with variation in 11 phenotypic traits likely responsible for reproductive isolation and fitness. QTL were dispersed throughout the genome, with the exception of one region of a single linkage group (LG) where QTL for flowering time, sterility, and fruit production clustered. In most cases, homologous QTL were not identified in both backcross populations, however, homologous QTL for flowering time, number of growth points per rhizome, number of nodes per inflorescence, and number of flowers per node were identified on several linkage groups. CONCLUSIONS Two different traits affecting reproductive isolation, flowering time and sterility, exhibit different genetic architectures, with numerous QTL across the Iris genome controlling flowering time and fewer, less distributed QTL affecting sterility. QTL for traits affecting fitness are largely distributed across the genome with occasional overlap, especially on LG 4, where several QTL increasing fitness and decreasing sterility cluster. Given the distribution and effect direction of QTL affecting reproductive isolation and fitness, we have predicted genomic regions where introgression may be more likely to occur (those regions associated with an increase in fitness and unlinked to loci controlling reproductive isolation) and those that are less likely to exhibit introgression (those regions linked to traits decreasing fitness and reproductive isolation).
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Affiliation(s)
| | | | | | | | | | - Sunni J Taylor
- Department of Biology, Texas State University, San Marcos, TX, USA
| | | | - Noland H Martin
- Department of Biology, Texas State University, San Marcos, TX, USA
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Kim SC. Mapping unexplored genomes II: genetic architecture of species differences in the woody Sonchus alliance (Asteraceae) in the Macaronesian Islands. JOURNAL OF PLANT RESEARCH 2012; 125:125-136. [PMID: 21505946 DOI: 10.1007/s10265-011-0424-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Accepted: 03/23/2011] [Indexed: 05/30/2023]
Abstract
Despite numerous, well-documented evolutionary histories of plant groups which underwent rapid radiation in various oceanic archipelagos, very little is known about the genetic basis of species differences and adaptive radiation. This paper represents the first such study in the Macaronesian Islands using non-model endemic plants, the woody Sonchus alliance. Here I inferred the genetic basis of species differences between two Canary Island endemics, the herbaceous perennial, shade tolerant Lactucosonchus webbii and the woody, coastal desert perennial Sonchus radicatus by quantitative trait locus (QTL) mapping using AFLP markers. A total of 23 QTL (7.3-23.8% PVE; phenotypic variance explained) for 11 morphological traits were found, one for flowering time (31% PVE), and five QTL (7-10.7% PVE) for two physiological traits (intrinsic water use efficiency and stomatal conductance). Interpreted cautiously, these results suggest that major morphological and some physiological differences between the two species are controlled by numerous genes with small to moderate effect. This implies that major morphological changes in island plants can be more complex than suggested by other studies, such as in Tetramolopium in the Hawaiian Islands. The genetic basis of arborescence on islands, one of the most spectacular convergent features of plants across different lineages and archipelagos, is also discussed.
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Affiliation(s)
- Seung-Chul Kim
- Department of Biological Sciences, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do, 440-746, Korea.
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Hybrid fitness, adaptation and evolutionary diversification: lessons learned from Louisiana Irises. Heredity (Edinb) 2011; 108:159-66. [PMID: 21792222 DOI: 10.1038/hdy.2011.65] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Estimates of hybrid fitness have been used as either a platform for testing the potential role of natural hybridization in the evolution of species and species complexes or, alternatively, as a rationale for dismissing hybridization events as being of any evolutionary significance. From the time of Darwin's publication of The Origin, through the neo-Darwinian synthesis, to the present day, the observation of variability in hybrid fitness has remained a challenge for some models of speciation. Yet, Darwin and others have reported the elevated fitness of hybrid genotypes under certain environmental conditions. In modern scientific terminology, this observation reflects the fact that hybrid genotypes can demonstrate genotype × environment interactions. In the current review, we illustrate the development of one plant species complex, namely the Louisiana Irises, into a 'model system' for investigating hybrid fitness and the role of genetic exchange in adaptive evolution and diversification. In particular, we will argue that a multitude of approaches, involving both experimental and natural environments, and incorporating both manipulative analyses and surveys of natural populations, are necessary to adequately test for the evolutionary significance of introgressive hybridization. An appreciation of the variability of hybrid fitness leads to the conclusion that certain genetic signatures reflect adaptive evolution. Furthermore, tests of the frequency of allopatric versus sympatric/parapatric divergence (that is, divergence with ongoing gene flow) support hybrid genotypes as a mechanism of evolutionary diversification in numerous species complexes.
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Hermann K, Kuhlemeier C. The genetic architecture of natural variation in flower morphology. CURRENT OPINION IN PLANT BIOLOGY 2011; 14:60-65. [PMID: 20934369 DOI: 10.1016/j.pbi.2010.09.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2010] [Accepted: 09/11/2010] [Indexed: 05/30/2023]
Abstract
A pollination syndrome is defined as a suite of floral traits that are associated with the attraction of a specific group of animals as pollinators. Traits such as flower morphology, color, scent, and rewards contribute to the plant's reproductive success by attracting pollinators. Here we focus on the genetics of natural variation in flower morphology and how the adaptation between plants and their cognate pollinator class contributes to plant's reproductive success. We review recent work on the genetic basis of interspecific differences in reproductive organ morphology and discuss possible genetic mechanisms for coordinated changes in complex syndromes.
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Affiliation(s)
- Katrin Hermann
- Institute of Plant Sciences, University of Berne, Altenbergrain 21, CH-3013 Berne, Switzerland
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Floral genetic architecture: an examination of QTL architecture underlying floral (co)variation across environments. Genetics 2010; 186:1451-65. [PMID: 20837996 DOI: 10.1534/genetics.110.119982] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Genetic correlations are expected to be high among functionally related traits and lower between groups of traits with distinct functions (e.g., reproductive vs. resource-acquisition traits). Here, we explore the quantitative-genetic and QTL architecture of floral organ sizes, vegetative traits, and life history in a set of Brassica rapa recombinant inbred lines within and across field and greenhouse environments. Floral organ lengths were strongly positively correlated within both environments, and analysis of standardized G-matrices indicates that the structure of genetic correlations is ∼80% conserved across environments. Consistent with these correlations, we detected a total of 19 and 21 additive-effect floral QTL in the field and the greenhouse, respectively, and individual QTL typically affected multiple organ types. Interestingly, QTL×QTL epistasis also appeared to contribute to observed genetic correlations; i.e., interactions between two QTL had similar effects on filament length and two estimates of petal size. Although floral and nonfloral traits are hypothesized to be genetically decoupled, correlations between floral organ size and both vegetative and life-history traits were highly significant in the greenhouse; G-matrices of floral and vegetative traits as well as floral and life-history traits differed across environments. Correspondingly, many QTL (45% of those mapped in the greenhouse) showed environmental interactions, including approximately even numbers of floral and nonfloral QTL. Most instances of QTL×QTL epistasis for floral traits were environment dependent.
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Tang S, Okashah RA, Knapp SJ, Arnold ML, Martin NH. Transmission ratio distortion results in asymmetric introgression in Louisiana Iris. BMC PLANT BIOLOGY 2010; 10:48. [PMID: 20298609 PMCID: PMC2923522 DOI: 10.1186/1471-2229-10-48] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2009] [Accepted: 03/18/2010] [Indexed: 05/03/2023]
Abstract
BACKGROUND Linkage maps are useful tools for examining both the genetic architecture of quantitative traits and the evolution of reproductive incompatibilities. We describe the generation of two genetic maps using reciprocal interspecific backcross 1 (BC1) mapping populations from crosses between Iris brevicaulis and Iris fulva. These maps were constructed using expressed sequence tag (EST)- derived codominant microsatellite markers. Such a codominant marker system allowed for the ability to link the two reciprocal maps, and compare patterns of transmission ratio distortion observed between the two. RESULTS Linkage mapping resulted in markers that coalesced into 21 linkage groups for each of the reciprocal backcross maps, presumably corresponding to the 21 haploid chromosomes of I. brevicaulis and I. fulva. The composite map was 1190.0-cM long, spanned 81% of the I. brevicaulis and I. fulva genomes, and had a mean density of 4.5 cM per locus. Transmission ratio distortion (TRD) was observed in 138 (48.5%) loci distributed in 19 of the 21 LGs in BCIB, BCIF, or both BC1 mapping populations. Of the distorted markers identified, I. fulva alleles were detected at consistently higher-than-expected frequencies in both mapping populations. CONCLUSIONS The observation that I. fulva alleles are overrepresented in both mapping populations suggests that I. fulva alleles are favored to introgress into I. brevicaulis genetic backgrounds, while I. brevicaulis alleles would tend to be prevented from introgressing into I. fulva. These data are consistent with the previously observed patterns of introgression in natural hybrid zones, where I. fulva alleles have been consistently shown to introgress across species boundaries.
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Affiliation(s)
- Shunxue Tang
- Center for Applied Genetic Technologies, The University of Georgia, Athens, GA 30602, USA
- Dow AgroSciences LLC, Indianapolis, IN 46268, USA
| | - Rebecca A Okashah
- Center for Applied Genetic Technologies, The University of Georgia, Athens, GA 30602, USA
| | - Steven J Knapp
- Center for Applied Genetic Technologies, The University of Georgia, Athens, GA 30602, USA
| | - Michael L Arnold
- Department of Genetics, The University of Georgia, Athens, GA 30602, USA
| | - Noland H Martin
- Department of Biology, Texas State University - San Marcos, San Marcos, TX 78666, USA
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Affiliation(s)
- James M Sobel
- Department of Plant Biology and Ecology, Evolutionary Biology and Behavior Program, Michigan State University, East Lansing, Michigan 48824, USA.
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Kay KM, Sargent RD. The Role of Animal Pollination in Plant Speciation: Integrating Ecology, Geography, and Genetics. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2009. [DOI: 10.1146/annurev.ecolsys.110308.120310] [Citation(s) in RCA: 223] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Kathleen M. Kay
- Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, California 95064;
| | - Risa D. Sargent
- Department of Biology, University of Ottawa, Ontario, K1N6N5, Canada;
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Keck BP, Near TJ. GEOGRAPHIC AND TEMPORAL ASPECTS OF MITOCHONDRIAL REPLACEMENT INNOTHONOTUSDARTERS (TELEOSTEI: PERCIDAE: ETHEOSTOMATINAE). Evolution 2009; 64:1410-28. [DOI: 10.1111/j.1558-5646.2009.00901.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Taylor SJ, Arnold M, Martin NH. THE GENETIC ARCHITECTURE OF REPRODUCTIVE ISOLATION IN LOUISIANA IRISES: HYBRID FITNESS IN NATURE. Evolution 2009; 63:2581-94. [PMID: 19549289 DOI: 10.1111/j.1558-5646.2009.00742.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Sunni J Taylor
- Department of Biology, Texas State University, San Marcos, Texas 78666, USA.
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Tang S, Okashah RA, Cordonnier-Pratt MM, Pratt LH, Ed Johnson V, Taylor CA, Arnold ML, Knapp SJ. EST and EST-SSR marker resources for Iris. BMC PLANT BIOLOGY 2009; 9:72. [PMID: 19515254 PMCID: PMC2703627 DOI: 10.1186/1471-2229-9-72] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2008] [Accepted: 06/10/2009] [Indexed: 05/02/2023]
Abstract
BACKGROUND Limited DNA sequence and DNA marker resources have been developed for Iris (Iridaceae), a monocot genus of 200-300 species in the Asparagales, several of which are horticulturally important. We mined an I. brevicaulis-I. fulva EST database for simple sequence repeats (SSRs) and developed ortholog-specific EST-SSR markers for genetic mapping and other genotyping applications in Iris. Here, we describe the abundance and other characteristics of SSRs identified in the transcript assembly (EST database) and the cross-species utility and polymorphisms of I. brevicaulis-I. fulva EST-SSR markers among wild collected ecotypes and horticulturally important cultivars. RESULTS Collectively, 6,530 ESTs were produced from normalized leaf and root cDNA libraries of I. brevicaulis (IB72) and I. fulva (IF174), and assembled into 4,917 unigenes (1,066 contigs and 3,851 singletons). We identified 1,447 SSRs in 1,162 unigenes and developed 526 EST-SSR markers, each tracing a different unigene. Three-fourths of the EST-SSR markers (399/526) amplified alleles from IB72 and IF174 and 84% (335/399) were polymorphic between IB25 and IF174, the parents of I. brevicaulis x I. fulva mapping populations. Forty EST-SSR markers were screened for polymorphisms among 39 ecotypes or cultivars of seven species - 100% amplified alleles from wild collected ecotypes of Louisiana Iris (I.brevicaulis, I.fulva, I. nelsonii, and I. hexagona), whereas 42-52% amplified alleles from cultivars of three horticulturally important species (I. pseudacorus, I. germanica, and I. sibirica). Ecotypes and cultivars were genetically diverse - the number of alleles/locus ranged from two to 18 and mean heterozygosity was 0.76. CONCLUSION Nearly 400 ortholog-specific EST-SSR markers were developed for comparative genetic mapping and other genotyping applications in Iris, were highly polymorphic among ecotypes and cultivars, and have broad utility for genotyping applications within the genus.
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Affiliation(s)
- Shunxue Tang
- Institute of Plant Breeding, Genetics, and Genomics, The University of Georgia, Athens, GA 30602, USA
| | - Rebecca A Okashah
- Institute of Plant Breeding, Genetics, and Genomics, The University of Georgia, Athens, GA 30602, USA
| | | | - Lee H Pratt
- Laboratory for Genomics and Bioinformatics, The University of Georgia, Athens, GA 30602, USA
| | - Virgil Ed Johnson
- Laboratory for Genomics and Bioinformatics, The University of Georgia, Athens, GA 30602, USA
| | - Christopher A Taylor
- Institute of Plant Breeding, Genetics, and Genomics, The University of Georgia, Athens, GA 30602, USA
| | - Michael L Arnold
- Department of Genetics, The University of Georgia, Athens, GA 30602, USA
| | - Steven J Knapp
- Institute of Plant Breeding, Genetics, and Genomics, The University of Georgia, Athens, GA 30602, USA
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Lexer C, Widmer A. Review. The genic view of plant speciation: recent progress and emerging questions. Philos Trans R Soc Lond B Biol Sci 2008; 363:3023-36. [PMID: 18579476 DOI: 10.1098/rstb.2008.0078] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The genic view of the process of speciation is based on the notion that species isolation may be achieved by a modest number of genes. Although great strides have been made to characterize 'speciation genes' in some groups of animals, little is known about the nature of genic barriers to gene flow in plants. We review recent progress in the characterization of genic species barriers in plants with a focus on five 'model' genera: Mimulus (monkey flowers); Iris (irises); Helianthus (sunflowers); Silene (campions); and Populus (poplars, aspens, cottonwoods). The study species in all five genera are diploid in terms of meiotic behaviour, and chromosomal rearrangements are assumed to play a minor role in species isolation, with the exception of Helianthus for which data on the relative roles of chromosomal and genic isolation factors are available. Our review identifies the following key topics as being of special interest for future research: the role of intraspecific variation in speciation; the detection of balancing versus directional selection in speciation genetic studies; the timing of fixation of alleles of major versus minor effects during plant speciation; the likelihood of adaptive trait introgression; and the identification and characterization of speciation genes and speciation gene networks.
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Affiliation(s)
- Christian Lexer
- Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3DS, UK.
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Lowry DB, Modliszewski JL, Wright KM, Wu CA, Willis JH. Review. The strength and genetic basis of reproductive isolating barriers in flowering plants. Philos Trans R Soc Lond B Biol Sci 2008; 363:3009-21. [PMID: 18579478 PMCID: PMC2607309 DOI: 10.1098/rstb.2008.0064] [Citation(s) in RCA: 321] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Speciation is characterized by the evolution of reproductive isolation between two groups of organisms. Understanding the process of speciation requires the quantification of barriers to reproductive isolation, dissection of the genetic mechanisms that contribute to those barriers and determination of the forces driving the evolution of those barriers. Through a comprehensive analysis involving 19 pairs of plant taxa, we assessed the strength and patterns of asymmetry of multiple prezygotic and postzygotic reproductive isolating barriers. We then reviewed contemporary knowledge of the genetic architecture of reproductive isolation and the relative role of chromosomal and genic factors in intrinsic postzygotic isolation. On average, we found that prezygotic isolation is approximately twice as strong as postzygotic isolation, and that postmating barriers are approximately three times more asymmetrical in their action than premating barriers. Barriers involve a variable number of loci, and chromosomal rearrangements may have a limited direct role in reproductive isolation in plants. Future research should aim to understand the relationship between particular genetic loci and the magnitude of their effect on reproductive isolation in nature, the geographical scale at which plant speciation occurs, and the role of different evolutionary forces in the speciation process.
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Affiliation(s)
- David B Lowry
- University Program in Genetics and Genomics, Duke University Medical Center, Durham, NC 27710, USA.
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Widmer A, Lexer C, Cozzolino S. Evolution of reproductive isolation in plants. Heredity (Edinb) 2008; 102:31-8. [PMID: 18648386 DOI: 10.1038/hdy.2008.69] [Citation(s) in RCA: 203] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Martin NH, Sapir Y, Arnold ML. THE GENETIC ARCHITECTURE OF REPRODUCTIVE ISOLATION IN LOUISIANA IRISES: POLLINATION SYNDROMES AND POLLINATOR PREFERENCES. Evolution 2008; 62:740-52. [DOI: 10.1111/j.1558-5646.2008.00342.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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