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Owens GL, Huang K, Todesco M, Rieseberg LH. Re-evaluating Homoploid Reticulate Evolution in Helianthus Sunflowers. Mol Biol Evol 2023; 40:6989481. [PMID: 36648104 PMCID: PMC9907532 DOI: 10.1093/molbev/msad013] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Revised: 01/03/2023] [Accepted: 01/11/2023] [Indexed: 01/18/2023] Open
Abstract
Sunflowers of the genus Helianthus are models for hybridization research and contain three of the best-studied examples of homoploid hybrid speciation. To understand a broader picture of hybridization within the annual sunflowers, we used whole-genome resequencing to conduct a phylogenomic analysis and test for gene flow between lineages. We find that all annual sunflower species tested have evidence of admixture, suggesting hybridization was common during the radiation of the genus. Support for the major species tree decreases with increasing recombination rate, consistent with hybridization and introgression contributing to discordant topologies. Admixture graphs found hybridization to be associated with the origins of the three putative hybrid species (Helianthus anomalus, Helianthus deserticola, and Helianthus paradoxus). However, the hybridization events are more ancient than suggested by previous work. Furthermore, H. anomalus and H. deserticola appear to have arisen from a single hybridization event involving an unexpected donor, rather than through multiple independent events as previously proposed. This means our results are consistent with, but not definitive proof of, two ancient independent homoploid hybrid speciation events in the genus. Using a broader data set that covers the whole Helianthus genus, including perennial species, we find that signals of introgression span the genus and beyond, suggesting highly divergent introgression and/or the sorting of ancient haplotypes. Thus, Helianthus can be viewed as a syngameon in which largely reproductively isolated species are linked together by occasional or frequent gene flow.
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Affiliation(s)
| | - Kaichi Huang
- Department of Botany and Beaty Biodiversity Center, University of British Columbia, Vancouver, BC, Canada
| | - Marco Todesco
- Department of Botany and Beaty Biodiversity Center, University of British Columbia, Vancouver, BC, Canada
| | - Loren H Rieseberg
- Department of Botany and Beaty Biodiversity Center, University of British Columbia, Vancouver, BC, Canada
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2
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Wong ELY, Hiscock SJ, Filatov DA. The Role of Interspecific Hybridisation in Adaptation and Speciation: Insights From Studies in Senecio. FRONTIERS IN PLANT SCIENCE 2022; 13:907363. [PMID: 35812981 PMCID: PMC9260247 DOI: 10.3389/fpls.2022.907363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2022] [Accepted: 06/03/2022] [Indexed: 05/08/2023]
Abstract
Hybridisation is well documented in many species, especially plants. Although hybrid populations might be short-lived and do not evolve into new lineages, hybridisaiton could lead to evolutionary novelty, promoting adaptation and speciation. The genus Senecio (Asteraceae) has been actively used to unravel the role of hybridisation in adaptation and speciation. In this article, we first briefly describe the process of hybridisation and the state of hybridisation research over the years. We then discuss various roles of hybridisation in plant adaptation and speciation illustrated with examples from different Senecio species, but also mention other groups of organisms whenever necessary. In particular, we focus on the genomic and transcriptomic consequences of hybridisation, as well as the ecological and physiological aspects from the hybrids' point of view. Overall, this article aims to showcase the roles of hybridisation in speciation and adaptation, and the research potential of Senecio, which is part of the ecologically and economically important family, Asteraceae.
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Affiliation(s)
- Edgar L. Y. Wong
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
- *Correspondence: Edgar L. Y. Wong,
| | - Simon J. Hiscock
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
- Oxford Botanic Garden and Arboretum, Oxford, United Kingdom
| | - Dmitry A. Filatov
- Department of Plant Sciences, University of Oxford, Oxford, United Kingdom
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3
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Li C, Sun X, Conover JL, Zhang Z, Wang J, Wang X, Deng X, Wang H, Liu B, Wendel JF, Gong L. Cytonuclear Coevolution following Homoploid Hybrid Speciation in Aegilops tauschii. Mol Biol Evol 2019; 36:341-349. [PMID: 30445640 PMCID: PMC6367959 DOI: 10.1093/molbev/msy215] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The diploid D-genome lineage of the Triticum/Aegilops complex has an evolutionary history involving genomic contributions from ancient A- and B/S-genome species. We explored here the possible cytonuclear evolutionary responses to this history of hybridization. Phylogenetic analysis of chloroplast DNAs indicates that the D-genome lineage has a maternal origin of the A-genome or some other closely allied lineage. Analyses of the nuclear genome in the D-genome species Aegilops tauschii indicate that accompanying and/or following this ancient hybridization, there has been biased maintenance of maternal A-genome ancestry in nuclear genes encoding cytonuclear enzyme complexes (CECs). Our study provides insights into mechanisms of cytonuclear coevolution accompanying the evolution and eventual stabilization of homoploid hybrid species. We suggest that this coevolutionary process includes likely rapid fixation of A-genome CEC orthologs as well as biased retention of A-genome nucleotides in CEC homologs following population level recombination during the initial generations.
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Affiliation(s)
- Changping Li
- Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, China
| | - Xuhan Sun
- Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, China
| | - Justin L Conover
- Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA
| | - Zhibin Zhang
- Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, China
| | - Jinbin Wang
- Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, China
| | - Xiaofei Wang
- Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, China
| | - Xin Deng
- Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, China
| | - Hongyan Wang
- Laboratory of Plant Epigenetics and Evolution, School of Life Science, Liaoning University, Shenyang, China
| | - Bao Liu
- Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, China
| | - Jonathan F Wendel
- Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA
| | - Lei Gong
- Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, China
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Marques I, Draper D, López-Herranz ML, Garnatje T, Segarra-Moragues JG, Catalán P. Past climate changes facilitated homoploid speciation in three mountain spiny fescues (Festuca, Poaceae). Sci Rep 2016; 6:36283. [PMID: 27808118 PMCID: PMC5093761 DOI: 10.1038/srep36283] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 10/03/2016] [Indexed: 11/25/2022] Open
Abstract
Apart from the overwhelming cases of allopolyploidization, the impact of speciation through homoploid hybridization is becoming more relevant than previously thought. Much less is known, however, about the impact of climate changes as a driven factor of speciation. To investigate these issues, we selected Festuca picoeuropeana, an hypothetical natural hybrid between the diploid species F. eskia and F. gautieri that occurs in two different mountain ranges (Cantabrian Mountains and Pyrenees) separated by more than 400 km. To unravel the outcomes of this mode of speciation and the impact of climate during speciation we used a multidisciplinary approach combining genome size and chromosome counts, data from an extensive nuclear genotypic analysis, plastid sequences and ecological niche models (ENM). Our results show that the same homoploid hybrid was originated independently in the two mountain ranges, being currently isolated from both parents and producing viable seeds. Parental species had the opportunity to contact as early as 21000 years ago although niche divergence occurs nowadays as result of a climate-driven shift. A high degree of niche divergence was observed between the hybrid and its parents and no recent introgression or backcrossed hybrids were detected, supporting the current presence of reproductive isolation barriers between these species.
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Affiliation(s)
- I Marques
- Departamento de Ciencias Agrarias y del Medio Natural, Escuela Politécnica Superior de Huesca, Universidad de Zaragoza, C/Carretera de Cuarte Km 1, E22071 Huesca, Spain
| | - D Draper
- Centro de Ecologia, Evolução e Alterações Ambientais (CE3C - Centre for Ecology, Evolution and Environmental Changes), C2, Universidade de Lisboa, Campo Grande, 1749-016 Lisbon, Portugal
| | - M L López-Herranz
- Departamento de Ciencias Agrarias y del Medio Natural, Escuela Politécnica Superior de Huesca, Universidad de Zaragoza, C/Carretera de Cuarte Km 1, E22071 Huesca, Spain
| | - T Garnatje
- Institut Botànic de Barcelona (IBB-CSIC-ICUB), Passeig del Migdia s/n, 08038 Barcelona, Spain
| | - J G Segarra-Moragues
- Departamento de Biología Vegetal, Facultad de Ciencias Biológicas, Universitat de València, Avda. Dr. Moliner, 50, E-46100, Burjassot, Spain
| | - P Catalán
- Departamento de Ciencias Agrarias y del Medio Natural, Escuela Politécnica Superior de Huesca, Universidad de Zaragoza, C/Carretera de Cuarte Km 1, E22071 Huesca, Spain.,Department of Botany, Institute of Biology, Tomsk State University, Lenin Av. 36, 634050 Tomsk, Russia
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5
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Renaut S, Rowe HC, Ungerer MC, Rieseberg LH. Genomics of homoploid hybrid speciation: diversity and transcriptional activity of long terminal repeat retrotransposons in hybrid sunflowers. Philos Trans R Soc Lond B Biol Sci 2015; 369:rstb.2013.0345. [PMID: 24958919 DOI: 10.1098/rstb.2013.0345] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Hybridization is thought to play an important role in plant evolution by introducing novel genetic combinations and promoting genome restructuring. However, surprisingly little is known about the impact of hybridization on transposable element (TE) proliferation and the genomic response to TE activity. In this paper, we first review the mechanisms by which homoploid hybrid species may arise in nature. We then present hybrid sunflowers as a case study to examine transcriptional activity of long terminal repeat retrotransposons in the annual sunflowers Helianthus annuus, Helianthus petiolaris and their homoploid hybrid derivatives (H. paradoxus, H. anomalus and H. deserticola) using high-throughput transcriptome sequencing technologies (RNAseq). Sampling homoploid hybrid sunflower taxa revealed abundant variation in TE transcript accumulation. In addition, genetic diversity for several candidate genes hypothesized to regulate TE activity was characterized. Specifically, we highlight one candidate chromatin remodelling factor gene with a direct role in repressing TE activity in a hybrid species. This paper shows that TE amplification in hybrid lineages is more idiosyncratic than previously believed and provides a first step towards identifying the mechanisms responsible for regulating and repressing TE expansions.
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Affiliation(s)
- Sebastien Renaut
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
| | - Heather C Rowe
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4
| | - Mark C Ungerer
- Division of Biology, Kansas State University, 426 Ackert Hall, Manhattan, KS 66506, USA
| | - Loren H Rieseberg
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4 Department of Biology, Indiana University, 1001 East Third St., Bloomington, IN 47405, USA
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6
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Frey M, Spring O. Molecular traits to elucidate the ancestry of Helianthus x multiflorus. BIOCHEM SYST ECOL 2015. [DOI: 10.1016/j.bse.2014.10.008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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López-Caamal A, Tovar-Sánchez E. Genetic, morphological, and chemical patterns of plant hybridization. REVISTA CHILENA DE HISTORIA NATURAL 2014. [DOI: 10.1186/s40693-014-0016-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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8
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Xing F, Mao JF, Meng J, Dai J, Zhao W, Liu H, Xing Z, Zhang H, Wang XR, Li Y. Needle morphological evidence of the homoploid hybrid origin of Pinus densata based on analysis of artificial hybrids and the putative parents, Pinus tabuliformis and Pinus yunnanensis. Ecol Evol 2014; 4:1890-902. [PMID: 24963383 PMCID: PMC4063482 DOI: 10.1002/ece3.1062] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Revised: 03/11/2014] [Accepted: 03/17/2014] [Indexed: 11/07/2022] Open
Abstract
Genetic analyses indicate that Pinus densata is a natural homoploid hybrid originating from Pinus tabuliformis and Pinus yunnanensis. Needle morphological and anatomical features show relative species stability and can be used to identify coniferous species. Comparative analyses of these needle characteristics and phenotypic differences between the artificial hybrids, P. densata, and parental species can be used to determine the genetic and phenotypic evolutionary consequences of natural hybridization. Twelve artificial hybrid families, the two parental species, and P. densata were seeded in a high-altitude habitat in Linzhi, Tibet. The needles of artificial hybrids and the three pine species were collected, and 24 needle morphological and anatomical traits were analyzed. Based on these results, variations in 10 needle traits among artificial hybrid families and 22 traits among species and artificial hybrids were predicted and found to be under moderate genetic control. Nineteen needle traits in artificial hybrids were similar to those in P. densata and between the two parental species, P. tabuliformis and P. yunnanensis. The ratio of plants with three needle clusters in artificial hybrids was 22.92%, which was very similar to P. densata. The eight needle traits (needle length, the mean number of stomata in sections 2 mm in length of the convex and flat sides of the needle, mean stomatal density, mesophyll/vascular bundle area ratio, mesophyll/resin canal area ratio, mesophyll/(resin canals and vascular bundles) area ratio, vascular bundle/resin canal area ratio) relative to physiological adaptability were similar to the artificial hybrids and P. densata. The similar needle features between the artificial hybrids and P. densata could be used to verify the homoploid hybrid origin of P. densata and helps to better understand of the hybridization roles in adaptation and speciation in plants.
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Affiliation(s)
- Fangqian Xing
- National Engineering Laboratory for Forest Tree Breeding, Key Laboratory for Genetics and Breeding of Forest Trees and Ornamental Plants of Ministry of Education, Beijing Forestry UniversityBeijing, 100083, China
| | - Jian-Feng Mao
- National Engineering Laboratory for Forest Tree Breeding, Key Laboratory for Genetics and Breeding of Forest Trees and Ornamental Plants of Ministry of Education, Beijing Forestry UniversityBeijing, 100083, China
| | - Jingxiang Meng
- National Engineering Laboratory for Forest Tree Breeding, Key Laboratory for Genetics and Breeding of Forest Trees and Ornamental Plants of Ministry of Education, Beijing Forestry UniversityBeijing, 100083, China
| | - Jianfeng Dai
- National Engineering Laboratory for Forest Tree Breeding, Key Laboratory for Genetics and Breeding of Forest Trees and Ornamental Plants of Ministry of Education, Beijing Forestry UniversityBeijing, 100083, China
| | - Wei Zhao
- State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of SciencesBeijing, 100093, China
| | - Hao Liu
- College of Resources and Environment, College of agriculture and animal husbandry of Tibet UniversityLinzhi, 860000, China
| | - Zhen Xing
- College of Resources and Environment, College of agriculture and animal husbandry of Tibet UniversityLinzhi, 860000, China
| | - Hua Zhang
- College of Resources and Environment, College of agriculture and animal husbandry of Tibet UniversityLinzhi, 860000, China
| | - Xiao-Ru Wang
- National Engineering Laboratory for Forest Tree Breeding, Key Laboratory for Genetics and Breeding of Forest Trees and Ornamental Plants of Ministry of Education, Beijing Forestry UniversityBeijing, 100083, China
- Department of Ecology and Environmental Science, Umeå UniversitySE-901 87, Umeå, Sweden
| | - Yue Li
- National Engineering Laboratory for Forest Tree Breeding, Key Laboratory for Genetics and Breeding of Forest Trees and Ornamental Plants of Ministry of Education, Beijing Forestry UniversityBeijing, 100083, China
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Kantar MB, Baute GJ, Bock DG, Rieseberg LH. Genomic variation in Helianthus: learning from the past and looking to the future. Brief Funct Genomics 2014; 13:328-40. [DOI: 10.1093/bfgp/elu004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
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10
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Marques I, Draper D, Riofrío L, Naranjo C. Multiple hybridization events, polyploidy and low postmating isolation entangle the evolution of neotropical species of Epidendrum (Orchidaceae). BMC Evol Biol 2014; 14:20. [PMID: 24495351 PMCID: PMC3927766 DOI: 10.1186/1471-2148-14-20] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Accepted: 01/30/2014] [Indexed: 12/30/2022] Open
Abstract
BACKGROUND Hybridization and polyploidy are central processes in evolution and speciation. These mechanisms often lead to complex patterns of genetic variation and the creation of novel genotypes, which may establish if they become isolated from gene flow. However, in the absence of reproductive isolation, species boundaries might easily be disrupted. Here, we used a combination of AFLPs, chloroplast DNA markers and flow cytometry to investigate the evolutionary outcomes of hybridization between two endemic Ecuadorian species of Epidendrum (E. madsenii and E. rhopalostele) in three hybrid zones. Postmating isolation was also quantified to determine the role of this barrier in restraining gene flow between hybrids and the parental species. In addition, future ecological niche models were constructed to predict the outcomes of hybridization between these species. RESULTS Our results confirmed the presence of hybrids in all hybrid zones, but revealed that a third parental species (E. falcisepalum) has contributed to one of the hybrid zones studied. Backcross genotypes were frequent in all hybrid zones, which was in accordance with the absence of strong reproductive barriers. The process of hybridization was highly asymmetric and followed in some cases by polyploidy. The projection of future niche models predicted a severe reduction in the area suitable for the occurrence of these species, although favorable conditions will still occur for the existence of the current hybrid zones. CONCLUSIONS The recurrent process of hybridization has compromised the genetic integrity of the parental species. Most individuals of the parental species can no longer be considered as pure-bred individuals because most were classified as backcrossed hybrids. Novel genetic lineages occur in all hybrid zones implying that hybrids are fertile and can compete with the parental species. These results, together with the prediction of suitable conditions for the future occurrence of these hybrid zones, highlight the importance of conserving these geographic areas as sources of novel taxonomic entities.
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Affiliation(s)
- Isabel Marques
- Department of Agriculture (Botany), High Polytechnic School of Huesca, University of Zaragoza, C/ Carretera de Cuarte Km 1, Huesca E22071, Spain
- Departamento de Ciencias Naturales, Universidad Técnica Particular de Loja, San Cayetano Alto s/n, Loja 1101608, Ecuador
- Current address: UBC Botanical Garden & Centre for Plant Research, and Department of Botany, University of British Columbia, 3529-6270 University Blvd, Vancouver BC V6T 1Z4, Canada
| | - David Draper
- Departamento de Ciencias Naturales, Universidad Técnica Particular de Loja, San Cayetano Alto s/n, Loja 1101608, Ecuador
| | - Lorena Riofrío
- Departamento de Ciencias Naturales, Universidad Técnica Particular de Loja, San Cayetano Alto s/n, Loja 1101608, Ecuador
| | - Carlos Naranjo
- Departamento de Ciencias Naturales, Universidad Técnica Particular de Loja, San Cayetano Alto s/n, Loja 1101608, Ecuador
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11
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Genomic islands of divergence are not affected by geography of speciation in sunflowers. Nat Commun 2013; 4:1827. [PMID: 23652015 DOI: 10.1038/ncomms2833] [Citation(s) in RCA: 209] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 04/04/2013] [Indexed: 01/28/2023] Open
Abstract
Genomic studies of speciation often report the presence of highly differentiated genomic regions interspersed within a milieu of weakly diverged loci. The formation of these speciation islands is generally attributed to reduced inter-population gene flow near loci under divergent selection, but few studies have critically evaluated this hypothesis. Here, we report on transcriptome scans among four recently diverged pairs of sunflower (Helianthus) species that vary in the geographical context of speciation. We find that genetic divergence is lower in sympatric and parapatric comparisons, consistent with a role for gene flow in eroding neutral differences. However, genomic islands of divergence are numerous and small in all comparisons, and contrary to expectations, island number and size are not significantly affected by levels of interspecific gene flow. Rather, island formation is strongly associated with reduced recombination rates. Overall, our results indicate that the functional architecture of genomes plays a larger role in shaping genomic divergence than does the geography of speciation.
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Piwczyński M, Ponikierska A, Puchałka R, Corral JM. Expression of anatomical leaf traits in homoploid hybrids between deciduous and evergreen species of Vaccinium. PLANT BIOLOGY (STUTTGART, GERMANY) 2013; 15:522-530. [PMID: 22823251 DOI: 10.1111/j.1438-8677.2012.00656.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
We investigated the anatomical expression of leaf traits in hybrids between evergreen Vaccinium vitis-idaea and deciduous V. myrtillus. We compared parents from four populations with their respective F1 hybrids and tested whether (i) transgression can be the source of novel anatomical traits in hybrids; (ii) expression of transgressive traits is more probable for traits with similar values in parents and intermediate for more distinct values, as predicted by theory; and (iii) independent origin of hybrids leads to identical trait expression profiles among populations. We found that anatomical leaf traits can be divided into four categories based on their similarity to parents: intermediate, parental-like, transgressive and non-significant. Contrary to the common view, parental-like trait values were equally important in shaping the hybrid profile, as were intermediate traits. Transgression was revealed in 17/144 cases and concerned mainly cell and tissue sizes. As predicted by theory, we observed transgressive segregation more often when there was little phenotypic divergence, but intermediate values when parental traits were differentiated. It is likely that cell and tissue sizes are phylogenetically more conserved due to stabilising selection, whereas traits such as leaf thickness and volume fraction of the intercellular spaces, showing a consistent intermediate pattern across populations, are more susceptible to directional selection. Hybrid populations showed little similarity in expression profile, with only three traits identically expressed across all populations. Thus local adaptation of parental species and specific genetic background may be of importance.
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Affiliation(s)
- M Piwczyński
- Department of Animal Ecology, Nicolaus Copernicus University, Toruń, Poland.
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13
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Nice CC, Gompert Z, Fordyce JA, Forister ML, Lucas LK, Buerkle CA. Hybrid speciation and independent evolution in lineages of alpine butterflies. Evolution 2013; 67:1055-68. [PMID: 23550755 DOI: 10.1111/evo.12019] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The power of hybridization between species to generate variation and fuel adaptation is poorly understood despite long-standing interest. There is, however, increasing evidence that hybridization often generates biodiversity, including via hybrid speciation. We tested the hypothesis of hybrid speciation in butterflies occupying extreme, high-altitude habitats in four mountain ranges in western North America with an explicit, probabilistic model, and genome-wide DNA sequence data. Using this approach, in concert with ecological experiments and observations and morphological data, we document three lineages of hybrid origin. These lineages have different genome admixture proportions and distinctive trait combinations that suggest unique and independent evolutionary histories.
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Affiliation(s)
- Chris C Nice
- Department of Biology, Population and Conservation Biology Program, Texas State University, San Marcos, Texas 78666, USA.
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14
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Clay DL, Novak SJ, Serpe MD, Tank DC, Smith JF. Homoploid hybrid speciation in a rare endemic Castilleja from Idaho (Castilleja christii, Orobanchaceae). AMERICAN JOURNAL OF BOTANY 2012; 99:1976-1990. [PMID: 23211568 DOI: 10.3732/ajb.1200326] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
PREMISE OF THE STUDY Hybridization is an important evolutionary force in the history of angiosperms; however, there are few examples of stabilized species derived through homoploid hybrid speciation. Homoploid hybrid species are generally detected via the presence of genetic additivity of parental markers, novel ecological and spatial distinctions, and novel morphological traits, all of which may aid in the successful establishment of hybrid species from parental types. Speciation and diversification within the genus Castilleja (Orobanchaceae) has been attributed to high levels of hybridization and polyploidy, though currently there are no examples of homoploid hybrid speciation within the genus. We employed multiple lines of evidence to examine a putative hybrid origin in C. christii, a rare endemic, known only from 80 hectares at the summit of Mt. Harrison (Cassia Co., Idaho). • METHODS We used granule-bound starch synthase II (waxy) sequences and 26 morphological characters to address hybridization between C. christii and widespread congeners C. miniata and/or C. linariifolia in an area of sympatry. Chromosomes of C. christii were also counted for the first time. • KEY RESULTS All 230 direct-sequenced C. christii individuals had the additive genomes of both C. miniata and C. linariifolia. Castilleja christii shares traits with both parents but also has floral characters that are unique and transgressive. Cytological counts indicated that all three taxa are diploid. • CONCLUSIONS We conclude that C. christii is a stabilized homoploid hybrid derivative of C. linariifolia and C. miniata and is likely following an independent evolutionary trajectory from its progenitors.
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Affiliation(s)
- Danielle L Clay
- Department of Biological Sciences, Boise State University, 1910 University Drive, Boise, Idaho 83725-1515, USA.
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15
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Andrew RL, Kane NC, Baute GJ, Grassa CJ, Rieseberg LH. Recent nonhybrid origin of sunflower ecotypes in a novel habitat. Mol Ecol 2012; 22:799-813. [DOI: 10.1111/mec.12038] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2012] [Revised: 07/27/2012] [Accepted: 07/30/2012] [Indexed: 02/04/2023]
Affiliation(s)
- Rose L. Andrew
- Department of Botany; University of British Columbia; 3529-6270 University Blvd; Vancouver; BC; Canada; V6T 1Z4
| | - Nolan C. Kane
- Department of Botany; University of British Columbia; 3529-6270 University Blvd; Vancouver; BC; Canada; V6T 1Z4
| | - Greg J. Baute
- Department of Botany; University of British Columbia; 3529-6270 University Blvd; Vancouver; BC; Canada; V6T 1Z4
| | - Christopher J. Grassa
- Department of Botany; University of British Columbia; 3529-6270 University Blvd; Vancouver; BC; Canada; V6T 1Z4
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16
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Kane NC, Burke JM, Marek L, Seiler G, Vear F, Baute G, Knapp SJ, Vincourt P, Rieseberg LH. Sunflower genetic, genomic and ecological resources. Mol Ecol Resour 2012; 13:10-20. [PMID: 23039950 DOI: 10.1111/1755-0998.12023] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2011] [Revised: 08/22/2012] [Accepted: 08/24/2012] [Indexed: 11/29/2022]
Abstract
Long a major focus of genetic research and breeding, sunflowers (Helianthus) are emerging as an increasingly important experimental system for ecological and evolutionary studies. Here, we review the various attributes of wild and domesticated sunflowers that make them valuable for ecological experimentation and describe the numerous publicly available resources that have enabled rapid advances in ecological and evolutionary genetics. Resources include seed collections available from germplasm centres at the USDA and INRA, genomic and EST sequences, mapping populations, genetic markers, genetic and physical maps and other forward- and reverse-genetic tools. We also discuss some of the key evolutionary, genetic and ecological questions being addressed in sunflowers, as well as gaps in our knowledge and promising areas for future research.
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Affiliation(s)
- Nolan C Kane
- Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Boulder, CO 80309, USA.
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17
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Moody ML, Rieseberg LH. Sorting through the chaff, nDNA gene trees for phylogenetic inference and hybrid identification of annual sunflowers (Helianthus sect. Helianthus). Mol Phylogenet Evol 2012; 64:145-55. [PMID: 22724134 DOI: 10.1016/j.ympev.2012.03.012] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
The annual sunflowers (Helianthus sect. Helianthus) present a formidable challenge for phylogenetic inference because of ancient hybrid speciation, recent introgression, and suspected issues with deep coalescence. Here we analyze sequence data from 11 nuclear DNA (nDNA) genes for multiple genotypes of species within the section to (1) reconstruct the phylogeny of this group, (2) explore the utility of nDNA gene trees for detecting hybrid speciation and introgression; and (3) test an empirical method of hybrid identification based on the phylogenetic congruence of nDNA gene trees from tightly linked genes. We uncovered considerable topological heterogeneity among gene trees with or without three previously identified hybrid species included in the analyses, as well as a general lack of reciprocal monophyly of species. Nonetheless, partitioned Bayesian analyses provided strong support for the reciprocal monophyly of all species except H. annuus (0.89 PP), the most widespread and abundant annual sunflower. Previous hypotheses of relationships among taxa were generally strongly supported (1.0 PP), except among taxa typically associated with H. annuus, apparently due to the paraphyly of the latter in all gene trees. While the individual nDNA gene trees provided a useful means for detecting recent hybridization, identification of ancient hybridization was problematic for all ancient hybrid species, even when linkage was considered. We discuss biological factors that affect the efficacy of phylogenetic methods for hybrid identification.
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Affiliation(s)
- Michael L Moody
- School of Plant Biology, University of Western Australia, Crawley, WA 6009, Australia.
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18
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Gao J, Wang B, Mao JF, Ingvarsson P, Zeng QY, Wang XR. Demography and speciation history of the homoploid hybrid pine Pinus densata on the Tibetan Plateau. Mol Ecol 2012; 21:4811-27. [PMID: 22849551 DOI: 10.1111/j.1365-294x.2012.05712.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Pinus densata is an ecologically successful homoploid hybrid that inhabits vast areas of heterogeneous terrain on the south-eastern Tibetan Plateau as a result of multiple waves of colonization. Its region of origin, route of colonization onto the plateau and the directions of introgression with its parental species have previously been defined, but little is known about the isolation and divergence history of its populations. In this study, we surveyed nucleotide polymorphism over eight nuclear loci in 19 representative populations of P. densata and its parental species. Using this information and coalescence simulations, we assessed the historical changes in its population size, gene flow and divergence in time and space. The results indicate a late Miocene origin for P. densata associated with the recent uplift of south-eastern Tibet. The subsequent differentiation between geographical regions of this species began in the late Pliocene and was induced by regional topographical changes and Pleistocene glaciations. The ancestral P. densata population had a large effective population size but the central and western populations were established by limited founders, suggesting that there were severe bottlenecks during the westward migration out of the ancestral hybrid zone. After separating from their ancestral populations, population expansion occurred in all geographical regions especially in the western range. Gene flow in P. densata was restricted to geographically neighbouring populations, resulting in significant differentiation between regional groups. The new information on the divergence and demographic history of P. densata reported herein enhances our understanding of its speciation process on the Tibetan Plateau.
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Affiliation(s)
- Jie Gao
- State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
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19
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Wallace LE, Culley TM, Weller SG, Sakai AK, Kuenzi A, Roy T, Wagner WL, Nepokroeff M. Asymmetrical gene flow in a hybrid zone of Hawaiian Schiedea (Caryophyllaceae) species with contrasting mating systems. PLoS One 2011; 6:e24845. [PMID: 21949765 PMCID: PMC3176226 DOI: 10.1371/journal.pone.0024845] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2011] [Accepted: 08/22/2011] [Indexed: 01/21/2023] Open
Abstract
Asymmetrical gene flow, which has frequently been documented in naturally occurring hybrid zones, can result from various genetic and demographic factors. Understanding these factors is important for determining the ecological conditions that permitted hybridization and the evolutionary potential inherent in hybrids. Here, we characterized morphological, nuclear, and chloroplast variation in a putative hybrid zone between Schiedea menziesii and S. salicaria, endemic Hawaiian species with contrasting breeding systems. Schiedea menziesii is hermaphroditic with moderate selfing; S. salicaria is gynodioecious and wind-pollinated, with partially selfing hermaphrodites and largely outcrossed females. We tested three hypotheses: 1) putative hybrids were derived from natural crosses between S. menziesii and S. salicaria, 2) gene flow via pollen is unidirectional from S. salicaria to S. menziesii and 3) in the hybrid zone, traits associated with wind pollination would be favored as a result of pollen-swamping by S. salicaria. Schiedea menziesii and S. salicaria have distinct morphologies and chloroplast genomes but are less differentiated at the nuclear loci. Hybrids are most similar to S. menziesii at chloroplast loci, exhibit nuclear allele frequencies in common with both parental species, and resemble S. salicaria in pollen production and pollen size, traits important to wind pollination. Additionally, unlike S. menziesii, the hybrid zone contains many females, suggesting that the nuclear gene responsible for male sterility in S. salicaria has been transferred to hybrid plants. Continued selection of nuclear genes in the hybrid zone may result in a population that resembles S. salicaria, but retains chloroplast lineage(s) of S. menziesii.
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Affiliation(s)
- Lisa E Wallace
- Department of Biological Sciences, Mississippi State University, Mississippi State, Mississippi, United States of America.
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20
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Wang B, Mao JF, Gao J, Zhao W, Wang XR. Colonization of the Tibetan Plateau by the homoploid hybrid pine Pinus densata. Mol Ecol 2011; 20:3796-811. [PMID: 21689188 DOI: 10.1111/j.1365-294x.2011.05157.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Pinus densata is an intriguingly successful homoploid hybrid species that occupies vast areas of the southeastern Tibetan Plateau in which neither of its parental species are present, but the colonization processes involved are poorly understood. To shed light on how this species colonized and became established on the plateau, we surveyed paternally inherited chloroplast (cp) and maternally inherited mitochondrial (mt) DNA variation within and among 54 populations of P. densata and its putative parental species throughout their respective ranges. Strong spatial genetic structure of both cp and mtDNA were detected in P. densata populations. Mitotypes specific to P. densata were likely generated by complex recombination events. A putative ancestral hybrid zone in the northeastern periphery of P. densata was identified, and we propose that the species then colonized the plateau by migrating westwards. Along the colonization route, consecutive bottlenecks and surfing of rare alleles caused a significant reduction in genetic diversity and strong population differentiation. The direction and intensity of introgression from parental species varied among geographic regions. In western parts of its range, the species seems to have been isolated from seed and pollen flow from its parent species for a long time. The observed spatial distribution of genetic diversity in P. densata also appears to reflect the persistence of this species on the plateau during the last glaciation. Our results indicate that both ancient and contemporary population dynamics have contributed to the spatial distribution of genetic diversity in P. densata, which accordingly reflects its evolutionary history.
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Affiliation(s)
- Baosheng Wang
- Department of Ecology and Environmental Science, Umeå University, SE-901 87 Umeå, Sweden
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Sun M, Lo EYY. Genomic markers reveal introgressive hybridization in the Indo-West Pacific mangroves: a case study. PLoS One 2011; 6:e19671. [PMID: 21589927 PMCID: PMC3092761 DOI: 10.1371/journal.pone.0019671] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Accepted: 04/03/2011] [Indexed: 11/18/2022] Open
Abstract
Biodiversity of mangrove ecosystems is difficult to assess, at least partly due to lack of genetic verification of morphology-based documentation of species. Natural hybridization, on the one hand, plays an important role in evolution as a source of novel gene combinations and a mechanism of speciation. However, on the other hand, recurrent introgression allows gene flow between species and could reverse the process of genetic differentiation among populations required for speciation. To understand the dynamic evolutionary consequences of hybridization, this study examines genomic structure of hybrids and parental species at the population level. In the Indo-West Pacific, Bruguiera is one of the dominant mangrove genera and species ranges overlap extensively with one another. Morphological intermediates between sympatric Bruguiera gymnorrhiza and Bruguiera sexangula have been reported as a variety of B. sexangula or a new hybrid species, B. × rhynchopetala. However, the direction of hybridization and extent of introgression are unclear. A large number of species-specific inter-simple sequence repeat (ISSR) markers were found in B. gymnorrhiza and B. sexangula, and the additive ISSR profiling of B. × rhynchopetala ascertained its hybrid status and identified its parental origin. The varying degree of scatterness among hybrid individuals in Principal Coordinate Analysis and results from NewHybrids analysis indicate that B. × rhynchopetala comprises different generations of introgressants in addition to F1s. High genetic relatedness between B. × rhynchopetala and B. gymnorrhiza based on nuclear and chloroplast sequences suggests preferential hybrid backcrosses to B. gymnorrhiza. We conclude that B. × rhynchopetala has not evolved into an incipient hybrid species, and its persistence can be explained by recurrent hybridization and introgression. Genomic data provide insights into the hybridization dynamics of mangrove plants. Such information can assist in biodiversity assessment by helping detect novel taxa and/or define species boundaries.
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Affiliation(s)
- Mei Sun
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America.
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Chiurugwi T, Beaumont MA, Wilkinson MJ, Battey NH. Adaptive divergence and speciation among sexual and pseudoviviparous populations of Festuca. Heredity (Edinb) 2011; 106:854-61. [PMID: 20959864 PMCID: PMC3186240 DOI: 10.1038/hdy.2010.128] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2010] [Revised: 07/26/2010] [Accepted: 09/06/2010] [Indexed: 11/09/2022] Open
Abstract
Pseudovivipary is an environmentally induced flowering abnormality in which vegetative shoots replace seminiferous (sexual) inflorescences. Pseudovivipary is usually retained in transplantation experiments, indicating that the trait is not solely induced by the growing environment. Pseudovivipary is the defining characteristic of Festuca vivipara, and arguably the only feature separating this species from its closest seminiferous relative, Festuca ovina. We performed phylogenetic and population genetic analysis on sympatric F. ovina and F. vivipara samples to establish whether pseudovivipary is an adaptive trait that accurately defines the separation of genetically distinct Festuca species. Chloroplast and nuclear marker-based analyses revealed that variation at a geographical level can exceed that between F. vivipara and F. ovina. We deduced that F. vivipara is a recent species that frequently arises independently within F. ovina populations and has not accumulated significant genetic differentiation from its progenitor. We inferred local gene flow between the species. We identified one amplified fragment length polymorphism marker that may be linked to a pseudovivipary-related region of the genome, and several other markers provide evidence of regional local adaptation in Festuca populations. We conclude that F. vivipara can only be appropriately recognized as a morphologically and ecologically distinct species; it lacks genetic differentiation from its relatives. This is the first report of a 'failure in normal flowering development' that repeatedly appears to be adaptive, such that the trait responsible for species recognition constantly reappears on a local basis.
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Affiliation(s)
- T Chiurugwi
- School of Biological Sciences, University of Reading, Reading, UK.
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Kawakami T, Dhakal P, Katterhenry AN, Heatherington CA, Ungerer MC. Transposable element proliferation and genome expansion are rare in contemporary sunflower hybrid populations despite widespread transcriptional activity of LTR retrotransposons. Genome Biol Evol 2011; 3:156-67. [PMID: 21282712 PMCID: PMC3048363 DOI: 10.1093/gbe/evr005] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Hybridization is a natural phenomenon that has been linked in several organismal groups to transposable element derepression and copy number amplification. A noteworthy example involves three diploid annual sunflower species from North America that have arisen via ancient hybridization between the same two parental taxa, Helianthus annuus and H. petiolaris. The genomes of the hybrid species have undergone large-scale increases in genome size attributable to long terminal repeat (LTR) retrotransposon proliferation. The parental species that gave rise to the hybrid taxa are widely distributed, often sympatric, and contemporary hybridization between them is common. Natural H. annuus × H. petiolaris hybrid populations likely served as source populations from which the hybrid species arose and, as such, represent excellent natural experiments for examining the potential role of hybridization in transposable element derepression and proliferation in this group. In the current report, we examine multiple H. annuus × H. petiolaris hybrid populations for evidence of genome expansion, LTR retrotransposon copy number increases, and LTR retrotransposon transcriptional activity. We demonstrate that genome expansion and LTR retrotransposon proliferation are rare in contemporary hybrid populations, despite independent proliferation events that took place in the genomes of the ancient hybrid species. Interestingly, LTR retrotransposon lineages that proliferated in the hybrid species genomes remain transcriptionally active in hybrid and nonhybrid genotypes across the entire sampling area. The finding of transcriptional activity but not copy number increases in hybrid genotypes suggests that proliferation and genome expansion in contemporary hybrid populations may be mitigated by posttranscriptional mechanisms of repression.
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Abbott RJ, Hegarty MJ, Hiscock SJ, Brennan AC. Homoploid hybrid speciation in action. TAXON 2010; 59:1375-1386. [PMID: 0 DOI: 10.1002/tax.595005] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Affiliation(s)
- Richard J. Abbott
- School of Biology; University of St Andrews; St Andrews, Fife KY16 9TH U.K
| | - Matthew J. Hegarty
- Institute of Biological, Environmental & Rural Sciences; Aberystwyth University; Penglais, Aberystwyth, Ceredigion SY23 3DA U.K
| | - Simon J. Hiscock
- School of Biological Sciences; University of Bristol; Bristol, Somerset BS8 1UG U.K
| | - Adrian C. Brennan
- School of Biology; University of St Andrews; St Andrews, Fife KY16 9TH U.K
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Sakiroğlu M, Doyle JJ, Charles Brummer E. Inferring population structure and genetic diversity of broad range of wild diploid alfalfa (Medicago sativa L.) accessions using SSR markers. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2010; 121:403-15. [PMID: 20352180 DOI: 10.1007/s00122-010-1319-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2009] [Accepted: 03/05/2010] [Indexed: 05/10/2023]
Abstract
Diversity analyses in alfalfa have mainly evaluated genetic relationships of cultivated germplasm, with little known about variation in diploid germplasm in the M. sativa-falcata complex. A collection of 374 individual genotypes derived from 120 unimproved diploid accessions from the National Plant Germplasm System, including M. sativa subsp. caerulea, falcata, and hemicycla, were evaluated with 89 polymorphic SSR loci in order to estimate genetic diversity, infer the genetic bases of current morphology-based taxonomy, and determine population structure. Diploid alfalfa is highly variable. A model-based clustering analysis of the genomic data identified two clearly discrete subpopulations, corresponding to the morphologically defined subspecies falcata and caerulea, with evidence of the hybrid nature of the subspecies hemicycla based on genome composition. Two distinct subpopulations exist within each subsp. caerulea and subsp. falcata. The distinction of caerulea was based on geographical distribution. The two falcata groups were separated based on ecogeography. The results show that taxonomic relationships based on morphology are reflected in the genetic marker data with some exceptions, and that clear distinctions among subspecies are evident at the diploid level. This research provides a baseline from which to systematically evaluate variability in tetraploid alfalfa and serves as a starting point for exploring diploid alfalfa for genetic and breeding experiments.
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DONOVAN LA, ROSENTHAL DR, SANCHEZ-VELENOSI M, RIESEBERG LH, LUDWIG F. Are hybrid species more fit than ancestral parent species in the current hybrid species habitats? J Evol Biol 2010; 23:805-16. [DOI: 10.1111/j.1420-9101.2010.01950.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Raduski AR, Rieseberg LH, Strasburg JL. Effective population size, gene flow, and species status in a narrow endemic sunflower, Helianthus neglectus, compared to its widespread sister species, H. petiolaris. Int J Mol Sci 2010; 11:492-506. [PMID: 20386650 PMCID: PMC2852850 DOI: 10.3390/ijms11020492] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2009] [Revised: 01/17/2010] [Accepted: 01/21/2010] [Indexed: 11/16/2022] Open
Abstract
Species delimitation has long been a difficult and controversial process, and different operational criteria often lead to different results. In particular, investigators using phenotypic vs. molecular data to delineate species may recognize different boundaries, especially if morphologically or ecologically differentiated populations have only recently diverged. Here we examine the genetic relationship between the widespread sunflower species Helianthus petiolaris and its narrowly distributed sand dune endemic sister species H. neglectus using sequence data from nine nuclear loci. The two species were initially described as distinct based on a number of minor morphological differences, somewhat different ecological tolerances, and at least one chromosomal rearrangement distinguishing them; but detailed molecular data has not been available until now. We find that, consistent with previous work, H. petiolaris is exceptionally genetically diverse. Surprisingly, H. neglectus harbors very similar levels of genetic diversity (average diversity across loci is actually slightly higher in H. neglectus). It is extremely unlikely that such a geographically restricted species could maintain these levels of genetic variation in isolation. In addition, the two species show very little evidence of any genetic divergence, and estimates of interspecific gene flow are comparable to gene flow estimates among regions within H. petiolaris. These results indicate that H. petiolaris and H. neglectus likely do not represent two distinct, isolated gene pools; H. neglectus is probably more accurately thought of as a geographically restricted, morphologically and ecologically distinct subspecies of H. petiolaris rather than a separate species.
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Affiliation(s)
- Andrew R. Raduski
- Department of Biology, Indiana University, Bloomington, IN 47405, USA; E-Mail:
| | - Loren H. Rieseberg
- Department of Botany, University of British Columbia, Vancouver, B.C. V6T 1Z4, Canada; E-Mail:
| | - Jared L. Strasburg
- Department of Biology, Indiana University, Bloomington, IN 47405, USA; E-Mail:
- Author to whom correspondence should be addressed; E-Mail:
; Tel.: +1-812-855-9018; Fax: +1-812-855-6705
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28
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Ma F, Zhao C, Milne R, Ji M, Chen L, Liu J. Enhanced drought-tolerance in the homoploid hybrid species Pinus densata: implication for its habitat divergence from two progenitors. THE NEW PHYTOLOGIST 2010; 185:204-16. [PMID: 19804499 DOI: 10.1111/j.1469-8137.2009.03037.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The homoploid hybrid species Pinus densata is restricted to alpine habitats that exceed the altitude range of its two parental species, Pinus tabulaeformis and Pinus yunnanensis. Alpine habitats usually generate cold-induced water stress in plants. To understand the ecological differentiation between these three species, we examined their physiological responses to drought stress. Potted seedlings of three species were subjected to low, mild, moderate and severe water stress in an automatic-controlled glasshouse. Fifteen indicators of fitness were measured for each species in each treatment, and most of these decreased as drought increased. Pinus densata exhibited higher fitness than both parental species in terms of total dry mass production (TDM) and long-term water use efficiency (WUE(L)) across all treatments; several other ecophysiological traits were also extreme but not across every treatment, and not always in the highest stress treatment. These results indicate that extreme characters that have become well fixed in P. densata, confer a faster seedling growth rate and more efficient water use, which in turn should confer increased drought tolerance. These traits of P. densata likely promoted its ecological separation from its parental species and facilitated its successful colonization and establishment in high-altitude habitats.
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Affiliation(s)
- Fei Ma
- Key Laboratory of Arid and Grassland Ecology, School of Life Sciences, Lanzhou University, Lanzhou 730000, Gansu, China
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SHERMAN NATASHAA, BURKE JOHNM. Population genetic analysis reveals a homoploid hybrid origin ofStephanomeria diegensis(Asteraceae). Mol Ecol 2009; 18:4049-60. [DOI: 10.1111/j.1365-294x.2009.04349.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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30
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Donovan LA, Ludwig F, Rosenthal DM, Rieseberg LH, Dudley SA. Phenotypic selection on leaf ecophysiological traits in Helianthus. THE NEW PHYTOLOGIST 2009; 183:868-879. [PMID: 19552693 DOI: 10.1111/j.1469-8137.2009.02916.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Habitats that differ in soil resource availability are expected to differ for selection on resource-related plant traits. Here, we examined spatial and temporal variation in phenotypic selection on leaf ecophysiological traits for 10 Helianthus populations, including two species of hybrid origin, Helianthus anomalus and Helianthus deserticola, and artificial hybrids of their ancestral parents. Leaf traits assessed were leaf size, succulence, nitrogen (N) concentration and water-use efficiency (WUE). Biomass and leaf traits of artificial hybrids indicate that the actively moving dune habitat of H. anomalus was more growth limiting, with lower N availability but higher relative water availability than the stabilized dune habitat of H. deserticola. Habitats differed for direct selection on leaf N and WUE, but not size or succulence, for the artificial hybrids. However, within the H. anomalus habitat, direct selection on WUE also differed among populations. Across years, direct selection on leaf traits did not differ. Leaf N was the only trait for which direct selection differed between habitats but not within the H. anomalus habitat, suggesting that nutrient limitation is an important selective force driving adaptation of H. anomalus to the active dune habitat.
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Affiliation(s)
- L A Donovan
- Department of Plant Biology, University of Georgia, Athens GA 30606, USA
| | - F Ludwig
- Department of Plant Biology, University of Georgia, Athens GA 30606, USA
| | - D M Rosenthal
- Department of Plant Biology, University of Georgia, Athens GA 30606, USA
| | - L H Rieseberg
- Department of Botany, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
| | - S A Dudley
- Department of Biology, McMaster University, Hamilton, Ontario, L8S 4K1, Canada
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31
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Ungerer MC, Strakosh SC, Stimpson KM. Proliferation of Ty3/gypsy-like retrotransposons in hybrid sunflower taxa inferred from phylogenetic data. BMC Biol 2009; 7:40. [PMID: 19594956 PMCID: PMC2715380 DOI: 10.1186/1741-7007-7-40] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Accepted: 07/14/2009] [Indexed: 11/13/2022] Open
Abstract
Background Long terminal repeat (LTR) retrotransposons are a class of mobile genetic element capable of autonomous transposition via an RNA intermediate. Their large size and proliferative ability make them important contributors to genome size evolution, especially in plants, where they can reach exceptionally high copy numbers and contribute substantially to variation in genome size even among closely related taxa. Using a phylogenetic approach, we characterize dynamics of proliferation events of Ty3/gypsy-like LTR retrotransposons that led to massive genomic expansion in three Helianthus (sunflower) species of ancient hybrid origin. The three hybrid species are independently derived from the same two parental species, offering a unique opportunity to explore patterns of retrotransposon proliferation in light of reticulate evolutionary events in this species group. Results We demonstrate that Ty3/gypsy-like retrotransposons exist as multiple well supported sublineages in both the parental and hybrid derivative species and that the same element sublineage served as the source lineage of proliferation in each hybrid species' genome. This inference is based on patterns of species-specific element numerical abundance within different phylogenetic sublineages as well as through signals of proliferation events present in the distributions of element divergence values. Employing methods to date paralogous sequences within a genome, proliferation events in the hybrid species' genomes are estimated to have occurred approximately 0.5 to 1 million years ago. Conclusion Proliferation of the same retrotransposon major sublineage in each hybrid species indicates that similar dynamics of element derepression and amplification likely occurred in each hybrid taxon during their formation. Temporal estimates of these proliferation events suggest an earlier origin for these hybrid species than previously supposed.
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Affiliation(s)
- Mark C Ungerer
- Division of Biology, Kansas State University, Manhattan, Kansas, USA.
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Frajman B, Eggens F, Oxelman B. Hybrid Origins and Homoploid Reticulate Evolution within Heliosperma (Sileneae, Caryophyllaceae)—A Multigene Phylogenetic Approach with Relative Dating. Syst Biol 2009; 58:328-45. [DOI: 10.1093/sysbio/syp030] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Božo Frajman
- Department of Systematic Botany, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-75236 Uppsala, Sweden
- Biology Department, Biotechnical Faculty, University of Ljubljana, Večna pot 111, SI-1000 Ljubljana, Slovenia
| | - Frida Eggens
- Department of Systematic Botany, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-75236 Uppsala, Sweden
| | - Bengt Oxelman
- Department of Systematic Botany, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-75236 Uppsala, Sweden
- Department of Plant and Environmental Sciences, Göteborg University, Box 461, SE-405 30 Göteborg, Sweden; E-mail:
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Strasburg JL, Scotti-Saintagne C, Scotti I, Lai Z, Rieseberg LH. Genomic patterns of adaptive divergence between chromosomally differentiated sunflower species. Mol Biol Evol 2009; 26:1341-55. [PMID: 19276154 PMCID: PMC2727376 DOI: 10.1093/molbev/msp043] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/05/2009] [Indexed: 01/13/2023] Open
Abstract
Understanding the genetic mechanisms of speciation and basis of species differences is among the most important challenges in evolutionary biology. Two questions of particular interest are what roles divergent selection and chromosomal differentiation play in these processes. A number of recently proposed theories argue that chromosomal rearrangements can facilitate the development and maintenance of reproductive isolation and species differences by suppressing recombination within rearranged regions. Reduced recombination permits the accumulation of alleles contributing to isolation and adaptive differentiation and protects existing differences from the homogenizing effects of introgression between incipient species. Here, we examine patterns of genetic diversity and divergence in rearranged versus collinear regions in two widespread, extensively hybridizing sunflower species, Helianthus annuus and Helianthus petiolaris, using sequence data from 77 loci distributed throughout the genomes of the two species. We find weak evidence for increased genetic divergence near chromosomal break points but not within rearranged regions overall. We find no evidence for increased rates of adaptive divergence on rearranged chromosomes; in fact, collinear chromosomes show a far greater excess of fixed amino acid differences between the two species. A comparison with a third sunflower species indicates that much of the nonsynonymous divergence between H. annuus and H. petiolaris probably occurred during or soon after their formation. Our results suggest a limited role for chromosomal rearrangements in genetic divergence, but they do document substantial adaptive divergence and provide further evidence of how species integrity and genetic identity can be maintained at many loci in the face of extensive hybridization and gene flow.
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Affiliation(s)
- Jared L Strasburg
- Department of Biology, Indiana University, Bloomington, Indiana, USA.
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Kane NC, King MG, Barker MS, Raduski A, Karrenberg S, Yatabe Y, Knapp SJ, Rieseberg LH. Comparative genomic and population genetic analyses indicate highly porous genomes and high levels of gene flow between divergent helianthus species. Evolution 2009; 63:2061-75. [PMID: 19473382 DOI: 10.1111/j.1558-5646.2009.00703.x] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
While speciation can be found in the presence of gene flow, it is not clear what impact this gene flow has on genome- and range-wide patterns of differentiation. Here we examine gene flow across the entire range of the common sunflower, H. annuus, its historically allopatric sister species H. argophyllus and a more distantly related, sympatric relative H. petiolaris. Analysis of genotypes at 26 microsatellite loci in 1015 individuals from across the range of the three species showed substantial introgression between geographically proximal populations of H. annuus and H. petiolaris, limited introgression between H. annuus and H. argophyllus, and essentially no gene flow between the allopatric pair, H. argophyllus and H. petiolaris. Analysis of sequence divergence levels among the three species in 1420 orthologs identified from EST databases identified a subset of loci showing extremely low divergence between H. annuus and H. petiolaris and extremely high divergence between the sister species H. annuus and H. argophyllus, consistent with introgression between H. annuus and H. petiolaris at these loci. Thus, at many loci, the allopatric sister species are more genetically divergent than the more distantly related sympatric species, which have exchanged genes across much of the genome while remaining morphologically and ecologically distinct.
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Affiliation(s)
- Nolan C Kane
- Department of Biology, Indiana University, Bloomington, Indiana, USA.
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Maureira-Butler IJ, Pfeil BE, Muangprom A, Osborn TC, Doyle JJ. The Reticulate History of Medicago (Fabaceae). Syst Biol 2008; 57:466-82. [DOI: 10.1080/10635150802172168] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Affiliation(s)
- Iván J. Maureira-Butler
- Department of Plant Biology, Cornell University Ithaca, NY 14853, USA; E-mail: (J.J.D.)
- Agro aquaculture Nutritional Genomic Center (CGNA) Plant Biotechnology Unit INIA-Carillanca P.O. Box 58-D, Temuco, Chile
| | - Bernard E. Pfeil
- Department of Plant Biology, Cornell University Ithaca, NY 14853, USA; E-mail: (J.J.D.)
- CSIRO Plant Industry GPO Box 1600, Canberra, ACT 2601, Australia I.J.M.-B. and B.E.P. contributed equally to this work
| | - Amorntip Muangprom
- National Center for Genetic Engineering and Biotechnology Klong Luang, Pathumthani 12120, Thailand
| | - Thomas C. Osborn
- Seminis Vegetable seeds (A Division of Monsanto) State Highway 16, Woodland, CA 95695, USA
| | - Jeff J. Doyle
- Department of Plant Biology, Cornell University Ithaca, NY 14853, USA; E-mail: (J.J.D.)
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Strasburg JL, Rieseberg LH. Molecular demographic history of the annual sunflowers Helianthus annuus and H. petiolaris--large effective population sizes and rates of long-term gene flow. Evolution 2008; 62:1936-50. [PMID: 18462213 DOI: 10.1111/j.1558-5646.2008.00415.x] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Hybridization between distinct species may lead to introgression of genes across species boundaries, and this pattern can potentially persist for extended periods as long as selection at some loci or genomic regions prevents thorough mixing of gene pools. However, very few reliable estimates of long-term levels of effective migration are available between hybridizing species throughout their history. Accurate estimates of divergence dates and levels of gene flow require data from multiple unlinked loci as well as an analytical framework that can distinguish between lineage sorting and gene flow and incorporate the effects of demographic changes within each species. Here we use sequence data from 18 anonymous nuclear loci in two broadly sympatric sunflower species, Helianthus annuus and H. petiolaris, analyzed within an "isolation with migration" framework to make genome-wide estimates of the ages of these two species, long-term rates of gene flow between them, and effective population sizes and historical patterns of population growth. Our results indicate that H. annuus and H. petiolaris are approximately one million years old and have exchanged genes at a surprisingly high rate (long-term N(ef)m estimates of approximately 0.5 in each direction), with somewhat higher rates of introgression from H. annuus into H. petiolaris than vice versa. In addition, each species has undergone dramatic population expansion since divergence, and both species have among the highest levels of genetic diversity reported for flowering plants. Our results provide the most comprehensive estimate to date of long-term patterns of gene flow and historical demography in a nonmodel plant system, and they indicate that species integrity can be maintained even in the face of extensive gene flow over a prolonged period.
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Affiliation(s)
- Jared L Strasburg
- Department of Biology, Indiana University, 915 E. 3rd Street #150, Bloomington, Indiana 47405, USA.
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Pauwels M, Roosens N, Frérot H, Saumitou-Laprade P. When population genetics serves genomics: putting adaptation back in a spatial and historical context. CURRENT OPINION IN PLANT BIOLOGY 2008; 11:129-34. [PMID: 18329331 DOI: 10.1016/j.pbi.2008.01.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Revised: 01/21/2008] [Accepted: 01/21/2008] [Indexed: 05/10/2023]
Abstract
Recent advances in molecular biology have opened new perspectives for the study of plant adaptation, especially at the intraspecific level. Nowadays, scientists employing -omic results in multiple scientific fields can be optimistic of their chances of revealing mechanisms involved in adaptive population divergence. However, the investment required by integrative studies greatly reduces the number of experiments that can be performed. In this context, a comprehensive choice of accessions under study is crucial. We maintain this choice could be appreciably enlightened by population genetics because it helps putting adaptive population divergence in a spatial and historical context. As an example, we highlight the usefulness of knowledge about population genetic structure in the integrative study of metal tolerance in Arabidopsis halleri.
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Affiliation(s)
- Maxime Pauwels
- Laboratoire de Génétique et Evolution des Populations Végétales, UMR CNRS 8016, Université des Sciences et Technologies de Lille - Lille1, F-59655 Villeneuve d'Ascq Cedex, France
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Gross BL, Turner KG, Rieseberg LH. Selective sweeps in the homoploid hybrid species Helianthus deserticola: evolution in concert across populations and across origins. Mol Ecol 2008; 16:5246-58. [PMID: 18092993 DOI: 10.1111/j.1365-294x.2007.03574.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The evolution of different populations within a species in response to selective pressures can potentially happen in three different ways. It can occur in parallel, where similar changes occur independently in each population in response to selection; in concert, where the spread of an adaptive mutation across a species' range results in a single allele fixing in each population; or populations can diverge in response to local selective pressures. We explored these possibilities in populations of the homoploid hybrid species Helianthus deserticola relative to its parental species Helianthus annuus and Helianthus petiolaris using an analysis of variation in 96 expressed sequence tag-based microsatellites. A total of nine loci showed evidence consistent with recent selection at either the species or population level, although two of these genes were discarded because the apparent sweep did not occur relative to the parent from which the locus was derived. Between one and five loci showed a putative sweep across the entire species range with the same microsatellite allele fixed in each population. This pattern is consistent with evolution in concert despite geographical isolation and potential independent origins of the populations. Only one population of H. deserticola showed candidate sweeps that were unique compared to the rest of the species, and this population has also potentially experienced recent admixture with the parental species.
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Affiliation(s)
- Briana L Gross
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
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Abstract
Homoploid hybrid speciation has been recognized for its potential rapid completion, an idea that has received support from experimental and modeling studies. Following initial hybridization, the genomes of parental species recombine and junctions between chromosomal blocks of different parental origin leave a record of recombination and the time period before homogenization of the derived genome. We use detailed genetic maps of three hybrid species of sunflowers and models to estimate the time required for the stabilization of the new hybrid genome. In contrast to previous estimates of 60 or fewer generations, we find that the genomes of three hybrid sunflower species were not stabilized for hundreds of generations. These results are reconciled with previous research by recognizing that the stabilization of a hybrid species' genome is not synonymous with hybrid speciation. Segregating factors that contribute to initial ecological or intrinsic genetic isolation may become stabilized quickly. The remainder of the genome likely becomes stabilized over a longer time interval, with recombination and drift dictating the contributions of the parental genomes. Our modeling of genome stabilization provides an upper bound for the time interval for reproductive isolation to be established and confirms the rapid nature of homoploid hybrid speciation.
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Affiliation(s)
- C Alex Buerkle
- Department of Botany, 1000 E. University Ave., University of Wyoming, Laramie, Wyoming 82071, USA.
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Abstract
Although the evolutionary importance of natural hybridization has been debated for decades, it has become increasingly clear that hybridization plays a fundamental role in the evolution of many plant and animal taxa, sometimes resulting in the formation of entirely new species. Although some hybrid species retain the base chromosome number of their parents, others combine the full chromosomal complements of their progenitors. Hybrid speciation can thus produce two fundamentally different types of evolutionary lineages, yet relatively little is known about the factors influencing ploidy level in hybrid neospecies. We estimated genetic divergence between species pairs that have given rise to homoploid and polyploid hybrid species and found that divergence is significantly greater for the parents of polyploids, even after controlling for potentially confounding factors. Our data thus provide the first direct evidence in support of the notion that the extent of genomic divergence between hybridizing species influences the likelihood of diploid versus polyploid hybrid speciation.
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Affiliation(s)
- Mark A Chapman
- University of Georgia, Department of Plant Biology, Miller Plant Sciences Building, Athens, Georgia 30602, USA.
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Karrenberg S, Lexer C, Rieseberg LH. Reconstructing the history of selection during homoploid hybrid speciation. Am Nat 2007; 169:725-37. [PMID: 17479459 PMCID: PMC2442913 DOI: 10.1086/516758] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2006] [Accepted: 11/27/2006] [Indexed: 11/03/2022]
Abstract
This study aims to identify selection pressures during the historical process of homoploid hybrid speciation in three Helianthus (sunflower) hybrid species. If selection against intrinsic genetic incompatibilities (fertility selection) or for important morphological/ecological traits (phenotypic selection) were important in hybrid speciation, we would expect this selection to have influenced the parentage of molecular markers or chromosomal segments in the hybrid species' genomes. To infer past selection, we compared the parentage of molecular markers in high-density maps of the three hybrid species with predicted marker parentage from an analysis of fertility selection in artificial hybrids and from the directions of quantitative trait loci effects with respect to the phenotypes of the hybrid species. Multiple logistic regression models were consistent with both fertility and phenotypic selection in all three species. To further investigate traits under selection, we used a permutation test to determine whether marker parentage predicted from groups of functionally related traits differed from neutral expectations. Our results suggest that trait groups associated with ecological divergence were under selection during hybrid speciation. This study presents a new method to test for selection and supports earlier claims that fertility selection and phenotypic selection on ecologically relevant traits have operated simultaneously during sunflower hybrid speciation.
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Affiliation(s)
- Sophie Karrenberg
- Institute of Integrative Biology, Eidgenössische Technische Hochschule Zürich, Zürich, Switzerland.
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Yamaji H, Fukuda T, Yokoyama J, Pak JH, Zhou CZ, Yang CS, Kondo K, Morota T, Takeda S, Sasaki H, Maki M. Reticulate evolution and phylogeography in Asarum sect. Asiasarum (Aristolochiaceae) documented in internal transcribed spacer sequences (ITS) of nuclear ribosomal DNA. Mol Phylogenet Evol 2007; 44:863-84. [PMID: 17383903 DOI: 10.1016/j.ympev.2007.01.011] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2006] [Revised: 01/04/2007] [Accepted: 01/29/2007] [Indexed: 11/22/2022]
Abstract
Phylogenetic analyses were performed for the taxonomically complicated group, Asarum sect. Asiasarum, using internal transcribed spacers (ITS) of nuclear ribosomal DNA. Direct sequences for 99 samples of a total of 14 taxa and geographic races and cloning analyses for 32 of these samples provided new insights that extensive reticulate evolution has occurred in this group. Eight taxa had slight or no polymorphism of the ITS sequences. On the other hand, the other five taxa had polymorphic ITS sequences composed of two ribotypes that were completely the same or almost the same as the sequences recognized in the taxa with only slight or no polymorphism, and were probably of diploid hybrid origin and to have retained their parental ribotypes. In terms of biogeographic implications, at least four interactions including migration, hybridization, and introgression, were presumed between the Japanese Archipelago and the continents, two times via a southern route, from the Korean Peninsula, and two times via a northern route, from Sakhalin or directly from the Eurasian continent.
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Affiliation(s)
- Hiroki Yamaji
- Biological Institute, Graduate School of Science, Tohoku University, Aoba, Sendai, Japan.
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Yatabe Y, Kane NC, Scotti-Saintagne C, Rieseberg LH. Rampant gene exchange across a strong reproductive barrier between the annual sunflowers, Helianthus annuus and H. petiolaris. Genetics 2007; 175:1883-93. [PMID: 17277373 PMCID: PMC1855124 DOI: 10.1534/genetics.106.064469] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Plant species may remain morphologically distinct despite gene exchange with congeners, yet little is known about the genomewide pattern of introgression among species. Here we analyze the effects of persistent gene flow on genomic differentiation between the sympatric sunflower species Helianthus annuus and H. petiolaris. While the species are strongly isolated in testcrosses, genetic distances at 108 microsatellite loci and 14 sequenced genes are highly variable and much lower (on average) than for more closely related but historically allopatric congeners. Our analyses failed to detect a positive association between levels of genetic differentiation and chromosomal rearrangements (as reported in a prior publication) or proximity to QTL for morphological differences or hybrid sterility. However, a significant increase in differentiation was observed for markers within 5 cM of chromosomal breakpoints. Together, these results suggest that islands of differentiation between these two species are small, except in areas of low recombination. Furthermore, only microsatellites associated with ESTs were identified as outlier loci in tests for selection, which might indicate that the ESTs themselves are the targets of selection rather than linked genes (or that coding regions are not randomly distributed). In general, these results indicate that even strong and genetically complex reproductive barriers cannot prevent widespread introgression.
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Affiliation(s)
- Yoko Yatabe
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA
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45
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Brouillette LC, Rosenthal DM, Rieseberg LH, Lexer C, Malmberg RL, Donovan LA. Genetic architecture of leaf ecophysiological traits in Helianthus. ACTA ACUST UNITED AC 2007; 98:142-6. [PMID: 17208933 PMCID: PMC2442921 DOI: 10.1093/jhered/esl063] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
We investigated quantitative trait loci (QTLs) for several leaf chemistry traits in early-generation hybrids between Helianthus annuus and Helianthus petiolaris, the parental species of the ancient diploid hybrid sunflower species Helianthus anomalus, Helianthus deserticola, and Helianthus paradoxus. We grew individuals of a second-generation backcross (BC(2)) toward H. petiolaris under optimum conditions in a glass house experiment. Trait values were measured once for each individual. In addition, genotypic data previously determined for each individual were employed for composite interval mapping of QTLs. We detected QTLs for leaf carbon concentration, leaf nitrogen concentration, leaf nitrogen per unit area, and photosynthetic nitrogen use efficiency. Leaf carbon isotope discrimination (delta(13)C) and leaf nitrogen isotopic composition (delta(15)N) were analyzed, but no significant QTLs were found for these traits. Interestingly, two neighboring loci explained a relatively large percentage of the variation in leaf nitrogen per unit area. This was notable because leaf nitrogen has been shown to strongly affect the fitness of early-generation sunflower hybrids in the H. anomalus habitat, and QTLs of large effect are expected to respond relatively quickly to selection. We speculate that the genetic architecture underlying leaf nitrogen may have facilitated the colonization of active desert sand dunes by H. anomalus.
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Donovan LA, Dudley SA, Rosenthal DM, Ludwig F. Phenotypic selection on leaf water use efficiency and related ecophysiological traits for natural populations of desert sunflowers. Oecologia 2006; 152:13-25. [PMID: 17165094 DOI: 10.1007/s00442-006-0627-5] [Citation(s) in RCA: 104] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2006] [Accepted: 11/20/2006] [Indexed: 11/28/2022]
Abstract
Plant water-use efficiency (WUE) is expected to affect plant fitness and thus be under natural selection in arid habitats. Although many natural population studies have assessed plant WUE, only a few related WUE to fitness. The further determination of whether selection on WUE is direct or indirect through functionally related traits has yielded no consistent results. For natural populations of two desert annual sunflowers, Helianthus anomalus and H. deserticola, we used phenotypic selection analysis with vegetative biomass as the proxy for fitness to test (1) whether there was direct and indirect selection on WUE (carbon isotope ratio) and related traits (leaf N, area, succulence) and (2) whether direct selection was consistent with hypothesized drought/dehydration escape and avoidance strategies. There was direct selection for lower WUE in mesic and dry H. anomalus populations, consistent with dehydration escape, even though it is the longer lived of the two species. For mesic H. anomalus, direct selection favored lower WUE and higher N, suggesting that plants may be "wasting water" to increase N delivery via the transpiration stream. For the shorter lived H. deserticola in the direr habitat, there was indirect selection for lower WUE, inconsistent with drought escape. There was also direct selection for higher leaf N, succulence and leaf size. There was no direct selection for higher WUE consistent with dehydration avoidance in either species. Thus, in these natural populations of two desert dune species higher fitness was associated with some combination direct and indirect selection for lower WUE, higher leaf N and larger leaf size. Our understanding of the adaptive value of plant ecophysiological traits will benefit from further consideration of related traits such as leaf nitrogen and more tests in natural populations.
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Affiliation(s)
- Lisa A Donovan
- Department of Plant Biology, University of Georgia, Athens, GA 30602-7271, USA.
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47
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Guo YP, Vogl C, Van Loo M, Ehrendorfer F. Hybrid origin and differentiation of two tetraploid Achillea species in East Asia: molecular, morphological and ecogeographical evidence. Mol Ecol 2006; 15:133-44. [PMID: 16367836 DOI: 10.1111/j.1365-294x.2005.02772.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Achillea (Asteraceae-Anthemideae) offers classical models for speciation by hybridization and polyploidy. Here, we test the suspected allotetraploid origin of two species, Achillea alpina and Achillea wilsoniana between phylogenetically distinct lineages in East Asia. A total of 421 AFLP bands from 169 individuals and 19 populations of five 2x- and two 4x-species were obtained. The data set was analysed with a newly developed model that accounts for polyploidy and assumes lack of recombination between the parental chromosome sets (i.e. disomic inheritance). A. alpina and A. wilsoniana then appear to be allotetraploids between Achillea acuminata-2x (sect. Ptarmica) and Achillea asiatica-2x (sect. Achillea). The two 4x-species share 44% and 48% of their AFLP bands with A. acuminata-2x, and 39% and 38% with A. asiatica-2x, respectively. Eight plastid haplotypes (A-H) were detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analyses. A. alpina-4x and A. wilsoniana-4x share haplotype F only with A. asiatica-2x. This is consistent with the hybrid origin(s) involving the latter as the maternal ancestor. This result corroborates our previous DNA sequence data, where A. alpina-4x and A. wilsoniana-4x are also placed close to A. asiatica-2x. Morphology, ecology, and amplified fragment length polymorphism (AFLP) profiles of the two 2x-species are distinct, whereas the two 4x-species, grouped as A. alpina aggregate, form a nearly continuous link between them. Considering all evidence, this 4x-aggregate is regarded as the product of a hybridization between genetically distant 2x-ancestors limited to China and adjacent areas: one A. acuminata-like, and the other A. asiatica-like. The allopolyploid A. alpina agg. exhibits considerable morphological variation and ecological flexibility, and has expanded throughout eastern Asia and to northern North America, far beyond the ranges of their presumed 2x-ancestors.
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Affiliation(s)
- Y-P Guo
- Department of Systematic and Evolutionary Botany, Faculty of Life Sciences, University of Vienna, A-1030 Vienna, Austria
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48
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Rieseberg LH, Kim SC, Randell RA, Whitney KD, Gross BL, Lexer C, Clay K. Hybridization and the colonization of novel habitats by annual sunflowers. Genetica 2006; 129:149-65. [PMID: 16955330 PMCID: PMC2442915 DOI: 10.1007/s10709-006-9011-y] [Citation(s) in RCA: 236] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2004] [Accepted: 09/25/2005] [Indexed: 11/26/2022]
Abstract
Although invasive plant species often have a hybrid ancestry, unambiguous evidence that hybridization has stimulated the evolution of invasive behaviors has been difficult to come by. Here, we briefly review how hybridization might contribute to the colonization of novel habitats, range expansions, and invasiveness and then describe work on hybrid sunflowers that forges a direct link between hybridization and ecological divergence. We first discuss the invasion of Texas by the common sunflower and show that the introgression of chromosomal segments from a locally adapted species may have facilitated range expansion. We then present evidence that the colonization of sand dune, desert floor, and salt marsh habitats by three hybrid sunflower species was made possible by selection on extreme or "transgressive" phenotypes generated by hybridization. This body of work corroborates earlier claims regarding the role of hybridization in adaptive evolution and provides an experimental and conceptual framework for ongoing studies in this area.
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Affiliation(s)
- Loren H. Rieseberg
- Department of Biology, Indiana University, Bloomington, IN 47405, USA, e-mail:
| | - Seung-Chul Kim
- Department of Botany and Plant Science, University of California, Riverside, CA 92521, USA
| | - Rebecca A. Randell
- Department of Biology, Indiana University, Bloomington, IN 47405, USA, e-mail:
| | - Kenneth D. Whitney
- Department of Biology, Indiana University, Bloomington, IN 47405, USA, e-mail:
| | - Briana L. Gross
- Department of Biology, Indiana University, Bloomington, IN 47405, USA, e-mail:
| | - Christian Lexer
- Jodrell Laboratory, Royal Botanic Gardens Kew, Richmond, Surrey TW9 3DS, UK
| | - Keith Clay
- Department of Biology, Indiana University, Bloomington, IN 47405, USA, e-mail:
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Lai Z, Gross BL, Zou Y, Andrews J, Rieseberg LH. Microarray analysis reveals differential gene expression in hybrid sunflower species. Mol Ecol 2006; 15:1213-27. [PMID: 16626449 DOI: 10.1111/j.1365-294x.2006.02775.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This paper describes the creation of a cDNA microarray for annual sunflowers and its use to elucidate patterns of gene expression in Helianthus annuus, Helianthus petiolaris, and the homoploid hybrid species Helianthus deserticola. The array comprises 3743 ESTs (expressed sequence tags) representing approximately 2897 unique genes. It has an average clone/EST identity rate of 91%, is applicable across species boundaries within the annual sunflowers, and shows patterns of gene expression that are highly reproducible according to real-time RT-PCR (reverse transcription-polymerase chain reaction) results. Overall, 12.8% of genes on the array showed statistically significant differential expression across the three species. Helianthus deserticola displayed transgressive, or extreme, expression for 58 genes, with roughly equal numbers exhibiting up- or down-regulation relative to both parental species. Transport-related proteins were strongly over-represented among the transgressively expressed genes, which makes functional sense given the extreme desert floor habitat of H. deserticola. The potential adaptive value of differential gene expression was evaluated for five genes in two populations of early generation (BC2) hybrids between the parental species grown in the H. deserticola habitat. One gene (a G protein-coupled receptor) had a significant association with fitness and maps close to a QTL controlling traits that may be adaptive in the desert habitat.
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Affiliation(s)
- Zhao Lai
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
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50
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Lai Z, Nakazato T, Salmaso M, Burke JM, Tang S, Knapp SJ, Rieseberg LH. Extensive chromosomal repatterning and the evolution of sterility barriers in hybrid sunflower species. Genetics 2006; 171:291-303. [PMID: 16183908 PMCID: PMC1456521 DOI: 10.1534/genetics.105.042242] [Citation(s) in RCA: 150] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
New species may arise via hybridization and without a change in ploidy. This process, termed homoploid hybrid speciation, is theoretically difficult because it requires the development of reproductive barriers in sympatry or parapatry. Theory suggests that isolation may arise through rapid karyotypic evolution and/or ecological divergence of hybrid neospecies. Here, we investigate the role of karyotypic change in homoploid hybrid speciation by generating detailed genetic linkage maps for three hybrid sunflower species, Helianthus anomalus, H. deserticola, and H. paradoxus, and comparing these maps to those previously generated for the parental species, H. annuus and H. petiolaris. We also conduct a quantitative trait locus (QTL) analysis of pollen fertility in a BC2 population between the parental species and assess levels of pollen and seed fertility in all cross-combinations of the hybrid and parental species. The three hybrid species are massively divergent from their parental species in karyotype; gene order differences were observed for between 9 and 11 linkage groups (of 17 total), depending on the comparison. About one-third of the karyoypic differences arose through the sorting of chromosomal rearrangements that differentiate the parental species, but the remainder appear to have arisen de novo (six breakages/six fusions in H. anomalus, four breakages/three fusions in H. deserticola, and five breakages/five fusions in H. paradoxus). QTL analyses indicate that the karyotypic differences contribute to reproductive isolation. Nine of 11 pollen viability QTL occur on rearranged chromosomes and all but one map close to a rearrangement breakpoint. Finally, pollen and seed fertility estimates for F1's between the hybrid and parental species fall below 11%, which is sufficient for evolutionary independence of the hybrid neospecies.
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Affiliation(s)
- Zhao Lai
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA
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