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de Vos JM, Streiff SJR, Bachelier JB, Epitawalage N, Maurin O, Forest F, Baker WJ. Phylogenomics of the pantropical Connaraceae: revised infrafamilial classification and the evolution of heterostyly. PLANT SYSTEMATICS AND EVOLUTION = ENTWICKLUNGSGESCHICHTE UND SYSTEMATIK DER PFLANZEN 2024; 310:29. [PMID: 39105137 PMCID: PMC11297820 DOI: 10.1007/s00606-024-01909-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/02/2024] [Accepted: 05/28/2024] [Indexed: 08/07/2024]
Abstract
Connaraceae is a pantropical family of about 200 species containing lianas and small trees with remarkably diverse floral polymorphisms, including distyly, tristyly, homostyly, and dioecy. To date, relationships within the family have not been investigated using a targeted molecular phylogenetic treatment, severely limiting systematic understanding and reconstruction of trait evolution. Accordingly, their last infrafamilial classification was based only on morphological data. Here, we used phylogenomic data obtained using the Angiosperms353 nuclear target sequence capture probes, sampling all tribes and almost all genera, entirely from herbarium specimens, to revise infrafamilial classification and investigate the evolution of heterostyly. The backbone of the resulting molecular phylogenetic tree is almost entirely resolved. Connaraceae consists of two clades, one containing only the African genus Manotes (4 or 5 species), which we newly recognize at the subfamily level. Vegetative and reproductive synapomorphies are proposed for Manotoideae. Within Connaroideae, Connareae is expanded to include the former Jollydoreae. The backbone of Cnestideae, which contains more than half of the Connaraceae species, remains incompletely resolved. Reconstructions of reproductive system evolution are presented that tentatively support tristyly as the ancestral state for the family, with multiple parallel losses, in agreement with previous hypotheses, plus possible re-gains. However, the great diversity of stylar polymorphisms and their phylogenetic lability preclude a definitive answer. Overall, this study reinforces the usefulness of herbarium phylogenomics, and unlocks the reproductive diversity of Connaraceae as a model system for the evolution of complex biological phenomena. Supplementary Information The online version contains supplementary material available at 10.1007/s00606-024-01909-y.
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Affiliation(s)
- Jurriaan M. de Vos
- Department of Environmental Sciences - Botany, University of Basel, Schönbeinstrasse 6, 4056 Basel, Switzerland
| | - Serafin J. R. Streiff
- Department of Environmental Sciences - Botany, University of Basel, Schönbeinstrasse 6, 4056 Basel, Switzerland
- UMR DIADE, Université de Montpellier, IRD, CIRAD, 911 Avenue Agropolis, 34090 Montpellier, France
| | - Julien B. Bachelier
- Institüt für Biologie/Dahlem Centre of Plant Sciences, Freie Universität Berlin, Altensteinstrasse 6, 14195 Berlin, Germany
| | - Niroshini Epitawalage
- Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE UK
- The New York Botanical Garden, 2900 Southern Blvd, Bronx, NY 10458 USA
| | - Olivier Maurin
- Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE UK
| | - Félix Forest
- Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE UK
| | - William J. Baker
- Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE UK
- Department of Biology, Aarhus University, Ny Munkegade 116, 8000 Aarhus, Denmark
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Garcia CB, da Silva AV, de Carvalho IAS, do Nascimento WF, Ramos SLF, Rodrigues DP, Zucchi MI, Costa FM, Alves-Pereira A, Batista CEDA, Amaral DD, Veasey EA. Low Diversity and High Genetic Structure for Platonia insignis Mart., an Endangered Fruit Tree Species. PLANTS (BASEL, SWITZERLAND) 2024; 13:1033. [PMID: 38611562 PMCID: PMC11013813 DOI: 10.3390/plants13071033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2024] [Revised: 02/17/2024] [Accepted: 03/06/2024] [Indexed: 04/14/2024]
Abstract
Platonia insignis is a fruit tree native to Brazil of increasing economic importance, with its pulp trading among the highest market values. This study aimed to evaluate the structure and genomic diversity of P. insignis (bacurizeiro) accessions from six locations in the Brazilian States of Roraima, Amazonas, Pará (Amazon biome), and Maranhão (Cerrado biome). A total of 2031 SNP markers were obtained using genotyping-by-sequencing (GBS), from which 625 outlier SNPs were identified. High genetic structure was observed, with most of the genetic variability (59%) concentrated among locations, mainly between biomes (Amazon and Cerrado). A positive and significant correlation (r = 0.85; p < 0.005) was detected between genetic and geographic distances, indicating isolation by distance. The highest genetic diversity was observed for the location in the Cerrado biome (HE = 0.1746; HO = 0.2078). The locations in the Amazon biome showed low genetic diversity indexes with significant levels of inbreeding. The advance of urban areas, events of burning, and expansion of agricultural activities are most probably the main factors for the genetic diversity reduction of P. insignis. Approaches to functional analysis showed that most of the outlier loci found may be related to genes involved in cellular and metabolic processes.
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Affiliation(s)
- Caroline Bertocco Garcia
- Genetics Department, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba 13418-900, SP, Brazil
| | - Allison Vieira da Silva
- Genetics Department, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba 13418-900, SP, Brazil
| | | | | | | | | | | | - Flaviane Malaquias Costa
- Genetics Department, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba 13418-900, SP, Brazil
| | | | | | | | - Elizabeth Ann Veasey
- Genetics Department, Luiz de Queiroz College of Agriculture, University of São Paulo, Piracicaba 13418-900, SP, Brazil
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Liu C, Jia Y, Li Y, Xiang Y, Pan Y, Liu Q, Ma K, Yin X. The rapid appearance of homostyly in a cultivated distylous population of
Primula forbesii. Ecol Evol 2022; 12:e9515. [PMID: 36415874 PMCID: PMC9674475 DOI: 10.1002/ece3.9515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2022] [Revised: 10/22/2022] [Accepted: 10/26/2022] [Indexed: 11/20/2022] Open
Abstract
Evolutionary breakdown from rigorous outbreeding to self‐fertilization frequently occurs in angiosperms. Since the pollinators are not necessary, self‐compatible populations often reduce investment in floral display characteristics and pollination reward. Primula forbesii is a biennial herb with distribution restricted to southwest China; it was initially a self‐incompatible distylous species, but after 20 years of artificial domestication, homostyly appeared. This change in style provides an ideal material to explore the time required for plant mating systems to adapt to new environmental changes and test whether flower attraction has reduced following transitions to selfing. We did a survey in wild populations of P. forbesii where its seeds were originally collected 20 years ago and recorded the floral morph frequencies and morphologies. The floral morphologies, self‐incompatibility, floral scent, and pollinator visitation between distyly and homostyly were compared in greenhouse. Floral morph frequencies of wild populations did not change, while the cultivated population was inclined to L‐morph and produced homostyly. Evidence from stigma papillae and pollen size supports the hypothesis that the homostyly possibly originated from mutations of large effect genes in distylous linkage region. Transitions to self‐compatible homostyly are accompanied by smaller corolla size, lower amounts of terpenoids, especially linalool and higher amounts of fatty acid derivatives. The main pollinators in the greenhouse were short‐tongued Apis cerana. However, homostyly had reduced visiting frequency. The mating system of P. forbesii changed rapidly in just about 20 years of domestication, and our findings confirm the hypothesis that the transition to selfing is accompanied by decreased flower attraction.
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Affiliation(s)
- Cai‐Lei Liu
- College of Landscape Architecture Sichuan Agricultural University Chengdu China
| | - Yin Jia
- College of Landscape Architecture Sichuan Agricultural University Chengdu China
| | - Yi‐Feng Li
- College of Landscape Architecture Sichuan Agricultural University Chengdu China
| | - Yuan‐Fen Xiang
- College of Landscape Architecture Sichuan Agricultural University Chengdu China
| | - Yuan‐Zhi Pan
- College of Landscape Architecture Sichuan Agricultural University Chengdu China
| | - Qing‐Lin Liu
- College of Landscape Architecture Sichuan Agricultural University Chengdu China
| | - Ke‐Hang Ma
- College of Landscape Architecture Sichuan Agricultural University Chengdu China
| | - Xian‐Cai Yin
- College of Landscape Architecture Sichuan Agricultural University Chengdu China
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Prior CJ, Busch JW. Selfing rate variation within species is unrelated to life-history traits or geographic range position. AMERICAN JOURNAL OF BOTANY 2021; 108:2294-2308. [PMID: 34632564 DOI: 10.1002/ajb2.1766] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2021] [Revised: 08/25/2021] [Accepted: 08/27/2021] [Indexed: 06/13/2023]
Abstract
PREMISE In plants, populations and species vary widely along the continuum from outcrossing to selfing. Life-history traits and ecological circumstances influence among-species variation in selfing rates, but their general role in explaining intraspecific variation is unknown. Using a database of plant species, we test whether life-history traits, geographic range position, or abundance predict selfing rate variation among populations. METHODS We identified species where selfing rates were estimated in at least three populations at known locations. Two key life-history traits (generation time and growth form) were used to predict within-species selfing rate variation. Populations sampled within a species' native range were assessed for proximity to the nearest edge and abundance. Finally, we conducted linear and segmented regressions to determine functional relationships between selfing rate and geographic range position within species. RESULTS Selfing rates for woody species varied less than for herbs, which is explained by the lower average selfing rate of woody species. Relationships between selfing and peripherality or abundance significantly varied among species in their direction and magnitude. However, there was no general pattern of increased selfing toward range edges. A power analysis shows that tests of this hypothesis require studying many (i.e., 40+) populations. CONCLUSIONS Intraspecific variation in plant mating systems is often substantial yet remains difficult to explain. Beyond sampling more populations, future tests of biogeographic hypotheses will benefit from phylogeographic information concerning specific range edges, the study of traits influencing mating system (e.g., herkogamy), and measures of abundance at local scales (e.g., population density).
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Affiliation(s)
- Carly J Prior
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Jeremiah W Busch
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
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Landscape and Climate Influence the Patterns of Genetic Diversity and Inbreeding in Cerrado Plant Species. DIVERSITY 2020. [DOI: 10.3390/d12110421] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The anthropization of the landscape of the Cerrado biome that has occurred over the past few decades has fragmented its natural environments, impacting the connectivity of the plant populations and altering their gene flow. Plant species may also reduce population size in response to sub-optimal climatic and environmental conditions, and observed distribution patterns may align with theoretical schemes, such as the center–periphery model, that is, it is possible that populations on the edge have lower genetic diversity than center populations, theoretically submitted to environmental conditions closer to the optimum. In this context, we evaluate whether the genetic diversity and inbreeding coefficients of Cerrado plant species are affected by landscape features and climate characteristics, and in particular, if the distribution of the genetic diversity of these plants is consistent with the center–periphery model. To do this, we conducted a literature search for genetic studies of Cerrado plant populations using Scopus, Web of Science, and Scielo databases and the species found were used as a proxy to explore patterns throughout the biome. The data were analyzed using generalized linear mixed models (GLMM) and multiple matrix regressions (MMRRs) to evaluate the effects of landscape features and climatic variables on the observed (HO) and expected heterozygosity (HE), allelic richness (AR) and inbreeding (Fis) patterns of the local populations. The landscape was evaluated in terms of the percentage land cover of agriculture (AG), forestry (FO), remnant vegetation (RV), urban areas (UA), pasture (PA), and water (WA) within buffers of 1 km, 3 km, and 5 km around the study populations. We analyzed 121 populations of 31 plant species. The GLMMs showed that HO was affected by FO regardless of buffer size, while HE was also affected by FO, but also by WA and UA. AR was affected by WA and UA in all three buffer zones while the Fis was affected by FO and AU. The MMRRs showed that WA may affect HO, HE, and Fis within the 1 km buffer, while FO affects HO and UA affects AR within the 5 km buffer. In the case of the 1 km and 3 km buffers, however, the geographic distance between populations was identified as a factor determining the genetic diversity and inbreeding indices, indicating that isolation by distance may be an important factor defining the breeding patterns of the Cerrado plant populations. The GLMMs and MMRRs also showed that the mean annual temperature (MAT) and, to a lesser extent, isothermality (ISO) can explain the variation in genetic diversity observed in the Cerrado plant populations. We also found that the center–periphery model fits the distribution pattern observed in most of the species evaluated, including Annona crassiflora,Annona coriacea, Copaifera langsdorffii, and Eugenia dysenterica. Our results indicate that changes in the climate and the landscape of Brazilian Cerrado must be considered carefully to guarantee minimizing the impacts of these processes on the genetic diversity of Cerrado plant species and ensuring the long-term conservation of these species in this biome.
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Wessinger CA, Hileman LC. Parallelism in Flower Evolution and Development. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2020. [DOI: 10.1146/annurev-ecolsys-011720-124511] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Flower evolution is characterized by widespread repetition, with adaptations to pollinator environment evolving in parallel. Recent studies have expanded our understanding of the developmental basis of adaptive floral novelties—petal fusion, bilateral symmetry, heterostyly, and floral dimensions. In this article, we describe patterns of trait evolution and review developmental genetic mechanisms underlying floral novelties. We discuss the diversity of mechanisms for parallel adaptation, the evidence for constraints on these mechanisms, and how constraints help explain observed macroevolutionary patterns. We describe parallel evolution resulting from similarities at multiple hierarchical levels—genetic, developmental, morphological, functional—which indicate general principles in floral evolution, including the central role of hormone signaling. An emerging pattern is mutational bias that may contribute to rapid patterns of parallel evolution, especially if the derived trait can result from simple degenerative mutations. We argue that such mutational bias may be less likely to govern the evolution of novelties patterned by complex developmental pathways.
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Affiliation(s)
- Carolyn A. Wessinger
- Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA
| | - Lena C. Hileman
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045, USA
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Barrett SCH. 'A most complex marriage arrangement': recent advances on heterostyly and unresolved questions. THE NEW PHYTOLOGIST 2019; 224:1051-1067. [PMID: 31631362 DOI: 10.1111/nph.16026] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Accepted: 05/23/2019] [Indexed: 05/09/2023]
Abstract
Heterostylous genetic polymorphisms provide paradigmatic systems for investigating adaptation and natural selection. Populations are usually comprised of two (distyly) or three (tristyly) mating types, maintained by negative frequency-dependent selection resulting from disassortative mating. Theory predicts this mating system should result in equal style-morph ratios (isoplethy) at equilibrium. Here, I review recent advances on heterostyly, focusing on examples challenging stereotypical depictions of the polymorphism and unresolved questions. Comparative analyses indicate multiple origins of heterostyly, often within lineages. Ecological studies demonstrate that structural components of heterostyly are adaptations improving the proficiency of animal-mediated cross-pollination and reducing pollen wastage. Both neutral and selective processes cause deviations from isoplethy in heterostylous populations, and, under some ecological and demographic conditions, cause breakdown of the polymorphism, resulting in either the evolution of autogamy and mixed mating, or transitions to alternative outcrossing systems, including dioecy. Earlier ideas on the genetic architecture of the S-locus supergene governing distyly have recently been overturned by discovery that the dominant S-haplotype is a hemizygous region absent from the s-haplotype. Ecological, phylogenetic and molecular genetic data have validated some features of theoretical models on the selection of the polymorphism. Although heterostyly is the best-understood floral polymorphism in angiosperms, many unanswered questions remain.
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Affiliation(s)
- Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, M5S 3B2, Canada
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Shao JW, Wang HF, Fang SP, Conti E, Chen YJ, Zhu HM. Intraspecific variation of self-incompatibility in the distylous plant Primula merrilliana. AOB PLANTS 2019; 11:plz030. [PMID: 32489575 PMCID: PMC6557196 DOI: 10.1093/aobpla/plz030] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 04/16/2019] [Accepted: 05/15/2019] [Indexed: 05/09/2023]
Abstract
Heteromorphic self-incompatibility can prevent self- and intramorph fertilization while favouring intermorph mating and the maintenance of morph-ratio stability in heterostylous populations. However, variation in the expression of self-incompatibility intraspecies has seldom been assessed. Through hand pollinations and microsatellite markers, the variation in the expression of self-incompatibility and genetic diversity were studied in distylous plant Primula merrilliana. We discovered that the strength of self-incompatibility varied extensively among individuals and populations, from pronounced to weaker self-incompatibility in distylous populations, all the way to strong self-compatibility in homostylous populations. Each distylous population included self-incompatible (SI), partly self-compatible (PSC) and self-compatible (SC) individuals, with the index of self-compatibility (ISC) ranging from 0.07 to 0.68 across populations. Self-compatible populations (ISC > 0.25) were not genetically clustered but were more closely related to populations with high SI and SC individuals were mixed with SI individuals within populations. The ISC and the proportions of SC and PSC individuals were higher in peripheral than in central populations, but no decrease of genetic diversity and no deviations of floral morph ratio from isoplethy were detected in peripheral populations. Additionally, the expression of self-incompatibility was stronger in long-styled flowers than in short-styled flowers. The variation in the strength of self-incompatibility documented in P. merrilliana cautions against the estimation of ISC from a few individuals or populations in distylous species and provides a more complex and nuanced understanding of the role of self-incompatibility in heterostyly.
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Affiliation(s)
- Jian-Wen Shao
- College of Life Sciences, Anhui Normal University, Wuhu, P.R. China
- The Key Laboratory of Conservation and Employment of Biological Resources of Anhui, Wuhu, P.R. China
| | - Hui-Feng Wang
- College of Life Sciences, Anhui Normal University, Wuhu, P.R. China
| | - Su-Ping Fang
- College of Life Sciences, Anhui Normal University, Wuhu, P.R. China
| | - Elena Conti
- Department of Systematic and Evolutionary Botany and Botanic Garden, University of Zurich, Zollikerstrasse, Zurich, Switzerland
| | - Ya-Jing Chen
- College of Life Sciences, Anhui Normal University, Wuhu, P.R. China
| | - Hu-Ming Zhu
- College of Life Sciences, Anhui Normal University, Wuhu, P.R. China
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Santangelo JS, Johnson MTJ, Ness RW. Modern spandrels: the roles of genetic drift, gene flow and natural selection in the evolution of parallel clines. Proc Biol Sci 2019; 285:rspb.2018.0230. [PMID: 29743253 DOI: 10.1098/rspb.2018.0230] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 04/12/2018] [Indexed: 11/12/2022] Open
Abstract
Urban environments offer the opportunity to study the role of adaptive and non-adaptive evolutionary processes on an unprecedented scale. While the presence of parallel clines in heritable phenotypic traits is often considered strong evidence for the role of natural selection, non-adaptive evolutionary processes can also generate clines, and this may be more likely when traits have a non-additive genetic basis due to epistasis. In this paper, we use spatially explicit simulations modelled according to the cyanogenesis (hydrogen cyanide, HCN) polymorphism in white clover (Trifolium repens) to examine the formation of phenotypic clines along urbanization gradients under varying levels of drift, gene flow and selection. HCN results from an epistatic interaction between two Mendelian-inherited loci. Our results demonstrate that the genetic architecture of this trait makes natural populations susceptible to decreases in HCN frequencies via drift. Gradients in the strength of drift across a landscape resulted in phenotypic clines with lower frequencies of HCN in strongly drifting populations, giving the misleading appearance of deterministic adaptive changes in the phenotype. Studies of heritable phenotypic change in urban populations should generate null models of phenotypic evolution based on the genetic architecture underlying focal traits prior to invoking selection's role in generating adaptive differentiation.
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Affiliation(s)
- James S Santangelo
- Department of Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada L5L 1C6 .,Centre for Urban Environments, University of Toronto Mississauga, Mississauga, Ontario, Canada L5L 1C6.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2
| | - Marc T J Johnson
- Department of Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada L5L 1C6.,Centre for Urban Environments, University of Toronto Mississauga, Mississauga, Ontario, Canada L5L 1C6.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2
| | - Rob W Ness
- Department of Biology, University of Toronto Mississauga, Mississauga, Ontario, Canada L5L 1C6.,Centre for Urban Environments, University of Toronto Mississauga, Mississauga, Ontario, Canada L5L 1C6.,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2
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Yuan S, Barrett SCH, Li C, Li X, Xie K, Zhang D. Genetics of distyly and homostyly in a self-compatible Primula. Heredity (Edinb) 2018; 122:110-119. [PMID: 29728676 DOI: 10.1038/s41437-018-0081-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2017] [Revised: 03/16/2018] [Accepted: 03/17/2018] [Indexed: 12/23/2022] Open
Abstract
The transition from outcrossing to selfing through the breakdown of distyly to homostyly has occurred repeatedly among families of flowering plants. Homostyles can originate by major gene changes at the S-locus linkage group, or by unlinked polygenic modifiers. Here, we investigate the inheritance of distyly and homostyly in Primula oreodoxa, a subalpine herb endemic to Sichuan, China. Controlled self- and cross-pollinations confirmed that P. oreodoxa unlike most heterostylous species is fully self-compatible. Segregation patterns indicated that the inheritance of distyly is governed by a single Mendelian locus with the short-styled morph carrying at least one dominant S-allele (S-) and long-styled plants homozygous recessive (ss). Crossing data were consistent with a model in which homostyly results from genetic changes at the distylous linkage group, with the homostylous allele (Sh) dominant to the long-styled allele (s), but recessive to the short-styled allele (S). Progeny tests of open-pollinated seed families revealed high rates of intermorph mating in the L-morph but considerable selfing and possibly intramorph mating in the S-morph and in homostyles. S-morph plants homozygous at the S-locus (SS) occurred in several populations but may experience viability selection. The crossing data from distylous and homostylous plants are consistent with either recombination at the S-locus governing distyly, or mutation at gene(s) controlling sex-organ height; both models predict the same patterns of segregation. Recent studies on the molecular genetics of distyly in Primula demonstrating the hemizygous nature of genes at the S-locus make it more likely that homostyles have resulted from mutation rather than recombination.
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Affiliation(s)
- Shuai Yuan
- Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.,University of Chinese Academy of Sciences, Beijing, 10049, China
| | - Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks St., Toronto, Ontario, M5S 3B2, Canada
| | - Cehong Li
- Biological Resources Research Station at E'mei Mountain, Sichuan, Leshan, 614201, China
| | - Xiaojie Li
- Biological Resources Research Station at E'mei Mountain, Sichuan, Leshan, 614201, China
| | - Kongping Xie
- Biological Resources Research Station at E'mei Mountain, Sichuan, Leshan, 614201, China
| | - Dianxiang Zhang
- Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China.
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Camargo ID, Nattero J, Careaga SA, Núñez-Farfán J. Flower-level developmental plasticity to nutrient availability in Datura stramonium: implications for the mating system. ANNALS OF BOTANY 2017; 120:603-615. [PMID: 28981570 PMCID: PMC5737225 DOI: 10.1093/aob/mcx093] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2016] [Accepted: 07/10/2017] [Indexed: 05/13/2023]
Abstract
BACKGROUND AND AIMS Studies of phenotypic plasticity in plants have mainly focused on (1) the effect of environmental variation on whole-plant traits related to the number of modules rather than on (2) the phenotypic consequences of environmental variation in traits of individual modules. Since environmental and developmental factors can produce changes in traits related to the mating system, this study used the second approach to investigate whether within-individual variation in herkogamy-related traits is affected by the environment during plant development in two populations of Datura stramonium , an annual herb with a hypothesized persistent mixed mating system, and to determine which morphological traits may promote self-fertilization. METHODS Full-sib families of two Mexican populations of D. stramonium , with contrasting ecological histories, were grown under low, mid and high nutrient availability to investigate the effects of genetic, environmental and within-plant flower position on flower size, corolla, stamen and pistil lengths, and herkogamy. KEY RESULTS Populations showed differences in familial variation, plasticity and familial differences in plasticity in most floral traits analysed. In one population (Ticumán), the effect of flower position on trait variation varied among families, whereas in the other (Pedregal) the effect of flower position interacted with the nutrient environment. Flower size varied with the position of flowers, but in the opposite direction between populations in low nutrients; a systematic within-plant trend of reduction in flower size, pistil length and herkogamy with flower position increased the probability of self-fertilization in the Pedregal population. CONCLUSIONS Besides genetic variation in floral traits between and within populations, environmental variation affects phenotypic floral trait values at the whole-plant level, as well as among flower positions. The interaction between flower position and nutrient environment can affect the plant's mating system, and this differs between populations. Thus, reductions in herkogamy with flower positions may be expected in environments with either low pollinator abundance or low nutrients.
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Affiliation(s)
- Iván Darío Camargo
- Laboratorio de Genética Ecológica y Evolución, Departamento de Ecología Evolutiva, Universidad Nacional Autónoma de México, Mexico City, 04510 Distrito Federal, Mexico
- Departamento de Ecología y Territorio, Facultad de Estudios Ambientales y Rurales, Pontificia Universidad Javeriana, Bogotá, 110231594, Colombia
| | - Julieta Nattero
- Instituto de Ecología, Genética y Evolución de Buenos Aires, CONICET, EGE, FCEyN, UBA, Buenos Aires, C1428EGA, Argentina
| | - Sonia A Careaga
- Comisión Nacional para el Conocimiento y Uso de la Biodiversidad, CONABIO, Mexico City, 14010, Distrito Federal, Mexico
| | - Juan Núñez-Farfán
- Laboratorio de Genética Ecológica y Evolución, Departamento de Ecología Evolutiva, Universidad Nacional Autónoma de México, Mexico City, 04510 Distrito Federal, Mexico
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
- For correspondence. E-mail
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Zhou W, Barrett SCH, Li HD, Wu ZK, Wang XJ, Wang H, Li DZ. Phylogeographic insights on the evolutionary breakdown of heterostyly. THE NEW PHYTOLOGIST 2017; 214:1368-1380. [PMID: 28176339 DOI: 10.1111/nph.14453] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Accepted: 12/20/2016] [Indexed: 06/06/2023]
Abstract
The breakdown of heterostyly to homostyly is a classic system for the investigation of evolutionary transitions from outcrossing to selfing. Loss of sexual polymorphism is characterized by changes to population morph structure and floral morphology. Here, we used molecular phylogeography to investigate the geographical context for the breakdown process in Primula chungensis, a species with distylous and homostylous populations. We genotyped plants from 20 populations throughout the entire range in south-west China using the chloroplast intergenic spacer (trnL-trnF), nuclear internal transcribed spacer (ITS) and 10 nuclear microsatellite loci, and determined the genetic relationships among populations and the variation in floral traits associated with homostyle evolution. The marker data identified two multi-population lineages (Tibet and Sichuan) and one single-population lineage (Yunnan), a pattern consistent with at least two independent origins of homostyly. Evidence from flower and pollen size variation is consistent with the hypothesis that transitions to selfing have arisen by the same genetic mechanism involving recombination and/or mutation at the distyly linkage group. Nevertheless, flowers of homostylous lineages have followed divergent evolutionary trajectories following their origin, resulting in populations with both approach and reverse herkogamy. Our study illustrates a rare example of the near-complete replacement of sexual polymorphism by floral monomorphism in a heterostylous species.
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Affiliation(s)
- Wei Zhou
- Plant Germplasm and Genomics Center, Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China
| | - Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, M5S 3B2, Canada
| | - Hai-Dong Li
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China
| | - Zhi-Kun Wu
- Lijiang Forest Ecosystem Research Station, Kunming Institute of Botany, Chinese Academy of Sciences, Lijiang, Yunnan, 674100, China
| | - Xin-Jia Wang
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China
- University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing, 100049, China
| | - Hong Wang
- Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China
| | - De-Zhu Li
- Plant Germplasm and Genomics Center, Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, 132 Lanhei Road, Kunming, Yunnan, 650201, China
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Arunkumar R, Wang W, Wright SI, Barrett SCH. The genetic architecture of tristyly and its breakdown to self-fertilization. Mol Ecol 2016; 26:752-765. [DOI: 10.1111/mec.13946] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2016] [Revised: 11/02/2016] [Accepted: 11/07/2016] [Indexed: 11/29/2022]
Affiliation(s)
- Ramesh Arunkumar
- Department of Ecology and Evolutionary Biology; University of Toronto; 25 Willcocks Street Toronto Ontario Canada M5S 3B2
| | - Wei Wang
- Department of Ecology and Evolutionary Biology; University of Toronto; 25 Willcocks Street Toronto Ontario Canada M5S 3B2
| | - Stephen I. Wright
- Department of Ecology and Evolutionary Biology; University of Toronto; 25 Willcocks Street Toronto Ontario Canada M5S 3B2
| | - Spencer C. H. Barrett
- Department of Ecology and Evolutionary Biology; University of Toronto; 25 Willcocks Street Toronto Ontario Canada M5S 3B2
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Arunkumar R, Maddison TI, Barrett SCH, Wright SI. Recent mating-system evolution in Eichhornia is accompanied by cis-regulatory divergence. THE NEW PHYTOLOGIST 2016; 211:697-707. [PMID: 26990568 DOI: 10.1111/nph.13918] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Accepted: 01/30/2016] [Indexed: 06/05/2023]
Abstract
The evolution of predominant self-fertilization from cross-fertilization in plants is accompanied by diverse changes to morphology, ecology and genetics, some of which likely result from regulatory changes in gene expression. We examined changes in gene expression during early stages in the transition to selfing in populations of animal-pollinated Eichhornia paniculata with contrasting mating patterns. We crossed plants from outcrossing and selfing populations and tested for the presence of allele-specific expression (ASE) in floral buds and leaf tissue of F1 offspring, indicative of cis-regulatory changes. We identified 1365 genes exhibiting ASE in floral buds and leaf tissue. These genes preferentially expressed alleles from outcrossing parents. Moreover, we found evidence that genes exhibiting ASE had a greater nonsynonymous diversity compared to synonymous diversity in the selfing parents. Our results suggest that the transition from outcrossing to high rates of self-fertilization may have the potential to shape the cis-regulatory genomic landscape of angiosperm species, but that the changes in ASE may be moderate, particularly during the early stages of this transition.
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Affiliation(s)
- Ramesh Arunkumar
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
| | - Teresa I Maddison
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
| | - Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
| | - Stephen I Wright
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada
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Cruzan MB, Barrett SCH. Postpollination discrimination between self and outcross pollen covaries with the mating system of a self-compatible flowering plant. AMERICAN JOURNAL OF BOTANY 2016; 103:568-576. [PMID: 26507113 DOI: 10.3732/ajb.1500139] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Accepted: 05/28/2015] [Indexed: 06/05/2023]
Abstract
PREMISE OF THE STUDY Variation in the mating system of hermaphroditic plant populations is determined by interactions between genetic and environmental factors operating via both pre- and postmating processes. Models predicting the maintenance of intermediate outcrossing rates in animal-pollinated plants often assume that the mating system is primarily controlled by floral morphology and pollinator availability, but rarely has the influence of postpollination processes on variation in outcrossing been examined. METHODS We investigated the influence of stylar discrimination between illegitimate and legitimate pollen-tube growth and the pollen-load capacity of stigmas on mating-system variation in the annual, tristylous species Eichhornia paniculata using controlled crosses and genetic markers. This species exhibits an exceptionally broad range of outcrossing rates in natural populations. KEY RESULTS There was significant variation among populations in the pollen-load capacity of stigmas and the ability of styles to discriminate between illegitimate vs. legitimate pollen. There was strong correspondence between stylar-discrimination ability and variation in outcrossing rate among populations and style morphs. The combination of stigmatic pollen-load capacity and stylar discrimination explained more than 80% of the variation in outcrossing rates among populations. CONCLUSIONS The finding that stigmatic pollen-load capacity and stylar-discrimination ability contributed significantly to explaining the wide range of outcrossing rates in E. paniculata suggests that postpollination mechanisms play an important role in governing mating patterns in this species. The difference in levels of stylar discrimination between outcrossing and selfing populations may reflect a trade-off between selection for increased outcrossing and greater reproductive assurance.
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Affiliation(s)
- Mitchell B Cruzan
- Department of Biology, Portland State University, Portland, Oregon 97207 USA
| | - Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Ontario M5S 3B2 Canada
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Abstract
Flowering plants possess an unrivaled diversity of mechanisms for achieving sexual and asexual reproduction, often simultaneously. The commonest type of asexual reproduction is clonal growth (vegetative propagation) in which parental genotypes (genets) produce vegetative modules (ramets) that are capable of independent growth, reproduction, and often dispersal. Clonal growth leads to an expansion in the size of genets and increased fitness because large floral displays increase fertility and opportunities for outcrossing. Moreover, the clonal dispersal of vegetative propagules can assist "mate finding," particularly in aquatic plants. However, there are ecological circumstances in which functional antagonism between sexual and asexual reproductive modes can negatively affect the fitness of clonal plants. Populations of heterostylous and dioecious species have a small number of mating groups (two or three), which should occur at equal frequency in equilibrium populations. Extensive clonal growth and vegetative dispersal can disrupt the functioning of these sexual polymorphisms, resulting in biased morph ratios and populations with a single mating group, with consequences for fertility and mating. In populations in which clonal propagation predominates, mutations reducing fertility may lead to sexual dysfunction and even the loss of sex. Recent evidence suggests that somatic mutations can play a significant role in influencing fitness in clonal plants and may also help explain the occurrence of genetic diversity in sterile clonal populations. Highly polymorphic genetic markers offer outstanding opportunities for gaining novel insights into functional interactions between sexual and clonal reproduction in flowering plants.
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Affiliation(s)
- Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada M5S 3B2
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Simón-Porcar VI, Picó FX, Arroyo J. Range-wide population genetics and variation in morph ratio in style-dimorphic Narcissus papyraceus. AMERICAN JOURNAL OF BOTANY 2015; 102:449-456. [PMID: 25784478 DOI: 10.3732/ajb.1400209] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
UNLABELLED • PREMISE OF THE STUDY Theoretical models state that natural selection and mating patterns account for floral morph ratio in style-polymorphic plants. However, the demographic history of populations can also influence variation in morph ratios. If so, we hypothesize an association between the morph ratios and the genetic structure across populations.• METHODS We used nuclear microsatellites to assess genetic variation and structure in populations of Narcissus papyraceus, a style-dimorphic plant whose floral morph ratios (L-morph to S-morph) gradually vary throughout its distribution range in the southwestern Mediterranean Basin. We implemented analyses to relate the genetic features of populations with their morph ratios.• KEY RESULTS We found greater frequencies of the S-morph in central populations and declining frequencies toward the periphery. This geographic pattern was not associated with the genetic structure of populations. Instead, we found two distinct genetic groups, mainly separated by the Strait of Gibraltar, with a mixture of morph ratios within each one. Overall, there was a weak genetic structure. Genetic diversity was greater in central and southern dimorphic populations than in northern L-monomorphic populations.• CONCLUSIONS Altogether, our results do not support the hypothesis that the demographic history of populations can account for the observed geographical pattern of morph ratios in N. papyraceus. We suggest that adaptive processes shown in previous studies in the species are the main determinant of the existing variation in the morph composition of populations.
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Affiliation(s)
- Violeta I Simón-Porcar
- Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, Apartado 1095 41080 Sevilla, Spain Biological and Environmental Sciences, University of Stirling, Stirling, FK9 4LA, UK
| | - F Xavier Picó
- Departamento de Ecología Integrativa, Estación Biológica de Doñana (EBD), Consejo Superior de Investigaciones Científicas (CSIC) 41092 Sevilla, Spain
| | - Juan Arroyo
- Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, Apartado 1095 41080 Sevilla, Spain
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Barrett SCH, Arunkumar R, Wright SI. The demography and population genomics of evolutionary transitions to self-fertilization in plants. Philos Trans R Soc Lond B Biol Sci 2015; 369:rstb.2013.0344. [PMID: 24958918 DOI: 10.1098/rstb.2013.0344] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The evolution of self-fertilization from outcrossing has occurred on numerous occasions in flowering plants. This shift in mating system profoundly influences the morphology, ecology, genetics and evolution of selfing lineages. As a result, there has been sustained interest in understanding the mechanisms driving the evolution of selfing and its environmental context. Recently, patterns of molecular variation have been used to make inferences about the selective mechanisms associated with mating system transitions. However, these inferences can be complicated by the action of linked selection following the transition. Here, using multilocus simulations and comparative molecular data from related selfers and outcrossers, we demonstrate that there is little evidence for strong bottlenecks associated with initial transitions to selfing, and our simulation results cast doubt on whether it is possible to infer the role of bottlenecks associated with reproductive assurance in the evolution of selfing. They indicate that the effects of background selection on the loss of diversity and efficacy of selection occur rapidly following the shift to high selfing. Future comparative studies that integrate explicit ecological and genomic details are necessary for quantifying the independent and joint effects of selection and demography on transitions to selfing and the loss of genetic diversity.
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Affiliation(s)
- Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2
| | - Ramesh Arunkumar
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2
| | - Stephen I Wright
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2
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The evolution of selfing is accompanied by reduced efficacy of selection and purging of deleterious mutations. Genetics 2014; 199:817-29. [PMID: 25552275 DOI: 10.1534/genetics.114.172809] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The transition from outcrossing to selfing is predicted to reduce the genome-wide efficacy of selection because of the lower effective population size (Ne) that accompanies this change in mating system. However, strongly recessive deleterious mutations exposed in the homozygous backgrounds of selfers should be under strong purifying selection. Here, we examine estimates of the distribution of fitness effects (DFE) and changes in the magnitude of effective selection coefficients (Nes) acting on mutations during the transition from outcrossing to selfing. Using forward simulations, we investigated the ability of a DFE inference approach to detect the joint influence of mating system and the dominance of deleterious mutations on selection efficacy. We investigated predictions from our simulations in the annual plant Eichhornia paniculata, in which selfing has evolved from outcrossing on multiple occasions. We used range-wide sampling to generate population genomic datasets and identified nonsynonymous and synonymous polymorphisms segregating in outcrossing and selfing populations. We found that the transition to selfing was accompanied by a change in the DFE, with a larger fraction of effectively neutral sites (Nes < 1), a result consistent with the effects of reduced Ne in selfers. Moreover, an increased proportion of sites in selfers were under strong purifying selection (Nes > 100), and simulations suggest that this is due to the exposure of recessive deleterious mutations. We conclude that the transition to selfing has been accompanied by the genome-wide influences of reduced Ne and strong purifying selection against deleterious recessive mutations, an example of purging at the molecular level.
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20
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Zuellig MP, Kenney AM, Sweigart AL. Evolutionary genetics of plant adaptation: insights from new model systems. CURRENT OPINION IN PLANT BIOLOGY 2014; 18:44-50. [PMID: 24561539 PMCID: PMC7659028 DOI: 10.1016/j.pbi.2014.01.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2013] [Revised: 01/21/2014] [Accepted: 01/26/2014] [Indexed: 05/18/2023]
Abstract
Flowering time and mating system divergence are two of the most common adaptive transitions in plants. We review recent progress toward understanding the genetic basis of these adaptations in new model plant species. For flowering time, we find that individual crosses often reveal a simple genetic basis, but that the loci involved almost always vary within species and across environments, indicating a more complex genetic basis species-wide. Similarly, the transition to self-fertilization is often genetically complex, but this seems to depend on the amount of standing variation and time since species divergence. Recent population genomic studies also raise doubts about the long-term adaptive potential of self-fertilization, providing evidence that purifying selection is less effective in highly selfing species.
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Affiliation(s)
- Matthew P Zuellig
- University of Georgia, Department of Genetics, Fred C. Davidson Life Sciences Complex, Athens, GA 30602, United States
| | - Amanda M Kenney
- University of Georgia, Department of Genetics, Fred C. Davidson Life Sciences Complex, Athens, GA 30602, United States
| | - Andrea L Sweigart
- University of Georgia, Department of Genetics, Fred C. Davidson Life Sciences Complex, Athens, GA 30602, United States.
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Meeus S, Honnay O, Jacquemyn H. Differences in fine-scale spatial genetic structure across the distribution range of the distylous forest herb Pulmonaria officinalis (Boraginaceae). BMC Genet 2013; 14:101. [PMID: 24134743 PMCID: PMC4015958 DOI: 10.1186/1471-2156-14-101] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2012] [Accepted: 10/10/2013] [Indexed: 01/21/2023] Open
Abstract
Background Geographical ranges of plants and their pollinators do not always entirely overlap and it has been suggested that the absence of specialized pollinators at range margins may induce changes in mating systems. Because a species’ mating system is known to have a considerable effect on within-population pollen movement, the extent of fine-scale spatial genetic structure (SGS) can be expected to differ between populations located at different parts of their geographical range. To test this prediction, we compared the fine-scale SGS between two core and two disjunct populations of the distylous forest herb Pulmonaria officinalis. Because in disjunct populations of this species the heteromorphic self-incompatibility system showed relaxation in the long-styled morph, but not in the short-styled morph, we also hypothesized that the extent of fine-scale SGS and clustering differed between morphs. Results Spatial autocorrelation analyses showed a significant decrease in genetic relatedness with spatial distance for both core and disjunct populations with the weakest SGS found in one of the core populations (Sp = 0.0014). No evidence of stronger SGS in the long-styled morph was found in the center of the range whereas one disjunct population showed a significantly (P = 0.029) higher SGS in the long-styled morph (SpL = 0.0070) than in the short-styled morph (SpS = 0.0044). Conclusions Consistent with previous analyses on distylous plant species, we found weak, but significant spatial genetic structure. However, the extent of SGS varied substantially between populations within regions, suggesting that population characteristics other than mating system (e.g. local pollinator assemblages, population history) may be as important in determining variation in SGS.
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Affiliation(s)
- Sofie Meeus
- Plant Conservation and Population Biology, Biology Department, University of Leuven, Kasteelpark Arenberg 31, Heverlee, 3001, Belgium.
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Kissling J, Barrett SCH. Variation and evolution of herkogamy in Exochaenium (Gentianaceae): implications for the evolution of distyly. ANNALS OF BOTANY 2013; 112:95-102. [PMID: 23639954 PMCID: PMC3690988 DOI: 10.1093/aob/mct097] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2012] [Accepted: 03/15/2013] [Indexed: 05/14/2023]
Abstract
BACKGROUNDS AND AIMS The spatial separation of stigmas and anthers (herkogamy) in flowering plants functions to reduce self-pollination and avoid interference between pollen dispersal and receipt. Little is known about the evolutionary relationships among the three main forms of herkogamy - approach, reverse and reciprocal herkogamy (distyly) - or about transitions to and from a non-herkogamous condition. This problem was examined in Exochaenium (Gentianaceae), a genus of African herbs that exhibits considerable variation in floral morphology, including the three forms of herkogamy. METHODS Using maximum parsimony and maximum likelihood methods, the evolutionary history of herkogamic and non-herkogamic conditions was reconstructed from a molecular phylogeny of 15 species of Exochaenium and four outgroup taxa, based on three chloroplast regions, the nuclear ribosomal internal transcribed spacer (ITS1 and 2) and the 5·8S gene. Ancestral character states were determined and the reconstructions were used to evaluate competing models for the origin of reciprocal herkogamy. KEY RESULTS Reciprocal herkogamy originated once in Exochaenium from an ancestor with approach herkogamy. Reverse herkogamy and the non-herkogamic condition homostyly were derived from heterostyly. Distylous species possessed pendent, slightly zygomorphic flowers, and the single transition to reverse herkogamy was associated with the hawkmoth pollination syndrome. Reductions in flower size characterized three of four independent transitions from reciprocal herkogamy to homostyly. CONCLUSIONS The results support Lloyd and Webb's model in which distyly originated from an ancestor with approach herkogamy. They also demonstrate the lability of sex organ deployment and implicate pollinators, or their absence, as playing an important role in driving transitions among herkogamic and non-herkogamic conditions.
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Affiliation(s)
- Jonathan Kissling
- Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland.
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Ness RW, Siol M, Barrett SCH. Genomic consequences of transitions from cross- to self-fertilization on the efficacy of selection in three independently derived selfing plants. BMC Genomics 2012; 13:611. [PMID: 23145563 PMCID: PMC3533693 DOI: 10.1186/1471-2164-13-611] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Accepted: 10/05/2012] [Indexed: 11/10/2022] Open
Abstract
Background Transitions from cross- to self-fertilization are associated with increased genetic drift rendering weakly selected mutations effectively neutral. The effect of drift is predicted to reduce selective constraints on amino acid sequences of proteins and relax biased codon usage. We investigated patterns of nucleotide variation to assess the effect of inbreeding on the accumulation of deleterious mutations in three independently evolved selfing plants. Using high-throughput sequencing, we assembled the floral transcriptomes of four individuals of Eichhornia (Pontederiaceae); these included one outcrosser and two independently derived selfers of E. paniculata, and E. paradoxa, a selfing outgroup. The dataset included ~8000 loci totalling ~3.5 Mb of coding DNA. Results Tests of selection were consistent with purifying selection constraining evolution of the transcriptome. However, we found an elevation in the proportion of non-synonymous sites that were potentially deleterious in the E. paniculata selfers relative to the outcrosser. Measurements of codon usage in high versus low expression genes demonstrated reduced bias in both E. paniculata selfers. Conclusions Our findings are consistent with a small reduction in the efficacy of selection on protein sequences associated with transitions to selfing, and reduced selection in selfers on synonymous changes that influence codon usage.
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Affiliation(s)
- Rob W Ness
- Department of Ecology and Evolutionary Biology, University of Toronto, ON, Canada.
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Meeus S, Honnay O, Jacquemyn H. Strong differences in genetic structure across disjunct, edge, and core populations of the distylous forest herb Pulmonaria officinalis (Boraginaceae). AMERICAN JOURNAL OF BOTANY 2012; 99:1809-1818. [PMID: 23092991 DOI: 10.3732/ajb.1200223] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
PREMISE OF THE STUDY Populations at the edge of a species' distribution area are often small and have low levels of gene flow resulting in lower genetic variation and higher differentiation compared to core populations. This study examined genetic variation among populations of the distylous temperate forest herb Pulmonaria officinalis located in the core, the edge, and outside the species' main distribution range. METHODS We compared patterns of genetic variation for eight microsatellite loci between disjunct (Belgium), edge (western Germany), and core (eastern Germany) populations of P. officinalis. KEY RESULTS Disjunct populations contained only a subset of alleles found in edge and core populations and had significantly lower within-population genetic variation. No significant differences, however, in within-population genetic variation were found between edge and core populations, except for allelic and genotypic richness. Genetic differentiation was highest among disjunct (F(ST) = 0.11) and lowest among core populations (F(ST) = 0.03). Significant (P < 0.01) isolation by distance was found for disjunct and edge populations (r(M) = 0.29 and 0.50, respectively), but not for core populations (r(M) = 0.18). CONCLUSIONS The results are best interpreted from a "dynamic range" point of view in which the observed low levels of genetic diversity and high genetic differentiation in disjunct populations are best explained through historical processes, most likely the introduction of the species in medieval times. Lower levels of gene flow caused by the pronounced fragmentation of forests in Belgium may further have contributed to the genetic structure of P. officinalis in these disjunct populations.
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Affiliation(s)
- Sofie Meeus
- Plant Conservation and Population Biology, Biology Department, University of Leuven, Kasteelpark Arenberg 31, 3001 Heverlee, Belgium. sofi
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Abstract
Classic questions about trait evolution-including the directionality of character change and its interactions with lineage diversification-intersect in the study of plant breeding systems. Transitions from self-incompatibility to self-compatibility are frequent, and they may proceed within a species ("anagenetic" mode of breeding system change) or in conjunction with speciation events ("cladogenetic" mode of change). We apply a recently developed phylogenetic model to the nightshade family Solanaceae, quantifying the relative contributions of these two modes of evolution along with the tempo of breeding system change, speciation, and extinction. We find that self-incompatibility, a genetic mechanism that prevents self-fertilization, is lost largely by the cladogenetic mode. Self-compatible species are thus more likely to arise from the isolation of a newly self-compatible population than from species-wide fixation of self-compatible mutants. Shared polymorphism at the locus that governs self-incompatibility shows it to be ancestral and not regained within this family. We demonstrate that failing to account for cladogenetic character change misleads phylogenetic tests of evolutionary irreversibility, both for breeding system in Solanaceae and on simulated trees.
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Affiliation(s)
- Emma E Goldberg
- Department of Biological Sciences, University of Illinois at Chicago, 840 West Taylor Street MC067, Chicago, Illinois 60607, USA.
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Weber JJ, Weller SG, Sakai AK, Nguyen A, Tai ND, Domínguez CA, Molina-Freaner FE. Purging of inbreeding depression within a population of Oxalis alpina (Oxalidaceae). AMERICAN JOURNAL OF BOTANY 2012; 99:923-932. [PMID: 22539518 DOI: 10.3732/ajb.1100383] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
PREMISE OF THE STUDY Variation among individuals in levels of inbreeding depression associated with selfing levels could influence mating system evolution by purging deleterious alleles, but empirical evidence for this association is limited. METHODS We investigated the association of family-level inbreeding depression and presumed inbreeding history in a tristylous population of Oxalis alpina (Oxalidaceae). KEY RESULTS Mid-styled individuals possessed the greatest degree of self-compatibility (SC) and produced more autogamous capsules than short- or long-styled individuals. Offspring of highly self-compatible mid-styled individuals showed reduced inbreeding depression. Mid-styled plants that produced capsules autogamously exhibited reduced stigma-anther separation compared to mid-styled plants that produced no capsules autogamously. Reduced inbreeding depression was not correlated with stigma-anther separation, suggesting that self-compatibility and autogamy evolve before morphological changes in stigma-anther separation. CONCLUSIONS Purging of inbreeding depression occurred in SC mid-styled maternal families. Low inbreeding depression in SC mid-styled plants may lead to retention of the mid-styled morph in populations, despite the occurrence of higher selfing rates in mid-styled relative to short- or long-styled morphs. Variation among individuals in levels of self-fertilization within populations may lead to associations between inbreeding lineages and lower levels of inbreeding depression, influencing the evolution of mating systems.
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Affiliation(s)
- Jennifer J Weber
- Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA
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Karron JD, Ivey CT, Mitchell RJ, Whitehead MR, Peakall R, Case AL. New perspectives on the evolution of plant mating systems. ANNALS OF BOTANY 2012; 109:493-503. [PMID: 22210849 PMCID: PMC3278297 DOI: 10.1093/aob/mcr319] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
BACKGROUND The remarkable diversity of mating patterns and sexual systems in flowering plants has fascinated evolutionary biologists for more than a century. Enduring questions about this topic include why sexual polymorphisms have evolved independently in over 100 plant families, and why proportions of self- and cross-fertilization often vary dramatically within and among populations. Important new insights concerning the evolutionary dynamics of plant mating systems have built upon a strong foundation of theoretical models and innovative field and laboratory experiments. However, as the pace of advancement in this field has accelerated, it has become increasingly difficult for researchers to follow developments outside their primary area of research expertise. SCOPE In this Viewpoint paper we highlight three important themes that span and integrate different subdisciplines: the changes in morphology, phenology, and physiology that accompany the transition to selfing; the evolutionary consequences of pollen pool diversity in flowering plants; and the evolutionary dynamics of sexual polymorphisms. We also highlight recent developments in molecular techniques that will facilitate more efficient and cost-effective study of mating patterns in large natural populations, research on the dynamics of pollen transport, and investigations on the genetic basis of sexual polymorphisms. This Viewpoint also serves as the introduction to a Special Issue on the Evolution of Plant Mating Systems. The 15 papers in this special issue provide inspiring examples of recent discoveries, and glimpses of exciting developments yet to come.
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Affiliation(s)
- Jeffrey D Karron
- Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53201, USA.
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Ness RW, Siol M, Barrett SCH. De novo sequence assembly and characterization of the floral transcriptome in cross- and self-fertilizing plants. BMC Genomics 2011. [PMID: 21649902 DOI: 10.1186/1471‐2164‐12‐298] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND The shift from cross-fertilization to predominant self-fertilization is among the most common evolutionary transitions in the reproductive biology of flowering plants. Increased inbreeding has important consequences for floral morphology, population genetic structure and genome evolution. The transition to selfing is usually characterized by a marked reduction in flower size and the loss of traits involved in pollinator attraction and the avoidance of self-fertilization. Here, we use short-read sequencing to assemble, de novo, the floral transcriptomes of three genotypes of Eichhornia paniculata, including an outcrosser and two genotypes from independently derived selfers, and a single genotype of the sister species E. paradoxa. By sequencing mRNA from tissues sampled at various stages of flower development, our goal was to sequence and assemble the floral transcriptome and identify differential patterns of gene expression. RESULTS Our 24 Mbp assembly resulted in ~27,000 contigs that averaged ~900 bp in length. All four genotypes had highly correlated gene expression, but the three E. paniculata genotypes were more correlated with one another than each was to E. paradoxa. Our analysis identified 269 genes associated with floral development, 22 of which were differentially expressed in selfing lineages relative to the outcrosser. Many of the differentially expressed genes affect floral traits commonly altered in selfing plants and these represent a set of potential candidate genes for investigating the evolution of the selfing syndrome. CONCLUSIONS Our study is among the first to demonstrate the use of Illumina short read sequencing for de novo transcriptome assembly in non-model species, and the first to implement this technology for comparing floral transcriptomes in outcrossing and selfing plants.
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Affiliation(s)
- Rob W Ness
- Department of Ecology & Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5S 3B2, Canada.
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Ness RW, Siol M, Barrett SCH. De novo sequence assembly and characterization of the floral transcriptome in cross- and self-fertilizing plants. BMC Genomics 2011; 12:298. [PMID: 21649902 PMCID: PMC3128866 DOI: 10.1186/1471-2164-12-298] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Accepted: 06/07/2011] [Indexed: 12/28/2022] Open
Abstract
Background The shift from cross-fertilization to predominant self-fertilization is among the most common evolutionary transitions in the reproductive biology of flowering plants. Increased inbreeding has important consequences for floral morphology, population genetic structure and genome evolution. The transition to selfing is usually characterized by a marked reduction in flower size and the loss of traits involved in pollinator attraction and the avoidance of self-fertilization. Here, we use short-read sequencing to assemble, de novo, the floral transcriptomes of three genotypes of Eichhornia paniculata, including an outcrosser and two genotypes from independently derived selfers, and a single genotype of the sister species E. paradoxa. By sequencing mRNA from tissues sampled at various stages of flower development, our goal was to sequence and assemble the floral transcriptome and identify differential patterns of gene expression. Results Our 24 Mbp assembly resulted in ~27,000 contigs that averaged ~900 bp in length. All four genotypes had highly correlated gene expression, but the three E. paniculata genotypes were more correlated with one another than each was to E. paradoxa. Our analysis identified 269 genes associated with floral development, 22 of which were differentially expressed in selfing lineages relative to the outcrosser. Many of the differentially expressed genes affect floral traits commonly altered in selfing plants and these represent a set of potential candidate genes for investigating the evolution of the selfing syndrome. Conclusions Our study is among the first to demonstrate the use of Illumina short read sequencing for de novo transcriptome assembly in non-model species, and the first to implement this technology for comparing floral transcriptomes in outcrossing and selfing plants.
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Affiliation(s)
- Rob W Ness
- Department of Ecology & Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON M5S 3B2, Canada.
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Busch JW, Joly S, Schoen DJ. Demographic signatures accompanying the evolution of selfing in Leavenworthia alabamica. Mol Biol Evol 2011; 28:1717-29. [PMID: 21199892 DOI: 10.1093/molbev/msq352] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The evolution of selfing from outcrossing is a common transition, yet little is known about the mutations and selective factors that promote this shift. In the mustard family, single-locus self-incompatibility (SI) enforces outcrossing. In this study, we test whether mutations causing self-compatibility (SC) are linked to the self-incompatibility locus (S-locus) in Leavenworthia alabamica, a species where two selfing races (a2 and a4) co-occur with outcrossing populations. We also infer the ecological circumstances associated with origins of selfing using molecular sequence data. Genealogical reconstruction of the Lal2 locus, the putative ortholog of the SRK locus, showed that both selfing races are fixed for one of two different S-linked Lal2 sequences, whereas outcrossing populations harbor many S-alleles. Hybrid crosses demonstrated that S-linked mutations cause SC in each selfing race. These results strongly suggest two origins of selfing in this species, a result supported by population admixture analysis of 16 microsatellite loci and by a population tree built from eight nuclear loci. One selfing race (a4) shows signs of a severe population bottleneck, suggesting that reproductive assurance might have caused the evolution of selfing in this case. In contrast, the population size of race a2 cannot be distinguished from that of outcrossing populations after correcting for differences in selfing rates. Coalescent-based analyses suggest a relatively old origin of selfing in the a4 race (∼150 ka ago), whereas selfing evolved recently in the a2 race (∼12-48 ka ago). These results imply that S-locus mutations have triggered two recent shifts to selfing in L. alabamica, but that these transitions are not always associated with a severe population bottleneck, suggesting that factors other than reproductive assurance may play a role in its evolution.
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Affiliation(s)
- Jeremiah W Busch
- School of Biological Sciences and The Center for Reproductive Biology, Washington State University, WA, USA.
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Busch JW, Herlihy CR, Gunn L, Werner WJ. Mixed mating in a recently derived self-compatible population of Leavenworthia alabamica (Brassicaceae). AMERICAN JOURNAL OF BOTANY 2010; 97:1005-1013. [PMID: 21622470 DOI: 10.3732/ajb.1000032] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
PREMISE OF THE STUDY A mixture of outcrossing and selfing is often observed in plant populations. Although mixed mating is ubiquitous, it has several potential evolutionary explanations. Mixed mating may be actively maintained by selection, passively determined by the pollination environment, or a transitional stage during the evolution of self-fertilization. • METHODS We studied patterns of self-compatibility and selfing rates in a population of Leavenworthia alabamica that recently lost self-incompatibility. We also experimentally tested whether natural selection against selfing at the pre- or postzygotic stage is sufficient to explain mixed mating in this population. • KEY RESULTS Visualizing pollen tube growth following self-pollination, we found that nearly all plants were fully self-compatible. Progeny array analysis revealed that the average selfing rate of the population was s = 0.523. The inbreeding coefficient in the parents (F = 0.539) exceeded the amount expected if the selfing rate (s) were constant [F(eq) = s/(2 - s)], indicating either population subdivision or higher selfing rates in the past. Inference of family-level selfing rates revealed substantial variation. Experiments found that self and outcross pollen fertilized nearly equal numbers of ovules in competition. Comparison of seed production following self- or cross-pollination failed to implicate early acting inbreeding depression as a factor maintaining mixed mating. • CONCLUSIONS The results of our experiments suggest that mixed mating is not maintained by selection against self-pollen or zygotes in this population. Mixed mating is most likely a byproduct of the pollination process but may also be a transitional stage during the evolution of higher selfing rates.
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Affiliation(s)
- Jeremiah W Busch
- School of Biological Sciences and the Center for Reproductive Biology, Washington State University, P.O. Box 644236, Pullman, Washington 99164 USA
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Harder LD, Aizen MA. Floral adaptation and diversification under pollen limitation. Philos Trans R Soc Lond B Biol Sci 2010; 365:529-43. [PMID: 20047878 DOI: 10.1098/rstb.2009.0226] [Citation(s) in RCA: 119] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Pollen limitation (PL) of seed production creates unique conditions for reproductive adaptation by angiosperms, in part because, unlike under ovule or resource limitation, floral interactions with pollen vectors can contribute to variation in female success. Although the ecological and conservation consequences of PL have received considerable attention in recent times, its evolutionary implications are poorly appreciated. To identify general influences of PL on reproductive adaptation compared with those under other seed-production limits and their implications for evolution in altered environments, we derive a model that incorporates pollination and post-pollination aspects of PL. Because PL always favours increased ovule fertilization, even when population dynamics are not seed limited, it should pervasively influence selection on reproductive traits. Significantly, under PL the intensity of inbreeding does not determine whether outcrossing or autonomous selfing can evolve, although it can affect which response is most likely. Because the causes of PL are multifaceted in both natural and anthropogenically altered environments, the possible outcrossing solutions are diverse and context dependent, which may contribute to the extensive variety of angiosperm reproductive characteristics. Finally, the increased adaptive options available under PL may be responsible for positive global associations between it and angiosperm diversity.
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Affiliation(s)
- Lawrence D Harder
- Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
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Abstract
Flowering plants display spectacular floral diversity and a bewildering array of reproductive adaptations that promote mating, particularly outbreeding. A striking feature of this diversity is that related species often differ in pollination and mating systems, and intraspecific variation in sexual traits is not unusual, especially among herbaceous plants. This variation provides opportunities for evolutionary biologists to link micro-evolutionary processes to the macro-evolutionary patterns that are evident within lineages. Here, I provide some personal reflections on recent progress in our understanding of the ecology and evolution of plant reproductive diversity. I begin with a brief historical sketch of the major developments in this field and then focus on three of the most significant evolutionary transitions in the reproductive biology of flowering plants: the pathway from outcrossing to predominant self-fertilization, the origin of separate sexes (females and males) from hermaphroditism and the shift from animal pollination to wind pollination. For each evolutionary transition, I consider what we have discovered and some of the problems that still remain unsolved. I conclude by discussing how new approaches might influence future research in plant reproductive biology.
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Affiliation(s)
- Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
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Johnson SD. The pollination niche and its role in the diversification and maintenance of the southern African flora. Philos Trans R Soc Lond B Biol Sci 2010; 365:499-516. [PMID: 20047876 PMCID: PMC2838267 DOI: 10.1098/rstb.2009.0243] [Citation(s) in RCA: 201] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The flora of southern Africa has exceptional species richness and endemism, making it an ideal system for studying the patterns and processes of evolutionary diversification. Using a wealth of recent case studies, I examine the evidence for pollinator-driven diversification in this flora. Pollination systems, which represent available niches for ecological diversification, are characterized in southern Africa by a high level of ecological and evolutionary specialization on the part of plants, and, in some cases, by pollinators as well. These systems are asymmetric, with entire plant guilds commonly specialized for a particular pollinator species or functional type, resulting in obvious convergent floral evolution among guild members. Identified modes of plant lineage diversification involving adaptation to pollinators in these guilds include (i) shifts between pollination systems, (ii) divergent use of the same pollinator, (iii) coevolution, (iv) trait tracking, and (v) floral mimicry of different model species. Microevolutionary studies confirm that pollinator shifts can be precipitated when a plant species encounters a novel pollinator fauna on its range margin, and macroevolutionary studies confirm frequent pollinator shifts associated with lineage diversification. As Darwin first noted, evolutionary specialization for particular pollinators, when resulting in ecological dependency, may increase the risk of plant extinction. I thus also consider the evidence that disturbance provokes pollination failure in some southern African plants with specialized pollination systems.
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Affiliation(s)
- Steven D Johnson
- School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa.
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Barrett SCH. Darwin's legacy: the forms, function and sexual diversity of flowers. Philos Trans R Soc Lond B Biol Sci 2010; 365:351-68. [PMID: 20047864 PMCID: PMC2838255 DOI: 10.1098/rstb.2009.0212] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Charles Darwin studied floral biology for over 40 years and wrote three major books on plant reproduction. These works have provided the conceptual foundation for understanding floral adaptations that promote cross-fertilization and the mechanisms responsible for evolutionary transitions in reproductive systems. Many of Darwin's insights, gained from careful observations and experiments on diverse angiosperm species, remain remarkably durable today and have stimulated much current research on floral function and the evolution of mating systems. Here I review Darwin's seminal contributions to reproductive biology and provide an overview of the current status of research on several of the main topics to which he devoted considerable effort, including the consequences to fitness of cross- versus self-fertilization, the evolution and function of stylar polymorphisms, the adaptive significance of heteranthery, the origins of dioecy and related gender polymorphisms, and the transition from animal pollination to wind pollination. Post-Darwinian perspectives on floral function now recognize the importance of pollen dispersal and male outcrossed siring success in shaping floral adaptation. This has helped to link work on pollination biology and mating systems, two subfields of reproductive biology that remained largely isolated during much of the twentieth century despite Darwin's efforts towards integration.
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Affiliation(s)
- Spencer C H Barrett
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada.
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Johnson SD. The pollination niche and its role in the diversification and maintenance of the southern African flora. Philos Trans R Soc Lond B Biol Sci 2010. [PMID: 20047876 DOI: 10.1098/rstb.2009.024] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2023] Open
Abstract
The flora of southern Africa has exceptional species richness and endemism, making it an ideal system for studying the patterns and processes of evolutionary diversification. Using a wealth of recent case studies, I examine the evidence for pollinator-driven diversification in this flora. Pollination systems, which represent available niches for ecological diversification, are characterized in southern Africa by a high level of ecological and evolutionary specialization on the part of plants, and, in some cases, by pollinators as well. These systems are asymmetric, with entire plant guilds commonly specialized for a particular pollinator species or functional type, resulting in obvious convergent floral evolution among guild members. Identified modes of plant lineage diversification involving adaptation to pollinators in these guilds include (i) shifts between pollination systems, (ii) divergent use of the same pollinator, (iii) coevolution, (iv) trait tracking, and (v) floral mimicry of different model species. Microevolutionary studies confirm that pollinator shifts can be precipitated when a plant species encounters a novel pollinator fauna on its range margin, and macroevolutionary studies confirm frequent pollinator shifts associated with lineage diversification. As Darwin first noted, evolutionary specialization for particular pollinators, when resulting in ecological dependency, may increase the risk of plant extinction. I thus also consider the evidence that disturbance provokes pollination failure in some southern African plants with specialized pollination systems.
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Affiliation(s)
- Steven D Johnson
- School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg 3209, South Africa.
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Mating-system variation, demographic history and patterns of nucleotide diversity in the Tristylous plant Eichhornia paniculata. Genetics 2009; 184:381-92. [PMID: 19917767 DOI: 10.1534/genetics.109.110130] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Inbreeding in highly selfing populations reduces effective size and, combined with demographic conditions associated with selfing, this can erode genetic diversity and increase population differentiation. Here we investigate the role that variation in mating patterns and demographic history play in shaping the distribution of nucleotide variation within and among populations of the annual neotropical colonizing plant Eichhornia paniculata, a species with wide variation in selfing rates. We sequenced 10 EST-derived nuclear loci in 225 individuals from 25 populations sampled from much of the geographic range and used coalescent simulations to investigate demographic history. Highly selfing populations exhibited moderate reductions in diversity but there was no significant difference in variation between outcrossing and mixed mating populations. Population size interacted strongly with mating system and explained more of the variation in diversity within populations. Bayesian structure analysis revealed strong regional clustering and selfing populations were highly differentiated on the basis of an analysis of F(st). There was no evidence for a significant loss of within-locus linkage disequilibrium within populations, but regional samples revealed greater breakdown in Brazil than in selfing populations from the Caribbean. Coalescent simulations indicate a moderate bottleneck associated with colonization of the Caribbean from Brazil approximately 125,000 years before the present. Our results suggest that the recent multiple origins of selfing in E. paniculata from diverse outcrossing populations result in higher diversity than expected under long-term equilibrium.
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Harder LD, Johnson SD. Darwin's beautiful contrivances: evolutionary and functional evidence for floral adaptation. THE NEW PHYTOLOGIST 2009; 183:530-545. [PMID: 19552694 DOI: 10.1111/j.1469-8137.2009.02914.x] [Citation(s) in RCA: 221] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Although not 'a professed botanist', Charles Darwin made seminal contributions to understanding of floral and inflorescence function while seeking evidence of adaptation by natural selection. This review considers the legacy of Darwin's ideas from three perspectives. First, we examine the process of floral and inflorescence adaptation by surveying studies of phenotypic selection, heritability and selection responses. Despite widespread phenotypic and genetic capacity for natural selection, only one-third of estimates indicate phenotypic selection. Second, we evaluate experimental studies of floral and inflorescence function and find that they usually demonstrate that reproductive traits represent adaptations. Finally, we consider the role of adaptation in floral diversification. Despite different diversification modes (coevolution, divergent use of the same pollen vector, pollinator shifts), evidence of pollination ecotypes and phylogenetic patterns suggests that adaptation commonly contributes to floral diversity. Thus, this review reveals a contrast between the inconsistent occurrence of phenotypic selection and convincing experimental and comparative evidence that floral traits are adaptations. Rather than rejecting Darwin's hypotheses about floral evolution, this contrast suggests that the tempo of creative selection varies, with strong, consistent selection during episodes of diversification, but relatively weak and inconsistent selection during longer, 'normal' periods of relative phenotypic stasis.
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Affiliation(s)
- Lawrence D Harder
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
| | - Steven D Johnson
- School of Biological and Conservation Sciences, University of KwaZulu-Natal, Private Bag X01 Scottsville, Pietermaritzburg 3209, South Africa
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