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Rapini A, Bitencourt C, Luebert F, Cardoso D. An escape-to-radiate model for explaining the high plant diversity and endemism in campos rupestres†. Biol J Linn Soc Lond 2020. [DOI: 10.1093/biolinnean/blaa179] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Abstract
With extraordinary levels of plant diversity and endemism, the Brazilian campos rupestres across the Espinhaço Range have a species/area ratio 40 times higher than the lowland Amazon. Although diversification drivers in campos rupestres remain a matter of debate, the Pleistocene refugium hypothesis (PRH) is often adopted as the most plausible explanation for their high diversity. The PRH has two main postulates: highland interglacial refugia and a species pump mechanism catalysed by climatic changes. We critically assessed studies on campos rupestres diversification at different evolutionary levels and conclude that most of them are affected by sampling biases, unrealistic assumptions or inaccurate results that do not support the PRH. By modelling the palaeo-range of campos rupestres based on the distribution of 1123 species of vascular plants endemic to the Espinhaço Range and using climate and edaphic variables, we projected a virtually constant suitable area for campos rupestres across the last glacial cycle. We challenge the great importance placed on Pleistocene climatic oscillations in campos rupestres plant diversification and offer an alternative explanation named escape-to-radiate model, which emphasizes niche shifts. Under this biogeographic model of diversification, the long-term fragmentation of campos rupestres combined with recurrent extinctions after genetic drift and sporadic events of adaptive radiation may provide an explanation for the current diversity and endemism in the Espinhaço Range. We conclude that long-term diversification dynamics in campos rupestres are mainly driven by selection, while most endemic diversity is ephemeral, extremely fragile and mainly driven by drift.
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Affiliation(s)
- Alessandro Rapini
- Programa de Pós-graduação em Botânica, Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Av. Transnordestina s.n., Novo Horizonte, Feira de Santana, Bahia, Brazil
| | - Cássia Bitencourt
- Programa de Pós-graduação em Botânica, Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Av. Transnordestina s.n., Novo Horizonte, Feira de Santana, Bahia, Brazil
| | - Federico Luebert
- Departmento de Silvicultura y Conservación de la Naturaleza, Universidad de Chile, Santa Rosa 11315, La Pintana, Santiago, Chile
| | - Domingos Cardoso
- Programa de Pós-graduação em Botânica, Departamento de Ciências Biológicas, Universidade Estadual de Feira de Santana, Av. Transnordestina s.n., Novo Horizonte, Feira de Santana, Bahia, Brazil
- National Institute of Science and Technology in Interdisciplinary and Transdisciplinary Studies in Ecology and Evolution (INCT IN-TREE), Instituto de Biologia, Universidade Federal da Bahia, Rua Barão de Jeremoabo, s.n., Ondina, Salvador, Bahia, Brazil
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Fachardo ALS, Sigrist MR. Pre-zygotic reproductive isolation between two synchronopatric Opuntia (Cactaceae) species in the Brazilian Chaco. PLANT BIOLOGY (STUTTGART, GERMANY) 2020; 22:487-493. [PMID: 31782869 DOI: 10.1111/plb.13077] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Accepted: 11/20/2019] [Indexed: 06/10/2023]
Abstract
Opuntia (Cactaceae) is known for high rates of hybridization and ploidisation, resulting in the formation of new species. The occurrence of two sympatric and closely related species of Opuntia, O. elata and O. retrorsa, in Brazilian Chaco enabled us to test the hypothesis that pre-zygotic reproductive isolation mechanisms operate in both species. We monitored the flowering period, as well as floral biology, and compared the morphological variation of floral structures through measurements, performed intra- and interspecific cross-pollination tests, and recorded the guild of floral visitors and pollinators. Flowering was seasonal and highly synchronous. Floral biology exhibits similar strategies, and although floral morphology differs significantly in many of the compared structures, such morphological variation does not result in the selection of exclusive pollinators. Floral visitors and pollinators are oligolectic bees shared by both species. Opuntia elata and O. retrorsa are self-compatible. While interspecific cross-pollination (bidirectional) resulted in germination, the pollen tube did not penetrate the stigma. Opuntia elata and O. retrorsa are closely related; however, they are isolated and do not hybridise in Brazilian Chaco. We found that both have weak pre-pollination barriers, but that they are strongly isolated by pollen-pistil incompatibility, i.e. post-pollination barrier.
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Affiliation(s)
- A L S Fachardo
- Laboratório de Polinização, Reprodução e Fenologia de Plantas (LPRF) Instituto de Biociências, Universidade Federal de Mato Grosso do Sul, Cidade Universitária, Av. Costa e Silva s/no, Campo Grande, MS, 79070-900, Brazil
| | - M R Sigrist
- Laboratório de Polinização, Reprodução e Fenologia de Plantas (LPRF) Instituto de Biociências, Universidade Federal de Mato Grosso do Sul, Cidade Universitária, Av. Costa e Silva s/no, Campo Grande, MS, 79070-900, Brazil
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Hamlin JAP, Hibbins MS, Moyle LC. Assessing biological factors affecting postspeciation introgression. Evol Lett 2020; 4:137-154. [PMID: 32313689 PMCID: PMC7156103 DOI: 10.1002/evl3.159] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 11/26/2019] [Accepted: 01/12/2020] [Indexed: 12/14/2022] Open
Abstract
An increasing number of phylogenomic studies have documented a clear “footprint” of postspeciation introgression among closely related species. Nonetheless, systematic genome‐wide studies of factors that determine the likelihood of introgression remain rare. Here, we propose an a priori hypothesis‐testing framework that uses introgression statistics—including a new metric of estimated introgression, Dp—to evaluate general patterns of introgression prevalence and direction across multiple closely related species. We demonstrate this approach using whole genome sequences from 32 lineages in 11 wild tomato species to assess the effect of three factors on introgression—genetic relatedness, geographical proximity, and mating system differences—based on multiple trios within the “ABBA–BABA” test. Our analyses suggest each factor affects the prevalence of introgression, although our power to detect these is limited by the number of comparisons currently available. We find that of 14 species pairs with geographically “proximate” versus “distant” population comparisons, 13 showed evidence of introgression; in 10 of these cases, this was more prevalent between geographically closer populations. We also find modest evidence that introgression declines with increasing genetic divergence between lineages, is more prevalent between lineages that share the same mating system, and—when it does occur between mating systems—tends to involve gene flow from more inbreeding to more outbreeding lineages. Although our analysis indicates that recent postspeciation introgression is frequent in this group—detected in 15 of 17 tested trios—estimated levels of genetic exchange are modest (0.2–2.5% of the genome), so the relative importance of hybridization in shaping the evolutionary trajectories of these species could be limited. Regardless, similar clade‐wide analyses of genomic introgression would be valuable for disentangling the major ecological, reproductive, and historical determinants of postspeciation gene flow, and for assessing the relative contribution of introgression as a source of genetic variation.
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Affiliation(s)
| | - Mark S Hibbins
- Department of Biology Indiana University Bloomington Indiana 47405
| | - Leonie C Moyle
- Department of Biology Indiana University Bloomington Indiana 47405
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Emms SK, Hodges SA, Arnold ML. POLLEN-TUBE COMPETITION, SIRING SUCCESS, AND CONSISTENT ASYMMETRIC HYBRIDIZATION IN LOUISIANA IRISES. Evolution 2017; 50:2201-2206. [PMID: 28565672 DOI: 10.1111/j.1558-5646.1996.tb03610.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/1995] [Accepted: 05/14/1996] [Indexed: 11/30/2022]
Abstract
Postpollination mechanisms can play an important role in limiting natural hybridization in plants. Reciprocal hand pollination experiments were performed to study these mechanisms in two species of Louisiana iris: Iris brevicaulis and I. fulva. Relative pollen-tube growth rates changed significantly through time, with I. fulva tubes increasingly outperforming I. brevicaulis tubes in both conspecific and heterospecific styles. However, this pattern of change in relative performance was a poor predictor of siring success: the majority of seeds sired by both maternal species was conspecific rather than hybrid. Experimental crosses and field studies show consistent asymmetric hybridization in Louisiana irises, with I. fulva being a more successful father and a more selective mother than both I. brevicaulis and a third species, I. hexagona. The cause of this pattern is not yet clear, but the pattern itself is unusual. Typically, short-styled species tend to be less successful in reciprocal crosses than long-styled relatives, but I. fulva has shorter styles than either I. brevicaulis or I. hexagona. The effects of pollen-tube competition, differential fertilization, and selective abortion in causing this pattern of asymmetric hybridization is discussed.
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Affiliation(s)
- Simon K Emms
- Department of Genetics, University of Georgia, Athens, Georgia, 30602-7223
| | - Scott A Hodges
- Department of Genetics, University of Georgia, Athens, Georgia, 30602-7223
| | - Michael L Arnold
- Department of Genetics, University of Georgia, Athens, Georgia, 30602-7223
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Carney SE, Hodges SA, Arnold ML. EFFECTS OF DIFFERENTIAL POLLEN-TUBE GROWTH ON HYBRIDIZATION IN THE LOUISIANA IRISES. Evolution 2017; 50:1871-1878. [PMID: 28565590 DOI: 10.1111/j.1558-5646.1996.tb03574.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/1995] [Accepted: 03/19/1996] [Indexed: 11/29/2022]
Abstract
To elucidate the importance of hybridization in evolution, it is necessary to understand the processes that affect hybridization frequency in nature. Here we focus on postpollination, prefertilization isolating mechanisms using two hybridizing species of Louisiana iris as a study system. We compared the effects of differential pollen-tube growth on the frequency of F1 hybrid formation in experimental crosses between Iris fulva and Iris hexagona. Analyses of seed production in fruits from pure conspecific and heterospecific pollinations revealed that more seeds were produced in the top half than the bottom half of fruits for all four crosses. Heterospecific pollen was applied to flowers of each species at zero to 24 h prior to conspecific pollen, thereby giving a head start to the foreign pollen. Using diagnostic isozyme markers, the frequency of hybrid progeny was examined at the level of the whole fruit and separately for the top and bottom halves of fruits. In both species, the proportion of hybrid seeds per fruit increased significantly with increasing head starts, suggesting that differences in pollen-tube growth rates affect the frequency of hybridization. In I. fulva fruits, the increase in hybrid seeds occurred in both halves of the fruits, but in I. hexagona an increase was only detected in the top half of fruits. These findings are consistent with a model that assumes attrition of pollen tubes due to the greater length of I. hexagona styles. While pollen-tube growth rate appears to be the most important factor affecting hybridization frequency in I. fulva, both pollen-tube growth rate and pollen-tube attrition appear to be important in I. hexagona.
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Affiliation(s)
- Shanna E Carney
- Department of Genetics, University of Georgia, Athens, Georgia, 30602
| | - Scott A Hodges
- Department of Genetics, University of Georgia, Athens, Georgia, 30602
| | - Michael L Arnold
- Department of Genetics, University of Georgia, Athens, Georgia, 30602
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Gavrilets S, Cruzan MB. NEUTRAL GENE FLOW ACROSS SINGLE LOCUS CLINES. Evolution 2017; 52:1277-1284. [PMID: 28565387 DOI: 10.1111/j.1558-5646.1998.tb02009.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/1997] [Accepted: 05/04/1998] [Indexed: 12/01/2022]
Abstract
We study the strength of the genetic barrier to neutral gene flow in a general one-locus, two-allele model that includes viability selection as well as fertility selection and premating isolation. We have separately considered adult migration and pollen migration. Our theoretical results suggest that selection against hybrid formation in the form of fertility selection or assortative mating is more effective in preventing introgression of neutral alleles than is reduction in hybrid viability. We argue that in experimental studies of introgression testing of F1 hybrids is as important as testing of parental forms. To illustrate the utility of this approach, we estimate the strength of the barrier to neutral gene flow between Piriqueta caroliniana and P. viridis, between Iris hexagona and I. fulva, and between Chorthippus brunneus and C. biguttulus.
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Affiliation(s)
- Sergey Gavrilets
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, 37996-1610.,Department of Mathematics, University of Tennessee, Knoxville, Tennessee, 37996-1610
| | - Mitchell B Cruzan
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee, 37996-1610.,Department of Botany, University of Tennessee, Knoxville, Tennessee, 37996-1610
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Larcombe MJ, Costa E Silva J, Tilyard P, Gore P, Potts BM. On the persistence of reproductive barriers in Eucalyptus: the bridging of mechanical barriers to zygote formation by F1 hybrids is counteracted by intrinsic post-zygotic incompatibilities. ANNALS OF BOTANY 2016; 118:431-44. [PMID: 27401540 PMCID: PMC4998977 DOI: 10.1093/aob/mcw115] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Accepted: 05/04/2016] [Indexed: 05/04/2023]
Abstract
BACKGROUND AND AIMS Many previous studies conclude that pre-zygotic barriers such as mechanical isolation account for most reproductive isolation between pairs of taxa. However, the inheritance and persistence of barriers such as these after the first generation of hybridization is rarely quantified, even though it is a vital consideration in understanding gene flow potential. There is an asymmetrical pre-zygotic mechanical barrier to hybridization between Eucalyptus nitens and Eucalyptus globulus, which completely prevents small-flowered E. nitens pollen from mating with large E. globulus flowers, while the reverse cross is possible. We aimed to determine the relative importance of pre- and post-zygotic barriers in preventing gene flow following secondary contact between E. nitens and E. globulus, including the inheritance of barriers in advanced-generation hybrids. METHODS Experimental crossing was used to produce outcrossed E. nitens, E. globulus and their F1, F2, BCg and BCn hybrids. The strength and inheritance of a suite of pre- and post-zygotic barriers were assessed, including 20-year survival, growth and reproductive capacity. KEY RESULTS The mechanical barrier to hybridization was lost or greatly reduced in the F1 hybrid. In contrast, intrinsic post-zygotic barriers were strong and persistent. Line-cross analysis indicated that the outbreeding depression in the hybrids was best explained by epistatic loss. CONCLUSIONS The removal of strong mechanical barriers between E. nitens and E. globulus allows F1 hybrids to act as a bridge for bi-directional gene flow between these species. However, strong and persistent post-zygotic barriers exist, meaning that wherever F1 hybridization does occur, intrinsic post-zygotic barriers will be responsible for most reproductive isolation in this system. This potential transient nature of mechanical barriers to zygote formation due to additive inheritance in hybrids appears under-appreciated, and highlights the often important role that intrinsic post-mating barriers play in maintaining species boundaries at zones of secondary contact.
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Affiliation(s)
- Matthew J Larcombe
- Department of Botany, University of Otago, PO Box 56, Dunedin 9011, New Zealand
| | - João Costa E Silva
- Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal
| | - Paul Tilyard
- School of Biological Sciences, and ARC Centre for Forest Value, 10 University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
| | - Peter Gore
- seedEnergy Pty Ltd, 2 Derwent Avenue, Margate, Tasmania 7054, Australia
| | - Brad M Potts
- School of Biological Sciences, and ARC Centre for Forest Value, 10 University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia
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Itoh Y, Sato Y. Genetic dissection of an alien chromosomal segment may enable the production of a rice (Oryza sativa L.) genotype showing shoot developmental instability. Dev Genes Evol 2015; 225:63-78. [PMID: 25677854 DOI: 10.1007/s00427-015-0490-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Accepted: 01/13/2015] [Indexed: 10/24/2022]
Abstract
During the course of evolutionary history, organisms have acquired genes which cooperate harmoniously and subsequently express a stable pattern of development. In an earlier study we introduced a large chromosomal segment of chromosome 6 from a rice (Oryza sativa L.) ecotype, carrying the two flowering-time genes, which showed complex epistatic interactions in relation to environmental change, into a different ecotype by successive backcrossings. Four-near-isogenic lines (NILs) with respect to these two loci were obtained by subsequent hybridization with the recurrent parent. In the study reported here, these four NILs were the major plant material used to evaluate changes in days to leaf appearance (DLA) during shoot development using a quadratic-polynomial regression. The regressions were regarded as developmental norms because of the high values of R (2). Absolute Y-residuals (AYRs) (or size of deviation) of DLA from the norms were significantly affected by genotype. Dissections of the alien chromosomal segment resulted in one NIL that showed an increased level of AYR. Since this NIL also expressed a low survival rate in a stress environment, we suggest that the increased level of AYR during development might indicate an increased level of instability in shoot development.
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Affiliation(s)
- Youki Itoh
- Laboratory of Wildlife Ecology, Department of Environmental Symbiotic Science, College of Agriculture, Food and Environmental Sciences, Rakunogakuen University, Ebetsu, 069-8501, Hokkaido, Japan,
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Abstract
BACKGROUND Our understanding of the processes and dynamics of allopolyploid speciation, the long-term consequences of ploidal change, and the genetic and chromosomal changes in new emerged allopolyploids has substantially increased during the past few decades. Yet we remain uncertain about the time since lineage divergence when two taxa are capable of spawning such entities. Indeed, the matter has seemed intractable. Knowledge of the window of opportunity for allopolyploid production is very important because it provides temporal insight into a key evolutionary process, and a temporal reference against which other modes of speciation may be measured. SCOPE This Viewpoint paper reviews and integrates published information on the crossability of herbaceous species and the fertility of their hybrids in relation to species' divergence times. Despite limitations in methodology and sampling, the estimated times to hybrid sterility are somewhat congruent across disparate lineages. Whereas the waiting time for hybrid sterility is roughly 4-5 million years, the waiting time for cross-incompatibility is roughly 8-10 million years, sometimes considerably more. Strict allopolyploids may be formed in the intervening time window. The progenitors of several allopolyploids diverged between 4 and 6 million years before allopolyploid synthesis, as expected. This is the first study to propose a general temporal framework for strict allopolyploidy. This Viewpoint paper hopefully will stimulate interest in studying the tempo of speciation and the tempo of reproductive isolation in general.
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NOSRATI HOUSHANG, PRICE ADAMH, WILCOCK CHRISTOPHERC. Relationship between genetic distances and postzygotic reproductive isolation in diploid Fragaria (Rosaceae). Biol J Linn Soc Lond 2011. [DOI: 10.1111/j.1095-8312.2011.01744.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Chou JY, Hung YS, Lin KH, Lee HY, Leu JY. Multiple molecular mechanisms cause reproductive isolation between three yeast species. PLoS Biol 2010; 8:e1000432. [PMID: 20652018 PMCID: PMC2907292 DOI: 10.1371/journal.pbio.1000432] [Citation(s) in RCA: 118] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Accepted: 06/10/2010] [Indexed: 11/30/2022] Open
Abstract
Incompatibility between nuclear and mitochondrial genomes in yeast species may represent a general mechanism of reproductive isolation during yeast evolution. Nuclear-mitochondrial conflict (cytonuclear incompatibility) is a specific form of Dobzhansky-Muller incompatibility previously shown to cause reproductive isolation in two yeast species. Here, we identified two new incompatible genes, MRS1 and AIM22, through a systematic study of F2 hybrid sterility caused by cytonuclear incompatibility in three closely related Saccharomyces species (S. cerevisiae, S. paradoxus, and S. bayanus). Mrs1 is a nuclear gene product required for splicing specific introns in the mitochondrial COX1, and Aim22 is a ligase encoded in the nucleus that is required for mitochondrial protein lipoylation. By comparing different species, our result suggests that the functional changes in MRS1 are a result of coevolution with changes in the COX1 introns. Further molecular analyses demonstrate that three nonsynonymous mutations are responsible for the functional differences of Mrs1 between these species. Functional complementation assays to determine when these incompatible genes altered their functions show a strong correlation between the sequence-based phylogeny and the evolution of cytonuclear incompatibility. Our results suggest that nuclear-mitochondrial incompatibility may represent a general mechanism of reproductive isolation during yeast evolution. Hybrids between species are usually inviable or sterile, possibly due to functional incompatibility between genes from the different species. Incompatible genes are hypothesized to encode interacting components that cannot function properly when paired with alleles from another species. To understand how incompatible gene pairs result in hybrid sterility or inviability, it is important to identify these genes and reconstruct their evolutionary history. A previous study has shown that incompatibility between nuclear and mitochondrial genomes (cytonuclear incompatibility) causes hybrid sterility between two yeast species. To expand on these findings, we screened three yeast species for genes involved in cytonuclear incompatibility, discovering two nuclear genes, MRS1 and AIM22, which encode proteins that are unable to support full mitochondrial function in the hybrids. Of these two genes, Mrs1 is required for removing a specific intron in the mitochondrial COX1 gene. By comparing different yeast species, we find a clear coevolutionary relationship between Mrs1 function and the COX1 intron pattern. We also show that changes in three amino acids in the Mrs1 RNA-binding domain are sufficient to make Mrs1 incompatible in hybrids. Our results suggest that cytonuclear incompatibility may represent a general mechanism of reproductive isolation during yeast evolution.
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Affiliation(s)
- Jui-Yu Chou
- Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Yin-Shan Hung
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Kuan-Huei Lin
- Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Hsin-Yi Lee
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- Molecular Cell Biology, Taiwan International Graduate Program, Graduate Institute of Life Sciences, National Defense Medical Center and Academia Sinica, Taipei, Taiwan
| | - Jun-Yi Leu
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- * E-mail:
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Abstract
Gene flow from diploid to polyploid species could have significant effects on the morphology and ecology of polyploids. The potential of such introgression for bringing about evolutionary change within polyploids has long been recognized, although there are few examples of the process in the wild. Here, we focus on introgression between the diploid species, Senecio squalidus, and the tetraploid, S. vulgaris, which resulted in the origin of a variant form of S. vulgaris that produces radiate rather than nonradiate flower heads. The radiate variant of S. vulgaris is more attractive to pollinators and has a higher outcrossing rate. We review recent work that has isolated and characterized two regulatory genes, RAY1 and RAY2, that control presence of ray florets in radiate flower heads, and which have been introgressed into S. vulgaris from S. squalidus in the recent past. We identify a copy of RAY2 in S. vulgaris (RAY2b) homeologous to the copy (RAY2a) previously isolated, thus providing further evidence that S. vulgaris is allotetraploid. We also show that the RAY2a-R allele, which is fixed in radiate S. vulgaris, occurs at intermediate frequency in S. squalidus. Thus, based on this result, it is not possible to distinguish whether radiate S. vulgaris originated once or multiple times following hybridization between nonradiate S. vulgaris and S. squalidus.
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Montgomery BR, Soper DM, Delph LF. Asymmetrical conspecific seed-siring advantage between Silene latifolia and S. dioica. ANNALS OF BOTANY 2010; 105:595-605. [PMID: 20147372 PMCID: PMC2850797 DOI: 10.1093/aob/mcq013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2009] [Revised: 12/04/2009] [Accepted: 12/22/2009] [Indexed: 05/16/2023]
Abstract
BACKGROUND AND AIMS Silene dioica and S. latifolia experience only limited introgression despite overlapping flowering phenologies, geographical distributions, and some pollinator sharing. Conspecific pollen precedence and other reproductive barriers operating between pollination and seed germination may limit hybridization. This study investigates whether barriers at this stage contribute to reproductive isolation between these species and, if so, which mechanisms are responsible. METHODS Pollen-tube lengths for pollen of both species in styles of both species were compared. Additionally, both species were pollinated with majority S. latifolia and majority S. dioica pollen mixes; then seed set, seed germination rates and hybridity of the resulting seedlings were determined using species-specific molecular markers. KEY RESULTS The longest pollen tubes were significantly longer for conspecific than heterospecific pollen in both species, indicating conspecific pollen precedence. Seed set but not seed germination was lower for flowers pollinated with pure heterospecific versus pure conspecific pollen. Mixed-species pollinations resulted in disproportionately high representation of nonhybrid offspring for pollinations of S. latifolia but not S. dioica flowers. CONCLUSIONS The finding of conspecific pollen precedence for pollen-tube growth but not seed siring in S. dioica flowers may be explained by variation in pollen-tube growth rates, either at different locations in the style or between leading and trailing pollen tubes. Additionally, this study finds a barrier to hybridization operating between pollination and seed germination against S. dioica but not S. latifolia pollen. The results are consistent with the underlying cause of this barrier being attrition of S. dioica pollen tubes or reduced success of heterospecifically fertilized ovules, rather than time-variant mechanisms. Post-pollination, pre-germination barriers to hybridization thus play a partial role in limiting introgression between these species.
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Strong post-pollination pre-zygotic isolation between sympatric, food-deceptive Mediterranean orchids. ACTA ACUST UNITED AC 2010; 23:281-9. [DOI: 10.1007/s00497-010-0138-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2009] [Accepted: 03/03/2010] [Indexed: 10/19/2022]
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Ortiz-Barrientos D, Grealy A, Nosil P. The genetics and ecology of reinforcement: implications for the evolution of prezygotic isolation in sympatry and beyond. Ann N Y Acad Sci 2009; 1168:156-82. [PMID: 19566707 DOI: 10.1111/j.1749-6632.2009.04919.x] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Reinforcement, the evolution of prezygotic reproductive barriers by natural selection in response to maladaptive hybridization, is one of the most debated processes in speciation. Critics point to "fatal" conceptual flaws for sympatric evolution of prezygotic isolation, but recent theoretical and empirical work on genetics and ecology of reinforcement suggests that such criticisms can be overcome. New studies provide evidence for reinforcement in frogs, fish, insects, birds, and plants. While such evidence lays to rest the argument over reinforcement's existence, our understanding remains incomplete. We lack data on (1) the genetic basis of female preferences and the links between genetics of pre- and postzygotic isolation, (2) the ecological basis of reproductive isolation, (3) connections between prezygotic isolation between species and within-species sexual selection (potentially leading to a "cascade" of effects on reproductive isolation), (4) the role of habitat versus mate preference in reinforcement, and (5) additional detailed comparative studies. Here, we review data on these issues and highlight why they are important for understanding speciation.
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Ng CH, Lee SL, Ng KKS, Muhammad N, Ratnam W. Mating system and seed variation of Acacia hybrid (A. mangium x A. auriculiformis). J Genet 2009; 88:25-31. [PMID: 19417541 DOI: 10.1007/s12041-009-0004-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The mating system and seed variation of Acacia hybrid (A. mangium x A. auriculiformis) were studied using allozymes and random amplified polymorphic DNA (RAPD) markers, respectively. Multi-locus outcrossing rate estimations indicated that the hybrid was predominantly outcrossed (mean+/- s.e. t(m) = 0.86+/-0.01). Seed variation was investigated using 35 polymorphic RAPD fragments. An analysis of molecular variance (AMOVA) revealed the highest genetic variation among seeds within a pod (66%-70%), followed by among pods within inflorescence (29%-37%), and the least variation among inflorescences within tree (1%). In addition, two to four RAPD profiles could be detected among seeds within pod. Therefore, the results suggest that a maximum of four seeds per pod could be sampled for the establishment of a mapping population for further studies.
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Affiliation(s)
- Chin-Hong Ng
- Genetic Unit, Forest Biotechnology and Pharmaceutical Programme, Forest Research Institute Malaysia,52109 Kepong, Malaysia.
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17
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Xiao L, Lu C, Zhang B, Bo H, Wu Y, Wu G, Cao Y, Yu D. Gene transferability from transgenic Brassica napus L. to various subspecies and varieties of Brassica rapa. Transgenic Res 2009; 18:733-46. [PMID: 19357986 DOI: 10.1007/s11248-009-9261-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Accepted: 03/24/2009] [Indexed: 11/29/2022]
Abstract
Gene transferability from transgenic rapeseed to various subspecies and varieties of Brassica rapa was assessed in this study. Artificial crossability was studied in 118 cultivars of 7 B. rapa subspecies and varieties with the transgenic rapeseed GT73 (Brassica napus) as the pollen donor. On average 5.7 seeds were obtained per pollination, with a range from 0.05 to 19.4. The heading type of B. rapa L. showed significantly higher crossability than non-heading types of B. rapa. The spontaneous outcrossing rate between B. rapa (female) and the transgenic rapeseed Ms8 x Rf3 (B. napus) (male) ranged from 0.039 to 0.406%, with an average of 0.19%. The fertilization process and the development of the hybrid seeds as shown by fluorescent staining techniques indicated that the number of adhered pollens on the stigma was reduced by 80%, the number of pollen tubes in the style was reduced by 2/3 and the fertilization time was delayed by over 20 h when pollinated with the transgenic rapeseed Ms8 x Rf3 in comparison with the bud self-pollination of B. rapa as control. About 10-70% of the interspecific hybrid embryos were aborted in the course of development. Some seeds looked cracked in mature pods, which showed germination abilities lower than 10%. The spontaneous outcrossing rates were much lower than the artificial crossability, and their survival fitness of the interspecific hybrid was very low, indicating that it should be possible to keep the adventitious presence of the off-plants under the allowed threshold, if proper measures are taken.
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Affiliation(s)
- Ling Xiao
- National Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, 210095 Nanjing, China
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18
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Abstract
The importance of hybridization in plant speciation and evolution has been debated for decades, with opposing views of hybridization as either a creative evolutionary force or evolutionary noise. Hybrid speciation may occur at either the homoploid (i.e., between two species of the same ploidy) or the polyploid level, each with its attendant genetic and evolutionary consequences. Whereas allopolyploidy (i.e., resulting from hybridization and genome doubling) has long been recognized as an important mode of plant speciation, the implications of genome duplication have typically not been taken into account in most fields of plant biology. Recent developments in genomics are revolutionizing our views of angiosperm genomes, demonstrating that perhaps all angiosperms have likely undergone at least one round of polyploidization and that hybridization has been an important force in generating angiosperm species diversity. Hybridization and polyploid formation continue to generate species diversity, with several new allopolyploids having originated just within the past century or so. The origins of polyploid species-whether via hybridization between species or between genetically differentiated populations of a single species-and the immediate genetic consequences of polyploid formation are therefore receiving enthusiastic attention. The time is therefore right for a review of the role of hybridization in plant speciation.
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Affiliation(s)
- Pamela S Soltis
- The Genetics Institute, Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611, USA.
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19
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Kay KM, Schemske DW. Natural selection reinforces speciation in a radiation of neotropical rainforest plants. Evolution 2008; 62:2628-42. [PMID: 18637960 DOI: 10.1111/j.1558-5646.2008.00463.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The importance of reinforcement, that is, natural selection that strengthens reproductive isolation between incipient species, remains controversial. We used two approaches to test for reinforcement in a species radiation of Neotropical gingers in the genus Costus. First, we conducted an intensive study of Costus pulverulentus and Costus scaber, two recently diverged species that co-occur and share hummingbird pollinators. The hummingbird pollinators transfer pollen between these Costus species, but hybrids are rarely found in nature. By performing pollinations between populations of C. pulverulentus and C. scaber from three sites across the species' geographic ranges, we find that pollen-pistil incompatibilities acting prior to fertilization have evolved only between locally sympatric populations, whereas geographically distant populations within the region of sympatry and allopatric populations remain fully interfertile. Second, we conducted a comparative study of isolating mechanisms across the genus. We find lower seed set due to pollen-pistil incompatibility between species pairs that co-occur and experience pollen transfer in nature compared to species pairs that are otherwise isolated, regardless of genetic distance. Taken together, these studies indicate that crossing barriers prevent potentially maladaptive hybridization and effectively reinforce the speciation process. Our results add to mounting evidence for reinforcement from animal studies and show that plant speciation may also involve complex mate recognition systems. Reinforcement may be particularly important in rapidly diverging lineages where ecological factors play a primary role in reproductive isolation, as may often be the case in tropical communities.
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Affiliation(s)
- Kathleen M Kay
- Department of Plant Biology, 166 Plant Biology Building, Michigan State University, East Lansing, Michigan 48824, USA.
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20
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Tagane S, Hiramatsu M, Okubo H. Hybridization and asymmetric introgression between Rhododendron eriocarpum and R. indicum on Yakushima Island, southwest Japan. JOURNAL OF PLANT RESEARCH 2008; 121:387-395. [PMID: 18488138 DOI: 10.1007/s10265-008-0167-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2008] [Accepted: 04/10/2008] [Indexed: 05/26/2023]
Abstract
We examined natural hybridization between two morphologically and ecologically divergent species on Yakushima Island-the light-purple flowered Rhododendron eriocarpum native to seaside habitats and the red flowered R. indicum native to riverside habitats. By investigation of morphological traits and amplified fragment length polymorphisms (AFLP) we found that hybrid individuals morphologically and genetically intermediate between the two species grow mainly in the seaside areas of the island. The degree of morphological and genetic variation was different among the seaside hybrid populations. Although most pollinator species were exclusive to one of the two flower color groups, the halictine bees of Lasioglossum were observed in both the color types. The crucial interspecific incompatibility after pollination has not been previously described. Geographic distance between the populations is likely to be an important primary factor in bringing about natural hybridization and determining the degree of introgression between R. eriocarpum and R. indicum. The fact that hybrids occur mostly in the seaside area on Yakushima Island indicates that asymmetrical introgression occurs from R. indicum to R. eriocarpum. Alternatively, strong habitat-mediated selection from recurrent floods may prevent the hybrids from colonizing riverside habitats.
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Affiliation(s)
- Shuichiro Tagane
- Laboratory of Horticultural Science, Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Hakozaki 6-10-1, Fukuoka 812-858, Japan.
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21
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Zhou R, Gong X, Boufford D, Wu CI, Shi S. Testing a hypothesis of unidirectional hybridization in plants: observations on Sonneratia, Bruguiera and Ligularia. BMC Evol Biol 2008; 8:149. [PMID: 18485207 PMCID: PMC2409324 DOI: 10.1186/1471-2148-8-149] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2007] [Accepted: 05/16/2008] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND When natural hybridization occurs at sites where the hybridizing species differ in abundance, the pollen load delivered to the rare species should be predominantly from the common species. Previous authors have therefore proposed a hypothesis on the direction of hybridization: interspecific hybrids are more likely to have the female parent from the rare species and the male parent from the common species. We wish to test this hypothesis using data of plant hybridizations both from our own experimentation and from the literature. RESULTS By examining the maternally inherited chloroplast DNA of 6 cases of F1 hybridization from four genera of plants, we infer unidirectional hybridization in most cases. In all 5 cases where the relative abundance of the parental species deviates from parity, however, the direction is predominantly in the direction opposite of the prediction based strictly on numerical abundance. CONCLUSION Our results show that the observed direction of hybridization is almost always opposite of the predicted direction based on the relative abundance of the hybridizing species. Several alternative hypotheses, including unidirectional postmating isolation and reinforcement of premating isolation, were discussed.
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Affiliation(s)
- Renchao Zhou
- State Key Laboratory of Biocontrol and Key Laboratory of Gene Engineering of the Ministry of Education, Sun Yat-Sen University, Guangzhou 510275, PR China
| | - Xun Gong
- Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204, PR China
| | - David Boufford
- Harvard University Herbaria, 22 Divinity Ave, Cambridge, Massachusetts 02138, USA
| | - Chung-I Wu
- Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637, USA
| | - Suhua Shi
- State Key Laboratory of Biocontrol and Key Laboratory of Gene Engineering of the Ministry of Education, Sun Yat-Sen University, Guangzhou 510275, PR China
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22
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Scopece G, Widmer A, Cozzolino S. Evolution of postzygotic reproductive isolation in a guild of deceptive orchids. Am Nat 2008; 171:315-26. [PMID: 18198999 DOI: 10.1086/527501] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The evolution of reproductive barriers is of central importance for speciation. Here, we investigated three components of postzygotic isolation-embryo mortality, hybrid inviability, and hybrid sterility-in a group of food-deceptive Mediterranean orchids from the genera Anacamptis, Neotinea, and Orchis. In these orchids, pollinator-mediated isolation is weak, which suggests that postpollination barriers exist. Based on crossing experiments and a literature survey, we found that embryo mortality caused complete reproductive isolation among 36.3% of the species pairs, and hybrid inviability affected 55.6% of the potentially hybridizing species pairs. Hybrid sterility was assessed experimentally for seven species pairs. A strong reduction of fertility in all investigated hybrids was found, together with clear differences between male and female components of hybrid sterility. Postzygotic isolation was found to evolve gradually with genetic divergence, and late postzygotic isolation (i.e., hybrid inviability and sterility) evolved faster than embryo mortality, which is an earlier postzygotic isolation stage. These results reveal that intrinsic postzygotic isolation strongly contributes to maintaining species boundaries among Mediterranean food-deceptive orchids while establishing a prominent role for these reproductive barriers in the early stage of species isolation.
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Affiliation(s)
- Giovanni Scopece
- Dipartimento delle Scienze Biologiche, Università degli Studi di Napoli Federico II, Via Foria 223, I-80139 Naples, Italy
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23
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DIJK PETERVAN, HARTOG MARIJKE, DELDEN WILKEVAN. Single cytotype areas in autopolyploid Plantago media L.*. Biol J Linn Soc Lond 2008. [DOI: 10.1111/j.1095-8312.1992.tb00867.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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24
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Scopece G, Musacchio A, Widmer A, Cozzolino S. Patterns of reproductive isolation in Mediterranean deceptive orchids. Evolution 2007; 61:2623-42. [PMID: 17908246 DOI: 10.1111/j.1558-5646.2007.00231.x] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The evolution of reproductive isolation is of central interest in evolutionary biology. In plants, this is typically achieved by a combination of pre- and postpollination mechanisms that prevent, or limit, the amount of interspecific gene flow. Here, we investigated and compared two ecologically defined groups of Mediterranean orchids that differ in pollination biology and pollinator specificity: sexually deceptive orchids versus food-deceptive orchids. We used experimental crosses to assess the strength of postmating prezygotic, and postzygotic reproductive isolation, and a phylogenetic framework to determine their relative rates of evolution. We found quantitative and qualitative differences between the two groups. Food-deceptive orchids have weak premating isolation but strong postmating isolation, whereas the converse situation characterizes sexually deceptive orchids. Only postzygotic reproductive isolation among food-deceptive orchids was found to evolve in a clock-like manner. Comparison of evolutionary rates, within a common interval of genetic distance, showed that the contribution of postmating barriers was more relevant in the food-deceptive species than in the sexually deceptive species. Asymmetry in prezygotic isolation was found among food-deceptive species. Our results indicate that postmating barriers are most important for reproductive isolation in food-deceptive orchids, whereas premating barriers are most important in sexually deceptive orchids. The different rate of evolution of reproductive isolation and the relative strength of pre- and postmating barriers may have implication for speciation processes in the two orchid groups.
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Affiliation(s)
- Giovanni Scopece
- Dipartimento delle Scienze Biologiche, Università degli Studi di Napoli Federico II, Via Foria, 223, I-80139 Naples, Italy.
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25
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Gegear RJ, Burns JG. The birds, the bees, and the virtual flowers: can pollinator behavior drive ecological speciation in flowering plants? Am Nat 2007; 170:551-66. [PMID: 17891734 DOI: 10.1086/521230] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2006] [Accepted: 04/19/2007] [Indexed: 11/03/2022]
Abstract
Biologists have long assumed that pollinator behavior is an important force in angiosperm speciation, yet there is surprisingly little direct evidence that floral preferences in pollinators can drive floral divergence and the evolution of reproductive (ethological) isolation between incipient plant species. In this study, we expose computer-generated plant populations with a wide variation in flower color to selection by live and virtual hummingbirds and bumblebees and track evolutionary changes in flower color over multiple generations. Flower color, which was derived from the known genetic architecture and phenotypic variance of naturally occurring plant species pollinated by both groups, evolved in simulations through a genetic algorithm in which pollinator preference determined changes in flower color between generations. The observed preferences of live hummingbirds and bumblebees were strong enough to cause adaptive divergence in flower color between plant populations but did not lead to ethological isolation. However, stronger preferences assigned to virtual pollinators in sympatric and allopatric scenarios rapidly produced ethological isolation. Pollinators can thus drive ecological speciation in flowering plants, but more rigorous and comprehensive behavioral studies are required to specify conditions that produce sufficient preference levels in pollinators.
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Affiliation(s)
- Robert J Gegear
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada.
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26
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Barrett SCH. THE LIFE AND TIMES OF PLANT SPECIES: FROM METAPOPULATIONS TO MUTATIONAL MELTDOWN1. Evolution 2007. [DOI: 10.1111/j.0014-3820.2001.tb00798.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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27
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van der Niet T, Johnson SD, Linder HP. Macroevolutionary data suggest a role for reinforcement in pollination system shifts. Evolution 2006; 60:1596-601. [PMID: 17017060 DOI: 10.1554/05-705.1] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Reproductive isolation can evolve either as a by-product of divergent selection or through reinforcement. We used the Cape flora of South Africa, known for its high level of pollination specialization, as a model system to test the potential role of shifts in pollination system in the speciation process. Comparative analysis of 41 sister-species pairs (representing Geraniaceae, Iridaceae, and Orchidaceae) for which complete pollinator, edaphic, and distribution data are available showed that for sister species with overlapping distribution ranges, pollination system shifts are significantly associated with edaphic shifts. In contrast, there is no significant association between pollination system shifts and edaphic shifts for allopatric sister species. These results are interpreted as evidence for reinforcement.
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Affiliation(s)
- Timotheüs van der Niet
- Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, 8008, Zurich, Switzerland.
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28
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Niet T, Johnson SD, Linder HP. MACROEVOLUTIONARY DATA SUGGEST A ROLE FOR REINFORCEMENT IN POLLINATION SYSTEM SHIFTS. Evolution 2006. [DOI: 10.1111/j.0014-3820.2006.tb00504.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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29
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Kay KM. REPRODUCTIVE ISOLATION BETWEEN TWO CLOSELY RELATED HUMMINGBIRD-POLLINATED NEOTROPICAL GINGERS. Evolution 2006. [DOI: 10.1554/05-339.1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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30
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Ippolito A, Fernandes GW, Holtsford TP. Pollinator preferences for Nicotiana alata, N. forgetiana, and their F1 hybrids. Evolution 2004; 58:2634-44. [PMID: 15696743 DOI: 10.1111/j.0014-3820.2004.tb01617.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The role of pollinators in plant speciation and maintenance of species boundaries is dubious because most plant species are visited by several types of pollinators, and most pollinator species visit several species of plants. We investigated pollinator preferences and their efficacy as ethological isolation mechanisms between two interfertile species, Nicotiana alata and N. forgetiana and their F1 hybrids. Hawkmoths pollinate N. alata, while primarily hummingbirds and occasionally small hawkmoths visit N. forgetiana. F1 hybrids are easily produced in the greenhouse and although the species grow in similar habitats, hybrids have not been found in nature. In Rio Grande do Sul, Brazil, near where both species are found, experimental plots were studied containing both species, and both species plus F1 hybrids. In the mixed-species plots, hawkmoths showed a strong preference for N. alata. Hummingbirds were less common and only visited N. forgetiana. Hybrid seed was produced but plants made significantly fewer hybrid offspring than predicted by the frequency of interspecific pollinator movements. Nicotiana forgetiana was the seed parent of 97% of the F1 offspring, suggesting an asymmetry in pollen delivery or postpollination processes. In plots containing F1 hybrids plus both parental species, hawkmoths preferred N. alata and undervisited the other two phenotypes, except that in the third plot they visited hybrids in proportion to the hybrid frequency. Hummingbirds strongly preferred N. forgetiana in all plots but also visited F1 hybrids in proportion to their frequency in the third plot. Overall, F1 hybrids were well pollinated and were frequently visited immediately before or after one of the parental species. Thus hybrids could facilitate gene flow between the parental species. We conclude that pollinator discrimination among species is strong but is an imperfect isolation mechanism, especially if hybrids are present.
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Affiliation(s)
- Anthony Ippolito
- Division of Biological Sciences, University of Missouri [corrected] Columbia, Missouri [corrected] 65211-7400, USA
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31
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Abstract
Analyses among animal species have found that reproductive isolation increases monotonically with genetic distance, evolves more quickly for prezygotic than postzygotic traits, and is stronger among sympatric than allopatric species pairs. The latter pattern is consistent with expectations under the reinforcement hypothesis. To determine whether similar trends are found among plant species, patterns of reproductive isolation (postpollination prezygotic, postzygotic, and "total" isolation) in three plant genera (Glycine, Silene, Streptanthus) were examined using data from previously published artificial hybridization experiments. In Silene, all measures of reproductive isolation were positively correlated with genetic distance. In contrast, in Glycine and Streptanthus, correlations between reproductive isolation and genetic distance were weak or nonsignificant, possibly due to the influence of biologically unusual taxa, variable evolutionary forces acting in different lineages, or insufficient time to accumulate reproductive isolation. There was no evidence that postpollination prezygotic reproductive isolation evolved faster than postzygotic isolation in Glycine or Silene. We also detected no evidence for faster accumulation of postmating prezygotic isolation between sympatric than allopatric species pairs; thus we found no evidence for the operation of speciation via reinforcement. In Silene, which included six polyploid species, results suggest that changes in ploidy disrupt a simple monotonic relationship between isolation and genetic distance.
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Affiliation(s)
- Leonie C Moyle
- Department of Biology, Duke University, Durham, North Carolina 27708, USA.
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32
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Dagne K. Meiosis in Interspecific Hybrids and Genomic Interrelationships in Guizotia Cass. (Compositae). Hereditas 2004. [DOI: 10.1111/j.1601-5223.1994.00119.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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van der Velde M, Bijlsma R. Hybridization and asymmetric reproductive isolation between the closely related bryophyte taxa Polytrichum commune and P. uliginosum. Mol Ecol 2004; 13:1447-54. [PMID: 15140089 DOI: 10.1111/j.1365-294x.2004.02154.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Based on genetic differentiation, the haploid dioecious bryophyte taxa Polytrichum commune and P. uliginosum have been inferred to be completely reproductively isolated. However, analysing diploid sporophytes from a sympatric population for three diagnostic microsatellite markers, we show here that reproductive isolation between these taxa is far more complex and highly asymmetric. Isolation between female-P. communex male-P. uliginosum seems to be complete and prezygotic (or early postzygotic) as no hybrid sporophytes were observed on P. commune females. In the other direction ( female-P. uliginosumx male-P. commune) isolation was clearly postzygotic as high frequencies of hybrid sporophytes were found on P. uliginosum females. However, during maturation these sporophytes showed irregular development, indicating that hybrid sporophytes are unlikely to produce ripe spores. Mechanisms possibly underlying this asymmetric reproductive isolation pattern are discussed. Notwithstanding hybrid offspring being unlikely, the high frequency of hybrid sporophytes observed suggests that viable spores may be formed occasionally through such rare processes as chromosome nondisjunction, possibly giving rise to allodiploids. Allodiploids have been reported in Polytrichum (and other bryophyte genera). Studies such as the one presented here will therefore help to elucidate the evolutionary importance of interspecific hybridization and allodiploidization in bryophyte speciation.
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Affiliation(s)
- M van der Velde
- Evolutionary Genetics, University of Groningen, Kerklaan 30, NL-9751 NN Haren, The Netherlands.
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34
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Moyle LC, Olson MS, Tiffin P. PATTERNS OF REPRODUCTIVE ISOLATION IN THREE ANGIOSPERM GENERA. Evolution 2004. [DOI: 10.1554/03-511] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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35
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Ippolito A, Wilson Fernandes G, Holtsford TP. POLLINATOR PREFERENCES FOR NICOTIANA ALATA, N. FORGETIANA, AND THEIR F1 HYBRIDS. Evolution 2004. [DOI: 10.1554/02-686] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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36
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Kimball RT, Crawford DJ, Smith EB. EVOLUTIONARY PROCESSES IN THE GENUS COREOCARPUS: INSIGHTS FROM MOLECULAR PHYLOGENETICS. Evolution 2003. [DOI: 10.1554/0014-3820(2003)057[0052:epitgc]2.0.co;2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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37
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Kimball RT, Crawford DJ, Smith EB. Evolutionary processes in the genus Coreocarpus: insights from molecular phylogenetics. Evolution 2003; 57:52-61. [PMID: 12643567 DOI: 10.1111/j.0014-3820.2003.tb00215.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A molecular phylogenetic study of the plant genus Coreocarpus was conducted using nuclear (ITS) and plastid (rpl16 intron) DNA sequences, with phylogenies of the nuclear and plastid sequences highly congruent in defining a monophyletic group of six species (core Coreocarpus), although three other species often placed within the genus were excluded. Relationships within the genus are largely but not totally concordant with prior biosystematic studies. Despite strong molecular support, no morphological characters uniting the six species of core Coreocarpus have been identified; retention of plesiomorphic characters and the genetic lability of characters are two probable factors contributing to lack of consistent defining characters. The age of the core Coreocarpus is estimated at 1 million years because the basal species is endemic to a volcanic island that emerged in the past million years. Mapping the results of earlier breeding studies on the molecular phylogeny showed that use of cross-compatibility as a criterion for species delimitation would result in the recognition of paraphyletic species. Prior field, morphological, and biosystematic studies provided no indication of past hybridization in the evolution of Coreocarpus, and species in the genus appeared to be well defined morphologically. However, three instances of incongruence were observed. Two of these were between the nuclear and plastid partitions, and the third was between the morphological species assignment of one accession and the molecular data. If hybridization accounts for incongruence between the nuclear and plastid data, it occurred between species that now appear to be cross-incompatible and allopatric. The incongruence between morphological species assignment and the molecular data could be the result of parallel fixation of characters that have a simple genetic basis. This study suggests that the evolutionary history of Coreocarpus is much more complex than indicated from prior biosystematic investigations and that biosystematic and molecular phylogenetic studies may complement each other for elucidating the evolution and phylogeny of a group.
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Affiliation(s)
- Rebecca T Kimball
- Department of Zoology, University of Florida, PO Box 118525, Gainesville, Florida 32611, USA.
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38
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Abstract
Patterns of reproductive isolation between species may provide insight into the mechanisms and evolution of barriers to interspecific gene exchange. We used data from published interspecific hybridization experiments from 14 genera of angiosperms in order to test for the presence of asymmetrical barriers to gene exchange. Reproductive isolation was examined at three life-history stages: the ability of interspecific crosses to produce seeds, the viability of F1 hybrids, and the fertility of F1 hybrids. Statistically significant asymmetries in the strength of reproductive isolation between species were detected in all genera and at each of the three life-history stages. Asymmetries in seed production may be caused by a variety of mechanisms including differences in stigma/style lengths, self compatibility and differential fruit abortion. Asymmetries in post-zygotic isolation are probably caused by nuclear-cytoplasmic interactions. Asymmetrical reproductive isolation between plant taxa may have important implications for the dynamics of hybrid zones, the direction of genetic introgression and the probability of reinforcement.
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Affiliation(s)
- P Tiffin
- Department of Ecology and Evolutionary Biology, University of California Irvine, 92697, USA.
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Waser NM, Price MV, Shaw RG. Outbreeding depression varies among cohorts of Ipomopsis aggregata planted in nature. Evolution 2000; 54:485-91. [PMID: 10937225 DOI: 10.1111/j.0014-3820.2000.tb00051.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Outbreeding depression in progeny fitness may arise from disruption of local adaptation, disruption of allelic coadaptation, or a combination of these "environmental" and "physiological" mechanisms. Thus the minimum spatial scale over which outbreeding depression arises should depend on the spatial scale of gene dispersal and (with an environmental mechanism) of change in selection regimes. We previously reported substantial outbreeding depression in lifetime fitness of progeny resulting from crosses among parents separated by 100 m in natural populations of the herbaceous plant Ipomopsis aggregata. In this paper we explore the effect of crossing distance on fitness in two additional experiments begun in 1987 and 1990. We planted seed progeny derived from partial diallel crossing designs in randomized blocks in maternal environments and scored emergence of seedlings, survival, and eventual flowering of individuals over the subsequent six to eight years. Nested within each diallel design were crossing distances of 1 m, 10 m, and 100 m. Compared to 1-m and 10-m progeny, 100-m progeny of the 1987 diallel suffered a significant reduction in seedling emergence, and both 1-m and 100-m progeny that survived to flower achieved lower lambda-values on average than 10-m progeny. Total outbreeding depression suffered by 100-m relative to 10-m progeny was approximately 10%, compared to approximately 30% in our earlier study of I. aggregata. Progeny of 10-m crosses also outperformed 1-m and 100-m progeny of the 1990 diallel by approximately 5%, but no difference among crossing distance treatments was significant. Thus, the magnitude of outbreeding depression in 100-m crosses varied among experiments. This is not surprising given likely spatial and temporal variation in gene flow and selection regimes, different population histories, and different parental and progeny environments. Characterizing outbreeding depression on the shortest spatial scales over which it is expressed, as well as its variation and causes, is worthwhile because it promises to shed light on the earliest stages of angiosperm speciation.
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Affiliation(s)
- N M Waser
- Department of Biology, University of California, Riverside 92521, USA.
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Bohs L. Insights into the Witheringia solanacea (Solanaceae) Complex in Costa Rica. II. Insect Visitors and Pollination Biology of W. asterotricha and W. meiantha1. Biotropica 2000. [DOI: 10.1111/j.1744-7429.2000.tb00450.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Williams JH, Friedman WE, Arnold ML. Developmental selection within the angiosperm style: using gamete DNA to visualize interspecific pollen competition. Proc Natl Acad Sci U S A 1999; 96:9201-6. [PMID: 10430920 PMCID: PMC17757 DOI: 10.1073/pnas.96.16.9201] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Among flowering plants, females often have little control over the genetic relatedness of pollen deposited on stigmas. Thus, postpollination processes are of primary importance for mate discrimination. The ability to screen and select among male gametes during pollen tube growth within the female tissues of the stigma, style, and ovary is critical to the process of mate choice and reproductive isolation. However, direct evidence of the mechanistic/developmental processes associated with mate choice in flowering plants is sparse. We studied the contribution of postpollination, prefertilization processes to reproductive isolation in two wind-pollinated species of birch (Betula) that commonly hybridize in nature. We exploited the 3-fold difference in ploidy level between these two species to determine the paternity of individual pollen tubes growing within female reproductive tissues. We then tracked their developmental fate in conspecific, heterospecific, and mixed-species crosses. This design allowed a direct comparison of developmental processes responsible for reproductive isolation in both single-species and mixed-species pollinations. Our results have important implications for the population genetic outcome of hybridization dynamics in natural populations. Paternity analysis of progeny from mixed-species pollinations revealed that conspecific pollen tubes sired more than 98% of seedlings. Biased siring success was not the result of differential embryo abortion. We detected strong, early postpollination barriers such as pollen tube incompatibility, slower pollen tube growth, and delayed generative cell mitosis. Conspecific fertilization precedence was mediated by favorable or unfavorable male-female interactions, but there was no evidence for antagonistic male-male interactions.
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Affiliation(s)
- J H Williams
- Department of Genetics, University of Georgia, Athens, GA 30602-7223, USA.
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Van Dijkt P, Van Delden W. Evidence for autotetraploidy in Plantago media and comparisons between natural and artificial cytotypes concerning cell size and fertility. Heredity (Edinb) 1990. [DOI: 10.1038/hdy.1990.104] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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Pollination system and its significance on isolation and hybridization in JapaneseEpimedium (Berberidaceae). ACTA ACUST UNITED AC 1984. [DOI: 10.1007/bf02488670] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Wallace B, Timm MW, Strambi MPP. The Establishment of Novel Mate-Recognition Systems in Introgressive Hybrid Drosophila Populations. Evol Biol 1983. [DOI: 10.1007/978-1-4615-6971-8_9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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