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Journal ArticleDOI

Crop-to-wild gene flow, introgression and possible fitness effects of transgenes.

TL;DR: Key examples of crop/wild sympatry and overlapping flowering phenology, pollen and seed dispersal, the barriers to hybridisation and introgression, the evolution and fate of interspecific hybrids, their fitness, and the potential cost of transgenes are reviewed.
Abstract: Crop-to-wild gene flow has received close attention over the past ten years in connection with the development and cultivation of transgenic crops. In this paper, we review key examples of crop/wild sympatry and overlapping flowering phenology, pollen and seed dispersal, the barriers to hybridisation and introgression, the evolution and fate of interspecific hybrids, their fitness, and the potential cost of transgenes. We pay particular attention to ways in which the evolution and divergence between crops and their wild relatives may interfere with these successive steps. Our review suggests that crop-to-weed gene flow is highly idiosyncratic and that crop gene dispersion will certainly be very difficult to preclude totally. Future directions for research should thus focus on the long-term establishment and effects of transgenes on natural communities.

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Citations
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Journal ArticleDOI
TL;DR: Research effort should now focus on estimating any changes in the fitness of a population as a consequence of having a transgene, understanding genotype x environment interactions, and deducing the extent to which pathogens and herbivores (transgene targets) regulate wild relative populations.
Abstract: One of the concerns raised over the introduction of genetically modified crops is that transgenes will invade populations of wild relatives, causing ecologically significant changes in fitness. In recent years, this has given rise to several studies estimating hybridization rates and the fitness of crop–wild relative hybrids. These studies have established that transgenes are likely to move to F1 hybrids, albeit at low frequency. Hybridization, however, is not synonymous with introgression, and questions remain as to whether particular transgenes will cause ecologically significant changes in recipient plant populations. Research effort should now focus on estimating any changes in the fitness of a population as a consequence of having a transgene, understanding genotype × environment interactions, and deducing the extent to which pathogens and herbivores (transgene targets) regulate wild relative populations. This will involve a combination of manipulative experiments and empirically motivated mathematical models.

170 citations

Journal ArticleDOI
TL;DR: It is demonstrated that transgene flow from short‐term production can result in establishment of transgenic plants at multi‐kilometre distances from GM source fields or plants, both in the presence or absence of herbicide selection.
Abstract: Concerns about genetically modified (GM) crops include transgene flow to compatible wild species and unintended ecological consequences of potential transgene introgression. However, there has been little empirical documentation of establishment and distribution of transgenic plants in wild populations. We present herein the first evidence for escape of transgenes into wild plant populations within the USA; glyphosate-resistant creeping bentgrass ( Agrostis stolonifera L.) plants expressing CP4 EPSPS transgenes were found outside of cultivation area in central Oregon. Resident populations of three compatible Agrostis species were sampled in nonagronomic habitats outside the Oregon Department of Agriculture control area designated for test production of glyphosate-resistant creeping bentgrass. CP4 EPSPS protein and the corresponding transgene were found in nine A. stolonifera plants screened from 20 400 samples (0.04 ± 0.01% SE). CP4 EPSPS -positive plants were located predominantly in mesic habitats downwind and up to 3.8 km beyond the control area perimeter; two plants were found within the USDA Crooked River National Grassland. Spatial distribution and parentage of transgenic plants (as confirmed by analyses of nuclear ITS and chloroplast matK gene trees) suggest that establishment resulted from both pollen-mediated intraspecific hybridizations and from crop seed dispersal. These results demonstrate that transgene flow from short-term production can result in establishment of transgenic plants at multi-kilometre distances from GM source fields or plants. Selective pressure from direct application or drift of glyphosate herbicide could enhance introgression of CP4 EPSPS transgenes and additional establishment. Obligatory outcrossing and vegetative spread could further contribute to persistence of CP4 EPSPS transgenes in wild Agrostis populations, both in the presence or absence of herbicide selection.

146 citations

Journal ArticleDOI
TL;DR: Diversity in improved varieties grown by farmers needs to be monitored, as the introduction of transgenic technologies has led to a consolidation of the seed industry and a reduction in the diversity of the elite crop gene pool.
Abstract: Gene flow is a potential concern associated with the use of transgenic crops because it could affect genetic diversity of related landraces and wild relatives. This concern has taken on added importance with the looming introduction of transgenic crops in centers of crop domestication (Mexico, China) and those producing pharmaceutical compounds. For gene flow to take place among cultivars and their wild relatives, several steps have to be fulfilled, including the presence of cultivars or wild relatives within pollen or seed dispersal range, the ability to produce viable and fertile hybrids, at least partial overlap in flowering time, actual gene flow by pollen or seed, and the establishment of crop genes in the domesticated or wild recipient populations. In contrast with domestication genes, which often make crops less adapted to natural ecosystems, transgenes frequently represent gains of function, which might release wild relatives from constraints that limit their fitness. In most sexually reproducing organisms, the chromosomal region affected by selection of a single gene amounts to a small percentage of the total genome size. Because of gene flow, the level of genetic diversity present in the domesticated gene pool becomes a crucial factor affecting the genetic diversity of the wild gene pool. For some crops, such as cotton and maize, the introduction of transgenic technologies has led to a consolidation of the seed industry and a reduction in the diversity of the elite crop gene pool. Thus, diversity in improved varieties grown by farmers needs to be monitored. Several areas deserve further study, such as the actual magnitude of gene flow and its determinants in different agroecosystems, the long-term effects of gene flow on genetic diversity both across gene pools and within genomes, the expression of transgenes in new genetic backgrounds, and the effects of socio-economic factors on genetic diversity.

137 citations


Cites background from "Crop-to-wild gene flow, introgressi..."

  • ...For a more detailed analysis of some of the steps in this process, see the review by Jenczewski et al. (2003)....

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  • ...For a more detailed analysis of some of the steps in this process, see the review by Jenczewski et al. (2003). Each of these steps can be investigated with a series of experiments....

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01 Jan 2013
TL;DR: The status and trends in aquaculture genetic resources: a basis for international policy was discussed at a workshop organized by FAO and the World Fisheries Trust in 2006 as mentioned in this paper, where experts in the fields of agriculture, biotechnology, fishery genetics, international development and policy analyzed the status of aquatic genetic resources.
Abstract: In May 2006, the FAO’s Fisheries and Aquaculture Management Division and the Secretariat of the Commission convened, with the World Fisheries Trust, an international workshop on The Status and Trends in Aquatic Genetic Resources: a Basis for International Policy.This document provides a summary of the proceedings and the outcomes of the workshop. Experts in the fields of aquaculture, biotechnology, fishery genetics, international development and policy analyzed the status of aquatic genetic resources, and trends in their conservation and use, in both capture fisheries and aquaculture. The Report of the Workshop and its conclusions identify key policy issues, priorities and implications for the international development community, in particular FAO and its Commission on Genetic Resources for Food and Agriculture in addressing the rapidly evolving needs of the sector. The executive summaries of their presentations are also given in this document.

133 citations


Cites background from "Crop-to-wild gene flow, introgressi..."

  • ...The above are not requirements for gene flow, but they may significantly affect the frequency of flow and probability of introgression (Jenczewski et al., 2003)....

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  • ...The extent of this overlap can indicate the likelihood of hybridization (Jenczewski et al., 2003)....

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  • ...Therefore, plants that may normally fall outside of the necessary proximities and compatibilities are not definitively denied access to genes, but they may receive them less frequently (Jenczewski et al., 2003)....

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Journal ArticleDOI
Bao-Rong Lu1, Chao Yang1
TL;DR: A framework for assessing potential ecological consequences caused by transgene escape from GM rice to its wild relatives is discussed based on studies of gene flow and fitness changes.

115 citations


Cites background from "Crop-to-wild gene flow, introgressi..."

  • ...…from previous studies: 1) the frequency of gene flow that allows transgenes being transferred to wild populations; 2) the fitness of early hybrids relative to their wild parents, and 3) possible fitness costs or benefits that are associated with a particular transgene (Jenczewski et al., 2002)....

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  • ...For the estimation of long-term persistence and spread of transgenes in wild rice population in relation to the fitness change, three key factors should be take into consideration, given that knowledge of the close genetic relationships and high compatibility among the AA-genome Oryza species are obtained from previous studies: 1) the frequency of gene flow that allows transgenes being transferred to wild populations; 2) the fitness of early hybrids relative to their wild parents, and 3) possible fitness costs or benefits that are associated with a particular transgene (Jenczewski et al., 2002)....

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References
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Book
30 Jan 1997
TL;DR: This chapter discusses natural hybridization in the context of reproductive parameters, species concepts, and the role that technology has played in shaping human evolution.
Abstract: Chapter 1 Natural Hybridization: Definitions and History Chapter 2 Natural Hybridization and Species Concepts Chapter 3 Natural Hybridization: Frequency Chapter 4 Reproductive Parameters and Natural Hybridization Chapter 5 Natural Hybridization: Concepts and Theory Chapter 6 Natural Hybridization: Outcomes Chapter 7 Natural Hybridization: Emerging Patterns

2,053 citations


"Crop-to-wild gene flow, introgressi..." refers background in this paper

  • ...Note that mating systems and differences in ploidy levels are not the only reproductive barriers that can limit crop-to-wild gene flow (see Arnold, 1997; Rieseberg, 1997; Rieseberg and Carney, 1998 for review)....

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Journal ArticleDOI
TL;DR: The results indicate that the triploid bridge pathway can contribute significantly to autopolyploids formation regardless of the mating system, and to allopolyploid formation in outcrossing taxa.
Abstract: Polyploidy is widely acknowledged as a major mechanism of adaptation and speciation in plants. The stages in polyploid evolution include frequent fertility bottlenecks and infrequent events such as gametic nonreduction and interspecific hybridization, yet little is known about how these and other factors influence overall rates of polyploid formation. Here we review the literature regarding polyploid origins, and quantify parameter values for each of the steps involved in the principal pathways. In contrast to the common claim that triploids are sterile, our results indicate that the triploid bridge pathway can contribute significantly to autopolyploid formation regardless of the mating system, and to allopolyploid formation in outcrossing taxa. We estimate that the total rate of autotetraploid formation is of the same order as the genic mutation rate (10 i5 ), and that a high frequency of interspecific hybridization (0.2% for selfing taxa, 2.7% for outcrossing taxa) is required for the rate of tetraploid formation via allopolyploidy to equal that by autopolyploidy. We conclude that the rate of autopolyploid formation may often be higher than the rate of allopolyploid formation. Further progress toward understanding polyploid origins requires studies in natural populations that quantify: (a) the frequency of unreduced gametes, (b) the effectiveness of triploid bridge pathways, and (c) the rates of interspecific hybridization.

1,715 citations


"Crop-to-wild gene flow, introgressi..." refers background in this paper

  • ...The presence of either unreduced gametes or endomitosis after fertilization leads to production of fertile allopolyploid F1 hybrids containing each of the parental genomes at the diploid stage (Bretagnolle and Thompson, 1995; Ramsey and Schemske, 1998)....

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  • ...The resulting triploid hybrids are not as systematically sterile as previously considered; some of them are able to produce euploid gametes and can thus serve as a bridges for gene flow or the formation of new polyploid species (Ramsey and Schemske, 1998)....

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  • ...Detailed reviews have recently addressed the mechanisms controlling polyploidization (Bretagnolle and Thompson, 1995; Ramsey and Schemske, 1998) and hybrid speciation (Rieseberg, 1997)....

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Journal ArticleDOI
TL;DR: This model does not represent the only evolutionary pathway to invasiveness, but is clearly an underappreciated mechanism worthy of more consideration in explaining the evolution ofInvasiveness in plants.
Abstract: Invasive species are of great interest to evolutionary biologists and ecologists because they represent historical examples of dramatic evolutionary and ecological change. Likewise, they are increasingly important economically and environmentally as pests. Obtaining generalizations about the tiny fraction of immigrant taxa that become successful invaders has been frustrated by two enigmatic phenomena. Many of those species that become successful only do so (i) after an unusually long lag time after initial arrival, and/or (ii) after multiple introductions. We propose an evolutionary mechanism that may account for these observations. Hybridization between species or between disparate source populations may serve as a stimulus for the evolution of invasiveness. We present and review a remarkable number of cases in which hybridization preceded the emergence of successful invasive populations. Progeny with a history of hybridization may enjoy one or more potential genetic benefits relative to their progenitors. The observed lag times and multiple introductions that seem a prerequisite for certain species to evolve invasiveness may be a correlate of the time necessary for previously isolated populations to come into contact and for hybridization to occur. Our examples demonstrate that invasiveness can evolve. Our model does not represent the only evolutionary pathway to invasiveness, but is clearly an underappreciated mechanism worthy of more consideration in explaining the evolution of invasiveness in plants.

1,355 citations

Journal ArticleDOI

1,339 citations


"Crop-to-wild gene flow, introgressi..." refers background in this paper

  • ...Evolution and fate of interspecific hybrids: genetic mechanisms of introgression and speciation Introgression, the permanent incorporation of genes from one set of differentiated populations into another (Rieseberg and Wendel, 1993), is viewed as a common Environ....

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  • ...Although introgression between wild and domesticated plants is suspected to be widespread (De Wet and Harlan, 1975; Harlan, 1992; Rieseberg and Wendel, 1993; Ellstrand et al., 1999), it has rarely been demonstrated in wild populations (Luby and McNicol, 1995; Whitton et al., 1997; Linder et al.,…...

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Journal ArticleDOI
01 Jul 1927
TL;DR: This work shall first consider initial conditions, when only a few of the new type exist as the result of a single mutation; and then the course of events in a population where the new factor is present in such numbers as to be in no danger of extinction by mere bad luck.
Abstract: New factors arise in a species by the process of mutation. The frequency of mutation is generally small, but it seems probable that it can sometimes be increased by changes in the environment (1,2). On the whole mutants recessive to the normal type occur more commonly than dominants. The frequency of a given type of mutation varies, but for some factors in Drosophila it must be less than 10−6, and is much less in some human cases. We shall first consider initial conditions, when only a few of the new type exist as the result of a single mutation; and then the course of events in a population where the new factor is present in such numbers as to be in no danger of extinction by mere bad luck. In the first section the treatment of Fisher (3) is followed.

1,282 citations