His summary of the principal types of polyploids is useful and is provided below:. Segmental allopolyploid A s A s A t A t. Other investigators have classified polyploids using taxonomic rank as a criterion.
Lewis b used a strictly taxonomic approach, with autopolyploidy and allopolyploidy paralleling intraspecific and interspecific polyploidy, respectively. Perhaps the most widespread current view is to employ a taxonomic approach, reflecting the early views noted above.
Grant's Chapter 26 considered Natural Autopolyploids. Views on the importance of autopolyploidy have changed considerably since Stebbins ; pp. He included Galax aphylla , Biscutella laevigatum , Dactylis glomerata , and Solanum tuberosum Solanaceae. Genetic studies conducted during the s and early s indicated unambiguously that autopolyploidy was much more common than traditionally maintained.
Importantly, autopolyploids should exhibit tetrasomic or higher level inheritance, rather than disomic inheritance. Allozyme markers provided a mechanism for rapidly conducting genetic analyses and assessing mode of inheritance. In addition, genetic data also suggested that most autoploids were formed through some type of hybridization. Although it is now clear that autopolyploids are much more common than traditionally maintained, they are probably not as common as allopolyploids.
There are numerous examples of single taxonomic species with multiple cytotypes, but most of these have not been critically investigated. Many of these polyploid series likely represent autopolyploids or perhaps segmental autopolyploids. A disappointing facet of the current era of systematics is that there has been so much interest in reconstructing phylogenies that investigations of this type in natural populations have largely ceased.
In many ecological studies, for example, there seems to be little concern for the possibility of ploidal level differences putative autopolyploidy within a single taxonomic species. One possible mechanism for garnering attention to the prevalence of autopolyploids is to name diploids and autopolyploids as distinct species Schemske, pers. A related issue is how best to name autopolyploids. However, if each cytotype is named e.
It should be possible to append 2 x and 4 x directly to specific epithets as practical species names e. Tolmiea menziesii 2x and Tolmiea menziesii 4x. He also suggested pp. These include changes in plant size, flowering time, and reproductive output. Molecular data, largely available soon after the publication of Plant Speciation , provided obvious evidence of the intrinsic genetic advantages of allopolyploidy.
Allopolyploids exhibit fixed heterozygosity, representing permanent hybrids and possessing the genes and gene products of both parental diploids.
For dimeric or other multimeric proteins, allopolyploids also have the capacity to produce novel heterodimeric proteins not formed by either diploid parent. The classic analysis of fixed heterozygosity in allopolyploids involved the natural allotetraploids Tragopogon mirus and T.
Fixed heterozygosity could increase the biochemical flexibility of the allopolyploid via biochemical pathways and perhaps provide an advantage compared to diploid progenitors Levin, Enzyme electrophoretic studies revealed that autopolyploids do not have fixed heterozygosity. However, as a result of tetrasomic inheritance, they have higher heterozygosity than their diploid parents and can maintain three or four alleles at a single locus.
Thus, there are strong genetic reasons for the success of autopolyploids in natural populations as well. Several mechanisms may lead to polyploidy in plants. Somatic doubling, at the zygotic, embryonic, or meristematic stage of a plant's life cycle, will ultimately lead to the production of polyploid tissues and possibly the generation of polyploid offspring.
The high incidence of polyploidy in these regions has been accredited to the dominant life form in these floras, namely a perennial habit in which polyploidy is more frequent than annuals or trees Stebbins, ; Ehrendorfer, , or to the greater colonizing ability of polyploids Stebbins, Grant noted that some of the traditional views of polyploid distribution should be discarded, while others required more detailed evaluation. Grant's coverage of ecological factors contributing to the success of polyploids was brief one page. He mentioned two general approaches to the problem: study the frequency of polyploids in different ecological facies of a given flora; make detailed studies of the geographical and ecological distribution of related diploid and polyploid plant species in a particular group.
In recent years there have been exciting discoveries in ecological research and via the second of these approaches. We summarize these results in several new sections below not present in Grant The second hypothesis suggests that a new polyploid may coexist with its diploid parent s as the result of habitat differentiation immediately following the origin of the polyploid. Replacement and habitat differentiation should not be mutually exclusive.
For example, habitat differentiation could contribute to the initial establishment of a new polyploid, but because of higher fitness, this neopolyploid may be able to replace one or both of its diploid progenitors, at least in some areas. Views on the fitness of diploid hybrids have also focused on the availability of novel habitats for hybrid derivatives Anderson, ; Stebbins, Several studies suggest evidence of habitat differentiation among cytotypes e. In general, greater variability in polyploids for morphological, demographic, and phenotypic traits relative to their diploid progenitors is believed to contribute to habitat differentiation.
Octoploid Fragaria chiloensis and F. Habitat differentiation may be so great that polyploids and diploids have different geographic ranges, with little or no overlap e.
[PDF] Biological relevance of polyploidy : ecology to genomics - Semantic Scholar
In some cases, the range of the diploid may represent a subset of the range of the polyploid e. Although the ecological factors at work in these cases have not been examined, differences in the geographic distribution of diploid and tetraploid cytotypes of A. The proportions of insect visitors to plants of different ploidy differ significantly.
However, no major visitor is restricted to plants of either ploidy, allowing for possible gene flow between cytotypes of H. These coordinated studies of the effects of polyploidy on interactions with insect herbivores and pollinators indicate that polyploidy certainly affects patterns of attack and visitation, respectively, and suggest that these effects may differ even among closely related species of herbivores e.
Greya politella and G. Most notable are: are herbivores and pathogens more or less likely to colonize polyploid plants than diploid plants? Answers to these and related questions may clarify the role that plant polyploidy plays in shaping the evolution of interspecific interactions and the organization of terrestrial biodiversity. This pathway to gender dimorphism has occurred in 12 genera involving at least 20 independent evolutionary events.
The Hawaiian silversword alliance Argyroxiphium , Dubautia , and Wilkesia represents perhaps the best known example of adaptive radiation on islands. These species are morphologically diverse in habit rosettes, cushion plants, shrubs, trees, and lianas and floral morphology, and also occupy a wide variety of habitats on six of the eight main islands Baldwin, Bromus carinatus , B.
Magnoliaceae, Cerciphyllaceae, Salicaceae, Hippocastanaceae, and Platanaceae. Several groups of plants have served as models of the study of polyploidy.
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Rather than review all of these examples in detail here, we will point readers to a series of recent reviews from the Polyploidy symposium held in London in May , published in Biological Journal of the Linnean Society. Similarly, molecular genetic work has focused on polyploidy in the legume genus Glycine.
Grant could not have anticipated that Arabidopsis would become a model for the study of floral organ identity and genome evolution including polyploidy.
Crops will continue to be the model systems of choice for the investigation of genetic and genomic aspects of polyploidization. However, several natural systems provide unique model systems in their own right. The time of origin of only a few polyploids is known with certainty. Tragopogon mirus , T. As such, these species represent model systems for the study of recent allopolyploidy.
Recent studies of these three systems illustrate that different polyploids respond to the evolutionary challenges of recent polyploid formation using different mechanisms. In Tragopogon and Senecio , recurrent polyploidy has been important in the spread and success of these plants.
Recurrent polyploidy is also a source of new populations, which is important not only for the success of these new species, but also because local extinction plays a role for these polyploid populations. In contrast to Tragopogon and Senecio , Spartina anglica is the result of a single origin. In fact, a single genotype may be largely involved in the spread of this plant on a worldwide basis much of this mediated by deliberate human introduction.
Related Polyploidy: Biological Relevance
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