<h4>Background</h4>Biological invasions are a major ecological and socio-economic problem in many parts of the world. Despite an explosion of research in recent decades, much remains to be understood about why some species become invasive whereas others do not. Recently, polyploidy (whole genome duplication) has been proposed as an important determinant of invasiveness in plants. Genome duplication has played a major role in plant evolution and can drastically alter a plant's genetic make-up, morphology, physiology and ecology within only one or a few generations. This may allow some polyploids to succeed in strongly fluctuating environments and/or effectively colonize new habitats and, thus, increase their potential to be invasive.<h4>Scope</h4>We synthesize current knowledge on the importance of polyploidy for the invasion (i.e. spread) of introduced plants. We first aim to elucidate general mechanisms that are involved in the success of polyploid plants and translate this to that of plant invaders. Secondly, we provide an overview of ploidal levels in selected invasive alien plants and explain how ploidy might have contributed to their success.<h4>Conclusions</h4>Polyploidy can be an important factor in species invasion success through a combination of (1) 'pre-adaptation', whereby polyploid lineages are predisposed to conditions in the new range and, therefore, have higher survival rates and fitness in the earliest establishment phase; and (2) the possibility for subsequent adaptation due to a larger genetic diversity that may assist the 'evolution of invasiveness'. Alternatively, polyploidization may play an important role by (3) restoring sexual reproduction following hybridization or, conversely, (4) asexual reproduction in the absence of suitable mates. We, therefore, encourage invasion biologists to incorporate assessments of ploidy in their studies of invasive alien species.

The role of natural selection in speciation, first described by Darwin, has finally been widely accepted. Yet, the nature and time course of the genetic changes that result in speciation remain mysterious. To date, genetic analyses of speciation have focused almost exclusively on retrospective analyses of reproductive isolation between species or subspecies and on hybrid sterility or inviability rather than on ecologically based barriers to gene flow. However, if we are to fully understand the origin of species, we must analyze the process from additional vantage points. By studying the genetic causes of partial reproductive isolation between specialized ecological races, early barriers to gene flow can be identified before they become confounded with other species differences. This population-level approach can reveal patterns that become invisible over time, such as the mosaic nature of the genome early in speciation. Under divergent selection in sympatry, the genomes of incipient species become temporary genetic mosaics in which ecologically important genomic regions resist gene exchange, even as gene flow continues over most of the genome. Analysis of such mosaic genomes suggests that surprisingly large genomic regions around divergently selected quantitative trait loci can be protected from interrace recombination by “divergence hitchhiking.” Here, I describe the formation of the genetic mosaic during early ecological speciation, consider the establishment, effects, and transitory nature of divergence hitchhiking around key ecologically important genes, and describe a 2-stage model for genetic divergence during ecological speciation with gene flow.

Rare yet accumulating evidence in both plants and animals shows that whole genome duplication (WGD, leading to polyploidy) can break down reproductive barriers, facilitating gene flow between otherwise isolated species. Recent population genomic studies in wild, outcrossing Arabidopsis arenosa and Arabidopsis lyrata indicate that this WGD-potentiated gene flow can be adaptive and highly specific in response to particular environmental and intracellular challenges. The mechanistic basis of WGD-mediated easing of species barrier strength seems to primarily lie in the relative dosage of each parental genome in the endosperm. While generalisations about polyploids can be fraught, this evidence indicates that the breakdown of these barriers, combined with diploid to polyploid gene flow and gene flow between polyploids, allows some polyploids to act as adaptable 'allelic sponges', enjoying increased potential to respond to challenging environments.

The highest frequency of polyploidy among plants is considered to occur in the Pteridophytes. In this study, we focused on polyploidy displayed by a specific fern taxon, the genus Pteris L. (Pteridaceae), comprising over 250 species. Cytological data from 106 Pteris species were reviewed. The base number of chromosomes in Pteris is 29. Polyploids are frequently found in Pteris, including triploids, tetraploids, pentaploids, hexaploids, and octoploids. In addition, an aneuploid species, P. deltodon Bak., has been recorded. Furthermore, the relationship between polyploidy and reproductive biology is reviewed. Among these 106 Pteris species, 60% exhibit polyploidy: 22% show intraspecific polyploidy and 38% result from polyploid speciation. Apogamous species are common in Pteris. Diploids are the most frequent among Pteris species, and they can be sexual or apogamous. Triploids are apogamous; tetraploids are sexual or apogamous. Most Pteris species have one to two ploidy levels. The diverse ploidy levels suggest that these species have a complex evolutionary history and their taxonomic problems require further clarification.

Mulberry, belonging to the order Rosales, family Moraceae, and genus Morus, has received attention because of both its economic and medicinal value, as well as for its important ecological function. The genus Morus has a worldwide distribution, however, its taxonomy remains complex and disputed. Many studies have attempted to classify Morus species, resulting in varied numbers of designated Morus spp. To address this issue, we used information from internal transcribed spacer (ITS) genetic sequences to study the taxonomy of all the members of generally accepted genus Morus. We found that intraspecific 5.8S rRNA sequences were identical but that interspecific 5.8S sequences were diverse. M. alba and M. notabilis showed the shortest (215 bp) and the longest (233 bp) ITS1 sequence length, respectively. With the completion of the mulberry genome, we could identify single nucleotide polymorphisms within the ITS locus in the M. notabilis genome. From reconstruction of a phylogenetic tree based on the complete ITS data, we propose that the Morus genus should be classified into eight species, including M. alba, M. nigra, M. notabilis, M. serrata, M. celtidifolia, M. insignis, M. rubra, and M. mesozygia. Furthermore, the classification of the ITS sequences of known interspecific hybrid clones into both paternal and maternal clades indicated that ITS variation was sufficient to distinguish interspecific hybrids in the genus Morus.

Groups with morphological stasis are an interesting framework to address putative cryptic species that may be hidden behind traditional taxonomic treatments, particularly when distribution ranges suggest disjunct and environmentally heterogeneous biogeographic patterns. New hypotheses of delimitation of evolutionary independent units can lead to the identification of different biogeographic processes, laying the foundation to investigate their historical and ecological significance. Jasione is a plant genus with a distribution centered in the Mediterranean basin, characterized by significant morphological stasis. Within the western Mediterranean J. gr. crispa species complex, J. sessiliflora s.l. and allied taxa form a distinct group, occupying environmentally diverse regions. At least two ploidy levels, diploid and tetraploid, are known to occur in the group. The internal variability is assessed with phylogenetic tools, viz. GMYC and ASAP, for species delimitation. The results are compared with other lines of evidence, including morphology and cytology. The fitting of distribution patterns of the inferred entities to chorological subprovinces is also used as a biogeographical and environmental framework to test the species hypothesis. Despite the scarcity of diagnostic morphological characters in the group, phylogenetic delimitation supports the description of at least one cryptic species, a narrow endemic in the NE Iberian Peninsula. Moreover, the results support the segregation of a thermophilic group of populations in eastern Iberia from J. sessiliflora. Ploidy variation from a wide geographical survey supports the systematic rearrangement suggested by species delimitation. Taxonomic reorganization in J. sessiliflora s.l. would allow ecological interpretations of distribution patterns in great accordance with biogeographical regionalization at the subprovince level, supporting geobotanical boundaries as a framework to interpret species ecological coherence of cryptic lineages. These results suggest that species differentiation, together with geographic isolation and polyploidization, is associated with adaptation to different environments, shifting from more to less thermophilic conditions. Thus, the recognition of concealed evolutionary entities is essential to correctly interpret biogeographical patterns in regions with a complex geologic and evolutionary history, such as the Mediterranean basin, and biogeographical units emerge as biologically sound frameworks to test the species hypothesis.

Polyploid organisms evolve from their initial doubled genomic condition through a number of processes collectively termed diploidization, whose tempo and mode remain poorly understood mainly due to the difficulty of discriminating de novo evolution subsequent to polyploidy from variation inherited from progenitors. Here, we generated chromosome-scale genome assemblies for the wild rice allopolyploid <i>Oryza minuta</i> and its two diploid progenitors, <i>Oryza punctata</i> and <i>Oryza officinalis</i>, and employed a population genomic approach to investigate the diploidization process in <i>O. minuta</i> at the sequence and transcriptomic level. We show that this wild rice allopolyploid originated around 0.7 Mya, and during subsequent diploidization, its two subgenomes have retained highly conserved synteny with the genomes of its extant diploid progenitors. This populational approach allowed us to distinguish parental legacy of inherited variation from postpolyploidy evolution, and our analyses revealed that whereas gene fractionation occurred in an early burst, accumulation of transposable elements (TEs) and homoeologous exchanges has been gradual. Patterns of homoeolog expression bias are highly variable across tissues, with no consistent subgenome expression bias. Our assessments of the impact of DNA methylation, TE distribution, and parental legacy on expression patterns provide some support for the TE load theory (the theory that the TE densities in flanking regions surrounding genes strongly influence expression levels), while also illustrating the complexity of transcription regulation.

Abstract Background Polyploidy (whole-genome duplication) is an important speciation mechanism, particularly in plants. Gene loss, silencing, and the formation of novel gene complexes are some of the consequences that the new polyploid genome may experience. Despite the recurrent nature of polyploidy, little is known about the genomic outcome of independent polyploidization events. Here, we analyze the fate of genes duplicated by polyploidy (homoeologs) in multiple individuals from ten natural populations of Tragopogon miscellus (Asteraceae), all of which formed independently from T. dubius and T. pratensis less than 80 years ago. Results Of the 13 loci analyzed in 84 T. miscellus individuals, 11 showed loss of at least one parental homoeolog in the young allopolyploids. Two loci were retained in duplicate for all polyploid individuals included in this study. Nearly half (48%) of the individuals examined lost a homoeolog of at least one locus, with several individuals showing loss at more than one locus. Patterns of loss were stochastic among individuals from the independently formed populations, except that the T. dubius copy was lost twice as often as T. pratensis . Conclusion This study represents the most extensive survey of the fate of genes duplicated by allopolyploidy in individuals from natural populations. Our results indicate that the road to genome downsizing and ultimate genetic diploidization may occur quickly through homoeolog loss, but with some genes consisten

Polyploidy, the presence of more than two chromosome sets, is rare in animals, but is wide spread in plants. Polyploidy is believed to play an important role in speciation and diversification of plants. It is conjectured that almost all angiosperms are likely to be ancient polyploids i.e. palaeopolyploids that have undergone diploidization through differential mutation, elimination and inversion of duplicated chromosomes. Therefore, understanding of consequences of gene duplication on functional divergence, developmental behavior and genome stability is of utmost importance from utilitarian view point. Studies conducted by our group for over a quarter century on the cyotogenetics of polyploids on an array of medicinal and aromatic plants have enabled us to develop strategies to realize high fertility in the autotetraploids. It is surmised that pre-selection of diploid progenitor with low chiasmate association, preferably with distal chiasma localization facilitates high bivalent pairing and balanced meiotic segregation in the derived autotetraploid, and thereby promising high fertility. This has implications in ploidy mediated fixation of heterozygosity and genetic enhancement. However, the elevated ploidy level does not always bring about increase in body size. Both, increase or decrease in body size happen to occur consequent to genomic duplication, depending upon the species and composition of native secondary metabolites / cost of metabolic load. Of course, polyploidizati

Abstract Background Most, if not all, green plant (Virdiplantae) species including angiosperms and ferns are polyploids themselves or have ancient polyploid or whole genome duplication signatures in their genomes. Polyploids are not only restricted to our major crop species such as wheat, maize, potato and the brassicas, but also occur frequently in wild species and natural habitats. Polyploidy has thus been viewed as a major driver in evolution, and its influence on genome and chromosome evolution has been at the centre of many investigations. Mechanistic models of the newly structured genomes are being developed that incorporate aspects of sequence evolution or turnover (low-copy genes and regulatory sequences, as well as repetitive DNAs), modification of gene functions, the re-establishment of control of genes with multiple copies, and often meiotic chromosome pairing, recombination and restoration of fertility. Scope World-wide interest in how green plants have evolved under different conditions – whether in small, isolated populations, or globally – suggests that gaining further insight into the contribution of polyploidy to plant speciation and adaptation to environmental changes is greatly needed. Forward-looking research and modelling, based on cytogenetics, expression studies, and genomics or genome sequencing analyses, discussed in this Special Issue of the Annals of Botany, consider how new polyploids behave and the pathways available for genome evolution. They add

These new gametes will be incompatible with the normal gametes that this plant species produces. However, they could either self-pollinate or reproduce with other autopolyploid plants with gametes having the same diploid number. In this way, sympatric speciation can occur quickly by forming offspring with 4n that we call a tetraploid. These individuals would immediately be able to reproduce only with those of this new kind and not those of the ancestral species. The other form of polyploidy occurs when individuals of two different species reproduce to form a viable offspring that we call an allopolyploid. The prefix “allo-” means “other” (recall from allopatric): therefore, an allopolyploid occurs when gametes from two different species combine. Figure 18.16 illustrates one possible way an allopolyploid can form. Notice how it takes two generations, or two reproductive acts, before the viable fertile hybrid results. The cultivated forms of wheat, cotton, and tobacco plants are all allopolyploids. Although polyploidy occurs occasionally in animals, it takes place most commonly in plants.

The cultivated forms of wheat, cotton, and tobacco plants are all allopolyploids. Although polyploidy occurs occasionally in animals, it takes place most commonly in plants. (Animals with any of the types of chromosomal aberrations described here are unlikely to survive and produce normal offspring.) Scientists have discovered more than half of all plant species studied relate back to a species evolved through polyploidy. With such a high rate of polyploidy in plants, some scientists hypothesize that this mechanism takes place more as an adaptation than as an error. Create a visual representation such as a diagram with annotation to explain how island chains provide ideal conditions for allopatric speciation and adaptive radiation to occur. Then design a plan for collecting data to support the claim that speciation has occurred. Given enough time, the genetic and phenotypic divergence between populations will affect characters that influence reproduction: if individuals of the two populations were to be brought together, mating would be less likely, but if mating occurred, offspring would be non-viable or infertile.

major contributor to speciation is the subject of much ongoing discussion. Rapid sympatric speciation can take place through polyploidy, such as by doubling Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages. Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book On the Origin of Species. He also identifie Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within lineages. Charles Darwin was the first to describe the role of natural selection in speciation in his 1859 book On the Origin of Species. He also identified sexual selection as a likely mechanism, but found it problematic. There are four geographic modes of speciation in nature, based on the extent to which speciating populations are isolated from one another: allopatric, peripatric, parapatric, and sympatric. Whether genetic drift is a minor or major contributor to speciation is the subject of much ongoing discussion. Rapid sympatric speciation can take place through polyploidy,… Polyploidy is a mechanism that has caused many rapid speciation events in sympatry because offspring of, for example, tetraploid x diploid matings often result in triploid sterile progeny. However, among plants, not all polyploids are reproductively isolated from their parents, and gene flow may still occur, such as through triploid hybrid x diploid matings that produce tetraploids, or matings between meiotically unreduced gametes from diploids and gametes from tetraploids (see also hybrid speciation). It has been suggested that many of the existing plant and most animal species have undergone an event of polyploidization in their evolutionary history. Reproduction of successful polyploid species is sometimes asexual, by parthenogenesis or apomixis, as for unknown reasons many asexual organisms are polyploid. Rare instances of polyploid mammals are known, but most often result in prenatal death.

Hybridization and polyploidy are the two main evolutionary mechanisms that fundamentally drive plant speciation. With the use of contemporary genomic techniques like long-read sequencing, pangenomics, phylogenomic networks, and epigenomic profiling, these processes long acknowledged by evolutionary biologists have now been revealed in previously unheard-of detail. While polyploidy, particularly allopolyploidy, produces immediate reproductive isolation, unique gene interactions, and subgenome specialization, hybridization promotes adaptive introgression, gene flow, and the creation of hybrid species. When combined, these processes result in ecological innovation, regulatory divergence, and genetic reorganization, allowing plants to quickly diversify and colonize new habitats. This review emphasizes important case studies, summarizes genetic insights into hybridization and polyploidy, and addresses upcoming difficulties in comprehending reticulate evolution and the intricate histories of plant lineages.

and 17-year Magicicada species. allo-parapatric speciation A mode of speciation where divergence occurs in allopatry and is completed upon secondary contact This glossary of genetics and evolutionary biology is a list of definitions of terms and concepts used in the study of genetics and evolutionary biology, as well as sub-disciplines and related fields, with an emphasis on classical genetics, quantitative genetics, population biology, phylogenetics, speciation, and systematics. It has been designed as a companion to Glossary of cellular and molecul hybrid The offspring that results from combining the qualities of two organisms of different genera, species, breeds, or varieties through sexual reproduction. Hybrids may occur naturally or artificially, as during selective breeding of domesticated animals and plants. Reproductive barriers typically prevent hybridization between distantly related organisms, or at least ensure that hybrid offspring are sterile, but fertile hybrids may result in speciation.

interdemic selection 196 Speciation through polyploidy 199 The role of hybridization in … with it. Given enough time, marked changes can occur in this way. Thus, the genetic composition … this l- of the "general" type, which can occur within a caste, sex, age, and or seasonal