Polyploidization (whole-genome duplication, WGD) is a widespread large-effect macromutation with far-reaching genomic, phenotypic, and evolutionary consequences. Yet, we do not know whether the consistent phenotypic changes that are associated with polyploidization translate into predictable changes in ecological preferences. Niche modeling studies in mixed-ploidy species provide an opportunity to compare recently originated polyploids with their lower-ploidy ancestors. However, the available isolated studies provide contrasting results and the diverse methodologies used limit generalization. Based on 25,857 georeferenced ploidy-verified occurrence data for 129 mixed-ploidy flowering plant species, we tested in a unified statistical framework whether WGD is associated with consistent changes in climatic niche and in past, current, and predicted future range size. We found that 74% of species exhibited significant niche shifts associated with ploidy transition. However, there was no consistent environmental parameter underlying ploidy differentiation across species, nor was there consistent support for polyploid range or niche expansion in a subset of 75 densely sampled species with sufficient data for modeling. Our results demonstrate that polyploidization is an important factor affecting niche evolution of a species, but the environmental parameters underlying the ploidy-related niche shifts vary from species to species, demonstrating limited predictability of the outcomes of WGD in ecological space.

• Keywords
• ecological differentiation, environmental niche modelling, meta-analysis, niche evolution, polyploidy,
• MeSH
• Biological Evolution MeSH
• Gene Duplication * MeSH
• Ecosystem * MeSH
• Genome, Plant * MeSH
• Magnoliopsida * genetics   MeSH
• Ploidies MeSH
• Climate * MeSH
• Polyploidy * MeSH
• Publication type
• Journal Article MeSH

The triploid block, primarily caused by endosperm developmental issues, is known as a significant barrier to interploidy hybridization among flowering plants and, thereby, polyploid speciation. However, its strength varies across taxa, with some instances of leakiness, questioning its universal role as a barrier. We conducted a literature survey to explore the causes of the variation in the strength of the triploid block across 11 angiosperm families. We assessed the impact of interploidy cross direction, types of endosperm development, endosperm persistence at seed maturity, and divergence between cytotypes using a Bayesian meta-analysis. We found a significant influence of the type of endosperm in shaping variation in triploid block strength. Other factors tested had no impact on triploid seed viability, probably due to limited data and inconsistencies in estimation methods across the literature. In addition, triploid seed viability in experimental crosses was sometimes correlated to the occurrence of triploid hybrids in nature, sometimes not, suggesting a mixed role for the triploid block in shaping interspecies gene flow. Altogether, our study highlights the need for unified approaches in future studies on the triploid block to advance our understanding of its variation and evolutionary implications.

• Keywords
• Endosperm development, hybrid seed lethality, interploidy gene flow, natural variation, polyploidy speciation, triploid block,
• MeSH
• Biological Evolution * MeSH
• Endosperm genetics   growth & development   MeSH
• Hybridization, Genetic MeSH
• Magnoliopsida * genetics   MeSH
• Polyploidy * MeSH
• Seeds genetics   MeSH
• Gene Flow MeSH
• Triploidy * MeSH
• Genetic Speciation * MeSH
• Publication type
• Journal Article MeSH
• Meta-Analysis MeSH
• Review MeSH

Polyploidisation is a significant reproductive barrier, yet genetic evidence indicates that interploidy admixture is more common than previously thought. Theoretical models and controlled crosses support the 'triploid bridge' hypothesis, proposing that hybrids of intermediate ploidy facilitate gene flow. However, comprehensive evidence combining experimental and genetic data from natural mixed-ploidy species is missing. Here, we investigated the rates and directionality of gene flow within a diploid-autotetraploid contact zone of Cardamine amara, a species with abundant natural triploids. We cytotyped over 400 individuals in the field, conducted reciprocal interploidy crosses, and inferred gene flow based on genome-wide sequencing of 84 individuals. Triploids represent a conspicuous entity in mixed-ploidy populations (5%), yet only part of them arose through interploidy hybridisation. Despite being rarely formed, triploid hybrids can backcross with their parental cytotypes, producing viable offspring that are often euploid (in 42% of cases). In correspondence, D-statistics and coalescent simulations documented a significant genome-wide signal of bidirectional gene flow in sympatric but not allopatric populations. Triploids, though rare, thus seem to play a key role in overcoming polyploidy-related reproductive barriers in C. amara. In sum, we present integrative evidence for interploidy gene flow mediated by a triploid bridge in natural populations.

• Keywords
• introgression, polyploidy, population genomics, speciation, whole genome duplication,
• MeSH
• Cardamine * genetics   MeSH
• Genetic Introgression * MeSH
• Hybridization, Genetic MeSH
• Ploidies * MeSH
• Polyploidy MeSH
• Genetics, Population MeSH
• Gene Flow * MeSH
• Triploidy * MeSH
• Publication type
• Journal Article MeSH

BACKGROUND: The genus Allium is known for its high chromosomal variability, but most chromosome counts are based on a few individuals and genome size (GS) reports are limited in certain taxonomic groups. This is evident in the Allium sect. Codonoprasum, a species-rich (> 150 species) and taxonomically complex section with weak morphological differences between taxa, the presence of polyploidy and frequent misidentification of taxa. Consequently, a significant proportion of older karyological reports may be unreliable and GS data are lacking for the majority of species within the section. This study, using chromosome counting and flow cytometry (FCM), provides the first comprehensive and detailed insight into variation in chromosome number, polyploid frequency and distribution, and GS in section members, marking a step towards understanding the unresolved diversification and evolution of this group. RESULTS: We analysed 1578 individuals from 316 populations of 25 taxa and reported DNA ploidy levels and their GS, with calibration from chromosome counts in 22 taxa. Five taxa had multiple ploidy levels. First estimates of GS were obtained for 16 taxa. A comprehensive review of chromosome number and DNA-ploidy levels in 129 taxa of the section revealed that all taxa have x = 8, except A. rupestre with two polyploid series (x = 8, descending dysploidy x = 7), unique for this section. Diploid taxa dominated (72.1%), while di- & polyploid (12.4%) and exclusively polyploid (15.5%) taxa were less common. Ploidy diversity showed that diploid taxa dominated in the eastern Mediterranean and decreased towards the west and north, whereas only polyploid cytotypes of di- & polyploid taxa or exclusively polyploid taxa dominated in northern and northwestern Europe. A 4.1-fold variation in GS was observed across 33 taxa analysed so far (2C = 22.3-92.1 pg), mainly due to polyploidy, with GS downsizing observed in taxa with multiple ploidy levels. Intra-sectional GS variation suggests evolutionary relationships, and intraspecific GS variation within some taxa may indicate taxonomic heterogeneity and/or historical migration patterns. CONCLUSIONS: Our study showed advantages of FCM as an effective tool for detecting ploidy levels and determining GS within the section. GS could be an additional character in understanding evolution and phylogenetic relationships within the section.

• Keywords
• Chromosome number, Cytogeography, DNA ploidy level, Flow cytometry, Genome size, Polyploidy,
• Publication type
• Journal Article MeSH

BACKGROUND: Whole-genome duplication (polyploidization) is a dominant force in sympatric speciation, particularly in plants. Genome doubling instantly poses a barrier to gene flow owing to the strong crossing incompatibilities between individuals differing in ploidy. The strength of the barrier, however, varies from species to species and recent genetic investigations revealed cases of rampant interploidy introgression in multiple ploidy-variable species. SCOPE: Here, we review novel insights into the frequency of interploidy gene flow in natural systems and summarize the underlying mechanisms promoting interploidy gene flow. Field surveys, occasionally complemented by crossing experiments, suggest frequent opportunities for interploidy gene flow, particularly in the direction from diploid to tetraploid, and between (higher) polyploids. However, a scarcity of accompanying population genetic evidence and a virtual lack of integration of these approaches leave the underlying mechanisms and levels of realized interploidy gene flow in nature largely unknown. Finally, we discuss potential consequences of interploidy genome permeability on polyploid speciation and adaptation and highlight novel avenues that have just recently been opened by the very first genomic studies of ploidy-variable species. Standing in stark contrast with rapidly accumulating evidence for evolutionary importance of homoploid introgression, similar cases in ploidy-variable systems are yet to be documented. CONCLUSIONS: The genomics era provides novel opportunity to re-evaluate the role of interploidy introgression in speciation and adaptation. To achieve this goal, interdisciplinary studies bordering ecology and population genetics and genomics are needed.

• Keywords
• Adaptation, evolution, genetic introgression, polyploidy, speciation, whole-genome duplication,
• MeSH
• Biological Evolution MeSH
• Genome, Plant genetics   MeSH
• Ploidies MeSH
• Polyploidy * MeSH
• Plants genetics   MeSH
• Reproduction genetics   MeSH
• Gene Flow * MeSH
• Genetic Speciation MeSH
• Publication type
• Journal Article MeSH
• Review MeSH

Odd ploidy-level cytotypes in sexually reproducing species are considered a dead end due to absent or reduced fertility. If sterility is only partial, however, their contribution to the population gene pool can be augmented by longevity and clonal growth. To test this, we investigated the cytotype origin and spatial pattern, and pollen viability in three relict shrub species of the genus Daphne (Thymelaeaceae Juss.) in central Europe. Daphne cneorum subsp. cneorum is a widespread European species that has a broad ecological amplitude, whereas D. cneorum subsp. arbusculoides and D. arbuscula are narrow endemics of the western Pannonian Plain and the Western Carpathians, respectively. Our study confirmed that all three taxa are diploid. However, of more than a thousand analysed individuals of D. cneorum subsp. cneorum, five in four different populations were triploid. Our data indicate that these triploids most likely originate from recurrent autopolyploidization events caused by the fusion of reduced and unreduced gametes. High pollen viability was observed in all three taxa and in both diploid and triploid cytotypes, ranging from 65 to 100 %. Our study highlights the significant role of odd ploidy-level cytotypes in interploidy gene flow, calling for more research into their reproduction, genetic variability, and overall fitness. Interestingly, while the endemic D. arbuscula differs from D. cneorum based on genetic and genome size data, D. cneorum subsp. arbusculoides was indistinguishable from D. cneorum subsp. cneorum. However, our study reveals that the subspecies differ in the number of flowers per inflorescence. This is the first comprehensive cytogeographic study of this intriguing genus at a regional scale, and in spite of its karyological stability, it contributes to our understanding of genomic evolution in plant species with a wide ecological amplitude.

• Keywords
• Carpathians, Daphne, ITS, Pannonian Basin, endemics, genome size stasis, pollen fertility, polyploidy, relicts, triploids,
• Publication type
• Journal Article MeSH

BACKGROUND AND AIMS: Reproductive isolation and local establishment are necessary for plant speciation. Polyploidy, the possession of more than two complete chromosome sets, creates a strong postzygotic reproductive barrier between diploid and tetraploid cytotypes. However, this barrier weakens between polyploids (e.g. tetraploids and hexaploids). Reproductive isolation may be enhanced by cytotype morphological and environmental differentiation. Moreover, morphological adaptations to local conditions contribute to plant establishment. However, the relative contributions of ploidy level and the environment to morphology have generally been neglected. Thus, the extent of morphological variation driven by ploidy level and the environment was modelled for diploid, tetraploid and hexaploid cytotypes of Campanula rotundifolia agg. Cytotype distribution was updated, and morphological and environmental differentiation was tested in the presence and absence of natural contact zones. METHODS: Cytotype distribution was assessed from 231 localities in Central Europe, including 48 localities with known chromosome counts, using flow cytometry. Differentiation in environmental niche and morphology was tested for cytotype pairs using discriminant analyses. A structural equation model was used to explore the synergies between cytotype, environment and morphology. KEY RESULTS: Tremendous discrepancies were revealed between the reported and detected cytotype distribution. Neither mixed-ploidy populations nor interploidy hybrids were detected in the contact zones. Diploids had the broadest environmental niche, while hexaploids had the smallest and specialized niche. Hexaploids and spatially isolated cytotype pairs differed morphologically, including allopatric tetraploids. While leaf and shoot morphology were influenced by environmental conditions and polyploidy, flower morphology depended exclusively on the cytotype. CONCLUSIONS: Reproductive isolation mechanisms vary between cytotypes. While diploids and polyploids are isolated postzygotically, the environmental niche shift is essential between higher polyploids. The impact of polyploidy and the environment on plant morphology implies the adaptive potential of polyploids, while the exclusive relationship between flower morphology and cytotype highlights the role of polyploidy in reproductive isolation.

• Keywords
• Campanula rotundifolia agg, allopatry, contact zone, cytotype distribution, diploid, environmental niche shift, hexaploid, morphological differentiation, parapatry, polyploidy, reproductive isolation, tetraploid,
• MeSH
• Campanulaceae * MeSH
• Diploidy MeSH
• Ploidies MeSH
• Polyploidy MeSH
• Tetraploidy * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Spatial segregation of cytotypes reduces the negative effect of frequency-dependent mating on the fitness of minority cytotype(s) and thus allows its establishment and coexistence with the majority cytotype in mixed-ploidy populations. Despite its evolutionary importance, the stability of spatial segregation is largely unknown. Furthermore, closely related sympatric cytotypes that differ in their life histories might exhibit contrasting spatial dynamics over time. We studied the temporal stability of spatial structure at a secondary contact zone of co-occurring monocarpic diploids and polycarpic tetraploids of Centaurea stoebe, whose tetraploid cytotype has undergone a rapid range expansion in Europe and became invasive in North America. Eleven years after the initial screening, we re-assessed the microspatial distribution of diploids and tetraploids and their affinities to varying vegetation-cover density in three mixed-ploidy populations in Central Europe. We found that overall, spatial patterns and frequencies of both cytotypes in all sites were very similar over time, with one exception. At one site, in one previously purely 2x patch, diploids completely disappeared due to intensive succession by shrubby vegetation. The remaining spatial patterns, however, showed the same cytotype clumping and higher frequency of 2x despite subtle changes in vegetation-cover densities. In contrast to the expected expansion of polycarpic tetraploids having higher colonization ability when compared to diploids, the tetraploids remained confined to their former microsites and showed no spatial expansion. Spatial patterns of coexisting diploids and tetraploids, which exhibit contrasting life histories, did not change over more than a decade. Such temporal stability is likely caused by relatively stable habitat conditions and very limited seed dispersal. Our results thus imply that in the absence of a disturbance regime connected with frequent human- or animal-mediated seed dispersal, spatial patterns may be very stable over time, thus contributing to the long-term coexistence of cytotypes.

• Keywords
• Centaurea stoebe, colonization, cytotype coexistence, disturbance, flow cytometry, invasion, mixed-ploidy population, polycarpy, polyploidy, secondary contact zone, spatial cytotype structure, spatial segregation,
• Publication type
• Journal Article MeSH

Polyploidization is generally considered to be an important evolutionary driver affecting the genetic diversity, that can alter the morphology, phenology, physiology or ecology of plants, which in turn may make the taxonomy of polyploids more difficult. One such example is the Symphytum officinale complex, a polyploid species group represented by three major cytotypes: tetraploids (2n = 48), less common, geographically restricted diploids (2n = 24) and hypotetraploids (2n = 40). In most European floras only one polymorphic species, S. officinale, is widely recognized, while the particular cytotypes are usually considered conspecific. Our study provided a thorough evaluation of the ploidy level diversity, morphological and ecological variation, with a special attempt to clarify the status of 'white-flowered' diploids. Using flow cytometry, we identified three cytotypes: widespread tetraploids (76.1 %); less frequent diploids (23.6 %) with scattered distribution across the range of tetraploids and confined only to several areas of Europe; and extremely rare triploids (0.3 %). Diploids and tetraploids showed diffuse parapatric pattern of distribution, with only four mixed-cytotype populations (2.7 %) found, but almost entirely without triploids, suggesting reproductive isolation between di- and tetraploids. Niche of diploids falls nearly completely within the niche of tetraploids that showed niche expansion. Tetraploids also showed a shift in niche optimum towards a less continental and colder climate, coupled with expansion to more disturbance-prone sites with higher nutrient availability. Diploids were clearly distinguishable morphologically from tetraploids. The morphological differentiation of studied cytotypes appears to be taxonomically significant, especially in combination with ecological differences and the apparent presence of hybridization barriers. Both cytotypes should be treated as separate species (i.e. S. bohemicum and S. officinale s. str.).

• Keywords
• Autopolyploidy, Boraginaceae, cytogeography, flow cytometry, niche modelling, taxonomy,
• Publication type
• Journal Article MeSH

One promising area in understanding the responses of plants to ongoing global climate change is the adaptative effect of polyploidy. This work examines whether there is a coupling between the distribution of cytotypes and their biogeographical niche, and how different niches will affect their potential range. The study uses a range of techniques including flow cytometry, gradient and niche analysis, as well as distribution modelling. In addition, climatic, edaphic and habitat data was used to analyse environmental patterns and potential ranges of cytotypes in the first wide-range study of Festuca amethystina-a mixed-ploidy mountain grass. The populations were found to be ploidy homogeneous and demonstrate a parapatric pattern of cytotype distribution. Potential contact zones have been identified. The tetraploids have a geographically broader distribution than diploids; they also tend to occur at lower altitudes and grow in more diverse climates, geological units and habitats. Moreover, tetraploids have a more extensive potential range, being six-fold larger than diploids. Montane pine forests were found to be a focal environment suitable for both cytotypes, which has a central place in the environmental space of the whole species. Our findings present polyploidy as a visible driver of geographical, ecological and adaptive variation within the species.

• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH