Distribution Of Cytotypes Research Articles

Friends without benefits: Extensive cytotype sympatry and polyploid persistence in an African geophyte.

Polyploidy is a major factor in plant adaptation and speciation. Multiple mechanisms contribute to autopolyploid frequency within populations, but uncertainties remain regarding mechanisms that facilitate polyploid establishment and persistence. Here we aimed to document and predict cytotype distributions of Oxalis obliquifolia Steud. ex A. Rich. across Gauteng, South Africa, and test for evidence of possible mechanisms, including morphological, phenological, and reproductive traits, that may potentially facilitate polyploid persistence. Over 320 O. obliquifolia plants from 25 sites were cytotyped using flow cytometry, and DNA ploidy was confirmed using meiotic chromosome squashes. Cytotypes were mapped and correlations with abiotic variables assessed using ordinations. To assess morphological and phenological associations with cytotype, we grew multiple cytotypes in a common garden, measured phenotypic traits and compared them using linear models and discriminant analyses. Intercytotype reproductive isolation was assessed using crossing experiments, and AMOVAs based on ITS DNA sequences tested for cytogeographic structure. Six cytotypes were identified, and most sites had multiple cytotypes. Abiotic variables were not predictive of cytotype distribution. A clear gigas effect was present. Differences in flower size and phenology suggested pollinator interactions could play a role in polyploid persistence. Intercytotype crosses produced seed at low frequency. DNA data suggested diploids and polyploids were largely reproductively isolated in situ, and polyploidization events were not frequent enough to explain high cytotype sympatry. Diploids and polyploids are behaving as separate species, despite little observable niche differentiation and non-zero potential intercytotype seed set. Tests on biotic interactions and intercytotype F1 fitness may provide insights into diploid and polyploid coexistence.

Diploid and tetraploid cytotypes of the flagship Cape species Dicerothamnus rhinocerotis (Asteraceae): variation in distribution, ecological niche, morphology and genetics.

The Greater Cape Floristic Region is one of the world's biodiversity hotspots and is considered poor in polyploids. To test this assumption, ploidy variation was investigated in a widespread Cape shrub, Dicerothamnus rhinocerotis (renosterbos, Asteraceae). The aim was to elucidate the cytotype distribution and population composition across the species range, and to assess differences in morphology, environmental niches and genetics. Ploidy level and genome size were determined via flow cytometry and cytotype assignment was confirmed by chromosome counting. Restriction site-associated DNA sequencing (RADseq) analyses were used to infer genetic relationships. Cytotype climatic and environmental niches were compared using a range of environmental layers and a soil model, while morphological differences were examined using multivariate methods. The survey of 171 populations and 2370 individuals showed that the species comprises diploid and tetraploid cytotypes, no intermediates and only 16.8 % of mixed populations. Mean 2C values were 1.80-2.06 pg for diploids and 3.48-3.80 pg for tetraploids, with very similar monoploid genome sizes. Intra-cytotype variation showed a significant positive correlation with altitude and longitude in both cytotypes and with latitude in diploids. Although niches of both cytotypes were highly equivalent and similar, their optima and breadth were shifted due to differences mainly in isothermality and available water capacity. Morphometric analyses showed significant differences in the leaves and corolla traits, the number of florets per capitulum, and cypsela dimensions between the two cytotypes. Genetic analyses revealed four groups, three of them including both cytotypes. Dicerothamnus rhinocerotis includes two distinct cytotypes that are genetically similar. While tetraploids arise several times independently within different genetic groups, morphological and ecological differences are evident between cytotypes. Our results open up new avenues for questions regarding the importance of ploidy in the megadiverse Cape flora, and exemplify the need for population-based studies focused on ploidy variation.

Ecological niches in the polyploid complex Linum suffruticosum s.l.

The high frequency of polyploidy in the evolutionary history of many plant groups occurring in the Mediterranean region is likely a consequence of its dynamic paleogeographic and climatic history. Polyploids frequently have distinct characteristics that allow them to overcome the minority cytotype exclusion. Such traits may enable polyploid individuals to grow in habitats different from their parentals and/or expand to new areas, leading to spatial segregation. Therefore, the successful establishment of polyploid lineages has long been associated with niche divergence or niche partitioning and the ability of polyploids to cope with different, often more stressful, conditions. In this study, we aimed to explore the role of environmental variables associated with the current distribution patterns of cytotypes within the polyploid complex Linum suffruticosum s.l.. The distribution and environmental niches of the five main cytotypes of Linum suffruticosum s.l. (diploids, tetraploids, hexaploids, octoploids and decaploids) were studied across its distribution range. Realized environmental niche of each cytotype was determined using niche modelling tools, such as maximum entropy modelling and niche equivalency and similarity tests. Differences in the environmental conditions of L. suffruticosum s.l. cytotypes were observed, with polyploids being associated with habitats of increased drought and soil pH, narrower temperature ranges and decreased soil water and cation exchange capacities. Diploids present the widest environmental niche, and polyploids occupy part of the diploid niche. Although some polyploids have equivalent potential ecological niches, cytotypes do not co-occur in nature. Additionally, the ecological niche of this polyploid complex is different between continents, with North African habitats being characterised by differences in soil texture, higher pH, and low cation exchange capacity, precipitation and soil water capacity and higher temperatures than habitats in southwest Europe. The different ecological conditions played a role in the distribution of cytotypes, but the mosaic distribution could not be entirely explained by the environmental variables included in this study. Other factors, such as reproductive isolation and competitive interactions among cytotypes, could further explain the current diversity and distribution patterns in white flax. This study provides relevant data on the niche requirements of each cytotype for further competition and reciprocal transplant experiments. further competition and reciprocal transplant experiments.

The effects of climate change on cytotype distributions of endemic genera in the North American Coastal Plain

ABSTRACT Background Approximately 33% of plant species face extinction due to climate change. Polyploidisation, a process resulting in more than two complete sets of chromosomes, may be promoted by periods of climate fluctuations. Ecological niche modelling (ENM) using occurrences of endemic plants in the North American Coastal Plain (NACP) biodiversity hotspot could be used to evaluate the potential effects of climate change on cytotype distributions. Aims We used known diploid and polyploid taxa endemic to the NACP to test hypotheses that diploids and polyploids differed in habitat preferences, considerable overlap existed between cytotypes, and polyploid distributions would increase under climate change projections. Methods We examined niche identity and overlap of 28 congeneric ploidy level pairs and performed ENM to evaluate how climate change could affect these groups. Results Congeneric ploidy level pairs differed significantly in niche identity, and overlap varied across genera. Eleven genera showed greater than 100% increases in habitat suitability and six genera showed almost no remaining suitable habitat in at least one future climate scenario. Conclusions With 70% of the species that showed substantial declines in projected suitable habitat being of conservation concern, we propose that future studies of these genera should be a primary focus in the NACP.

Aneuploidy promotes intraspecific diversification of the endemic East Asian herb Lycoris aurea complex.

Polyploidy has received considerable interest in the past, but aneuploidy and partial rearrangements may also influence genomic divergence. In this study, we reported a comprehensive cytogeographic, morphological and genetic analysis of Lycoris aurea complex throughout its range and attempted to explore the association between aneuploidy and species diversification. The karyotypes of this complex presented aneuploidy variations mainly divided into four cytotypes: I (2n = 10m + 2T), II (2n = 8m + 6T), III (2n = 7m + 8T), and IV (2n = 6m + 10T). Cytotype distributions were highly structured geographically. Two main cytotypes, II and IV, are geographically allopatric. The populations with cytotype II are mainly distributed in central China and the southern islands of Japan. Cytotypes IV is disjunctly distributed in southwestern and southeastern China. The cytotypes with fewer chromosome numbers tend to occur at high latitudes. For analyzing the phylogeographic pattern and genetic structure of this complex, we sequenced four chloroplast DNA fragments (4,748 bp in total) of 241 individuals from 42 populations. Extremely high diversity of cpDNA haplotypes was found, with genetic diversity index (Hd) being 0.932 and 98.61% of the genetic variation occurring among populations, indicating that this complex has undergone strong intraspecific differentiation. The cytotype II had the highest haplotype diversity (Hd = 0.885), while cytotype IV harbored the highest nucleotide diversity (π = 4.09 × 10–3). We detected significant leaf morphological differences not only between cytotype II and IV but also between west lineage and east lineage within cytotype IV. These results illustrated that aneuploidy contributed to extensive morphological and genetic differentiation in L. aurea complex. It was suggested that L. aurea complex should comprise multiple independent evolutionary lineages, and accurate species delimitation needs to be established further in an integrative taxonomic approach.

Using telomeric length measurements and methylation to understand the karyotype diversification of Ctenomys minutus (a small fossorial mammal).

The genus Ctenomys has been widely used in karyotype evolution studies due to the variation in their diploid numbers. Ctenomys minutus is characterized by intraspecific variation in diploid number (2n=42, 46, 48, and 50), which makes it an interesting model to investigate genomic rearrangements mechanisms that could lead to different cytotypes in this species. Thereupon, it has been already shown that DNA methylation may participate in chromosome structure. Therefore, we aimed to investigate whether telomeres and global DNA methylation had a role in the genome rearrangements that led to this variation in C. minutus. We also realized an analysis for the presence of intrachromosomal telomeric repeats (ITRs) by fluorescence in situ hybridization. Our study demonstrated that neither telomere length nor DNA methylation had significant differences among the cytotypes. However, if only females were considered, there were significant differences for telomere length and methylation. Young individuals, regardless of their cytotypes, had the most methylated DNA. Regarding the ITRs, we found a signal on chromosome 1 in 2n=50b. No evidence was found that telomere length or methylation could have influenced chromosomal rearrangements, although new cytotypes seem to have emerged within the distribution of parental cytotypes by the accumulation of different chromosomal rearrangements.

Cytogeography of the East Asian Tulips (Amana, Liliaceae)

Amana Honda (Liliaceae), known as ‘east Asian tulips’, is a spring ephemeral genus endemic to Sino-Japanese Floristic Subregion, mainly distributed in eastern and central China, Japan and the Korean peninsula. Chromosome numbers are reported here for the first time from 89 populations of Amana (representing all seven accepted species, two new species about to be published, and two suspected new species). Three ploidy levels are found in this genus. These are diploid (2n = 2x = 24) and tetraploid (2n = 4x = 48) in the widespread A. edulis, while all the narrow endemics are diploid, except for one population of A. tianmuensis, which is triploid (2n = 3x = 36). The northernmost and southernmost populations of A. edulis are diploid and tetraploid, respectively, while diploids and tetraploids coexist in between, with gradual transition to diploids as the latitude increases. This may indicate polyploids have an advantage in tolerance of environmental stress and are more adaptable to high-temperature environment in subtropical regions than diploids. The species and cytotype distributions in Amana are complex, and these results provide hypotheses about the origins of the genus and the polyploid cytotypes.

A unique diploid – triploid contact zone provides insights into the evolutionary mechanisms of cytotype coexistence in flowering rush (Butomus umbellatus)

Polyploidisation is an important evolutionary force in land plants. Due to its recurrent incidence, many plant species retain individuals of two or more different ploidy levels. However, particular ecological and evolutionary mechanisms facilitating intraspecific cytotype coexistence have been identified for just a handful of species and cannot yet be generalised. Our pilot data have revealed a unique complex of mixed diploid-triploid populations of the marshland perennial Butomus umbellatus in the Eastern Slovak Lowland (eastern Central Europe). Intensive flow-cytometric ploidy screening of 1,230 individuals sampled from 72 populations was conducted at both regional and local (within-population) scales to assess cytotype distribution patterns. Vegetation assessments along with phenotypic comparisons of cytotypes directly in the field and later under common garden cultivation served to provide insight into mechanisms of cytotype coexistence. Altogether 42 % of the sampled populations were mixed-ploidy, pointing to unexpectedly high rates of diploid-triploid coexistence. While the cytotype distribution was random at the regional scale, significant spatial clustering occurred at the local scale. No ecological niche differences between the cytotypes were detected. Triploids attained greater values of several morphological characters both in the field and under cultivation, differences in the shape of inner tepals even show potential for cytotype discrimination. Both cytotypes exhibited high and comparable investments into clonal traits, reproductive assurance provided by asexual reproduction likely plays a key role in cytotype coexistence and triploid predominance. The common cytotype coexistence in this region seems to be also facilitated by periodical seasonal floods promoting transport of vegetative propagules among populations (i.e. metapopulation dynamics) and providing long-term continuity of favourable sites by recurrent disturbances.

Genome Size, Cytotype Diversity and Reproductive Mode Variation of Cotoneaster integerrimus (Rosaceae) from the Balkans.

Cotoneaster integerrimus represents a multiploid and facultative apomictic system of widely distributed mountain populations. We used flow cytometry to determine genome size, ploidy level, and reproduction mode variation of the Balkan populations, supplemented by analysis of nuclear microsatellites in order to address: (i) geographic distribution and variation of cytotypes among the populations; (ii) variation of reproduction mode and the frequency of sexuality; (iii) pathways of endosperm formation among the sampled polyploids and their endosperm balance requirements; (iv) genotypic diversity and geographic distribution of clonal lineages of polyploids. The prevalence of apomictic tetraploid cytotype followed by sexual diploids and extremely rare triploids was demonstrated. This prevalence of tetraploids affected the populations’ structure composed from clonal genotypes with varying proportions. The co-occurrence of diploids and tetraploids generated higher cytotype, reproductive mode, and genotypic diversity, but mixed-ploidy sites were extremely rare. The endosperm imbalance facilitates the development and the occurrence of intermediate triploids in mixed-ploidy populations, but also different tetraploid lineages elsewhere with unbalanced endosperm. All these results showed that the South European populations of C. integerrimus have higher levels of cytotype and reproductive diversity compared to the Central European ones. Therefore, the South European populations can be considered as a potential reservoir of regional and global diversity for this species.

Whole genome duplication increases ecological niche breadth of the perennial herb Urtica dioica

Environmental niche modelling and associated species distribution models often ignore intraspecific ecological differentiation linked with ploidal differentiation, i.e. the occurrence of several cytotypes of the same species. Here we tested the hypotheses that (i) the tetraploid (4x) cytotype is characterized by a broader ecological niche than the diploid (2x), and (ii) niche differentiation at the regional scale can serve as a proxy measure for differentiation at a smaller landscape scale in Urtica dioica, a perennial herbaceous plant with two prevailing cytotypes (2x and 4x). We focused on southern Moravia (Czech Republic), an area with a high diversity of vegetation types and the occurrence of both diploid and tetraploid cytotypes of U. dioica. To explore the geographical distribution, ecological preferences and habitat affinities of the diploid and tetraploid plants, we collected individuals at two different spatial scales: regional (~1200 km2) and landscape (9.1 km2). We used flow cytometry to determine the ploidy level of all the plants collected and determined the distribution of the different cytotypes both in geographical and ecological space. We also compared the habitat affinities of the diploid and tetraploid plants. Analyses of ploidy revealed 93 diploids and 325 tetraploids (regional scale: 42 diploids, 85 tetraploids; landscape scale: 51 diploids and 240 tetraploids). Diploid plants occurred only in the wetter parts of the landscape and this pattern was very similar at both scales. In contrast, tetraploids occurred along the whole moisture gradient at both scales. Diploids and tetraploids differed also in their habitat affinities. While diploids occurred relatively more frequently in alluvial and wet forests, managed broadleaved forests, alluvial and wet meadows, and wetlands and riverbanks, tetraploids preferred oak and oak-hornbeam forests, ravine forests, actively managed meadows, human settlements and vineyards. Our data clearly show an ecological niche differentiation between diploid and tetraploid cytotypes of Urtica dioica. While tetraploids have a broad ecological tolerance and consequently a wide geographical distribution, diploids occur only in a narrow range of ecological conditions and their distribution is restricted to areas with a shallow water table in the bottoms of valleys. Thus, ploidal differentiation, confirmed for many plant species, should be included in environmental niche modelling and species distribution models.

Morphological and environmental differentiation as prezygotic reproductive barriers between parapatric and allopatric Campanula rotundifolia agg. cytotypes.

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. 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. 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. 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.

Polyploidy in Odontarrhena bertolonii (Brassicaceae) in relation to seed germination performance and plant phenotype, with taxonomic implications

Odontarrhena bertolonii is an endemic serpentine species of Tuscany and Liguria and a model system for nickel-hyperaccumulation research in plants. Phenotypic, genetic and karyological variability between populations was previously detected, but existence and distribution of cytotypes was unknown. Accordingly, we examined ploidy level in eight populations from the species range and tested the polyploid fitness hypothesis by analysing relationships with plant phenotype and seed germination capacity. Accessions from central-western Tuscany and Liguria resulted diploid, while those from the upper Tiber valley were tetraploid. Autopolyploidy via unreduced gametes is likely the mechanism for the origin of tetraploid plants. Size and mass were higher in tetraploid seeds, which germinated faster and to higher percentages than diploid ones. Tetraploid plants were more robust and taller, with more richly branched inflorescences. Silicle shape and size did not differ, but style was longer in tetraploids and seeds had a larger wing. Overall, these results supported a higher fitness in polyploids. Multivariate analysis showed continuous variation but consistent differentiation between diploid and tetraploid accessions. Taxonomically, the tetraploid populations at the eastern limit of the species range in the upper Tiber valley can be referred to a new subspecies, here described as O. bertolonii subsp. cesalpina.

Tetraploids expanded beyond the mountain niche of their diploid ancestors in the mixed-ploidy grass Festuca amethystina L.

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.

A Cytogenetic Study on Spermophilus Xanthoprymnus (Bennett, 1835) in Isparta Province

This study was conducted to explain the karyological characteristics of S. xanthoprymnus from Gencali in Turkey. The chromosomes of the specimens were traditionally stained and examined according to standard procedures. The chromosomes were determined according to centromere positions by examining the photographs of metaphase cells. The karyotype of S. xanthoprymnus contained 42 chromosomes (2n=42) and fundamental number of chromosomal arms NF=81 and the number of autosomal arms NFa=78. The karyotype includes four metacentric chromosomes ranging from large to small, three pairs of large and medium-sized submetacentric autosome, twelve ranging from large to medium size subtelocentric, and a pair of acrocentric autosomes. The X chromosome was determined as large subtelocentric and Y chromosome as small acrocentric. Due to there is no karyological information and geographical distribution of existentence cytotypes in Turkey, revelation of chromosomal structure in Anatolian ground squirrel populations will provide properly assessment of taxonomy of those rodents in further studies.

Two cytotype niche shifts are of different magnitude in Solidago gigantea.

Polyploidy may serve to contribute to range size if autopolyploid cytotypes are adapted to differing ecological conditions. This study aims to establish the geographic distribution of cytotypes within the giant goldenrod (Solidago gigantea), and to assess whether cytotypes exhibit differing ecological tolerances and morphology. A range-wide set of 629 Solidago gigantea individuals was obtained through field collecting, sampling from herbarium specimens, and incorporating existing chromosome counts. Cytotype of each unknown sample was estimated by observing allele numbers at twelve microsatellite loci, a strategy that was assessed by comparing estimated to known cytotype in 20 chromosome-counted samples. Abiotic ecological differentiation was assessed for two transitions: diploid-tetraploid and tetraploid-hexaploid. Morphological differentiation among cytotypes was assessed. Microsatellite repeat variation accurately estimated cytotype in 85% of samples for which ploidy was known. Applying this approach to samples of unknown ploidy established that the three cytotypes are non-randomly distributed. Although niche modeling and MANOVA approaches identified significant differences in macro-climatic conditions for both cytotype transitions, the tetraploid to hexaploid transition was more substantial. Leaf length and width did not differ among cytotypes. Although leaf vestiture exhibited strong trends, no absolute differences were observed among cytotypes. With the largest such study to date, we established niche transitions among giant goldenrod cytotypes of differing magnitudes. Collectively, this suggests that whole-genome duplication has contributed to Solidago gigantea's large range.

Heritable variation in root secondary metabolites is associated with recent climate

Abstract Plants can adapt to changing environments by adjusting the production and maintenance of diverse sets of bioactive secondary metabolites. To date, the impact of climatic conditions relative to other factors such as soil abiotic factors and herbivore pressure on the evolution of plant secondary metabolites is poorly understood, especially for plant roots. We explored associations between root latex secondary metabolites in 63 Taraxacum officinale populations across Switzerland and climatic conditions, soil abiotic parameters, root herbivore pressure and cytotype distribution. To assess the contribution of environmental effects, root secondary metabolites were measured in F0 plants in nature and F2 plants under controlled greenhouse conditions. Concentrations of root latex secondary metabolites were most strongly associated with climatic conditions, while current soil abiotic factors or root herbivore pressure did not show a clear association with root latex chemistry. Results were similar for natural and controlled conditions, suggesting heritable variation rather than environmental plasticity as underlying factor. Synthesis. We conclude that climatic conditions likely play a major role in the evolution of root secondary metabolites. These results may hint at a novel role of root latex metabolites in tolerance of abiotic stress.

Different Patterns of Ecological Divergence Between Two Tetraploids and Their Diploid Counterpart in a Parapatric Linear Coastal Distribution Polyploid Complex.

Polyploidization is a widespread mechanism of evolutionary divergence in flowering plants. Ecological divergence of polyploid lineages has been proposed as a key process shaping the distribution of cytotypes in nature (niche shift hypothesis); however, evidence for the role of niche separation in replicated diploid-polyploid species pairs is still needed. This study aimed to assess the role of abiotic factors shaping current cytotype distributions. For that, we examined the distribution and environmental niches of two varieties recognized in diploid-tetraploid Jasione maritima across the species range and within a putative contact zone on the Iberian Peninsula. We counted chromosomes, screened for ploidy across Iberian Peninsula and characterized environmental requirements using niche modeling tools. We found that J. maritima var. maritima is composed by diploids with disjunct distribution in the west coast of France and northwest Iberian Peninsula, and by tetraploids in Iberian Peninsula, while var. sabularia is tetraploid. In the Iberian Peninsula, two parapatric contact zones along a linear coastal distribution were detected, one between diploid and tetraploid var. maritima, and the other between tetraploids of the two varieties. Environmental variables of diploid populations from France are distinct from those of southern diploid populations, which are more similar to tetraploids. In general, niche modeling results are congruent with the observed distribution patterns, although the results suggest a wider contact zone between varieties and cytotypes. Tetraploids of both varieties revealed different degrees of environmental divergence in comparison with their diploid counterpart. Tetraploid var. sabularia differed environmentally from diploids suggesting niche divergence. In contrast, tetraploid var. maritima overlapped with diploid environmental niche and currently occupies its entire predicted range, whereas diploids are restricted to northern areas of their suitable environment. Differences in ecological envelopes facilitate the recognition of functional units of biodiversity within polyploid groups, allowing the study of factors related to post-polyploidization divergence. Thus, whereas changes in environmental requirements may have allowed tetraploid var. sabularia to spread in habitats not favorable to diploids, other factors are involved with the distribution of diploid and tetraploid var. maritima.

Invasion, isolation and evolution shape population genetic structure in Campanula rotundifolia.

The distribution and genetic structure of most plant species in Britain and Ireland bear the imprint of the last ice age. These patterns were largely shaped by random processes during recolonization but, in angiosperms, whole-genome duplication may also have been important. We investigate the distribution of cytotypes of Campanula rotundifolia, considering DNA variation, postglacial colonization, environmental partitioning and reproductive barriers. Cytotypes and genome size variation from across the species’ range were determined by flow cytometry and genetic variation was assessed using cpDNA markers. A common garden study examined growth and flowering phenology of tetraploid, pentaploid and hexaploid cytotypes and simulated a contact zone for investigation of reproductive barriers. Irish populations were entirely hexaploid. In Britain, hexaploids occurred mostly in western coastal populations which were allopatric with tetraploids, and in occasional sympatric inland populations. Chloroplast markers resolved distinct genetic groups, related to cytotype and geographically segregated; allopatric hexaploids were distinct from tetraploids, whereas sympatric hexaploids were not. Genome downsizing occurred between cytotypes. Progeny of open-pollinated clones from the contact zone showed that maternal tetraploids rarely produced progeny of other cytotypes, whereas the progeny of maternal hexaploids varied, with frequent pentaploids and aneuploids. The presence of distinctive hexaploid chloroplast types in Ireland, Scottish islands and western mainland Britain indicates that its establishment preceded separation of these land masses by sea-level rise c. 16 000 years BP. This group did not originate from British tetraploids and probably diverged before postglacial invasion from mainland Europe. The combination of cytotype, molecular, contact zone and common garden data shows an overall pattern reflecting postglacial colonization events, now maintained by geographic separation, together with more recent occasional local in situ polyploidisation. Reproductive barriers favour the persistence of the tetraploid to the detriment of the hexaploid.

Environmental differences are correlated with the distribution pattern of cytotypes in Veronica subsection Pentasepalae at a broad scale.

The distribution of cytotypes and its potential correlation with environmental variables represent a cornerstone to understanding the origin and maintenance of polyploid lineages. Although many studies have addressed this question in single species at a regional scale, only a few have attempted to decipher this enigma in groups of closely related species at a broad intercontinental geographical scale. Here, we consider approx. 20 species of a diploid-polyploid complex (Veronica subsect. Pentasepalae) of recent and rapid diversification represented in Europe and North Africa to study the frequency and distribution of cytotypes and their relationship to environmental variables. A total of 680 individuals (207 populations) were sampled. Ploidy levels were determined using flow cytometry. Ecological differentiation among cytotypes was tested using climatic and environmental variables related to temperature, precipitation, vegetation and biogeographical region, among others, and by performing univariate and multivariate (constrained principal coordinates analysis) analyses. Four ploidy levels (2x, 4x, 6x and 8x) were found and genome downsizing was observed to occur within the group. Plants of different ploidy level are ecologically differentiated, with hexaploids and octoploids occurring in wetter and colder habitats with a higher seasonality than diploids. A south to north distribution pattern was found, with diploids occupying southern refugial areas and octoploids being more frequent in northern regions of Europe above the permafrost boundary. The distribution of cytotypes can be explained by ecological differentiation, the geographical position of refuge areas during the Quaternary climatic oscillations as well as by ice and permafrost retreat patterns. The Balkan Peninsula constitutes the most important contact zone between cytotypes. This work provides the first comprehensive ploidy screening within V. subsect. Pentasepalae at a broad scale and indicates that polyploidy and genome downsizing might have contributed to the colonization of new habitats in a recently diverged polyploid complex.

Are buffalograss (Buchloë dactyloides) cytotypes spatially and ecologically differentiated?

Although autopolyploidy is common among dominant Great Plains grasses, the distribution of cytotypes within a given species is typically poorly understood. This study aims to establish the geographic distribution of cytotypes within buffalograss (Buchloë dactyloides) and to assess whether individual cytotypes have differing ecological tolerances. A range-wide set of 578 B. dactyloides individuals was obtained through field collecting and sampling from herbarium specimens. The cytotype of each sample was estimated by determining allele numbers at 13 simple sequence repeat loci, a strategy that was assessed by comparing estimated to known cytotype in 79 chromosome-counted samples. Ecological differentiation between the dominant tetraploid and hexaploid cytotypes was assessed with analyses of macroclimatic variables. Simple sequence repeat variation accurately estimated cytotype in 89% of samples from which a chromosome count had been obtained. Applying this approach to samples of unknown ploidy established that diploids and pentaploids are rare, with the common tetraploid and hexaploid cytotypes generally occurring in sites to the north/west (tetraploid) or south/east (hexaploid) portions of the species range. Both MANOVA and niche modeling approaches identified significant but subtle differences in macroclimatic conditions at the set of locations occupied by these two dominant cytotypes. Incorporating chromosome count vouchers and cytotype-estimated herbarium records allowed us to perform the largest study of cytotype niche differentiation to date. Buffalograss cytotypes differ greatly in frequency, the common tetraploid and hexaploid cytotypes are non-randomly distributed, and these two cytotypes are subtly ecologically differentiated.