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A detailed knowledge of cytotype distribution can provide important insights into the evolutionary history of polyploid systems. This study aims to explore the spatial distribution of different cytotypes in Pilosella echioides at various spatial scales (from the whole distributional range to the population level) and to outline possible evolutionar...
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... Šafářová and Duchoslav 2010;Castro et al. 2012), through parapatric distribution, where cytotypes are intermingled in a very narrow part of a mixed-ploidy site (Baack 2004;Kolář et al. 2009;Castro et al. 2012), to probably the most often observed mosaic-like pattern with allopatric and sympatric patches variously arranged across a contact zone (e.g. Šafářová and Duchoslav 2010;Trávníček et al. 2011a). Importantly, these patterns are scale-dependent; the coexistence of cytotypes is likely over larger spatial scales, while at shorter distances ploidy-uniform clusters prevailed (Trávníček et al. 2011a;Šingliarová et al. 2019). ...
... Šafářová and Duchoslav 2010;Trávníček et al. 2011a). Importantly, these patterns are scale-dependent; the coexistence of cytotypes is likely over larger spatial scales, while at shorter distances ploidy-uniform clusters prevailed (Trávníček et al. 2011a;Šingliarová et al. 2019). Non-random cytotype distribution over small spatial scales can be linked to strong cytotype exclusion, clonal reproduction (Chrtek et al. 2017;Duchoslav et al. 2020), different microhabitat preferences (Fowler and Levin 1984;Sonnleitner et al. 2010) or non-adaptive processes, like a founder event with subsequent seed dispersal limitation (Baack 2005;Mráz et al. 2012b). ...
... Third, we computed the Ripley's K-function values (Ripley 1977) using the 'Kest' function implemented in the 'spatstat' package (Baddeley and Turner 2005). K-function, which has been successfully applied in a couple of studies focused on the microspatial cytotype patterns (Trávníček et al. 2011a, b), determines the type of spatial patterns, i.e. either regular, independent (= random) or clumped. The K-function procedure is based on a comparison of the observed mean density of neighbour plants within a circle of radius r of each mapped individual plant within a plot area and the expected density derived from the total number of mapped individuals and the total plot area. ...
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 reassessed the microspatial distribution of diploids and tetraploids and their affinities to varying vegetation-cover density in three mixed-ploidy populations in Central Europe. 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 co-existing 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.
... Pilosella echioides je dalším druhem s obrovským areálem směrem na východ od nás. U nás je obvykle diploidní; na lokalitě Havraníky na jižní Moravě se však vyskytuje ve čtyřech cytotypech, di-, tri-, tetra-a pentaploidním (Trávníček et al. 2011). ...
This paper summarises the principal factors underlying the variation of Pilosella populations in the fi eld:
1. Variation of taxa (basic, and hybridogenous species, recent hybrids); 2. Variation in chromosome number;
3. Variation in breeding systems; 4. Hybridization; 5. Population structure. Suggestions on how to
study Pilosella populations are given.
... Kliber & Eckert 2005, Castro et al. 2012, Godsoe et al. 2013, Kolář et al. 2013 or even within their populations (e.g. Kao 2007, Šafářová & Duchoslav 2010, Sonnleitner et al. 2010, Trávníček et al. 2011). Based on available, but still scarce, data, ecological divergence between cytotypes is rather common, but autopolyploids, unlike allopolyploids, do not generally tolerate harsher environments and do not always show a broader ecological niche than their diploid progenitors (Levin 2002, Parisod et al. 2010. ...
... With the application of flow cytometry (FCM), which allows us to order more sample analyses, it has also become clear that mixed-ploidy populations are much more frequent than previously anticipated ones (e.g., Halverson et al., 2008;Cires et al., 2010;Marhold et al., 2010;Trávníček et al., 2010Trávníček et al., , 2011aČertner et al., 2017. In the past, cases of locally coexisting cytotypes were assumed to represent transient situations following the frequent generation or, in the case of secondary contacts, immigration of an alternative cytotype (Kao, 2007). ...
The establishment and success of polyploids are thought to often be facilitated by ecological niche differentiation from diploids. Unfortunately, most studies compared diploids and polyploids, ignoring variation in ploidy level in polyploids. To fill this gap, we performed a large-scale study of 11,163 samples from 1,283 populations of the polyploid perennial geophyte Allium oleraceum with reported mixed-ploidy populations, revealed distribution ranges of cytotypes, assessed their niches and explored the pattern of niche change with increasing ploidy level. Altogether, six ploidy levels (3x−8x) were identified. The most common were pentaploids (53.6%) followed by hexaploids (22.7%) and tetraploids (21.6%). Higher cytotype diversity was found at lower latitudes than at higher latitudes (>52° N), where only tetraploids and pentaploids occurred. We detected 17.4% of mixed-ploidy populations, usually as a combination of two, rarely of three, cytotypes. The majority of mixed-ploidy populations were found in zones of sympatry of the participating cytotypes, suggesting they have arisen through migration (secondary contact zone). Using coarse-grained variables (climate, soil), we found evidence of both niche expansion and innovation in tetraploids related to triploids, whereas higher ploidy levels showed almost zero niche expansion, but a trend of increased niche unfilling of tetraploids. Niche unfilling in higher ploidy levels was caused by a contraction of niche envelopes toward lower continentality of the climate and resulted in a gradual decrease of niche breadth and a gradual shift in niche optima. Field-recorded data indicated wide habitat breadth of tetraploids and pentaploids, but also a pattern of increasing synanthropy in higher ploidy levels. Wide niche breadth of tetra- and pentaploids might be related to their multiple origins from different environmental conditions, higher “age”, and retained sexuality, which likely preserve their adaptive potential. In contrast, other cytotypes with narrower niches are mostly asexual, probably originating from a limited range of contrasting environments. Persistence of local ploidy mixtures could be enabled by the perenniality of A. oleraceum and its prevalence of vegetative reproduction, facilitating the establishment and decreasing exclusion of minority cytotype due to its reproductive costs. Vegetative reproduction might also significantly accelerate colonization of new areas, including recolonization of previously glaciated areas.
... Moreover, even at the microscale within the mixed-ploidy sites, there was significant clustering of similar ploidies together (Table 1). This strong separation of ploidies at short distances suggests spatial arrangement acts as a strong barrier against ploidy interaction, as has been observed in other plant species (Schönswetter et al., 2007;Trávníček et al., 2011a, b;Hanzl TABLE 1. Ploidy composition and spatial segregation of Arabidopsis arenosa at two spatial scales. At the landscape level, populations are analyzed at each contact zone separately, and additionally, using the combined dataset. ...
PREMISE: Whole genome duplication is a major evolutionary event, but its role in ecological divergence remains equivocal. When populations of different ploidy (cytotypes) overlap in space, “contact zones” are formed, allowing the study of evolutionary mechanisms contributing toward ploidy divergence. Multiple contact zones per species’ range are often described but rarely leveraged as natural replicates. We explored whether the strength of niche differentiation of diploid and autotetraploid Arabidopsis arenosa varies over distinct contact zones and if the frequency of triploids decreases from seedling to adult stage.
METHODS: We characterized ploidy composition and habitat preferences in 264 populations across three contact zones using climatic niche modeling. Ecological differences of cytotypes were also assessed using local vegetation surveys at 110 populations within two contact zones, and at the finer scale within five mixed-ploidy sites.
This was complemented by flow cytometry of seedlings.
RESULTS: We found no niche differences between diploid and tetraploid populations within contact zones for either climatic or local environmental variables. Comparisons of cytotypes within mixed-ploidy sites found weak niche differences that were inconsistent in direction. Triploid individuals were virtually absent (0.14%) in the field, and they were at a similarly low frequency (0.2%) in ex situ germinated seedlings.
CONCLUSIONS: This study demonstrates the strength in investigating different spatial scales across several contact zones when addressing ecological niche differentiation between ploidies. The lack of consistent habitat differentiation of ploidies across the scales and locations supports the recently emerging picture that processes other than ecological differentiation may underlie ploidy coexistence in diploid-autopolyploid systems.
... Longevity along with the ability to reproduce vegetatively and by selfing and, consequently, the lack of a need for regular sexual reproduction probably enabled V. uliginosum s. lat. to escape minority cytotype exclusion (see also Chrtek et al. 2017). In other polyploid complexes spatial segregation is identified as an important driver of successful cytotype co-occurrence, for example in Chamerion angustifolium (Sabara et al. 2013), Gymnadenia conopsea (Trávníček et al. 2011b), Knautia arvensis (Kolář et al. 2009), Pilosella echioides (Trávníček et al. 2011a) and Senecio carniolicus s. lat. (Sonnleitner et al. 2010). ...
... this is only partly possible because of a mismatch of genetic lineages and morphological groups (Trávníček et al. 2011b). In several other groups no taxonomic recognition is envisaged, usually due to the impossibility of morphologically characterizing the cytotypes, for instance in Chamerion angustifolium (Kennedy et al. 2006), Galax urceolata (Nesom 1983), Pilosella echioides (Trávníček et al. 2011a), Ranunculus kuepferi (Cosendai et al. 2013) and Solidago altissima (subspecies are described but are doubtful; Etterson et al. 2016). We strongly emphasise that it is premature to draw taxonomic conclusions about a species complex with a Holarctic distribution based on results from three sites in the Austrian Central Alps. ...
... Bip. (Trávníček & al. 2011), or affinity among allopatric taxa/sympatric cytotypes comprising the P. alpicola group (Šingliarová & al. 2011a, 2011b). However, many Pilosella populations in Central Europe are species-mixed, and large amounts of interspecific hybrids, both stabilized and recent, suggest rather weak hybridization barriers among species in this area (e.g. ...
... (2) Unlike in Bulgaria, sexual taxa exceeding the tetraploid ploidy level occur in Central Europe (Rotreklová & al. 2002;Mráz & al. 2008;Trávníček & al. 2011). Similarly, the tetraploid sexual biotype of Pilosella officinarum, which is the most common sexual parent of both recent (Table 3) and stabilized hybrids in Central Europe (e.g. ...
The species-mixed Pilosella populations comprising diploid sexual and polyploid facultatively apomictic biotypes were studied in Bulgaria. Parentage of co-occurring recent hybrids was inferred from a combination of morphology and ploidy level that corresponded to simple/multiple crosses of basic species via either reduced or unreduced gametes. The flow cytometric seed screening illustrated the capacity for heteroploid hybridization both in open-pollinated plants in the mixed-ploidy populations and in crossing experiments. The diploid sexual species in Bulgaria have a limited impact on interspecific hybridization, and simple inter-cytotype hybrids are only sporadically formed. The origin of the most common hybrids in Bulgaria that are apomictic and retain the pentaploid/hexaploid ploidy level of a co-occurring putative apomictic parent remains unclear. The absence of stabilized hybridogeneous species and scarcity of commonly hybridizing polyploid sexual biotypes are crucial attributes that distinguish the Pilosella populations in Bulgaria from those in the Czech Republic and Germany. No recent high-polyploid hybrids of 2n + n origin that would potentially become drivers of ongoing hybridization in the mixed sexual-Apomictic Pilosella populations similar to those in Central Europe have been recorded in Bulgaria. The pattern of co-occurring cytotypes in Bulgaria likely limits interspecific hybridization due to stronger ploidy barriers.
... In core distribution areas, seasonal environmental variables foster cytotype stability. Dispersion of cytotypes following a seasonal-latitudinal gradient as observed in P. intermedium is not rare in nature (Španiel et al., 2008;Trávnícek et al., 2011;Zozomová-Lihová et al., 2015). Diploid-tetraploid coexistence is possible by different pre-and post-zygotic isolation barriers (Husband and Sabara, 2003) or by character displacement and ecological differentiation (Beans, 2014). ...
Background and aims:
Niche divergence between polyploids and their lower ploidy progenitors is one of the primary mechanisms fostering polyploid establishment and adaptive divergence. However, within-species chromosomal and reproductive variability have usually been neglected in community ecology and biodiversity analyses even though they have been recognized to play a role in the adaptive diversification of lineages.
Methods:
We used Paspalum intermedium, a grass species with diverging genetic systems (diploidy vs. autopolyploidy, allogamy vs. autogamy and sexuality vs. apomixis), to recognize the causality of biogeographic patterns, adaptation and ecological flexibility of cytotypes. Chromosome counts and flow cytometry were used to characterize within-species genetic systems diversity. Environmental niche modelling was used to evaluate intraspecific ecological attributes associated with environmental and climatic factors and to assess correlations among ploidy, reproductive modes and ecological conditions ruling species' population dynamics, range expansion, adaptation and evolutionary history.
Key results:
Two dominant cytotypes non-randomly distributed along local and regional geographical scales displayed niche differentiation, a directional shift in niche optima and signs of disruptive selection on ploidy-related ecological aptitudes for the exploitation of environmental resources. Ecologically specialized allogamous sexual diploids were found in northern areas associated with higher temperature, humidity and productivity, while generalist autogamous apomictic tetraploids occurred in southern areas, occupying colder and less productive environments. Four localities with a documented shift in ploidy and four mixed populations in a zone of ecological transition revealed an uneven replacement between cytotypes.
Conclusions:
Polyploidy and contrasting reproductive traits between cytotypes have promoted shifts in niche optima, and increased ecological tolerance and niche divergence. Ecologically specialized diploids maintain cytotype stability in core areas by displacing tetraploids, while broader ecological preferences and a shift from sexuality to apomixis favoured polyploid colonization in peripheral areas where diploids are displaced, and fostered the ecological opportunity for autotetraploids supporting range expansion to open southern habitats.
... The dynamics of mixed-ploidy populations are presumed to be dominated by minority cytotype exclusion, a frequency-dependent process in which a rare cytotype (as a rule diploid or tetraploid) experiences a transmission disadvantage due to the combined effect of a high proportion of inter-cytotype crosses and strong incompatibility between cytotypes (triploid block [19][20][21]). On the other hand, the coexistence of different cytotypes can be more or less stable thanks to either (i) reproductive isolation as a consequence of a diverse array of preand postzygotic inter-cytotype breeding barriers [22][23][24][25][26] or, alternatively, (ii) an absence of breeding barriers linked with interfertility between cytotypes [27,28]. The most interesting are systems with free mating because they allow us to study intercytotype interactions and evolutionary dynamics of mixed-ploidy stands. ...
... In most of its geographic range (largely in steppe grasslands from southern Russia westwards to Central Europe [41]), P. echioides is a perennial, sexual and self-incompatible species with a capability for clonal growth via daughter rosettes. It possesses several features that make it a good candidate for such studies: (i) Up to five cytotypes may coexist within one population at a very fine spatial scale; (ii) It is an extremely dynamic system of cytotype coexistence due to the fertility of all cytotypes and interfertility amongst them, both in experiments and presumably also in wild populations; and (iii) No significant differences between cytotypes in morphology, phenology or habitat preferences were found [28]. ...
... Secondly, we performed computer simulations of dynamics of theoretical populations of individuals whose progeny structure is identical to that determined by the hybridization experiment, examined over a broad range of initial conditions, including those found in the field. We used these simulations to ascertain the equilibrium proportions of individual cytotypes and to compare them with field data on the frequency of cytotypes (diploids -6%, triplioids -73%, tetraploids -20% and pentaploids -1% [28]). Finally, as the mating structure alone cannot account for the observed frequencies, we examine the possible impacts of two other parameters which may be responsible for the cytotype frequencies in the field, namely plant longevity and clonal growth. ...
Background:
Processes driving ploidal diversity at the population level are virtually unknown. Their identification should use a combination of large-scale screening of ploidy levels in the field, pairwise crossing experiments and mathematical modelling linking these two types of data. We applied this approach to determine the drivers of frequencies of coexisting cytotypes in mixed-ploidy field populations of the fully sexual plant species Pilosella echioides. We examined fecundity and ploidal diversity in seeds from all possible pairwise crosses among 2x, 3x and 4x plants. Using these data, we simulated the dynamics of theoretical panmictic populations of individuals whose progeny structure is identical to that determined by the hybridization experiment.
Results:
The seed set differed significantly between the crossing treatments, being highest in crosses between diploids and tetraploids and lowest in triploid-triploid crosses. The number of progeny classes (with respect to embryo and endosperm ploidy) ranged from three in the 2x-2x cross to eleven in the 3x-3x cross. Our simulations demonstrate that, provided there is no difference in clonal growth and/or survival between cytotypes, it is a clear case of minority cytotype exclusion depending on the initial conditions with two stable states, neither of which corresponds to the ploidal structure in the field: (i) with prevalent diploids and lower proportions of other ploidies, and (ii) with prevalent tetraploids and 9% of hexaploids. By contrast, if clonal growth differs between cytotypes, minority cytotype exclusion occurs only if the role of sexual reproduction is high; otherwise differences in clonal growth are sufficient to maintain triploid prevalence (as observed in the field) independently of initial conditions.
Conclusions:
The projections of our model suggest that the ploidal structure observed in the field can only be reached via a relatively high capacity for clonal growth (and proportionally lower sexual reproduction) in all cytotypes combined with higher clonal growth in the prevailing cytotype (3x).
... genetic relationShipS betWeen diploid and tetraploid M. guttatus in Shetland Our genetic results are consistent with the hypothesis of a single neopolyploidization event of M. guttatus in the admixed QUA population in Shetland. In other taxa, the hypothesis of a primary contact zone is seen as the most plausible explanation for isolated mixedploidy populations (Trávníček et al., 2011), although genetic evidence is scarce (but see, e.g. Halverson et al., 2008). ...
Polyploidization can trigger rapid changes in morphology, ecology and genomics even in the absence of associated hybridization. However, disentangling the immediate biological consequences of genome duplication from the evolutionary change that subsequently accumulates in polyploid lineages requires the identification and analysis of recently formed polyploids. We investigated the incidence of polyploidization in introduced populations of Mimulus guttatus in the UK and report the discovery of a new mixed diploid–autopolyploid population in the Shetland Isles. We conducted a genetic analysis of six Shetland populations to investigate whether tetraploid individuals may have originated from local diploid plants and compared the morphology of tetraploids and local diploids to assess the phenotypic consequences of genome duplication. Autotetraploids are genetically close to sympatric diploids, suggesting that they have originated locally. Phenotypically, whole genome duplication has resulted in clear differences between ploidies, with tetraploids showing delayed phenology and larger flowers, leaves and stems than diploids. Our results support the hypothesis that novel evolutionary lineages can rapidly originate via polyploidization. The newly discovered autopolyploidization event in a non-native Mimulus population provides an opportunity to investigate the early causes and consequences of polyploidization in the wild.
