Clinal differentiation during invasion: <Emphasis Type="Italic">Senecio inaequidens</Emphasis> (Asteraceae) along altitudinal gradients in Europe

The dynamics of plant population differentiation may be integral in predicting aspects of introduced species invasion. In the present study, we tested the hypothesis that European populations of Senecio inaequidens (Asteraceae), an invasive species with South African origins, differentiated during migration from two independent introduction sites into divergent altitudinal and climatic zones. We carried out 2 years of common garden experiments with eight populations sampled from Belgian and ten populations from French altitudinal transects. The Belgian transect followed a temperature and precipitation gradient. A temperature and summer drought gradient characterized the French transect. We evaluated differentiation and clinal variation in plants germinated from field-collected seed using the following traits: days to germination, days to flowering, height at maturity, final plant height and aboveground biomass. Results showed that S. inaequidens populations differentiated in growth traits during invasion. During the 1st year of sampling, the results indicated clinal variation for growth traits along both the Belgium and French altitudinal transects. Data from the 2nd year of study demonstrated that with increasing altitude, a reduction in three growth traits, including plant height at maturity, final plant height and aboveground biomass, was detected along the French transect, but no longer along the Belgian one. Phenological traits did not exhibit a clear clinal variation along altitudinal transects. The possible evolutionary causes for the observed differentiation are discussed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Polyploidy and habitat differentiation in Dactylis glomerata L. from Galicia (Spain)

Summary The microdistribution of diploid and tetraploid plants of Dactylis glomerata L. was examined and related to their immediate environment in several sites in central Galicia, where morphologically indistinguishable individuals of both ploidies grow in sympatry. The two related cytotypes differed in habitat preference. Diploids were mainly confined to the low-density forest-floor habitat in woodlands of mostly ancient origin, whereas tetraploids were widespread in varied habitats but clearly predominant in open areas, particularly in disturbed anthropic sites. The in situ comparison of plant performance showed that where plants of each ploidy were more common they produced more tillers, panicles and seeds. This habitat preference closely reflected differences in life-history characteristics. The tetraploids had an early and short flowering time almost always completed before the aestival drought, whereas the diploids began to flower several weeks later and flowered throughout the drought. Comparisons along artificial gradients of soil water availability and light transmittance indicated that the cytotypes had distinct physiological requirements which probably originated in metabolic and more general genetic differentiation and could be directly attributable to ploidy. Habitat differentiation increases the species' colonizing ability. It also amplifies divergence in reproductive strategy between diploids and tetraploids, which reduces ineffective crossing between cytotypes and thereby permits them to coexist in sympatry. The effect of hybridization at the polyploid level on the differentiation between cytotypes was assessed from the recent introduction of a foreign tetraploid entity into the study area. Hybridization between the two distinct tetraploids was found to increase habitat differentiation between the diploids and the tetraploids, but the major part of this differentiation is probably attributable to ploidy itself.     

Anthropogenic disturbance and habitat differentiation between sexual diploid and apomictic triploidTaraxacum sect.Ruderalia

Co-occurrence of sexual diploid and apomictic triploidTaraxacum sectionRuderalia has been reported frequently. Many suggestions have been put forward with respect to the existence of an ecological differentiation between the cytotypes. In a study of 116Ruderalia populations in the area around Neuchatel (Switzerland) such a habitat differentiation has been proven. Large differences in the diploid/triploid ratio have been found between different field types. Adjacent fields of different types sometimes had significantly different cytotype ratios. In a canonical correspondence analysis significant vegetation differences were found between fields with mainly diploidRuderalia and fields with mainly triploidRuderalia. Two environmental indicators were significantly positively correlated with ploidy levels, altitude with diploids, and the percentage of therophytes in a vegetation with triploids. The percentage of therophytes is thought to be an indicator of the amount of disturbance due to human activities. At lower altitudes, the diploid/triploid ratio is largely determined by the amount of disturbance. Highly-disturbed fields contain mainly triploids whereas relatively stable fields contain mainly diploids. At higher altitudes there are mainly diploids. The presence of triploidTaraxacum sect.Ruderalia in the region around Neuchatel appears to be the result of the high amount of human activities of the last few hundred years. Whether the triploid presence is due to immigration or to local formation from diploids is yet unknown.     

Large differences in the composition of herbivore communities and seed damage in diploid and autotetraploid plant species

Herbivory is one of the key interactions affecting plant fitness. Despite the large amount of data available on the effects of herbivores on various plant groups, we still know very little information about the interactions of herbivores with individuals having different ploidy levels. We studied the relationship of diploid and tetraploid Centaurea phrygia in natural and experimental garden conditions to the community of pre‐dispersal seed predators developing in flower heads of the plants. In addition, we collected a set of data on flowering phenology, and flower head morphology and chemistry to investigate potential mechanisms underlying the differences between cytotypes. The two cytotypes are strongly differentiated in their flower head morphology and chemistry as well as in their flowering phenology, with flower heads of diploids being larger, containing more secondary metabolites and flowering later. Also, the two cytotypes strongly differed in the composition of insect communities in the flower heads and tetraploids suffered higher seed damage than the diploids. The differences between cytotypes in seed damage were generally consistent across datasets, indicating that the differences are not due to differences in the habitats in which the cytotypes occur but are due to differences in particular biological characteristics of the plants. The diversity and composition of insect communities, however, strongly varied between years and environments. Flowering phenology could explain part, but not all of the differences observed between cytotypes, indicating that other factors such as flower head morphology or chemistry could also play a role. The study indicated that the differences between the two cytotypes are important determinant of the plant–herbivore interactions in the system. Although we identified multiple factors that could explain the different associations, further research is needed to assess the relative importance of each of these factors. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 270–287.     

Effects of soil nitrogen on diploid advantage in fireweed,Chamerion angustifolium (Onagraceae)

In many ecosystems, plant growth and reproduction are nitrogen limited. Current and predicted increases of global reactive nitrogen could alter the ecological and evolutionary trajectories of plant populations. Nitrogen is a major component of nucleic acids and cell structures, and it has been predicted that organisms with larger genomes should require more nitrogen for growth and reproduction and be more negatively affected by nitrogen scarcities than organisms with smaller genomes. In a greenhouse experiment, we tested this hypothesis by examining whether the amount of soil nitrogen supplied differentially influenced the performance (fitness, growth, and resource allocation strategies) of diploid and autotetraploid fireweed (Chamerion angustifolium). We found that soil nitrogen levels differentially impacted cytotype performance, and in general, diploids were favored under low nitrogen conditions, but this diploid advantage disappeared under nitrogen enrichment. Specifically, when nitrogen was scarce, diploids produced more seeds and allocated more biomass toward seed production relative to investment in plant biomass or total plant nitrogen than did tetraploids. As nitrogen supplied increased, such discrepancies between cytotypes disappeared. We also found that cytotype resource allocation strategies were differentially dependent on soil nitrogen, and that whereas diploids adopted resource allocation strategies that favored current season reproduction when nitrogen was limiting and future reproduction when nitrogen was more plentiful, tetraploids adopted resource allocation strategies that favored current season reproduction under nitrogen enrichment. Together these results suggest nitrogen enrichment could differentially affect cytotype performance, which could have implications for cytotypes’ ecological and evolutionary dynamics under a globally changing climate.     

Altitudinal zonation of Andean cryptogam communities

To test whether cryptogamic plant communities in tropical Andean rain forests are distributed in floristically discrete communities corresponding to altitudinal belts, I subjected the elevational distribution of pteridophytes along two elevational gradients in Bolivia, and of bryophytes and lichens along two transects in Peru and Colombia (data from Gradstein & Frahm, 1987 ; Wolf, 1993 ) to an analysis of deviance. All well‐defined elevational boundaries in floristic composition were related to marked ecological changes: the transition from the steep mountains to the hilly lowland zone coupled with a change in geological substrate at 400 m along the Bolivian Carrasco transect, a strong humidity gradient at 1000 m at the Bolivian Masicurí transect and at 1250–1980 m along the Colombian transect, and the transition from mixed cloud forests to forests dominated by Polylepis or Podocarpus at 3400–3600 m in Carrasco, at 1650–1800 m in Masicurí, and at 3670 m in Colombia. Consequently, floristic elevational belts appear to be well‐defined at strong environmental boundaries and in fairly species‐poor forest communities where the presence or absence of one or a few tree species influences the whole ecosystem while they are ill‐defined in species‐rich communities such as tropical forests at low to mid‐elevations.     

Spatial ecological and genetic structure of a mixed population of sexual diploid and apomictic triploid dandelions

Ecological differentiation is widely seen as an important factor enabling the stable coexistence of closely related plants of different ploidy levels. We studied ecological and genetic differentiation between co-occurring sexual diploid and apomictic triploid Taraxacum section Ruderalia by analysing spatial patterns both in the distribution of cytotypes and in the distribution of genetic variation within and between the cytotypes. A significant relationship between ploidy level and elevation was found. This mode of ecological differentiation however, was not sufficient to explain the significant spatial structure in the distribution of diploids and triploids within the population. Strong congruence was found between the spatial genetic patterns within the diploids and within the triploids. We argue that this congruence is an indication of gene flow between neighbouring plants of different ploidy levels.     

What limits the altitudinal distribution of Craspedolepta species (Sternorrhyncha: Psylloidea) on fireweed?

Abstract.  1.  Craspedolepta nebulosa and C. subpunctata were studied on their shared host plant Epilobium angustifolium along an altitudinal transect in the Hardangervidda area of southern Norway.
2. The following was investigated: whether (a) the altitudinal distribution and abundance of each psyllid species was determined by summer heat budgets, acting directly on rates of insect development and/or through their host plant and (b) whether parasitism, predation, and interspecific competition played any role in restricting the distribution of the two species .
3.  Craspedolepta nebulosa extended to higher elevations than C. subpunctata but within their ranges neither species showed a clear altitudinal trend in abundance per plant. However, the former species grew to a smaller size with increasing elevation.
4. There was little evidence for interspecific competitive effects and observed levels of parasitism and predation were negligible across the transect.
5. Development and distribution of both species mirrored significant differences in the phenology, size, leaf number, and reproductive output of E. angustifolium with increasing altitude.
6. Distributions were related to available heat budgets acting on psyllid/plant development rates, with C. nebulosa developing more efficiently at lower heat availability.
7. Population transplant experiments supported the overall conclusions, with neither psyllid species able to establish viable populations above their current upper altitudinal range limit, despite the presence of their host plant.     

An experimental test of local adaptation among cytotypes within a polyploid complex

The geographic distributions of polyploids suggest they can have distinct and sometimes broader niches compared to diploids. However, relatively few field experiments have investigated whether range differences are associated with local adaptation or reflect other processes, such as dispersal limitation. In three years of transplants across the elevational ranges of five cytotypes in the Claytonia perfoliata complex, we found evidence for local adaptation. In at least one study year germination was higher within the natural range for each cytotype, and four of the five cytotypes attained larger biomass within their natural range. Fitness within and beyond range varied across years, with two instances of cytotypes showing higher fitness beyond the range, highlighting a potential role of temporal variability in cytotype differentiation. Polyploids as a group did not outperform diploids, but the cytotype with highest fitness across environments was a hexaploid reported to be invasive. Our results suggest that differences in geographic ranges within the C. perfoliata complex reflect local adaptation of cytotypes. Although we did not find a general polyploid advantage, our findings support the idea that occasional polyploid cytotypes exhibit high fitness relative to other cytotypes, and contribute to growing evidence supporting ecological differentiation of cytotypes within polyploid complexes.     

不同植物类群物种丰富度垂直格局分形特征的比较

格局和过程一直是生态学的核心问题,该文应用“非布朗运动随机分形”模型,在北京东灵山远离人为干扰地区的阴坡设置了两条宽2 m的样带,描述和比较了暖温带落叶阔叶林区乔木、灌木、草本以及总的植物物种丰富度在不同尺度上沿海拔梯度变异特征,以及相关的生态过程。研究结果表明:1)直接梯度法刻画了植物物种丰富度在海拔梯度上的总体变化趋势,并不能从中获得更多的信息。“非布朗运动随机分形”模型揭示了不同尺度上物种丰富度的空间变化并能和生态过程相联系,研究表明该模型适合对乔木、灌木和草本植物物种丰富度的垂直梯度格局特征进行描述,但对总的植物物种丰富度有一定的局限性。2)乔木物种丰富度在海拔梯度上的变化主要受两种生态过程的控制,小尺度上分形维数接近于2,主要受独立的不具有长程相关的生态过程控制,呈近随机分布;大尺度上分形维数接近于1,主要受自相关范围大、具有长程关联特性的生态过程控制,随海拔上升呈近似单调下降的趋势。灌木和草本物种丰富度在海拔梯度上的变化主要受3种生态过程的控制,小尺度和大尺度上的特征与乔木相似;但在中等尺度上,分形维数接近于1.5,它们以近似布朗运动的形式变化。虽然乔木和灌木物种丰富度在海拔梯度上变化的尺度范围相似,但决定它们的主要生态过程完全不同,或相同的生态过程以截然不同的方式作用于两种不同的植物类群。总的植物物种丰富度在整个尺度范围内呈现标度不变性,这可能是由于决定其变化的生态过程作用尺度紧密相关,也可能因为该文研究范围的局限性。     

Morphological and cytotype variation of wild kiwifruit (Actinidia chinensis complex) along an altitudinal and longitudinal gradient in central‐west China

The Actinidia chinensis complex, a group of commercially important fruits (kiwifruit), is a complex of functionally dioecious lianas of variable ploidy. To understand the cytogeography better and to facilitate breeding in this complex, we examined the ploidy and morphological variations in 16 natural populations of A. chinensis var. chinensis and A. chinensis var. deliciosa across an ecogeographical gradient. Four ploidy levels were found, var. chinensis consisting of diploids and tetraploids and var. deliciosa consisting of tetraploids, pentaploids and hexaploids. Hexaploids were centred in the western Yun‐Gui plateau, tetraploids coexisted with hexaploids or diploids in the middle Yun‐Gui plateau and the Wuling‐Xuefeng mountains, and diploids occurred in the eastern Wuling‐Xuefeng mountains and the Hunan foothills. These findings indicate a gradual, clinal transition from hexaploid to diploid across the elevational and longitudinal gradient. The clear geographical segregation of diploids and hexaploids may have arisen from their differential ecological adaptation in response to altitude and climate, whereas the coexistence of cytotypes (2x–4x, 4x–6x and 4x–5x–6x) might be a result of reproductive barriers, with a particular contribution from the postzygotic reproductive isolation between ploidy races. The geographical pattern and morphological variation of cytotypes suggest a hybrid zone between the varieties in the Wuling‐Xuefeng mountains. The differences in cytotypes which have arisen as a result of ecological adaptation, distribution and morphological characteristics will provide important baseline data for the selection of germplasm and the breeding of kiwifruit. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 72–83.     

Polyploidy associated with altered and broader ecological niches in the Claytonia perfoliata (Portulacaceae) species complex

? Premise of the study: Polyploids are often hypothesized to have distinct and broader niches than their diploid progenitors. Differences in geographic distributions between diploid and polyploids are frequently used to infer niche differentiation and increased breadth, but they are seldom used to test these hypotheses explicitly. ? Methods: Niche overlap and breadth were compared for diploids, tetraploids, and hexaploids of three taxa in the Claytonia perfoliata complex (C. parviflora, C. perfoliata, and C. rubra) with the use of species distribution models. Resampling and randomization approaches were used to test hypotheses of niche differentiation, breadth, and conservatism. ? Key results: Niche differentiation was detected between polyploid and diploid cytotypes assigned to the same taxon (e.g., C. parviflora 2× vs. 4×) but not between hexaploids and tetraploids within a taxon (e.g., C. parviflora 4× vs. 6×). Individual hexaploid cytotypes had broader ecological niches than individual diploid cytotypes. However, as a group the three hexaploid taxa did not exceed the combined niche breadth of the three diploids, suggesting that polyploidy does not result in transgressive niche breadth for this group. Niche overlap was lowest among diploids and was highest among the three hexaploid cytotypes, consistent with introgression associated with polyploidy resulting in greater ecological similarity. Although cytotypes possessed nonidentical niches, after accounting for environmental differences among ranges, cytotypes were more similar than expected, suggesting niche conservatism and similar responses to environmental characteristics. ? Conclusions: These results suggest that polyploids occupy distinct and broader niches relative to diploids but that cytotypes also share fundamentally similar responses to environmental variation across ploidy levels.     

Adaptive characteristics of grassland community structure and leaf traits along an altitudinal gradient on a subtropical mountain in Chongqing,China

Community structure and leaf traits are important elements of terrestrial ecosystems. Changes of community structure and leaf traits are of particular use in the study of the influence of climate change on terrestrial ecosystems. Patterns of community structure (including species richness, above- and below-ground biomass) and leaf traits (including leaf mass per area (LMA), nitrogen content both on mass and area bases (N _mass and N _area), and foliar δ¹³C) from 19 grassland plots along an altitudinal transect at Hongchiba in Chongqing, China, were analyzed. Species richness along the altitudinal transect had a hump-shaped pattern. Above-ground biomass had a quadratic decrease along the altitudinal gradient whereas below-ground biomass had the opposite pattern. Change of above-ground biomass of various taxonomic groups with altitude was also studied. Poaceae showed strong negative relationships and Asteraceae showed a hump-shaped relationship with increase of altitude. Five common species of the grassland, Trifolium pratense, Geranium wilfordii, Aster tataricus, Leontopodium leontopodioides, and Spiraea prunifolia, were particularly studied for variation of leaf traits along the altitudinal gradient. Averaged for all species, LMA, N _area and foliar δ¹³C had positive correlations with altitude. N _mass did not change significantly as altitude increased. LMA and N _area showed significant positive relationships with foliar δ¹³C. The adaptive features of leaf traits among different species were not consistent. The study highlights specific adaptation patterns in relation to altitude for different plant species, provides further insights into adaptive trends of community structure and leaf traits in a specific ecological region filling a gap in the definition of global patterns, and adds to the understanding of how adaptive patterns of plants may respond to global climate change.     

EVOLUTION OF PHENOTYPIC PLASTICITY IN THE STELLARIA LONGIPES COMPLEX: COMPARISONS AMONG CYTOTYPES AND HABITATS

Variation in the amount and pattern of plasticity was studied in three cytotypes (4x, 6x, and 8x) of Stellaria longipes and diploids of its suspected progenitor S. longifolia. All 13 traits considered showed plasticity. There were significant differences among cytotypes and habitats in plasticity for many traits. Overall, the diploids, S. longifolia, were most plastic, and the three cytotypes of S. longipes did not differ in amount of plasticity. Stellaria longifolia showed divergence from S. longipes in the pattern of plasticity as well. In general, cytotypes with more similar chromosome numbers had the same pattern of plasticity for more traits. Individuals from tundra populations differed in their pattern of plasticity from those of montane, boreal, and prairie origin, which were more similar to one another. Differences in plasticity among cytotypes were due primarily to divergence in amount, while differences among habitats were most often accounted for by divergent patterns of plasticity. We conclude that both polyploidy and natural selection have affected the evolution of plastic responses in this species complex. Analysis of the correlation between pairs of traits provided evidence that the pattern and amount of plasticity operate independently of one another and may be evolving separately.     

Difference in reproductive mode rather than ploidy explains niche differentiation in sympatric sexual and apomictic populations of Potentilla puberula

Apomicts tend to have larger geographical distributional ranges and to occur in ecologically more extreme environments than their sexual progenitors. However, the expression of apomixis is typically linked to polyploidy. Thus, it is a priori not clear whether intrinsic effects related to the change in the reproductive mode or rather in the ploidy drive ecological differentiation. We used sympatric sexual and apomictic populations of Potentilla puberula to test for ecological differentiation. To distinguish the effects of reproductive mode and ploidy on the ecology of cytotypes, we compared the niches (a) of sexuals (tetraploids) and autopolyploid apomicts (penta‐, hepta‐, and octoploids) and (b) of the three apomictic cytotypes. We based comparisons on a ploidy screen of 238 populations along a latitudinal transect through the Eastern European Alps and associated bioclimatic, and soil and topographic data. Sexual tetraploids preferred primary habitats at drier, steeper, more south‐oriented slopes, while apomicts mostly occurred in human‐made habitats with higher water availability. Contrariwise, we found no or only marginal ecological differentiation among the apomictic higher ploids. Based on the pronounced ecological differences found between sexuals and apomicts, in addition to the lack of niche differentiation among cytotypes of the same reproductive mode, we conclude that reproductive mode rather than ploidy is the main driver of the observed differences. Moreover, we compared our system with others from the literature, to stress the importance of identifying alternative confounding effects (such as hybrid origin). Finally, we underline the relevance of studying ecological parthenogenesis in sympatry, to minimize the effects of differential migration abilities.     

Variations between diploids and tetraploids of Allium przewalskianum, an important vegetable and/or condiment in the Himalayas

Allium przewalskianum, a wild onion species growing at altitudes ranging from 1800 to 4500 m, has long been commonly used as an important vegetable and/or condiment by Tibetans, Indians, and Nepalese in the highlands of the Himalayas and adjacent regions. This species comprises both diploids and tetraploids. In this study, we examined the nutritional content and biomass accumulation profiles of two cytotypes, collected from 29 sites, with different altitudinal origins but cultivated in a common garden. On an average, this species has superior qualities in the minerals and amino acids compared to other edible congeners. When compared with the diploids, the tetraploids grew faster and accumulated more biomass; in addition, the tetraploids had higher values of moisture and energy, higher contents of cystine and phosphorus, but lower fiber levels. Moreover, the tetraploids from the higher altitudes had greater biomasses than the other tetraploids, in addition to having increased levels of proteins, fats, and the minerals Mg, Fe, Mn, and Cu. These results illustrate the large variations in nutritional efficacy and growth within this single morphological species, and provide critical information for its effective consumption in the future.     

Spatial variation in plant interactions across a severity gradient in the sub-Antarctic

The stress–gradient hypothesis predicts that the intensity of interspecific positive interactions increases along environmental severity (i.e. stress and disturbance) gradients faster than the intensity of negative interactions. This study is the first to test if the stress–gradient hypothesis is supported for a location in the climatically extreme and species-poor sub-Antarctic. To do so, we investigate the fine-scale spatial distribution of plant species across altitude- and aspect-related abiotic severity gradients on a scoria cone on Marion Island. A clear altitudinal severity gradient was observed across the scoria cone, with lower temperatures, stronger winds and greater soil movement at higher altitudes. The altitudinal severity gradient was matched by stronger interspecific spatial association between the four dominant species at higher altitudes and in areas of lower vegetation cover. This suggests that, relative to the intensity of competition, the intensity of facilitation is greater under more severe conditions, supporting the stress–gradient hypothesis at the community level (i.e. for multiple pairs of species) and corroborating its usefulness for predicting variation in plant interactions at high latitudes and altitudes. Furthermore, the directional intraspecific aggregation and interspecific association plant cover patterns found within the gradient suggest that protection from the prevailing wind and from burial by loose substrate are the dominant facilitative mechanisms. Thus, plants benefit from the presence of neighbours when they provide shelter and substrate stability, and the relative intensity of this positive interaction is greatest at higher altitudes, and varies between species pairs. This study, therefore, not only provides support for the stress–gradient hypothesis in the sub-Antarctic, but also demonstrates fine-scale directional spatial patterns between multiple species nested within the severity gradient. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Competition between cytotypes changes across a longitudinal gradient in Centaurea stoebe (Asteraceae)

? Premise of the Study: Polyploidy resulting from whole genome duplication has contributed to the adaptive evolution of many plant species. However, the conditions necessary for successful polyploid evolution and subsequent establishment and persistence in sympatry with diploid progenitors are often quite limited. One condition thought to be necessary for establishment is a substantial competitive superiority of the polyploid. ? Methods: We conducted a pairwise competition experiment using diploid and tetraploid cytotypes of Centaurea stoebe L. to determine whether (1) tetraploids have greater competitive ability than diploids, (2) cytotypes from mixed-cytotype populations have more balanced competitive abilities than single-cytotype populations, and (3) competitive abilities change along a longitudinal gradient. ? Key Results: Across sampling localities, tetraploids did not produce greater aboveground biomass than diploids but suffered from greater intracytotypic competition. Tetraploids allocated greater biomass belowground than diploids, regardless of competition treatment, and had greater performance for traits associated with long-term persistence (bolted more frequently and produced more accessory rosettes). Competitive ability of tetraploids did not differ between single- and mixed-cytotype populations but varied along a longitudinal gradient. Tetraploids were stronger intercytotypic competitors in Western Europe (Switzerland and Germany) than in Eastern Europe (Hungary and Slovakia), which indicates that cytotype coexistence may be more likely in Eastern Europe, the proposed origin of tetraploids, than in Western Europe. ? Conclusions: Our study addresses the importance of examining competitive interactions between cytotypes across their distributional range, as competitive interactions were not consistent across sampling localities.     

Patterns of cytotype variation of <Emphasis Type="Italic">Turnera sidoides</Emphasis> subsp. <Emphasis Type="Italic">pinnatifida</Emphasis> (Turneraceae) in mountain ranges of central Argentina

Cytogeographical variability among 564 plants from 26 populations of Turnera sidoides subsp. pinnatifida in mountain ranges of central Argentina was analysed with meiotic chromosome counts and flow cytometry and is described at regional and local scales. Populations were primarily tetraploids (2n = 4x = 28), although diploid (2n = 2x = 14), hexaploid (2n = 2x = 42), and mixed populations of diploids and triploids (2n = 3x = 21) were also found. Diploids, triploids, and hexaploids were fewer in number and restricted to narrow areas, while tetraploids were the most common and geographically widespread cytotype. Diploids grew at higher altitudes and in colder and wet locations; tetraploids had the broadest ecological spectrum, while hexaploids occurred at the lowest altitudes and in drier conditions. The cytotypes were also spatially segregated at a microgeographical scale. Diploids grew in the piedmont, tetraploids were in the adjacent valley, and in the contact zone of both cytotypes, patches of diploids and triploids were found. At a regional scale, the distribution of the cytotypes may be governed by a combination of ecological and historical variables, while segregation in the contact zone may be independent of the selective environment because the cytotypes are unable to coexist as a result of reproductive exclusion. The role of triploids is also discussed.