Relationships between genome size and environmental variables suggest that DNA content might be adaptive and of evolutionary importance in plants. The genus Larrea provides an interesting system to test this hypothesis, since it shows both intra- and interspecific variation in genome size. Larrea has an amphitropical distribution in North and South American deserts, where it is most speciose. Larrea tridentata in North America shows a gradient of increasing autopolyploidy; while three of the four studied South American species are diploids, Larrea divaricata, Larrea nitida, Larrea ameghinoi, and the fourth is an allopolyploid, Larrea cuneifolia. We downloaded available focal species' georeferenced records from seven data reservoirs. We used these records to extract biologically relevant environmental variables from WorldClim at 30 arc seconds scale, to have a broad characterization of the variable climatic conditions of both regions, and a climatic envelope for each species. We estimated relative DNA content index and relative monoploid genome values, by flow cytometry, of four most abundant Larrea species throughout their respective ranges. Then we winnow the bioclimatic dataset down to uncorrelated variables and sampled locales, to analyse the degree of association between both intra- and interspecific relative DNA content and climatic variables that are functionally relevant in arid environments using Pearson correlations, general linear and mixed effects models. Within the genus Larrea, relative DNA content increases with rising temperature and decreases with rising precipitation. At the intraspecific level, all four species show relative DNA content variation across climatic conditions. Larrea is a genus that shows genome size variation correlated with climate. Our results are also consistent with the hypothesis that extreme environmental pressures may have facilitated repeated whole genome duplication events in North America, while in South America, reticulate evolution, as allopolyploidization, and speciation might have been climate-dependent since the Oligocene.

• Keywords
• DNA content, Drylands, Genome size, Jarilla, Larrea, Zygophyllaceae,
• Publication type
• Journal Article MeSH

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).

• Keywords
• Cytotype diversity, Mating interactions, Minority cytotype exclusion, Pilosella echioides, Polyploidy, Triploid bridge,
• MeSH
• Asteraceae genetics   MeSH
• Diploidy MeSH
• Fertility MeSH
• Hybridization, Genetic MeSH
• Crosses, Genetic MeSH
• Computer Simulation MeSH
• Polyploidy * MeSH
• Reproduction MeSH
• Seeds genetics   MeSH
• Publication type
• Journal Article MeSH

Despite their complex evolutionary histories, aquatic plants are highly underrepresented in contemporary biosystematic studies. Of them, the genus Callitriche is particularly interesting because of such evolutionary features as wide variation in chromosome numbers and pollination systems. However, taxonomic difficulties have prevented broader investigation of this genus. In this study we applied flow cytometry to Callitriche for the first time in order to gain an insight into evolutionary processes and genome size differentiation in the genus. Flow cytometry complemented by confirmation of chromosome counts was applied to an extensive dataset of 1077 Callitriche individuals from 495 localities in 11 European countries and the USA. Genome size was determined for 12 taxa. The results suggest that many important processes have interacted in the evolution of the genus, including polyploidization and hybridization. Incongruence between genome size and ploidy level, intraspecific variation in genome size, formation of autotriploid and hybridization between species with different pollination systems were also detected. Hybridization takes place particularly in the diploid-tetraploid complex C. cophocarpa-C. platycarpa, for which the triploid hybrids were frequently recorded in the area of co-occurrence of its parents. A hitherto unknown hybrid (probably C. hamulata × C. cophocarpa) with a unique chromosome number was discovered in the Czech Republic. However, hybridization occurs very rarely among most of the studied species. The main ecological preferences were also compared among the taxa collected. Although Callitriche taxa often grow in mixed populations, the ecological preferences of individual species are distinctly different in some cases. Anyway, flow cytometry is a very efficient method for taxonomic delimitation, determination and investigation of Callitriche species, and is even able to distinguish homoploid taxa and identify introduced species.

• MeSH
• Genome Size * MeSH
• Genome, Plant genetics   MeSH
• Flowers genetics   MeSH
• Evolution, Molecular * MeSH
• Plantago genetics   MeSH
• Polyploidy MeSH
• Flow Cytometry MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH

Introgressive hybridization is an important evolutionary process frequently contributing to diversification and speciation of angiosperms. Its extent in other groups of land plants has only rarely been studied, however. We therefore examined the levels of introgression in the genus Diphasiastrum, a taxonomically challenging group of Lycopodiophytes, using flow cytometry and numerical and geometric morphometric analyses. Patterns of morphological and cytological variation were evaluated in an extensive dataset of 561 individuals from 57 populations of six taxa from Central Europe, the region with the largest known taxonomic complexity. In addition, genome size values of 63 individuals from Northern Europe were acquired for comparative purposes. Within Central European populations, we detected a continuous pattern in both morphological variation and genome size (strongly correlated together) suggesting extensive levels of interspecific gene flow within this region, including several large hybrid swarm populations. The secondary character of habitats of Central European hybrid swarm populations suggests that man-made landscape changes might have enhanced unnatural contact of species, resulting in extensive hybridization within this area. On the contrary, a distinct pattern of genome size variation among individuals from other parts of Europe indicates that pure populations prevail outside Central Europe. All in all, introgressive hybridization among Diphasiastrum species in Central Europe represents a unique case of extensive interspecific gene flow among spore producing vascular plants that cause serious complications of taxa delimitation.

• MeSH
• Biological Evolution MeSH
• Genome Size * MeSH
• Diploidy MeSH
• DNA, Plant genetics   MeSH
• Species Specificity MeSH
• Ecosystem MeSH
• Genetic Variation MeSH
• Genetic Markers MeSH
• Genome, Plant * MeSH
• Hybridization, Genetic * MeSH
• Crosses, Genetic MeSH
• Plant Leaves anatomy & histology   MeSH
• Lycopodiaceae anatomy & histology   classification   genetics   physiology   MeSH
• Spores MeSH
• Plant Stems anatomy & histology   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Comparative Study MeSH
• Geographicals
• Europe MeSH
• Names of Substances
• DNA, Plant MeSH
• Genetic Markers MeSH

BACKGROUND AND AIMS: Plants endemic to areas covered by ice sheets during the last glaciation represent paradigmatic examples of rapid speciation in changing environments, yet very few systems outside the harsh arctic zone have been comprehensively investigated so far. The Galium pusillum aggregate (Rubiaceae) is a challenging species complex that exhibits a marked differentiation in boreal parts of Northern Europe. As a first step towards understanding its evolutionary history in deglaciated regions, this study assesses cytological variation and ecological preferences of the northern endemics and compares the results with corresponding data for species occurring in neighbouring unglaciated parts of Central and Western Europe. METHODS: DNA flow cytometry was used together with confirmatory chromosome counts to determine ploidy levels and relative genome sizes in 1158 individuals from 181 populations. A formalized analysis of habitat preferences was applied to explore niche differentiation among species and ploidy levels. KEY RESULTS: The G. pusillum complex evolved at diploid and tetraploid levels in Northern Europe, in contrast to the high-polyploid evolution of most other northern endemics. A high level of eco-geographic segregation was observed between different species (particularly along gradients of soil pH and competition) which is unusual for plants in deglaciated areas and most probably contributes to maintaining species integrity. Relative monoploid DNA contents of the species from previously glaciated regions were significantly lower than those of their counterparts from mostly unglaciated Central Europe, suggesting independent evolutionary histories. CONCLUSIONS: The aggregate of G. pusillum in Northern Europe represents an exceptional case with a geographically vicariant and ecologically distinct diploid/tetraploid species endemic to formerly glaciated areas. The high level of interspecific differentiation substantially widens our perception of the evolutionary dynamics and speciation rates in the dramatically changing environments of Northern Europe.

• Keywords
• Endemism, environmental change, flow cytometry, genome size, glaciation, niche differentiation, ploidy level, polyploid evolution,
• MeSH
• Ecosystem MeSH
• Genetic Variation MeSH
• Ploidies * MeSH
• Rubiaceae genetics   MeSH
• Gene Flow MeSH
• Geography MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Comparative Study MeSH
• Geographicals
• Europe MeSH

BACKGROUND AND AIMS: 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 evolutionary scenarios for the observed geographic pattern. METHODS: DNA-ploidy levels were estimated using DAPI flow cytometry in 4410 individuals of P. echioides from 46 populations spread over the entire distribution range in central Europe. Special attention was paid to the cytotype structure in the most ploidy-diverse population in south-west Moravia. KEY RESULTS: Five different cytotypes (2x, 3x, 4x, 5x and 6x) were found, the last being recorded for the first time. Although ploidy-uniform (di- or tetraploid) sites clearly prevailed, nearly one-quarter of the populations investigated harboured more (up to all five) cytotypes. Whereas penta- and hexaploids constituted only a minority of the samples, a striking predominance of the triploid cytotype was observed in several populations. CONCLUSIONS: The representative sampling confirmed previous data on cytotype distribution, i.e. the spatial aggregation of mixed-ploidy populations in south-west Moravia and Lower Austria and the predominance of ploidy-uniform populations in other parts of the area investigated. Recurrent origin of polyploids from diploid progenitors via unreduced gametes and their successful establishment are considered the key factors promoting intrapopulational ploidy mixture ('primary hybrid zones'). As an alternative to the generally accepted theory of cytotype co-existence based on the development of different means of inter-ploidy reproductive isolation, it is suggested that a long-term ploidy mixture can also be maintained in free-mating populations provided that the polyploids originate with a sufficient frequency. In addition, the prevalence (or subdominance) of the triploid cytotype in several mixed-ploidy populations represents the first evidence of such a phenomenon in plant systems with exclusively sexual reproduction.

• MeSH
• Asteraceae genetics   physiology   MeSH
• Biological Evolution * MeSH
• Chromosomes, Plant genetics   MeSH
• DNA, Plant genetics   MeSH
• Phylogeography MeSH
• Genetic Variation * MeSH
• Ploidies MeSH
• Flow Cytometry MeSH
• Reproduction MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Europe MeSH
• Names of Substances
• DNA, Plant MeSH