1,721,073 research outputs found
Phylogeography reveals a potential cryptic invasion in the Southern Hemisphere of Ceratophyllum demersum, New Zealand's worst invasive macrophyte
Full text linkCeratophyllum demersum (common hornwort) is presently considered the worst invasive submerged aquatic macrophyte in New Zealand. We explored the global phylogeographic pattern of the species, based on chloroplast and nuclear DNA, in order to identify the origin of the invasive populations in New Zealand and to clarify if there were multiple introductions. The phylogeographic study identified geographically differentiated gene pools in North America, tropical Asia, Australia, and South Africa, likely native to these regions, and a recent dispersal event of a Eurasian-related haplotype to North America, New Zealand, Australia, and South Africa. At least two different invasive genotypes of this Eurasian-related haplotype have been found in New Zealand. One genotype is closely related to genotypes in Australia and South Africa, while we could not trace the closest relatives of the other genotype within our C. demersum sample set. Contrasting spectra of genetic distances in New Zealand and in a region within the native range (Denmark), suggest that the invasive population was founded by vegetative reproduction, seen as low genetic distances among genotypes. We also discovered the introduction of the same Eurasian-related haplotype in Australia and South Africa and that a cryptic invasion may be occurring in these continents
Increased invasive potential of non-native Phragmites australis: Elevated CO2 and temperature alleviate salinity effects on photosynthesis and growth
No full textThe prospective rise in atmospheric CO2 and temperature may change the distribution and invasive potential of a species; and intraspecific invasive lineages may respond differently to climate change. In this study, we simulated a future climate scenario with simultaneously elevated atmospheric CO2 and temperature, and investigated its interaction with soil salinity, to assess the effects of global change on the ecophysiology of two competing haplotypes of the wetland grass Phragmites australis, that are invasive in the coastal marshes of North America. The two haplotypes with the phenotypes 'EU-type' (Eurasian haplotype) and 'Delta-type' (Mediterranean haplotype), were grown at 0‰ and 20‰ soil salinity, and at ambient or elevated climatic conditions (700 ppm CO2, +5 °C) in a phytotron system. The aboveground growth of both phenotypes was highest at the elevated climatic conditions. Growth at 20‰ salinity resulted in declined aboveground growth, lower transpiration rates (E), stomata conductance (gs), specific leaf area, photosynthetic pigment concentrations, and a reduced photosynthetic performance. The negative effects of salinity were, however, significantly less severe at elevated CO2 and temperature than at the ambient climatic conditions. The Delta-type P. australis had higher shoot elongation rates than the EU-type P. australis, particularly at high salinity. The Delta-type also had higher maximum light-saturated rates of photosynthesis (Asat), maximum carboxylation rates of Rubisco (Vcmax), maximum electron transport rates (Jmax), triose phosphate utilization rates (Tp), stomata conductance (gs), as well as higher Rubisco carboxylation-limited, RuBP regeneration-limited and Tp-regeneration limited CO2 assimilation rates than the EU-type under all growth conditions. Our results suggest that the EU-type will not become dominant over the Delta-type, since the Delta-type has superior ecophysiological traits. However, the projected rise in atmospheric CO2 and temperature will alleviate the effects of salinity on both phenotypes and facilitate their expansion into more saline areas. © 2013 John Wiley & Sons Ltd
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Phenotypic traits of the Mediterranean Phragmites australis M1 lineage: differences between the native and introduced ranges
No full textThe environmental conditions in the new ranges of introduced plant species are often different from the conditions in their native ranges, and invasive plant species have been assumed to adapt to different environmental conditions by rapid ecological evolution in the invasive range after the introduction. Another interpretation of the change in plant traits after their introduction, however, is ecological fitting, which is based on the inherently high phenotypic plasticity of the species rather than on evolution. The Mediterranean haplotype M1 lineage of the wetland grass Phragmites australis was introduced to the coastal wetlands along the Gulf Coast of North America, where it is exposed to a different climate compared to its original range. The climate in the native range is arid or temperate with dry and hot summers, whereas the climate in the introduced range is warmer and has a higher and more uniform precipitation than that in the native range. This warmer and more humid environment is likely to pose different selection pressures to the plants in the introduced range and thus cause rapid evolutionary change and phenotypic differentiation in the introduced range. Here, we compared phenotypic traits of the M1 lineage from the native and introduced ranges in a common garden experiment to study the processes assisting the successful spread in the introduced range. Overall, the native and introduced groups were similar, but we detected a few phenotypic traits that diverged. Ecological fitting could be the fundamental mechanism by which the P. australis M1 lineage survives and spreads in the introduced Gulf Coast region. However, further research is needed to assess how the diverging traits observed in our study in Denmark (lower photosynthetic rates, lower chlorophylls concentration and higher leaf K concentration for the introduced than for the native genotypes) are expressed in the two ranges
Exploring the borders of European Phragmites within a cosmopolitan genus
Full text linkBackground and aims Two Phragmites australis taxa are recognized in Europe: P. australis ssp. altissimus, also known as Phragmites isiaca, in the Mediterranean region and P. australis in the temperate region. Another taxonomic group in the Mediterranean is Phragmites frutescens. European genotypes are diverse genetically, cytologically and morphologically, and are related to African, Asiatic and American genotypes. We investigated chloroplast DNA (cpDNA) diversity in Europe and defined the current borders of the European gene pool. Methodology We analysed chloroplast variation with parsimony and genetic distance methods, and compared it with that of nuclear amplified fragment length polymorphism and microsatellites. We also investigated the phenological pattern of 188 genotypes collected worldwide in a common garden in Denmark. We assumed that non-flowering genotypes could indicate climatic, geographic and/or reproductive barriers to dispersal and would have been recorded in the genetic pattern as groups genetically isolated from, or within, the European pool. Principal results The European P. australis gene pool extends from North America to the Far East and South Africa. However, African and North American genotypes are differentiating from the European genotypes. Mediterranean P. australis is genetically different from temperate P. australis and shares several similarities with Phragmites mauritianus in Africa and Phragmites karka in Asia. Phragmites frutescens shares the cpDNA sequences with both these tropical species. Two DNA bands can distinguish Mediterranean P. australis from P. frutescens and P. mauritianus and from temperate P. australis, and reveal possible hybrids among these species in the Mediterranean region. Phenological data confirmed possible gene flow within the temperate region of Europe, whereas the Mediterranean genotypes did not set inflorescences in Denmark, suggesting reproductive barriers between temperate and Mediterranean P. australis. Conclusions European P. australis appears as one of four main Phragmites groups known in the world. Further research is needed to understand the implications of long-distance dispersal at the population level
Photosynthesis of co-existing Phragmites haplotypes in their non-native range: Are characteristics determined by adaptations derived from their native origin?
Full text linkThe Gulf Coast of North America (GC) is a 'hot spot' of Phragmites diversity as several lineages (defined according to the haplotypes of their chloroplast DNA) differing in origin, genetic traits and phenotype co-exist and interbreed in this area. We analysed differences in photosynthetic characteristics among and within four haplotypes to understand if differences in gas exchange can be attributed to adaptations acquired in their native ranges. We collected rhizomes of four GC haplotypes (I2, M1, M and AI; including the phenotypes 'Land-type', 'Delta-type', 'EU-type' and 'Greeny-type') and propagated them in a common controlled environment to compare photosynthesis- irradiance responses, CO2 responses, chlorophyll fluorescence, the activity of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco), specific leaf area (SLA), pigment contents, stomatal density and guard cell length. The maximum light-saturated photosynthetic rate, Amax, in the haplotype I2 (Land-type) and haplotype M1 (Delta-type) (34.3-36.1 μmol CO2 m-2 s1) was higher than that in the invasive Eurasian haplotype M (22.4±2.3 μmol CO2 m-2 s 1). The Amax of haplotype AI (Greeny3-type) was 29.1±4.0 μmol CO2 m-2 s1 and did not differ from the Amax of the other haplotypes. The carboxylation rate (Vcmax) and electron transport rate (Jmax) followed the same pattern as Amax. The haplotypes also differed in SLA (17.0-24.3 m2 kg-1 dry mass) and pigment content, whereas stomatal density and guard cell length, Rubisco activity and chlorophyll fluorescence did not differ significantly among haplotypes. The high photosynthetic activity and gas-exchange capacity of the two haplotypes originating in tropical Africa and the Mediterranean area (haplotypes I2 and M1) are apparently adaptations derived from their native ranges. Hence, the haplotypes can be regarded as ecotypes. However, it remains unclear how these differences relate to plant competitiveness and fitness in the GC of North America environment. © 2013 The Authors
Phragmites australis: How do genotypes of different phylogeographic origins differ from their invasive genotypes in growth, nitrogen allocation and gas exchange?
No full textIt has been suggested that in plant invasions, species may develop intrinsically higher gas exchange and growth rates, and greater nitrogen uptake and allocation to shoots, in their invasive range than in their native habitat under excess nutrients. In this study, native populations of two old world Phragmitesaustralis phylogeographic groups (EU and MED) were compared with their invasive populations in North America [NAint (M) and NAint (Delta)] under unlimited nutrient availability and identical environmental conditions in a common garden. We expected that both introduced groups would have higher growth, nitrogen uptake and allocation, and gas exchange rates than their native groups, but that these enhanced traits would have evolved in different ways in the two introduced ranges, because of different evolutionary histories. Biomass, leaf area, leaf nitrogen concentrations (NH4+ and NO3−) and transpiration rates increased in introduced versus native groups, whereas differences in SLA, leaf pigment concentrations and assimilation rates were due to phylogeographic origins. Despite intrinsic differences in the allocation of C and N in leaves, shoots and rhizome due to phylogeographic origin, the introduced groups invested more biomass in above-ground tissues than roots and rhizomes. Our results support the concept that invasive populations develop enhanced morphological, physiological and biomass traits in their new ranges that may assist their competiveness under nutrient-enriched conditions, however the ecophysiological processes leading to these changes can be different and depend on the evolutionary history of the genotypes
Phenotypic traits of phragmites australis clones are not related to ploidy level and distribution range
Full text linkBackground and aims: Phragmites australis is a wetland grass with high genetic variability, augmented by its cosmopolitan distribution, clonal growth form and large variation in chromosome numbers. Different ploidy levels and ecotypes differ in morphology and ecophysiological traits, and may possess different levels of phenotypic variation. The aim of this study was to quantify the natural variation in ecophysiological characteristics of P. Australis, and to explore whether differences in ecophysiological traits can be related to ploidy levels or to the geographic origin of the clones. Methodology: Fifteen clones of P. australis from Europe and Asia/Australia, representing five ploidy levels (4x, 6x, 8x, 10x and 12x), were grown in a common garden design for 119 days. Plant growth and light-saturated rate of photosynthesis (Pmax), stomatal conductance (gs), water use efficiency (WUE) and concentrations of photosynthetic pigments and mineral ions in the leaves were measured. Principal results: The growth of the plants and most ecophysiological parameters differed significantly between clones. The mean maximum shoot height varied from 0.9 to 1.86 m, Pmax from 9.7 to 27 μmol m-2 s-1, gs from 0.22 to 1.41 mol m-2s-1 and WUE from 13 to 47 μmol mol-1. The concentrations of chlorophylls did not vary significantly between clones, but the chlorophyll a/b ratio and the concentrations of total carotenoids did. The observed differences were not explained either by the ploidy level per se or by the geographic origin or phylogenetic relationships of the clones. Conclusions: Phylogeographic relationships in P. australis on a global scale do not mirror the environment where the adaptations have evolved, and high phenotypic variation among and within clones complicates comparative studies. Future studies aimed at explaining differences in plant behaviour between P. australis populations should be careful in the selection of target genotypes and/or populations, and should avoid generalizing their findings beyond the genotypes and/or populations studied. © The Authors 2012
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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