1,721,050 research outputs found
Genetic structure of the submersed Ranunculus baudotii (sect. Batrachium) population in a lowland stream in Denmark
No full textUnidirectional hydrochory, reproduction mode and mating system have different impacts on the ecology of stream plants, and variation in the combination of these processes shapes unique genetic patterns which can have different consequences for the fitness of stream populations.
We studied the genetic structure inferred by AFLPs, ITS SNPs and matK sequences of three populations of the common clonal macrophyte Ranunculus baudotii in River Aarhus in order to understand the role of vegetative and sexual reproduction in the stream and how genetic variation is distributed along the stream. We also explored the genetic relationships of the R. baudotii population in River Aarhus with other species of sect. Batrachium, because hybrids have been identified in the stream and they might affect the structure of the populations.
The three studied populations were genetically distinct despite low genetic diversity and plant fragmentation is likely the main form of reproduction in the river system. The establishment of a few seeds, sexual recombination, the occurrence of putative hybrids and genetic drift in the establishment of fragments and seeds dramatically changed the genetic diversity of the populations along the stream and led to differentiation among populations. Further research is needed to understand the conditions favoring sexual reproduction and gene flow distances
Exploring the borders of European Phragmites within a cosmopolitan genus
Get PDFBackground 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
Growth and morphology in relation to temperature and light availability during the establishment of three invasive aquatic plant species
No full textInvasive freshwater plants are currently spreading rapidly and this is likely to continue with further changes in global climate resulting in changes in physical and chemical conditions in freshwaters. We studied the effect of summer temperature (20. °C, 25. °C and 30. °C) and light availability (25% and 50% of incident light availability) on shoot establishment in terms of growth rate, photosynthesis, and morphology of three invasive aquatic plants (. Elodea canadensis, . Egeria densa and . Lagarosiphon major) in order to assess their interspecific competition. Light availability had an overall stronger effect on growth rate and plant morphology than temperature in the three species. Growth rate increased three-fold from low to high light, and low light reduced belowground biomass, increased stem length, and reduced branching and lateral spread. Photosynthetic rates were the only parameter for which temperature had an equal or stronger effect than light availability. The results show that . E. canadensis has the most competitive establishment of the three species in both high and low temperature and light availability. . E. densa is most competitive in warm water compared to colder water, whereas the opposite pattern is present for . L. major which is most competitive in colder water. In conclusion, we suggest that that . E. densa will dominate warmer, shallower waters, whereas . L. major will dominate in colder, clear-water lakes, while . E. canadensis continues its established role as a pioneer species that is quickly replaced by the two taller species after their arrival. © 2012 Elsevier B.V.
Invasion strategies in clonal aquatic plants: Are phenotypic differences caused by phenotypic plasticity or local adaptation?
No full textBackground and Aims: The successful spread of invasive plants in new environments is often linked to multiple introductions and a diverse gene pool that facilitates local adaptation to variable environmental conditions. For clonal plants, however, phenotypic plasticity may be equally important. Here the primary adaptive strategy in three non-native, clonally reproducing macrophytes (Egeria densa, Elodea canadensis and Lagarosiphon major) in New Zealand freshwaters were examined and an attempt was made to link observed differences in plant morphology to local variation in habitat conditions. Methods: Field populations with a large phenotypic variety were sampled in a range of lakes and streams with different chemical and physical properties. The phenotypic plasticity of the species before and after cultivation was studied in a common garden growth experiment, and the genetic diversity of these same populations was also quantified. Key Results: For all three species, greater variation in plant characteristics was found before they were grown in standardized conditions. Moreover, field populations displayed remarkably little genetic variation and there was little interaction between habitat conditions and plant morphological characteristics. Conclusions: The results indicate that at the current stage of spread into New Zealand, the primary adaptive strategy of these three invasive macrophytes is phenotypic plasticity. However, while limited, the possibility that genetic diversity between populations may facilitate ecotypic differentiation in the future cannot be excluded. These results thus indicate that invasive clonal aquatic plants adapt to new introduced areas by phenotypic plasticity. Inorganic carbon, nitrogen and phosphorous were important in controlling plant size of E. canadensis and L. major, but no other relationships between plant characteristics and habitat conditions were apparent. This implies that within-species differences in plant size can be explained by local nutrient conditions. All together this strongly suggests that invasive clonal aquatic plants adapt to a wide range of habitats in introduced areas by phenotypic plasticity rather than local adaptation. © 2010 The Author. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved
Tracing the origin of Gulf Coast Phragmites (Poaceae): A story of long-distance dispersal and hybridization
No full text• Premise of the study: Long-distance dispersal can affect speciation processes in two opposing ways. Dispersal can promote geographic isolation or it can bring together geographically distant and distantly related genotypes, thus counteracting local differentiation. We used the Gulf Coast of North America (GC), a "hot spot" of reed diversity and evolutionary dynamics, as a model system to study the diversification processes within the invasive, cosmopolitan, polyploid grass Phragmites. • Methods: Genetic diversity was studied using collections representing all species of the genus and from all continents (except Antarctica). A range of molecular markers, including chloroplast and nuclear sequences, microsatellites, and AFLPs, was analyzed to detect DNA variation from the population to the species level and to infer phylogenetic relationships across continents. • Key results: An interspecific hybrid, Phragmites mauritianus × P. australis, and four P. australis cp-DNA haplotypes from Africa, Europe, and North America have been dispersed to the GC and interbreed with each other. • Conclusions: Long-distance dispersal and weak breeding barriers appear to be recurring phenomena, not only in the GC, but worldwide. We present data strongly suggesting that interspecific hybridization and introgression among different Phragmites species take place and appear to have contributed significantly to the diversification processes within the genus. Hence, the application of traditional species concepts within Phragmites might be inappropriate. © 2012 Botanical Society of America
Eutrophication effects on stream macrophytes
No full textMacrophytes are large, autotrophic organisms residing in aquatic environments. In streams they play important roles as substrate, shelter, and food for higher trophic levels, alter water movements and perform biochemical transformations. Unfortunately, macrophyte diversity worldwide is under threat from multiple anthropogenic factors. Eutrophication, the process of nutrient enrichment following land use intensification, is a major driver of negative stream ecosystem change, often in combination with other anthropogenic pressures such as deforestation and introduction of non-native species. The current paradigm of macrophyte response to eutrophication notes the importance of the hydrological setting and substrate type, but always encompasses modification to competitive interactions between macrophyte growth forms as nutrient concentrations become less limiting and competition for light increases. However, details of the responses of macrophytes to increased nutrient inputs under multiple stressor environments are complex and still warrant investigation if effective guidance on macrophyte management is to be developed.
In this thesis, I have addressed questions related to nutrient concentrations at which macrophytes start to accrue excessive biomass, how this relates to community shifts, what these community shifts look like and how they may be modulated by other variables. Specifically, I have used a mix of field observations and mesocosm experiments to:
i) investigate differences in community composition of macrophyte communities in streams along a eutrophication gradient.
ii) experimentally explore how external nutrient concentrations affect internal nutrient status, and consequently the growth, morphology, and photosynthesis of stream macrophytes across a range of irradiances.
iii) investigate if these responses lead to differences in competitive outcomes between species in mixed cultures.
To investigate relationships between eutrophication and macrophytes in streams in Aotearoa New Zealand, I surveyed 30 lowland streams on the country’s North Island, focusing on the Waikato region. I targeted sites with as few confounding factors as possible by using existing stream classification data to select reaches in each stream that had low slope, were unshaded, and a discharge of around 1 m3 s-1. From those meeting these criteria I used a pre-existing, land-use based nutrient yield model to selected streams expected to provide a range of nutrient concentration. At each site I sampled nutrients (N and P) in water and sediment and analyzed the dominant macrophyte species for internal N and P content. I quantified community structure on five transects across each stream.
To explore links between environment and macrophytes I combined stream descriptors from national datasets in combination with the macrophyte community data and a list of trait scores of the encountered species in a RLQ multivariate analysis. The results showed a gradient in macrophyte community structure, a striking feature of which was the change in percentage of non-native species in the streams: eutrophic streams have almost no native species present. Additionally, many nutrient enriched streams were heavily clogged by macrophyte biomass, with species showing traits related to high performance and effective dispersal. A subsidiary gradient in the RLQ analysis, driven by nitrate and sediment phosphorous, saw a high presence of emergent species in eutrophic streams. This can be because the emergent species have a high nitrogen use efficiency compared to submerged species and can deal with a high turbidity by growing out of the water. A second subsidiary gradient, driven by water column phosphorous, correlated with eutrophic streams having a high degree of submerged non-native species; Ceratophyllum demersum, Egeria densa, Lagarosiphon major, and Elodea canadensis, all species that disperse primarily through fragmentation and can utilize bicarbonate as a carbon source. Phosphorous and carbon availability probably is a major driver for the presence of these species in these streams.
To test inferences made from observational field investigations, growth, morphological, and photosynthetic responses to different levels of nutrient concentration were investigated in a new experimental mesocosm setup. The system comprised four flumes fed by local groundwater stripped of ions by a reverse osmosis system, then dosed with major ions, macro- and micronutrient elements in controlled amounts to ensure finely controlled growth conditions.
The first experiment addressed hypotheses around the impact of nitrate concentration on growth of two pondweed species common to Aotearoa New Zealand, Potamogeton crispus and P. ochreatus, and possible interactions between nutrient and irradiance. Four nutrient concentrations (control ~0 µg NO3—N L-1, low ~20 µg NO3—N L-1, medium ~250 µg NO3—N L-1, and, high ~5000 µg NO3—N L-1) were combined with four light levels (67.7, 44.5, 30.9, and 7.8 mol photons m-2 d1) in a full factorial design. I measured internal nitrogen (N) and carbon (C) content, growth rates, and morphology and used pulse amplitude modulated fluorometry to make photosynthesis-irradiance curves. The four external nutrient concentrations gave rise to two distinct groupings of plants based on their final internal nutrient content: a high-N group (2-4 % N) from high and medium nitrate treatments and a low-N group (~1 % N) from the low and control nitrate treatments. High-N plants of both species had faster growth rates and grew wider and taller than the low-N plants, but P. crispus grew widest and branched more, especially at high light levels. Low light availability negated any significant difference between N groups and, notably, low-N individuals of P. ochreatus performed better in this treatment than those of P. crispus. In general, the native P. ochreatus performed better than the non-native P. crispus under low nutrient stress, and the latter was best at high light and high nutrients. The results suggest that P. crispus has a great proliferation potential in eutrophic areas, and that lowering resource levels can help manage not only macrophyte proliferation, but also invasive species. A potential competitive advantage can be inferred for P crispus in eutrophic, well-lit waters.
The second mesocosm experiment investigated competitive interactions between the non-native and native pondweed. Four nutrient treatments were again used (0, 40, 120, and 400 µg NO3—N L-1), combined with two light treatments (18 and 3 mol photons m-2 d-1) in a full factorial design. In each treatment I compared growth of each species when plated in monoculture and mixed culture pots. For each replicate, growth rate and morphological traits (main stem length, lateral spread, branching degree, and root length) were measured. Neither species performed differently in mixed- or mono-specific cultures, indicating no inter-specific interactions under the experimental conditions. Rather, in mixed culture plots the outcome, in terms of growth differentials between taxa, reflected the responses of each species to the treatment. Increasing irradiance tended to result in P. crispus outperforming P. ochreatus, while increasing nutrient levels shifted allowed P. ochreatus to outperform P. ochreatus, particularly at low irradiance. Based on the results of this study, there is no direct short term competitive suppression of either species by the other, but differences in trait expression at different resource levels/combinations might still lead to competitive exclusion in a more natural setting.
In this thesis I have shown that macrophytes respond to increases in external nutrient level by taking up more nutrients, increasing growth and expressing morphological plasticity. This is species dependent, however, and it is these differences in the ability to respond that appear to shape the macrophyte communities in streams. Streams with high light and nutrient supplies are susceptible to high accrual of biomass by a subset of responsive species that may ultimately end up being the only species present in these streams. I found that the eutrophication threshold for nitrogen is quite low, below 250 µg NO3-N L 1. Macrophyte growth was evident at nitrate concentrations only seen in quite pristine streams and several nutrient species seem to determine community compositions in streams. Thus, management actions for the protection of stream ecosystems would benefit from managing resource levels in general rather than focusing on a specific stressor
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Genetic diversity in three invasive clonal aquatic species in New Zealand
Get PDFAbstract Background Elodea canadensis, Egeria densa and Lagarosiphon major are dioecious clonal species which are invasive in New Zealand and other regions. Unlike many other invasive species, the genetic variation in New Zealand is very limited. Clonal reproduction is often considered an evolutionary dead end, even though a certain amount of genetic divergence may arise due to somatic mutations. The successful growth and establishment of invasive clonal species may be explained not by adaptability but by pre-existing ecological traits that prove advantageous in the new environment. We studied the genetic diversity and population structure in the North Island of New Zealand using AFLPs and related the findings to the number of introductions and the evolution that has occurred in the introduced area. Results Low levels of genetic diversity were found in all three species and appeared to be due to highly homogeneous founding gene pools. Elodea canadensis was introduced in 1868, and its populations showed more genetic structure than those of the more recently introduced of E. densa (1946) and L. major (1950). Elodea canadensis and L. major, however, had similar phylogeographic patterns, in spite of the difference in time since introduction. Conclusions The presence of a certain level of geographically correlated genetic structure in the absence of sexual reproduction, and in spite of random human dispersal of vegetative propagules, can be reasonably attributed to post-dispersal somatic mutations. Direct evidence of such evolutionary events is, however, still insufficient.</p
Variations on the Author
Get PDF“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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