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- Åhlén, Imenne, 1991-
(author)
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Ecosystem services of wetlands and wetlandscapes under hydro-climatic change : Impacts of water flow and inundation patterns
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Wetlands provide ecosystem services valuable for human society and are therefore often considered as nature based solution to different environmental problems. However, with centuries of wetland degradation due to anthropogenic pressures, such as agricultural expansion and forest industry, as well as pressures from climate change, there are large challenges for sustainable wetland management. Thus, for wetland protection and restoration practices to be successful, a deepened understanding on the actual mechanisms controlling wetland functions is required. Understanding how wetlands are connected, with and influenced, by their surrounding environment is also needed. Although most pressures experienced by wetlands operate on scales beyond the individual wetland scale, relatively few studies have thus far addressed large-scale functions and ecosystem service provision from hydrologically interconnected wetlands at the scale of wetlandscapes (i.e., the wetlands’ aggregated hydrological catchments in the landscape). The aim of this thesis is to investigate ecosystem service delivery from wetlands and wetlandscapes under hydro-climatic changes, considering 25 different wetlandscapes located in four different climate zones of the world. The thesis also systematically quantifies ecohydrological characteristics important for ecosystem service delivery and biodiversity support of wetlands and wetlandscapes in the Norrström Drainage basin located near Stockholm, Sweden. Conducted hydro-climatic analyses showed that impacts of climate change on wetlandscapes cannot be fully understood from average changes in climatic variables of the climate zones within which the wetlandscapes are located. This may be due to the fact that wetlands are not randomly and evenly distributed within climate zones, but may be located in areas subject to stronger climatic changes than regional means. In addition, anthropogenic pressures were on average shown to have higher impacts on runoff in wetlandscapes in comparison to climate change. The pressures however showed relatively large variability between different wetlandscapes, which needs to be considered in mitigation strategies against wetland degradation and deterioration. Similarly, regarding wetlandscape ecohydrological characteristics, results indicated that there are variability between wetlandscapes of different sizes, where larger wetlandscapes showed features that can support ecosystem services to larger degree than small wetlandscapes. Large spatial variability in wetland ecohydrological characteristics was also seen within a wetlandscape. For instance, water storage dynamics and buffering capacity varied depending on the position of the wetland in the landscape. These differences in hydrological conditions were shown to result in different inundation dynamics between wetlands, which for instance also showed to impact insect community composition.Overall, this thesis shows that assessments of wetland ecosystem services need to be addressed using a wetlandscape approach, combined with actual on site hydrological measurements. The approach used in this thesis could help decrease uncertainties related to the impacts of hydro-climatic changes and anthropogenic pressures on wetlands and wetlandscapes, supporting location-specific wetland management strategies related to creation, restoration and sustainable use of wetlands and their ecosystems.
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| 2. |
- Horvath, Robert, 1988-
(author)
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Population genomic analyses of regulatory variation and selection in Brassicaceae species
- 2020
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Doctoral thesis (other academic/artistic)abstract
- The impact of selection on regulatory variation and the contribution of regulatory changes to phenotypic variation has long been debated in evolutionary genetics. Because cis-regulatory elements such as promoters and enhancers can be difficult to identify, it has been more challenging to quantify the impact of selection on variation in cis-regulatory regions than in protein-coding regions. In this thesis, I use genomic tools to investigate gene expression variation and selection in Brassicaceae species. First, I investigated the genomic impact of selection on putative cis-regulatory regions in the genome of the crucifer species Capsella grandiflora (Brassicaceae) (Paper I). I used an assay for transposase-accessible chromatin with high throughput sequencing (ATAC-seq) to empirically identify putative cis-regulatory regions as those located in accessible chromatin regions (ACRs) in the genome of the crucifer species Capsella grandiflora. Based on whole-genome resequencing data from a natural population, I then showed that ACRs are under stronger purifying selection than other intergenic regions and that they are depleted for transposable element (TE) insertions and enriched for expression quantitative trait loci (eQTL), as would be expected if ACRs are enriched for functional elements affecting gene expression. Second, I explored how the location and silencing of transposable elements (TEs) affects selection against TEs (Paper II). Specifically, I tested a trade-off model on epigenetic TE silencing, according to which the positive effects of TE silencing on preventing TE movement conflict with negative effects of TE silencing on nearby gene expression. I found that TE silencing through the RNA-directed DNA methylation (RdDM) pathway affects selection against TEs close to genes in C. grandiflora, which is consistent with the trade-off model. Third, I used Arabidopsis thaliana single-cell expression data to investigate the relationship between gene body methylation (gbM) and transcriptional regulation (Paper III). I found that there was an indirect correlation between gbM and gene expression noise as well as a direct correlation between gbM and gene expression consistency and potentially intron retention in Arabidopsis thaliana. Fourth, I investigated the impact of demographic history on genomic signatures of selection at linked sites (linked selection) (Paper IV). This study revealed that neutral genetic diversity in C. grandiflora with a stable effective population size is influenced by linked selection whereas in Arabidopsis lyrata, which underwent a recent and strong bottleneck, neutral diversity is mainly affected by population size change. In summary, this thesis offers new insights into determinants of gene expression variation, selection on genomic features linked to gene expression alteration, as well as on the effect of demographic history on linked selection patterns in Brassicaceae.
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| 3. |
- Faticov, Maria, 1991-
(author)
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Spatial and temporal ecology of oak-associated fungal communities
- 2021
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Doctoral thesis (other academic/artistic)abstract
- Plants host a large diversity of microorganisms, which includes fungi, bacteria and archaea. Among these, fungi are highly diverse, and known to play a vital role in plant health and in regulation of the essential ecosystem functions. Nevertheless, we still lack a comprehensive understanding of the forces structuring plant-associated fungal communities in space and time. The main aim of this thesis was to decipher the drivers of the spatial patterns and temporal dynamics of fungal communities on plants. To this aim, I focused on Quercus robur and its associated fungi. Using a combination of observational and experimental studies, I assessed i) the distribution and drivers of the above- and belowground fungal communities at the landscape scale; ii) the role of climatic and trophic factors in defining the niches of cryptic species within a pathogen complex on oak and iii) the relative importance of warming, plant genotype and their interaction in shaping oak phenology and the seasonal dynamics of the associated fungal and insect communities.I found that aboveground fungal communities were highly variable among leaves within a single tree, and that belowground fungal communities had a stronger spatial structure than aboveground fungi at the landscape scale. Yet, climate, tree phenology or the distribution of the host tree did not explain spatial patterns in the above- and belowground communities. When focusing on three cryptic powdery mildew species within a pathogen complex on oak, I demonstrated that the climatic dimension is more important than the species interaction dimension for niche differentiation of these cryptic pathogens. A field heating experiment showed strong seasonal change in the structure of the foliar fungal community, with experimental warming playing an important role in driving this change. This experiment also revealed that warming and plant genotype jointly shape plant phenology, disease levels and insect abundance across the growing season.In conclusion, my findings suggest that abiotic forces can override biotic forces in structuring spatial patterns and temporal dynamics of fungal communities associated with plants. The particularly strong impact of warmer temperatures on foliar fungi in some of my studies indicates that climate warming has the potential to structure foliar fungal communities, with important implications for plant health, interactions between plants and other organisms and ecosystem functions.
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| 4. |
- Yang, Xuyue
(author)
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Coevolution and molecular background of species interactions in geographic mosaics
- 2021
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Doctoral thesis (other academic/artistic)abstract
- In complex food webs, species often interact with each other indirectly through mediating species. As a result of geographic mosaic of coevolution, such interactions are often evolutionarily unstable and the traits governing the interaction sometimes vary over time. A common example is the interactions between hosts and endoparasitoids, in which the phenotypic variation has been studied in terms of both host immunity and parasitoid virulence. This thesis focuses on characterizing the genetic background underlying the coevolution between host immune response and parasitoid virulence in a host-parasitoid interaction system. For this purpose, I used Galerucella-Asecodes system, which contains three leaf beetle species (Galerucella calmariensis, G. pusilla and G. tenella) and their shared parasitic wasp, Asecodes parviclava as the study model. By integrating next generation sequencing techniques and ab initio evidence-driven annotation approach, I generated genome assemblies and annotation of both the wasp and the three Galerucella species (Paper I & IV). In order to study variation in immune capacity at the expression level, I de novo assembled and annotated the transcriptome of G. pusilla and G. calmariensis, which have contrasting immunocompetence against the Asecodes wasp (Paper II). Using a time-course differential expression analysis, I investigated gene expression in parasitized larvae of G. pusilla and G. calmariensis after the wasp attack, and suggested that signaling and hematopoiesis genes play a key role in the host immunity in Galerucella against wasps (Paper II). Using comparative analysis of Galerucella species, I identified important genes and pathways under natural selection which potentially explain the divergence in their morphology and immunity (Paper III). I also focused on the geographic variation in the Asecodes wasp using population comparisons and identified several candidate regions of the genome for host adaptation. We also detected that genes involved in the inhibition of host immune systems and odorant/gustatory receptors are associated with variation in virulence (Paper IV).
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| 5. |
- Åhlén, David, 1988-
(author)
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Arthropods in Constructed Wetlands : Ecosystem Processes and Riparian Biodiversity
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Constructed wetlands in the agricultural landscape are known to harbor immense arthropod biodiversity, however, riparian arthropod communities have often been neglected compared to aquatic communities when studying environmental responses. These wetlands are highly productive, but vary in form and composition based on its purpose, which influences the communities that inhabit them. Both biotic and abiotic wetland characteristics are known to drive aquatic arthropod community compositions, whereas knowledge is currently lacking as to the influence from characteristic wetland properties on riparian arthropods.This thesis aimed to shed a light on characteristic wetland drivers on riparian arthropod populations and communities. We explored how chironomid emergence rates and diversities responded to wetland nutrient loads and primary production (Chapter I), and subsequently if trophic cascading relationships could be observed across the aquatic-terrestrial boundary to riparian predator abundances (Chapter II). We also explored how riparian arthropod community compositions responded to wetland hydrologic dynamism, shoreline inclines and vegetation height, and grazing management (Chapter III), and finally how characteristic wetland shoreline properties influenced riparian arthropod diversities and habitat specializations (Chapter IV).In Chapter I we found that emergence rates and diversities of chironomids increased with aquatic chlorophyll concentrations during parts of the season but decreased during others, and that chironomid taxonomic diversity correlated with the aquatic concentration of methane. These findings support previously suggested trade-offs relationship between emerging chironomids and methane. We expanded on these findings in Chapter II, where we found that both primary-and secondary consumer abundances responded to wetland nutrient loads and chlorophyll concentrations, but that this trophic pathway was more complex than from primary producers, through primary consumers to secondary consumers. In Chapter III we found that some riparian arthropods responded to hydrological dynamism, but that surprisingly many groups were unaffected. We also found that many groups responded to shoreline vegetation height, but that responses were group specific. Similarly, in Chapter IV we found that shoreline properties greatly influenced spider, beetle and predatory Diptera diversities in constructed wetlands, and that their habitat specialized species richness varied greatly between groups. Altogether, these findings illustrate the complexity of wetland arthropod ecology, and the need for attention to these previously understudied systems. It also highlights the importance of comprehension regarding constructed biodiversity wetlands if the aim is to improve biodiversity across multiple taxa.
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