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Coming dissertations at Uppsala university

  • Genetic Adaptation and Speciation in Darwin’s Finches and Atlantic Herring Author: Fan Han Link: Publication date: 2020-01-13 13:30

    Natural selection acts on existing genetic variation to drive genetic adaptation of organisms to various ecological niches. Interaction between closely related populations, through processes such as competition and hybridization, may either lead to their divergence or population fusion, which has consequences for adaptation and the formation of species. This thesis aims to use two natural populations, Darwin’s finches and Atlantic herring, as models to explore the genetic mechanisms underlying ecological adaptation and speciation.

    The ecological adaptation of Darwin’s finches across the Galápagos Islands is primarily reflected by variation in beak morphology. Using whole-genome re-sequencing of all Darwin’s finch species, we discover that a locus, HMGA2, is highly associated with variation in beak size. Data collected before and after a severe drought show that this locus plays a critical role for ecological character displacement in large ground finches Geospiza magnirostris and medium ground finches G. fortis.

    Genomic islands of divergence refer to genomic regions of elevated divergence when comparing the genomes of closely related taxa. Establishment of these genomic islands can reflect a role in reproductive isolation or be related to ecological adaptation or background selection. Investigating their properties can shed light on how new species evolve. We study the landscape of genomic islands in Darwin’s finches, and find that the most pronounced genomic islands are likely ancient balanced polymorphisms, which govern adaptive variation in beak morphology.

    Hybridization is increasingly recognized as an important evolutionary process which may lead to speciation. We study two cases of hybridization in Darwin’s finches. In the first case, a new lineage of Darwin’s finches was founded through hybridization between a resident medium ground finch G. fortis and an immigrant Española cactus finch G. conirostris. In the second case, female-biased introgression occurred predominantly from medium ground finches G. fortis to common cactus finches G. scandens. Our genetic analysis on the mosaic genomes of hybrid finches show that non-random mating and natural selection primarily determine the outcome of hybridization.

    We generate a chromosome-level assembly of the Atlantic herring with a total size of 726 Mb, which coincides with a high-resolution linkage map and an LD-based recombination map. This facilitates the identification of an ~8Mb inversion, which is likely to be associated with ecological adaptation in herring to differences in water temperature. The contiguity of the assembly sorts placement of loci under selection that were identified based on a previous, highly fragmented draft assembly of the herring genome.

  • Atomic Scale Modelling in Photoelectrocatalysis : Towards the Development of Efficient Materials for Solar Fuel Production Author: Giane B. Damas Link: Publication date: 2020-01-10 12:10

    Using sunlight to produce valuable chemicals has been pointed out as an interesting alternative to deal with the well-known environmental problem related to the use of fossil fuels for energy generation. Thus, it is crucial for this field the development of novel photocatalysts that could drive the uphill reactions with high efficiency while presenting low price and toxicity. In this context, conjugated polymers with a donor-acceptor architecture have shown good photoactivity for the hydrogen evolution reaction (HER) due to their advantageous properties, including a broad UV-Vis absorption spectrum and thermodynamic driving force to carry out the charge transfer processes. In this thesis, a series of fluorene- and benzothiadiazole-based polymers are evaluated by means of ab initio methods as potential candidates for photocatalytic HER. A set of small-molecules with well-defined molecular weight have also been considered for this application. In general, tailoring a chemical unit has enabled an improvement of the absorption capacity in benzo(triazole-thiadiazole)-based polymers and cyclopentadithiophene-based polymers, with a higher impact exhibited upon acceptor tailoring. On the other hand, all systems under investigation present favorable thermodynamics for proton reduction or hole removal by an appropriate sacrificial agent. In particular, it is demonstrated the active role played by nitrogen atoms from the acceptor units in the hydrogenation process, whose binding strength is significantly decreased in benzo(triazole-thiadiazole)-based polymers. Furthermore, the extension of the electron-hole separation has been assessed through the calculation of the exciton binding energies, which are diminished with an improvement in the donating ability on cyclopentadithiophene-based materials.

    In another approach to deal with the aforementioned problem, it has been considered the direct conversion of carbon dioxide into formic acid, an important chemical that finds applications in fuel cells, medicine and food industries. In this thesis, such electrocatalytic process has been investigated by using Sn-based electrodes and Ru-complexes. In the former case, a solid-state modelling approach based on slab geometries to model surface states has been employed to explore the reaction thermochemistry. The outcomes support the reaction mechanism where the carbon dioxide insertion into the Sn-OH bond is a thermodynamically favorable step prior to reduction, which has a redox potential in fair agreement with the measurements carried out by our collaborators. In a Ru-complex, the reaction mechanism is likely to follow the route with natural production of CO due to ligand release after the first reduction process, which is further protonated to originate the active species. In this case, the insertion occurs at the Ru-H bond to generate a carbon-bound species that is the intermediate in the formic acid production after the second protonation step. Finally, it has been studied the physical adsorption of carbon dioxide in metal-organic frameworks with a varying metallic center in a theoretical point of view.

  • The Water Taboo : Restraining the Weaponisation of Water in International Conflict Author: Charlotte Grech-Madin Link: Publication date: 2019-12-20 13:52

    Why do nation states in conflict with one another refrain from weaponising water? Water has long been a standard weapon of armed conflict. In the post-World War II period, however, nation states in international conflict have made concerted efforts to restrain its weaponisation. This is puzzling given the absolute vitality of water to an adversary, a long historical record of water weaponisation, and water’s heightened military utility in the face of rising scarcity. Distinct from existing scholarship, this study contends that water has become embedded in a global normative inhibition – a “water taboo” – that denounces its weaponisation as morally unacceptable. Through qualitative case research involving elite interviewing and historical analysis, this study examines the water taboo. Three focal points include its existence, how it evolved over time, and most importantly, how it influences states’ decisions on whether or not to weaponise water. The study first outlines the water taboo. Next it analyses the taboo’s historical origins, and later its strengthening from the 1950s to the present via a confluence of broader humanitarian and environmental protection movements. It then examines the taboo’s influence in a “hard” case of India in the 1999 Kargil War, and “deviant” case of the US in the 1991 Gulf War. Altogether, the study contributes that: (i) a moral aversion to weaponising water exists; (ii) it has evolved through multiple phases of norm strengthening in the past seventy years; and (iii) it influences state behaviour at an instrumental level and, in some cases, more internalised level of compliance. Where the taboo is not fully internalised, this study finds that the taboo’s influence is mediated by levels of military necessity, operational dependence of the military on politicians, and embeddedness of belligerents in the international community. These findings firmly extend IR and Peace and Conflict literature into the domain of water, and suggest future avenues for research and policy to charter long-term peace and security around water.