Doctoral Theses / Doktorsavhandlingar Institutionen för biologi och miljövetenskap

Permanent URI for this collectionhttps://gupea-staging.ub.gu.se/handle/2077/29053

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Are Alternatives to Conventional Plastics really Safer? Exploring Toxicity of Biobased, Biodegradable and Recycled Microplastics in Fish: The Role of Polymer Type, Associated Chemicals, and Exposure Conditions Across Multiple Biological Endpoints
(2025-10-03) König-Kardgar, Azora
Microplastics are a pervasive and complex class of contaminants in aquatic environments, raising concerns about both their physical and chemical impacts on organisms. The plastic pollution crisis has been identified as a global threat, and several possible solutions have been proposed, though these must be evaluated to ensure that they are safer and more sustainable than conventional, fossil fuel-based plastics. This thesis investigates the biological effects of microplastics in fish, with a focus on polymer type, life stage, and associated chemicals, including those leaching from recycled plastics. Using a combination of chronic or acute dietary exposure experiments and early-life stage embryo assays, I explored how conventional, biobased/biodegradable, and recycled polymers affect behavior, physiology, and gene expression in freshwater fish. In juvenile European perch, chronic ingestion of poly(L-lactide) (PLA), a biobased and biodegradable polymer, significantly altered social behavior, indicating the risk of toxicity from a polymer often marketed as eco-friendly. The following connecting experiment, also in juvenile perch, investigated a comparison of biobased/ biodegradable and conventional polymer mixtures. It revealed that only the biobased plastics induced significant changes in fish growth and hepatic gene expression related to oxidative stress and inflammation, while conventional polymers had no detectable effects on any measured endpoints. These findings challenge assumptions about the relative safety of bioplastics. To address chemical exposure risks, leachates from recycled polyethylene pellets collected from recycling facilities in different countries were analyzed and found to contain a complex mixture of plastic additives and contaminants (NIAS), such as pesticides and pharmaceuticals. Zebrafish embryos exposed to these leachates exhibited upregulation of genes involved in adipogenesis and endocrine pathways, though no effects on behavior, morphology or survival occurred. Lastly, dietary exposure to a conventional plastic mixture in Nile tilapia demonstrated potential life stage- and exposure duration-dependent effects: inflammatory responses were observed in juveniles over long-term exposure but not in adults under acute exposure. Together, my studies highlight that polymer type, chemical content, and organismal life stage all influence the effects of microplastic exposure and toxicity of plastics chemicals. Importantly, biobased/biodegradable and recycled plastics, though widely promoted as sustainable alternatives, can exert biological effects equal to or greater than those of conventional plastics, underscoring the need for critical evaluation of emerging new plastic materials.
Unveiling pesticide effects and antibiotic resistance in freshwater microorganisms through genomics.
(2025-09-29) Gómez Martínez, Daniela
A large proportion of the rivers worldwide are impacted by human activities and pollution. Freshwater microorganisms, including bacteria, algae, and fungi are crucial for nutrient cycling and primary production. Chemical pollution can alter aquatic microorganisms at both cellular and community-levels, sometimes leading to acclimation or adaptation responses. Antibiotic resistance is the mechanism by which bacteria increase their tolerance towards antibiotic exposure. The rapid increase of antibiotic resistance in pathogenic bacteria during the last decades has become a major global health problem. River sediments, can act as reservoirs of ARGs that persist and spread in the environment. The four papers in this thesis investigate how freshwater microorganisms respond and acclimate to pesticides at both cellular and community levels and explore the presence and characteristics of ARGs in a high-flow Scandinavian river. Altogether, this thesis combines single-organism and community approaches in laboratory and field settings, integrating metagenomics, transcriptomic, phenotypic, and chemical profiling tools. Paper I showed that the green alga Raphidocelis subcapitata acclimated within four weeks to toxic but environmental levels of the herbicide diflufenican. This acclimation was accompanied by fitness trade-offs. Acclimated cells were smaller and overexpressed stress-related genes, such as genes related to DNA repair and replication, and cellular division. Paper II demonstrated that aquatic biofilms exposed to environmental levels of the fungicide tebuconazole exhibited a reduction in fungal biomass, while algae and bacteria were unaffected. As a response to tebuconazole, the fungal community composition shifted. Moreover, biofilms also partly degraded tebuconazole, releasing unknown transformation products, suggesting a potential acclimation or adaptation mechanism. In paper III, a field ecotoxicological assessment was performed using periphyton. A reduction in algal species richness was observed, accompanied by changes in community composition in periphyton of agricultural streams, compared to non-agricultural streams. Agricultural streams had a higher pesticide mixture toxic pressure, and green algae (Chlorophyta), decreased in relative abundance in the agricultural streams, while opportunistic cyanobacteria (Cyanobacteriota) increased, likely replacing them. Paper IV characterized the sediment resistome of the Göta Älv river and examined the potential influence of WWTP effluents as sources of antimicrobials and ARGs. ARGs were found to accumulate downstream, with distinct resistome composition and taxonomic diversity compared to the upstream sites. Overall, this thesis investigates how human activities influence freshwater microorganisms using high-throughput molecular methods. The studies reveal molecular mechanisms, cellular responses, community shifts, and ecologically or clinically relevant genes in freshwater microbial communities resulting from pesticide exposure as well as agricultural and urban activities.
Resolving pollination paradoxes: Bridging theory and empirical observations to understand pollination ecology and evolution
(2025-05-14) Osterman, Wilhelm H. A.
Animal‐mediated pollination underpins the sexual reproduction of an estimated 230,000 flowering‐plant species and involves at least 300,000 florivorous animals. Yet we lack a broad, community‐level synthesis of how variation in animal pollination shapes both ecosystem function and species assemblages. Here, I review key challenges and opportunities in pollination ecology, introduce and examine ‘paradoxes’ of pollination biology, and argue that much can be gained from examining and discussing contradictions in the pollination literature. I use community ecological theory to explore the role of pollination in plant community assembly and vice versa in three Arctic sites (Chapter I). I then discuss how pollination and frequency-dependent effects arising from rarity impact plant diversification by limiting the establishment of new polyploid populations (Chapter II and III). I then discuss how the theoretical framework for understanding sexual selection in hermaphroditic plants can develop in the light of community ecological theory (Chapter IV). In the last two chapters, I focus on how implementing theoretical frameworks in pollination ecology can improve our understanding of threats from global change. Specifically, I show that implementing a more mechanistic framework can improve predictions of how pollinators contribute to ecosystem services, which impacts how both agricultural and natural ecosystems will be influenced by pollinator decline (Chapter V). Finally I show that understanding the mechanistic underpinnings of plant reproduction and how it is associated with plant size is crucial for understanding the consequences of shifting flower phenology (Chapter VI). I suggest that a conceptual synthesis in pollination biology is necessary to advance our understanding of how pollination contributes to the maintenance of natural ecosystems, how it contributes to society, and how pollination may be altered due to anthropogenic activities.
Heat and drought responses of tropical trees in a warming world
(2024-12-11) Manzi, Olivier Jean Leonce
Tropical trees face increasing heat and drought stress under climate change, yet their physiological responses remain poorly understood. This thesis explores the mechanisms underlying heat and drought tolerance in tropical trees, focusing on leaf temperature regulation, heat tolerance, and tree water use responses. We studied different tree species grown in common gardens at three sites along an elevation and climate gradient in Rwanda. Paper I demonstrates that leaf temperatures (Tleaf) can exceed air temperatures (Tair) by up to 20°C. Moreover, Tleaf of sun-exposed leaves greatly exceeds simultaneously measured canopy temperatures (Tcan). As a result, thermal safety margins are overestimated when based on Tcan or Tair instead of Tleaf, emphasizing the need to account for within-canopy variation in Tleaf to understand and predict leaf physiological heat stress. Results also emphasizes the role of traits such as leaf size and stomatal conductance (gs) in controlling interspecific variation in Tleaf. Papers II and III reveal that species with traits predisposing them to higher Tleaf (i.e., larger leaves, lower gs) tend to exhibit greater photosynthetic heat tolerance. While partial thermal acclimation of heat tolerance through membrane lipid adjustments was observed, it was insufficient to offset the increase in growth temperature, resulting in reduced thermal safety margins. More costly leaves, with higher leaf mass per area, had higher heat tolerance. Paper IV highlights significant acclimation in tree water use traits, with increased gs (at standard conditions) alleviating leaf overheating under moist conditions and reduced minimum conductance limiting water losses under periods of water shortage. Leaf osmotic potential, however, showed no plasticity. Paper V identifies variability in tree water use and status responses to declining soil water content. Larger trees, likely supported by deeper root systems, maintained higher water status, transport and growth during drought, suggesting tree size-related advantages in young forests or tree plantations under water-limited conditions. Together, these findings advance our understanding of how tropical trees respond to heat and drought stress and how these responses vary among species. The results underscore the critical role of species-specific traits in modulating resilience and highlight limitations in acclimation capacity under changing climatic conditions. These insights contribute to improving vegetation models, guiding forest restoration efforts, and informing climate-resilient forest management strategies.
Drivers of biological diversity and responses to global changes in marine invertebrates
(2024-11-08) Duvane, Jossias
Human activities, in particular global changes (e.g., ocean warming - OW and ocean acidification - OA) are projected to drive some marine species to extinction within the coming decades. Marine invertebrates are amongst the most vulnerable to these changes due to the increased energetic cost to maintain intracellular pH homeostasis. To mitigate extinction, organisms may migrate, acclimate or adapt genetically. While these mechanisms are increasingly documented, they are not fully understood. This knowledge is critical for assessment of extinction risks, an important index for effective conservation and management of marine biodiversity. This thesis aims to increase our understanding on the drivers of biological diversity and sensitivity of marine invertebrates to OW and OA. Specifically, I assess (1) the quality of inferences on adaptive evolution in recent publications on responses of marine invertebrates to OW or OA and summarize the current knowledge and identify the gaps (Paper I); (2) the drivers of genetic diversity, structure, connectivity among Acropora austera populations across Mozambique coral reefs (Paper II); (3) the sensitivity to low pH in larvae of the sea urchin, Tripneustes gratilla, from subtidal and intertidal seagrass meadows with contrasting pH variability at Inhaca Island, Mozambique (Paper III); (4) the role of natural fluctuation in pH on the response of larvae of the sea urchin Echinus esculentus to low pH (Paper IV). Field genome scans surveys, laboratory experiments and systematic literature review were used. My systematic literature review (Paper I) highlights that publication on adaptive responses of marine invertebrates to OW or OA used more frequently strong methods for inferences of genetic change, such as common garden experiments and molecular genetic analysis. Methods for weaker inferences, such as comparison to model prediction, were less frequently used. On the other hand, reciprocal transplants, the stronger method for inferring adaptive change was less used in comparison with weaker methods such as phenotypic and genotypic selection. I also showed different levels of genetic variability and connectivity between populations of corals along the Mozambique coast. These geographic differences in levels of genetic diversity and connectivity may be explained by oceanographic factors and mode of reproduction of the corals (Paper II). Larvae of the sea urchin T. gratilla from Inhaca Island had reduced fitness when exposed to low pH. Moreover, larvae from adults collected in an intertidal habitat were more sensitive to low pH as compared to larvae from adults collected in a subtidal population. This result reveals population specific responses to low pH and challenges current theories that predict higher tolerance in individuals living in habitats with higher pH range (Paper III). Under present day natural variability in pH, the extreme low pH does not appear to be the main driver of biological responses in larvae of the sea urchin E. esculentus and adaptation to such conditions might be associated with a cost of plasticity but not a cost of canalization (Paper IV). Overall, this thesis shows that oceanographic factors and natural variability in pH influence the levels of genetic diversity and biological sensitivity in populations of marine invertebrates. These parameters should be considered to better evaluate the ability of marine invertebrates to withstand environmental changes and to sustain the provision of ecological functions, and guide conservation strategies.
Aquatic ecotoxicity of nanomaterials in fish in vitro models: Cytotoxicity and sublethal effect screening of pristine and transformed nanoparticles.
(2024-10-07) Brookman-Amissah, Marianne Gloria
With the increased production and use of engineered nanoparticles (ENPs) came an increased risk of release into the aquatic environment. This has raised concerns about the unknown impact on the aquatic ecosystem. To improve our understanding of the situation we face, knowledge of nanoparticle effects on aquatic organisms needs to be extensively studied. Enquiry into a better understanding of the transformation processes these particles undergo in the environment is essential for ecotoxicological risk assessment. This thesis explores the effects of pristine ENPs on fish in vitro models. It presents results on the impact of natural organic matter (NOM) and chemical mixtures on the environmental transformation of nanoparticles ranging from metal/metal oxides to rare earth elements and plastics. Results revealed a dose-dependent reduction in cellular metabolic activity, membrane integrity and lysosomal activity after particle exposure in higher concentrations with some particles exerting more damage than others. An increase in ROS and EROD activity indicates cellular infiltration of the NPs, which leads to redox imbalances which could induce oxidative stress and cell damage. At the same time, in most particles, the presence of NOM generally reduced the intracellular ROS generation The plastic particles did not significantly affect the cytotoxicity, though the trends observed were particle size and concentration dependent. Co-exposures with high-dosed WAF significantly decreased cell viability and increased ROS generation with an additive effect, while lower concentrations were found to be protective compared to the single exposures. The combined exposure of these products was indeed found to induce complex results that cannot be attributed to a single contributor, even though WAF was found to be highly toxic. This thesis emphasizes the need for more sensitive methods and biomarkers to assess toxicity and that environmental transformation of nanoparticles and mixtures with other environmental pollutants do impact the overall toxicity of the particles. It also highlights the critical need to incorporate these factors into nanoparticle risk evaluations to better inform policy and regulation.
Extensions of the Multispecies Coalescent in Bayesian Phylogenetics: A Study of the Southern African-centred Stoebe Clade (Gnaphalieae: Asteraceae)
(2024-09-30) Shaik, Zaynab
The Tree of Life represents the complex relationships between all species, and recent advances in phylogenetic methods have dramatically expanded our ability to study these connections. However, there is still no universal solution to the species problem, and methodology to account for migration is in its infancy. This thesis evaluates extensions of the multispecies coalescent for species delimitation, and phylogenetic inference while accounting for post-divergence gene flow. We focus on the Stoebe clade of paper daisies (Gnaphalieae: Asteraceae), centred in the diverse Cape Floristic Region of South Africa. Analytical species delimitation and complementary taxonomic evidence are employed to resolve the Seriphium plumosum complex, revealing four species new to science, which we formally describe. Our phylogenetic analysis provides a refined resolution of the internal relationships within the Stoebe clade, supporting an updated classification that merges most genera under Stoebe L. Further analysis using target-capture sequencing largely corroborates previously inferred relationships and shows that probes designed with ingroup taxon sequences spanning intronic regions markedly enhance both sequence retrieval and length relative to the Asteraceae-wide Conserved Orthologous Probe Set II. We also introduce a robust method for rectifying sample misidentification by cross-referencing with existing molecular datasets. Further, we explore phylogenetic inference approaches that account for time-decaying migration after lineage divergence and demonstrate that models incorporating migration improve phylogenetic accuracy with relatively few loci while reducing computational demands relative to the standard multispecies coalescent. Collectively, this work refines the classification of species as monophyletic entities and advances our understanding of methods for reconstructing phylogenetic relationships while capturing the complex evolutionary processes that shape allele distributions through time.
Bridging the past to the present: investigating species boundaries with herbarium specimens and next-generation-sequencing. A case study of circumpolar Silene sect. Physolychnis
(2023-10-30) Quatela, Anne-Sophie
During the recent decades, genetic information enclosed in herbarium collections have been partly revealed, largely due to the fast-moving high-throughput sequencing technologies. However, the genetic outcome from herbarium material is limited by its degradation over time, often worsened by certain preservation methods. The primary goal of this thesis is to use high-throughput sequencing and target capture to optimize the use of herbaria in systematics, with a focus on disentangling evolutionary relationships within diploid circumpolar members of Silene sect. Physolychnis. In Manuscript I, I investigate whether Silene herbarium specimens can yield long DNA reads with target capture and a Silene-specific bait panel, enriching 48 low copy nuclear genes. To isolate long DNA fragments, I optimize wet lab protocols to increase the DNA output and the recovery of long DNA fragments post-size selection. The sequencing is performed with highly accurate hifi reads from PacBio SMRT Sequel. The results show that specimens less than thirty years old yield long DNA reads with high sequencing depth, giving hope for accessing genomic complexity from young herbarium material. In Manuscript II, the design of a target capture experiment is described step-by-step. Even though universal kits are available, the development of group-specific kits is gaining in popularity. This review shows how to choose orthologous genes and how to design probes tailored to a group of interest. It breaks down the actual target captures to three steps: hybridization, incubation and wash. In Manuscript III, I give an overview of species delimitation methods based on a multi-locus dataset. I describe how multi-locus approaches have revealed gene tree discordance, caused by incomplete lineage sorting and gene flow. I emphasize that coalescent-based methods are models of choice to take into account incomplete lineage sorting, and how they are implemented. I also describe how allopolyploidization impacts species boundaries, and how it is implemented in multilabelled- and network-like trees. In Manuscript IV, I test a recently proposed taxonomy of the diploid and circumpolar Silene uralensis group using 42 low copy nuclear genes and the multispecies coalescent model STACEY. The phylogenetic inference shows little support to the taxonomy of the complex, suggesting the need to revise the group taxonomically. The group includes diploid and polyploid taxa difficult to tell apart morphologically. To identify allopolyploid plants, I developed a novel method based on allele phasing. The method is demonstrated as being efficient in determining allopolyploids, also from very old herbarium specimens. This thesis shows that herbarium material may hold unsuspected potential to study genomic complexity and disentangle taxonomic complex groups. This is made possible by the fast development of high-throughput sequencing, bioinformatic pipelines and computational resources.
Morphological and chemical leaf traits of tropical montane tree species and their responses to warming
(2023-10-26) Manishimwe, Aloysie
Leaf morphological and chemical traits of tropical trees vary along climate gradients, but it is currently unclear how they will respond to a rapidly warming climate and how this will vary among species. Considering this, tropical trees native to East and Central Africa were investigated in three complementary studies in Rwanda. Differently aged trees of both early (ES) and late (LS) successional species from two types of upland forest, Lake Victoria transitional rainforest (LVTF;1600-2000 m a.s.l.) and Tropical montane rainforest (TMF; 2000–3000 m a.s.l.) were included. The three studies were: (i) an elevation gradient study on young trees of 18 species planted at three sites, from 2400 m to 1300 m a.s.l (15.2-20.6 ºC mean annual temperature, MAT); (ii) an elevation gradient study on mature trees of four species growing at five sites from 2700 to 1700 m a.s.l (13.3-19.5 ºC MAT); and (iii) a study of 20 mature tree species growing in 15 permanent monitoring plots in Nyungwe TMF located between 2500 to 1950 m a.s.l. (14.1-16.1 ºC MAT). The variation in leaf morphology (LMA: leaf mass per area, LA: leaf size or area, leaf W/L: leaf width to length ratio or leaf shape) and leaf macro- and micronutrients were investigated. LA and LMA decreased while leaf W/L increased with decreasing elevation in most species. The decline in LMA with declining elevation was mostly due to decreasing leaf density rather than leaf volume per unit area. The leaf morphological elevation responses of young and mature trees were essentially the same for the four species included in all three studies. The elevation gradient site effects on leaf morphology are likely related to both increasing temperature and vapour pressure deficit (VPD) from high to the low elevation sites. The most limiting nutrient was P independently of ontogeny, successional strategy, and elevation, although for some species and age classes also K, S, Zn, Cu could potentially be co-limiting. The ratios of most nutrient elements (except K, Ca, Mn) to N were higher in mature compared to young trees. Leaf nutrient resorption efficiency varied among species but not between successional groups. The juvenile tree leaf concentration of most nutrients across species and sites correlated significantly with its soil concentration (N, P, K, Ca, Mg, Fe, Zn, and Cu) and soil pH (K, Ca, Mg, Fe, Mn, Zn, B, Cu, and Mo). Down the elevation gradient, mass-based leaf contents of Ca, Mg, Fe, B and Mo increased while N, P, Zn, and Cu decreased with most species responding similarly., while the elevation effect of other elements were more variable among species. The nutrients declining down the elevation were all potentially limiting and warming will therefore likely enhance nutrient limitation and possibly lead to reduced productivity of these species. However, no such elevation trend was observed for mature trees. The elevation effect may therefore be transient with age. In general, and independently of tree age, the variation in both leaf morphology and leaf nutrient content and ratios was considerably larger between species than between sites, despite large site differences in both soil and climate conditions. Several morphological and nutrient variables differed significantly between successional groups, but the species identity explained more the main variation between species than the successional strategy. This study therefore clearly shows the risk of predicting forest responses to climate change using only few species, highlighting the need for more data from tropical trees.
Novel Marine Ingredients for Aquaculture - Fish Nutrition, Physiology and Intestinal Health
(2023-10-24) Warwas, Niklas
Aquaculture is among the fastest growing food production sectors globally and supplies more fish to the growing human population than capture fisheries. One of the major challenges in salmonid aquaculture is to find renewable and sustainable feed ingredients which also satisfy the nutritional requirements of the fish. Feed production accounts for the majority of both the environmental and economic footprints of modern aquaculture operations. It is therefore clear that sustainable aquaculture can only be achieved using sustainable feed. The overarching aim of this thesis is to expand the pool of alternative feed ingredients by developing and evaluating novel marine ingredients using both a nutritional and a physiological approach. The aspiration is further to carry out this work in the framework of a circular economy approach where side streams and their nutrients are reintroduced into the food production system rather than discarded. Paper I demonstrates that marine yeast (C. sake) can be cultivated on processing water of the fish processing industry. Marine yeast could therefore be used transform side streams into a promising feed ingredient for salmonid fish. C. sake contained 55% protein and significant levels of omega-3 fatty acids. Additionally, C.sake was highly digestible by rainbow trout and therefore can be used in diet formulations at up to 20% of the overall content without negative effects on animal health and growth. Furthermore, there is potential to use C. sake as an immunostimulant due to its complex polysaccharide and nucleotide content. Paper II assesses the potential of using a marine insect in fish feed. Marine insects contain higher levels of essential nutrients, such as unsaturated fatty acids and amino acids, compared to terrestrial insects. However, they have not been evaluated as feed ingredients for salmonid fish. This thesis shows that the seaweed fly (Coelopa frigida) can be cultivated on side streams from an algae farm producing brown seaweed. Furthermore, seaweed fly larvae could substitute 40% of fish meal content without negative effects on growth and intestinal health. Compared to black soldier fly larvae, C. frigida inclusion resulted in higher feed intake and growth for rainbow trout. Papers III & IV address the possibility to use fish processing side streams in feed formulations without additional processing. Fish processing side streams are highly nutritious and currently contribute to about 30% of the global fishmeal and fish oil production. However, due to the additional processing costs and the lower price of fishmeal and oil produced from sides streams compared to whole fish fishmeal, large amounts of such side streams remain unused or are converted to lower value commodities. In paper III, three different fish processing side streams (fillets and trimming) were included in diets for rainbow trout without separating oil and protein fractions. The results show that whether side streams can be used directly as ingredients, depends on storage condition and handling. The inclusion of 50% fresh sprat trimmings, resulting in high growth rates, high feed intake and good intestinal health, while the inclusion of suboptimal stored marinated herring fillets impaired growth, intestinal health, and appetite. To evaluate if these results are transferable to an industry setting, 500 kg of feed containing moist sprat trimmings (paper IV) were extruded using industrial scale equipment. The pellet quality was generally comparable to commercial feed except for a slightly lower boyancy. Compared to a state of the art commercial diet, fish fed the experimental diet displayed slightly lower feed intake and growth. However, the differences in growth and weight gain were largely due to lower lipid deposition in the muscle and intraperitoneal cavity, which would suggest higher product quality of fish fed the experimental diet. Overall, moist side streams can be incorporated in extruded diets which reduce costs and emission. This thesis demonstrates for the first time, that marine yeast and marine insects are promising alternative marine ingredients for future aquaculture. Additionally, side streams with high nutritional value may be utilized as feed ingredients with no or minimal additional processing. Nonetheless, additional processing has clear benefits regarding storage, transport, and maximum inclusion levels in the feed. The results of this thesis can therefore by applied to both the development of local sustainable aquaculture in Sweden but also to the global aquafeed market, which currently lacks realistic marine alternatives, exhibits increasingly unstable supply chains, and high prices.
Tomorrow is yesterday: early-life conditions shape ectotherm life histories
(2023-09-29) Hansson, Alexander
Life history theory seeks to explain the overwhelming diversity of resource allocation strategies in nature by exploring how evolutionary forces optimise survival and reproduction within an organism’s environment. Central to this theory is that resources are finite, and thus increased investment into one trait may reduce resources available for another trait. Understanding proximate drivers of resource allocation is therefore of great interest in evolutionary biology. In ectotherms, temperature is the most influential external factor and affects most physiological and behavioural functions. While temperature can influence traits at any life stage, changes during development are often irreversible and therefore most influential to fitness. However, predicting the direction of effects is challenging as these are often context-dependent and vary considerably among species and populations. This thesis aims to add to our understanding of proximate and long-term effects of early-life thermal conditions on traits associated with survival and reproduction. This work is the outcome of a collaboration between the University of Gothenburg and the University of Tasmania. I used two well-established ectotherm systems; the Swedish sand lizard and the Tasmanian spotted snow skink, to explore early-life effects on long-term life history traits. Both these systems are ideal models with decades of accumulated research detailing their physiology, life history and population structures. Leveraging this knowledge, I combined experimental manipulations and long-term mark-recapture data to examine the effects of early-life thermal conditions on key life history traits. I initially explored how incubation temperature affected sex determination and sex-specific telomere dynamics in neonate sand lizards. Sex is a crucial factor shaping life history strategies across all life stages. Telomeres, which protect chromosome ends, are vital components for organismal health, and their shortening has been linked to individual fitness and population structures. I showed that certain incubation temperatures can override chromosomal sex causing an overproduction of daughters. Additionally, incubation temperature influenced neonatal telomere maintenance, but sex was the strongest predictor of telomere dynamics. Female neonates had longer telomeres and better maintained them compared to males. This is likely explained by sex-specific selection on telomere length, in which it is a better predictor of fitness in females compared to males. I then used longitudinal mark-recapture data to investigate the influence of early-life thermal conditions on the developmental rates of wild spotted snow skinks, and whether maturing decisions have costs to survival and reproduction later in life. Warmer early-life conditions caused females to mature earlier, grow larger, produce more offspring by midlife and live longer. This presented a life history paradox. To solve it, I applied survival trajectory models to the same long-term dataset to determine the latent costs of developmental rates. Specifically, whether females maturing early or large suffer increased rates of age-dependent declines in survival or fecundity (senescence). While maturing early did not cause increased rates of senescence, females that exhibited faster growth and matured large suffered significantly higher mortality rates later in life compared to smaller females maturing at the same age. This thesis highlights the importance of considering variation in early-life conditions as drivers of individual heterogeneity in life history traits and resource allocation strategies. With constantly rising global temperatures, thermal effects on such traits have never been more relevant and can clearly affect the future health of ectotherm populations and influence their evolution.
Phylogenetic Relationships, Biogeography and Species Delimitation: A case study on southern African Silene (Caryophyllaceae)
(2023-09-20) Moiloa, Ntwai
The primary aim of this thesis was to explore the phylogenetic relationships and historical biogeography of African members of the plant genus Silene (Caryophyllaceae), with special focus on the eight native southern African taxa. Three loci (the nuclear ribosomal internal transcribed spacer region, and the rps16 and matK regions from the plastid genome) generated using traditional Sanger sequencing were used to infer the phylogenetic positions of African taxa, while sequence data from 28 low copy nuclear loci were generated using the target capture method to explore shallow phylogenetic relationships within southern African taxa. Bayesian multispecies coalescent methods (StarBeast2, STACEY) were used for species-tree estimation with historical diffusion models (GEO_SPHERE) used simultaneously to infer the biogeographic origins of the monophyletic groups identified. The results indicate that southern African members of Silene belong to two different groups (sect. Elisanthe and Silene) which are relatively distantly related and have different colonisation histories in southern Africa. For North African species of Silene, similar analytical approaches resolved the phylogenetic positions of many hitherto understudied taxa but with lack of resolution in the deeper nodes. By leveraging the large amount of sequence data produced via target capture from a comprehensive sample of southern African section Elisanthe the monophyly and phylogenetic relationships of S. rigens, S. saldanhensis, and S. ornata, all local endemics to the South African southwest coast, were resolved and in agreement with a recently established taxonomy. However, the results also indicate that the widespread S. undulata may not be monophyletic. Several recovered well supported clades within S. undulata are congruent with geographical distribution rather than ecology, indicating a spatial differentiation pattern. The work carried out in this thesis demonstrates that target capture sequencing is a valuable method for generating informative sequence data and useful for resolving phylogenetic relationships at shallow levels. Additionally, the thesis also demonstrates how phylogenetic analyses performed under explicitly parameterized statistical models such as the multispecies coalescent can be expanded by incorporation of other sources of information (e.g., biogeographic) to better understand evolutionary relationships of young lineages and thus inform or test existing taxonomic classifications.
Integrative physiology as a tool towards good animal welfare and sustainability in aquaculture: Focus on intestinal function and health
(2023-08-21) Hedén, Ida
The human population is growing, and the world’s leaders are trying to provide humans with food resources and at the same time setting goals promoting sustainable food production. This means that we need to find new food sources that are not in conflict with future generations’ right to a world without hunger and environmental destruction. We need to move away from traditional linear economy take, make, consume, and dispose and work towards circular economy where waste becomes resources. Aquaculture is the fastest growing food production industry in the world. 70 % of the earth’s surface consist of oceans and only a fraction is used for marine aquaculture. Therefore, marine aquaculture has potential for increasing the world food production. However, aquaculture like all industrial food productions has an environmental footprint and animals produced for food consumption should be treated according to animal welfare guidelines. In the current thesis we use several integrative physiological measurements to work towards sustainable food production without compromising animal welfare. There are many ways to achieve sustainability in aquaculture and not all are within the scope of this thesis. One of the unsustainable targets is feed production and optimal nutrient uptake. Feed carries the largest environmental impact. If there is a gap between the amount of feed given to the fish and how much that is converted into growth it will be reflected in profitability. Protein is the most important macronutrient for fish growth and normal body function. Fishmeal is considered the golden standard in animal feed but has its limitations and cannot increase in the same pace as the growth of the aquaculture industry. Vegetable sources has largely replaced fishmeal, but they also have their down sides because of incorrect nutritional profile and content of fibers and anti-nutritional factors. This has promoted the search for alternative protein ingredients that have equal qualities to fishmeal. In paper I we examined the dietary replacement of fishmeal with a shrimp and herring protein recovered from industry side-stream waters in feed for Atlantic salmon. We found that these proteins can be used as alternative ingredients in fish feed without compromising fish welfare based on the biological assessment using several indicators of intestinal and physiological impairment. These new ingredients can therefore be a sustainable alternative protein in fish feed contribute to circular economy where a previously wasted product becomes a resource. In paper II we investigate the mechanisms driving the intestinal amino acid transport in salmonids. The information found can contribute with some important basic knowledge that can be used in fish nutrition. Another way to achieve sustainability on a local scale is to secure the local food production and increase the number of species cultured through so called diversification. In this thesis we explore the basic physiological functions in Atlantic wolffish (Anarhichas lupus) that has been proposed as a new species for Swedish aquaculture because it is a native species with good temperament and high-quality meat. In paper III we found that Atlantic wolffish is a stress-tolerant fish with little detrimental effect on several welfare indicators after an acute stress treatment in form of air exposure and chasing. This is probably an attribute to its calm and docile behavior. Paper IV investigated the basic intestinal characteristics and paper V investigated the digestive capacity and nutrient uptake in Atlantic wolffish fed either in the morning or evening. Our data on intestinal morphology and functions revealed that Atlantic wolffish has interesting features such as higher methionine transport and lower resistance and high digestive enzyme activity in the distal intestine. These are characteristics for a nutrient transporting epithelium normally found in the proximal region of fish. Further, there was a difference in digestive capacity between the different regions. The research also shows that the plasma concentration of nutrients differs between fish fed at different time points. This information can be used for further studies when optimizing the feeding regimes for Atlantic wolffish.
Effects of contaminant mixtures on marine zooplankton diversity and function
(2023-05-02) Jönander, Christina
Chemicals have important roles in our society and can be used as ingredients in personal care products, pesticides, pharmaceuticals, as well as be components of fuels used in cars or ships. More than 350 000 chemicals and mixtures have been registered for use, which only covers a part of all the chemicals that we may come into contact with. The frequent use of chemicals can result in both intentional and unintentional release of many substances to the environment, where many eventually end up in the sea. These contaminant mixtures have the potential to adversely affect marine organisms, particularly as mixtures of chemicals are known to cause larger effects than when applied individually. Some of the organisms that first encounter contaminants in the water are zooplankton. This diverse community consists of organisms that span many phyla, and that have many important functions in the pelagic food web. Some of these include grazing on microalgae that can cause harmful blooms, and constituting an important food source for larger organisms such as fish. In this thesis, I aim to investigate the impacts of both unintentional mixtures (generated from a single source) and coincidental mixtures (originating from several sources) on the biodiversity and function of two trophic levels of marine zooplankton, and to find out which chemicals in the respective mixtures that are the main contributors to their toxicities. The first two papers focus on the effects from unintentional mixtures originating from shipping activities, and the second two focus on effects from coincidental mixtures found in marine surface water near urban areas with industry. All studies involve effects of contaminant mixtures on natural marine zooplankton communities used in laboratory experiments. The results in this thesis show evidence of clear mixture toxicity of all tested mixtures, in line with what has been observed elsewhere. The findings include effects on both alpha and beta diversity in zooplankton, and on mesozooplankton ability to feed and reproduce, at concentrations of contaminants that already exist or are likely to exist in the marine environment. The findings demonstrate that the estimated toxicity is generally lower using a component-based approach, where toxicity is modelled using the individual toxicities of the substances, than when using a whole mixture approach, where zooplankton are exposed to an entire mixture. The results demonstrate that there are generally few substances in each mixture that are driving the toxicity, although the number of these toxicity-drivers vary between different mixtures. The findings of this thesis contribute to a broader perspective of how contaminant mixtures affect marine zooplankton in their environment, by including endpoints such as species diversity, and ability to feed and reproduce, which are normally not included in chemical risk assessment. Furthermore, the findings suggest that there are cause for concern regarding the impact of chemicals present in coastal environments near industry, as well as from wastewater discharged from ships with exhaust gas cleaning systems (closed-loop scrubbers), as they have the potential to harm zooplankton in coastal waters.
Characterization of ion transport proteins involved in chloroplast function from land plants and algae
(2022-10-21) Dukic Marinkov, Emilija
Evolved around 2.4 billion years ago and even earlier, according to the new geochemical evidence, oxygenic photosynthesis is the crucial turning point in the history of our planet. Used by cyanobacteria, algae, and land plants, photosynthesis represents the most important process in which absorbed sunlight is converted into the chemical energy and stored for later use. From the moment photosynthesis appeared until today, photosynthetic organisms have developed new and improved regulatory mechanisms to be able to cope with changes in light intensity, nutrient availability, different temperatures, altitudes, etc. Availability of nutrients (e.g., K+, Cl–, Mg2+) varies in the environment where photosynthetic organisms live and with that also the internal concentration of ions within the organism’s different compartments. To overcome such changes in the chloroplast, organelle specialized in photosynthesis, several important processes and specialized proteins are required to coordinate ion transport across different membranes and manage ion homeostasis. This thesis answers a few important questions and reveals ion transporters and channels involved in chloroplast function from land plants and green algae. These transport proteins are either localized to the thylakoid membrane (Paper I, II, and III) or chloroplast inner envelope (Paper IV) of Arabidopsis thaliana and Chlamydomonas reinhardtii. Potassium and chloride fluxes across the thylakoid membrane are mediated by the K+ /H+ antiporter KEA3, the Cl− channel/transporter ClCe, and the voltage-dependent Cl− channel VCCN1. In Paper I, we show that they act independently from each other in regulation of the proton motive force (PMF), and adjust electron transport and non-photochemical quenching (NPQ) at different light intensities. Paper II reveals one more important role of ClCe, namely in state transitions, by regulation of the ATP synthase activity in conditions of low light. In Paper III, we show that the Chlamydomonas bestrophin-like transporter BST4 when introduced in Arabidopsis affects PMF, NPQ and ATP synthase activity by a mechanism involving bicarbonate transport and interaction with RuBisCo. Paper IV reveals that the envelope magnesium transporters MGR8, MGR9, and MGT10/MRS4 activate NPQ by a mechanism building the pH gradient across the thylakoid membrane. MGT10/MRS4 also play role in thylakoid ultrastructure. Taken together, these findings help us to better understand the ion transporters across the chloroplast inner envelope and thylakoid membrane and their role in regulation of photosynthesis by different mechanisms.
Thermal plasticity and limitations in tropical trees
(2022-09-12) Wittemann, Maria
Tropical forests are the most carbon dense and biodiverse terrestrial biome on earth. In a time of global warming and biodiversity crisis, their preservation must be of high priority. At the same time, they likely operate close to their thermal limits because of a historically and seasonally stable environment. With climate change, thermal limits may be crossed more regularly, leading to increased physiological heat stress and tree mortality, which may decrease forest carbon storage. This thesis explores how physiological strategies dealing with climate change differ between tropical tree species, giving them a chance at survival, and how flexible different species are in their strategies. A variety of tree species were studied at differing temperatures along an experimental elevation gradient in Rwanda as well as in controlled climate chambers. Drought effects were included in some studies. Thermal acclimation was found for both leaf physiological and water-use traits. With an increase in growth temperature, the photosynthetic optimum temperature (Topt) increased, while a strong downregulation of leaf respiration capacity acted to maintain constant or even decreased respiration rates (R). Traits relevant for tree water use responded to warmer climate by decreasing hydraulic conductance (Kplant) and leaf minimum conductance (gmin), while leaf osmolality and stomatal conductance did not change. In comparison with studies from other biomes, the acclimation in Topt of photosynthesis was lower and not even statistically significant in the field study. The downregulation in respiratory capacity was stronger than in trees from other biomes. Leaf osmolality, a trait related to water acquisition and status, showed no increase, contrary to results from drought studies from other biomes. Acclimation in traits related to water transport (Kplant and gs) and minimum leaf water loss (gmin) was similar to studies from other biomes. Successional groups were found to make use of highly differing physiological strategies. Early successional (ES) species had high water use and reached high rates of photosynthesis to facilitate fast growth. Late successional (LS) species were more conservative in water use and lower in defoliation, reflecting a low growth, resource saving strategy. Tree mortality due to warming was higher in the LS species. With their low transpiration rates, excessive overheating occurs more frequently than in ES species, leading to photosynthetic heat stress and potential carbon starvation. The ES species showed higher sensitivity to drought, likely due to wasteful water-use strategies, increasing the risk for hydraulic failure. The work in this thesis improves our understanding on thermal acclimation capacities of tropical trees and species differences in the susceptibility to heat and drought. It shows a generally lower acclimation capacity of tropical trees compared to trees from other biomes and contrasting heat and drought sensitivity in ES and LS species. This is valuable information for models predicting the future of tropical forests under climate change. If the interspecific differences in climate sensitivity observed here lead to corresponding shifts in tree community composition, this would greatly impact the carbon storage and biodiversity of this biome.
Wood-living beetle diversity and Swedish forest management
(2022-08-29) Gran, Oskar
Humans have impacted Fennoscandian forests for thousands of years, through grazing, burning, and since the industrial revolution increasingly through efficient industrial forestry. These impacts have changed the composition and structure of these forests, by reducing forest age, simplifying forest structure, and reducing the amount of broadleaved trees, among other things. To achieve a forestry model that is sustainable, the consequences of these changes on forest biodiversity need to be evaluated. In this thesis, I focus on saproxylic (wood-living) beetles, within south-central Swedish forestry and forest conservation. This ecological group utilizes dead wood in various forms and is species-rich (1,200 Swedish species), threatened (400 red-listed Swedish species), ecologically diverse, and of high conservation and management relevance. In Paper I, I test the 10-year effect of conservation-oriented thinning on oakassociated saproxylic beetles in 8 pairs of 1-hectare oak-dominated forest plots spread across southern Sweden. For each pair, one plot was treated with thinning in 2002/2003, and one was left as a minimal intervention reference plot. Beetles were sampled shortly before, shortly after, and in my study, 10 years after thinning. The number of beetle species in the thinning plots relative to the reference plots increased slightly and non-significantly shortly after thinning, but significantly 10 years later, equaling around a 33% increase. In Paper II, I compare the diversity of saproxylic beetles and several ecological subgroups between a common spruce forestry stage (young pre-commercially thinned stands), and small broadleaf-dominated unmanaged semi-natural stands (Woodland Key Habitats). Ten pairs of stands of the two forest types were used, spread across Jönköping county in southern Sweden. While the local (alpha) diversity of beetles was similar between the forest types, the total (gamma) diversity was higher for red-listed and broadleaf-associated species in the Woodland Key Habitats. Further, the species composition differed between the forest types, and Woodland Key Habitats had higher compositional (beta) diversity. Paper III uses related but broader comparisons, between middle-aged commercially thinned spruce stands, middle-aged not recently thinned spruce stands, sprucedominated Woodland Key Habitats and spruce-dominated nature reserves. Here, sampling was spread over two regions, one with higher occurrence of Woodland Key Habitats (Örebro county) and one with lower (Jönköping county). A total of 10 pairs, 10 triplets, and 3 single stands were used. Local diversity was higher in the thinned stands than in Woodland Key Habitats, but did not differ for the other forest types. Total diversity of most ecological groups did not differ between forest types, but red-listed species were more diverse in Woodland Key Habitats than in thinned stands in the region with more Woodland Key Habitats, but not in the region with less. The species composition did not differ between the forest types, but Woodland Key Habitats had higher compositional diversity. Paper IV combines data from the two previous papers, this time looking at the influence of characteristics of the surrounding landscape on local diversity of saproxylic beetles. Four landscape variables (volume of broadleaf forest, amount of old forest, amount of conservation forest, amount of clear-cut) were examined, at three scales (within 250 m, 1,250 m, and 2,500 m from stands). At the scale of 2,500 m, the volume of broadleaf forest influenced saproxylic beetle diversity positively, while the amount of old forest surprisingly influenced red-listed species negatively. Overall, the studies show the varied and complex ways management can affect beetle diversity and communities. Beetle diversity patterns are clearly scale-dependent, and aspects of the surrounding landscape are important for local diversity. Thinning seems to have a positive influence on the local number of saproxylic beetle species, in oak and to a certain extent spruce forests, and for the former at least for 10 years. Several common spruce forestry stages have as many or more saproxylic beetle species per stand as nearby conservation stands. However, the managed stages are more homogenous, lowering their contribution to overall saproxylic diversity. Conservation stands, including Woodland Key Habitats, strengthen conservation of Swedish saproxylic beetles. A crucial aspect seems to be the amount and diversity of broadleaved trees, an increase of which both within forestry and conservation should benefit saproxylic beetles.
The aquatic ecotoxicity of manufactured silica nanomaterials and their interactions with organic pollutants
(2022-05-20) Book, Frida
Manufactured silica nanomaterials are one of the nanomaterials consumed in the highest volumes (more than 4 000 000 tons/year/globally) and are used in a wide range of products and industries such as food, cosmetics, coatings, paints, textiles, concrete and the paper and pulp industry. They also provide promising properties that help solving societal challenges, such as water remediation, by binding contaminants. However, their large and wide use leads to an inevitable release into surface waters, which raises concerns of potential environmental impacts, because of their small size, reactive surfaces and the risk of facilitating biological uptake of other co-occurring chemicals (“trojan horse effect”). Therefore, this thesis systematically investigates the aquatic ecotoxicity of manufactured silica nanomaterials alone and in combination with toxic organic chemicals. The thesis is based on an in-depth ecotoxicological evaluation of nine silica nanomaterials with different size, charge, surface modification and shape in experiments with bacteria (Pseudomonas putida), algae (Raphidocelis subcapitata), crustacean (Daphnia magna) and fish gill cells (Oncorhynchus mykiss). These data are then complemented with data from other scientific publications in a systematic review in the ecotoxicology of silica nanomaterials, in order to derive the maximum acceptable environment concentration in the aquatic environment (PNEC, the predicted no effect concentration). Finally, this thesis examinesthe ability of silica materials to adsorb organic pollutants with different charges: paraquat (cationic), hexadecylpyridinium (cationic), pentachlorophenol (anionic), diflufenican (neutral) and whether this interaction alters the ecotoxicity of exposed organisms and cells. The results show that impacts are a result of surface area, surface chemistry and exposed organism/cell type. Silica nanomaterial that is sterically stabilized with glycerol propyl tails is benign in all assays showing no signs of toxic action. This is likely due to a steric hindrance that prevents contact between the material and the cells/species. Weakly anionic (non-modified) and strongly anionic (aluminium-modified) silica are toxic to fish gill cells with EC50 values between 12 and 93 mg/L. This toxicity in fish cells depends on the total surface area of the nanomaterial that is covered with deprotonated silanol groups which binds to and interrupts membrane proteins function. As a consequence, if concentrations are expressed as surface area instead of mass, the toxicity of different nanomaterials becomes quite similar, with EC50 values differing not more than by a mere factor of 1.4 (1.8-2.5 m2 /L). In contrast to experiments with fish cells, strongly anionic silica is not toxic to algae at concentrations up to 500 mg/L, likely due to the presence of a cell wall, which hampers nanomaterial-cell interactions. However, cationic and non-modified silica nanomaterials cause an inhibition of algal growth, EC50 values of 124 mg/L and 200 mg/L, respectively. This effect is likely caused by an adsorption of the material to the algae, shading them and thereby impacting the photosynthetic production of physiological energy. The results from the exposures to mixtures of silica nanomaterial and organic pollutants show that strongly anionic nanomaterials bind cationic paraquat and thereby reduce paraquat toxicity to algal cells. In addition, the cationic material can bind and reduce toxicity of pentachlorophenol in algae, which is likely pH and phosphate dependant. Experiments with fish cells indicate that the anionic NMs bind the cationic hexadecylpyridinium, but do not reduce the toxicity in exposed fish cells. Instead, the observed effects correspond well with the effects predicted with the two concepts independent action and concentration addition. In general, the mixture experiments indicate that silica nanomaterials possess promising properties to bind and remove certain pollutants in water. However, the use of silica nanomaterials for such purpose in industrial applications requires additional research on the water types that can be cleaned (industrial wastewater, household wastewater, raw drinking water, surface waters etc.), life-cycle based assessments of costs and benefits, and a comparison with other materials for water treatment.
A landscape of values - a study of non-epistemic values in Swedish upper secondary science education
(2022-04-26) Nordqvist, Ola
This thesis sets out to investigate the role of non-epistemic values in science education from three actors’ perspectives – the science student, the science teacher, and the science teacher educator. More specifically, the focus is on exploring the variation of values among these three key actors in science education, and what characterizes these values. Also, to use the empirical findings to discuss how these values (may) affect and inform science education research. Previous work on values in science education has failed to address the role of different actors in one specific educational context, which this thesis aims to achieve by studying the upper secondary school science education. In addition, values held by university scientists teaching science student teachers seem to be missing in previous research in the domain. In order to tackle the research questions, empirics were collected from all three actors targeted, in one specified science education context, and then use viable analytical methods and tools to describe the variation, character, and nuances of values held by the actors. To empirically investigate the variation and character of these values, an analysis was performed by a systematic literature review of the research domain. This was followed by surveying and statistically analyzing responses from representative samples of Swedish upper secondary school biology students and teachers respectively, and finally thematically analyzing interviews with university biology scientists in education of science teachers. Results showed that values held by science students and science teachers affect science education in schools. For example, teachers’ non-epistemic values affect the content and methods selected and implemented in their science teaching. Further, it was found that the interviewed science teacher educators considered their teaching offered to science student teachers as largely value-free, while they acknowledged that values-inclusion in school science is something important. The key impact of the research presented, is that continued development of the growing research domain of the importance of values in science education is crucial, as there are many aspects in the domain not yet or thoroughly explored. Examples include the role of scientists in science teacher education, and how values held by science teachers affect their classroom practice. By incorporating findings from this study into the larger research discourse on values in science education, there is promise that research is one small step closer to suggest changes in curriculum and classroom practice. This could in turn change the current negative trend in student interest and motivation to study school science.
Mutagenesis in wheat: An approach to make saline green!
(2022-04-01) Lethin, Johanna
The raising salinity in the soils around the world have been widely studied during the last decades due to the massive loss in agricultural land. Today, nearly 8% of the world’s arable land can no longer be used for crop cultivation due to salt contaminations, and more than half of the countries in the world are affected. Wheat is the second most grown cereal after corn and covers more growth area on the earth than any other crop. Wheat production therefore needs to be increased to meet the demand of a growing world population. Thus, the possibility to grow wheat on salt-effected soil is crucial to feed the population and avoid economic loss for the countries involved. In this thesis, the Bangladeshi wheat variety of BARI Gom-25 that is moderately salt tolerant was used as a source to create a mutagenized population with point mutations, and thereafter it acted as a control to the mutated lines. The benefit of point mutations is that a population with high genetic variation can be created. From such a population novel salt tolerant varieties can be developed, as well as many other valuable traits. From a germination screening of approximately 2000 lines on saline filter paper (200 mM NaCl), 70 lines were identified that exhibited a higher germination rate than the BARI Gom-25 control. These lines were further tested in the field in Bangladesh (Paper I). Thirty-five of those lines were also analyzed in the Australian Plant Phenomics Facility at Adelaide. In these experiments yield, growth, ion content, and water use were determined (Paper II). In Paper III and IV bioinformatic tools were used as an approach to look for transcription factor genes in the wheat genome involved in salt tolerance. The focus was on two different transcription factor families; WRKY (Paper III) and MYB (Paper IV). These studies illustrated the importance of the biological regulation of salt tolerance, and enhanced the understanding behind the mechanisms involved. Moreover, it highlighted putative target genes regulated by WRKY and MYB transcription factors that could be key ones to understand findings from Paper I and II. This thesis points out the importance of salt tolerant crops in general, and wheat in particular, and shows how mutational breeding can be a great asset in the development of salt tolerant varieties. Specific mutagenized wheat lines with strong salt tolerance are identified based on their performance against various parameters, and the importance of WRKY and MYB transcription factor families in the biological regulation of salt tolerance is shown. Finally, downstream candidate genes encoding the observed phenotypes observed.

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