Bio- ja ympäristötieteellinen tiedekunta

 

Recent Submissions

  • Svensson, Jonas (Helsingin yliopisto, 2017)
    Snow and ice are essential components of the Earth system, modulating the energy budget by reflecting sunlight back into the atmosphere, and through its importance in the hydrological cycle by being a reservoir for fresh water. Light-absorbing impurities (LAI), such as black carbon (BC) and mineral dust (MD), have a unique role in influencing the reflectance of the cryosphere. Deposition of the anthropogenic and natural LAI constituents onto these bright surfaces initiates powerful albedo feedbacks that will accelerate melt. This is important globally, but especially for regions such as the Arctic and the Himalaya. In this thesis, observations from both ambient and laboratory experiments are presented. The overarching research goal has been to better understand the climatic effect of LAI on snow. More specifically, an emphasis has been placed on exploring the process-level interactions between LAI and snow, which will enable better comprehension of LAI affecting the cryosphere. Key findings in this thesis involves the investigations on the horizontal variability of BC concentrations in the surface snow that indicate a larger variability on the order of meter scale at a pristine Arctic site compared to a polluted site nearby a major urban area. In outdoor experiments, where LAI were used to artificially dope natural snow surfaces, the snow albedo was observed to decrease following LAI deposition. The albedo decrease was on the same order as in situ measurements of LAI and albedo conducted elsewhere. As snow melted during the experiment, the snow density was observed to decrease with increasing LAI concentration, while this effect was not observed in non-melting snow. The water retention capacity in melting snow is likely to be decreased by the presence of LAI. Measurements examining the absorption of BC indicate that BC particles in the snow have less absorbing potential compared to BC particles generated in the laboratory. The LAI content of snow pit investigations from two glaciers in the Sunderdhunga valley, northern India, an area not previously examined for LAI, presented high BC and MD content, affecting the radiative balance of the glacier snow. At different points, MD may be greater than BC in absorbing light at the snow surface. A continued monitoring of LAI in the cryosphere, both on the detailed scale explored here, as well as on the larger modelling perspective is needed in order to understand the overall response of the cryosphere to climate change.
  • Salomaa, Anna (Unigrafia, 2017)
    Scientific knowledge shows compelling evidence of intensifying global environmental problems such as biodiversity loss and climate change. Unfortunately, this knowledge has not been directly translated into actions that would have reversed these worrying trends. The effectiveness of conservation, i.e. its ability to produce a desired result, is the outcome of interaction between knowledge and policy process. Efforts have recently been made to use existing scientific knowledge to combine current policy instruments and to develop new innovative approaches to conservation. In this PhD thesis I empirically study the perspectives of various actors and their roles in topical Finnish conservation efforts: green infrastructure, voluntary forest conservation and conflicting peatland policy. I examine how different knowledge types and policy instruments contribute to conservation effectiveness. The study utilizes an expert survey, focus groups, combining multiple methods using the case study approach, and integrating social and ecological data. The results illustrate how actors may interpret differently complex concepts, such as ecosystem services and ecological connectivity; the use of these concepts may even be politically coloured. Ambiguity concerning the definition of green infrastructure may create obstacles for practical implementation. In the peatland conservation policy case, where actors’ interests differed, implemented policy instruments did not match existing knowledge. The role of other knowledge types along with ecological knowledge may be more important when designing voluntary rather than compulsory instruments, because participation to voluntary actions needs to be attractive. The collaboration of actors is an integral part of increasing conservation efforts in the voluntary conservation. Interaction and valuation of various knowledge types may have a complicating effect on conservation practices, but different knowledge types can be integrated for more effective results. The study shows that policies should be designed in a way that allows the practical application of knowledge. The study elucidates what kind of challenges and opportunities for increasing effectiveness are faced in different phases of a policy process. I argue that the use of scientific evidence must be combined with the usage of other knowledge types and involvement of various actors. In addition, potential interest differences of actors should be considered when planning participation. In this way a combination of policy instruments can be developed, which simultaneously increases evidence uptake, acceptance and effectiveness leading to a more sustainable future.
  • Le Tortorec, Anniina (Helsingin yliopisto, 2017)
    Phytoplankton constitute the basis of food webs and are responsible for almost all photosynthesis in the open sea. Occasionally, given suitable conditions, one phytoplankton species can increase in abundance and form a mass occurrence known as a bloom. Harmful Algal Blooms (HABs), in turn, can have adverse effects on the ecosystem, for example causing oxygen depletion, clogging of fish gills, or toxicity. HABs are common in shallow and stratified coastal waters and the number, frequency and coverage of areas affected by HABs are increasing globally mainly due to eutrophication, changes in nutrient ratios and global climate change. One of the main phytoplankton groups forming HABs are dinoflagellates. Among dinoflagellates the genus Alexandrium is particularly notorious with many species in this genus producing a variety of potent neurotoxins. Dinoflagellates are the only known photosynthetic organisms that can produce bioluminescence and the majority of bioluminescence in marine surface waters is produced by dinoflagellates. Bioluminescence in dinoflagellates is considered a defensive mechanism against grazing and many harmful dinoflagellate taxa produce bioluminescence. The dinoflagellate Alexandrium ostenfeldii forms dense bioluminescent blooms in shallow and sheltered areas of the Baltic Sea during the late summer. These blooms pose a potential threat to humans and ecosystems in the region due to observed production of toxins. The distribution and abundance of A. ostenfeldii is poorly known in the coastal waters of the Baltic Sea. The aim of this thesis was to study the variability of A. ostenfeldii bioluminescence production to evaluate whether bioluminescence can be used as an early warning signal of harmful dinoflagellate blooms in the Baltic Sea. More precisely, the aim was to study the expression of A. ostenfeldii bioluminescence to learn how much genetic, phenotypic and environmentally induced variability there is in bioluminescence production in the species. Studies conducted on luciferase genes and bioluminescence emission showed that bioluminescence is a prominent feature in Baltic A. ostenfeldii. Measurements on individual cell cultures and natural populations revealed large daily and seasonal variation in bioluminescence emission relating to the circadian rhythm in bioluminescence expression and seasonal changes in A. ostenfeldii abundance. Large intraspecific variation in bioluminescence production was observed in response to changes in temperature and salinity. A. ostenfeldii abundance, toxin concentrations and bioluminescence intensity were positively correlated in our field data. All tested A. ostenfeldii strains produced both bioluminescence and toxins and it can be assumed that concurrent production of both is a predominant property in Baltic A. ostenfeldii. The obtained results show that it is possible to relate bioluminescence to A. ostenfeldii bloom succession using automated measurements. However, the highly-localized distribution of blooms may require advance knowledge of potential bloom locations to be able to target the monitoring efforts. Species distribution modelling showed promise to address this problem by identifying potentially suitable habitats for A. ostenfeldii.
  • Piirainen, Mikko (Helsingin yliopisto, 2017)
    The subfamily Salicornioideae (Amaranthaceae) consists of 11 genera and c. 100 species of obligatory halophytes with a reduced morphology mainly in coastal and inland salt marshes from tropical mangroves to the subarctic. The plants are succulent, often with articulated stems and highly reduced leaves and flowers. This, together with their phenotypic plasticity, has caused much confusion in the morphology-based taxonomy. The study starts with the morphology, taxonomy and nomenclature of the genus Salicornia in northern Europe, extends to cover the whole Eurasian continent and use of molecular data and finally proceeds to a comprehensive DNA-based phylogeny and phylogeography of the subfamily. The new taxonomy of the annual Eurasian Salicornia presented aims to reflect a plausible phylogeny, using monophyly as the main criterion. Several taxa with a limited geographical distribution are neither supported in the molecular analysis nor morphologically separable and are thus placed in synonymy. On the other hand, unresolved clades, cryptic speciation and the fact that all involved taxa were not available in the molecular analysis offer a challenge for future studies. The monophyly of Salicornioideae is confirmed by the phylogenetic analysis. Five clades are found: 1) Kalidium, 2) Halopeplis, 3) Halocnemum/Halostachys and 4) Allenrolfea/Heterostachys. 5) The remainder of the subfamily forms the fifth clade, in which Eurasian Arthrocnemum macrostachyum, Microcnemum, the North American Arthrocnemum subterminale and Tecticornia form an unresolved polytomy. Sarcocornia and Salicornia form a monophyletic clade in which the American and Eurasian species of Sarcocornia and Salicornia respectively form well-supported clades. The Southern and Eastern African and Australian Sarcocornia are moderately supported. Salicornioideae probably originated in Eurasia during the late Eocene to early Oligocene. The divergence of the early main clades took place in the middle Oligocene. Long-distance dispersal has taken place several times to the Americas, South Africa and Australia. An updated generic classification of Salicornioideae is proposed with two main novelties: 1) the two species of Arthrocnemum are separated and described as two different genera, Arthrocaulon and Arthroceras, 2) Sarcocornia is treated as congeneric with Salicornia. In addition, all Australian plants are treated under Tecticornia as proposed earlier by Australian researchers. For Salicornia a new infrageneric classification is proposed to accommodate the four phylogenetically and geographically well-supported lineages within the genus.
  • Kinaret, Pia (Helsingin yliopisto, 2017)
    Nanotechnology and engineered nanomaterials (ENM) are providing outstanding innovations in several fields of science and technology, spanning from medicine to aeronautics. However, some ENM are known to be harmful to humans and the environment, thus, their toxic potential need to be thoroughly tested. The production of ENM is drastically increasing, making traditional toxicity testing impractical and in some cases impossible. The classical hazard assessment involves extensive animal exposures, which are not applicable to vast growing number of novel nanomaterials. Their unique properties and behaviour in biological entities are differing from their bulk sized counterparts, making predictions of the effects difficult. Thus, new efficient and rapid methods need to be developed for nanomaterial toxicity testing and hazard assessment. The main ENM exposure route to humans is through airways. Studying the effects of nanoparticles and their toxic potential on the airways is hence necessary for creating a comprehensive understanding of the ENM-induced phenotypic, cellular and molecular changes. Inhalation exposure to murine models is considered as the state of the art method for studying the pulmonary responses. This expensive and laborious method is not practical for testing all nanomaterials with all the relevant doses. In another airway exposure method, the oropharyngeal aspiration, the ENM are introduced to the airways of test animals as a liquid dispersion under anesthesia. The aspiration method is debated, since the anesthesia and the dispersion might cause additional effects and responses. In the first part of this thesis, these two different airway exposure methods were compared, aiming at understanding whether the easier and faster oropharyngeal aspiration method could substitute the time-consuming and expensive whole-body inhalation method. The conjecture was indeed valid, as both methods showed similar outcomes at cellular and molecular level in response to rigid multi-walled carbon nanotubes after four-day exposure. Since the ongoing effort in reducing laboratory animal testing in hazard assessment as well as for faster and simpler testing, methods for replacing animals are being examined also by in vitro exposures. Cell exposures are even more argued, since they do not resemble the comprehensive responses of an animal and even less of the human organism, where different cell types are interacting and communicating in very intricated manner. Novel computational methods are being developed to mine the large exposure datasets for finding relevant features, that would explain and predict the human responses to ENM from in vitro and in vivo exposures. In the second part of the thesis, the possibility to interpret the complicated pulmonary responses by examining the transcriptional patterns of human macrophages and mouse lungs when exposed to carbon nanomaterials (CNM) were investigated. Gene co-expression networks revealed specific molecular patterns related to distinct properties of the CNM, namely aspect ratio, length, diameter and surface area, but which were common between in vitro and in vivo. These results aid the establishment of systems toxicology approaches in ENM hazard assessment and the shift from the classical, animal-based hazard assessment towards predictive models, ultimately supporting the development of new “safe-by-design” nanomaterials (safe design, safe production, and safe use).
  • Jonsson, Martina (Helsingin yliopisto, 2017)
    The red mold Fusarium, is a fungal pathogen, infecting mainly small-grain cereals in the temperate regions of the world. In Scandinavia, F. avenaceum, F. culmorum, F. poae, and F. sporotrichioides infections are most common, but in recent years F. graminearum and F. langsethiae infections have increased, as well. Most Fusarium species are capable of producing a variety of mycotoxins, possibly providing an edge over competing strains at the site of infection. Mycotoxins can evoke a broad range of toxic effects in humans and animals, including neurotoxicity, immunotoxicity, reproductive-, and developmental toxicity and carcinogenicity. The most toxic fusariatoxins include the tricothecenes, fumonisins and zearalenone. However, less studied mycotoxins, as enniatins (Enns) and moniliformin (MON) are frequently found in grain products, hence, causing a risk of a daily, low-level exposure of human and livestock, the significance of which is still unclear. The aim of this study was to provide further insights into the toxicity of Enns and MON, and into the mechanism of action of EnnB, monitored at gene expression level. Furthermore, the acute oral toxicity and repeated, low-dose, oral toxicity of MON in Sprague-Dawley rats was assessed, adapting OECD Guidelines 423 and 407. We report clear toxic outcomes of EnnB in vitro, as it affected cellular energy metabolism by reducing ATP levels in cell cultures and cell proliferation, already at low concentrations (below 10 μM) in the cell lines Balb 3T3 and HepG2. EnnB exposure slightly increased the proportion of early apoptotic cells, as well. Gene expression studies revealed alteration of energy metabolism, due to effects on gene expression of genes associated with mitochondrial organization and function and assembly of complex I of the electron transport chain. Moniliformin (MON) did not induce significant toxicity in vitro. However, high doses of MON (50 mg/kg b.w.) caused acute toxicity in rats, seen as cardiovascular changes and respiratory distress, resulting in death. According to the OECD Globally Harmonized System, the toxicity of MON could be classified into category 2, and a LD50 cut of value of 25 mg/kg b.w. was determined. Long term, low dose exposure affected mainly the innate immunity, by reducing the phagocytic activity of rat neutrophils in all tested groups. Hence, a LOAEL of 3 mg/kg b.w. for MON was suggested. The rats of the lowest dose groups (3-6 mg/kg b.w.) remained clinically healthy. Two rats of five in the highest dose group (15 mg/kg b.w.) showed similar signs as in the acute oral toxicity test and died. Excretion kinetics revealed that MON is rapidly excreted in urine, in less than 6 h, but only 1-2% was found in feces. This indicates that the urinary excretion is the main route for elimination.
  • Gateva, Gergana (Helsingin yliopisto, 2017)
    The ability of cells to migrate, adhere, and contract is an essential feature, governing basically every process in the human body. These include fundamental functions such as development, muscle contraction, immune responses, wound healing, and a plethora of diseases including cancer metastasis, vascular diseases, and cardiomyopathies. Contractile actomyosin bundles are the central cellular structures, which enable the cell to perform all these processes, and thus it is crucial to understand how such structures are assembled in cells. Assembly of actomyosin bundles both in non-muscle and in muscle cells is regulated by a multitude of proteins, acting synchronously in a fascinating complexity. Many aspects of this process have remained mysterious, because of the sheer number of the involved actin-binding proteins, the intricate signalling pathways, and the complexity of the underlying interactions. This thesis aimed at understanding of some of the fundamental processes behind the assembly of contractile structures in non-muscle cells (human osteosarcoma cells U2OS), and in heart muscle cells (primary rat cardiomyocytes). Previous studies revealed that contractile actomyosin bundles in U2OS cells, called ventral stress fibers, are generated from a network of precursors, named dorsal stress fibers and transverse arcs. This work revealed that the tropomyosin family proteins (Tpm) play central role in stress fiber assembly. Our studies on U2OS cells indicate that four functionally distinct tropomyosins orchestrate stress fiber assembly. Tpms 1.6/1.7, Tpm 2.1, and Tpms 3.1/ 3.2 stabilize specific stress fiber regions. In contrast, Tpm 4.2 regulates the recruitment of myosin II to diaphanous (Dia) 2 formin-nucleated actin filament population in stress fiber precursors. Our in vitro experiments revealed that these tropomyosin isoforms possess an intrinsic ability to segregate to different actin filaments and bind F-actin with distinct dynamics. Our results revealed that these tropomyosins determine some of the biochemical properties of actin filaments, such as their ability to associate with non-muscle myosin II and actin depolymerizing factor (ADF)/cofilin. Additionally, our studies demonstrated that the interaction between palladin and vasodilator-stimulated phosphoprotein (VASP) promotes dorsal stress fiber assembly. In contrast, the tension generated by transverse arcs inhibits this process. Tension also controls the length of ventral stress fibers and inhibits ADF/cofilin-mediated stress fiber disassembly. Furthermore, our studies in primary rat cardiomyocytes revealed that ADF/cofilins are also crucial for the length regulation and proper function of muscle sarcomeres. Collectively these studies reveal important biochemical and mechanobiological principles that regulate the assembly of contractile actin bundles in non-muscle and in muscle cells.
  • Luukkonen, Tiia Maria (Helsingin yliopisto, 2017)
    Genetic alterations can have a dramatic impact on essential gene function through “natural” gene knockouts. This thesis explores two such alterations: balanced translocations and loss-of-function (LoF) mutations in two Finnish cohorts. In parts I-III we studied the consequences of balanced translocations in three Finnish families. Part IV focuses on the effect of skin barrier gene LoF mutations in Finnish atopic dermatitis patients. In studies I-III, we investigated potential disease-associated chromosomal translocations. Balanced translocations are caused by the rearrangement of segments between non-homologous chromosomes. Such rearrangements may have an impact on gene expression, and subsequently the phenotype. The current estimate of the prevalence of disease-associated de novo balanced chromosomal rearrangements (DBCRs) is 6 – 9%. Here, we aimed to genotype-phenotype delineation of three balanced translocations. Three DBCRs were identified using paired end (PES) and mate pair (MPS) next generation sequencing. The phenotypes were (1) aortic (AA) and intracranial aneurysm (IA), (2) strokes and vascular manifestations, and (3) developmental verbal dyspraxia. In study I, we showed that the t(10;11) translocation disrupts intron 1 of neurotrimin (NTM) at 11q24, in a strong candidate region for aneurysm and subsequent hemorrhage due to rupture. In study II, we identified identical t(1;12) translocations in two apparently independent families with distinct vascular phenotypes. In study III, we demonstrated that t(1;18) breaks intron 1 of the solute carrier family 14 member 2 (SLC14A2) gene in a family with verbal dyspraxia. Our results from the balanced translocation studies demonstrate the feasibility of PES and MPS for the identification of candidate genes in patients with potentially disease-associated chromosome rearrangements. Study I facilitated the identification of a potential candidate gene for IA/AA. In study II, we identified identical translocations within conserved haplotypes, outside putative genes, pointing to a gene malfunction caused by a position effect. Study III facilitated the identification of a potential candidate gene for developmental verbal dyspraxia. Study IV focused on LoF mutations in atopic dermatitis (AD). Since the mid-20th century, the lifetime prevalence of AD has increased up to 30% in several Nordic countries. Prevalent filaggrin (FLG) LoF mutations are the most significant risk factors for AD. Due to its genetic makeup Finland provides special opportunities for studying the medical impact of low frequency (0.5% ≤ 5%) LoF variants. We aimed to assess the effect of FLG LoF mutations on the risk of AD and treatment response, and to evaluate their usefulness as possible biomarkers. In addition, we included variants in ten essential skin barrier genes into the study. Study IV represents the first analysis of FLG and other barrier gene mutations in relation to AD in the Finnish population. Our data confirmed FLG mutations as risk factors for AD in Finns, but we observed that the FLG carrier frequencies were notably lower in Finns compared with reported frequencies in other populations. We can conclude that despite the significant effect of FLG mutations in Finnish AD patients, they explain only a portion of the total genetic burden of AD. Finally, we also observed that disease severity and treatment response were independent of patient FLG status, which questions the feasibility of FLG mutations as biomarkers in predicting treatment response.
  • Enberg, Sara (Helsingin yliopisto, 2017)
    The winter season in polar and sub-polar areas is commonly described as a dormant phase for microalgae, especially in the water column, although the sea ice is a habitat for diverse and active communities. However, these areas are subject to changing environmental conditions due to global warming and changes in ultraviolet radiation. This thesis describes the natural succession of microalgal communities in the water column and sea ice during the cold-water winter season. Results show that the cold-water season is dynamic with various microalgal communities and their variable photosynthetic activity in the water column and sea ice. Although microalgal biomass is relatively low throughout the cold-water season, especially in the water column, natural succession during the cold-water season can be divided into five different groups based on microalgal community composition. Similar to the water column, algal succession in the sea ice begins with low biomass and domination of various flagellates. Thereafter the biomass in the ice increases and the community shifts to being diatom and dinoflagellate dominated. In late spring, sea ice algae communities differ between the ice layers from the top to the bottom ice, and the highest biomass in the bottom ice layer (dominated by colonial pennate diatoms). However, the contribution of released dominant sea ice algae to the water column community is not significant, and the spring bloom community is largely formed by pelagic species of the early open-water season. This thesis also describes the effect of enhanced solar irradiance on the microalgal community at various ice depths.We studied the effects of enhanced solar irradiance (including PAR and UVR) on the microalgal community at various depths of the spring ice during a three-week experimental in situ study. Results show that the largest effect of enhanced solar irradiance occurs in the top 10-cm layer of ice, but even beneath this layer the diminishing amount of irradiance and change in light quality increase the photosynthetic activity and change the community composition of the sea ice algae. Exposure to ultraviolet radiation also increases the concentration of mycosporine-like amino acids (MAA) and the variety of MAA compounds in the sea ice algae. Global warming is likely to result in thinner ice and could thus lead to changes in sea ice algae community structure in the Baltic Sea area, i.e. changes in the sea-ice pennate diatom community. The altered community and population dynamics in the sea ice may decrease the productivity and change the functioning of the system in the sea ice-pelagic coupling and bentho-pelagic coupling.
  • Woestmann, Luisa (Helsingin yliopisto, 2017)
    With increasing global warming and habitat fragmentation, environmental conditions are becoming more variable, and the risk and prevalence of diseases may increase in nature. As a consequence, many species have to adapt or respond to rapid changes in their environment. Ectotherms, such as insects, are thought to be especially prone to such changes and thus are interesting and relevant species for assessing life-history responses towards variable conditions. In my thesis, I investigated how the Glanville fritillary butterfly responds to different environmental conditions, and how this translates to fitness-related traits and offspring performance. I was further interested in the potential positive and negative correlations between immunity and other life-history traits. I used experimental approaches conducted in the laboratory to generate changes in individual condition, resulting from variable environmental conditions that were induced via altered nutrition, bacterial and viral infection or via forced flight. Flight was included, as it represents a key life-history trait for this species and is a stressful and energy demanding physiological process. I compared female reproductive strategies, but also assessed how male contribution to female reproduction was affected by variable conditions. Moreover, I assessed potential trans-generational effects on the offspring, and whether the strength or direction of the effect depended on the type of poor condition the individual experienced. Overall the results of this thesis suggest that the Glanville fritillary butterfly is highly sensitive to its surrounding environment, and is able to rapidly change its reproductive strategy according to the conditions it experiences. While more optimal conditions lead to higher offspring quantity, poor or stressful conditions often result in the production of fewer but of higher quality offspring, indicated by e.g. increased hatching success. An increase in offspring quality further translates to increased offspring performance in response to nutritional deficit, thus implying adaptive trans-generational effects. Flight, a key trait in many organisms, has been previously shown to interact with immune response in the Glanville fritillary butterfly. Results from this thesis confirmed this relationship but suggest that the relationship is a general stress response rather than an adaptive response to cope with infections. Bacterial and viral infections drastically reduce lifespan, and hence have the potential to influence population dynamics. Responses to variable environmental conditions including risk of infection are complex in the wild, as several conditions are often acting simultaneously, making it difficult to generalize the observed results. However, the data of this thesis provides important insights in condition-dependent responses of the Glanville fritillary butterfly to stress, and how this translates to fitness-related traits and even offspring performance. Further studies on the adaptive nature and underlying mechanisms behind the observed responses will further contribute to our understanding of the drivers of maintenance of life-history variation and evolution in this species.
  • Pereira, Pedro (Helsingin yliopisto, 2017)
    Parkinson’s disease (PD) and Primary Sclerosing Cholangitis (PSC) are idiopathic diseases for which an external agent, e.g. a microorganism, has been hypothesised as being causally related to the condition or as having a potential role in disease progression. In the present work, we present evidence that gut and oral microbiota, but not nasal, differ between controls and PD patients, and that, regardless of hypothetical causal relationships, some of these changes show potential for use as biomarkers for diagnostic purposes. Although none of our studies are designed to investigate causality, we nevertheless find no suggestion that the bile microbiota is aetiologically related to PSC. On the other hand, our results suggest that Streptococcus may contribute to disease progression. All the studies are unified by the same methodology, consisting on case-control studies using high-throughput amplicon sequencing of the bacterial 16S rRNA gene, followed by bioinformatic processing of the raw data, and finally by statistical analysis.
  • Stucki, Dimitri (Helsingin yliopisto, 2017)
    Compared to solitary insects, the social organization and interactions in eusocial insects are expected to render them more vulnerable to parasitic exploitation. As a consequence, eusocial insects in turn evolved social immune defenses – sophisticated behaviors that complement the individual immune defenses and increase their resistance against parasitic exploitation. Thus, within the network of the eusocial community, host-parasite interactions occur not only between a single host and its parasites,but among all individuals in the network. Yet, although in eusocial insects host-parasite interactions and other ecological stresses affect the entire community, the individuals provide the basic physiological responses in the defense against external influences. Thus, individual stress responses are an important factor in mediating the variation within the colony to ecological stresses. In this thesis I investigated the physiological stress responses of the ant F. exsecta in the light of host-parasite interactions. I found that oral exposure to bacteria can have a beneficial effect on the survival of food deprivation. Yet, the response to the infection in combination with starvation showed temporal variation. Furthermore, I found striking similarities in the immune responses of young males and foraging workers,as compared to young queens and nursing workers. This suggests that the residual life expectancy may have a role in mediating immune defenses among the castes of F. exsecta. Stress responses not only varied among the castes, but also between two natural populations. I found different reaction norms to temperature and humidity, possibly due to the different environmental conditions that the ants experience in their natural habitat. Given that these reaction norms also affected the expression of immune genes, it is likely that variation in the environmental conditions can affect the immune defenses, and thus, may influence host-parasite interactions. In conclusion, this thesis provides insight into the impact of ecological factors on the resistance and responses to stress in a social insect. I show that individual stress responses are tightly linked to immune defenses, which in turn may affect the stress response of the entire community. As a consequence, variation in the environmental conditions, and thus, exposure to different ecological stresses, may result in different evolutionary trajectories among populations, and even among colonies.
  • Tiainen, Joni (Helsingin yliopisto, 2017)
    Pike (Esox lucius) is a keystone species and top predator, which has an important role in lake ecosystems and in recreational fishing. Recreational fishing is strongly size-selective on large fish, which can have detrimental effects on fish populations. The aim of this thesis was to study the ecologically sustainable recreational fishing of pike, and the importance of large pike to population resilience and ecosystem balance. The field studies of this thesis were conducted in four small and almost pristine forest lakes in southern Finland in years 2006-2013. Two different size-selective fishing procedure for pike were applied; minimum length limit -regulation (MLL) of 40 cm and harvestable slot length limit -regulation (HSL) of 40-64.9 cm. During the study, fishing-induced responses in pike population abundance, demographics, production and consumption, as well as reflection of these changes in prey fish populations were monitored. Changes of pike diet and trophic position were studied by stomach content and stable isotope analysis. Also the relation of size-dependent maternal and juvenile characteristics was examined. The main finding of this thesis is that HSL is capable to maintain viable pike populations. HSL preserved population density, biomass and diverse size-structure, as well as high pike production and consumption by diverse sized pike. By MLL those features were greatly degenerated. By protecting large fish, HSL is able to preserve the productivity of the fish population, because fishing mortality is compensated by increased recruitment and growth. In addition, HSL maintained stability of pike consumption, which enables a strong piscivore effect on the ecosystem. Based on the high quality and amount of reproductive products of large females, they are important for the reproduction of pike populations, which should be considered in fisheries management.
  • Kuuluvainen, Emilia (Helsingin yliopisto, 2017)
    Precise control of transcription, the copying of the genetic DNA code to an expressed RNA molecule, is fundamental for all processes of an organism. Transcriptional regulation is dependent on the activity of proteins and protein complexes including general and cell specific transcription factors and co-activators. Studying how these transcriptional regulators function is crucial for understanding processes such as development and disease. This PhD thesis focuses on the function of one evolutionarily conserved transcriptional co-activator, called the Mediator complex, and in particular on the role of its kinase module. This kinase module consists of four proteins: Cdk8, cyclin C, Med12 and Med13 in lower metazoans and CDK8 or CDK19, cyclin C, MED12 or MED12L and MED13 or MED13L in vertebrates. The Mediator kinase module regulates transcription through various mechanisms, including association with transcription factors and regulation of enhancer-dependent transcription. Kinase module deregulation is implicated in developmental disorders and cancer, but the molecular mechanisms underlying these diseases remain poorly understood. CDK8 was found to be dispensable for cell-autonomous survival but required for mouse embryonic development at the pre-implantation stage. Cdk8-CycC-mediated regulation of transcription was dependent on Med12-Med13 while Cdk8 and CycC depletion caused distinct and even opposite effects on gene expression as compared to Med12 and Med13 depletion in fruit fly cells. This work identified highly similar effects on transcription after depletion of fruit fly Med12 or Med13, suggesting limited Med12-independent functions for Med13. Kinase module subunit hierarchy was conserved in human colon cancer cells where depletion of MED12 or double depletion of the redundant MED13 and MED13L also resulted in highly similar transcriptional responses. Med12 and Med13 were found to be activators of innate immunity genes that are dependent on the serpent/GATA transcription factor in fruit fly cells and larvae. In human colon cancer cells, MED12, MED13 and MED13L were disproportionally required for the expression of genes associated with cancer-acquired super-enhancers. MED12 or MED13 and MED13L depletion caused a dramatic decrease in the expression of the super-enhancer associated MYC oncogene and impaired proliferation of colon cancer cells, suggesting that targeting of these kinase module subunits is a possible future therapeutic opportunity. This thesis extends the present understanding of the relationships between Mediator kinase module subunits in metazoan species and identifies kinase module-dependent functions in development, immunity and cancer-acquired transcription. Further research should be directed at studying the molecular mechanisms of kinase module functions in vivo and at the potential to target this complex with the goal of treating human diseases such as cancer.