Bio- ja ympäristötieteellinen tiedekunta

 

Recent Submissions

  • Gruber, Christina (Helsingin yliopisto, 2015)
    Both the ability to gain a high dominance status and having an efficient immune defence are favourable qualities that typically increase fitness in social and host-parasite interactions. Individuals with a high dominance status are predicted to gain fitness-related benefits from prior access to limited, defensible resources, such as food and matings. Immune defence mechanisms, on the other hand, have evolved to minimize the fitness costs of parasitic infections. The relative significance of a high dominance status and strong immune defence for individual fitness is, however, affected by the quality of the environment. The aim of this thesis is to improve the understanding of environmentally determined variation in dominance status, immune defence and their consequences for individual fitness. I use the native noble crayfish (Astacus astacus), the invasive signal crayfish (Pacifastacus leniusculus) and the highly virulent, invasive Aphanomyces astaci, the causative agent of the crayfish plague, as my study models. I first experimentally test theoretical predictions on how major ecological factors, including food availability, predation risk and population density, influence behavioural decision-making in fight contests, especially with regard to the maintenance of dominance hierarchies between size-matched crayfish. Using natural noble crayfish subpopulations with different crayfish plague history, I then explore whether variation in immune defence and crayfish plague resistance is potentially explained by local adaptation to the disease, or alternatively by geographical divergence. By keeping noble crayfish experimentally under constant environmental conditions, I finally determine whether seasonal variation in immune defence is endogenously regulated. My results show that individuals that had achieved dominant status in non-resource fight contests have an advantage in monopolising a limited, defendable food resource in a future contest. Furthermore, I find evidence that as population density increases, the division of the resource between dominants and subdominants becomes more unequal. Generally, my results suggest that due to ecological factors the dominance status of individuals can be more dynamic than theory predicts, especially when the contestants have similar fighting ability. For example, in line with the asset-protection principle, individuals having achieved dominant status in a non-predation risk contest increase their submissive behaviours in the presence of a predation threat, giving subdominants the opportunity to win a larger percentage of bouts in the predation risk contest. My results also reveal evidence for geographical variation in resistance to the crayfish plague and immune defence that is, however, independent of historical disease outbreaks in the study subpopulations. Furthermore, for the first time in invertebrates, my results demonstrate reproduction-related endogenous seasonal variation in the immune defence of noble crayfish. Overall, my results suggest that ecological factors, such as population density, predation risk and disease history, have to be taken in to account to better understand the causes and consequences of dominance status and immune defence in any individual species.
  • Tumiati, Manuela (Helsingin yliopisto, 2015)
    Breast cancer is the second most common cancer in the world and the most common cancer among women. Germ-line mutations in the DNA repair gene RAD51C (RAD51 paralog C) predispose women to breast and ovarian cancers, yet the mechanisms by which a lack of RAD51C causes tumorigenesis are poorly understood. RAD51C deficiency is thought to promote cancer by preventing correct repair of DNA double-strand breaks, leading to accumulation of somatic mutations and genomic instability, a cancer hallmark. Similarly, defects in other genes involved in repair of DNA double-strand breaks, such as BRCA1 (breast cancer 1, early onset), BRCA2 (breast cancer 2, early onset), or PALB2 (partner and localizer of BRCA2), are linked to breast cancer, suggesting that the mammary gland is particularly susceptible to genomic instability. We know that RAD51C-null cells from several organisms present a number of chromosomal aberrations, and Rad51c knockout mice die during early embryogenesis from massive Trp53-mediated apoptosis. A previously generated mouse model demonstrated that when Rad51c is lost together with Trp53, multiple tumors develop approximately at one year of age. However, while Trp53 knock-out mice predominantly develop osteo- and myosarcomas, a spontaneous loss of both Rad51c and Trp53 in double-mutant mice leads mostly to development of epithelial-derived carcinomas, especially in mammary glands, skin, and skin-associated specialized sebaceous glands. While suggesting a possible role for Trp53 in the Rad51c-mediated tumorigenesis, this study left several questions unaddressed. First, the ability of Rad51c loss to induce tumor formation independently of Trp53 stood as an open question. Second, the mechanisms by which Rad51c might cause malignant transformation remained unclear. Last, there was complete absence of information about the role of RAD51C in the mammary gland. We set out to fill these gaps by generating a skin and skin-associated Rad51c knock-out mouse model. For this purpose, we conditionally deleted Rad51c and/or Trp53 from basal cells of the epidermis and ectodermal-derived glands using Keratin 14 Cre-mediated recombination. With this model, we demonstrated that deletion of Rad51c alone is not sufficient to drive tumorigenesis but impairs the proliferation of sebaceous cells and causes their transdifferentiation into terminally differentiated keratinocytes. In addition, we reported that Rad51c/p53 double mutant mice develop multiple tumors in skin and mammary and sebaceous glands at around six months of age, while Trp53-mutants have a tumor-free survival of 11 months and a lower tumor burden. We also observed that in situ carcinomas are detectable in Rad51c/p53 double mutant mice as early as four months of age, which provided a tool for studying the early phases of tumorigenesis. Notably, we reported that mouse mammary tumors recapitulate several histological features of human RAD51C-associated breast cancers, especially a luminal-like, hormone receptor-positive status. Finally, we described that loss of RAD51C causes chromosomal aberrations in both mouse and human cells, providing a direct translational link between the phenotype observed in the two species.
  • Silvennoinen, Reija (Helsingin yliopisto, 2015)
    Atherosclerosis is a multifactorial progressive disease characterized by the appearance of inflamed lesions in the inner arterial wall (intima). The clinical manifestations of atherosclerosis afflict more than half of the population globally. The main component of an atherosclerotic lesion is a cholesterol-filled macrophage (a foam cell); the degree of cholesterol accumulation within these cells is a major determinant of the disease process. In addition to macrophages, the inflamed intima contains numerous mast cells which, upon activation, acutely secrete serine proteases and other mediators that can influence the progression of atherosclerotic lesions. HDL-mediated removal of cholesterol from the lipid-filled macrophages and its transfer to the liver and feces for ultimate excretion, a process termed macrophage- reverse cholesterol transport (m-RCT), is an important anti-atherogenic mechanism. The multi-step m-RCT pathway appears to be modulated at the various steps. Mast cell-derived proteases, by degrading HDL lipoproteins, may affect the early steps of m-RCT, a possibility that has not been investigated in vivo. Psychological stress, an established risk factor for cardiovascular diseases and a potent activator of mast cells, might also interfere with m-RCT. With an aim to answer the question whether cholesterol flux through the m-RCT pathway could be physiologically modulated by mast cell activation and stress, this thesis assessed the functionality of the various components of the m-RCT pathway using the mouse as the experimental model. In the first study, a short-term m-RCT in vivo analysis was validated and performed to investigate the consequence of local mast cell activation for the functionality of HDL in m-RCT. The following study utilized the same method to address the effects of acute psychological stress on m-RCT. In the third study, the effects of stress on m-RCT were assessed in a chronic setting. An inhibitory role of peritoneal mast cell activation in vivo on the initial step of the m-RCT was established. Conversely, stress exposure, both acute and repetitive, induced multiple m-RCT-promoting responses in the liver and intestine. Mice exposed to acute psychophysical stress exhibited accelerated m-RCT due to compromised intestinal absorption of cholesterol, uncovering a novel functional connection between the stress hormone corticosterone and m-RCT. Repeated exposure to the same stressor resulted in increased fecal excretion of bile acids which also stimulated the rate of m-RCT. Altogether, the results presented in this thesis demonstrate that the m-RCT pathway is effectively modulated by two physiological factors, psychological stress and mast cell activation, which are involved in the pathology of atherosclerosis.
  • Morandin, Claire (Helsingin yliopisto, 2015)
    Understanding how the interaction of genotypes and environment may result in distinct phenotypes from similar sets of genes is a central theme in evolutionary biology. Social insects have been important study organisms for this question, with sociality evolving in parallel in unrelated taxa. The defining feature of advanced sociality, the separate reproductive queen and non-reproductive worker castes of social insects, is central to social evolution. Queens and workers share, most of the time, a similar genome, suggesting that the basis of this dimorphism must result from differences in expression of the same genes. Furthermore, workers forgo their own reproduction to help raise the offspring of the queen, thus queen and worker genes are expected to experience natural selection in unique ways. Yet, the regulatory architecture that governs queen and worker phenotypes remains largely unknown in social insects. This thesis demonstrates the plasticity of caste-biased expression patterns in ants at several levels. It shows that few genes retain their caste-biased expression patterns across closely related species, lineages, or development stages. For the first time, this thesis shows that biological functions, through conserved sets of genes, are strongly associated with caste phenotypic differences across the ant phylogeny. These sets of genes also appear to be co-opted for other types of key social phenotypes and likely serve as building blocks of phenotypic innovation. My thesis furthermore focuses on the interactions between caste-biased expression patterns and rates of molecular evolution to comprehend the origins and results of caste-biases. The work presented in this thesis shows that evolutionary constraints strongly affect evolutionary rates of protein-coding genes, gene expression evolutionary stability, and the ability of a gene to become caste-biased. These constraints are significant features that have been greatly under-appreciated in previous studies. The work in this thesis takes advantage of the power of genomic methodologies and technologies to provide new insights into mechanisms of social evolution, and the evolution of plastic gene expression in a more general framework. It builds on existing knowledge to provide the field of social insect research with novel concepts (e.g. co-expressed network) to understand the molecular mechanisms behind the origin and the maintenance of the two female castes.
  • Luchkina, Natalia V. (Helsingin yliopisto, 2015)
    Activity-dependent synaptic plasticity, and long-term potentiation in particular, represents the predominant model of memory and learning at the cellular level. In addition, synaptic plasticity plays a critical role in the activity-dependent refinement and fine-tuning of neuronal circuits during development by maintaining and stabilising certain synaptic connections and eliminating others. The main goal of this project was to increase our understanding of the molecular mechanisms underlying activity-dependent synaptic plasticity in the developing brain, with particular emphasis on the mechanisms that are specific to early postnatal development. First, we characterise in detail the properties of developmentally restricted neonatal presynaptic long-term potentiation (LTP) in CA1 area of the hippocampus and demonstrate its susceptibility to regulation via protein kinase C (PKC) signalling. Next, we explore the physiological functions of GluA4 subunit-containing AMPA type glutamate receptors, predominantly expressed at developing CA3 CA1 synapses. We show that GluA4 expression is necessary for protein kinase A (PKA)-dependent LTP at immature synapses. Further, the loss of GluA4 expression in parallel with circuit maturation explains the developmental switch in LTP signalling requirements from PKA- to Ca2+/calmodulin-dependent protein kinase II (CaMKII)-dependent. Further, we also explore the role of GluA4 C-terminal interaction partners in synaptic trafficking of GluA4-containing AMPA receptors and its importance for synapse maturation. We confirm a critical role for the membrane proximal region of GluA4 C-terminal domain in trafficking and identify a novel mechanism for activity-dependent synaptic delivery of GluA4 by the extreme C-terminal region. Finally, we show an important role of the GluA4 subunit in strengthening of AMPA receptor-mediated transmission, observed during early postnatal development. In summary, we provide novel information on the pre- and postsynaptic plasticity mechanisms operating at hippocampal CA3 CA1 synapses during the critical period of activity-dependent maturation of glutamatergic neuronal circuitry in rodents. This expands our knowledge on the cellular mechanisms guiding development of synaptic connectivity in the brain. Dysfunction of such mechanisms may play fundamental roles in the underlying pathophysiological causes of various neurodevelopmental disorders.
  • Lindgren, Hanna (Helsingin yliopisto, 2015)
    Lichens are symbiotic associations of heterotrophic fungi and photoautotrophic green algae or cyanobacteria. Bryoria is a lichenized euascomycete genus of approximately 50 currently accepted species. Although Bryoria is a conspicuous, easily recognized and frequently collected genus, species boundaries in this group are poorly known. This is especially the case with species in section Implexae where morphological and chemical variation is high even between individuals of the same species and genetic variation has been shown to be low in the examined markers. The aim of this study was to elucidate the taxonomic delimitation of the genus Bryoria, to examine the identity and selectivity of photobionts associated with Bryoria and to study the identity and phylogenetic placement of tremellalean fungi discovered from Bryoria. Possible correlations between the identity of the photobiont and the secondary chemistry of the lichen, and the identity of the secondary fungi and the secondary chemistry of the host lichen were particularly searched for. To study these questions, the taxon sampling focused on the chemically variable section Implexae. In addition, ecological characteristics and the distribution of Bryoria section Implexae species and their chemotypes in Finland were investigated to see if they corroborate recent taxonomic concepts. The results show that B. pseudocapillaris and B. spiralifera previously considered as members of section Implexae actually belong to the genus Sulcaria. Phylogenetic analyses also revealed that these two species are conspecific and thus a new combination, Sulcaria spiralifera, is introduced. In agreement with other studies, genetic differentiation in section Implexae was found to be minimal. Although most species of section Implexae are genetically indistinguishable, in this study, many of them were observed to have different ecological preferences. Bryoria capillaris favors managed stands in southern Finland whereas B. implexa and B. kuemmerleana prefer the habitats of long continuity of northern Finland. Bryoria vrangiana is a common species throughout the country but the three chemotypes of this species have slightly different habitat preferences chemotype lacking secondary substances being more common in the northern parts of the country, gyrophoric acid containing chemotype preferring the central parts of the country and fumarprotocetraric acid containing chemotype favoring the southern habitats. All Bryoria species studied here, except B. smithii, associate with a photobiont belonging to the Trebouxia simplex group. Selectivity of Bryoria spp. towards their photobiont varies among species. Bryoria bicolor, B. furcellata, B. smithii and B. tenuis are selective towards their photobionts whereas B. americana and B. fremontii seem to be less selective in their choice of a photobiont. All species in the section Implexae associate with the same photobiont making them selective at the section level. Lichen secondary chemistry was not found to correlate with the photobiont identity in section Implexae. The three basidiomycete fungi discovered in this study belong to the order Tremellales and they represent two undescribed endolichenic species and one hyperparasitic species. The hyperparasitic species is described in this study as Tremella huuskonenii. Tremella huuskonenii is a parasite infecting Phacopsis huuskonenii, a lichenicolous fungus growing obligately on Bryoria spp. Neither T. huuskonenii nor the endolichenic fungi examined in this study were found to make host preferences based on the secondary chemistry of the host lichen.
  • Tokariev, Anton (Helsingin yliopisto, 2015)
    In humans the few months surrounding birth comprise a developmentally critical period characterised by the growth of major neuronal networks as well as their initial tuning towards more functionally mature large-scale constellations. Proper wiring in the neonatal brain, especially during the last trimester of pregnancy and the first weeks of postnatal life, relies on the brain’s endogenous activity and remains critical throughout one’s life. Structural or functional abnormalities at the stage of early network formation may result in a neurological disorder later during maturation. Functional connectivity measures based on an infant electroencephalographic (EEG) time series may be used to monitor these processes. A neonatal EEG is temporally discrete and consists of events (e.g., spontaneous activity transients (SATs)) and the intervals between them (inter-SATs). During early maturation, communication between areas of the brain may be transmitted through two distinct mechanisms: synchronisation between neuronal oscillations and event co-occurrences. In this study, we proposed a novel algorithm capable of assessing the coupling on both of these levels. Our analysis of real data from preterm neonates using the proposed algorithm demonstrated its ability to effectively detect functional connectivity disruptions caused by brain lesions. Our results also suggest that SAT synchronisation represents the dominant means through which inter-areal cooperation occurs in an immature brain. Structural disturbances of the neuronal pathways in the brain carry a frequency selective effect on the functional connectivity decreasing at the event level. Next, we used mathematical models and computational simulations combined with real EEG data to analyse the propagation of electrical neuronal activity within the neonatal head. Our results show that the conductivity of the neonatal skull is much higher than that found in adults. This leads to greater focal spread of cortical signals towards the scalp and requires high-density electrode meshes for quality monitoring of neonatal brain activity. Additionally, we show that the specific structure of the neonatal skull fontanel does not represent a special pathway for the spread of electrical activity because of the overall high conductivity of the skull. Finally, we demonstrated that the choice of EEG recording montage may strongly affect the fidelity of non-redundant neuronal information registration as well as the output of functional connectivity analysis. Our simulations suggest that high-density EEG electrode arrays combined with mathematical transformations, such as the global average or current source density (CSD), provide more spatially accurate details about the underlying cortical activity and may yield results more robust against volume conduction effects. Furthermore, we provide clear instruction regarding how to optimise recording montages for different numbers of sensors.
  • Li, Jianyong (Helsingin yliopisto, 2015)
    Assessing the numerical relationships among pollen spectra, human influence and climate is a critical prerequisite for obtaining reliable and robust pollen-based quantitative reconstructions for past climatic variations and human-induced environmental changes. Here, modern pollen data from small river catchments in human-influenced mountainous ecosystems of northern China are collected to investigate the pollen/vegetation/land-use relationships. The effects of human influence index (HII) in comparison with key climate variables on influencing modern pollen distribution are evaluated using a continental-scale dataset. The importance of different climate variables accounting for modern pollen distribution is quantified for identifying the determinant variables that can be reconstructed in different bioclimatic regions of China. Furthermore, pollen-based calibration models for HII and climate parameters are developed and applied to a set of fossil pollen data for quantitative human influence and climate reconstructions. In addition, the bias caused by long-term and intensive human influence on vegetation in quantitative pollen-based palaeoclimatic reconstructions is examined, and pollen-based climate reconstructions are used to validate the reliability of climate model simulations. The results reveal that pollen assemblages from surface sediment samples in the Tuoliang and Qipanshan catchments from northern China are dominated by Artemisia, Chenopodiaceae, Pinus and Selaginella sinensis. Pollen types indicative of human activities such as Cerealia-type are common but not abundant. Artemisia and Chenopodiaceae percentages decline with decreasing altitude, whereas Pinus and S. sinensis percentages increase, suggesting that saccate Pinus pollen and S. sinensis spores can be transported further than non-saccate pollen types and that pollen sorting is taking place over water transportation. There is a positive linear relationship between percentages of Cerealia-type pollen and proportions of farmland, whereas correlation between percentages of trees, shrubs and herbs pollen and proportions of woodland, scrubland and grassland respectively is poor. This can be attributed to the differences in pollen productivity, deposition and dispersal. These findings may provide the basis for a modeling approach to reconstruct past land-cover changes at small catchment scale in northern China. The effects of HII on accounting for modern pollen distribution are smaller than annual precipitation (PANN) or annual average temperature (TANN) in most regions of China, with the exception of east-central China that has a significant pollen–HII relationship. The quantified importance of six climate variables (PANN; TANN; actual/potential evapotranspiration ratio, Alpha; mean temperature of the warmest month, MTWA; mean temperature of the coldest month, MTCO; annual sum of the growing degree days above 5 °C, GDD5) for the geographical distribution of modern pollen data differs among regions in China. Hydrological variables are more important than temperature-related variables in north-western and -eastern China and the Tibetan Plateau, whilst temperature-related variables are dominant in east-central and southern China. This suggests that the critical climate variables which can be optimally reconstructed from pollen data vary regionally in China. These regional differences are common to other large-scale surface pollen datasets and need to be taken into considerations in pollen-based climate reconstructions. The calibration models for HII, PANN and TANN show good statistical performances and are applied to a fossil pollen sequence from Lake Tianchi in east-central China. The inferred HII increases abruptly at 1100 cal. yr BP and remains high until present-day. Correspondingly, the reconstructed PANN shows a sudden decrease since 1100 cal. yr BP, whereas TANN displays an increase. However, other independent palaeoclimatic records mostly contradict the reconstructed climatic trends for the last 1100 years, suggesting that the Tianchi climate reconstructions for this period are biased by the intensification of human influence. This bias probably occurs in other palaeoclimatic reconstructions using pollen data from other regions where human impact on vegetation is also intensive and long-lasting. The calibration models for the summer monsoon precipitation (Pjja) also exhibit good predictive performances and are applied to a set of fossil pollen data from monsoonal China. The Holocene Pjja reconstructions from northern China are stacked to one record, showing that Pjja increases since 9500 cal. yr BP, reaches the maximum at 7000–4000 cal. yr BP, and falls down to present-day. The reconstructions are compared with Pjja simulations from the Kiel Climate Model (KCM). The model output and reconstructions are different for the early-Holocene for which the model suggests higher Pjja. The simulated Pjja changes for the Holocene summer monsoon maximum (HSMM) are lower than the reconstructed changes. The increasing or decreasing Pjja trends before or after the HSMM are more pronounced in the reconstructions than in the model results. Other palaeoclimatic data show substantial Holocene monsoon precipitation changes. This suggests that the KCM underestimates the magnitude of the summer monsoon precipitation changes. The results obtained in this work highlight the necessity for critically assessing the modern pollen/human-influence/climate relationships at various spatial scales and can be used to improve the correctness and robustness of pollen-based climate and human influence reconstructions in China and other regions of the world with large-scale surface pollen datasets. The pollen-based calibration models and their forthcoming applications can be employed to further quantitatively explore the past environmental changes and climatic dynamics and to validate the accuracy of climate model output.
  • Müller, Susann (Helsingin yliopisto, 2015)
    Biogeochemical processes in sea ice and the ice-water interface depend on abiotic processes and biological activity. Abiotic processes in sea ice are controlled by the crystallization process of freezing water and the associated formation of saline brine. Also the heat budget of sea ice and the resulting changes in abiotic properties such as porosity and salinity need to be taken into account. The dissolved fraction of sea ice brines contain ions and dissolved organic matter (DOM). Ions are rejected from the ice by diffusion and gravity drainage whereas dissolved organic matter with highly complex and diverse chemical composition can react in many ways with other molecules and surfaces. Hence, the present work compares the behavior of different fractions of DOM to the ones of salts during initial sea ice formation. Controlled tank studies were combined with natural sea ice sampling to exclude the disadvantages of both systems such as the effects of small-scale experiments, artificial additions in tank experiments and the unknown history of natural samples. The studies were conducted with brackish sea ice from the Baltic Sea with its high nutrient and DOM concentrations, but also with oceanic sea ice from the North Sea and the Arctic Ocean. This allows a general conclusion about the behavior of solutes during the formation of sea ice. The present studies indicate that the major seawater ions are significantly fractionated due to differential diffusion and coupled diffuse-convective salt transport through the brine channel network. Ions with a lower diffusivity than Cl¯, in this study SO42¯, Ca+ and Mg2+, remained longer in the brine channel network and got therefore enriched in sea ice relative to Cl¯. K+, on the other hand, diffused faster than Cl¯ and was depleted in sea ice in this study. The behavior of DOM in sea ice was more complex compared to ions because of the complex structure of DOM and the effect of secondary processes on DOM, such as biological production and degradation in sea ice. The quantification of DOM is challenging since only certain fractions such as chromophoric DOM can be measured instead of estimating the total concentration of DOM. Nevertheless, the present studies on DOM in sea ice from Baltic and North Sea water indicated enrichment of DOM compared to sea water ions. The magnitude of this enrichment was higher than expected from diffusion and convection following the transport of salts. The enrichment varied among DOM fractions with highest enrichment of amino-acid like DOM and lowest enrichment of humic-like substances. The results therefore suggest that additional processes, such as selective drainage that depends on the chemical properties of the DOM molecules, affect the enrichment of DOM in sea ice. The optical properties of sea ice were used to develop a bio-optical model. The model estimates the primary production in Baltic Sea ice based on the absorption by particles and chromophoric DOM and the quantum yield for C fixation calculated from photosynthesis-irradiance curves. The results were compared to in situ primary production measurements. The combination of modelled primary production estimates and the measurements of optical properties and primary production in different types of Baltic Sea ice gave a good overview over bio-optical properties in Baltic Sea ice and can be used as a tool to improve different parameters of ecosystem models.
  • Helle, Inari (Helsingin yliopisto, 2015)
    Coastal and marine ecosystems across the globe are heavily impacted by various anthropogenic stressors, which has led to a significant loss of biodiversity and ecosystem services in recent decades. In order to find means to counteract this trend, there is a need to develop methods for assessing the environmental impacts of human activities and the effectiveness of management practices to mitigate the harmful effects. However, this is a challenging task due to the complex interactions within and between the ecosystems and human components, and various uncertainties related to them. Bayesian networks (BNs) are graphical models for reasoning under uncertainty. A BN consists of a set of probabilistic variables connected with links describing causalities within the system. As the states of the variables are described with probability distributions, uncertainty can be described in an explicit manner. BNs also enable integration of qualitative and quantitative knowledge from various sources such as observational data sets, models and expert knowledge. In this thesis I have developed BN models to study environmental risks related to anthropogenic stressors in the Gulf of Finland and the Finnish Archipelago Sea. The main aim is to quantify human impacts on the environment, and to assess the ability of different management measures to lessen these impacts. I focus especially on oil spills resulting from potential tanker accidents and I set out to fill various information gaps related to this recently emerged threat. The thesis includes five papers. In paper I, the main aim is to assess the spatial risk posed by oil spills in the Gulf of Finland and the Finnish Archipelago Sea, and identify species and habitat types with the highest risk. In paper II, I focus on the effectiveness of different oil combating methods to mitigate the negative impacts of oil spills on the ecosystem, and paper III widens the approach to a probabilistic cost-benefit analysis of preventive and post-spill measures. Paper IV deals with multiple risks as, in addition to oil spills, eutrophication and harvesting of species are studied. Paper V reviews and discusses various methods that can be applied to evaluate the uncertainty related to deterministic models, which could increase their usefulness in decision-making. The results suggest that risks related to tanker accidents are distributed unevenly between areas, habitats and species. Furthermore, the results support the current Finnish strategy to base oil combating primarily on offshore recovery vessels instead of chemical dispersants. However, as the efficiency of mechanical recovery is dependent on several factors, there is also a need to develop preventive measures. Although major oil accidents are estimated to be rare events, the costs can be very high, if a spill occurs. The work offers new insights to the oil spill risks in the study area and provides examples how Bayesian networks can be applied in environmental risk assessment. The thesis is a part of the work needed in order to develop comprehensive decision support tools related to environmental risk management in the northern Baltic Sea.
  • Björklund, Heidi (Helsingin yliopisto, 2015)
    Human-caused habitat changes have led to declines of many species by impairing their occurrence, reproduction and interactions with other species. In Northern Europe, intensive forestry has transformed boreal forests and worsened conditions of species dependent on old forest, but the mechanisms by which habitat changes affect species are often unknown. In my dissertation, I examined habitat changes, their effects and habitat-associated breeding performances of three declining forest-dwelling hawks, the northern goshawk (Accipiter gentilis), the common buzzard (Buteo buteo) and the honey buzzard (Pernis apivorus). These species can compete for nest sites and goshawks can also predate the buzzards. Raptors may lack nest sites in managed forests which is why their nesting has been supported by constructing artificial nests. I analysed the breeding success of the hawks in artificial nests since their benefits as a conservation measure were not previously analysed. Finally, I studied the conditions when dominant species can exclude subordinate ones in competition for suitable nest sites. According to my results, old forests have decreased and young forests increased throughout southern Finland. These changes are adverse for the goshawk whose breeding success improves when old spruce forests are more abundant and young forests scarce around their nests. Breeding performances of the common buzzard and honey buzzard were not significantly associated with habitats. However, common buzzards were reluctant to re-occupy nests surrounded by a vastness of old forest. The breeding success of the goshawk and common buzzard was lower in artificial nests than in natural ones. Thus, this measure aimed at enabling hawk breeding in managed forests seems to conflict with its conservation objectives. I discuss the possible contributing factors and directions for further investigations. Interspecific interactions with other raptors proved to be important when a subordinate hawk decided on territory occupancy. Common buzzards prefer to occupy safe territories, where threats of goshawk predation and interference competition with other raptors are small. Thus, interspecific raptors that are predators or competitors may exclude subordinate raptors from their territories, and thereby contribute to their occurrence. Adverse interactions with other raptors may even impede a subordinate raptor from fully exploiting the periodic food peaks. My dissertation shows that for each species, it is crucial to identify the most relevant spatiotemporal scales in order to identify, how external disturbances affect them most. Long-term data is of paramount importance to detect these scales.
  • Virtanen, Laura (Helsingin yliopisto, 2015)
    Water quality in streams usually changes fast, and sensitive biological indicators are essential for monitoring these changes. Diatoms are widely used in biological stream quality assessments. However, there are temporal and spatial variations in diatom communities that may result in unreliable quality assessments. Under different kinds of environmental stressors, diatoms can produce deformed frustules. Heavy metals are among the most common causes of these teratological forms. In addition to eutrophication and organic pollution, diatoms could potentially be used for indicators of heavy metal enrichment. The aim here was to examine the interannual and intra-annual turnover of stream diatom communities. The focus of this study was on whether specific species traits and species local abundance and regional distribution affected temporal occurrence of diatom species. The study also included an examination of how stable diatom inferred stream classifications are in time and if pure spatial variation in diatoms should be considered when assessing stream water quality based on diatoms. The final aspect of the study was to determine which heavy metals, and to what extent, trigger the occurrence of deformations in diatom Achnanthidium minutissimum. Our results imply that abundant and widely distributed species with larger niches and the ability to attach to the substratum sustain persistent populations in varying environmental conditions typical for streams. The most persistent species are thus perhaps the most reliable species to be used as indicators of water quality. The stream classification based on diatoms resulted in temporally stable and statistically distinct community types. Thus, the results suggest that sampling of diatoms in every three years seems to be a reliable procedure to assess biological water quality. The investigation also revealed that study regions differ in their diatom species composition more than in their environmental features indicating that diatoms are structured not only by the local environment but also by large-scale processes, possibly related to climate, dispersal and history. As diatom species composition varies between regions, future bioassessments would benefit from regional stratification. Finally, study results indicated that two metals, copper and zinc, and a metalloid, antimony, were the most likely triggers of A. minutissimum deformations. The definition of their morphological and quantitative characteristics, along with a better taxonomic circumscription of the affected species, should allow the use of deformations as a reliable indicator of heavy metal enrichment in freshwater habitats.
  • Xu, Enjun (Helsingin yliopisto, 2015)
    Regulation of cellular homeostasis is crucial for proper development, survival, defense responses, programmed cell death and ultimately survival. Maintaining cellular homeostasis requires tight regulation of multiple highly interactive signaling pathways. The apoplast lies at the frontier between the cell and the environment, where the plant perceives environmental cues. Since the apoplast is also a site for cell-to-cell communication, it has an important role in mediating plant-environment interactions. Reactive oxygen species (ROS) are known as both toxic agents and indispensable signaling molecules in all aerobic organisms. A ROS burst in the apoplast is one of the first measurable events produced in response to different biotic and abiotic stresses, eventually leading to the initiation of signal transduction pathways and altered gene expression. Apoplastic ROS signaling is well known to dynamically coordinate multiple signaling pathways in the activation of defense responses in plants. Dissection of the signaling crosstalk within such a signaling network could therefore reveal the molecular mechanisms underlying defense responses. Treatments with ozone (O3) have been adopted as an efficient tool to study apoplastic ROS signaling. Plants exposed to O3 trigger a ROS burst in the apoplast and induce extensive changes in gene expression and alteration of defense hormones, such as salicylic acid (SA), jasmonic acid (JA), and ethylene. Genetic variation in O3 sensitivity among Arabidopsis thaliana accessions or mutants highlights the complex genetic architecture of plant responses to ROS. To gain insight into the genetic basis of apoplastic ROS signaling, a recombinant inbred line (RIL) population from a reciprocal cross between two Arabidopsis accessions C24 (O3 tolerant) and Tenela (O3 sensitive) was used for quantitative trait loci (QTL) mapping. Through a combination of QTL mapping and transcriptomic analyses in the response to apoplastic-ROS treatment, three QTL regions containing several potential candidate genes were identified in this study. In addition, multiple mutants with varying O3-sensitivities were employed to dissect the signaling components involved in the early apoplastic ROS signaling and O3-triggered cell death. A combination of global and targeted gene expression profiling, genetic analysis, and cell death assays was performed to dissect the contribution of hormone signaling and various transcription factors to the regulation of apoplastic ROS-triggered gene expression and cell death. The contributions of SA, JA and ethylene were assessed through analysis of mutants deficient in these hormones, mutants with constitutively activated hormone signaling and the exogenous application of hormones. Plants with elevated SA levels were found to be associated with an attenuated O3 response, whereas simultaneous elimination of SA-dependent and SA- independent signaling components enhanced the response to apoplastic ROS treatment. JA could act as both a positive and negative modifier of apoplastic ROS signaling, which was enhanced when ethylene signaling was also impaired. However, transcriptome analysis of a triple mutant deficient in SA, JA and ethylene revealed that these hormones signaling only contributed part (about 30%) of early-apoplastic ROS-triggered changes in gene expression, suggesting multiple signaling pathways could be required to regulate the apoplastic ROS response via combinatorial or overlapping mechanisms.
  • Ruppel, Meri M. (Helsingin yliopisto, 2015)
    The Arctic has been warming twice as fast as the rest of the world during the last decades of global warming. Reasons for the amplified Arctic warming are thought to partly relate to positive feedbacks affecting the radiative budget of the area. Black carbon (BC) is a light-absorbing particulate produced by incomplete combustion of biomass and fossil fuels. BC strongly warms the atmosphere, and its climate effects are amplified in the Arctic where its deposition on light surfaces decreases their reflectivity, resulting in elevated heat absorption and further hastening melt of snow and ice. Globally, BC is estimated to be the second most important climate-warming agent after carbon dioxide. Historical information on BC deposition plays a significant role in the assessment of long-term climate effects of BC, but scarce data on this past variability has been available from the Arctic. Historical BC records can be attained from environmental archives, such as ice cores, peat deposits and marine and lake sediments, which store direct evidence of past BC deposition in chronological order. The objective of this thesis is to collect new spatial and temporal data on BC deposition in the European Arctic from the preindustrial to the present (i.e., the last ca. 300 years), and assess BC sources and climatic implications, by analysing five lake sediment cores from Arctic Finland and an ice core from Svalbard. No standard method exists to determine BC, and the precise definition of BC depends on the methodology used for its quantification. Here, three different analytical methods were used to quantify different components of BC. Spheroidal Carbonaceous Particles (SCP) and soot-BC (SBC) were analysed from the Arctic Finland lake sediments by SCP analysis and chemothermal oxidation at 375 °C, respectively, and elemental carbon (EC) from the Svalbard ice core with a thermal optical method. The results suggest temporal variation in past BC trends, both between study sites and between methods. While SCPs show a marked trend with fluxes peaking around 1980 and declining afterwards, they represent only a minor fraction of total BC. SBC and EC are better suited to indicate general historical BC trends. SBC fluxes vary between sites but some regional patterns are noticeable. The two northernmost lakes indicate generally decreasing SBC fluxes during the latter half of the 20th century which is in line with previous data from Greenland ice cores, modelling studies and atmospheric measurements. However, two other lake sites indicate increasing SBC fluxes from ca. 1970 to the end of the records, likely caused by local emissions from the Kola Peninsula, Russia. Moreover, an increasing EC deposition trend from ca. 1970 to 2004 is also recorded in the Svalbard ice core. This increasing trend is unexpected and unparalleled among available arctic records. The observed increase in the ice core is likely caused by flaring emissions from northern Russia. The fact that a similar trend in BC fluxes and deposition is recorded in two separate environmental archives analysed with different methods and receiving atmospheric transport from mostly different source areas, highlights the plausibility of such a trend, and implies that it may also be observable at other locations in the Arctic. In such a case, BC may have exerted a significant impact on the radiative forcing and thereby past climatic warming of the Arctic, in the most recent three or four decades. However, the present study indicates that local results cannot necessarily be extrapolated over wider areas, and therefore further studies are required to establish regional BC deposition trends within the Arctic. In addition, the study highlights that BC results obtained using different analytical methods should be compared with caution.
  • Anttila, Jani (Helsingin yliopisto, 2015)
    Environmental opportunist pathogens are a class of organisms that are able to both infect multicellular hosts and grow in the outside-host environment as free-living organisms. Environmental opportunism differs from obligate parasitism in that direct host-to-host contact is not necessary for disease transmission and that there are environmental pathogen reservoirs which in suitable conditions act as sources of infection. Because of this, environmental opportunist pathogens form a persistent threat to human health, livestock, and wildlife, and cannot be eradicated by treating hosts. Three well-known examples of pathogens of this class are Vibrio cholerae, Flavobacterium columnare, and Bacillus anthracis, all of which cause sporadic outbreaks. Between infections, these pathogens are subject to multiple biotic and abiotic environmental pressures in the outside-host environment. While environmental opportunist pathogens are not dependent on live hosts for transmission and thus benefit from increased virulence, balancing between the two environments, within-host and outside-host, might incur trade-offs and thus limitations to their spread. In this thesis I have developed mathematical models of environmental opportunist pathogen dynamics and studied the effects of environmental variation and outsidehost interactions on patterns of pathogen outbreaks. The studies included in the thesis address (i) the origin of a sigmoidal dose-dependent infectivity response, (ii) the effect of competition in the outside-host environment on opportunist pathogen outbreaks, (iii) the effect of environmental variation on environmental opportunist dynamics, and (iiii) how environmental variation enables invasions of emerging opportunist pathogen strains. The modelling approach has enabled identification of factors such as alleviation of competitive pressure and certain kinds of environmental variation as outside-host environmental factors that promote outbreaks. Additionally, modelling results can be used to suggest control strategies to reduce the probability of environmental opportunist pathogen outbreaks.