Browsing by Subject "biologia"

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  • Merikanto, Ilona (Helsingin yliopisto, 2016)
    Many existing and emerging microbial infectious diseases are caused by environmentally growing opportunist pathogens. These pathogens are, contrary to obligatory pathogens, able to survive and replicate in the outside-host environment as free-living microbes that use within-host growth as an alternative replication strategy. This disease class has eco-evolutionary implications in natural populations and causes a serious health and economical threat to humans, our food production and to wildlife. Because of the ability of environmentally growing opportunists to survive and replicate independently of hosts, these diseases are hard to eradicate with conventional methods. The conditions that favor or disfavor environmental opportunism are still poorly understood. Better understanding of the dynamics of these diseases is needed in order to develop proper control methods against them. In this thesis I have developed novel epidemiological models to describe the disease dynamics of environmentally growing pathogens. These models modify the traditional Susceptible-Infected host (SI-model) framework by combining it to the outside-host community of an environmentally growing pathogen. I have considered how the environmental growth of the pathogens and the antagonistic ecological interactions these pathogens face in the outside-host environment, such as competition, predation and parasitism, affect the disease dynamics, invasion of novel pathogens and biological control of environmentally growing infectious diseases. The analyses show that the disease dynamics of environmentally growing pathogens differ from obligatory pathogens. Importantly, ability to grow in the outside-host environment promotes disease outbreaks and can lead to the extinction of the host, which is untypical in the case of obligatory pathogens. Antagonistic interactions the pathogen faces in the outside-host environment can on the other hand limit disease outbreaks and prevent extinction of the hosts that would otherwise occur due to the disease. I conclude that the eradication can be accomplished 1) by increasing the outside-host competition, 2) through predation of pathogens, or 3) through viral infections in pathogens.
  • Hoikkala, Laura (Helsingin yliopisto, 2012)
    Dissolved organic matter (DOM) in surface waters originates from allochthonous and autochthonous sources, the latter of which includes exudation by phytoplankton, viral lysis of planktonic organisms and 'sloppy' feeding by zooplankton. The concentration of DOM in seawater exceeds by one to two orders of magnitude that of particulate organic matter. Thus the DOM pool may be crucial to nutrition of pelagic osmotrophs, such as bacteria and algae, which are capable of exploiting dissolved organic substrates. In this thesis, monitoring surveys and laboratory experiments were used to examine the seasonal dynamics of DOM, including interactions of DOM and heterotrophic bacteria, in the Gulf of Finland, northern Baltic Sea, which is rich in allochthonous humic DOM. Despite the large ambient DOM pools and their potentially marked influence in the planktonic food webs and biogeochemical cycles of carbon and nutrients, few investigations in the Baltic Sea have focused on the dynamics of DOM, and information from the Gulf of Finland is almost lacking. In this thesis, seasonal changes in the net pools of dissolved organic C (DOC), N (DON) and P (DOP) were followed along with ambient key physical, chemical and biological variables on a shore-to-open-sea salinity gradient once in January and biweekly during the phytoplankton growth season. Horizontal coverage of these data was complemented with DOM samplings along a transect from the western to the eastern part of the Gulf. Autochthonous DOM accumulated throughout the productive season and the accumulated DOM was N- and P-rich compared with the bulk DOM pool in the surface layer of the Gulf of Finland. Notable DOM accumulation occurred during the actively growing and declining phases of spring and late summer blooms. Total export estimates of surface DOC, DON and DOP by autumn overturn corresponded to about 11 25% of reported annual particulate organic matter sedimentation in our study area. Seasonal variation in the availability of the net DOC and DON pools for bacterial utilization was investigated with incubations of natural bacterial samples for 2 3 wk. The concentrations of labile DOC were low in spring and during the summer minimum period, whereas the pools of labile DON were more variable. The labile DOM accumulated during and after the late summer cyanobacterial bloom, with low C:N ratios. For determination of factors that control the net DOM pools, limitation of bacterial growth by inorganic nutrients (N and P), labile C and temperature was followed in natural surface and deep-water bacterial samples during the main postspring bloom stages of phytoplankton growth. Agreeing with the low degradability of the ambient DOC pool, bacterial production was consistently C-limited in the surface layer, with N or both N and P as the secondary limiting nutrients from spring to early summer and in late summer, respectively. In deep water, bacterial growth showed combined temperature and C limitation. Sunlight induces photochemical transformation of DOM, and the importance of this process to bacterial growth during summer was investigated with samples representing extensive spatial and temporal coverage. In addition, photochemical transformation of refractory DOM and its effects on growth and composition of the microbial community were studied in further detail during a late summer cyanobacterial bloom. Photochemical transformation of DOM generally resulted in increased bacterial production, and photoproduced labile DOC was estimated to support < 10% of the daily bacterial C production in the surface layers during summer. Photochemical transformation of DOM led to clear changes in the composition of the bacterial community, with notable increases in the relative percentage of a few typical freshwater bacteria. The results further indicated that bacterial taxa benefiting from labile photoproducts included specialists growing strictly on the photoproducts of humic matter. The results of this thesis suggest that the C-limited bacterial community is for most of the productive season capable of efficient utilization of the labile C compounds released in the Gulf of Finland. The accumulation of phytoplankton-derived, autochthonous DOC during the productive season and subsequent DOC export to deep water are thus lower than in situations where nutrient-limited bacteria would allow accumulation of labile DOC, decreasing the efficiency of the plankton system in incorporating atmospheric CO2. Nevertheless, accumulation in the DOM pool forms a notable temporary storage of phytoplankton-derived C, N and P. The pool of labile DON, which accounted for up to 95% of the available N in surface water during summer, is a notable nutrient source for the N-limited plankton community. Photochemical transformation of DOM seems to contribute relatively little to the bacterial C demand, which is satisfied by autochthonous DOM released from the plankton food web in the Gulf of Finland. However, photoproduction of labile DOM appears to have notable qualitative effects on the composition of the bacterial community, probably contributing to the success in the Baltic Sea of bacteria originating in freshwater.
  • Suomalainen, Marika (Helsingin yliopisto, 2010)
    Tooth development is regulated by sequential and reciprocal interactions between epithelium and mesenchyme. The molecular mechanisms underlying this regulation are conserved and most of the participating molecules belong to several signalling families. Research focusing on mouse teeth has uncovered many aspects of tooth development, including molecular and evolutionary specifi cs, and in addition offered a valuable system to analyse the regulation of epithelial stem cells. In mice the spatial and temporal regulation of cell differentiation and the mechanisms of patterning during development can be analysed both in vivo and in vitro. Follistatin (Fst), a negative regulator of TGFβ superfamily signalling, is an important inhibitor during embryonic development. We showed the necessity of modulation of TGFβ signalling by Fst in three different regulatory steps during tooth development. First we showed that tinkering with the level of TGFβ signalling by Fst may cause variation in the molar cusp patterning and crown morphogenesis. Second, our results indicated that in the continuously growing mouse incisors asymmetric expression of Fst is responsible for the labial-lingual patterning of ameloblast differentiation and enamel formation. Two TGFβ superfamily signals, BMP and Activin, are required for proper ameloblast differentiation and Fst modulates their effects. Third, we identifi ed a complex signalling network regulating the maintenance and proliferation of epithelial stem cells in the incisor, and showed that Fst is an essential modulator of this regulation. FGF3 in cooperation with FGF10 stimulates proliferation of epithelial stem cells and transit amplifying cells in the labial cervical loop. BMP4 represses Fgf3 expression whereas Activin inhibits the repressive effect of BMP4 on the labial side. Thus, Fst inhibits Activin rather than BMP4 in the cervical loop area and limits the proliferation of lingual epithelium, thereby causing the asymmetric maintenance and proliferation of epithelial stem cells. In addition, we detected Lgr5, a Wnt target gene and an epithelial stem cell marker in the intestine, in the putative epithelial stem cells of the incisor, suggesting that Lgr5 is a marker of incisor stem cells but is not regulated by Wnt/β-catenin signalling in the incisor. Thus the epithelial stem cells in the incisor may not be directly regulated by Wnt/β-catenin signalling. In conclusion, we showed in the mouse incisors that modulating the balance between inductive and inhibitory signals constitutes a key mechanism regulating the epithelial stem cells and ameloblast differentiation. Furthermore, we found additional support for the location of the putative epithelial stem cells and for the stemness of these cells. In the mouse molar we showed the necessity of fi ne-tuning the signalling in the regulation of the crown morphogenesis, and that altering the levels of an inhibitor can cause variation in the crown patterning.
  • Lindfors, Päivi (Helsingin yliopisto, 2006)
    Glial cell line-derived neurotrophic factor (GDNF) family ligands: GDNF, neurturin, persephin and artemin, signal through a receptor tyrosine kinase Ret by binding first to a co-receptor (GFRα1-4) that is attached to the plasma membrane. The GDNF family factors can support the survival of various peripheral and central neuronal populations and have important functions also outside the nervous system, especially in kidney development. Activating mutations in the RET gene cause tumours in neuroendocrine cells, whereas inactivating mutations in RET are found in patients with Hirschsprung s disease (HSCR) characterized by loss of ganglionic cells along the intestine. The aim of this study was to examine the in vivo functions of neurturin receptor GFRα2 and persephin receptor GFRα4 using knockout (KO) mice. Mice lacking GFRα2 grow poorly after weaning and have deficits in parasympathetic and enteric innervation. This study shows that impaired secretion of the salivary glands and exocrine pancreas contribute to growth retardation in GFRα2-KO mice. These mice have a reduced number of intrapancreatic neurons and decreased cholinergic innervation of the exocrine pancreas as well as reduced excitatory fibres in the myenteric plexus of the small intestine. This study also demonstrates that GFRα2-mediated Ret signalling is required for target innervation and maintenance of soma size of sympathetic cholinergic neurons and sensory nociceptive IB4-binding neurons. Furthermore, lack of GFRα2 in mice results in deficient perception of temperatures above and below thermoneutrality and in attenuated inflammatory pain response. GFRα4 is co-expressed with Ret predominantly in calcitonin-producing thyroid C-cells in the mouse. In this study GFRα4-deficient mice were generated. The mice show no gross developmental deficits and have a normal number of C-cells. However, young but not adult mice lacking GFRα4 have a lower production of calcitonin in thyroid tissue and consequently, an increased bone formation rate. Thus, GFRα4/Ret signalling may regulate calcitonin production. In conclusion, this study reveals that GFRα2/Ret signalling is crucial for the development and function of specific components of the peripheral nervous system and that GFRα4-mediated Ret signalling is required for controlling transmitter synthesis in thyroid C-cells.
  • Bargum, Katja (Helsingin yliopisto, 2007)
    Social groups are common across animal species. The reasons for grouping are straightforward when all individuals gain directly from cooperating. However, the situation becomes more complex when helping entails costs to the personal reproduction of individuals. Kin selection theory has offered a fruitful framework to explain such cooperation by stating that individuals may spread their genes not only through their own reproduction, but also by helping related individuals reproduce. However, kin selection theory also implicitly predicts conflicts when groups consist of non-clonal individuals, i.e. relatedness is less than one. Then, individual interests are not perfectly aligned, and each individual is predicted to favour the propagation of their own genome over others. Social insects provide a solid study system to study the interplay between cooperation and conflict. Breeding systems in social insects range from solitary breeding to eusocial colonies displaying complete division of reproduction between the fertile queen and the sterile worker caste. Within colonies, additional variation is provided by the presence of several reproductive individuals. In many species, the queen mates multiply, which causes the colony to consist of half-sib instead of full-sib offspring. Furthermore, in many species colonies contain multiple breeding queens, which further dilutes relatedness between colony members. Evolutionary biology is thus faced with the challenge to answer why such variation in social structure exists, and what the consequences are on the individual and population level. The main part of this thesis takes on this challenge by investing the dynamics of socially polymorphic ant colonies. The first four chapters investigate the causes and consequences of different social structures, using a combination of field studies, genetic analyses and laboratory experiments. The thesis ends with a theoretical chapter focusing on different social interactions (altruism and spite), and the evolution of harming traits. The main results of the thesis show that social polymorphism has the potential to affect the behaviour and traits of both individuals and colonies. For example, we found that genetic polymorphism may increase the phenotypic variation between individuals in colonies, and that socially polymorphic colonies may show different life history patterns. We also show that colony cohesion may be enhanced even in multiple-queen colonies through patterns of unequal reproduction between queens. However, the thesis also demonstrates that spatial and temporal variation between both populations and environments may affect individual and colony traits, to the degree that results obtained in one place or at one time may not be applicable in other situations. This opens up potential further areas of research to explain these differences.
  • Venn, Stephen (Helsingin yliopisto, 2013)
    In this thesis I use carabid beetles (Coleoptera, Carabidae) and vascular plants to investigate the ecological effects of urbanization on forested and dry meadow habitats in the city of Helsinki, Finland. I also investigate factors that affect species diversity and the occurrence of rare and sensitive species in particular, in order to draft recommendations for habitat management for the enhancement of urban biodiversity. Urbanization gradient analyses are conducted using multivariate ordination analyses to elucidate assemblage level responses, ANOVA is applied to determine the assemblage level response of spruce forest carabid assemblages and GLMM is used to model individual species responses. The results suggest that, in contrast to Gray s suggestion, Preston s log-normal does not accurately describe the species distributions of carabid beetles in the studied habitats but rather they follow the predictions of Fisher s log series and Hubbell s unified neutral theory. I conclude that fragmentation, isolation and homogenization are the main problems regarding maintenance of urban biodiversity, and that biodiversity strategies should focus on the conservation of stenotopic species. In particular, habitats and ecologically important microhabitat conditions should be retained in as large and contiguous a form as possible. For instance, spruce forest habitats need to be managed to maintain shady, cool and moist conditions and dry meadows should be mown late in the season and the cut vegetation removed. Additionally, supplementation of habitat networks should be implemented, by habitat restoration and habitat creation, such as the construction of dry meadows on landfills and noise abatement banks.
  • Murtomäki, Aino (Helsingin yliopisto, 2016)
    Mammals have two parallel vascular systems, the blood and the lymphatic vascular system. The blood vascular system transports oxygen and nutrients to tissues and metabolic wastes from the tissues to excretory organs. Lymphatic vessels collect excess fluid from the interstitial space and return it back into the bloodstream, thus maintaining fluid homeostasis. Like veins, lymphatic collecting ducts contain intraluminal valves that ensure unidirectional flow. Notch signaling is an evolutionary conserved signaling pathway that mediates cell fate decisions and regulates cellular functions through its modulation of downstream targets. Using transgenic mouse models, we studied the role of Notch in embryonic lymphatic development and postnatal blood vascular development. Better understanding of these basic mechanisms is crucial for developing new treatments for diseases associated with abnormal blood or lymphatic vessels function. Embryonically, the lymphatic system develops as a subset of endothelial cells in the cardinal veins start expressing Prox1 and other lymphatic markers and become committed to the lymphatic lineage. We show that loss of Notch during the initiation phase leads to an increase in lymphatic progenitor cells emerging from the cardinal vein and lymphatic overgrowth. Thus, Notch is required in the cardinal vein to limit the number of endothelial cells adopting the lymphatic endothelial fate. Lymphatic valve development occurs during collecting duct maturation as subsets of lymphatic endothelial cells in the lymphatic duct walls adopt a lymphatic valve fate. We show that loss of Notch signaling in lymphatic endothelial cells at the time of valve initiation results in a decrease in the number of valves, abnormal valve morphology and reduced expression of valve-specific markers in valve-forming lymphatic endothelial cells. Thus, Notch signaling is required for proper lymphatic valve development. Blood endothelial cells interact with contractile smooth muscle cells and non-contractile pericytes, which are collectively called mural cells. Endothelial cell-mural cell interactions provide mechanical support to vessels as well as regulate many vessel functions that are crucial for vascular integrity such as permeability, sprouting and quiescence. Notch1 is expressed in both endothelial cells and mural cells while Notch3 is restricted to vascular mural cells. We show that global Notch1 heterozygocity combined with global Notch3 deficiency results in impaired vascular smooth muscle cell recruitment in the mouse retina leading to abnormal vascular development. We also demonstrate that biological inhibition of Notch signaling using soluble Notch1 decoys results in defective vascular smooth muscle coverage in the mouse retina. Our data show that both Notch1 and Notch3 are required for proper vascular smooth muscle cell function during vascular development and thus report a novel role for Notch1 in mural cells.
  • Högnabba, Filip (Helsingin yliopisto, 2007)
    Phylogenetic studies of cyanobacterial lichens Lichens are symbiotic assemblages between fungi (mycobiont) and green algae (phycobiont) or/and cyanobacteria (cyanobiont). Fossil records show that lichen-like symbioses occurred already 600 million years ago. Lichen symbiosis has since then become an important life strategy for the Fungi, particularly for species in the phylum Ascomycota as approximately 98% of the lichenized fungal species are ascomycetes. The taxonomy of lichen associations is based on the mycobiont. We reconstructed, using DNA sequence data, hypotheses of phylogenetic relationships of lichen-forming fungi that include species associated with cyanobacteria. These hypotheses of phylogeny should form the basis for the taxonomy. They also allowed studies of the origin and the evolution of specific symbioses. Genetic diversity and phylogenetic relationships of symbiotic cyanobionts were also studied in order to examine selectivity of cyanobionts and mycobionts as well as possible co-evolution between partners involved in lichen associations. The suggested circumscription of the family Stereocaulaceae to include Stereocaulon and Lepraria is supported. The recently described crustose Stereocaulon species seem to be correctly placed in the genus, although Stereocaulon traditionally included only fruticose species. The monospecific crustose genus Muhria is also shown to be best placed in Stereocaulon. Family Lobariaceae as currently delimited is monophyletic. Within Lobariaceae genus Sticta including Dendriscocaulon dendroides form a monophyletic group while the genera Lobaria and Pseudocyphellaria are non-monophyletic. A new classification of Lobariaceae is obviously needed. Further studies are however required before a final proposal for a new classification can be made. Our results show that the cyanobacterial symbiotic state has been gained repeatedly in the Ascomycota while losses of symbiotic cyanobacteria appear to be rare. The symbiosis with green algae is confirmed to have been gained repeatedly in Ascomycota but also repeatedly lost. Cyanobacterial symbioses therefore seem to be more stable than green algal associations. Cyanobacteria are perhaps more beneficial for the lichen fungi and therefore maintained. The results indicate a dynamic association of the lichen symbiosis. This evolutionary instability will perhaps be important for the lichen fungi as the utilization of options will perhaps enable lichens to colonize new substrates and survive environmental changes. Some cyanobacterial lichen genera seem to be highly selective towards the cyanobiont while others form symbioses with a broad spectrum of cyanobacteria. No evidence of co-evolution between fungi and cyanobacteria in cyanolichens could be demonstrated.
  • Munne, Pauliina (Helsingin yliopisto, 2010)
    This thesis work focuses on the role of TGF-beta family antagonists during the development of mouse dentition. Tooth develops through an interaction between the dental epithelium and underlying neural crest derived mesenchyme. The reciprocal signaling between these tissues is mediated by soluble signaling molecules and the balance between activatory and inhibitory signals appears to be essential for the pattern formation. We showed the importance of Sostdc1 in the regulation of tooth shape and number. The absence of Sostdc1 altered the molar cusp patterning and led to supernumerary tooth formation both in the molar and incisor region. We showed that initially, Sostdc1 expression is in the mesenchyme, suggesting that dental mesenchyme may limit supernumerary tooth induction. We tested this in wild-type incisors by minimizing the amount of mesenchymal tissue surrounding the incisor tooth germs prior to culture in vitro. The cultured teeth phenocopied the extra incisor phenotype of the Sostdc1-deficient mice. Furthermore, we showed that minimizing the amount of dental mesenchyme in cultured Sostdc1-deficient incisors caused the formation of additional de novo incisors that resembled the successional incisor development resulting from activated Wnt signaling. Sostdc1 seemed to be able to inhibit both mesenchymal BMP4 and epithelial canonical Wnt signaling, which thus allows Sostdc1 to restrict the enamel knot size and regulate the tooth shape and number. Our work emphasizes the dual role for the tooth mesenchyme as a suppressor as well as an activator during tooth development. We found that the placode, forming the thick mouse incisor, is prone to disintegration during initiation of tooth development. The balance between two mesenchymal TGF-beta family signals, BMP4 and Activin is essential in this regulation. The inhibition of BMP4 or increase in Activin signaling led to the splitting of the large incisor placode into two smaller placodes resulting in thin incisors. These two signals appeared to have different effects on tooth epithelium and the analysis of the double null mutant mice lacking Sostdc1 and Follistatin indicated that these TGF-beta inhibitors regulate the mutual balance of BMP and Activin in vivo. In addition, this work provides an alternative explanation for the issue of incisor identity published in Science by Tucker et al. in 1998 and proposes that the molar like morphology that can be obtained by inhibiting BMP signaling is due to partial splitting of the incisor placodes and not due to change in tooth identity from the incisor to the molar. This thesis work presents possible molecular mechanisms that may have modified the mouse dental pattern during evolution leading to the typical rodent dentition of modern mouse. The rodent dentition is specialized for gnawing and consists of two large continuously growing incisors and toothless diastema region separating the molars and incisors. The ancestors of rodents had higher number of more slender incisors together with canines and premolars. Additionally, murine rodents, which include the mouse, have lost their ability for tooth replacement. This work has revealed that the inhibitory molecules appear to play a role in the tooth number suppression by delineating the spatial and temporal action of the inductive signals. The results suggest that Sostdc1 plays an essential role in several stages of tooth development through the regulation of both the BMP and Wnt pathway. The work shows a dormant sequential tooth forming potential present in wild type mouse incisor region and gives a new perspective on tooth suppression by dental mesenchyme. It reveals as well a novel mechanism to create a large mouse incisor through the regulation of mesenchymal balance between inductive and inhibitory signals.
  • Li, Hong (Helsingin yliopisto, 2008)
    Cation chloride cotransporters (CCCs) are critical for controlling intracellular chloride homeostasis. The CCC family is composed of four isoforms of K-Cl cotransporters (KCC1-4), two isoforms of Na-K-2Cl cotransporters (NKCC1-2), one Na-Cl cotransporter (NCC) and two the structurally related proteins with unknown function, CCC8 also known as cation-chloride cotransporter interaction protein, CIP, and CCC9. KCC2 is a neuron-specific isoform, which plays a prominent role in controlling the intracellular Cl- concentration in neurons and is responsible for producing the negative shift of GABAA responses from depolarizing to hyperpolarizing during neuronal maturation. In the present studies we first used in situ hybridization to examine the developmental expression patterns of the cation-chloride cotransporters KCC1-4 and NKCC1. We found that they display complementary expression patterns during embryonic brain development. Most interestingly, KCC2 expression in the embryonic central nervous system strictly follows neuronal maturation. In vitro data obtained from primary and organotypic neuronal cultures support this finding and revealed a temporal correlation between the expression of KCC2 and synaptogenesis. We found that KCC2 is highly expressed in filopodia and mature spines as well as dendritic shaft and investigated the role of KCC2 in spine formation by analyzing KCC2-/- neurons in vitro. Our studies revealed that KCC2 is a key factor in the maturation of dendritic spines. Interestingly, the effect of KCC2 in spine formation is not due to Cl- transport activity, but mediated through the interaction between KCC2 C-terminal and intracellular protein associated with cytoskeleton. The interacting protein we found is protein 4.1N by immunoprecipitation. Our results indicate a structural role for KCC2 in the development of functional glutamatergic synapses and suggest KCC2 as a synchronizer for the functional development of glutamatergic and GABAergic synapses in neuronal network. Studies on the regulatory mechanisms of KCC2 expression during development and plasticity revealed that synaptic activity of both the glutamatergic and GABAergic system is not required for up-regulation of KCC2 during development, whereas in acute mature hippocampal slices which undergo continuous synchronous activity induced by the absence of Mg2+ solution, KCC2 mRNA and protein expression were down-regulated in CA1 pyramidal neurons subsequently leading to a reduced capacity for neuronal Cl- extrusion. This effect is mediated by endogenous BDNF-TrkB down-stream cascades involving both Shc/FRS-2 and PLCγ-CREB signaling. BDNF mediated changes in KCC2 expression indicate that KCC2 is significantly involved in the complex mechanisms of neuronal plasticity during development and pathophysiological conditions.
  • Vlieger, Leon (Helsingin yliopisto, 2010)
    When organisms compete for mates and fertilisations, the process of sexual selection drives the evolution of traits that increase reproductive success. The traits targeted by selection, and the extent to which they change, are constrained by the local environment. Sexual selection due to female mate choice can be undermined by alternative reproductive tactics (ARTs), which refers to discontinuous variation in traits or behaviours used in reproduction. As human activities are rapidly changing our planet, this raises the question how ARTs will be affected. Fish show a bewildering diversity of ARTs, which make them good model organisms to answer these questions. One example of human-induced environmental change, which is affecting aquatic ecosystems around the world, is eutrophication, the over-enrichment of water bodies with nutrients. One of its effects is decreased underwater visibility due to increases in both turbidity and vegetation density. The aims of this thesis were to investigate the effects increased turbidity and vegetation density have on an ART in sticklebacks, a fish common to marine and fresh water bodies of the Northern hemisphere. I furthermore investigated how this affected sexual selection for male size, a trait commonly under selection. I used a combination of behavioural observations in microcosms, where I manipulated underwater visibility, with collection of genetic material to reconstruct parentage of broods, and thus identify sneak fertilisations. The results show that turbidity might have weak negative effects on the frequency of sneaking behaviour, although this behaviour was rather infrequent in these experiments, which complicates firm conclusions. In dense vegetation the number of sneak fertilisations decreased slightly, as fewer nesting males sneaked, while the number of non-nesting males sneaking remained constant. The paternity analyses revealed that a significantly smaller fraction of eggs was sneak fertilised under dense vegetation. Furthermore, amongst the nesting males that sneaked, the amount of eggs sneak fertilised correlated positively with courtship success. A reduction in sneaking by these males under dense vegetation equalised the distribution of fertilisation success, in turn contributing to a decrease in the opportunity for selection. Under dense vegetation significantly more males built nests, which has also been observed in previous field studies. In a separate experiment we addressed if such changes in the proportion of nesters and non-nesters, without changes in visibility, affected the incidence of sneak fertilisation. My results show this was not the case, likely because sneaking is an opportunistic tactic shown by both nesters and non-nesters. Non-nesters did sneak proportionately more when there were many of them, which could be due to changes in the cost-benefit ratio of sneaking. As nesters can only attack one intruder at a time, the costs and risks per sneaker will decrease as the number of sneakers increases. The defensive behaviours shown by the nesters before spawning shifted to a more aggressive form of nest defence. This could be because less aggressive behaviours lose their effectiveness when the number of intruders increases. It could also indicate that the risks associated with aggressive behaviours decrease when there are fewer fellow nesters, as other studies indicate nesters are competitive and aggressive individuals. Under turbid conditions I did not detect changes in the opportunity for selection, based on fertilisation success, nor was male size under significant selection under clear or turbid conditions. More thorough analyses under densely vegetated conditions across the nesting, courtship and fertilisation stages revealed a decrease in the opportunity for selection across all stages. A reduction in sneaking by nesters contributed to this. During the nesting stage, but not during later stages, body size was under significant directional selection under sparse, but not dense vegetation. This illustrates the importance of considering all selection stages to get a complete picture of how environmental changes affect sexual selection. Leaving out certain stages or subgroups can result in incomplete or misleading results.
  • Meller, Kalle (Helsingin yliopisto, 2016)
    As the climate of our planet is warming, there is an urgent need to understand how temperature changes affect nature and how the species are able to cope with the changing environment. In my thesis I used Finnish long-term monitoring data to examine the effects of fluctuations in temperature and other environmental variables on the migration behavior and breeding performance of birds. I found that during warm springs birds started to breed earlier, which increased the length of the time period spent in the breeding area because the timing of autumn migration remained mostly constant (only the young from the latest broods migrated later). After warm springs productivity (the number of offspring per adult) was moderately but uniformly higher than after cold springs in the study community passerine birds. The annual productivities and population sizes varied synchronously among the species. Despite I found connections between the annual temperature, productivity and population size, the long-term population trends were not connected to changes in productivity. This implies that changes in survival during the non-breeding period would be driving the trends. Mild winter temperatures caused higher proportion of partially migratory waterbirds to overwinter in Finland than in cold winters. Climate warming related lack of severe ice winters arguably was behind the steep increase in the proportion of resident in waterbirds, while there were no trends in terrestrial species during the study period. The annual wintering area choice of terrestrial species was little affected by temperature, but in several species the seed crop of trees had a strong impact. Modelling the distribution of migration phenology is often essential for studying whether the temperature related adjustments in phenology are sufficient to cope with the effects of climate change. My comparison of methods showed that usually relative simple distributions describe the migration phenology well. I also provided a simple novel method to account for the day-to-day variation in migration data. My findings indicate that the life-history traits of the northern bird species are responsive to the variation in temperatures, but there are differences between taxa and functional groups in the responses, which underlines the importance of studying numerous taxa in order to draw general conclusions and predict the effects of continuing climate change.
  • Hafrén, Anders (Helsingin yliopisto, 2010)
    Plus-stranded (plus) RNA viruses multiply within a cellular environment as tightly integrated units and rely on the genetic information carried within their genomes for multiplication and, hence, persistence. The minimal genomes of plus RNA viruses are unable to encode the molecular machineries that are required for virus multiplication. This sets requisites for the virus, which must form compatible interactions with host components during multiplication to successfully utilize primary metabolites as building blocks or metabolic energy, and to divert the protein synthesis machinery for production of viral proteins. In fact, the emerging picture of a virus-infected cell displays tight integration with the virus, from simple host and virus protein interactions through to major changes in the physiological state of the host cell. This study set out to develop a method for the identification of host components, mainly host proteins, that interact with proteins of Potato virus A (PVA; Potyvirus) during infection. This goal was approached by developing affinity-tag based methods for the purification of viral proteins complexed with associated host proteins from infected plants. Using this method, host membrane-associated viral ribonucleoprotein (RNP) complexes were obtained, and several host and viral proteins could be identified as components of these complexes. One of the host proteins identified using this strategy was a member of the heat shock protein 70 (HSP70) family, and this protein was chosen for further analysis. To enable the analysis of viral gene expression, a second method was developed based on Agrobacterium-mediated virus genome delivery into plant cells, and detection of virally expressed Renilla luciferase (RLUC) as a quantitative measure of viral gene expression. Using this method, it was observed that down-regulation of HSP70 caused a PVA coat protein (CP)-mediated defect associated with replication. Further experimentation suggested that CP can inhibit viral gene expression and that a distinct translational activity coupled to replication, referred to as replication-associated translation (RAT), exists. Unlike translation of replication-deficient viral RNA, RAT was dependent on HSP70 and its co-chaperone CPIP. HSP70 and CPIP together regulated CP turnover by promoting its modification by ubiquitin. Based on these results, an HSP70 and CPIP-driven mechanism that functions to regulate CP during viral RNA replication and/or translation is proposed, possibly to prevent premature particle assembly caused by CP association with viral RNA.
  • Liimatainen, Kare (Helsingin yliopisto, 2013)
    Towards a better understanding of the systematics and diversity of Cortinarius, with an emphasis on species growing in boreal and temperate zones of Europe and North America Cortinarius is the largest genus of Agaricales with a global distribution and thousands of species. Cortinarius species are important ectomycorrhizal fungi associated with different trees. At the moment, any estimation of the true diversity of Cortinarius is impossible to determine. Species level taxonomy is the foundation of biological studies, without knowing the species and their boundaries it is very difficult to do ecological, applied or other research. Our aims as taxonomists are to discover and describe all species, define relationships, and provide tools for unambiguous identification. It is clear that with morphology we are not able to achieve that goal. The development and use of molecular methods in taxonomic studies of fungi has revolutionized our field of science. Molecular data is more objective and has a better repeatability than morphological data. This thesis project has been the biggest effort to stabilize the nomenclature of Cortinarius so far and also is an example of using only reliable names in taxonomic studies by excluding names without sequences from type material. Also, our view on the amount of diversity has changed dramatically, e.g. estimation of diversity of Cortinarius in Finland is now about same than it was previously estimated to be in Europe. Our studies have revealed much needed information about species composition and have allowed for comparisons between North-America and Europe. New information about potential cryptic species in Cortinarius and limitations of ITS for species level taxonomy has been gained. The sequences of type specimens published create thus far the largest, reliable ITS identification database for Cortinarius containing over 200 species. Our results also confirm the finding of earlier molecular studies that the traditional infra-generic groupings are at least partly artificial and should be reevaluated.
  • Van Teeffelen, Astrid (Helsingin yliopisto, 2007)
    Ongoing habitat loss and fragmentation threaten much of the biodiversity that we know today. As such, conservation efforts are required if we want to protect biodiversity. Conservation budgets are typically tight, making the cost-effective selection of protected areas difficult. Therefore, reserve design methods have been developed to identify sets of sites, that together represent the species of conservation interest in a cost-effective manner. To be able to select reserve networks, data on species distributions is needed. Such data is often incomplete, but species habitat distribution models (SHDMs) can be used to link the occurrence of the species at the surveyed sites to the environmental conditions at these locations (e.g. climatic, vegetation and soil conditions). The probability of the species occurring at unvisited location is next predicted by the model, based on the environmental conditions of those sites. The spatial configuration of reserve networks is important, because habitat loss around reserves can influence the persistence of species inside the network. Since species differ in their requirements for network configuration, the spatial cohesion of networks needs to be species-specific. A way to account for species-specific requirements is to use spatial variables in SHDMs. Spatial SHDMs allow the evaluation of the effect of reserve network configuration on the probability of occurrence of the species inside the network. Even though reserves are important for conservation, they are not the only option available to conservation planners. To enhance or maintain habitat quality, restoration or maintenance measures are sometimes required. As a result, the number of conservation options per site increases. Currently available reserve selection tools do however not offer the ability to handle multiple, alternative options per site. This thesis extends the existing methodology for reserve design, by offering methods to identify cost-effective conservation planning solutions when multiple, alternative conservation options are available per site. Although restoration and maintenance measures are beneficial to certain species, they can be harmful to other species with different requirements. This introduces trade-offs between species when identifying which conservation action is best applied to which site. The thesis describes how the strength of such trade-offs can be identified, which is useful for assessing consequences of conservation decisions regarding species priorities and budget. Furthermore, the results of the thesis indicate that spatial SHDMs can be successfully used to account for species-specific requirements for spatial cohesion - in the reserve selection (single-option) context as well as in the multi-option context. Accounting for the spatial requirements of multiple species and allowing for several conservation options is however complicated, due to trade-offs in species requirements. It is also shown that spatial SHDMs can be successfully used for gaining information on factors that drive a species spatial distribution. Such information is valuable to conservation planning, as better knowledge on species requirements facilitates the design of networks for species persistence. This methods and results described in this thesis aim to improve species probabilities of persistence, by taking better account of species habitat and spatial requirements. Many real-world conservation planning problems are characterised by a variety of conservation options related to protection, restoration and maintenance of habitat. Planning tools therefore need to be able to incorporate multiple conservation options per site, in order to continue the search for cost-effective conservation planning solutions. Simultaneously, the spatial requirements of species need to be considered. The methods described in this thesis offer a starting point for combining these two relevant aspects of conservation planning.