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  • Laurinavicius, Simonas (Helsingin yliopisto, 2008)
    In this study we used electro-spray ionization mass-spectrometry to determine phospholipid class and molecular species compositions in bacteriophages PM2, PRD1, Bam35 and phi6 as well as their hosts. To obtain compositional data of the individual leaflets, phospholipid transbilayer distribution in the viral membranes was studied. We found that 1) the membranes of all studied bacteriophage are enriched in PG as compared to the host membranes, 2) molecular species compositions in the phage and host membranes are similar, and 3) phospholipids in the viral membranes are distributed asymmetrically with phosphatidylglycerol enriched in the outer leaflet and phosphatidylethanolamine in the inner one (except Bam35). Alternative models for selective incorporation of phospholipids to phages and for the origins of the asymmetric phospholipid transbilayer distribution are discussed. Notably, the present data are also useful when constructing high resolution structural models of bacteriophages, since diffraction methods cannot provide a detailed structure of the membrane due to high motility of the lipids and lack of symmetric organization of membrane proteins.
  • Peltovuori, Tommi (Helsingin yliopisto, 2006)
    An overwhelming majority of all the research on soil phosphorus (P) has been carried out with soil samples taken from the surface soils only, and our understanding of the forms and the reactions of P at a soil profile scale is based on few observations. In Finland, the interest in studying the P in complete soil profiles has been particularly small because of the lack of tradition in studying soil genesis, morphology, or classification. In this thesis, the P reserves and the retention of orthophosphate phosphorus (PO4-P) were examined in four cultivated mineral soil profiles in Finland (three Inceptisols and one Spodosol). The soils were classified according to the U.S. Soil Taxonomy and soil samples were taken from the genetic horizons in the profiles. The samples were analyzed for total P concentration, Chang and Jackson P fractions, P sorption properties, concentrations of water-extractable P, and for concentrations of oxalate-extractable Al and Fe. Theoretical P sorption capacities and degrees of P saturation were calculated with the data from the oxalate-extractions and the P fractionations. The studied profiles can be divided into sections with clearly differing P characteristics by their master horizons Ap, B and C. The C (or transitional BC) horizons below an approximate depth of 70 cm were dominated by, assumingly apatitic, H2SO4-soluble P. The concentration of total P in the C horizons ranged from 729 to 810 mg kg-1. In the B horizons between the depths of 30 and 70 cm, a significant part of the primary acid-soluble P has been weathered and transformed to secondary P forms. A mean weathering rate of the primary P in the soils was estimated to vary between 230 and 290 g ha-1 year-1. The degrees of P saturation in the B and C horizons were smaller than 7%, and the solubility of PO4-P was negligible. The P conditions in the Ap horizons differed drastically from those in the subsurface horizons. The high concentrations of total P (689-1870 mg kg-1) in the Ap horizons are most likely attributable to long-term cultivation with positive P balances. A significant proportion of the P in the Ap horizons occurred in the NH4F- and NaOH-extractable forms and as organic P. These three P pools, together with the concentrations of oxalate-extractable Al and Fe, seem to control the dynamics of PO4-P in the soils. The degrees of P saturation in the Ap horizons were greater (8-36%) than in the subsurface horizons. This was also reflected in the sorption experiments: Only the Ap horizons were able to maintain elevated PO4-P concentrations in the solution phase − all the subsoil horizons acted as sinks for PO4-P. Most of the available sorption capacity in the soils is located in the B horizons. The results suggest that this capacity could be utilized in reducing the losses of soluble P from excessively fertilized soils by mixing highly sorptive material from the B horizons with the P-enriched surface soil. The drastic differences in the P characteristics observed between adjoining horizons have to be taken into consideration when conducting soil sampling. Sampling of subsoils has to be made according to the genetic horizons or at small depth increments. Otherwise, contrasting materials are likely to be mixed in the same sample; and the results of such samples are not representative of any material present in the studied profile. Air-drying of soil samples was found to alter the results of the sorption experiments and the water extractions. This indicates that the studies on the most labile P forms in soil should be carried out with moist samples.
  • Väänänen, Riitta (2008)
    Phosphorus (P) retention properties of soils typical for boreal forest, i.e. podzolic soil and peat soils, vary significantly, but the range of this variation has not been sufficiently documented. To assess the usefulness of buffer zones used in forestry in removing P from the discharge by chemical sorption in soil, and to estimate the risk of P leaching after forestry operations, more data is needed on soil P retention properties. P retention properties of soils were studied at clear-cut areas, unharvested buffer zones adjoining the clear-cut and at peatland buffer zone areas. Desorption-sorption isotherms were determined for the humus layer, the mineral soil horizons E, B and C of the Podzol profile and for the surface layer peat (0-15 cm) and the subsurface layer peat (15-30 cm). The efficiency of buffer zones in retaining P was studied at six peatland buffer zone areas by adding P-containing solute in the inflow. A tracer study was conducted at one of the buffer zone areas to determine the allocation of the added P in soil and vegetation. Measured sorption or desorption rather than parameter values of fitted sorption equations described P desorption and sorption behaviour in soil. The highest P retention efficiency was in the B horizon and consequently, if contact occurred or was established between the soluble P in the water and the soil B horizon, the risk of P leaching was low. Humus layer was completely incapable of retaining P after clear-cutting. In the buffer zones, the decrease in P retention properties in the humus layer and the low amount of P sorbed by it indicated that the importance of the layer in the functioning of buffer zones is low. The peatland buffer zone areas were efficient in retaining soluble P from inflow. P sorption properties of the peat soil at the buffer zone areas varied largely but the contribution of P sorption in the peat was particularly important during high flow in spring, when the vegetation was not fully developed. Factors contributing to efficient P retention were large buffer size and low hydrological load whereas high hydrological load combined with the formation of preferential flow paths, especially during early spring or late autumn was disadvantageous. However, small buffer zone areas, too, may be efficient in reducing P load.
  • Lignell, Hanna (Helsingin yliopisto, 2014)
    In this thesis, fundamentally and atmospherically relevant species, their heterogeneous chemistry, and photolytic processing in multiple phases are explored both experimentally and computationally, providing important new insights and mechanistic understanding of these complicated systems. HArF is a covalently bonded neutral ground-state molecule of argon that is found to form at very low temperatures. This thesis explores the HArF low temperature formation mechanism and kinetics, and discusses the effect of the environment to the formation. In the next part, a computational study of an atmospherically relevant molecule N2O4 and its isomerization and ionization on model ice and silica surfaces is presented. N2O4 is known to produce HONO, which is a major source of atmospheric OH, an important atmospheric oxidant. The isomerization mechanism is found to be connected to the dangling surface hydrogen atoms at both surfaces, and we suggest that this mechanism could be expanded to other atmospherically relevant surfaces as well. Atmospheric aerosols play a critical role in controlling climate, driving chemical reactions in the atmosphere, acting as surfaces catalyzing heterogeneous reactions, and contributing to air pollution problems and indoor air quality issues. Low-volatility organic compounds that are produced in the oxidation of biogenic and anthropogenic Volatile Organic Compounds (VOC s) are known collectively as Secondary Organic Aerosol (SOA). In this thesis, a comprehensive investigation of aqueous photochemistry of cis-pinonic acid, a common product of ozonolysis of α-pinene (an SOA precursor) is presented. Various experimental techniques are used to study the kinetics, photolysis rates, quantum yields, and photolysis products, and computational methods are used to explore the photolysis mechanisms. Atmospheric implications and importance of aqueous photolysis vs. OH-mediated aging is discussed. The viscosity effects on SOA chemistry are then explored by a novel approach where an environmentally relevant probe molecule 2,4-dinitrophenol is embedded directly inside the SOA matrix, and its photochemistry is studied at different temperatures and compared to reaction efficiency in other reaction media (octanol and water). It is observed that decreasing temperature significantly slows down the photochemical process in the SOA matrix, and this behavior is ascribed to increasing viscosity of the SOA material.
  • Isoniemi, Esa (Helsingin yliopisto, 2003)
  • Kulmala, Liisa (Helsingin yliopisto, 2011)
    Research on carbon uptake in boreal forests has mainly focused on mature trees, even though ground vegetation species are effective assimilators and can substantially contribute to the CO2 uptake of forests. Here, I examine the photosynthesis of the most common species of ground vegetation in a series of differently aged Scots pine stands, and at two clear-cut sites with substantial differences in fertility. In general, the biomass of evergreen species was highest at poor sites and below canopies, whereas grasses and herbs predominated at fertile sites and open areas. Unlike mosses, the measured vascular species showed clear annual cycles in their photosynthetic activity, which increased earlier and decreased later in evergreen vascular species than in deciduous species. However, intraspecific variation and self-shading create differences in the overall level of photosynthesis. Light, temperature history, soil moisture and recent possible frosts could explain the changes in photosynthesis of low shrubs and partially also some changes in deciduous species. Light and the occurrence of rain events explained most of the variation in the photosynthesis of mosses. The photosynthetic production of ground vegetation was first upscaled, using species-specific and mass-based photosynthetic activities and average biomass of the site, and then integrated over the growing season, using changes in environmental factors. Leaf mass-based photosynthesis was highest in deciduous species, resulting in notably higher photosynthetic production at fertile sites than at poor clear-cut sites. The photosynthetic production decreased with stand age, because flora changed towards evergreen species, and light levels diminished below the canopy. In addition, the leaf mass-based photosynthetic activity of some low shrubs declined with the age of the surrounding trees. Different measuring methods led to different momentary rate of photosynthesis. Therefore, the choice of measuring method needs special attention.
  • Jansen, Gunther (Helsingin yliopisto, 2009)
    Understanding the overwhelming diversity of life calls for complex organisational schemes. The field of systematics may thus be seen as the cornerstone of evolutionary biology. In the last few decades, systematics has been rejuvenated through the introduction of molecular methods such as DNA barcoding and multi-gene phylogenetic approaches. These methods may shed new light on established taxonomic ideas and problems. For example, the classification of ants has aroused much debate due to reinterpretation of morphological characters or contradictions between molecular data and morphology. Only in the last few years a consensus was reached regarding the phylogeny of ant subfamilies. However, the situation remains deplorable for lower taxonomic ranks such as subfamilies, tribes and genera. This thesis describes the systematics and evolution of the Holarctic ant genus Myrmica and the tribe to which it belongs, Myrmicini. Using barcoding, molecular-phylogenetic data and divergence time estimations, it addresses questions regarding the taxonomy, morphology and biogeography of this group. Furthermore, the interrelationships between socially parasitic Myrmica species and their hosts (other species in the genus) were inferred. The phylogeny suggests that social parasitism evolved several times in Myrmica. Finally, this thesis investigated whether coevolution shaped the phylogeny of socially parasitic Maculinea butterflies that live inside Myrmica colonies. No evidence was found for coevolution.
  • Vahtera, Varpu (Helsingin yliopisto, 2008)
    Throughout the history of Linnean taxonomy, species have been described with varying degrees of justification. Many descriptions have been based on only a few ambiguous morphological characters. Moreover, species have been considered natural, well-defined units whereas higher taxa have been treated as disparate, non-existent creations. In the present thesis a few such cases were studied in detail. Often the species-level descriptions were based on only a few specimens and the variation previously thought to be interspecific was found to be intraspecific. In some cases morphological characters were sufficient to resolve the evolutionary relationships between the taxa, but generally more resolution was gained by the addition of molecular evidence. However, both morphological and molecular data were found to be deceptive in some cases. The DNA sequences of morphologically similar specimens were found to differ distinctly in some cases, whereas in other closely related species the morphology of specimens with identical DNA sequences differed substantially. This study counsels caution when evolutionary relationships are being studied utilizing only one source of evidence or a very limited number of characters (e.g. barcoding). Moreover, it emphasizes the importance of high quality data as well as the utilization of proper methods when making scientific inferences. Properly conducted analyses produce robust results that can be utilized in numerous interesting ways. The present thesis considered two such extensions of systematics. A novel hypothesis on the origin of bioluminescence in Elateriformia beetles is presented, tying it to the development of the clicking mechanism in the ancestors of these animals. An entirely different type of extension of systematics is the proposed high value of the white sand forests in maintaining the diversity of beetles in the Peruvian Amazon. White sand forests are under growing pressure from human activities that lead to deforestation. They were found to harbor an extremely diverse beetle fauna and many taxa were specialists living only in this unique habitat. In comparison to the predominant clay soil forests, considerably more elateroid beetles belonging to all studied taxonomic levels (species, genus, tribus, and subfamily) were collected in white sand forests. This evolutionary diversity is hypothesized to be due to a combination of factors: (1) the forest structure, which favors the fungus-plant interactions important for the elateroid beetles, (2) the old age of the forest type favoring survival of many evolutionary lineages and (3) the widespread distribution and fragmentation of the forests in the Miocene, favoring speciation.
  • 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.
  • Laurenne, Nina (Helsingin yliopisto, 2008)
    The parasitic wasps are one of the largest insect groups and their life histories are remarkably variable. Common to all parasitic wasps is that they kill their hosts, which are usually beetles, butterflies and sometimes spiders. Hosts are often at a larval or pupal stage and live in concealed conditions, such as in plant tissue. Parasitic wasps have two main ways of finding their host. 1) They can detect chemical compounds emitted by damaged plant material or released by larvae living in plant tissue, and 2) detect the larvae by sound vibrations. Even though pupae are immobile and silent, and therefore do not cause vibration, parasitoids have, however, adapted to find passive developmental stages by producing vibration themselves by knocking the substrate with their antennae, and then detecting the echoes with their legs. This echolocation allows a parasitoid to locate its potential hosts that are deeply buried in wood. This study focuses on the relationships of the subfamily Cryptinae (Hymenoptera: Ichneumonidae) and related taxa, and the evolution of host location mechanism. There are no earlier studies of the phylogeny of the Cryptinae, and the position of related taxa are unclear. According to the earlier classification, which is entirely intuitional, the Cryptinae is divided into three tribes: Cryptini, Hemigasterini and Phygadeuontini. Further, these tribes are subdiveded into numerous subtribes. This work, based on molecular characters, shows that the cryptine tribes Cryptini, Phygadeuon¬tini and Hemigasterini come out largely as monophyletic groups, thus agreeing with the earlier classification. The earlier subtribal classification had no support. In addition, it is shown that modified antennal structures are associated with host usage of wood-boring coleopteran hosts. The cryptines have a clear modification series on their antennal tips from a simply tip to a hammer-like structure. The species with strongly modified antennae belong mostly to the tribe Cryptini and they utilise wood-boring beetles as hosts. Also, field observations on insect behaviour support this result.
  • 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.
  • Mäkinen, Hannu (Helsingin yliopisto, 2007)
    Genetic studies on phylogeography and adaptive divergence in Northern Hemisphere fish species such as three-spined stickleback (Gasterosteus aculeatus) provide an excellent opportunity to investigate genetic mechanisms underlying population differentiation. According to the theory, the process of population differentiation results from a complex interplay between random and deterministic processes as well historical factors. The main scope in this thesis was to study how historical factors like the Pleistocene ice ages have shaped the patterns molecular diversity in three-spined stickleback populations in Europe and how this information could be utilized in the conservation genetic context. Furthermore, identifying footprints of natural selection at the DNA level might be used in identifying genes involved in evolutionary change. Overall, the results from phylogeographic studies indicate that the three-spined stickleback has colonized the Atlantic basin relatively recently but constitutes three major evolutionary lineages in Europe. In addition, the colonization of freshwater appears to result from multiple and independent invasions by the marine conspecifics. Molecular data together with morphology suggest that the most divergent freshwater populations are located in the Balkan Peninsula and these populations deserve a special conservation genetic status without warranting further taxonomical classification. In order to investigate the adaptive divergence in Fennoscandian three-spined stickleback populations several approaches were used. First, sequence variability in the Eda-gene, coding for the number of lateral plates, was concordant with the previously observed global pattern. Full plated allele is in high frequencies among marine populations whereas low plated allele dominates in the freshwater populations. Second, a microsatellite based genome scan identified both indications of balancing and directional selection in the three-spined stickleback genome, i.e. loci with unusually similar or unusually different allele frequencies over populations. The directionally selected loci were mainly associated with the adaptation to freshwater. A follow up study conducting a more detailed analysis in a chromosome region containing a putatively selected gene locus identified a fairly large genomic region affected by natural selection. However, this region contained several gene predictions, all of which might be the actual target of natural selection. All in all, the phylogeographic and adaptive divergence studies indicate that most of the genetic divergence has occurred in the freshwater populations whereas the marine populations have remained relatively uniform.
  • Kontula, Tytti (Helsingin yliopisto, 2003)
  • Nikula, Raisa (Helsingin yliopisto, 2008)
    This study addressed the large-scale molecular zoogeography in two brackish water bivalve molluscs, Macoma balthica and Cerastoderma glaucum, and genetic signatures of the postglacial colonization of Northern Europe by them. The traditional view poses that M. balthica in the Baltic, White and Barents seas (i.e. marginal seas) represent direct postglacial descendants of the adjacent Northeast Atlantic populations, but this has recently been challenged by observations of close genetic affinities between these marginal populations and those of the Northeast Pacific. The primary aim of the thesis was to verify, quantify and characterize the Pacific genetic contribution across North European populations of M. balthica and to resolve the phylogeographic histories of the two bivalve taxa in range-wide studies using information from mitochondrial DNA (mtDNA) and nuclear allozyme polymorphisms. The presence of recent Pacific genetic influence in M. balthica of the Baltic, White and Barents seas, along with an Atlantic element, was confirmed by mtDNA sequence data. On a broader temporal and geographical scale, altogether four independent trans-Arctic invasions of Macoma from the Pacific since the Miocene seem to have been involved in generating the current North Atlantic lineage diversity. The latest trans-Arctic invasion that affected the current Baltic, White and Barents Sea populations probably took place in the early post-glacial. The nuclear genetic compositions of these marginal sea populations are intermediate between those of pure Pacific and Atlantic subspecies. In the marginal sea populations of mixed ancestry (Barents, White and Northern Baltic seas), the Pacific and Atlantic components are now randomly associated in the genomes of individual clams, which indicates both pervasive historical interbreeding between the previously long-isolated lineages (subspecies), and current isolation of these populations from the adjacent pure Atlantic populations. These mixed populations can be characterized as self-supporting hybrid swarms, and they arguably represent the most extensive marine animal hybrid swarms so far documented. Each of the three swarms still has a distinct genetic composition, and the relative Pacific contributions vary from 30 to 90 % in local populations. This diversity highlights the potential of introgressive hybridization to rapidly give rise to new evolutionarily and ecologically significant units in the marine realm. In the south of the Danish straits and in the Southern Baltic Sea, a broad genetic transition zone links the pure North Sea subspecies M. balthica rubra to the inner Baltic hybrid swarm, which has about 60 % of Pacific contribution in its genome. This transition zone has no regular smooth clinal structure, but its populations show strong genotypic disequilibria typical of a hybrid zone maintained by the interplay of selection and gene flow by dispersing pelagic larvae. The structure of the genetic transition is partly in line with features of Baltic water circulation and salinity stratification, with greater penetration of Atlantic genes on the Baltic south coast and in deeper water populations. In all, the scenarios of historical isolation and secondary contact that arise from the phylogeographic studies of both Macoma and Cerastoderma shed light to the more general but enigmatic patterns seen in marine phylogeography, where deep genetic breaks are often seen in species with high dispersal potential.
  • Leppänen, Jenni (Helsingin yliopisto, 2012)
    One of the main questions in evolutionary biology is what causes genetic differentiation among populations and the origin of new species. In this thesis I studied genetic differentiation of populations by testing how changes in the environment and behaviour have affected populations of Myrmica ants (Formicidae, Hymenoptera). First, I used a phylogeographic approach to find out how climatic changes during and after the last glaciation have affected populations of two Palearctic ant species Myrmica rubra and M. ruginodis. The aim was to locate their glacial refugia and postglacial recolonization routes, and to test whether differences in their cold tolerance and life-history traits have affected their phylogeographic structures and locations of their glacial refugia. Second, I studied the effect of behavioural differences on populations of M. rubra. I examined genetic differentiation and reproductive isolation of an intraspecific microgynous social parasite and its macrogynous host using both genetic and behavioural approaches. The aim was to clarify whether social parasitism as an alternative reproductive tactic may lead to speciation in sympatry. The results of this thesis show that differences in life-history traits have had no effect on the phylogeographic structures of M. rubra and M. ruginodis. Both species have survived the last glaciation in several refugia in Southern Europe but probably also in regions further east and north. Circumstantial evidence suggests that the more cold-tolerant M. ruginodis has survived in refugia more north than M. rubra. Both species have recolonized the northern areas from the south-west and south-east, and probably also from the east. Both genetic and behavioural evidence suggested that in M. rubra the parasite and host are reproductively isolated. They differed substantially in their nuclear DNA, indicating that the parasite is in the process of speciation. However, the mitochondrial lineages of the host and the parasite have not yet diverged. This thesis brings new information on the history of Palearctic insects and the effects of the past environmental changes on their populations. This thesis also clarifies the evolution of social parasitism and provides new evidence for a probable example of sympatric speciation through an alternative reproductive tactic, social parasitism.
  • Knopp, Theresa (Helsingin yliopisto, 2008)
    The ongoing climate change along with increasing levels of pollutants, diseases, habitat loss and fragmentation constitute global threats to the persistence of many populations, species and ecosystems. However, for the long-term persistence of local populations, one of the biggest threats is the intrinsic loss of genetic variation. In order to adapt to changes in the environment, organisms must have a sufficient supply of heritable variation in traits important for their fitness. With a loss of genetic variation, the risk of extinction will increase. For conservational practices, one should therefore understand the processes that shape the genetic population structure and also the broader (historical) phylogenetic patterning of the species in focus. In this thesis, microsatellite markers were applied to study genetic diversity and population differentiation of the protected moor frog (Rana arvalis) in Fennoscandia from both historical (evolutionary) and applied (conservation) perspectives. The results demonstrate that R. arvalis populations are highly structured over rather short geographic distances. Moreover, the results suggest that R. arvalis recolonized Fennoscandia from two directions after the last ice age. This has had implications for the genetic structuring and population differentiation, especially in the northernmost parts where the two lineages have met. Compared to more southern populations, the genetic variation decreases and the interpopulation differentiation increases dramatically towards north. This could be an outcome of serial population bottlenecking along the recolonization route. Also, current isolation and small population sizes increase the effect of drift, thus reinforcing the observed pattern. The same pattern can also be seen in island populations. However, though R. arvalis on the island of Gotland has lost most of its neutral genetic variability, our results indicate that the levels of additive genetic variation have remained high. This conforms to the conjecture that though neutral markers are widely used in conservation purposes, they may be quite uninformative about the levels of genetic variation in ecologically important traits. Finally, the evolutionary impact of the typical amphibian mating behaviour on genetic diversity was investigated. Given the short time available for larval development, it is important that mating takes place as early as possible. The genetic data and earlier capture-recapture data suggest that R. arvalis gather at mating grounds they are familiar with. However, by forming leks in random to relatedness, and having multiple paternities in single clutches, the risk of inbreeding may be minimized in this otherwise highly philopatric species.
  • Laakkonen, Hanna (Helsingin yliopisto, 2015)
    The Northern Pacific and Atlantic Oceans share a faunal element consisting of pairs of closely related vicariant taxa or populations and known as the amphi-boreal fauna. The inter-oceanic systematic affinities reflect a history of shared ancestry since past dispersal through the Bering Strait and across the Arctic basin, starting from the initial opening of the Bering Strait at the end of the Miocene. This thesis examines the biogeographical history of the amphi-boreal faunal element using information from molecular marker characters. The aim is to document the dynamics and consequences of the faunal interchange between the two oceans, spanning from the end of Miocene to the present. This is done by comparing differences in the mitochondrial gene sequence variation in different taxonomic groups and across the circum-boreal geographical scale, encompassing 70 taxa. The consequences of dispersal to genetic diversity was examined more closely and with additional markers in two exemplary genera, herrings and bivalve molluscs of the genus Hiatella. The phylogeographical histories of the vicariant Pacific-Atlantic populations and taxa are found remarkably variable. A simple vicariant history, with a single early invasion in the Pliocene or Early Pleistocene, was inferred only in about 50% of the examined taxa and in 30% signatures of more than one trans-Arctic invasion were found in the molecular data. Overall the estimates of inter-oceanic divergence within each of the broader taxonomic groups studied (fishes, molluscs, crustaceans, echinoderms, polychaetes) varied greatly, up to 10 20 fold, and suggest that trans-Arctic faunal dispersal has been a dynamic and repeated process through the entire time frame considered. Nevertheless, from the molecular divergence, several instances of putative cryptic vicariant species were revealed in invertebrates. In the nearly cosmopolitan bivalve mollusc Hiatella, altogether 11 cryptic taxa were discovered in the Northern Hemisphere and a hypothesis of their repeated inter-oceanic movements was presented. In some 40% of the amphi-boreal genera a close inter-oceanic relationship was found, often seen as incomplete mtDNA lineage sorting and implying recent trans-Arctic dispersal or ongoing migration. The consequences of secondary dispersal from the Pacific to Atlantic were examined more closely in the model cases of the genera Clupea and Hiatella. The Pacific herring C. pallasii, of East Asian origin, invaded the Northeast European seas after the last glacial period and then differentiated into separate regional populations. In Europe, the species has hybridized with the native sister species C. harengus, the Atlantic herring. The amount of introgression from the Atlantic to the Pacific herring has varied between the various contact regions of the two taxa. Particularly the Norwegian local Balsfjord herring stock seems to represent a heavily introgressed hybrid swarm. Secondary contacts of differentiated lineages were found to be a common phenomenon in all of the broader taxonomic groups studied. The introgression between old lineages, but also the effects of shorter isolation-dispersal cycles, may be important but so far overlooked phenomena in shaping the genomic composition and adaptive properties of taxa that inhabit the post-glacially colonized marginal habitats of the northern seas. Due to the current global warming and changing navigation practices in the Arctic, trans-Arctic inter-oceanic faunal exchange is expected to increase. The topic requires closer studies in the near future, in order to understand what kind of ecological and genetic consequences the exchange will have on the present day faunal communities.