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1.
  • Caputo, Andrea, 1988- (författare)
  • Genomic and morphological diversity of marine planktonic diatom-diazotroph associations : a continuum of integration and diversification through geological time
  • 2019
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Symbioses between eukaryotes and nitrogen (N2)-fixing cyanobacteria (or diazotrophs) are quite common in the plankton community. A few genera of diatoms (Bacillariophyceae) such as Rhizosolenia, Hemiaulus and Chaetoceros are well known to form symbioses with the heterocystous diazotrophic cyanobacteria Richelia intracellularis and Calothrix rhizosoleniae. The latter are also called diatom-diazotroph associations, or DDAs. Up to now, the prokaryotic partners have been morphologically and genetically characterized, and the phylogenetic reconstruction of the well conserved nifH gene (encodes for the nitrogenase enzyme) placed the symbionts in 3 clusters based on their host-specificity, i.e. het-1 (Rhizosolenia-R. intracellularis), het-2 (Hemiaulus-R. intracellularis), and het-3 (Chaetoceros-C- rhizosoleniae). Conversely, the diatom-hosts, major representative of the phytoplankton community and crucial contributors to the carbon (C) biogeochemical cycle, have been understudied.The first aim of this thesis was to genetically and morphologically characterize the diatom-hosts, and to reconstruct the evolutionary background of the partnerships and the symbiont integration in the host. The molecular-clock analysis reconstruction showed the ancient appearance of the DDAs, and the traits characterizing the ancestors. In addition, diatom-hosts bearing internal symbionts (with more eroded draft genomes) appeared earlier than diatom-hosts with external symbionts. Finally a blast survey highlighted a broader distribution of the DDAs than expected.The second aim of this thesis was to compare genetic and physiological characteristics of the DDAs symbionts with the other eukaryote-diazotroph symbiosis, i.e. prymnesiophyte-UCYN-A (or Candidatus Atelocyanobacterium thalassa). The genome comparison highlighted more genes for transporters in het-3 (external symbiont) and in the UCYN-A based symbiosis, suggesting that symbiont location might be relevant also for metabolic exchanges and interactions with the host and/or environment. Moreover, a summary of methodological biases that brought to an underestimation of the DDAs is reported.The third aim of this thesis was to determine the distribution of the DDAs in the South Pacific Ocean using a quantitative polymerase chain reaction (qPCR) approach and to outline the environmental drivers of such distribution. Among the het-groups, het-1 was the most abundant/detected and co-occurred with the other 2 symbiotic strains, all responding similarly to the influence of abiotic factors, such as temperature and salinity (positive and negative correlation, respectively). Globally, Trichodesmium dominated the qPCR detections, followed by UCYN-B. UCYN-A phylotypes (A-1, A-2) were detected without their proposed hosts, for which new oligonucleotides were designed. The latter suggested a facultative symbiosis. Finally, microscopy observations of the het-groups highlighted a discrepancy with the qPCR counts (i.e. the former were several order of magnitudes lower), leading to the idea of developing a new approach to quantify the DDAs.  The fourth aim of this thesis was to develop highly specific in situ hybridization assays (CARD-FISH) to determine the presence of alternative life-stages and/or free-living partners. The new assays were applied to samples collected in the South China Sea and compared with abundance estimates from qPCR assays for the 3 symbiotic strains. Free-living cells were indeed detected along the transect, mainly at deeper depths. Free-living symbionts had two morphotypes: trichomes and single-cells. The latter were interpreted as temporary life-stages. Consistent co-occurrence of the 3 het-groups was also found in the SCS and application of a SEM model predicted positive interactions between the het groups. We interpreted the positive interaction as absence of intra-specific competition, and consistent with the previous study, temperature and salinity were predicted as major drivers of the DDAs distribution.
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2.
  • Pettersson, Ulf (författare)
  • Människoraser, finns dom?
  • 2009
  • Ingår i: Rasen och vetenskapen. - Uppsala : Centrum för multietnisk forskning / Programmet för studier kring Förintelsen och folkmord. - 9789197743426 ; , s. 13-22
  • Bokkapitel (övrigt vetenskapligt)abstract
    • Föredrag från föreläsningsserien Rasen och vetenskapen vid Uppsala universitet våren 2008. Artikeln av professorn i medicinsk genetik Ulf Pettersson (Uppsala) behandlar rasbegreppets ställning i människans utvecklingshistoria inom genetiken.
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3.
  • den Tex, Robert-Jan, 1969- (författare)
  • Patterns and Processes of Evolution in Sundaland
  • 2011
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Biodiversity in the tropics is disproportionately high compared to other habitats, and also under disproportionate threat from human impact. It is necessary to understand how this diversity evolved and how it is partitioned across space in order to preserve it. In this thesis I construct phylogenies of tropical forest dependent vertebrates from Southeast Asia and the islands of the Sunda shelf, a region referred to as Sundaland. I focus on the tree squirrels (genus Sundasciurus) and Asian barbets (Aves: Family Megalaimidae), two taxa with similar ecological characteristics. I use these phylogenies to test hypotheses that have been put forward to explain high levels of tropical diversity including the Pleistocene pump and museum hypotheses. I also use phylogenies to elucidate phylogeographic patterns within the region. I find no evidence for an increase in speciation in the Pleistocene, but I do find within species structure that dates to this period. Common phylogeographic patterns were identified between many forest dependent vertebrates that suggest that populations on the island of Sumatra are generally more closely related to Malay Peninsula populations than to populations on Borneo. From a methodological viewpoint we propose careful usage of universal primers in ancient DNA studies because of our finding of increased risk of amplifying pseudogenes of the mtDNA.
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4.
  • Klevebring, Daniel, 1981- (författare)
  • On Transcriptome Sequencing
  • 2009
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This thesis is about the use of massive DNA sequencing to investigate the transcriptome. During recent decades, several studies have made it clear that the transcriptome comprises a more complex set of biochemical machinery than was previously believed. The majority of the genome can be expressed as transcripts; and overlapping and antisense transcription is widespread. New technologies for the interroga- tion of nucleic acids have made it possible to investigate such cellular phenomena in much greater detail than ever before. For each application, special requirements need to be met. The work presented in this thesis focuses on the transcrip- tome and the development of technology for its analysis. In paper I, we report our development of an automated approach for sample preparation. The procedure was benchmarked against a publicly available reference data set, and we note that our approach outperformed similar manual procedures in terms of reproducibility. In the work reported in papers II-IV, we used different massive sequencing technologies to investigate the transcriptome. In paper II we describe a concatemerization approach that increased throughput by 65% using 454 sequencing,and we identify classes of transcripts not previously described in Populus. Papers III and IV both report studies based on SOLiD sequencing. In the former, we investigated transcripts and proteins for 13% of the human gene and detected a massive overlap for the upper 50% transcriptional levels. In the work described in paper IV, we investigated transcription in non-genic regions of the genome and detected expression from a high number of previ- ously unknown loci.
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5.
  • Larsson, Kjell, 1958-, et al. (författare)
  • Population differentiation in the redshank (Tringa totanus) as revealed by mitochondrial DNA and amplified fragment length polymorphism markers
  • 2005
  • Ingår i: Conservation Genetics. - : Springer. - 1566-0621 .- 1572-9737. ; 6, s. 321-331
  • Tidskriftsartikel (refereegranskat)abstract
    • The redshank (Tringa totanus) is declining throughout Europe and to implement efficient conservation measures, it is important to obtain information about the population genetic structure. The aim of the present study was two-fold. First, we analysed the genetic variation within and between populations in the Baltic region in southern Scandinavia. Evidence of genetic structure would suggest that different populations might require separate management strategies. Second, in an attempt to study large-scale genetic structure we compared the Baltic populations with redshanks from northern Scandinavia and Iceland. This analysis could reveal insights into phylogeography and long-term population history. DNA samples were collected from six breeding sites in Scandinavia presumed to include two subspecies (totanus and britannica) and a further sample from Iceland (subspecies robusta). Two methods were used to study the population genetic structure. Domain II and III of the mitochondrial control region was analysed by DNA sequencing and nuclear DNA was analysed by screening amplified fragment length polymorphism (AFLP) markers. Mitochondrial DNA showed no variation between individuals in domain II. When analysing an 481 bp fragment of domain III seven haplotypes were found among birds. On the basis of mtDNA sequences, redshanks showed some evidence of a recent expansion from a bottlenecked refugial population. Bayesian analyses of AFLP data revealed a significant genetic differentiation between suggested subspecies but not between populations within the Baltic region. Our results indicate that populations of redshanks in Europe constitute at least three separate management units corresponding to the recognised subspecies.
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6.
  • Lind, Peter A, 1980- (författare)
  • Evolutionary Dynamics of Mutation and Gene Transfer in Bacteria
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The study of bacterial evolution is fundamental for addressing current problems of antibiotic resistance and emerging infectious diseases and lays a solid foundation for successful and rational design in biotechnology and synthetic biology. The main aim of this thesis is to test evolutionary hypotheses, largely based on theoretical considerations and sequence analysis, by designing scenarios in a laboratory setting to obtain experimental data. Paper I examines how genomic GC-content can be reduced following a change in mutation rate and spectrum. Transcription-related biases in mutation location were found, but no replicative bias was detected. Paper II explores the distribution of fitness effects of random substitutions in two ribosomal protein genes using a highly sensitive fitness assay. The substitutions had a weakly deleterious effect, with low frequencies of both neutral and inactivating mutations. The surprising finding that synonymous and non-synonymous substitutions have very similar distribution of fitness effects suggests that, at least for these genes, fitness constraints are present mainly on the level of mRNA instead of protein. Paper III examines selective barriers to inter-species gene transfer by constructing mutants with a native gene replaced by an orthologue from another species. Results suggest that the fitness costs of these gene replacements are large enough to provide a barrier to this kind of horizontal gene transfer in nature. The paper also examines possible compensatory mechanisms that can reduce the cost of the poorly functioning alien genes and found that gene amplification acts as a first step to improve the selective contribution after transfer. Paper IV investigates the fitness constraints on horizontal gene transfer by inserting DNA from other species into the Salmonella chromosome. Results suggest that insertion of foreign DNA often is neutral and the manuscript provides new experimental data for theoretical analysis of interspecies genome variation and horizontal gene transfer between species.
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7.
  • Söderberg, Jonas, 1977- (författare)
  • Surviving the ratchet : Modelling deleterious mutations in asexual populations
  • 2011
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • One of the most unforgiving processes in nature is that of Muller's ratchet, a seemingly irreversible accumulation of deleterious mutations that all organisms have to deal with or face extinction. The most obvious way to avoid fitness collapse is recombination, though asexual populations usually do not have the luxury of recombining freely.  With the aid of computational and mathematical models, we have studied other situations where this threat is averted and the organism can survive the ratchet. The results show that a ratchet where all mutations have the same deleterious fitness effect is very effectively stalled for large effects. However, if mutations are allowed to have a broad range of effects, the fitness-loss rate can be substantial even with the same mean effect as the one-type ratchet, but we have  identified parameter regions where even the broad-range effects are effectively stopped. The fitness-loss from a ratchet is very sensitive to the mutation rate and a mutation that increases the mutation rate (mutator) can easily start an otherwise stalled ratchet. Large effect mutators are heavily counter-selected, but smaller mutators can spread in the population. They can be stopped by reversals (antimutators), but even if the mutation rate is equilibrated in this way, there will be large fluctuations in mutation rate and even larger in the fitness-loss rate due to the feedback amplification in their coupling.    Another way of preventing the ratchet is by reversal of the deleterious mutations themselves through back-mutations or compensatory mutations. The rate required to stop the ratchet using only back-mutations before the fitness collapses is very large. A detailed comparison between the deleterious mutations in the ratchet and in a sexual population was made and the difference was found to be greatest for large populations with large genomes. There are obviously many ways to survive the ratchet, but even more ways to drive a species to extinction by enhancing and speeding up the ratchet. By modelling and testing the ratchet for numerous different situations, we show the effects of some of these threats and benefits.
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8.
  • Valdiosera, Cristina, et al. (författare)
  • Typing single polymorphic nucleotides in mitochondrial DNA as a way to access Middle Pleistocene DNA
  • 2006
  • Ingår i: Biology Letters. - 1744-9561 .- 1744-957X. ; 2:4, s. 601-603
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, we have used a technique designed to target short fragments containing informative mitochondrial substitutions to extend the temporal limits of DNA recovery and study the molecular phylogeny of Ursus deningeri. We present a cladistic analysis using DNA recovered from 400 kyr old U. deningeri remains, which demonstrates U. deningeri's relation to Ursus spelaeus. This study extends the limits of recovery from skeletal remains by almost 300 kyr. Plant material from permafrost environments has yielded DNA of this age in earlier studies, and our data suggest that DNA in teeth from cave environments may be equally well preserved.
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9.
  • Hall, David, 1974-, et al. (författare)
  • Adaptive evolution of the Populus tremula photoperiod pathway
  • 2011
  • Ingår i: Molecular Ecology. - 0962-1083 .- 1365-294X. ; 20:7, s. 1463-1474
  • Tidskriftsartikel (refereegranskat)abstract
    • Environmental cues entrain the circadian clock, a core component of the photoperiod pathway in plants, to daily and seasonal changes. The circadian clock mediates input signals from light and temperature receptors to downstream target genes through feedback loops. Several studies have shown that a correct timing of the circadian system is a fitness advantage and genes in photoperiod network have been implied to evolve in response to the diversifying selection in heterogeneous environment. In an attempt to quantify the extent of the historical patterns of selection on genes in the photoperiod pathway in the widely distributed tree species European aspen (Populus tremula) we obtained sequences for twenty-five of the genes in the network and these genes were compared to patterns of nucleotide diversity in 77 randomly chosen genes from across the genome of P. tremula. We found a significant reduction in synonymous diversity in photoperiod genes while non-synonymous diversity was in line with data from control genes. A substantial fraction of the genes show signs of selection, with eight genes showing signs of rapid protein evolution. In contrast to our expectations, genes closely associated with the core circadian clock show rapid protein evolution despite their central position in the pathway. Furthermore, selection on non-synonymous mutations is negatively correlated with synonymous diversity across all genes, indicating the action of recurrent selective sweeps.
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10.
  • Janson, S., et al. (författare)
  • Population genetic structure of crucian carp (Carassius carassius) in man-made ponds and wild populations in Sweden
  • 2015
  • Ingår i: Aquaculture International. - 0967-6120 .- 1573-143X. ; 23:1, s. 359-368
  • Tidskriftsartikel (refereegranskat)abstract
    • Although once popular prior to the last century, the aquaculture of crucian carp Carassius carassius (L. 1758) in Sweden gradually fell from favour. This is the first genetic comparison of crucian carp from historic man-made ponds in the Scandinavian Peninsula. The aim was to identify old populations without admixture and to compare the relationship of pond populations from different provinces in Sweden. In total, nine microsatellite loci from 234 individuals from 20 locations in varied parts of Sweden were analysed. The genetic distances of crucian carp populations indicated that the populations in the southernmost province of Sweden, Scania, shared a common history. A pond population in the province SmAyenland also showed a common inheritance with this group. In the province Uppland, further north in Sweden, the population genetic distances suggested a much more complex history of crucian carp distributions in the ponds. The data showed that there are some ponds with potentially old populations without admixture, but also that several ponds might have been stocked with fish from many sources.
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