<p>Climatic variation and change affect the dynamics of organisms and ecosystem processes. This thesis examines phytoplankton as a target variable to trace climatic impacts on Lake Erken (Sweden) with special emphasis on the spring bloom. </p><p>A strong correlation between the timing of the spring bloom and the North Atlantic Oscillation (NAO) illustrates the link between atmospheric pressure variations and local biological processes. The predictive power increased by applying a recently established regional Scandinavian Circulation Index (SCI). Changes to an earlier timing of the spring bloom and elevated water temperature were induced by the global warming trend. The climate signal was still persistent in summer manifested by an enhanced summer phytoplankton biomass. </p><p>Between spring and summer, the phytoplankton was mainly controlled by phosphorus limitation. The application of a new method to measure alkaline phosphatase activity revealed that P-limitation varied between species and among individual cells.</p><p>Combining the above knowledge and literature data, the impact of the NAO on the timing of life history events, biomass and trophic cascade in aquatic and terrestrial ecosystems was quantitatively tested with a meta-analysis. In all environments, pronounced effects of the NAO were apparent, indicating the generality of climate effects found in different ecosystems. </p><p>Finally, a regional climate model was applied, forcing a physical lake model from which future lake conditions were simulated. The simulation revealed a one-month shorter ice cover period with two years out of ten being completely ice free. Internal eutrophication is one of the expected consequences. </p><p>In conclusion, the strong influences of global and regional climate are apparent in local physical, chemical and biological variables and will most probably also in future affect the structure and function of processes in lakes. </p>

<p>Persistent environmental pollutants were examined for their interaction with the glucocorticoid hormone system. The focus was placed on interference with the glucocorticoid synthesis and the glucocorticoid-signalling pathway in various <i>in vitro</i> test systems.</p><p>Several aryl methyl sulphones competitively inhibited CYP11B1 activity in mouse adrenocortical Y1 cells. The DDT metabolite, 3-methylsulphonyl-2,2’-bis(4-chlorophenyl)-1,1’-dichloroethene (3-MeSO₂-DDE) had a higher affinity to the enzyme than the endogenous substrate, 11-deoxycorticosterone. In fact, 3-MeSO₂-DDE (K_i 1.6 μM) was almost as potent as the drug metyrapone (K_i 0.8 μM), a well-known inhibitor of the enzyme. 3-MeSO₂-DDE inhibited CYP11B1 activity in human adrenocortical H295R carcinoma cells, and at higher concentrations the CYP21 activity. The human H295R cell line seems to be a useful test system for studies of enzyme activities and could be used to screen endocrine disrupting chemicals interfering with the glucocorticoid hormone synthesis.</p><p>Several chiral PCB methyl sulphones and the fungicide tolylfluanid proved to be antagonists to the glucocorticoid receptor (GR) in rat hepatoma cells and/or Chinese hamster ovary cells stable transformed with a human GR and a responsive reporter vector. The 4-methylsulphonyl-2,3,6,2’,4’,5’-hexachlorobiphenyl (4-MeSO₂-CB149) enantiomers had similar antagonistic effect on the GR. Co-exposure of substances led to additive inhibitory effects on glucocorticoid-regulated protein synthesis in rat hepatoma cells. In general, 4-substituted but not 3-substituted methylsulphonyl-PCBs interacted with the glucocorticoid hormone system.</p><p>In the environment, humans and wildlife are constantly exposed to a wide range of chemicals. Considering the effects of these substances via mechanisms of actions described in this thesis, interference of xenobiotics with the glucocorticoid hormone system deserves further attention. In conclusion, environmental pollutants can interact with the glucocorticoid hormone system <i>in vitro</i>, yet the effects of the tested substances on this hormone system remain to be established <i>in vivo.</i></p>

<p>Picophytoplankton were inferior competitors for inorganic phosphorus compared to heterotrophic bacteria. This may be due to the source of energy available for the heterotrophs, while cell-size was of minor importance. However, picophytoplankton were superior to large phytoplankton in the competition for nutrients at low concentrations. </p><p>Biomass of picophytoplankton was low in brownwater lakes and high in clearwater lakes, compared to the biomass of heterotrophic bacteria. The results suggest that picophytoplankton are inferior to heterotrophic bacteria in the competition for inorganic nutrients in brownwater lakes, where the production of heterotrophic bacteria is subsidized by humic dissolved organic carbon (DOC) </p><p>Relative to large phytoplankton, picophytoplankton were most important in lakes with intermediate water colour, despite the fact that the lowest nutrient concentrations were found in the clearwater lakes. Large phytoplankton in the clearwater lakes may be able to overcome nutrient competition with picophytoplankton by vertical migration.</p><p>In conclusion, changes in nutrient content, light availability and concentrations of DOC affect the interactions of heterotrophic bacteria, picophytoplankton and large phytoplankton and are therefore important factors for the structure of the food web in the pelagic zones of lakes.</p><p>Picophytoplankton (planktonic algae and cyanobacteria, < 2 µm) constitute an important component of pelagic food webs. They are linked to larger phytoplankton and heterotrophic bacteria through complex interactions including competition, commensalism and predation. In this thesis, field and laboratory studies on the competitive ability of picophytoplankton are reported.</p>

<p>Understanding the diversity of life is one of the main aims of evolutionary biology, and requires knowledge of the occurrence and causes of adaptive genetic differentiation among geographically distinct populations. Environmental stress caused by acidity may cause strong directional selection in natural populations, but is little explored from an evolutionary perspective. In this thesis, a series of laboratory experiments and field data was used to study evolutionary and ecological responses of amphibians to environmental acidity. </p><p>Local adaptation to acid stress was studied in the moor frog (<i>Rana arvalis)</i>.The results show that acid origin populations have higher acid stress tolerance during the embryonic stages than neutral origin populations, and that acid and neutral origin populations have diverged in embryonic and larval life-histories. The mechanisms underlying adaptive differentiation are partially mediated by maternal effects related to extra-embryonic membranes and egg size. Acid origin females invest in larger eggs and have a stronger egg size-fecundity trade-off than females from neutral areas, likely reflecting adaptive differentiation in maternal investment patterns. </p><p>Potential carry-over effects of low pH, and the effects of UV-b/pH interaction were investigated in the common frog (<i>R. temporaria</i>). The results suggest that amphibian larvae are able to compensate for the negative effects of acidity experienced early in life, if conditions later turn beneficial. <i>R. temporaria</i> populations differed in their sensitivity to synergistic effects of low pH/UV-B, indicating variation in population responses to environmental stress.</p><p>In conclusion, these results suggest rapid evolution in response to human induced environmental change, much of which may be mediated via adaptive maternal effects. Acidification may be a powerful selective force shaping life-history evolution.</p>

<p>The great difference in the level of chloroplast variation and its geographic structure among the three main species studied here demonstrates that forest species do not form a homogeneous group. Hazel shows a genetic structure similar to many other thermophilous species and this structure, in combination with fossil evidence, indicates that the post-glacial colonisation of most of Europe originated in a refugium in western France while the Balkan and Italy were colonised from a south-eastern refugium.</p><p>In sallow and silver birch the chloroplast DNA variation and its structure does not fit with a scenario of glacial restriction to southern refugia and survival at intermediate latitudes is suggested for both species. The chloroplast DNA variation in silver birch suggests the presence of one western and one eastern European post-glacial colonisation route and limited contribution of southern populations in the colonisation of the rest of Europe. Unique haplotypes by the Ural Mountains indicates the possibility of a separate glacial origin of these populations.</p><p>The study of chloroplast DNA in species closely related to sallow and silver birch indicate that extensive hybridisation and cytoplasmic gene flow occurs within both the Salix and Betula genera in Europe. The nuclear and chloroplast phylogenies of 14 Betula species were not in complete agreement with each other or with the classical division of the Betula genus into subgenera or sections. The phylogenetic structure implies that hybridisation has played a role in the evolution of the Betula genus.</p><p>This thesis focuses on the chloroplast DNA variation in three forest tree genera: Corylus, Betula and Salix. Chloroplast PCR-RFLP is used to evaluate the post-glacial history of hazel, Corylus avellana, silver birch, Betula pendula and sallow, Salix caprea and to explore the possibility of introgression in the Salix and Betula genera. In addition, the chloroplast matK gene, its flanking regions and the nuclear ADH gene were used to study the phylogenetic relationships within the Betula genus.</p>

<p>Vanguerieae is a tribe in the mainly tropical angiosperm family Rubiaceae. The tribe currently comprises around 600 species in 27 genera, with the major part of the species distributed in Africa south of the Sahara. </p><p>The phylogeny of the tribe was investigated using both molecular and morphological data. ITS sequences of the nuclear ribosomal DNA are used in all of the included papers, and in three papers also in combination with sequences from the plastid <i>trnT-F</i> region and/or the <i>rpl16</i> intron. Thirty morphological characters were also investigated and used in combination with molecular data. Several strongly supported groups are found, but eight of the currently recognized genera are also revealed as para- or polyphyletic, i.e., <i>Canthium</i>, <i>Fadogia</i>, <i>Lagynias</i>, <i>Pachystigma</i>, <i>Pyrostria</i>, <i>Rytigynia</i>, <i>Tapiphyllum</i>, and <i>Vangueria</i>. A new classification based on the phylogenetic analyses is suggested and a review of the morphology of Vanguerieae with a focus on taxonomically informative characters is also included. </p><p>The morphologically similar <i>Ancylanthos</i>, <i>Lagynias</i>, <i>Pachystigma</i>, and <i>Tapiphyllum</i> together with a species of <i>Rytigynia</i>, <i>R</i>. <i>fuscosetulosa</i>, are suggested for transfer to <i>Vangueria</i>. All dioecious species of Vanguerieae are found to form a strongly supported group. A study of the group is performed in which all dioecious genera and also twelve undescribed species from Madagascar are included. It is concluded that the whole group should be included in <i>Pyrostria</i>, which necessitates transfers of <i>Canthium</i> subgenus <i>Bullockia</i> and <i>Scyphochlamys</i>. <i>Canthium</i> subgenus <i>Afrocanthium</i> is found to have a position isolated from the type species of the genus and it is suggested that the subgenus is given generic rank as <i>Afrocanthium</i>. A comparison of nuclear and chloroplast phylogenies shows that several species in a subgroup of the tribe have incongruent positions, and possible explanations for the incongruencies are discussed. </p>

<p>This thesis integrates the fields of sexual selection, parental investment and sex role theory by investigating mutual mate choice and mate competition in the sex role reversed deep snouted pipefish <i>Syngnathus typhle</i> (Pisces: Syngnathidae) through a series of laboratory experiments. In<i> S. typhle</i>, the female transfers her eggs to the male's brood pouch where they are nourished and oxygenated for about a month, when the male gives birth to the independent fry.</p><p>Mate choice was found to be adaptive. Both sexes benefited from mating with preferred partners in terms of increased offspring viability and got larger, or faster growing, offspring when mating with large fish. Females were also shown to prefer males with thicker brood pouches. Thus, females, the more competitive sex, had multiple preferences. Both male and female choice behaviour was found to be flexible and influenced by available information on partner quality. In addition, males, but not females, copied the mate choice of consexuals. </p><p>Both sexes were found to take their own quality in relation to surrounding competitors into account when deciding whether to display to potential partners. Male-male competition was found to influence both the mate choice of males and, potentially, overrule the mate choice of females. Males did not compete as intensely as females, nor did they use their sexual ornament in this context as females do. Rather, the ornament was used in interactions with females, and males that displayed more received more eggs.</p><p>The findings in this thesis emphasise the importance of not viewing mate choice and competition as opposite behaviours, but rather to apply a dynamic approach in mate choice studies, integrating choice and competition in both sex</p>

<p>This thesis deals with the highly potent olfactory mucosa toxicant 2,6-dichlorophenyl methylsulphone (2,6-diClPh-MeSO₂) and its non-toxic 2,5-chlorinated isomer (2,5-diClPh-MeSO₂). In mice, both substances bind firmly in the olfactory mucosa and the olfactory bulb, which are important components of the sensory system. The 2,6-isomer induces olfactory mucosal necrosis with permanent loss of olfactory neuroepithelium and olfactory nerves. A major objective was to clarify the cause of this isomer-specific toxicity, and to identify which physicochemical characteristics determine the olfactory toxicity. The neurobehavioural toxicity of these substances was also examined.</p><p>The results revealed a rapid CYP-catalysed covalent binding of 2,6-diClPh-MeSO₂ in the rat olfactory mucosa, whereas the 2,5-dichlorinated isomer was not covalently bound. </p><p>Acute and chronic olfactory mucosal pathology were investigated and compared in rats and mice. Twenty-four hours after dosing to rats, 2,6-diClPh-MeSO₂ induced Bowman’s glands necrosis and sloughing of the olfactory epithelium similar to that previously reported in mice. At 3 weeks, however, there were dramatic differences in histological lesions. In mice, large parts of olfactory epithelium were replaced by respiratory-like epithelium. Large, bilateral, fibrous, cartilage and bone containing polyps occluding the lumen were confirmed. In rats, only minor patches of olfactory epithelium were replaced by a metaplastic atypical respiratory-like epithelium. 2,5-diClPh-MeSO₂ was non-toxic in rats as well as in mice.</p><p>In mice, 2,6-diClPh-MeSO₂ induced a dose-dependent and long-lasting ( ≥12 weeks) hyperactivity as well as long-lasting maze learning deficits. At 2 weeks hyperactivity and maze learning deficits were observed also in rats. Unexpectedly, 2,5-diClPh-MeSO₂ induced hyperactivity that lasted for two weeks. No effect on maze learning was observed with this isomer. No major differences between male and female rats or mice were found.</p><p>In conclusion, the results show that a CYP-catalysed formation and covalent binding of a reactive 2,6-diClPh-MeSO₂-metabolite in the Bowman’s glands precede the high olfactory mucosal toxicity in rodents. As determined by QSAR-modelling, a 2,6-dichlorinated benzene derivative with a large, polar, and strong electron withdrawing substituent in the primary position has the potential of being an olfactory mucosal toxicant. The observed 2,6-diClPh-MeSO₂-induced increase in motor activity, and maze learning deficits, were not correlated to the olfactory mucosal lesions. I propose that 2,6-diClPh-MeSO₂ causes a direct effect in the brain leading to neurobehaviuoral deficits. </p>

<p>Krüppel-related zinc finger proteins constitute the largest single class of transcription factors within the human genome. Members of this protein family have the ability to either activate or repress transcription depending on the presence of specific activator or repressor domains within the protein. Approximately one third of the Krüppel-related zinc finger proteins contain an evolutionarily well-conserved repressor domain termed the KRAB domain. This domain acts as a potent repressor of transcription by interacting with the co-repressor protein, TIF1β. TIF1β then, in turn, recruits HP1 proteins, HDACs and probably other proteins involved in gene silencing. In order to identify novel KRAB-containing zinc finger proteins, one mouse monocytic cDNA library and two testis cDNA libraries were screened for novel members of this multigene family. Six novel KRAB-ZNF cDNAs, four mouse and two human, were isolated. The corresponding proteins were all shown to contain N-terminally located KRAB domains as well as varying numbers of C-terminally located zinc finger motifs. An extensive comparative sequence analysis of the KRAB domains of these proteins together with KRAB domains from a large number of previously identified KRAB-ZNF proteins resulted in a clear subdivision into three different subfamilies, A+B, A+b and A. Later, we also isolated a fourth KRAB box, which is present downstream of the KRAB A box in a few proteins of the KRAB A family. This module was named KRAB C. Potential functional differences between these different subfamilies were investigated. In line with previous observations, the KRAB A box was shown to repress transcription, an activity which was enhanced by the presence of the KRAB B box. However, addition of neither the KRAB b box nor the KRAB C box had any effect on repression. Moreover, all KRAB A motifs had the ability to bind TIF1β, and this binding was increased both by the presence of the KRAB B box and by the KRAB C box. The KRAB b box, however, did not seem to contribute to TIF1β-binding. One of the novel human cDNAs, HKr19, was found to be a member of the large ZNF91 family of KRAB zinc finger genes. Interestingly, the expression of HKr19 and a number of other closely related genes were restricted to lymphoid cells, indicating that these genes may be involved in regulating lineage commitment. The effect of HKr19 on cell viability was investigated by transfection into human embryonic kidney cells (HEK 293). The results indicated that HKr19, or its zinc finger domain in isolation, were toxic to these cells when expressed at high levels. The MZF6D protein, on the other hand, showed a testis-specific expression. <i>In situ</i> hybridization analysis located this expression to meiotic germ cells, suggesting a role for this protein in spermatogenesis. Further, the evolutionary perspectives of this large gene family were addressed, and its enormous expansion throughout evolution probably includes numerous duplication events. The results from two extensive sequence analyses give clues to how the repetitive nature of the ZNF motif has given rise to both internal duplications of single motifs as well as duplications of entire genes resulting in gene clusters.</p>

<p>All living organisms consist of cells and the identity of a cell is defined by the genes it expresses. To assure proper function, a cell receives continuous information on which genes to turn on and off. This information is, to a large extent, provided by transcription factors. Krüppel-related zinc finger proteins probably constitute the largest family of transcription factors in mammals and many of these proteins carry a potent repressor domain called Krüppel-associated box (KRAB). The human genome alone encodes more than 200 KRAB zinc finger proteins but still very little is known about their biological functions. </p><p>The Krüppel-related zinc finger genes appear to have been involved in a massive expansion throughout evolution. To unravel some of the secrets underlying this evolutionary success, we studied the molecular evolution of KRAB zinc finger genes. We show that the frequently occurring duplications of these genes are accompanied by a low sequence constraint in their zinc finger region. In addition, we show that the number of zinc finger motifs carried within these proteins is far from fixed. New zinc finger motifs are frequently added while others are inactivated or even discarded from the coding region. The structurally independent Krüppel zinc finger motif has, through these mechanisms, served as a highly adaptive building block for the generation of new transcriptional regulators. </p><p>The mouse, rat and human genomes carry four different variants of the KRAB domain – KRAB(AB), KRAB(Ab), KRAB(AC) and KRAB(A). This thesis presents the identification of a novel KRAB domain, KRAB C, as well as a functional analysis of the different KRAB domains. We conclude that all different KRAB domains share a common co-repressor, TIFβ, and effectively repress transcription. These functions are mainly mediated by the KRAB A box but are clearly influenced by the presence of a KRAB B, b or C box. Furthermore, we show that all KRAB zinc finger gene subfamilies originate from the KRAB(AB) zinc finger genes.</p><p>In addition, this thesis includes a structural and functional analysis of four novel mouse and human KRAB zinc finger genes; <i>MZF6D</i>, <i>HKr18</i>, <i>HKr19</i> and <i>HZF12</i>. Whereas <i>HKr18</i> and <i>HZF12</i> seem to be ubiquitously expressed, <i>MZF6D</i> and <i>HKr19</i> show a more restricted expression pattern. Northern blot and <i>in situ</i> hybridisation analyses of <i>MZF6D</i> showed that the expression of this gene is restricted to meiotic germ cells. <i>MZF6D</i> might thus be involved in the formation of male gametes. The expression of <i>HKr19</i>, on the other hand, seems to be restricted to lymphoid cells, indicating a possible role for this KRAB zinc finger gene in the regulation of lineage commitment.</p>