The work included in this thesis aims at exploring the environmental sensitivity of benefits and costs of sexual selection through a combined empirical and theoretical effort, to increase our understanding of the impact of environmental change on sexually reproducing populations.Can sexual selection promote adaptation to novel environments? Sexual selection for good genes should accelerate adaptation by granting higher reproductive success to individuals of high genetic quality. However, sexual conflict is a frequent outcome of sexual reproduction and may often be detrimental to population fitness. Experimental evolution has shown that the role of sexual selection in adaptation is variable, because of a complex balance between the detrimental and beneficial effects described above.The present thesis is investigating the role of sexual selection in adaptation by focusing on the sex-specific strength of selection and the intensity of intralocus sexual conflict (IaSC) in ancestral and novel environments. The sex-specific strength of selection is a valuable proxy for the benefits of sexual reproduction, since a male-bias in selection caused by sexual selection should allow efficient purging of deleterious alleles with little impact on female fecundity and cost to population fitness.This thesis investigates both sex-specific selection and IaSC across benign and novel environments in two species of seed beetles, Callosobruchus maculatus and Acanthoscelides obtectus, and includes a theoretical model of the effect of environmental change on of sexual selection. The empirical part of my results indicates that, generally, selection at the adult stage is male biased but that this male bias may be reduced under stress, pointing towards reduced benefits of sexual selection under rapid environmental change. Additional simulations suggest that the frequency dependent nature of sexual selection alone could explain this trend. No empirical support was found for the reduction of IaSC under stress.It is becoming crucial today to understand the impact of environmental change on natural populations. This thesis brings new material adding to our understanding of the role of sexual selection within that particular issue. The outcome of sexual selection is dependent on a variety of mechanisms, such as good genes processes and sexual conflict, which are very likely to be dependent on ecological factors and specificity of the system studied. For that reason, carefully controlled experiments on laboratory systems and mathematical modelling are necessary steps that should ultimately lead to the study of similar questions in natural systems.

If sexual selection acts in a sex-limited way on a trait that has a shared genetic basis between males and females, the resulting intralocus sexual conflict can have a considerable impact on the opposite sex. A prime example of sexual conflict affecting a shared characteristic would be the reproductive organs in males and females. This study investigates how artificial selection on the female-specific trait egg size influences male reproductive success, particularly male testes morphology, by analysing the density and number of seminiferous tubules within the testes. It was found that selection on female reproductive investment has a concordant effect on male reproductive success, by demonstrating increased density of seminiferous tissue in the testes of males originating from high investment selection lines. Interestingly, a non-significant trend suggested that the density of seminiferous tissue influences testes size in a negative way. This study therefore provides evidence that female-specific selection on reproductive investment influences testes morphology in males, and that testes size depends on more than sperm-producing tissue.

How come the same species of plants can naturally occur under various conditions in different parts of the world? A plant's ability to adapt in response to a changing climate hinges on the presence of genetic variation in traits, such as flowering phenology. In this study, I examine whether flowering start varies genetically within populations and compare this variation to differences between populations. This study quantifies genetic variation in flowering time in two Italian populations of Arabidopsis thaliana whilst using two Swedish populations as a reference. This was done using a randomized block design where plants were grown in a controlled climate. To characterize and measure flowering phenology, time of bolting and flowering were recorded. The experiment included four populations, a total of 150 maternal lines, and 2980 plants. One-way ANOVAs conducted separately by population indicated significant among-line variation in the two Italian populations. Flowering time differed between the Italian and Swedish populations, but not between the two Italian populations. More data would be needed to draw conclusions about the among-line variation in the Swedish populations. The results indicate that the Italian populations have the potential to respond to selection on flowering time, which is a likely consequence of a changing climate.

To understand animal behaviour, it is important to consider the environment in which it occurs. The environment, consisting of both abiotic factors and social context, is usually highly variable and leads to variation in individual’s and group’s behaviour. To better understand the environmental influences on behaviour of pygmy halfbeaks (Dermogenys collettei), a small live-bearing fish, I viewed videos of shoals of wild halfbeaks in Singapore. I investigated effects of environmental variation (water depth, canopy cover and water vegetation) and social environment (group size and male to female sex ratio) on halfbeaks’ aggression and mating behaviours. I found that environment had little effect and most variation between studied shoals was probably due to social factors. I found some evidence for aggression increase in larger shoals, primarily in males. Sex ratio had different relation with aggression for individual sexes and mating behaviours decreased when sex ratio became more male biased. This study shows that halfbeaks probably modify their behaviour in relation to social environment. I also show that these changes are similar to those described in other species, which strengthens the validity of using halfbeaks to study social interactions.

Islands have been considered natural laboratories to study evolutionary processes. Ibiza is a  small island in Spain whose population stands out from other Spanish populations due to its  particular demographic and historical processes. War, famine, and several epidemics have af fected Ibizans, and these phenomena could have left signatures of positive selection in their  genomes. Here, we used three different methodologies to detect positive selection: The Popu lation Branch Statistic (PBS), the Integrated Haplotype Score (iHS), and the Cross-Population  Extended Haplotype Homozygosity (XP-EHH). We used a sliding windows approach to control  for spurious results. The candidate windows for selection were chosen using three different  criteria for each test: maximum and mean score within each window, and proportion of high  scores in each window. Only the windows being simultaneously on the top of each of the three  criteria were selected for annotation and enrichment analyses. The most common traits asso ciated with the SNPs present in the candidate windows were blood function, cardiovascular  diseases, body mass measures, lipid metabolism, renal function, and skin diseases. We sug gest some hypotheses to explain the selection signatures related to some of these traits and  some recommendations for further studies to overcome the present research's limitations.

DNA methylation patterns are sex and tissue specific in many species, yet many studies useblood samples, due to its accessibility, to establish links between the DNA methylation anddifferent phenotypes. This raises the question of whether DNA methylation in blood samplesreflect the DNA methylation pattern in other tissues that are more relevant to the phenotypebeing studied. In this research, samples were collected from the brain, blood, liver and gonadof 16 house sparrow (Passer domesticus), half of them were female, while the others weremale. Reduced representation bisulfite sequencing (RRBS) was performed to get themethylation profile in each sample. The result showed a tissue specific methylation profile inthe four investigated tissues, a strong and positive correlation between 0.74 – 0.85 was foundbetween tissues, in which a weaker correlation was found between blood and other tissue. Indifferential methylation analysis, most of the differently methylated sites between sexes werefound in gonads, while the fewest was found in blood, and Z chromosome wasoverrepresented place in all four tissues where the majority of the differently methylated sitesbetween sexes were found. Comparison with the house sparrow genome annotation foundabout half of the differentially methylated sites between sexes were within genes and about 20 % of them were in the exon or coding region of a gene. The result suggested that bloodcould be useful in reflecting the general DNA methylation level in other tissues, but it was nota reliable bioindicator for further detailed study in DNA methylation pattern or in geneontology enrichment pathway analysis.

Nickel enzymes have been suggested, through numerous phylogenetic studies, to have been among the very first catalytic compounds on the early Earth, possibly present in the last universal common ancestor (LUCA) or prior to the onset of life. This is because of the type of reactions catalyzed by some of these enzymes, the nature of organisms that utilize them, their distribution in the tree of life, and their key roles in what is now thought of as possibly one of the oldest carbon fixation pathways, the Wood-Ljungdahl (WL) pathway. Additionally, nickel is generally thought to have been an abundant element on the early Earth, highly soluble in what were, theoretically, euxinic (anoxic and sulfidic) ocean waters. This combined with the fact that the enzymes involved in the WL pathway have an active center configuration that resembles that of minerals found in hydrothermal vent walls, makes nickel enzymes a likely candidate to have evolved from what were proto-enzymes, responsible for the prebiotic catalysis of the first simple organic molecules prior to the origins of life, according to the so-called submarine alkaline hydrothermal vent theory, first presented by Michael J. Russell in 1993 (Russell et al. 1994). In this study, I expand the known coverage on the distribution of these enzymes by mapping them in 10,575 OTUs of microbial taxa. Using their pattern of distribution, I reconstruct their histories along the branches of a reference phylogenetic tree of the same taxa through methods of ancestral reconstruction of discrete traits. Additionally, I construct an individual gene tree for each of the enzymes in order to consolidate gene history with species history. My results showed that the redox nickel enzymes (except methyl-coenzyme M reductase) are ancestral to all prokaryotes, while non-redox enzymes are derived and with multiple origins, possibly due to lateral gene transfer events or convergent evolution. I propose that the patterns observed are a product of the drastic changes during early Earth history, namely a hypothesized “nickel famine” or the Great Oxidation Event, which acted as selective pressures.

This degree project examined the effect of time constraint on wing shape and phenotypic variation in wing shape along a latitudinal gradient in the damselfly species Lestes sponsa. Fore and hind wings from individuals originating from three different latitudes: North (66°N), Central (59°N) and South (54°N) Europe were treated with their native temperature and photoperiod. In addition, the north and south populations were treated with south and north conditions respectively, resulting in five groups in total. Morphometric analyses of the wings revealed a positive correlation between body mass and wing centroid size, along with a difference in wing shape between the groups. Forewings and hindwings from the northern group were broader and rounder than wings from the central and southern groups. Additionally, the wings from the transplant groups resembled those of the native group of their treatment, indicating a phenotypic plasticity in wing shape. Lastly, statistical tests of phenotypic variation revealed that variation was highest in relative warp 2 in the forewings and hindwings, and this warp represents the curvature of the wing both upwards/downwards or towards the inside/outside of the wing. These results on phenotypic variation indicate that even in a new or changing environment, L. sponsa could be capable of adapting to varying temperatures and environmental conditions. This study builds our understanding of how this damselfly species, and potentially insects, will be affected by current and future potential climate change.

Terrestrial plants exist in almost every habitat on the earth, ranging from warm and moist tropical rainforests, hot and dry deserts, and to cold and barren tundras. Furthermore, a single species may encounter different climatic conditionshabitats within its range distribution which climatic conditions differs from one to another. In this study, I examine the flowering phenology and fitness of two locally adapted genotypes of Arabidopsis thaliana, one from the southern range limit (Italy) and one from the northern range limit (Sweden) in Europe, in an outdoor common-garden experiment in Uppsala. Flowering start was recorded to characterize flowering phenology, whilst survival and fecundity was recorded to characterize fitness. Flowering start differed significantly between the two genotypes as with the Swedish genotype startinged flowering 24 days later than the Italian genotype. The Italian genotype had higher fitness (number of fruits per seedling planted), which was due to a slightly higher survival and fecundity. The relative fitness of the two genotypes was thus intermediate to that observed in reciprocal transplants between the native sites of origin of the two populations.

With increasingly warming climate, many bird species have been forced to respond to environmental changes, and the long-tailed duck (Clangula hyemalis) is no exception. The populations of the long-tailed duck have been in decline the past few decades and the species is classified as globally vulnerable and near threatened in both Iceland and Sweden. The long-tailed duck is a circumpolar, migratory sea duck. Its migratory routes and wintering and breeding sites might play an important part in gene flow between populations. The aim of this project was to get a clearer image of the substructure of the long-tailed duck in the northern hemisphere to help identify populations possibly at risk. This was investigated by exploring differences in mitochondrial DNA between the global populations, and by studying the Icelandic wintering and breeding populations in particular applying whole genome sequencing. To do this, samples were obtained for mitochondrial DNA analyses from a previous study by Wilson et al. (2016) from North America and East Russia, samples from other populations around the northern hemisphere as well and new samples from Iceland. Museum samples from Iceland were used for whole genome resequencing. Mitochondrial analyses included haplotype identification, population comparisons, mismatch and neutrality tests. Whole genome analyses included neutrality tests, principal component analysis and genetic admixture analysis.The mitochondrial results revealed two distinct lineages for the long-tailed duck. Two populations showed a difference from the other populations; the Icelandic breeding population and the Yukon-Kuskokwim Delta population from Alaska, which are the southernmost breeding populations. The Yukon population might have been previously isolated with refugial population intermixing. For the Icelandic populations, the mitochondrial results showed little intermixing between the winter and breeding populations. The whole genome results showed more complicated results for the Icelandic populations, with admixture in some individuals. This suggests that there seems to be more variation in the genome than implied by the mitochondrial DNA.