Traditionally, females have been considered to be strictly monogamous. Today, we know that females in the majority of species actively seek out and mate with several males. Trying to understand female preferences, including what benefits mate choice entails, has been the focus of intense research during the last decades. Females can gain both direct (e.g. access to better territories or paternal care) and indirect (i.e. genetic) benefits. The aim of this thesis is to further our understanding of the female reproductive strategies in the ruff, Philomachus pugnax (Aves, Scolopacidae). The ruff is a lekking wader, where males gather on leks to display to females that come there to mate. Males do not provide any paternal care to the offspring. Lekking systems are ideal for studying indirect benefits of female choice, as females do not gain any direct benefits from males. Females mated with several males and 50% of the broods were fathered by at least two males. The level of genetic similarity between two parents has previously been shown to be an important source of variation in offspring fitness. Males that were less closely related to the female fathered more offspring in broods with multiple paternity, such that females that mated multiply gained in terms of receiving more outbred offspring. There did not, however, appear to be an overall female preference for less closely related males. There are two genetically determined male reproductive strategies in the ruff, that differ in behaviour and morphology. There was no evidence for females taking male strategy into account when choosing a partner. Female post-fertilisation strategies may also influence fitness, e.g. through differential investment in eggs, gender of the offspring and choice of breeding habitat. Females allocated sex in a non-random manner dependent upon body condition, such that females in good condition had more daughters. Females were found to nest in higher than average vegetation and in areas with higher than average abundance of insects, factors likely to influence predation rates on both eggs and young, as well as foraging opportunities for the precocial young. Further, females were faithful to their previous breeding site and usually nested within meters of their previous nest. Hatching success did not, however, affect a female’s decision to return or not.

In the green-veined white butterfly (Pieris napi), females obtain direct fitness benefits from mating multiply and studies have shown that fitness increases seemingly monotonically with number of matings. The reason is that at mating males transfer a large nutritious gift (a so called nuptial gift) to the females that the females use to increase both their fecundity and lifespan. In addition, if exposed to poor food conditions as larvae, females mature at a smaller size compared to males. Accordingly, it was suggested that smaller females could compensate for their size through nuptial feeding by, for instance, mating more frequently. We did not find any support for that hypothesis. On the contrary, larger females remated sooner and had a higher lifetime number of matings. Neither were smaller females able to compensate in any other way, because singly mated females and multiply mated females suffered to the same extent from their smaller size. This thesis also shows that despite the positive relationship between fitness and number of matings, there is a large variation in female mating frequency in wild populations and about every second female mates only once or twice. This variation is not dependent on how often females get courted by males, because female mating frequency was shown not to be affected by male courtship intensity. Hence, the reason for the low mating frequency could either be that males have evolved the ability to manipulate females to mate at a suboptimal rate as a measure of protection against sperm competition, or alternatively, that female mating rate is suppressed by some costs. Using two selection lines, artificially selected for either a high or a low mating rate, we showed that the variation in mating rate was mainly a female trait because which line the females were from affected their mating rate whereas which line the male was from did not. This implies that females mate at a low rate due to hidden costs or due to constraints. The same study also showed that females with a high "intrinsic" mating rate lived shorter, but only when denied remating. This led us to test the hypothesis that the cost females face is to have the ability to mate at a high rate but the cost is only paid when remating opportunities are scarce. However, we found no support for such an idea, because females with a high intrinsic mating rate held in a cold environment where the butterflies were prevented from flying and feeding did not live shorter. Neither was there an effect of a female’s mating rate on her ability to quickly break down and convert male nutrient gifts into egg material. Female mating rate did, on the other hand, affect dispersal tendency, with low mating rate females being more inclined to fly between different habitats. The underlying reason for this is still to be explored.

Much of current ecological theory stems from experimental studies. These studies have often been conducted in closed systems, at spatial scales that are much smaller than the systems of interest. It is known that the outcome of these experiments may be seriously affected by artefacts associated with the caging procedures, as well as by the actual difference in spatial scale between experimental and target system. Yet, quantitative methods for estimating and removing artefacts of enclosure and for extrapolating experimental results to the scales of natural systems are largely lacking. The aim of this thesis was to confront some of the problems encountered when scaling from experiments to nature in studies on predator-prey systems, with focus on effects of changes in spatial heterogeneity. Specifically, I examined mechanisms that may cause consumption rate estimates to depend on the size of the experimental arena. I also studied methods for scaling up these process rate estimates to natural predator-prey systems. The studies were performed on invertebrate predator-prey systems found in the northern Baltic Sea. Initially, a descriptive study of small-scale distribution patterns was performed, in order to get background information on how the behaviour of the organisms was manifested in the spatial structure of the community. Experimental studies of two predator-prey systems exposed an artefact that may be widespread in experiments aiming at quantifying biotic interactions. It is caused by predator and prey aggregating along the walls of the experimental containers. This behaviour affects the encounter rate between predator and prey, thereby causing consumption rates to be scale-dependent. Opposing the common belief that larger arenas always produce less biased results, this scale effect may instead be reduced by decreasing arena size. An alternative method for estimating the magnitude of, and subsequently removing, the artefact caused by aggregation along the arena wall was presented. Once unbiased estimates of process functions have been derived, the next step is to scale up the functions to natural systems. This extrapolation entails a considerable increase in spatial heterogeneity, which may have important implications for the dynamics of the system. Moment approximation provides a method of taking the heterogeneity of natural populations into account in the extrapolation process. In the last study of the thesis, the concepts of moment approximation and how to estimate relevant heterogeneity were explained, and it was shown how the method may be used for adding space as a component to a dynamic predator-prey model. It was concluded that moment approximation provides a simple and useful technique for dealing with effects of spatial variation, and that a major benefit of the method is that it provides a way of visualising how heterogeneity affects ecological processes.

Industrial and domestic sewage effluents have been found to cause reproductive disorders in wild fish, often as a result of the interference of compounds in the effluents with the endocrine system. This thesis describes laboratory-based exposure experiments and a field survey that were conducted with juveniles of the three-spined stickleback, Gasterosteus aculeatus. This small teleost is a common fish in Swedish coastal waters and was chosen as an alternative to non-native test species commonly used in endocrine disruption studies, which allows the comparison of field data with results from laboratory experiments. The aim of this thesis was to elucidate 1) if genetic sex determination and differentiation can be disturbed by natural and synthetic steroid hormones and 2) whether this provides an endpoint for the detection of endocrine disruption, 3) to evaluate the applicability of specific estrogen- and androgen-inducible marker proteins in juvenile three-spined sticklebacks, 4) to investigate whether estrogenic and/or androgenic endocrine disrupting activity can be detected in effluents from Swedish pulp mills and domestic sewage treatment plants and 5) whether such activity can be detected in coastal waters receiving these effluents. Laboratory exposure experiments found juvenile three-spined sticklebacks to be sensitive to water-borne estrogenic and androgenic steroid substances. Intersex – the co-occurrence of ovarian and testicular tissue in gonads – was induced by 17β-estradiol (E2), 17α-ethinylestradiol (EE2), 17α-methyltestosterone (MT) and 5α-dihydrotestosterone (DHT). The first two weeks after hatching was the phase of highest sensitivity. MT was ambivalent by simultaneously eliciting masculinizing and feminizing effects. When applying a DNA-based method for genetic sex identification, it was found that application of MT only during the first two weeks after hatching caused total and apparently irreversible development of testis in genetic females. E2 caused gonad type reversal from male to female. E2 and EE2 induced vitellogenin - the estrogen-responsive yolk precursor protein, while DHT and MT induced spiggin – the androgen-responsive glue protein of the stickleback. None of the effluents from two pulp mills and two domestic sewage treatment plants had any estrogenic or androgenic activity. Juvenile three-spined sticklebacks were collected during four subsequent summers at the Swedish Baltic Sea coast in recipients of effluents from pulp mills and a domestic sewage treatment plant as well as remote reference sites. No sings of endocrine disruption were observed at any site, when studying gonad development or marker proteins, except for a deviation of sex ratios at a reference site. The three-spined stickleback – with focus on the juvenile stage – was found to be a sensitive species suitable for the study of estrogenic and androgenic endocrine disruption.

The focus of this thesis is the early detection of stress in the environment. It has been proposed that studies on the cellular level would detect stress reactions earlier in time compared to common physiological methods. In a series of experiments we investigated how different stress factors, both natural and introduced by man, affect levels of stress proteins. One- and two-dimensional gels were used to determine individual proteins and families of proteins. The two-dimensional gels were also used in a proteomic approach, were the presence and absence of proteins after treatment was observed, and the protein expression signatures (PES) were identified. Baltic Mytilus edulis was used in all experiments and it is evident that earlier observed differences in physiological rates and pollution sensitivity, compared to marine mussels, is also manifested as lower concentrations of stress proteins after exposure to copper and cadmium. When the Baltic mussels were allowed to acclimate for one month the difference decreased, suggesting an environmentally induced difference (paper I). Pre-exposure to heat before exposure to either a second heat-shock or cadmium was found to enhance the levels of HSP70 and thus tolerance, significantly (paper II). Exposure to a mixture of stress factors (PCB, copper and lowered salinity) revealed synergistic, additive and antagonistic effects in induction of 6 different stress proteins. When analyzing a large number of proteins it was shown that it is possible to identify PES with this technique, and we hypothesize that it could be possible to separate responses to mixtures of stress factors (Papers III and IV). Different techniques were also applied to analyze the protein expression pattern when mussels were exposed to PAH- and PCB-fractions extracted from Baltic Sea sediments. In this experiment the protein assays were accompanied by physiological measurements. All methods indicated stressed conditions, but the variation between individual mussels within treatments was smaller in terms of protein response than for physiological parameters (paper V). It is concluded that measuring the induction of stress proteins is a reliable way to detect stressful conditions. Proteins visualized on a one dimensional gel give a “gross” picture of an organism’s condition. The major challenge is to identify the origin and severity of the elucidated stress response. Further mapping of two-dimensional gels suggested that protein patterns are specific to type and level of stress. A most important future step is to establish links between sub-cellular protein response to well known physiological effects. This should include long term experiments where altered protein expression signatures are linked to life history characteristics like survival, growth and reproductive success.

In this thesis, I have studied long shoot performance in the monoecious, deciduous tree Betula pubescens ssp. czerepanovii. In field studies and a common garden experiment, I have a) studied how environmental variations affect the performance of long shoots in mountain birch, and b) described the relationship between long shoot performance and characteristics of the parent long shoot. I have shown that difference in long shoot performance to some extent can be explained by environmental variables such as temperature, precipitation and global radiation the current and previous summer, annual soil and air temperatures, and the length of growing season. For example, a low summer temperature the previous summer had a negative effect on a majority of long shoot characteristics. Variation in shoot characteristics was of the same magnitude along the regional east-western gradient as along the local altitudinal gradient. Variation among individual trees was of the same magnitude as variation among years. Further, long shoot performance was affected by the parent shoot characteristics and reflects that primordia of different organs are formed in the previous summer. On several occasions, freezing damage to mountain birch has been observed on Mt Njulla in northernmost Sweden. Following such damage, fewer but larger leaves emerge. Damages were compensated for with increased number of buds on long shoots produced the same year and one year after damage. Moreover, there were more new long shoots born on short shoots among damaged trees. Dormant buds and short shoots fulfil important functions in a fluctuating environment and as an adaptation to recurring damages of different origin and severity. Differences in the performance among mountain birch saplings grown in a common-garden at Abisko could to a large degree be explained by their origin. Further, saplings from Sweden and from Iceland responded differently to defoliation, and fertilization did not alter the responses to defoliation.

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Two decades ago the recruitment of YOY perch (Perca fluviatilis) started to decline along the Swedish east cost of the Baltic Sea. Factors that influence recruitment are e.g. eutrophication that causes habitat losses and overfishing of cod (Gadus morhua) which causes cascading effects in the food web. Filamentous cyanobacterial blooms are often toxic and has increased in the Baltic Sea and its coastal waters. The aim of this field study was to evaluate the effects of salinity and cyanobacterial exposure on fitness related parameters of young of the year (YOY) perch (Perca Fluviatilis) in a natural environment. Our study was performed in the Curonian Lagoon (Lithuania) in August 2009. The lagoon offers a temporary salinity gradient (wind induced influxes from the Baltic Sea) ranging from 7 psu in the north to 0 psu in the south. Submerged enclosures containing YOY perch were set up at three different locations along the salinity gradient in the Lagoon (referred to as North, Middle, South). The duration of the experiment was 21 or 27 days, depending on treatment. Measurements of perch condition were specific growth rate, somatic condition index (SCI) and whole fish lipid and protein content. Average chl a values for the three stations during the experimental time were: north 180 ± 70 µg/l chl a, middle 133 ± 36 µg/l chl a and south 180 ± 52 µg/l chl a. The North and the Middle stations experienced two different salinity influxes reaching a maximum salinity of 6.5 psu at the northern station. The duration of each saline influx was approximately 4-6 days. The saline water did not reach the Southern station at any time. Results show that perch from the southern station were in best condition in terms of specific growth rate and contents of total lipids. Compared to the South the perch condition declined to the Middle station and was lowest at the Northern station which experienced the highest degree of fluctuation in terms of salinity and cyanobacterial exposure. Examination of the abundance of the main food resource at the different stations revealed no statistical differences, which suggest that availability of food was not a factor in explaining the differences in growth.  The results possibly indicate that a changing environment with the potential synergistic negative effects of salinity and cyanobacteria has a higher negative impact on YOY perch condition compared to constantly high concentrations of cyanobacteria.