Rapid advances in the aquaculture industry pose an environmental challenge that is generated by outbreeding between escaped domesticated and wild individuals. Given that escapees genetically differ from wild individuals because of domestication and possibly by ancestry, periodic domesticated-wild outbreeding has the potential to influence fitness-related traits in wild populations. In Atlantic salmon (Salmo salar), the understanding of mechanisms and direction of domesticated influences are especially important because of the conservation concerns associated with many wild populations, notably in the southern parts of their North Atlantic range. My thesis investigates domestication-induced, genetically based changes during the parr stage by assessing growth, parr maturity and survival under predation for three salmon strains differing in their history of domestication, as examined in two semi-natural environments (predator present, absent). Growth and size-at-age increased with increasing generations of domestication, yet male parr maturation probability declined. Survival under gape-limited predation increased with domestication-conveyed increases in size and growth rate. Domesticated but not wild individuals exhibited stress-resistant growth in the presence of a predator. To assess mechanism and magnitudes of trait changes resulting from domesticated-wild outbreeding, a domesticated strain was crossed with a wild population (up to third-generation hybrids) and outbreeding effects were studied for different life stages, several controlled environmental laboratory conditions, and traits. Life stages included the developmental periods between egg and fry, and between immature and adult post smolts. Traits assessed included survival, yolk conversion efficiency, size-at-age, maturation probability, growth rate, mRNA transcript levels and their environmental plasticity. For many traits, both additive and non-additive genetic components in the between-population genetic architecture were revealed by cross means analyses. Furthermore, maternal outbreeding effects on early life stages were present. Altogether the results indicate that constant outbreeding effects of escapees on wild populations will increase present growth rates during all life stages and decrease early maturation probabilities for male parr and post-smolts, but by unpredictable magnitudes across hybrid generations. Maternally controlled co-adapted traits might be disrupted in hybrid mothers. Further, mixed-origin individuals might be temporarily at an advantage relative to wild individuals because of size and growth advantages and these might accelerate a wild genotypes displacement.

Habitat fragmentation is one of the main threats to semi-natural grasslands all over Europe, causing reductions in both numbers of populations and numbers of individuals withinpopulations. Small isolated populations are particularly vulnerable to fluctuations that reducespopulation size and could lead to loss of genetic variation due to inbreeding depression, orfixation of harmful alleles due to genetic drift. The aim of this study was to investigate if thecritically endangered eyebright Euphrasia stricta var. suecica experiences pollen limitation,inbreeding depression and heterosis or outbreeding depression. Low pollen limitation waspredicted as well as low inbreeding depression due to high selfing rate. Outbreedingdepression or heterosis was expected based on previous studies indicating strong geneticdifferentiation among populations. This study was conducted in two traditionally managedmeadows in the central part of Gotland, Sweden, using supplemental hand-pollinations andcontrolled crosses. Individuals were collected when the flowering period was over and seedswere counted and weighed. There were no signs of either pollen limitation, inbreedingdepression, heterosis or outbreeding depression in any of the two wooded hay meadows. Thedegree of autonomous selfing was high, indicating that E. stricta var. suecica is not dependenton pollinators for seed production. A significant difference between the meadows was foundin proportion of viable seeds. As there were no signs of local adaptation, individuals could betranslocated between the two studied populations or seed sowings could be used to increasepopulation size. However, before such conservation efforts are undertaken, it is important toconduct further studies that investigate several populations including more life-stages.

<p> </p> <p>The degree of self-fertilization in a population determines levels of genetic variation and high selfing rates could thus limit future adaptive potential. Theory predicts that intermediate selfing rates should not persist, yet many plants exhibit mixed mating. Cleistogamy is a floral heteromorphism where individuals produce both showy potentially outcrossing chasmogamous flowers and closed obligately selfing cleistogamous flowers. Reproduction via cleistogamous flowers is thought to be beneficial because of their greater energetic economy compared to chasmogamous flowers but can be costly if selfing leads to inbreeding depression or accelerates the fixation of deleterious mutations within populations. Cleistogamy has evolved independently multiple times and can be used to study the maintenance of adaptive mixed mating. To investigate this, I estimated the costs and benefits of selfing in three populations of <em>Ruellia humilis </em>Nutt (Acanthaceae) in greenhouse common garden experiments. To quantify the costs, I performed hand pollinations and quantified fitness components of progeny resulting from selfing and outcrossing within- and between-populations. To quantify the relative energetic advantage of cleistogamous flowers, I measured dry flower mass, fertility, seed number per fruit, and pollen-ovule ratios of both types of flowers. I found negative cumulative inbreeding depression in all populations, indicative of selfed progeny outperforming outcrossed progeny. While the fitness consequences of between population outcrossing ranged from heterosis to outbreeding depression. When looking at the energetic benefits of selfing, I found that the cost of reproduction via cleistogamous flowers was between 3 and 14-fold less than the cost for outcrossing flowers. Finally, I combined data on inbreeding depression and the energetic costs of reproduction and found that chasmogamous flowers of <em>R. humilis </em>must provide between a 3 to a 45-fold fitness advantage to be maintained, the magnitude of which was dependent upon maternal population. Overall, I conclude that none of the existing hypotheses are sufficient enough to provide the selective advantage needed to explain the persistence of chasmogamous flowers in <em>R. humilis</em>. Without any supported explanations for the maintenance of mixed mating, the exploration of genetic constraints on the loss of chasmogamous flowers could solve this long-standing mystery. </p>

The long-term genetic consequences of supportive breeding programs are not well understood. Nevertheless, stocking populations with hatchery-produced fish to compensate for losses of natural production are common practice, for example after constructions of hydroelectric power dams. Hatcheries typically fertilize eggs using ‘mixed-milt fertilizations’, without consideration to natural reproductive behaviours, and hence, natural selective regimes would be altered. Here, a series of experiments with focus on Mhc and mate choice in a population of brown trout (Salmo trutta L.) with a history of long-term stocking are presented. The major histocompatibility complex (Mhc) constitutes of genes coding for antigen presentation in the vertebrate immune system. In addition to the immunological function, Mhc genes might also influence reproductive behaviours such as mate choice. For example, in some species individuals are able to recognize Mhc genotypes of potential mates and to some extent base their mate choice on this information. Here, I address these questions on brown trout. Can the phenomena be observed in brown trout? Could such mechanisms help individuals to avoid inbreeding, or are other mechanisms important? How does the artificial rearing of fish for enhancement of natural populations relate to these issues? The results presented here, in combination with previous work, shows that several factors are important in the process of pair formation in salmonid species. For example, females of the studied population used more than a single criterion when choosing among the available mates Mhc genes and males with certain Mhc genotypes achieved more matings, possibly an effect from increased fighting ability. Further, the population appears to contain an unnatural high level of Mhc variation, and some results indicate that the population might suffer from outbreeding depression at the Mhc. These negative effects are most likely derived from compression of sub-populations after dam-construction, in combination with supportive breeding with no consideration to natural spawning behaviour.