Understanding the genetic basis of fitness differences has been a major goal for evolutionary biologists over the last two decades. Although there are many studies investigating how natural selection can promote local adaptation, few have succeeded to find the link between genotype and fitness of the phenotype. Polymorphic genes of the major histocompatibility complex (Mhc) are excellent candidates for such associations as they are a central component of the vertebrate immune system, playing an important role in parasite resistance, and hence can have direct effects on survival of their bearers. Although associations between Mhc and disease resistance are frequently documented, the epidemiological basis of the host-parasite interaction is often lacking and few studies have investigated the role that Mhc genes play in individual variation in fitness; thus comparatively little is known about the fitness consequences of Mhc in wild populations. Furthermore, the majority of work to date has involved testing associations between Mhc genotypes and disease. However, the mechanism by which any direct selection on the Mhc acts, depends on how genotypes map to the functional properties of Mhc molecules. The aim of this thesis was to characterize Mhc alleles in terms of their predicted functional properties and to investigate whether and how selection operates on Mhc class I functional variation using the great tit (Parus major) population at Wytham Woods as a model host species. Through a comprehensive characterization effort and the use of 454 pyrosequencing platform, I performed a detailed analysis of genetic variation at Mhc class I exon 3 and grouped alleles with similar antigen-binding affinities into supertypes to classify functionally distinct Mhc types. There was extreme complexity at the Mhc class I of the great tit both in terms of allelic diversity and gene number. A total of 862 alleles were detected from 857 individuals; the highest number yet characterized in a wild bird species. The functional alleles were clustered into 17 supertypes; there was clear evidence that functional alleles were under strong balancing selection. To understand the role of Mhc in disease resistance, I examined the linkage between Mhc supertypes, Plasmodium infection and great tit survival, and showed that certain functional variants of Mhc confer resistance to two divergent Plasmodium parasite species that are common in the environment. I further investigated the fitness consequences of functional variation at Mhc, using mark-recapture methods and long-term breeding data; and tested the hypotheses that selection: (i) maximizes Mhc diversity; (ii) optimizes Mhc diversity, or (iii) favours specific functional variants. I found that the presence of three different supertypes was associated with three different components of individual fitness: adult survival, annual recruitment probabilities and lifetime reproductive success. In contrast, there was no evidence for a selective advantage of Mhc functional diversity, either in terms of maximal or optimal supertype diversity. Finally, I explored the role that Mhc plays in female mate choice decisions and examined the reproductive fitness consequences of Mhc-dependent mating patterns. There was little evidence to suggest that functional dissimilarity at Mhc has any influence on female mate choice decisions or that dissimilarity at Mhc affects the reproductive output of the social pair. Overall, this thesis provides strong support for the suggestion that selection favours specific functional variants of Mhc, possibly as a result of supertype-specific resistance or susceptibility to parasites that exert strong selective pressures on their hosts; whereas there is no support for selection favouring maximal or optimal Mhc diversity. More importantly it demonstrates that functional variants of Mhc class I loci are an important determinant of individual fitness in natural populations.

The evolutionary processes that shape individual variation in continuous behavioural traits remain poorly understood. While the emerging discipline of animal personality is providing increasing evidence that consistent individual differences in behaviour have significant fitness consequences, cognitive traits are yet to be explored in the same manner. My general objective in this thesis was twofold. First, I aimed to examine the ecological significance and fitness consequences of the cognitive trait innovative problem solving-performance, using a population of great tits (Parus major). Second, I aimed to explore the mechanisms underlying the functional significance of ‘exploration behaviour’ a captive measure of the reactive- proactive personality axis, focusing specifically on foraging and risk-taking behaviour. This two-trait approach was expected to shed light on whether personality and cognition simultaneously influence fundamental behaviours. By carrying out behavioural assays on birds temporarily held in captivity, I showed that success at solving a food-motivated problem was repeatable within individuals, consistent between two different tasks and independent of exploration behaviour. Problem-solving performance was positively related to clutch size and fledgling number, established when birds were released back into the wild. Furthermore, when rearing offspring, solvers had shorter working day lengths than non-solvers and foraged over smaller ranges without compromising either provisioning quantity or quality. However, solver females were also more likely to desert their broods than non-solvers and consequently there was little evidence to suggest that directional selection acted on problem-solving performance. In comparison to non-solvers, solver males were also found to be poorer at competing for limited food resources during the winter. Together these findings suggest that costs and benefits are associated with problem-solving performance, which together may act to maintain variation in this trait. My thesis also provides some of the first evidence that exploration behaviour is related to both foraging and risk-taking behaviour in the wild. In comparison to relatively slow explorers, fast exploring males were better competitors at feeders during the winter. Relatively fast and slow explorers also differed in a number of foraging behaviours during offspring provisioning, although not always in the direction predicted from captive work on other populations. Finally, while exploration behaviour was positively correlated with risk- taking behaviour amongst breeding females during incubation, it did not predict nest desertion in response to the risk associated with being trapped by field workers. Collectively these findings suggest that personality measured in captivity has specific but not general power to predict behaviour in the wild. An important facet of evolution is that natural selection is rarely likely to act on a single trait in isolation owing to correlations between traits. This thesis demonstrates how important behaviours in the wild can be simultaneously linked to multiple sources of consistent behavioural variation. It also represents the first large-scale investigation of how variation in a cognitive trait relates to natural behaviour, reproductive life-history variation and fitness in wild animals. Using this individual-based approach in a natural setting may prove to be a useful tool for understanding how selection acts on cognitive traits.

Inbreeding occurs when relatives mate and have offspring. Inbreeding depression is hypothesized to have influenced the evolution of mating systems and behavioural mechanisms of inbreeding avoidance in the animal kingdom. Inbreeding in the wild is difficult to measure, as in order to build a pedigree allowing us to identify matings between relatives, the identity of as many as possible members of a population needs to be known. For a long time, the main source of knowledge about inbreeding depression was based on laboratory and agricultural studies, which did not reflect the array of environmental pressures wild populations have to cope with. In consequence, the deleterious consequences of inbreeding have often been underestimated. This is problematic because accurate estimates of the effect size of inbreeding depression are needed to study the strength of selection on inbreeding avoidance mechanisms, and are also of importance to conservation genetics. The aim of this thesis was to use pedigree data to infer the occurrence and effects of inbreeding using over forty years of breeding events of the great tit Parus major from Wytham Woods, Oxfordshire. The effects of inbreeding on fitness were investigated across a life-history continuum, and across environments. I found that close inbreeding (f=0.25) resulted in pronounced inbreeding depression, which acted independently on hatching success, fledging success, and recruitment success, and reduced the number of fledged grand-offspring by 55%. My results therefore suggest that estimates of fitness costs of inbreeding must focus on the entire life cycle. I also show that the variation in the strength of inbreeding depression varies across environments, particularly so the more the environmental variable considered is linked to fitness. These results emphasise the need of using relevant environmental contrasts when investigating inbreeding by environment interactions. I further asked whether individuals involved in matings with relatives differed relative to individuals mating with unrelated partners. I did not find any evidence for clear predictors of inbreeding, and I show that inbreeding depression in our population is entirely independent of any tendency for low quality parental genotypes, or phenotypes, to inbreed. Neither did I find any evidence for active inbreeding avoidance: great tits did not mate less often with kin than expected based on several scenarios of random mating, nor did I find increased rates of extra-pair paternity among birds breeding with relatives. In fact, I observed quite the contrary, as birds mating with kin exhibited a higher than average rate of close inbreeding relative to all scenarios of random mating investigated, showed lower rates of extra-pair paternity and divorce than birds mated to unrelated partners. I hypothesise that cases of occasional inbreeding in this population may result from mis-imprinting or a related process whereby some birds develop particularly strong bonds that are at odds with all predictions of avoiding inbreeding. Finally, I asked to what extent natal dispersal, a behaviour that is often hypothesized to play an important role in avoiding inbreeding, indeed reduces the likelihood of inbreeding. I found that male and female individuals breeding with a relative dispersed over several-fold shorter distances than those outbreeding. This led to a 3.4 fold increase (2.3-5, 95% CI) in the likelihood of close inbreeding relative to the population average when individuals dispersed less than 200m. This thesis demonstrates that inbreeding has deleterious effects on a wild population of birds, occurring throughout an individual’s life, and is of varying strength across environments. My findings strongly support the theory that natal dispersal should be considered as a mechanism of prime importance for inbreeding avoidance.

Abstract Animals need information about local conditions to make optimal fitness-enhancing decisions such as where to breed. Information can be acquired by personal sampling of the environment, but it can also be acquired from other individuals. The latter is termed social information use. Social information use has gained a lot of attention in modern ecology because it affects principal ecological phenomena such as animal distribution and resource use. Social information use is not restricted to obviously cognitive mammals and birds but is also found in e.g. reptiles, fish and insects. Social information use studies have thus far been concentrated on situations with one social information user and one (often the same) source species. The community-wide consequences of social information use have almost exclusively been considered in theoretical studies. In this thesis, I studied empirically social information use in the nest site selection within and between species in a cavity-nesting bird community consisting of the collared flycatcher (Ficedula albicollis), the great tit (Parus major) and the blue tit (P. caeruleus). I studied social information use on two time scales: social information gathered just before a breeding attempt, and social information gathered already during the previous breeding season for the following year’s breeding attempt. I used experiments in which different white geometric symbols represented nest site choices of earlier settled tutors and empty nest boxes, and I observed the symbol choices of later-breeding individuals. The symbol approach eradicates bias from innate and learned preferences enabling strong inference. My results demonstrate that collared flycatchers use social information from both con- and heterospecific tutors in different situations in a flexible manner. Hence, social information use seems to be context-dependent. Furthermore, I show that great tits avoid choosing nest site characteristics which were associated with either con- or heterospecifics nests the previous year and prefer symbols which depicted an empty nest box the previous year, probably to avoid nest ectoparasites. I also show that in great tits the male has greater influence on nest site selection than previously assumed even though the female builds the nest. My thesis deepens our understanding about the complexity of social information use and highlights its significance in future ecological research. / Tiivistelmä Eläimet tarvitsevat informaatiota paikallisista olosuhteista tehdäkseen edullisia päätöksiä esimerkiksi siitä, missä lisääntyä. Informaatiota voidaan hankkia tutkimalla ympäristöä itse, mutta sitä voidaan hankkia myös muilta yksilöiltä. Jälkimmäistä kutsutaan sosiaaliseksi informaatioksi. Eläinten sosiaalisen informaation käyttö on saavuttanut viime aikoina paljon huomiota ekologisessa tutkimuksessa, koska se vaikuttaa tärkeisiin ekologisiin ilmiöihin, kuten eläinten levinneisyyteen ja resurssien käyttöön. Sosiaalinen informaation käyttö ei rajoitu vain nisäkkäisiin ja lintuihin, vaan sitä on havaittu myös esimerkiksi matelijoilla, kaloilla ja hyönteisillä. Sosiaalisen informaation käyttöä on tutkittu lähes yksinomaan lajien sisällä tai käyttäen ainoastaan yhtä sosiaalisen informaation lähdelajia. Yhteisötason vaikutuksia on pohdittu miltei pelkästään teoreettisissa tutkimuksissa. Tässä väitöskirjatyössä tutkin kokeellisesti sosiaalisen informaation käyttöä pesäpaikan valinnassa lajin sisällä ja lajien välillä kolopesivien lintujen yhteisössä sepelsiepolla (Ficedula albicollis), talitiaisella (Parus major) ja sinitiaisella (P. caeruleus). Otin tutkimuksissani huomioon kaksi aikatasoa: tutkin juuri ennen pesimisyritystä kerätyn sekä jo edellisen lisääntymiskauden aikana seuraavan vuoden pesintää varten hankitun sosiaalisen informaation käyttöä. Kokeissani käytin linnunpönttöihin kiinnitettyjä erilaisia valkoisia geometrisia symboleita, jotka edustivat aiemmin pesinnän aloittaneiden lintujen eli tuutoreiden pesäpaikanvalintoja. Seurasin tämän jälkeen myöhemmin pesimään saapuvien parien symbolivalintoja. Tulosteni perusteella sepelsiepot hankkivat sosiaalista informaatiota sekä lajitovereiltaan että tiaisilta joustavasti eri tilanteissa. Lisäksi osoitan, että talitiaiset välttävät valitsemasta pesäpaikkoja, jotka olivat asuttuina edellisenä vuonna, ja suosivat sellaisia pesäpaikkoja, joissa ei pesitty edellisenä vuonna - todennäköisesti välttääkseen kirppuja ja muita pesäloisia. Osoitan myös, että talitiaiskoirailla on suurempi vaikutus pesäpaikan valintaan kuin aikaisemmin on oletettu, vaikka naaraat rakentavat pesän. Väitöskirjatyöni syventää käsitystämme sosiaalisen informaation käytön monitahoisuudesta eläinkunnassa ja korostaa sen merkitystä ekologisessa tutkimuksessa.

Avian malaria (Plasmodium spp.) is a popular model system to study the ecology and evolution of parasite-host-vector interactions in the wild. These studies have historically focused mostly on the avian hosts and the malaria parasites. Knowledge regarding the role of vectors is essential to our understanding of these wild systems, but has only very recently started to accumulate. This thesis aimed to contribute to this field by assessing mosquito-malaria-host associations for British mosquitoes and the role of mosquito ecology in shaping these parasite systems in a British woodland study site, using molecular, field ecology and statistical modelling methodologies. From the 12 mosquito species or species groups found, I showed that the Cx.pipiens/torrentium mosquito group is likely to have a major role in avian malaria transmission in Great Britain, while Cs. annulata may be transmitting P. circumflexum. I also demonstrated a positive spatial association between mosquito density per host and avian malaria prevalence, in accordance with theoretical expectations for malaria transmission. Findings here provide evidence that avian malaria transmission in British woodlands is limited mainly to June-August, being preceded by relapse of previous infections or, alternatively, by maintenance of chronic blood parasitaemia through the colder months; this agrees with theoretical expectations and findings elsewhere for temperate climates. This thesis also described local-scale spatial heterogeneity and seasonal variation in adult mosquito abundance within a British woodland where avian malaria is endemic, with differing patterns found between species or species groups. Spatially, variation in adult mosquito abundance was associated with microclimatic and landscape variables such as distances to mosquito breeding sites, microclimate and canopy height; seasonally, variation in mosquito abundance was associated with temperature and rainfall, alongside calendar date. The heterogeneity in mosquito parameters and associations with environmental variables found at a site where avian malaria is endemic highlights the need to anticipate such complexity when trying to understand Plasmodium transmission. By doing so, we further extend the potential of these parasite systems to improve our knowledge regarding the ecology and evolution of parasite-host-vector associations.