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Viele Vogelarten sind monogam, aber es kommt zugleich häufig zu Paarungen außerhalb des Paarbundes (Griffith et al. 2002). In einer großen Zahl von Studien wurde bereits der adaptive Wert der aus diesem Verhalten hervorgehenden „Fremdvaterschaften“, insbesondere für Weibchen, anhand einer Kosten-Nutzen-Analyse auf genetischer Ebene untersucht. Die Ergebnisse dieser Studien haben jedoch bisher nicht zu generalisierbaren Resultaten geführt (Akçay & Roughgarden 2007). Im Gegensatz dazu gibt es relativ wenig Informationen über verhaltensbegründete Kosten und Vorteile von Fremdvaterschaften, obwohl diese ein Verständnis der Mechanismen von Fremdverpaarungen erleichtern können. Die hier vorliegende Studie untersucht, wie zeitliche, räumliche, und soziale Faktoren beeinflussen wann, wo, und warum bestimmte Individuen Nachkommen mit einem anderen als ihrem sozialen Partner zeugen. Ich untersuche dies an der Blaumeise (Cyanistes caeruleus), einer Art, für die genetische Konsequenzen von Fremdvaterschaften bereits detailliert untersucht wurden, bei der die Kenntnisse im Bereich des außerpaarlichen Verhaltens selbst aber noch unvollständig sind. In den ersten beiden Studien stelle ich einen neuartigen Ansatz zur Untersuchung von Fremdvaterschaften vor und validiere diesen. Fremdverpaarungen erfordern als Beteiligte sowohl ein Weibchen als auch ein Männchen und beide können beeinflussen, ob eine Paarung stattfindet. In dem von mir vorgeschlagenen Ansatz werden nicht nur Informationen über das Individuum, sondern auch über potentielle und realisierte außerpaarliche Partner mit eingebunden. Bei Arten wie der Blaumeise, deren Territorien nicht nur in einzelnen, sondern in allen Aspekten des Brutverhaltens (Nahrungssuche, Balz, etc.) genutzt werden, sind Interaktionen räumlich oft auf Individuen aus nahegelegenen Territorien beschränkt. Auch außerpaarliches Verhalten zeigt eine solche Beschränkung. Im vorliegenden Ansatz werden daher räumliche Verhaltensstrukturen explizit in das Modell mit einbezogen. Um solche räumliche Verhaltensinformationen für einen Langzeitdatensatz über Brutverhalten (die hier eingesetzen Daten von Blaumeisen umfassen 12 Jahre und 2 Populationen) zu erhalten, ist es notwendig, im Nachhinein die Position der Territorien der Brutpaare abzuschätzen. In der Ökologie werden zu diesem Zweck immer häufiger Thiessen-Polygone eingesetzt (z.B. Wilkin et al. 2006, Valcu & Kempenaers 2008). Im 1. Kapitel (Chapter 1) belege ich daher zunächst die Gültigkeit einer solchen Abschätzung von Territorien mit Hilfe von Thiessen-Polygonen, basierend of 14 publizierten Studien, für die detaillierten Informationen über Territorien vorliegen. Im 2. Kapitel (Chapter 2) stelle ich dann den neuartigen Ansatz im Detail vor. Anschließend wende ich diesen auf den genannten Langzeitdatensatz an, nutze dabei Thiessen-Polygone als Approximation für die räumliche Beschränkung von außerpaarlichem Verhalten und untersuche gleichzeitig die Korrelation relevanter Parameter mit außerpaarlichem Fortpflanzungserfolg. Meine Resultate bestätigen die Ergebnisse früherer Studien und zeigen, dass dieser Ansatz genutzt werden kann, um Hypothesen zu testen, die mit bisherigen Methoden nicht statistisch robust überprüft werden konnten. Fremdverpaarungen können früh morgens stattfinden und aus einer Studie über die nahe verwandte Kohlmeise (Parus major) geht hervor, dass Weibchen, die ihren Schlafplatz morgens früher verließen, mit größerer Wahrscheinlichkeit außerpaarliche Nachkommen hatten. Im 3. Kapitel (Chapter 3) untersuche ich mit Hilfe von korrelativen Daten über vier Jahre diesen Zusammenhang für Blaumeisen. Darüber hinaus wurden die Aufstehzeiten von Weibchen über zwei Jahre hinweg experimentell manipuliert, um einen direkten kausalen Zusammenhang zwischen Aufstehzeiten und außerpaarlichem Fortpflanzungserfolg zu ergründen. Ich konnte keinen solchen Zusammenhang feststellen, jedoch führte das Experiment interessanterweise in den zwei Jahren zu entgegengesetzten Ergebnissen. Dies könnte ein Hinweis darauf sein, dass das Verhalten von Weibchen am frühen Morgen durchaus Relevanz für Fremdverpaarungen hat, dass jedoch eine Interaktion mit Umwelteinflüssen diese Zusammenhänge beeinflussen kann. Im 4. Kapitel (Chapter 4) beschreibe ich, dass Blaumeisen vor oder während der Legephase der Weibchen immer wieder die Nester fremder Paare besuchen. Für Männchen korrelierte dieses Verhalten auch mit ihrem außerpaarlichen Fortpflanzungserfolg. Es erwies sich nämlich, dass ein Männchen, welches das Nest eines Weibchens besucht, mit deutlich größerer Wahrscheinlichkeit außerpaarliche Nachkommen mit diesem Weibchen zeugt. Im Gegensatz zu einer früheren Studie an Blaumeisen (Kempenaers et al. 1992) zeigt dieses Ergebnis, dass nicht nur das Verhalten des Weibchens, sondern auch das des Männchens einen wichtigen Einfluss auf die außerpaarliche Fortpflanzung haben kann. Im 5. Kapitel (Chapter 5) betrachte ich abschließend das Balzverhalten der Blaumeisen. Dies erfolgt mittels Audioaufnahmen von Rufen, die speziell im Balzkontext eingesetzt werden (Bijnens & Dhondt 1984). Zunächst beschreibe ich das zeitliche Vorkommen dieser Rufe im Laufe der Brutsaison und im Tagesverlauf. Im nächsten Schritt vergleiche ich diese Daten mit früheren Studien, um zu verifizieren, dass Balzrufe tatsächlich als Maß für das Balzverhalten verwendet werden können. Anschließend untersuche ich dann speziell Balzrufe von Männchen, die in einem Kontext auftreten, der nahelegt, dass die Rufe nicht an das soziale Weibchen gerichtet sind. Es ist wahrscheinlich, dass diese (zu großen Teilen) außerpaarliche Balz anzeigen. Es gab keine Korrelation der „außerpaarlichen Balzversuche“ von Männchen mit ihrem außerpaarlichen Fortpflanzungserfolg, jedoch verloren Männchen mit vielen außerpaarlichen Balzversuchen weniger Vaterschaft in ihrem eigenen Nest. Dies könnte darauf hindeuten, dass die Qualität von Blaumeisenmännchen auf Verhaltensebene relevant für den außerpaarlichen Fortpflanzungserfolg ist. In der allgemeinen Einleitung (General Introduction) beschreibe ich detailliert den biologischen Hintergrund dieser fünf Studien. Weiterhin diskutiere ich die Relevanz von Studien im Bereich der Forschung über Fremdvaterschaften, die anstelle der rein genetischen Betrachtung darüber hinaus auch das Verhalten untersuchen. In der allgemeinen Diskussion (General Discussion) erörtere ich die Implikationen dieser fünf Studien für außerpaarliches Verhalten: Das zeitliche Vorkommen von Balz und Paarungen im Tagesverlauf und über die Saison hinweg, das räumliche Vorkommen, die relative Wichtigkeit des Verhaltens von Männchen und Weibchen und welche Faktoren beeinflussen, dass es zu Fremdverpaarungen zwischen einem ganz bestimmten Männchen und Weibchen kommt. / Most of the bird species that have to date been studied perform copulations outside the pair-bond (Griffith et al. 2002). A large body of literature is concerned with the investigation of genetic costs and benefits of such extra-pair paternity, for females in particular. However, results remain inconclusive (Akçay & Roughgarden 2007). The costs and benefits of extra-pair paternity in the behavioural domain have received much less attention, although this knowledge may help to understand the mechanisms which drive the patterns of extra-pair parentage that we observe. Here, I aim to investigate how the temporal, spatial, and social setting influences when, where, and why individuals have extra-pair offspring with one another. I investigate these proxies of extra-pair paternity in the blue tit, Cyanistes caeruleus, a species for which studies on genetic costs and benefits of extra-pair paternity are abundant, but the knowledge on the behavioural level is still incomplete. The first two studies propose and validate a novel approach for investigating extra-pair paternity patterns. Extra-pair paternity arises from extra-pair copulations. Therefore at least one male and one female are involved in the production of extra-pair offspring and they both can influence whether extra-pair copulations occur. The approach I propose therefore investigates not only an individual’s extra-pair paternity levels, but it also includes information on potential and realized extra-pair mates. In species with all-purpose territories (such as the blue tit), interactions are often majorly limited to individuals with close-by territories. This reduces the spatial scale at which extra-pair paternity occurs. For this reason, the approach I propose also includes spatial information which allows explicit modelling of the spatial framework in which extra-pair paternity occurs. To implement this spatial framework it was necessary to post-hoc estimate territories in our long-term dataset on blue tit breeding behaviour spanning over twelve years of data and two independent study populations. To this end I used Thiessen polygons, a method of growing importance in the field of ecology (e.g. Wilkin et al. 2006, Valcu & Kempenaers 2008). In Chapter 1, I validate the use of Thiessen polygons as an approximation for territories by comparing mapped territories from 14 published studies with the respective computed polygons. In Chapter 2, I propose and describe the novel approach in detail, and apply it to the long-term dataset. I define the spatial framework using Thiessen polygons as an estimate for territory sizes and locations, and investigate the correlation of several parameters with extra-pair paternity simultaneously. In short, I find that the proposed approach validates previous findings and at the same time allows testing hypotheses which previously could not be robustly tested. A study on great tits (Parus major) reported that females that emerged earlier in the morning from their roosting site were more likely to have extra-pair offspring. In Chapter 3, I test for this relationship using four years of correlational data. Additionally, I designed an experiment which advances female emergence times at dawn to robustly test for a direct causal link between emergence times and extra-pair paternity. I could not verify that emergence times immediately influenced female extra-pair paternity. The experiment led to opposite results in the two seasons, indicating that although female behaviour at dawn may have important consequences on extra-pair paternity, such effects may interact un unexpected ways with environmental conditions. In Chapter 4, I report on blue tits visiting other pair’s breeding nestboxes shortly before or during the egg-laying period of the female. I describe this behaviour and for males also link the behaviour to extra-pair paternity. I find that males that visit the nestbox of a female other than their social mate largely increase their chances of having extra-pair offspring with that female. In contrast to a previous study (Kempenaers et al. 1992) this suggests that not only female but also male behaviour influences the patterns of extra-pair paternity that we observe. Finally, in Chapter 5 I study the courtship behaviour of blue tits using sound recordings of specific calls that are uttered during courtships and copulations (Bijnens & Dhondt 1984). I describe the occurrence of calls throughout the day and season and validate that these courtship rates are similar to previously reported values. I then focus on courtship calls of territorial males which are apparently not directed towards the social female. These are likely to be – at least partly – extra-pair courtships. I therefore correlate the number of such presumed “extra-pair courtships” to male extra-pair gains and losses. I find no effect on extra-pair gains, but interestingly, males that performed more “extra-pair courtships” lost less paternity. This could indicate that on the behavioural level male quality may be important for the patterns of extra-pair paternity that we observe. In the General Introduction I present in detail the biological background for the five studies, and discuss the importance of studying extra-pair paternity not only from a genetic, but also from a behavioural perspective. In the General Discussion, I specifically address the behavioural implications of these five studies with regards to the daily timing, seasonal timing, and location of courtships or copulations. I then go on to discuss the importance of male vs. female behaviour in driving patterns of extra-pair paternity. Finally, I examine potential factors that may explain which individuals have extra-pair offspring with each other.

Behavioural ecologists aim at providing insights into the evolutionary and ecological processes that shape animal behaviour. Mate choice is a decision faced by most animals that can strongly affect an individual’s reproductive success, an important fitness component. This behaviour has therefore the potential to show many adaptations which have been the subject of a vivid research interest over the last decades. Studies on mate choice have typically focused on female preferences for traits that increase a male's overall attractiveness, which supposedly reflects the male’s absolute quality. Preferences for such traits are expected to provide females with benefits such as good paternal care or ‘good genes’ for their offspring. Nevertheless, in some species, individuals actually show little consensus on what represents a high-quality partner. Such individually-specific preferences are poorly understood, but it has been hypothesized that they have evolved to optimise genetic compatibility (to increase offspring viability) or, although rarely mentioned, to optimise behavioural compatibility (to facilitate joint parental care). The zebra finch is a life-time monogamous passerine whose mating preferences for putative quality traits have been widely studied but where no such quality indicator has been repeatedly shown to influence mating decisions. In this species, preferences seem instead largely idiosyncratic. In this thesis, I investigated whether female zebra finches choose genetically and/or behaviourally compatible social mates (Chapters 2 and 3). More precisely, I measured, in a large-scale breeding design, the fitness consequences of free mate choice for compatibility while experimentally controlling for effects of overall quality (Chapter 3). In this system, genetic incompatibility results in embryo mortality and therefore hatching failure, while behavioural incompatibility results in offspring mortality. I therefore expected social mate choice for genetic and/or behavioural compatibility to optimise embryo and offspring survival (Chapter 3). Moreover, I tested whether siblings who grew up together avoid choosing each other as social partner; in other words, if they avoid inbreeding depression by choosing a genetically more compatible partner (Chapter 2). In addition, I performed a meta-analysis of published experiments on zebra finches that allow for different mechanisms of kin discrimination to take place (Chapter 2). Finally, I investigated whether females enhance their extra-pair behaviour when paired to an apparently genetically incompatible male to obtain compatible genes benefits (Chapter 1). Indeed, extra-pair behaviour is largely hypothesized to be an adaptive response that would allow females to compensate for a potentially sub-optimal social mate choice. Specifically, I tested whether female extra-pair mating evolved as a counter strategy when females experience low hatching success with their social partner, that is to say whether female extra-pair mate choice targets fertility benefits and/or compatible genes benefits (Chapter 1). Contrary to all expectations derived from optimality, zebra finches were unable to identify partners with whom they would minimise embryo mortality (Chapter 3), or to recognize unfamiliar kin on the basis of genetic similarity per se to minimize inbreeding depression (meta-analysis of Chapter 2), and did not adjust their extra-pair mating behaviour in response to repeated hatching failure (Chapter 1). This suggests that, in zebra finches, individuals have not evolved any ability (other than avoiding familiar kin, experiment of Chapter 2) to judge genetic compatibility of any kind, despite the adaptive value of such behaviour. Finally, allowing free social mate choice did enhance pair fitness due to direct compatibility benefits (Chapter 3). This thesis provides therefore the first evidence of mate choice for behavioural compatibility. Nevertheless, the adaptive significance of the underlying choosiness remains speculative (Chapter 3). A null model consisting of random non-adaptive genetic variation in sensory systems and variation in phenotypes that are better at stimulating some sensory systems than others might well account for the observed fitness differences between compatible and incompatible pairs. This study highlights that there are limits to adaptation.

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Bacteria constantly need to monitor their environment and adapt the bacterial group-coordinated behaviour to changing habitats like nutrition alterations or host variations. Commonly cell-cell communication via acyl homoserine lactones (AHLs)is used to synchronise the behaviour of a bacterial population dependent on cell size. This process is referred to as quorum sensing (QS) and predominantly occurs in Gram-negative bacteria. The typical QS system consists of a LuxI-synthase that synthesises AHLs, and a LuxR-type receptor, which then responds to these AHLs. Upon AHL-binding, the LuxR-type receptor regulates the expression of different target genes and thus influences several processes, like biofilm formation, virulence, antibiotic production or cell-cell interaction. Interestingly, many proteobacteria possess additional LuxR homologs, but lack a cognate LuxI-type synthase. Those LuxR-type receptors are referred to as LuxR orphans or LuxR solos and can expand the regulatory QS network. Photorhabdus species are insect pathogenic bacteria, living in symbiosis with entomopathogenic nematodes. They all possess an exceptionally high number of LuxR solos, but lack LuxI homologs and therefore do not produce AHLs. The function of these LuxR solos, their role in cell-cell communication and the identification of their cognate signalling molecules in Photorhabdus species is the main focus of this work. In this thesis a novel signalling molecule used for QS could be identified for the first time in P. luminescens. This novel QS molecule is an α-pyrone named photopyrone (PPY) and produced endogenously by the photopyrone synthase (PpyS). The PPYs are specifically recognized by the LuxR solo regulator PluR, which then activates expression of the pcf (Photorhabdus clumping factor) operon leading to cell clumping of P. luminescens cells. Moreover, the PpyS/PluR quorum sensing system and its induced cell clumping contribute to the overall toxicity of P. luminescens. Furthermore, a second novel signalling molecule sensed by a LuxR solo of Photorhabdus species could be identified besides PPYs. The insect and human pathogenic bacteria P. asymbiotica lacks a PpyS homolog as well as a LuxI homolog, but harbours a pcf operon and a homologue to PluR, which is named PauR. The signalling molecule sensed by the LuxR-type receptor PauR could be identified, which is neither an AHL nor a PPY. PauR recognises a 2,5-dialkylresorcinol (DAR) produced by the DarABC pathway. Upon binding of the cognate signalling molecule, Summary XII PauR activates expression of the pcf operon. This also leads to cell clumping in P. asymbiotica. Furthermore, the DarABC/PauR QS system also contributes to the overall pathogenicity of P. asymbiotica against Galleria mellonella insect larvae. A bioinformatics approach revealed a high number of LuxR solos present in P. temperata and P. asymbiotica like in P. luminescens. Thereby, several conserved motives of amino acids could be identified, which are potentially important for signalbinding and -specificity. Variations in these amino acid motifs are assumed to reflect the overall variety of signals that can be sensed by LuxR solos. Furthermore, the specificity of the two LuxR solos PluR and PauR towards their cognate signalling molecules, PPYs and DARs, respectively, was analysed. Thereby, it could be shown that the previously identified conserved amino acid motives in the signal-binding domain (SBD), the TYDQCS-motif of PluR and the TYDQYI-motif of PauR, are essential but not sufficient for ligand-binding. Similar as for AHLs, it was unclear how the signalling molecules PPYs and DARs can cross the bacterial cell membrane. In the last part of this thesis the import mechanism for the Photorhabdus-specific signalling compounds PPYs and DARs were identified. Initial evidence could be provided that the membrane-integrated transporter FadL is mainly involved in the import of these hydrophobic compounds, and that they are not transported via simple diffusion across the cell membrane, which is assumed for AHLs. In conclusion, the data that is compiled presents two LuxR solos of Photorhabdus species adapted to sense and respond to novel non-AHL signalling molecules used for QS. Therefore, this thesis reveals that cell-cell communication via LuxR-type receptors goes far beyond AHL-signalling in nature.

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