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Behaviourally driven mating system variation in blue tits
Get PDFIn birds, mating is central to fitness and thus key to understanding the evolution of any behaviour. There are two levels to understanding avian mating patterns. First, social mating systems are used as categories for species or populations. They describe the social units formed by males and females and arise from variation in sex role divergence. Evolutionary theory suggests that variation in social mating systems and sex role divergence emerge as a consequence of sex differences in optimal allocation patterns between time invested in mating and time invested in other activities, such as parental care. If sex role divergence is viewed as an evolutionary gradient, then the social mating system provides a guideline in which general area of this gradient a species can be found.
Second, as a consequence of phenotypic plasticity, the empirically realised mating patterns of a species may shift within that general area such that mating patterns diverge a fair amount among species with the same social mating system. In birds, both mating and parenting are fundamentally rooted in social behaviour, a key property of which is flexible, context‐dependent adjustment. Plasticity in mating behaviour is expected to be particularly relevant in species subjected to variable ecological conditions, in species with highly evolved social behaviour and in species with well developed cognitive skills, all three of which are typical for many bird species.
This thesis investigates how plasticity in mating behaviour influences mating patterns in a socially monogamous passerine, the blue tit Cyanistes caeruleus. Among socially monogamous species, the two most common modifications of the social mating system arise from adjustments in social bonds via facultative social polygyny and from adjustments in copulation patterns via extra‐pair paternity. The aim of the studies presented here is to elucidate the factors underlying individual adjustment of mating decisions in blue tits, focusing on within‐ and between‐individual variation in social associations, in familiarity, in experience and in age as well as in age‐related competitive effects.
Chapter 1 presents a descriptive study on the origin and outcome of facultative polygyny in the blue tit. Regarding the origin of facultative social polygyny, it is found that laying date is a good proxy for mating order and allows reliable identification of the primary and secondary female. Time constraints are probably important in the origin of facultative social polygyny, especially in the context of replacement polygyny, while local breeding density, variation in habitat quality and individual traits (body size, age and arrival date) are less relevant. Pre‐breeding interactions indicate that in the study population facultative social polygyny may arise, because secondary females prefer to associate with a familiar male or with a male at a familiar location. Chapter 1 also considers the immediate and longer‐term consequences of facultative social polygyny for individuals. Socially polygynous males have smaller clutches in each of their broods than socially monogamous males in their single brood, possibly due to female anticipation of reduced paternal care: socially polygynous males contribute less paternal care at each of their two nests and at both nests combined than socially monogamous males at their single nest. This may partially be a result of coordination costs, because socially polygynous males rarely divide parental care between their two nests and, if they do, they seldomly intermingle visits, but instead focus their care first on one brood and then on the other brood. Secondary broods are more likely to contain extra‐pair young and circumstantial evidence suggests that secondary female may have copulated with additional males, either when they were originally mated with another male, which then disappeared, or when they were attempting to establish a pair bond after mate loss. Fledging success is reduced for both primary and secondary broods, mainly due to a higher rate of nest failure. The net effect of social polygyny on male reproductive success is negligible in this study population: due to a combination of smaller clutches, higher paternity loss and reduced fledging success socially polygynous males sire a similar number of fledglings as socially monogamous males. Facultative social polygyny then probably reflects females under time constraints making the best of a bad situation, whereby social inertia and the fundamental mechanisms of settlement and pair bonding determine the behavioural options available to males and females.
Chapter 2 explores the effect of male age on extra‐pair siring success. Age is the most consistent predictor of plasticity in mating success via extra‐pair paternity across studies, but the effect is not well understood. The analysis in Chapter 2 separates within‐ from between‐individual effects and establishes that in the study population extra‐pair siring success increases, when a male moves from yearling to older age. The shape of the age trajectory indicates that there is no ongoing improvement after that and, in comparison to the initial change, negligible senescence. There thus is a threshold effect mediated via age class that separates yearling from older individuals, an effect later also found for other traits relevant for reproduction (clutch size, arrival date; Appendix 2). A literature review also suggests that the consistency of the age effect across studies may be driven by a similar threshold in other species. Interestingly, the occurrence of extra‐pair paternity in a nest is independent of the age of either the male or the female tending the nest. The threshold effect observed between naïve yearlings and older individuals points to an influence of experience or of incomplete maturation on male competence or on female preferences when either males or females are seeking extra‐pair copulations.
Chapter 3 seeks to test, if the age effect on extra‐pair siring success studied in Chapter 2 is based on absolute or relative processes. That is, due to selection for life history optimisation or due to developmental constraints, yearlings may be incapable, incompetent or fundamentally unattractive in the extra‐pair context, independent of their social surroundings. For instance, learning to perform territory defence and courtship may fully absorb their time or energy reserves, preventing them from investing additionally in extra‐pair behaviour. Alternatively, yearlings may only fail, when inhibited by older males, because these directly or indirectly affect their success in competition or mate attraction.
To separate these two processes, Chapter 3 presents a large‐scale field manipulation which altered the presence of older males in the population. Removal of older males in the months preceding the breeding season created a population of breeding males in 2022 that consisted almost exclusively of yearlings. Following a preregistered research plan, the effects of the manipulation on the extra‐pair siring success of yearlings, on the population‐wide frequency of extra‐pair paternity and on the spatial patterns of extra‐pair paternity were inspected. While extra‐pair siring success of yearlings increased, the rate of extra‐pair paternity and its spatial organization remained unaffected. At the same time, the rate of polygyny increased. These results support the idea that yearlings can be as successful as older males in siring extra‐pair young, if the latter are not present. In the study population the age effect on extra‐pair paternity is likely to be mediated by social effects of competition between age classes.
Taken together, the results presented in the three chapters of this thesis emphasize the interacting roles of social effects, experience and age in modulating social bonds (via facultative social polygyny, Chapter 1 and Chapter 3) and copulation patterns (via extra‐pair copulations, Chapter 2 and Chapter 3) in a socially monogamous bird species. They indicate that the social mating system is not fixed, but flexible, and that behavioural plasticity is an important ingredient in shaping mating patterns in nature. Empirical studies can therefore contribute important insights that add to the theoretical underpinning provided by modelling approaches and further our understanding of avian mating systems
Interaction of closed strings with non-perturbative objects
Get PDFStreuamplituden stellen eine Verbindung zwischen experimenteller und theoretischer Physik her, weil der resultierende Wirkungsquerschnitt zur Überprüfung theoretischer Vorhersagen in Experimenten verwendet werden kann. Darüber hinaus können Streuamplituden genutzt werden, um Erkenntnisse über die Struktur der zugrunde liegenden Theorie zu erhalten. Da die Stringtheorie eine konsistente Theorie der Quantengravitation darstellt, sind insbesondere Gravitationsamplituden phänomenologisch interessant. Die ersten Quantenkorrekturen zur Einstein-Hilbert-Wirkung der Stringtheorie können durch Streuamplituden mit der Kreisscheibe oder der reellen projektiven Ebene als Weltflächen beschrieben werden und beinhalten nicht-perturbative Objekte wie Dp-Branen bzw. Op-Ebenen.
In dieser Dissertation untersuchen wir diese Amplituden. Für beide Konstellationen geben wir eine Vorschrift zur Berechnung der allgemeinen n-Punkt-Amplitude an und diskutieren die Auswirkungen dieser nicht-perturbativen Objekte auf die Welftflächen-Felder. Explizit berechnen wir die Streuamplituden von drei geschlossenen Strings auf der Kreisscheibe und der reellen projektiven Ebene im Pure Spinor Formalismus. Für beide Amplituden wird die analytische Fortsetzung berechnet, um die holomorphen und antiholomorphen Koordinaten der geschlossenen Strings auf den Weltflächen unabhängig voneinander betrachten zu können. Aufgrund der Verzweigungsstruktur des Koba-Nielsen-Faktors müssen Monodromien berücksichtigt werden, so dass wir kompakte Ergebnisse für die Streuung von drei geschlossenen Strings für beide Weltflächen erhalten. Letztendlich können beide Streuprozesse durch Amplituden von sechs offenen Strings auf der Kreisscheibe beschrieben werden. Mit Hilfe dieser Ergebnisse versuchen wir, unsere Erkenntnisse zu verallgemeinern und einen Ansatz für die Streuung von n geschlossenen Strings an einer Dp-Brane herzuleiten, der die allgemeine Struktur der Amplitude auf der Kreisscheibe beschreibt. Diese Verallgemeinerung für eine beliebige Anzahl geschlossener Strings kann durch Amplituden mit 2n offenen Strings ausgedrückt werden.
Diese Amplituden beschreiben gravitative Wechselwirkungen auf Baumniveau in Anwesenheit einer Dp-Brane oder Op-Ebene. Deshalb entwickeln wir die Amplitude von drei geschlossenen Strings auf der Kreisscheibe in der inversen Stringspannung und können so relevante gravitative Dp-Branen-Kopplungen analysieren, die mit Korrekturen zur Einstein-Hilbert-Wirkung verbunden sind. Außerdem vergleichen wir die String-Amplitude mit den feldtheoretischen Ergebnissen, die wir von der Dirac-Born-Infeld-Wirkung erhalten haben. Gleichzeitig können wir damit die Konsistenz unserer Berechnungen überprüfen.Scattering amplitudes provide a connection between experimental and theoretical physics, as the corresponding cross section can be used to check theoretical predictions in experiments. In addition, scattering amplitudes can be used to gain insight on the structure of the underlying theory. Since string theory provides a consistent theory of quantum gravity, especially gravitational amplitudes are phenomenologically interesting in this context. The first quantum corrections to the Einstein-Hilbert action of string theory can be captured by scattering amplitudes with the disk or the real projective plane as worldsheets and involve non-perturbative objects namely Dp-branes and Op-planes, respectively.
In this thesis we investigate these kinds of amplitudes: For both setups we provide an amplitude prescription for the general n-point amplitude and discuss the implications of these non-perturbative objects on the worldsheet fields. Explicitly, we calculate the scattering amplitudes of three closed strings on the disk and real projective plane in the pure spinor formalism. We analytically continue both amplitudes to disentangle the holomorphic and antiholomorphic closed string worldsheet coordinates on the disk and real projective plane. By introducing monodromy phases arising form the branch cut structure of the Koba-Nielsen factor we arrive at compact expressions for the scattering of three closed strings on the disk and real projective plane. In the end, both scattering processes can be described in terms color ordered amplitudes of six open strings on the disk. Using these results we try to generalize our findings and provide an ansatz for the scattering of n closed strings from a Dp-brane, which encompasses the general structure of the disk amplitude. This generalization for any number of closed strings can be written in terms of color ordered open string amplitudes involving 2n open strings.
Since these amplitudes probe tree-level gravitational interactions in the presence of a Dp-brane or Op-plane, we carry out the low energy expansion in the inverse string tension of the three-point disk amplitude and analyse some relevant gravitational Dp-brane couplings associated to corrections of the Einstein-Hilbert action. In particular, we compare the string amplitude to the analogue field theory calculation obtained from the Dirac-Born-Infeld action and thereby provide a consistency check for our calculations
Charge correlations in quantum simulation of mixed-dimensional Hubbard systems
Get PDFThe complex nature of strongly correlated materials, as the high-temperature superconducting cuprates, has proven to be a challenge in both theoretical and experimental studies for decades. With the advent of quantum simulation, new tools have emerged for the investigation of quantum systems on a microscopic level. Ultracold atoms confined in optical lattices offer an excellent platform for exploring strongly correlated phenomena in the minimal Fermi-Hubbard model. Starting from an antiferromagnetically ordered state, the intricate interplay between spin and charge degrees of freedoms in doped systems is supposed to be at the centre of collective effects such as paired states. Nevertheless, the ground state of the plain Fermi-Hubbard model is currently suspected to not be superconducting, instead favouring the formation of a charge density wave known as a stripe phase.
In this thesis, we leverage the capabilities of a quantum simulator with ultracold fermions to investigate the formation of stripes in the Fermi-Hubbard model. Under normal conditions, the temperature scales associated with stripe phases fall well beyond the limits of current state-of-the-art quantum simulators. Therefore, we adopt a specific mixed-dimensional setting, where tunnel couplings are restricted to one direction, while spin exchange coupling persists along both, thereby elevating the onset temperature of stripes to approximately the superexchange energy. Using single-site spin and charge resolution, we observe extended, fluctuating charge structures in the system, indicative of the presence of stripes. Moreover, signatures in the spin sector are consistent with local antiferromagnetic domains that change sign across stripes.
To access this mixed-dimensional regime, we designed, implemented and characterised a novel, highly-stable optical superlattice. By combining a bichromatic approach and enhanced environmental decoupling via evacuation and utilising appropriate materials, we achieve cutting-edge phase stability. Furthermore, we attain fast and wide tunability of the relative superlattice phase using two complementary methods. We characterise the setup using single and two-particle quantum walks, Rabi oscillations as well as spin correlations.
These results establish the groundwork for further investigations into the nuances of the stripe phase and other exotic low-temperature phases of the Fermi-Hubbard model. Finally, beyond its implications for quantum simulation, this endeavour signifies a stride towards a future fermionic quantum computing platform.Stark korrelierte Systeme, insbesondere im Zusammenhang mit Hochtemperatursupraleitung, stellen eine Herausforderung sowohl für theoretische als auch experimentelle Studien dar. Mit der Entstehung des Felds der Quantensimulation sind neue Werkzeuge zur präzisen Untersuchung quantenmechanischer Systeme entstanden. Ultrakalte Atome in optischen Gittern bilden eine herausragende Plattform für Studien solch stark korrelierter Phänomene mittels des minimalen Fermi-Hubbard Modells. Ausgehend von einem antiferromagnetisch geordneten Zustand wird vermutet, dass das komplexe Zusammenspiel zwischen Spin- und Ladungsfreiheitsgraden in dotierten Systemen im Mittelpunkt kollektiver Effekte wie gepaarter Fermionen steht. Allerdings ist im Moment der Konsens, dass der Grundzustand des einfachen Fermi-Hubbard Modells nicht supraleitend ist, sondern stattdessen eine Ladungsdichtewelle bildet, die als Streifenphase bezeichnet wird.
In dieser Arbeit nutzen wir einen hochauflösenden Quantensimulator mit ultrakalten Fermionen, um die Bildung von Streifen im Fermi-Hubbard-Modell zu untersuchen. Unter normalen Bedingungen liegen die Temperaturskalen für Streifenphasen weit unter dem derzeitigen Stand der Technik für Quantensimulatoren. Daher wählen wir eine spezifische Konfiguration, bei der Tunnelkopplungen nur entlang einer Richtung vorhanden sind, während der Spin-Austausch entlang beider Richtungen erfolgt, was die Temperatur, bei der Streifen beginnen aufzutreten, auf etwa die Spinwechselwirkungsenergie erhöht. Mittels der Spin- und Dichteauflösung bis zu einzelnen Gitterplätzen messen wir ausgedehnte, fluktuierende Ladungsstrukturen, die auf die Anwesenheit eines Streifens hindeuten. Darüber hinaus sind Signaturen im Spinsektor konsistent mit lokalen antiferromagnetischen Domänen, die über Streifen hinweg ihr Vorzeichen ändern.
Um auf dieses Kopplungsregime zugreifen zu können, haben wir ein neues, hoch-stabiles optisches Übergitter entworfen, implementiert und charakterisiert. Durch die Kombination eines bichromatischen Ansatzes mit verbesserter Entkopplung von der Umgebung mittels Evakuierung und spezifischen Materialien erreichen wir eine herausragende Phasenstabilität. Zusätzlich wird eine schnelle und breite Abstimmbarkeit der relativen Übergitterphase via zweier komplementärer Methoden erzielt. Wir charakterisieren den Aufbau mittels Ein- und Zwei-Teilchen-Quantenspaziergängen, Rabi-Oszillationen sowie Spin-Korrelationen.
Mit diesen Verbesserungen haben wir die Grundlagen für weitere Studien zu Details der Streifenphase sowie anderer exotischer Tieftemperaturphasen des Fermi-Hubbard-Modells gelegt. Neben der Relevanz für die Quantensimulation stellt dies außerdem einen Schritt hin zu einer zukünftigen fermionischen Quantencomputer-Architektur dar
Anwendungsmöglichkeiten optischer Untersuchungsmethoden bei Erkrankungen im Hals-Nasen-Ohrenbereich
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