11163 research outputs found
Sort by
Female fitness in wild Assamese macaques (Macaca assamensis)
No full textVariation in Fitness entsteht durch das Zusammenspiel von life-history-bedingten
Einschränkungen sowie sozialer und ökologischer Variabilität. Bei langlebigen,
langsam reproduzierenden Arten wie Primaten wirken Selektionsdrücke auf
Fitnesskomponenten wie Reproduktion über mehrere Lebensstadien hinweg und
beeinflussen so den Zeitpunkt, die Qualität und die Quantität der
Reproduktionsinvestitionen. In saisonalen Umgebungen stellen schwankende
ökologische Bedingungen zusätzliche Herausforderungen für Weibchen dar und
können Reproduktionsstrategien begünstigen, die Investitionen unter zeitlichen
Einschränkungen optimieren. Theoretische Modelle aus der life-history- und
sozioökologischen Forschung liefern starke Vorhersagen darüber, wie Trade-offs in
der Natur wirken sollten, jedoch sind empirische Daten aus Wildpopulationen,
insbesondere von saisonalen Reproduzenten, nach wie vor selten.
In dieser Dissertation untersuche ich die Einflussfaktoren weiblicher Fitness bei
wildlebenden Assam-Makaken (Macaca assamensis), einem strikt saisonalen
Reproduzenten, der in einer Umgebung mit schwankenden Ressourcen lebt. Mithilfe
von Langzeitdaten, die über zwei Jahrzehnte im Phu Khieo Wildlife Sanctuary in
Thailand gesammelt wurden, analysiere ich, wie soziale und ökologische Faktoren in
Kombination mit intrinsischen life-history-Einschränkungen zwei zentrale
Fitnesskomponenten beeinflussen: Reproduktionserfolg und Überleben. Während
soziale und ökologische Faktoren und deren Einfluss auf Fitness ein zentrales Thema
der Verhaltensökologie sind, haben die meisten Studien bisher ihre unabhängigen
Effekte getestet, jedoch häufig auf potenzielle Interaktionen hingewiesen. In dieser
Dissertation schließe ich diese Lücke, indem ich die Interaktionseffekte explizit teste
und prüfe, ob soziale Dynamiken ökologische Einflüsse auf die weibliche Fitness
verstärken oder abmildern.
In Kapitel 2 liegt der Fokus zunächst auf den life-history-bedingten Einschränkungen,
und ich untersuche das Vorhandensein des Trade-offs zwischen Anzahl und Qualität
der Nachkommen in dieser Population. Konkret habe ich getestet, ob Investitionen in
viele Nachkommen (gemessen anhand der Geburtenintervalle, IBI) zulasten der
Qualität (gemessen als Überleben) der Nachkommen gehen. Meine Ergebnisse liefern
Evidenz für diesen Trade-off: Das Überleben von Säuglingen war reduziert, wenn
Mütter während der Stillzeit des aktuellen Nachwuchses erneut empfingen oder in
zukünftige Reproduktion investierten. Zudem zeigte sich, dass Weibchen mit jungen
abhängigen Nachkommen seltener empfingen und die
Empfängniswahrscheinlichkeit mit dem Alter des Säuglings anstieg, was auf
energetische Einschränkungen hinweist. Weiterhin untersuchte ich den Einfluss
kurzer IBIs auf das Timing der Reproduktion und stellte fest, dass Weibchen nach
kurzen IBIs später in der Paarungszeit empfingen, was auf einen Erholungsbedarf
und das Erreichen einer guten körperlichen Verfassung für eine erneute Reproduktion
hindeutet. Diese Ergebnisse deuten darauf hin, dass maternale Erschöpfung dem
beobachteten Trade-off zwischen Anzahl und Qualität zugrunde liegt. Außerdem
beeinflusste das Alter der Weibchen die Empfängniswahrscheinlichkeit: Jüngere
Weibchen zeigten in den ersten Reproduktionsjahren eine geringere
Empfängniswahrscheinlichkeit, was wahrscheinlich den Ausgleich zwischen
somatischem Wachstum und früher Reproduktion widerspiegelt. Es zeigten sich
zudem Anzeichen reproduktiven Alterns. Insgesamt legen diese Ergebnisse nahe,
dass die Reproduktionsinvestitionen weiblicher Assam-Makaken durch intrinsische
life-history-Trade-offs limitiert sind.
In Kapitel 3 untersuchte ich die sozialen und ökologischen Einflussfaktoren und
analysierte, ob Variabilität in der Umwelt und soziale Dynamiken den
Reproduktionserfolg beeinflussen. Aufbauend auf der sozioökologischen Theorie
testete ich konkret, ob Dominanzrang, soziale Bindungsstärke, soziale Integration,
Gruppengröße und Fruchtverfügbarkeit in Wechselwirkung die jährliche Empfängnis
und das Überleben von Säuglingen beeinflussen. Entgegen meinen Vorhersagen fand
ich keinen Effekt ökologischer und sozialer Faktoren wie Rang, Bindungsstärke,
soziale Integration oder Gruppengröße auf die Empfängnisraten. Das Vorhandensein
eines jungen abhängigen Nachkommen war der stärkste Prädiktor für die
Empfängniswahrscheinlichkeit und unterstreicht erneut die Rolle energetischer und
physiologischer Bedingungen. Für das Überleben der Säuglinge fand ich keinen
Einfluss sozialer Faktoren, aber die Fruchtverfügbarkeit im ersten Lebensjahr des
Säuglings sagte das Überleben positiv voraus und betont damit ökologische Einflüsse.
Das Vorhandensein eines nahen jüngeren Geschwisters hatte einen negativen Effekt
auf das Säuglingsüberleben. Dies deutet darauf hin, dass das Überleben der Säuglinge
vermutlich sowohl durch maternale Investitionen als auch durch den eigenen
Nahrungserwerb eingeschränkt ist. Die Ergebnisse dieses Kapitels unterstreichen
erneut den starken Einfluss intrinsischer Trade-offs auf den Reproduktionserfolg
weiblicher Assam-Makaken, mit begrenztem Einfluss ökologischer Variabilität.
In Kapitel 4 habe ich die Analyse auf eine weitere wichtige Fitnesskomponente
ausgeweitet: das Überleben der Weibchen. Unter Verwendung der jährlichen
Überlebenswahrscheinlichkeit als Zielvariable habe ich untersucht, wie Prädiktoren
des Vorjahres – darunter soziale Bindungsstärke, soziale Integration,
Fruchtverfügbarkeit, Dominanzrang und Gruppengröße sowie deren Interaktion –
das Überleben unter Berücksichtigung des Alters beeinflussen. Im Einklang mit der
life-history-Theorie war das Alter der dominierende Prädiktor für die Mortalität:
Ältere Weibchen zeigten eine höhere Sterbewahrscheinlichkeit. Die meisten sozialen
und ökologischen Prädiktoren zeigten keine nachweisbaren Effekte, jedoch zeigte die
Stärke der sozialen Bindung eine schwache positive Assoziation mit der
Überlebenswahrscheinlichkeit. Dies deutet darauf hin, dass es möglicherweise einen
langfristigen oder kumulativen Nutzen starker sozialer Bindungen gibt, der
kurzfristig nicht erfasst wurde. Diese Ergebnisse legen nahe, dass das Überleben
weiblicher Assam-Makaken nicht stark von kurzfristigen Umwelt- oder
Sozialvariationen beeinflusst wird.
Die Gesamtergebnisse dieser Dissertation zeigen, dass Reproduktionserfolg und
Überleben bei weiblichen Assam-Makaken weitgehend durch energetische und life
history-Faktoren eingeschränkt sind, weniger durch unmittelbare soziale Dynamiken.
Obwohl soziale Beziehungen in vielen gruppenlebenden Arten ein wichtiger
Prädiktor für Fitness sind, könnten sie bei Arten mit strikter
Reproduktionssaisonalität eher sekundär gegenüber ökologischen Druckfaktoren
und intrinsischen life-history-Trade-offs sein. Durch die Kombination ökologischer,
sozialer und individueller Daten über einen langen Zeitraum hinweg und das Testen
nicht nur unabhängiger Effekte sozialer und ökologischer Prädiktoren, sondern auch
ihrer Interaktionen, versucht meine Dissertation, die Komplexität der Beziehungen
zwischen verschiedenen Variablen und deren Einfluss auf Fitnessergebnisse
abzubilden. Auch wenn die Interaktionseffekte nicht immer signifikant waren, ist
deren explizite Testung entscheidend für den Fortschritt der sozioökologischen
Theorie, und zukünftige Forschung sollte soziale, ökologische und life-history
Rahmen stärker integrieren, um die Fitness bei Primaten besser zu verstehen.Variation in fitness arises from the interaction of life-history constraints and social and
environmental variability. In long-lived, slow-reproducing species like primates,
selective pressure on fitness components such as reproduction acts across multiple life
stages to influence the timing, quality, and quantity of reproductive investment. In a
seasonal environment, varying ecological conditions pose additional challenges for
females and may favour reproductive strategies that optimize reproductive
investment under temporal constraints. Theoretical models in life-history and
socioecology provide strong predictions about how trade-offs should operate in
nature, however, empirical data from wild populations, especially in seasonal
breeders, remains scarce.
In this thesis, I investigate the drivers of female fitness in wild Assamese macaques
(Macaca assamensis), a strict seasonal breeder living in an environment with fluctuating
resources. Using long-term data collected over two decades from Phu Khieo Wildlife
Sanctuary in Thailand, I examined how social and ecological factors combined with
intrinsic life-history constraints influence two key fitness components: reproductive
success and survival. While social and ecological factors and their influence on fitness
have been a central topic in behavioural ecology, most of the studies have tested their
independent effects, but their potential interaction effect remains understudied. In this
thesis, I address this underexplored area by explicitly testing the interaction effects
and assessing whether social dynamics amplify or buffer ecological influences on
female fitness.
In Chapter 2, I first focused on life-history constraints and examined the presence of
the quantity-quality trade-off in this population. I specifically tested whether
investment in many offspring (measured in terms of interbirth intervals, IBI) comes at
the cost of the quality (measured as survival) of offspring. My results provide evidence
for this trade-off: infant survival was reduced when mothers conceived or invested in
future reproduction during the current infant’s nursing period. I also found that
females with young dependent offspring were less likely to conceive, and conception
probabilities increased with the age of the infant, reflecting energetic limitations on
reproduction. Further, I examined the effect of short IBIs on reproductive timing and
found that after shorter IBIs, females conceived later in the mating season, suggesting
the need for recovery and attaining good enough physical condition for reproducing
again. Together, these findings suggest that maternal depletion underlies the observed
quantity-quality trade-off. Additionally, maternal age also influenced conception
probability, with younger females showing lower conception probabilities in the first
few years of reproduction, likely balancing somatic growth with early reproduction.
There were also signs of reproductive senescence. Overall, these findings suggest that
reproductive investment in female Assamese macaques is limited by intrinsic life
history trade-offs.
In Chapter 3, I focused on the social and ecological factors and examined whether
variability in environment and social dynamics influenced reproductive success.
Drawing from the socio-ecological theory, I specifically tested whether dominance
rank, social bond strength, social integration, group size, and fruit availability interact
to influence annual conception and infant survival. I did not find any effect of
ecological and social factors like rank, strength of social bonds, social integration, or
group size on conception rates. The presence of a young dependent offspring strongly
predicted conception probabilities, reaffirming the role of energetic and physiological
conditions. For infant survival, I did not find any evidence of social factors, but fruit
availability during the infant’s first year positively predicted survival, emphasizing
ecological influences. The presence of a close-in-age younger sibling had a negative
effect on infant survival. This suggests that infant survival was likely constrained by
maternal investment as well as their foraging success. The findings from this chapter
again highlight the strong influence of intrinsic trade-offs on female reproductive
success in Assamese macaques, with a limited effect of ecological variations.
In Chapter 4, I extended the analysis to another important fitness component, female
survival. Using annual survival probability as the outcome variable, I examined how
predictors measured in the preceding year, including social bond strength, social
integration, fruit availability, dominance rank, group size, and their interaction,
influence survival while accounting for age. Consistent with life-history theory, age
was the dominant predictor of mortality, with older females showing higher
probabilities of dying. Most of the social and ecological predictors did not show any
detectable effects, except that the strength of the social bond showed a weak positive
association with survival probability. This suggests that there may be a possible long
term or cumulative benefit of social bond strength that was not captured in the short
term. These results suggest that female survival is not strongly influenced by
immediate environmental or social variation in Assamese macaques.
The overall findings from this thesis point out that in female Assamese macaques,
reproductive success and survival are largely constrained by energetic and life-history
factors rather than immediate social dynamics. While social relationships are an
important predictor of fitness in many group-living species, they may be secondary to
ecological pressures and intrinsic life-history trade-offs in species with strict
reproductive seasonality. By combining ecological, social, and individual data over a
longer timeframe and testing not only the independent effects of social and ecological
predictors but also their interactions, my thesis tried to capture the complexity of the
relationship between different variables and their influence on fitness outcomes. Even
though the interaction effects were not always significant, explicitly testing them is
crucial for advancing socioecological theory, and future research should consider
integrating social, ecological, and life-history frameworks in the study of primate
fitness.2025-09-1
Functional Characterization of Early Visual Neurons Using Machine Learning
No full textUnderstanding how early visual neurons represent and process sensory input remains a central challenge in systems neuroscience.
Key questions include how these neurons encode visual information, how their receptive fields adapt to changes in stimulus statistics, and how they organize into functional cell types.
Predictive models serve as essential tools for studying these phenomena: they link features of the visual stimulus to neural responses and enable the inference of functional cell properties from data.
Classical modeling approaches based on linear-nonlinear (LN) frameworks have played a foundational role in estimating receptive fields and characterizing neural input-output functions. And still today, extending these models with interpretable features presents significant opportunities for progress in understanding visual neurons.
Concurrently, recent developments in deep learning offer complementary approaches with models showing improved neural response prediction accuracy, but making direct insight more challenging.
In this dissertation, we use neural recordings from the retina and primary visual cortex (V1) of primates, salamanders, and mice to leverage both approaches in building and interpreting predictive models that address questions about the receptive field structure and functional properties of early visual system neurons.
First, using classical modeling, we demonstrate that retinal ganglion cells (RGCs) in primates systematically adapt their receptive fields when stimulus statistics shift from white noise to natural scenes.
We also show that a simple spatial contrast model, based on local mean and variance, can effectively capture nonlinear spatial integration in primate RGCs under naturalistic stimulation.
Next, to aid further predictive model development for the retina and V1, we establish benchmarks for both of these visual areas. For the retina, we systematically benchmark LN models against convolutional neural network (CNN) architectures to identify optimal designs and inductive biases for predicting RGC responses across species and visual stimuli.
In mouse V1, we establish a standardized large-scale benchmark in the form of a public competition for dynamic stimulus prediction.
Finally, by applying interpretability methods to CNN models, we uncover candidate stimuli that drive wide-field inhibitory interactions mediated by amacrine cells (ACs) and develop data-driven, unbiased approaches for identifying neuronal types based on their functional responses.
Together, this work advances predictive modeling techniques in visual neuroscience and directly applies them to expand our knowledge about the function of the early visual system.2025-10-0
Towards Resilient Energy Systems - Probabilistic Deep Learning for Forecasting and Control under Uncertainty
No full textThe integration of variable renewable energy source (RES) and the electrification of end-use sectors introduce significant uncertainty into energy systems, challenging traditional deterministic modeling and operational paradigms. This cumulative dissertation addresses these challenges by exploring, developing and applying probabilistic deep learning methods to improve uncertainty quantification and management in power grids and related domains.
This research advances novel probabilistic deep learning techniques, focusing on deep conditional transformation models (CTMs) and their extensions. Key contributions include: (i) Demonstrating that deep CTMs, particularly Bernstein normalizing flows (BNFs), deliver accurate and robust probabilistic short-term load forecasts at the low voltage (LV) level, outperforming conventional approaches, especially under data scarcity. (ii) Proposing a real-time grid operation framework that combines probabilistic forecasts with a graph neural network (GNN) based control model, enabling proactive management of distribution grids under uncertainty. (iii) Extending autoregressive deep CTMs to probabilistic indoor temperature forecasting, providing uncertainty estimates for heating, ventilation and air conditioning (HVAC) control through stochastic optimization strategies. (iv) Introducing hybrid Bernstein normalizing flows (HBNFs), a novel hybrid model class that integrates interpretable marginal modeling through CTMs with flexible multivariate modeling using neural network (NN) based autoregressive normalizing flows (NFs), addressing the trade-off between interpretability and expressiveness in multivariate density estimation.
Together, these contributions offer advanced methods and tools for uncertainty quantification and control in energy systems. By advancing probabilistic forecasting and decision-making, this work supports the development of more resilient, efficient and adaptable energy grids. The findings underscore the practical value of distributional modeling and the potential of hybrid statistical and deep learning approaches for addressing the limited interpretability arising from the black-box nature of pure deep learning methods.2025-10-1
A use case study on the analysis of image similarities using CNNs. The example of painter attribution on Attic vase paintings
No full textDiese Dissertation ist eine tiefgehende Fallstudie über den Einsatz von Methoden des maschinellen Lernens für Bildklassifizierungsaufgaben in den Geisteswissenschaften. Die konkrete Thematik behandelt die Zuschreibung von Malerhänden auf attischen Vasenbildern, was als Methode mit einer langen Tradition in der klassischen Archäologie einhergeht. Es ist allerdings nicht das Ziel dieser Arbeit, eine „Zuweisungsmaschine” zu schaffen oder die Malerzuweisungen früherer Wissenschaftler zu replizieren. Stattdessen handelt es sich um eine Gegenüberstellung des computergestützten und des traditionellen Vorgehens, wobei die Bildähnlichkeit als zentrale Kategorie hervortritt, insbesondere in der interdisziplinären Schnittstelle der Digital Humanities. Zu diesem Zweck ist das Handbuch in zwei Teile gegliedert: Zunächst wird die Aufgabe operationalisiert. Ein maschinelles Lernmodell muss trainiert werden, um die Zuweisung wie ein menschlicher Kenner durchzuführen. Hierbei müssen Fragen der Datenzusammenstellung, Biases, Bildannotation und Experimentaufbau behandelt werden. Der zweite Teil des Buches besteht aus sechs Fallstudien, die den epistemischen Wert der Ergebnisse und ihrer Erforschung aufzeigen. Ein theoretischer Rahmen begleitet verschiedene Phänomene der visueller Ähnlichkeit zwischen den Malerhänden und führt zu Schlussfolgerungen über die erlernten Merkmale und die Korrelationen verschiedener visueller Phänomene.
„Explorationsräume” ist ein konzeptioneller Ansatz zur Merkmalsraumerkundung unter Berücksichtigung des epistemischen Werts für die Geisteswissenschaften.This dissertation is an in-depth case study on the use of machine learning methods for humanities image classification tasks. The task examined is painter attribution on Attic vase paintings, which is a subject with a long tradition in classical archaeology. It is, however, not the goal of this thesis to create an ‘attribution-machine’ or to replicate the attributions by previous scholars. Instead, it is a juxtaposition of the computational with the traditional approach, addressing image similarity as a category of study in the interdisciplinary field of Digital Humanities. To achieve this, the book is divided into two parts: First, the task needs to be adequately operationalized. A machine learning model has to be trained to conduct painter attribution like a human connoisseur and for this purpose it is necessary to address issues of data compilation, biases, image annotation and experiment design. The second part of the book consists of six case studies, showcasing the epistemic value of the results and their exploration. A theoretical framework accompanies different phenomena of visual similarity between the painters, leading to conclusions on the features learned and on the correlations of different visual phenomena.
“Explorationsräume” – roughly translated to “exploration scapes” – is the conceptual approach of feature space exploration with the epistemic value for the humanities domains in mind.2025-10-1
Kohortenanalyse von Patienten mit chronischer Immunneuropathie an der Klinik für Neurologie
No full textChronic immunoneuropathies, particularly Chronic Inflammatory Demyelinating Polyradiculoneuropathy (CIDP), are rare disorders characterized by potentially severe neurological impairment. Given the risk of irreversible long-term consequences, early and accurate diagnosis as well as timely initiation of appropriate therapy are crucial.
This study aimed to (1) characterize a comparatively large cohort of patients, (2) identify parameters predictive of disease progression, (3) evaluate the correlation and predictive value of standardized clinical scales (INCAT, MRC, and ROD-B/ROD-S) with electrophysiological parameters, and (4) determine whether disease characteristics differ between male and female patients, considering previously reported epidemiological distinctions.
A total of 172 patients treated for suspected or confirmed immunoneuropathies at the Department of Neurology, University Medical Center Göttingen (UMG), between 1996 and 2020 were retrospectively analyzed. Data extracted from medical records included diagnostic results such as clinical scales and electrophysiological findings, as well as therapeutic interventions. The cohort was first analyzed descriptively (Part A). To model disease progression (Part B), mixed logistic regression was applied, while mixed linear regression was used to assess the predictive value of the three clinical scales (Part C). Finally, disease characteristics of male and female patients (Part D) were compared using independent t-tests and Mann–Whitney U tests.
Our findings provide a comprehensive characterization of 172 patients, 71% of whom were male, and 77% of whom were diagnosed with CIDP. Female sex was significantly associated with earlier disease progression. Additionally, progression correlated significantly with changes in demyelinating parameters on electrophysiological testing. The three clinical scales (INCAT, MRC, and ROD-B) were highly correlated, indicating that they reflect comparable levels of functional impairment. Moreover, MRC and INCAT scores demonstrated significant correlations with demyelinating electrophysiological parameters.
In summary, this study offers a detailed characterization of a large cohort of patients with chronic immunoneuropathies, consistent with findings from previous studies. Our results support the use of the three clinical scales (INCAT, MRC, ROD-B) as reliable tools for objectively assessing clinical status, complementary to electrophysiological measures. Although sex-specific differences in disease progression were observed, prospective studies with standardized assessments are needed to validate potential clinical and therapeutic implications. The data collected herein serves as an important foundation for improving future studies on chronic immunoneuropathies.2025-12-3
Molecular and Physiological Mechanisms of Cabbage Stem Flea Beetle (Psylliodes chrysocephala) Aestivation
No full textGerman Academic Exchange Service (DAAD)Saisonale Dormanz ist eine zentrale Anpassung, die Insekten das Überleben vorhersehbarer Umweltstressphasen ermöglicht. Die Ästivation, eine Form der Sommerruhe, bereitet Insekten auf hohe Temperaturen und geringe Luftfeuchtigkeit vor und ist gekennzeichnet durch physiologische und molekulare Veränderungen wie die Anreicherung von Energiereserven und die Unterdrückung des Stoffwechsels. Trotz ihrer ökologischen Bedeutung sind die molekularen Mechanismen der obligaten Ästivation bislang kaum erforscht, insbesondere bei nicht-modellhaften Insektenarten. Diese Dissertation untersucht die molekulare Grundlage der obligaten Ästivation beim Rapserdfloh (Psylliodes chrysocephala), einem univoltinen Schädling von Winterraps in Nordeuropa. Mithilfe einer Kombination aus Transkriptomik, Proteomik, physiologischen Analysen und RNA-Interferenz (RNAi) wird ein integriertes Bild der genetischen und regulatorischen Netzwerke gezeichnet, die der Ästivation in dieser Art zugrunde liegen. Kapitel 2 schafft eine Grundlage durch die Identifikation differentiell exprimierter Gene beim Übergang in die Ästivation und während ihrer Aufrechterhaltung, ergänzt durch physiologische Messungen wie die Analyse der Körperzusammensetzung. Aufbauend darauf untersucht Kapitel 3 die Rolle von Trehalosetransportern, die eine zentrale Funktion bei der Regulation des Energiehaushalts und der Stresstoleranz durch dynamische Kontrolle des Trehalose-Stoffwechsels übernehmen. Kapitel 4 widmet sich der regulatorischen Funktion von microRNAs (miRNAs) während der Ästivation. Durch die Integration von Small-RNA- und Degradom-Sequenzierungen werden miRNA-mRNA-Wechselwirkungen aufgedeckt, die an dormanzassoziierten Prozessen beteiligt sind. Kapitel 5 beleuchtet, inwieweit die transkriptionellen Veränderungen während der Ästivation auf Proteinebene widergespiegelt werden und liefert damit Einblicke in posttranskriptionelle Regulation. Kapitel 6 fasst die Ergebnisse zusammen und diskutiert ihre übergeordneten Implikationen. Insgesamt leistet diese Arbeit einen umfassenden Beitrag zum Verständnis der Ästivation bei P. chrysocephala, insbesondere auf molekularer Ebene. Die gewonnenen Erkenntnisse könnten zur Entwicklung innovativer RNAi-basierter Strategien im Pflanzenschutz beitragen – insbesondere vor dem Hintergrund klimatischer Veränderungen und zunehmender regulatorischer Einschränkungen.Seasonal dormancy is a key adaptation that enables insects to survive predictable periods of environmental stress. Aestivation, a form of summer diapause, prepares insects for high-temperature and low-humidity conditions through physiological and molecular changes, including energy reserve accumulation and metabolic suppression. Despite its ecological significance, the molecular mechanisms underlying obligate aestivation remain poorly understood, especially in non-model species. This thesis investigates the molecular basis of obligate aestivation in the cabbage stem flea beetle (Psylliodes chrysocephala), a univoltine pest of oilseed rape in northern Europe. Using a combination of transcriptomics, proteomics, physiological assays, and RNA interference (RNAi), this work provides an integrated view of the molecular and physiological mechanisms governing aestivation in this species. Chapter 2 establishes a foundational understanding by identifying differentially expressed genes during aestivation, supported by physiological measurements such as body composition. Building on these findings, Chapter 3 explores the role of trehalose transporters in mediating energy balance and stress resilience through dynamic trehalose regulation. Chapter 4 investigates the regulatory role of microRNAs in aestivation. Chapter 5 focuses on the proteomics associated with aestivation. Together, these studies advance our understanding of insect aestivation by investigating its molecular underpinnings and physiological features in P. chrysocephala. This knowledge may inform the development of RNAi-based pest control strategies, particularly under changing climatic and regulatory conditions.2025-12-0
Konnektivitätsanalyse des Routine-EEGs bei idiopathisch generalisierter Epilepsie
No full textEpilepsy is one of the most common neurological disorders and is characterized by a persistent predisposition to excessive synchronous neuronal activity leading to epileptic seizures. Idiopathic generalized epilepsy (IGE) accounts for approximately one-third of all epilepsy syndromes. Diagnostic accuracy may be constrained by limited clinical or electrophysiological information.
This study investigated whether functional brain networks in patients with IGE can be detected using routine EEG recordings with 21 electrodes. In a retrospective case–control design, routine EEGs from 79 patients with IGE and 43 healthy controls were analyzed. EEG data were processed using the FieldTrip toolbox, epochs containing epileptiform discharges were excluded, and source reconstruction was performed using a standardized MRI template. Functional activity was quantified using spectral power, and functional connectivity was assessed using the imaginary part of coherence across multiple frequency bands. Group comparisons additionally considered seizure freedom, antiseizure medication (ASM), presence of interictal epileptiform potentials, and disease duration.
IGE patients showed significantly increased global and region-specific spectral power across all frequency bands, with posterior predominance, and elevated functional connectivity in theta, alpha, and gamma frequencies in frontal, central, and posterior regions. ASM load, disease duration, and duration of seizure freedom showed no significant effects on functional measures. Patients with interictal epileptiform potentials exhibited higher delta power than those without. The pattern of altered connectivity overlapped with subregions of the default mode network, consistent with previous high-density EEG and MEG studies implicating thalamocortical and DMN-related network alterations in IGE.
These findings demonstrate that functional network abnormalities in IGE can be detected even in routine EEG recordings with low electrode density. Routine-EEG–based connectivity analysis may therefore represent a promising, widely accessible tool to support the diagnostic workup of epilepsy and to differentiate epilepsy subtypes, including potential subsyndromes of IGE.2025-12-3
Effectiveness of subcutaneously implanted loop recorders for the differential diagnosis of syncope and cardiac arrhythmias in children and adolescents
No full textThis dissertation is a single-center retrospective study that examines the effectiveness of subcutaneously implanted loop recorders for the differential diagnosis of syncope and cardiac arrhythmias in children and adolescents. The patient cohort consists of 52 children and adolescents who underwent implantation of a subcutaneous loop recorder for continuous recording of the cardiac rhythm between December 15th 2014 and December 10th 2021 at the Department of Pediatric Cardiology Intensive Care Medicine and Neonatology at Göttingen University Medical Center. Patients were included in this study at the time of implantation until they reached the age of 18.
The indications for loop recorder implantation were recurrent syncope, recurrent unexplained states of emergency or recurrent palpitations. Only the Reveal LINQ LNQ11 from Medtronic was implanted.
We were able to show that a total of 11/52 (21%) patients had a rhythmological cause for their symptoms, which was diagnosed using loop recorder. As a result, specific therapy for the documented cardiac arrhythmia could be offered. In addition, heart rhythm disorder could also be ruled out in some participants thus providing reassurance to their families.
In patients with palpitations as an indication for loop recorder implantation, heart rhythm disorder was documented more frequently than in patients with other indications. In addition, heart rhythm disorder was documented more frequently in patients with structural heart defects than in patients with structurally normal hearts.
With 57.7% of girls and 42.3% of boys, loop recorder implantation was slightly more common in girls than in boys. At the time of implantation, girls were significantly older than boys. The number of cardiac diagnoses detected, on the other hand, did not differ significantly between the sexes. A rhythmological diagnosis was made using LR in 20% of girls and 22.7% of boys.
The complication rate was low at 3.8%.
In summary, the implantation of a loop recorder in children and adolescents is very useful when indicated in order to obtain ECG recordings during symptoms and thus be able to make a well-founded diagnosis.2026-01-0
Photochemical Dinitrogen Activation and Functionalization
No full textPhotochemistry has emerged as a powerful tool for enabling challenging chemical transformations. In this thesis, light-driven strategies are explored for the conversion of dinitrogen into nitrogenous products beyond ammonia.
A key step in N2 fixation is the homolytic cleavage of dinitrogen into terminal nitrides. Understanding the electronic structure of µ−N2 bridging complexes is essential for the development of catalysts. The study of the electronic structure of N2 bridging rheniumcomplexes is discussed by the use of a several spectroscopic methods.
The combination of dinitrogen and dihydrogen with transition metal complexes remain rare. Identifying complexes capable of hydrogenating N2-derived molecules is therefore of crucial importance. By determining ground state and excited state properties of a novel photocatalyst in combination with Stern-Volmer analysis gives insight into the hydrogenation of the N2-derived ReV-imido complex. Further elucidation of the mechanism was done by transient absorption spectroscopy combined with TD-DFT. A new strategy for the conversion of dinitrogen into valuable organic nitrogen-containing chemicals is presented.2025-12-2
Dynamic Gain Analysis of Neuronal Response in Experimental and Computational Models under Electrical and Optogenetic Stimulation
No full textLocal cortical circuits in the mammalian neocortex encode and process information through the coordinated spiking activity of large neuronal populations. Despite the high variability and low firing rate of individual spike trains, cortical networks use population-level encoding strategies to reliably represent sensory, motor, and cognitive signals. A fundamental information channel in these circuits is the \emph{population-averaged firing rate} - the instantaneous probability of spiking averaged across a local network. Most cortical circuits operate in a fluctuation-driven regime, where a neuron's average membrane potential remains below firing threshold and spiking is triggered by transient fluctuations in synaptic input. While individual neurons fire sparsely and irregularly, their collective activity generates a stable and consistent signal.
In this thesis, we investigate the phenomenon of \emph{ultrafast population response} - the ability of the population firing rate to react to changes in the shared input mean or variance on a millisecond timescale. In the frequency domain, this capability is known as \emph{high-bandwidth encoding}, where the population firing rate can reliably follow low-amplitude, time-varying inputs with frequency components up to several hundred Hertz. To assess the fidelity of the population response to time-varying inputs, we use the \emph{dynamic gain function} , a spectral measure derived from linear response theory that quantifies how input fluctuations are translated into firing rate fluctuations. In this framework, neurons act as linear filters, and the dynamic gain function represents the filter kernel. This kernel characterizes which frequency components of the input are selectively amplified or suppressed. Unlike the kernel of a strictly linear system, the shape of the dynamic gain is strongly influenced by the statistical properties of the input - most notably, its correlation time. As a result, the neuronal population behaves as an adaptive filter, dynamically emphasizing different frequency components based on the overall structure of the input.
To dissect the mechanisms underlying this adaptive filtering, we decompose into two components: a subthreshold filter , known as the \emph{effective impedance}, which maps input current fluctuations to membrane potential fluctuations; and a suprathreshold filter , called the \emph{spike boost}, which maps voltage fluctuations to firing rate modulations. Using fluctuation-dissipation theory, both and can be expressed as a ratio of cross- and auto-covariances. For the leaky integrate-and-fire model we derive closed-form expressions for these quantities:
\begin{equation*}
G(\omega) \propto (1+\tau_m^2\omega^2)^{-1/4} \hspace{15mm} Z(\omega) \propto (1+\tau_m^2\omega^2)^{-1/2} \hspace{15mm} B(\omega) \propto (1+\tau_m^2\omega^2)^{1/4}
\end{equation*}
To investigate how passive neuronal morphology and active biophysical mechanisms shape , we performed dynamic gain analysis on two sets of experimental recordings from murine CA1 hippocampal neurons. First, we examined the effects of axon initial segment (AIS) destabilization in cells with otherwise normal morphology. The median cutoff frequency - a measure of encoding bandwidth - was reduced from 170.28 Hz in wild-type cells to 135.90 Hz in qv3J-mutants. This reduction was accompanied by a drop in action potential (AP) onset rapidity, from 12.49 to 6.74 , suggesting that \emph{suprathreshold contributions to the dynamic gain are largely determined by the precision of AP initiation in the AIS}.
Second, we investigated how dendritic arbour growth during development in culture affects . The mean cutoff frequency increased from 39.93 Hz at 8-10 DIV to 164.47 Hz at 21-37 DIV. This was accompanied by a rise in the impedance corner frequency from 4.58 to 7.81 Hz, indicating that the \emph{subthreshold contributions to dynamic gain are primarily shaped by electrotonic filtering and capacitive load of the dendritic compartment}. Together, these findings elucidate how distinct morphological and biophysical features shape the encoding bandwidth of cortical neuronal populations.
In both experimental paradigms, in-vivo-like operating conditions were emulated by mechanically injecting fluctuating inputs, modelled as Ornstein-Uhlenbeck (OU) processes. A parallel aim of this thesis is the development of optical methods to non-invasively replicate in vivo synaptic bombardment in neurons expressing channelrhodopsins. \emph{We demonstrate that stochastic noise illumination of Channelrhodopsin-2 and Chronos reliably generates conductances that follow Ornstein-Uhlenbeck statistics.} Using eight-state Markov models that have been shown to quantitatively reproduce the light-dependent conductance dynamics of these opsins, we derived a linear approximation of their response to time-varying illumination patterns. Inverting the corresponding linear transfer function allowed us to \emph{compute the specific illumination waveform required to generate a desired target conductance waveform}. The resulting channelrhodopsin conductances closely match the target OU processes, achieving a mean Pearson correlation coefficient of 97.7\% 1.1\% across illumination intensities between 0.01 and 10 and correlation times ranging from 5 to 50 ms. This novel approach enables the flexible synthesis of OU-like conductances, \emph{providing a non-invasive method for optogenetic dynamic gain measurements in channelrhodopsin-expressing neurons under in-vivo-like conditions.}
Together, these theoretical and methodological advances provide new insights into the biophysical basis of high-bandwidth encoding and establish an optogenetic framework for studying neuronal dynamics in fluctuating regimes. This work connects cellular biophysics with systems-level computation, advancing our understanding of how neural populations encode information on fast timescales.2025-12-2