Abstract: Throughout their life, wild species face periods of food-deprivation that induce energy trade-offs between survival, growth and reproduction. These fasting periods occur either when food availability is lacking due to adverse climatic conditions or because individuals are engaged in biological processes that prevent food access. This later reason is particularly well illustrated in the king penguin (Aptenodytes patagonicus), a sea bird that has to moult and reproduce on shore whereas he feed exclusively at sea. Moreover king penguin chicks exhibit exceptional survival capacities during their first year of life when they experience a long period of fast in winter. Thus, this species that lives in sub-Antarctic latitudes, is exposed to environmental and physiological energy constraints during food shortage periods.
Since king penguins are endotherms, they need to maintain their body temperature at high level despite variations of ambient temperature. Thus thermoregulation is one of the most expensive process and skeletal muscles account for the greater part of heat production in birds.
Several studies showed that despite long term cold exposure, energy expenditure of fasting birds decreases allowing energy savings and especially protein sparing. Since skeletal muscles have high implications in energy expenditure and heat production the question of their implication in energy saving mechanisms arises. During my PhD project I studied skeletal muscle metabolism through mitochondrial efficiency. These sub-cellular organelles are the last effectors of energy transduction from nutrient into ATP, an usable energy for cells. Our hypothesis is based on the flexibility of mitochondrial efficiency as a regulator of energy sparing mechanisms which would explain long term resistance to starvation.
My studies were conducted in a wild species, the king penguin chicks, that are naturally acclimated to cold environment and experienced long term fasting stage. To further investigate mitochondrial plasticity in response to energy constraints, I developed several experimental procedures in controlled conditions on a laboratory model (Muscovy ducklings).
The flexibility of mitochondrial efficiency observed in these two avian species suggests that this mechanism could highly decrease the cost of energy production during food-deprivation period even when birds were exposed to cold. Although, mitochondrial efficiency improvement was found in both species, it seems to depend on the phenotype and/or activity of skeletal muscles.

Abstract: Despite Their Increasingly Recognized Interest For Public Health And Biodiversity Conservation, Investigations On The Ecology And Evolution Of Infectious Diseases In Wildlife Have Been Hampered By The Difficulty Of Collecting Data Allowing Efficient Inference Of Underlying Processes. Serology (I.e., Detection Of Antibodies In Biological Samples) Is A Useful Tool To Detect Past Exposure To Specific Infectious Agents. Still, Interpreting Serological Data Is Not Straightforward. For Instance, The Prevalence Of Seropositive Individuals In A Population Is Driven By A Combination Of Epidemiological (E.g., Disease Incidence) And Demographic (E.g., Population Turnover) Dynamics. In This Context, The Objective Of This Thesis Is To Show How Processes Underlying Infectious Agent Circulation In Wild Populations Can Be Inferred From Serological Data. First, I Illustrate How Cross-sectional Studies Focusing On A Sentinel Species At The Wildlife-human Interface Can Efficiently Inform On Patterns At A Hierarchy Of Scales. Then, I Compare The Pros And Cons Of Such Crosssectional Approaches To Longitudinal Sampling Designs Involving Marked Individuals When Attempting To Quantify The Dynamics Of Infectious Agents And I Propose A Way To Integrate Those Two Approaches In Future Studies. Finally, Using Avian Cholera Epizootics In A Threatened Long-lived Seabird On An Isolated Island As A Case Study, I Illustrate The Benefits Of Combining Serology With Other Approaches. This Work Notably Highlights The Value Of Detailed Long-term Studies Of Host Exposure To Infectious Agents In The Wild, Where Ecological And Evolutionary Processes Are Likely Critical Drivers Of Disease Dynamics And Can Have Important Implications For Biodiversity Conservation.