Doctoral defence: Mari-Ann Lind “Internal constraints on energy processing and their consequences: an integrative study of behaviour, ornaments and digestive health in greenfinches”

On 24 August at 10:15 Mari-Ann Lind will defend her doctoral thesis “Internal constraints on energy processing and their consequences: an integrative study of behaviour, ornaments and digestive health in greenfinches” to obtain the degree of Doctor of Philosophy (in Zoology and Ecology).

Supervisors:
Professor Peeter Hõrak, University of Tartu
Associate Professor Tuul Sepp, University of Tartu

Opponent:
Professor Nicholas Mundy, University of Cambridge (United Kingdom)

Summary
Explaining the reasons why individuals differ in their performance is a central question in evolutionary and ecological research. Ability to absorb nutrients from food, produce energy in the mitochondria and energy mobilisation pose major internal constraints to energy processing. Energetic needs can vastly differ depending on the time of the day, season, individual’s life history stage and environmental conditions. Thus, organism's energy demands should be matched with energy output. The main goals of this thesis were to study the internal constraints to energy processing and its impact on survival, behaviour and production of sexually selected ornaments. Parasitic infections can reduce nutrient absorption in the digestive system. In this thesis, the application of the steatocrit method for birds was described for the first time. The steatocrit method enables to asess digestive effieciency nonivasivly and has wide potential for the use in ecological studies. Glucocorticoid hormones are important regulators of energy metabolism and stress response. Levels of the predominant glucocorticoid in birds, corticosterone (CORT), were on average 20% lower in lab-grown feathers than in wild-grown feathers, and birds who deposited more CORT into the feathers in one situation did the same in another, despite vastly different environmental conditions. CORT was also related to survival and behaviour. Therefore, CORT could indicate variation of energy requirements between individuals. Red and yellow carotenoid based integument coloration is sexually selected signal in many animals. Yellower feathers in greenfinches were not only related to absorption of nutrients in the gut, but also to carotenoid modification and deposition into signals. Biotransformation of carotenoids supposedly takes place in mitochondria. Thus, carotenoid signals might indicate the individual's capacity to produce energy. It is also possible that the gut microbiome could affect carotenoid colouration via modulation of mitochondrial function. In conclusion, an integrative view that incorporates animals' energetic needs, internal constraints to energy processing, and traits related to survival and reproductive success can help to understand why individuals differ in their performance and fitness.