How many offspring to produce, how often to reproduce and over how many years are key life history traits that describe the rate of living of organisms . The disposable soma theory of ageing pinpoints that variation in the rate of living is due to investment in reproduction at the expense of self-maintenance. It also predicts that this trade-off can vary among individuals and populations depending on extrinsic sources of mortality. Few studies have however attempted to test this hypothesis in the wild, and even less is known about the physiological and molecular mechanisms underpinning the trade-off between self-maintenance and reproduction.
This knowledge gap arises from the difficulty to quantify self-maintenance. Here we suggest that feather moulting in birds provides an ideal system to overcome this issue. Indeed, compared to other organisms, birds face a major additional constraint by their need to renew their flight feathers which are essential to e.g. obtain food and avoid predation. Remarkably, it has been recently shown in captive birds that moulting mirrors cellular self-maintenance as measured by telomere maintenance . Telomeres are repeated DNA sequences that protect the end of eukaryote chromosomes and regulate cell replicative potential and, by extension, organism life expectancy. Furthermore, secretion by the hypothalamo–pituitary–adrenal axis of the stress hormone corticosterone (CORT) has been proposed in birds to influence reproductive decision, moulting and telomere maintenance . Hence, one emerging hypothesis is that CORT regulates the trade-off between reproduction and self-maintenance and accounts for the linkage between moulting and telomere maintenance in birds.
In this project, we will take advantage of 4 intensive studies of tawny owl populations across Europe (UK, France, Spain, Switzerland) exposed to different environmental conditions such as food, predation and climate regimes (i) to test for a trade-off between reproduction and moulting, and (ii) to study whether this trade-off is modulated by environmental factors. The analysis of these exceptional long-term longitudinal data sets (>20 years) will be supplemented by measurements of the stress physiology and telomere maintenance of breeding individuals with known reproduction and moulting. We will test for the first time in a long-lived wild bird (iii) whether self-maintenance, measured at the organism level as moulting, mirrors self-maintenance at the cellular level measured as telomere maintenance, and (iv) whether inter-individual variation in CORT levels drives the trade-off between reproduction and self-maintenance and (v) furthermore links moulting strategy to telomere maintenance.
The student will be given a thorough multidisciplinary training including field and laboratory skills, and comparative analyses. Inter-individual variation in CORT levels will be measured using standard ELISA assay in feathers, and telomere length will be measured using a qPCR approach using genomic DNA extracted from blood samples. A range of state-of-the-art statistical modelling approaches using novel and existing data will be applied to test the different hypotheses. The student will actively participate in field work in Kielder Forest (UK) and work in partnership with Forest Enterprise England, the studentship CASE partner and coordinate work with collaborators in Europe who will use standardised sampling protocols.
 Millon, A., Petty, S.J., Little, B. & Lambin, X. (2011) Natal conditions alter age-specific reproduction but not survival or senescence in a long-lived bird of prey. Journal of Animal Ecology, 80, 968–975.
 Reichert, S., Bize, P., Arrivé, M., Zahn, S., Massemin-Challet, S. & Criscuolo, F. (2014). Experimental increase in telomere length leads to faster feather regeneration. Experimental Gerontology 52: 36-38.
 Monaghan, P. 2014. Organismal stress, telomeres and life histories. The Journal of Experimental Biology 217: 57-66.