Soos, CatherineMachin, Karen2022-08-252022-08-2520222022-082022-08-25August 202https://hdl.handle.net/10388/14118Wild animals are experiencing an increasing number and magnitude of stressors associated with the rapidly changing world. Repeated or prolonged stressors can trigger sustained elevations of glucocorticoids, resulting in detrimental effects on health and reproduction, with potential impacts on populations. This Ph.D. research validated the use of two novel techniques to investigate stress responses in wild birds: feather corticosterone and nuclear magnetic resonance spectrometry (NMR)- based metabolomics, and then used these approaches in field-based studies to investigate the impacts of a changing environment on stress responses or increased energetic demands on free-ranging migratory birds. Feather corticosterone (CORTf) is increasingly used to measure cumulative stress responses experienced during feather growth. CORTf is potentially a very useful tool as it is a non-invasive approach to investigate stress responses or energetic demands that a bird may have experienced during the previous moulting period and may provide historical information on responses to environmental changes over time if archived or museum specimens are available. However, a major criticism of the technique has been the limited support for the assumption that it reflects blood corticosterone levels during the period of feather growth. In Chapter 2, captive lesser scaup (Aythya affinis) were surgically implanted with CORT or placebo pellets during the natural moult period to test this assumption. Additionally, I used deuterium-labelled CORT (2H-CORT) pellets to evaluate the relative deposition of exogenous and endogenous CORT into growing feathers. I measured CORT in serum before, during, and after the active period of the implants, and in corresponding feather sections of the tail, wing (secondary coverts), and back feathers. Our results confirm that a) CORT deposited in feathers is primarily derived from serum CORT; b) a considerable amount of feather development (and hence CORT deposition) occurs within the follicle before the feather emerges from the surface of the skin and c) CORT is deposited throughout the length of the feather until that feather is no longer growing, and no longer has a blood supply. This research provides critical evidence to support a central assumption associated with the use of CORTf and offers new insight into the deposition of CORT into feathers. In Chapter 3, I validated the use of metabolomics, using NMR, to identify alterations in metabolite profiles related to energy metabolism resulting from prolonged stress. The energy required for maintenance or other important functions in a bird’s annual cycle may be re-routed towards coping with stressors, ultimately resulting in fluctuations in metabolite levels associated with energy metabolism. Environmental metabolomics is a discipline that assesses an organism's interactions with its environment, which includes responses to endogenous and exogenous stressors. However, the use of metabolomics to study stress in wild birds is still in its infancy. Serum samples collected during the experimental trial performed for Chapter 2 on captive lesser scaup were extracted and subjected to 1D 1H-NMR spectrometry. Quantitative targeted metabolite analysis revealed that metabolites related to energy metabolism: glucose, formate, lactate, glutamine, 3-hydroxybutyrate, ethanolamine, indole-3- acetate, and threonine differentiated ducks with higher circulatory CORT from controls on the second day post-implant. These metabolites function as substrates or intermediates in metabolic pathways related to energy production affected by elevated serum CORT. The use of metabolomics shows promise as a novel tool to identify and characterize physiological responses to stressors in wild birds and can also be used to link responses to environmental changes with downstream impacts on reproduction and survival. Variations in climate are occurring more rapidly in polar regions, and temperatures in the Arctic have increased at more than three times the global average rate over the last five decades. Climate change also affects mercury (Hg) cycles and impacts distribution and quality of prey. Given that future climate change models are predicting that Arctic ecosystems will continue to undergo significant environmental changes in years to come, it is critical to take a multi-stressor approach to examine impacts of a rapidly changing environment on Arctic wildlife health. In Chapter 4, using feather samples collected from frozen or archived museum specimens sampled over 119 years (1893-2012), I used multiple feather-based measures to assess temporal trends and impacts of rising temperatures, exposure to Hg, and variation in diet (as measured by stable isotopes of nitrogen (δ15N) and carbon (δ13C)) on stress responses or energetic demands in all four subspecies of common eider (Somateria mollissima; COEI) that breed in North America (S. m. borealis, S. m. dresseri, S. m. sedentaria, and S. m. v-nigra). All COEI subspecies are experiencing increased temperatures within their respective geographic ranges, and energetic costs experienced by COEI (as measured by CORTf) are progressively increasing over time. Rising temperatures for all three Northern COEI subspecies result in increased energetic costs, which have been shown to have significant carry-over effects on reproduction and survival in this species. In the southern S. m. dresseri, CORTf was negatively associated with climate, suggesting reduced energetic costs in relation to rising temperatures. In addition to rising temperatures over time, common eiders are experiencing an increase in other concurrent stressors over time, including increases in Hg exposure (S. m. borealis), a progressive reduction in δ15N in their diets suggesting lower trophic position diets over time (S. m. sedentaria and S. m. dresseri), and decreases in feather δ13C levels over time, suggesting changes in feeding ecology or locations (S. m. v-nigra). Results demonstrate that COEI are facing an increase in multiple concurrent stressors over time in response to largescale environmental changes and illustrate how energetic demands of distinct subspecies adapted to different climates or geographic ranges can be differentially affected by multiple stressors. Findings in Chapter 4 highlight the value of using non-invasive feather-based approaches to examine historical trends over time and over a large geographic range, to investigate relationships among climate, Hg exposure, trophic position, and how they impact stress responses or energetic demands, which have the potential to impact fitness, and lead to population-level impacts. In Appendix A, we used NMR-based metabolomics to differentiate wild arctic-nesting COEI (S. m. borealis) in relation to energetic demands experienced during moult (CORTf), pre-breeding body condition, arrival date, and nest-initiation date, all of which are indicators of breeding success in this subspecies. Metabolite profiles could differentiate free-living COEI with higher CORTf from those that had lower CORTf. To my knowledge, this is the first study that has investigated the use of NMR-based metabolomics to investigate stress responses in a wild marine duck population. These results link feather CORT variation (representing energetic demands experienced during the previous moult in August-September) with metabolite variation related to energy metabolism (representing energy metabolism at the time of sampling in early June) for the first time in any avian species. NMR-based metabolomics shows promise as a novel tool to link stress physiology and responses of wild avian species to environmental changes. Overall findings of this research contribute substantially to the current understanding of avian stress physiology as well as the application of novel techniques to study the causes and consequences of stress responses in wild bird species.application/pdfenstress physiology, feather corticosterone, metabolomics, wild birdsThesis2022-08-25