Date of Award


Degree Type


Degree Name

Doctor of Philosophy in Biological and Environmental Sciences


Ecology & Ecosystem Sciences


Natural Resources Science

First Advisor

Scott R. McWilliams


Diet mediates environmental influence on organismal performance, but diets must be broken down into their constituent compounds and integrated into organismal tissues before they can exert such influence. Thus, a full account of the relationship between diet and organismal performance requires descriptions of intermediate effects on body composition and tissue function, as well as the dynamics of composition and function over time. The work described in this dissertation investigates a case study of diet and organismal performance in songbirds: dietary polyunsaturated fats have been demonstrated to influence the metabolic performance of songbirds, but the influence of individual fatty acid compounds, the mechanisms mediating dietary influence, and the time scales on which dietary fatty acids are integrated into songbird tissues are largely unknown. Using diet manipulations, respirometry, and wind-tunnel flight training, we tested the influence of dietary linoleic acid (18:2n6), a fatty acid implicated in previous studies, on tissue fatty acid composition and whole-animal metabolic performance in European Starlings (Sturnus vulgaris; Manuscript I), as well as its effect on tissue function, measured in terms of the activity and expression of fatty acid transporters and catabolic enzymes (Manuscript II). In that same experiment we also considered the effects of dietary antioxidants and training, whose influence was hypothesized to interact with that of linoleic acid. To complement those studies, we also used a diet switch experiment and stable isotope analysis to estimate the turnover rates of tissue lipid compartments (Manuscript III) and individual fatty acid compounds (Manuscript IV) in Zebra Finch (Taeniopygia guttata) muscle in order to investigate the pace of changes in tissue composition and the mechanisms governing the turnover of lipids in avian tissues. Finally, in Manuscript V we conduct a literature review and discuss the importance of knowing the pace of changes in tissue composition and the speed of dietary influence for studying the ecology of a wide range of species.

We found that changes in dietary linoleic acid are enough to substantially change the fatty acid composition of muscle and to influence resting, maximal, and sustained metabolic rates in starlings, although this influence was more context dependent than has been found in previous studies. Similarly, dietary linoleic acid, antioxidants, and training did influence the activity of oxidative enzymes in starling muscle, but the effects of linoleic acid depended on the overall protein levels in the tissue, which were, in turn, variable over time. Together, these results suggest that the influence of dietary linoleic acid largely depends on its properties as a signaling molecule and that it could be used by songbirds to direct and control preparations for migration. We also found that lipid membranes turn over more quickly than triglyceride stores in zebra finch muscle and there is substantial variation in turnover rates among fatty acids, with linoleic acid and palmitic acid (16:0) having fast turnover and long chain polyunsaturated fatty acids having slow turnover. These results demonstrate that the lipid composition of songbird tissues, and especially cell and organelle membranes are highly dynamic and can respond to changes in diet within days. Furthermore, these results and those of similar studies provide information critical for the assessment of nutrition and ecology of wild animals.



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