Selection, Storage and Utilisation of Protein in the Zebra Finch (Taeniopygia guttata)

The role of protein in the physiological ecology of the zebra finch (Taeniopygia guttata) was investigated using a colony of captive birds at Glasgow University. Trials based on dietary protein supplementation investigated self-selective ability, effect on egg production, endogenous protein storage, repercussions for protein synthesis in body tissues, immuno-competence trade-offs and the potential of bill colour as an indicator of physiological state. A basic experimental diet was formulated for the investigation of self-selective ability in zebra finches. Nutrient supplements could be added to this without altering its visual / textural appearance, thus removing the non-nutritive cues to diet selection suggested to compromise previous studies. The outlined dietary formulation and delivery protocol facilitate the controlled nutritive provisioning of large numbers of birds with minimum disturbance. The ability of zebra finches to self-select between basic and protein-supplemented diets to maximise egg production was investigated. When presented with a choice between diets ostensibly differing only in protein content, finches differentiated between the two, selecting 70% basic to 30% supplement. Though daily consumption did not differ significantly between dietary groups, birds receiving a choice between diets tended to maintain their body weight while producing the largest clutches and eggs, in comparison with birds maintained solely on either one of the diets. Having shown dietary discrimination to occur, "perceived taste", influenced by a specific nutrient appetite, is suggested as the basis for diet selection. Implications for lab and field studies are discussed. Pectoral muscle is recognised as an important reserve of endogenous protein. Analysis of the sarcoplasm of the flight muscle of zebra finches supported previous observation of protein removal during egg production. However, SDS electrophoresis in combination with amino acid analysis of muscle protein fractions indicated this loss to be of a general nature and not confined to a specific protein. No evidence was found to support the previous findings of a high molecular weight storage protein specific to the amino acid requirements of egg production, and it is suggested that this observation may have arisen as an artefact of the experimental methodology. The theoretical benefits of specific storage proteins for free-living zebra finches are argued to be less advantageous than previously suggested. The effect of dietary history and egg production on protein synthesis in female zebra finches was investigated using a "flooding dose" method. Fractional synthesis rate (FSR) was determined for liver, leg muscle and pectoral muscle in laying and nonlaying birds. FSR of protein in the liver was elevated during egg production and by previous experience of a high protein dietary supplement. FSR of muscle types did not appear to differ significantly from one another, nor between experimental groups. Modification of liver FSR by previous dietary experience is suggested as a contributory mechanism for the promotional effects of protein supplementation on egg production. The repercussions of dietary history and breeding status on immuno-competence were investigated. It was predicted that, were a nutrient allocation trade-off between egg and antibody production to occur, this might be alleviated by protein supplementation of the diet. Female zebra finches of differing dietary histories were immunised with sheep red blood cells (SRBCs) to present them with a potential resource allocation trade-off between egg and antibody production. Egg productivity did not differ between birds maintained, prior to breeding, on seed or protein supplemented diets. However, primary immune response was reduced in breeding birds maintained on a seed diet in comparison with both non-breeding birds and protein-supplemented breeding birds. Hence, females from a good nutritional background were able to maintain egg productivity, without reducing the strength of their immune response. (Abstract shortened by ProQuest.)