The biological importance of individual variation in metabolic responses to environmental conditions

Abstract

Life-history theory was established to help understand the large diversity in life-history strategies among-species. Fundamentally, a trade-off between survival and reproduction underlies the evolution of different life-histories along the slow "" fast life-history continuum. The pace-of-life syndrome (POLS) hypothesis expands on life-history theory to help explain variation in life-histories at the population and individual levels. The POLS hypothesis proposes that variation in life-histories can only be completely understood when integrated with a suite of physiological and behavioural traits that have co-evolved to maximise fitness according to the life-history idiosyncrasies of different species and populations. Indeed, within populations, individuals differ considerably in their phenotypic expression of many important physiological and behavioural traits. Energy expenditure, for instance, is an important physiological trait of animals that drives ecological patterns and processes at individual to community levels. A primary area of research in animal physiology and evolutionary biology focuses on understanding the fitness consequences of among-individual variation in energy expenditure. Individual variation in basal metabolic rate (BMR) is by far the most common index of energy expenditure. Variation in BMR is often is assumed to reflect variation in other components of metabolism and energy expenditure and is expected to have fitness consequences. However, BMR excludes important ways in which metabolic rate can be adjusted in response to environmental conditions (e.g. air temperature and food availability). Therefore, BMR cannot incorporate how these responses might differ among individuals, nor predict their relative contribution to energy expenditure and their probable influence on fitness. Metabolic rate varies within- and among-individuals in response to environmental change. As such, quantifying among-individual variation in metabolic responses to environmental conditions could expand our current understanding of the fitness consequences of among-individual variation in energy expenditure. Therefore, the principal aim of this thesis was to examine the relationships among various measures of energy expenditure and determine whether metabolic responses to environmental conditions can be consistent and important individual traits. The results of this thesis provided a test of the ecological relevance of BMR as a single measure of metabolism. Furthermore, this thesis has provided robust evidence that individuals exhibit differences in their metabolic responses to environmental conditions and has shown that these differences could have important biological consequences. Individual metabolic responses to environmental conditions provide a powerful approach for future studies wishing to examine the evolutionary significance of among-individual variation in energy expenditure because they provide meaningful indices of metabolism measured under ecologically relevant conditions.

Date of Award	2019
Original language	English