Evolution of Metabolic Diversity in Animals

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Animals vary tremendously in their energy use and production capacity, their metabolic rate. The metabolic rate of species differs depending on their lifestyle and habitat, and evolutionary processes shape these differences. My research looks at why and how metabolic rate, and the underlying physiological and biochemical properties, evolve in animals. A first objective of the proposed research will focus on the cellular processes involved in energy production. Not only rates of energy production evolve in animals, but the fuels are used to produce energy also differ across species. Insects such as bees and wasps are thought to be sugar specialists, but we recently found an unusually high capacity to use the amino acid proline as a fuel to produce energy. How and why some species evolved the ability to use proline is unknown. To test whether proline is a substantial fuel used for flight in bumblebees, we will manipulate nectar diets with and without proline, and by inhibiting the central enzyme involved in proline metabolism. Furthermore, by comparing species of bees and wasps with diverse life-history strategies, we will address if proline is an energy source during overwintering. Also, this approach will test if species that generate a large amount of heat are doing so using metabolic fuels more efficient at heat production. A second objective will test how the size of animals drives the evolution of metabolic rate and underlying traits. In insects, body and wing size influence wingbeat frequency and flight muscle contraction rate, explaining differences in metabolic rate. To understand how the physiological properties of animals co-evolve with body mass and wing size, I plan on using fruit flies that differ in wing proportions. First, fly size and wing proportions can vary largely due to the influence of environmental conditions during development, and the consequences on flight metabolic rate, flight performance and muscle function will be studied. Next, artificial selection experiments will be conducted to evolve flies with larger and smaller wing proportions. This experiment will allow determining how metabolic rate, flight performance and muscle function co-evolve. We will determine the genetic basis of the traits studied by using breeding experiments and quantitative genetics analytical tools. Together this work will clarify how the use and production of energy evolve in animals. The proposed studies will involve at least five graduate students and over 15 undergraduates that will be trained in metabolic physiology using evolutionary biology analytical tools.