The energetic cost of living defines how animals interact with their environment. The rate at which animals capture and expend energy dictates where and how they can live, and their relative sensitivity to ecological and environmental change. Energetic traits face strong selection, and morphological features are often assumed to imply changes in bioenergetic traits. Energy is typically measured by assessing heat production or the oxygen consumption rates. Both of these approaches are extremely difficult to apply in field conditions or on fossil samples. Consequently, despite the fundamental importance of energy expenditure in ecology, evolution and conservation physiology, we have very little comparative quantitative information on the realised energetic costs of living for wild animals in either modern or fossil settings.
Recently, chemical proxies for realised metabolic rate have been proposed, based on carbon isotope compositions (Chung et al 2019), trace metals (Limberg et al 2018) and concentrations of respiratory macromolecules preserved in ancient biominerals (Weimann et al 2022). This project will refine, improve and intercompare proxies for field metabolic rate. You will apply metabolic proxies to provide the first empirical data for how metabolic level varies among modern and fossil organisms, linking physiology and evolutionary ecology.
You will focus on three main proxies for field metabolic rate.
(1) Carbon isotope-based estimates of metabolic rate are relatively well-established, but to date application has been limited to fish otoliths. Here you will expand the method to sharks and rays (fish without otoliths) and fossil ammonites and belemnites. You will test how well different host tissues (blood, bone and tooth enamel and mollusc shell) record variations in metabolic rate expected as a function of body size and temperature.
(2) Incorporation of Mg ions in biominerals has been proposed as a metabolic proxy. We have a large collection of otoliths with existing isotope-based estimates of metabolic rate. In this part you will compare both proxies to determine the extent to which they covary.
(3) Respiratory macromolecule preservation. You will explore a recently proposed macromolecule proxy for metabolic rate by measuring metabolite concentrations in fresh bone from fish with contrasting known metabolic rates. If successful you will extend these analyses to fossil materials including, but not limited to, extinct sharks, mammals and dinosaurs.
Following initial validation stages, you will be free to apply whichever metabolic proxy and application appears most promising and interests you most, either in modern or palaeontological settings.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. You will be registered and hosted at the University of Southampton.
You will receive extensive training in ecophysiology and conservation physiology. In particular focussing on how sensitive animal energy expenditure is to changes in the external environment, a key concern in the context of climate change. You will also receive training in biomineral composition and chemistry, providing you with expertise applicable to both palaeontological and short modern timescales and scientific disciplines including biomedicine, fish and fisheries ecology, palaeoclimate reconstruction, structural biology and natural materials chemistry.
You will benefit from access to state-of-the-art analytical equipment at the University of Southampton and to the world class collections and taxonomic expertise at the Natural History Museum in London.
Please see https://inspire-dtp.ac.uk/how-apply for details.
Chung et al 2019 Field metabolic rates of teleost fishes are recorded in otolith carbonate. Communications Biology 2, 24. https://www.nature.com/articles/s42003-018-0266-5
Limburg et al 2018 Making the Otolith Magnesium Chemical Calendar-Clock Tick: Plausible Mechanism and Empirical Evidence. Reviews in Fisheries Science and Aquaculture 26:4 https://www.tandfonline.com/doi/full/10.1080/23308249.2018.1458817
Wiemann et al 2022 Fossil biomolecules reveal an avian metabolism in the ancestral dinosaur. Nature 606, 522-526 https://www.nature.com/articles/s41586-022-04770-6