I.2 Physiological Ecology: Animals
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I.2 Physiological Ecology: Animals Martin Wikelski OUTLINE 1. Guiding concept: Trade-offs 2. Guiding concept: Performance as integrative measure of individual fitness 3. Process I: Acquisition of environmental information 4. Process II: Internal communication and regulation of physiological function 5. Process III: Energy expenditure as one central hub for trade-offs 6. Process IV: Key innovations 7. Process V: Self-defense: Immunoecology 8. Application: Conservation physiology 9. Future challenges Physiological ecologists study how animals live and function within environments that are constantly changing. Key guiding concepts in physiological ecology are that (1) individual animals are subject to trade-offs such that all (physiological) actions cannot be performed maximally at the same time. Trade-offs underlie the fact that ‘‘a jack of all physiological trades is a master of none,’’ which in turn is the basis of the generalist-specialist continuum that brings about much of the niche differentiation in ecology. (2) A second guiding concept is that whole-organism performance provides an integrative measure of individual success in life. Quantifying individual performance allows physiological ecologists to assess the integration of traits within an organism and to determine how natural selection orchestrates not just one but all characteristics of an organism at the same time. Whereas in the past, physiological ecologists have also often studied animals in laboratory situations, technological advances now allow researchers to ‘‘go wild’’ and address individual physiological functions in the very environment where such functions have evolved. The importance of studying animal function in the wild cannot be overestimated because many organismal tradeoffs are expressed only when food is scarce or predators are abundant. GLOSSARY constraints. These can absolutely limit certain actions of an organism. Even if all efforts in a trade-off scenario are devoted toward a particular action, this action is not sufficient to satisfy an organism’s current needs. energy. In biology, energy, which is essential for life, is gathered from the breaking of chemical bonds during metabolic processes. Energy is often stored by cells in the form of substances such as carbohydrate molecules (including sugars) and lipids, which release energy when reacting with oxygen. hormones. These substances are chemical messengers that carry information from one part of the organism (e.g.,thebrain)toanother(e.g.,thegonads)often via the blood transport system. Hormones bind to receptors on target cells and thus regulate the function of their targets. Various factors influence the effects of a hormone, including its pattern of secretion , transport processes, the response of the receiving tissue, and the speed with which the hormone is degraded. metabolic rate. Energy expenditure per unit time. Metabolic rate is normally expressed in terms of rate of heat production (kilojoules per time). performance. This refers to whole-organism performance capabilities (e.g., how fast an organism can sprint) that are determined by physiological traits (e.g., composition of muscle fibers). trade-offs. These attributes refer to the loss of one quality or aspect of something in return for gaining another quality or aspect. Physiological ecology occupies a central role in the biological sciences and has a long tradition of integrating other biological disciplines. Physiological systems provide the interface between genomics at the lowest mechanistic level to organismal life history and evolution at the highest level of biological integration. Every biological process linking genes to behavior will ultimately have to be understood mechanistically on the physiological level to truly provide a picture of how organisms function. There are many levels at which physiological ecologists attempt to discern how organisms work. On the lowest level, physiological ecology meets genomics and proteomics. For example, Chi-Hing Chris Cheng and Art DeVries from the University of Illinois, working on the antifreeze protein in Antarctic fish, discovered that the protein is coded by a simple but frequent DNA repeat derived from a snippet in a trypsinogen-like protein gene, initially presumably by chance. This protein appeared to have just the right structure to recognize the surface structure of ice crystals that enter into the blood of the fish. Working up the physiological levels, because ice that enters into the fish’s circulation always end up in the spleen, Cheng and DeVries hypothesized that the immune system, perhaps macrophages, of these fish living at subfreezing temperatures would take care of the nascent ice crystals encapsulated or presented by the antifreeze protein. Perhaps not unlike a pathogen, the immune system then either ‘‘kills’’ or lyses or excretes the nasty foreign body—a spiny ice crystal that would otherwise serve as...