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P416 Comparative Animal Physiology Fall Semester, 2005 Dr. Michael S. Finkler Much of What You Will Learn in This Course Will Someday Prove to Be Incorrect • Scientific discovery is limited by what can be perceived. • Always a chance that an idea is incorrect. – hypotheses and theories – No such thing as a scientific fact • Scientific knowledge is constantly revised as new insights into natural phenomena are gained. • Scientists must maintain a healthy skepticism and an open mind. Physiology is the study of how a living organism stays alive What is Physiology? The study of biological function • A difficult task! – Living organisms have complex, organized structures – Second Law of Thermodynamics: • Degree of disorder in the universe can only INCREASE • Living organisms must maintain order in a universe that tends to move towards disorder. How does a living organism stay alive? • Living organisms maintain order inside their bodies (the “internal environment”) by increasing disorder in the external environment • Maintenance of constant conditions in the internal environment necessary for order (life) to be maintained. Homeostasis • State of constancy within the internal environment of a living organism • A dynamic process – constant adjustment to counteract changes • Central principle of physiology 1 How does an organism maintain homeostasis? • Regulation – maintaining different attributes of the internal environment at relatively constant levels – Requires a regulatory mechanism: • Sensor - Detects changes (disturbances) in the internal environment • Effector - Performs an activity that compensates for the change Regulatory Mechanisms Work by Feedback • Feedback = return of output to the input part of a system • The response of the effector influences subsequent output by the effector • Controller/Integrator - controls activity of the effector based on information from the sensor Types of Feedback • Negative Feedback – activity of effectors opposes any deviation of the controlled variable from the regulated level – most common type in biology • Positive Feedback – activity of effectors enhances deviation of controlled variable from the regulated level – rare in biological systems, and always part of a larger negative feedback system Subdisciplines • Ecological Physiology – a.k.a. Environmental Physiology, Physiological Ecology – examines adaptations of organisms to their environment • Evolutionary Physiology – seeks understanding of evolutionary relationships based on physiological attributes Comparative Physiology Compares physiological functions between species to discern physiological and evolutionary patterns Adaptation • Evolution through natural selection leading to an organism whose physiology, anatomy and behavior are matched to the demands of its environment. • A slow process, over multiple generations • Central topic of comparative animal physiology 2 Adaptation is Sometimes Confused With: Differences • Acclimatization Acclimation/Acclimatization • changes occur in an individual • changes are generally reversible Adaptation • changes occur over multiple generations • changes not generally reversible – physiological/biochemical/anatomical change in an individual organism resulting to chronic exposure to new conditions in the natural environment • Acclimation – similar changes induced in laboratory settings Adaptive Approaches to Environmental Change A Characteristic is Adaptive If: It confers a maximal probability of survival and successful reproduction in comparison with available alternative states. Qualifiers: – Characters are adaptive only in specific environmental contexts. – Adaptive ≠ optimum 1. Tolerance (Conformity) – 2. Opposition (Active Resistance) – 3. Increase degree of tolerance to adverse conditions (decreased maintenance of homeostasis). Increase activity of regulatory mechanisms to maintain homeostasis at tight levels. Evasion (Escape) – Avoid change in conditions (behavioral) The alternative = Death (Failure) – not usually very adaptive 3