Individual variation in tolerance of hypoxia and high temperatures in teleost fish: mechanisms and implications

ended

Episodes of hypoxia and acute warming can be major environmental stressors for coastal marine fishes, that will increase in frequency and severity with global change. Hypoxia and warming share a common physiological mode of action in fishes, both challenge the animal's capacity to provide sufficient O2 to respiring tissues. Within fish populations, individuals may vary in tolerance of these stressors; the existence of such variation can define the ability of populations to persist in a more stressful world. Moreover, when individuals vary in tolerance, underlying physiological mechanisms for variation can be explored. Understanding of mechanisms is very valuable because the persistence of variation in tolerance, within populations, may indicate that there are functional trade-offs, whereby being tolerant is not systematically advantageous but has costs. Using controlled experiments on European sea bass, an emblematic coastal species, my aims are to: 1) document variation in sub-lethal tolerance of hypoxia and acute warming in a population of 200 juveniles, and reveal cross-tolerance; 2) demonstrate that relative tolerance depends upon each individual’s intrinsic respiratory physiology; 3) investigate how tolerance relates to underlying mitochondrial efficiency, and 4) evaluate whether tolerance trades-off against important individual traits, as growth rate and tendency to suffer from oxidative stress. The experiments comprise innovative state-of-the-art techniques of sea bass husbandry; in-vivo respirometry and exercise performance; sub-lethal tolerance endpoints based upon cardiorespiratory performance, and assays of mitochondrial function in fresh tissues. Data will be analyzed to reveal trait correlations and dependencies, and existence of functional trade-offs. These multiple level studies, to reveal functional trade-offs of tolerance to hypoxia and warming, will provide novel and important insights into the nature of fish populations in a more stressful world.