The makings of a robust and tolerant fish
Our oceans are in trouble. As climate change causes oceans to become warmer, they start to lose oxygen. This in turn can result in hypoxia, a condition where the water has a low concentration of dissolved oxygen. “Both warming and hypoxia could have significant consequences on marine life and the evolution of fish species,” says Julie Nati, a Marie Skłodowska-Curie fellow at the University of Montpellier. Her research was conducted in affiliation with the French National Centre for Scientific Research (CNRS) and at the Marine Biodiversity Exploitation and Conservation (website in French) (MARBEC) research unit of France’s National Institute for Ocean Science (Ifremer). With the support of the EU-funded INDITOL project, Nati is working to better understand how global warming and hypoxia impact fish. “This research will provide essential insights into how the selective effects of hypoxia and acute warming might shape emergent fish populations,” adds Nati.
Variations in tolerance
Populations vary their tolerance to hypoxia and warming. “The existence of variation in tolerance can define the population’s ability to persist – even thrive – when challenged by these stressors,” she explains. “Understanding this tolerance at the individual level opens the door to exploring the underlying mechanisms of the variation.” During the project, researchers investigated the mechanisms and implications of individual variations in tolerance to hypoxia and acute warming in the European sea bass, a valuable coastal species of fish. The research involved studies at the whole animal and subcellular levels, using state-of-the-art physiological methods. “We performed a careful investigation of individual variation tolerance using sublethal end points in a large experimental population of approximately 900 fish,” notes Nati. “This allowed us to examine how tolerance relates to individual metabolic phenotypes and cardiorespiratory performance.” Researchers also took a subset of 95 individual fish and measured mitochondrial respiration in fresh tissue samples from the liver and heart. “We collected the largest known data set for fish physiology,” adds Nati. “The sample size we used will allow us to get important genetic information, such as heritability, for some of the physiological traits we measured.”
Functional trade-offs
From this research, Nati successfully identified the underlying physiological characteristics that define a robust and tolerant individual fish. As she explains, this understanding is valuable because the persistence of variation in tolerance within populations may indicate that there are functional trade-offs. It could be that tolerance is not systematically advantageous but has consequences or costs. In other words, if environmental stressors provide fitness advantages to particular tolerance phenotypes, this may change the nature of the population as a whole. “Determining the adaptive responses of fish populations towards two major environmental stressors will help us identify robust strains,” concludes Nati. “Such information will prove invaluable to predicting the future of fishery stocks and improving the sustainability of aquaculture.”
Keywords
INDITOL, fish, climate change, evolution, oceans, hypoxia, marine life, global warming, fishery, aquaculture
