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Fish adaptation to freshwater hypoxia: developmental, transgenerational and evolutionary potential

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Hypoxia (i.e. condition of low oxygen dissolved) represents one of the most important challenges for freshwater ecosystems. While hypoxia events occur naturally, human activities have exacerbated their strength and temporal fluctuations. The possible adaptation to hypoxia events is likely to happen at different time scale. When directly exposed, organism may be able to adjust their phenotypes through phenotypic plasticity. However, continued responses to ongoing hypoxia change will depend on the phenotypic evolution of the species. In addition, some non-genetic transgenerational effects may also occur to facilitate evolution. It is thus essential to document all these type of responses to have a better understanding of the potential response of populations to changing environments. Therefore, the main aims of this project are: 1) to determine how hypoxic conditions may affect the plastic response (morphology, physiology, behaviour) of a fish species (three-spined sticklebacks, Gasterosteus aculeatus) within a generation, 2) to document phenotypic and genetic differences in populations of sticklebacks with different historical levels of hypoxia conditions, and 3) to investigate the occurrence of non-genetic transgenerational effects across generations. This project will use an innovative approach to investigate the mechanisms underlying fish response to environmental change as it will integrate the effects of plasticity, evolution and non-genetic transgenerational effects.

Hypoxic events (i.e. low oxygen concentration in water) are recognized as a major threat for freshwater ecosystems and bound to be more frequent and severe due to current global change. As aquatic organisms may be challenged by these changes, without a possibility to escape, we need to better understand how they can respond to these changes and across which time scale. Indeed, organisms can adjust their physiology (especially their metabolism) to cope with the reduction of oxygen in their environments, with potential implication for their morphology and behavior, but these adjustments could also have repercussions (either beneficial or not) on the following generations. If the environmental pressures persist, some genetic adaptation could even occur. Therefore, the aim of this project was to determine how the hypoxic conditions may affect the physiology, morphology, and behavior of a fish species (three-spined sticklebacks) within a generation, to investigate the cross-generational effect of hypoxia in the following generations, and to estimate the potential for genetic adaptations and evolvability to recent hypoxic conditions. This project used an innovative approach to investigate the mechanisms underlying fish response to current environmental change as it integrated the effects of plasticity, evolution and non-genetic cross-generational inheritance in a multidisciplinary framework. Our ability to understand how and through which mechanisms fish populations can adapt to these changing conditions is essential to better predict future responses of natural populations to hypoxic events and to advise more wisely the management of natural aquatic environments.

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