Abstract
In ectotherms such as teleost fish the external temperature affects directly their metabolism, physiology and behavior. In the past, they had to adapt to changes in global temperature that occurred within tens of thousands of years. Nowadays, the global climate change induces warming by several degrees within a few decades, inducing already detectable alterations such as in sex determination, emergence of new diseases, changes in distribution areas, or disruption of migration programs. Illustrating this last point the sustainability of Atlantic salmon Salmo salar of the basin Loire/Allier is now threatened. The Conservatoire National du Saumon Sauvage (CNSS), partner of this project, captures wild brood stocks to ensure reproduction and restocking of this emblematic unique strain. Once ready for downstream migration to the sea -a crucial stage in their life cycle- salmons are released in the river. Year after year, the CNSS observes a narrowing of the most favorable window for migration. This is due to a combination of factors including long-distance migration (900km), obstacles and now warming, due to global climate change and local human activities. The process of downstream migration is controlled by the interaction of photoperiod and temperature; the modes of action are partially elucidated for the former and largely unknown for the latter. Global climate change leads to a lag between temperature and photoperiod, with direct consequences on the downstream migration process. The future of the local Salmon population, already greatly threatened, depends on its degree of adaptability to this shift. This project aims to elucidate the mechanisms of preparation and initiation of downstream migration of wild salmon from the Loire/Allier basin and the impact of global warming on these processes. We will investigate, using in vivo and in vitro approaches, how photoperiod and temperature interact in controlling on the one hand the rate of production of melatonin, a time-keeping hormone and, on the other hand the neuroendocrine hypothalamic-pituitary axis involved in the preparation and triggering the downstream migration. We will test the hypothesis that some or all of the effects of temperature are mediated by membrane bound calcium channels (Transient Receptor Potential channels) acting on the pineal organ and the neuroendocrine axis. A large scale experiment will be implemented at the CNSS to study the impact of a 5°C warming on locomotor activity and downstream migration behavior as well as on the underlying molecular, endocrine and physiological processes. Putting all the results together will help understanding and predicting the impact of a temperature rise and the subsequent induced shift with photoperiod, on the downstream migration, survival of the population and sustainability of the restocking actions. /n By combining molecular, physiological and behavioral approaches, this project should lead to an understanding of the impact of temperature and photoperiod on the downstream migration of the Loire/Allier basin salmon. This should help offering optimal solutions for the preparation of young salmon as they enter at sea and thus to counter the negative effects of warming. More generally, we will be able to understand how salmon perceive, integrate and transmit temperature information, particularly at the levels of two integrating systems, the pineal (for time-keeping) and the neuroendocrine axis (for physiological regulations). The acquired data will bring new basic information for studies on the impact of temperature on other (migratory or not) species of economic value and/or ecological importance.
France