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Nutritional constraints on growth and metabolic rate of an ectotherm consumers (Daphnia magna) in a context of global change : Experimental approach by microcalorimetry

Abstract : In a context of global change, anticipating alterations in the structure and functioning of aquatic ecosystems is a major ecological issue. However, the fragmentation of ecology into a multitude of sub-disciplines is seen as an obstacle to all predictions, creating a growing desire to unify the different theoretical frameworks of ecology. In this context, the harmonizing of stoichiometric ecology and metabolic ecology is increasingly required (Allen and Gillooly, 2009; Hillebrand et al., 2009; Ott et al., 2009; Ott et al., 2009). al., 2014). This thesis work was mainly devoted to establishing the links between nutritional quality and consumers’ metabolic rate in order to understand how their interactions could affect the growth of organisms. The aim was also to understand how environmental factors associated with global change (warming, salinization) could affect this notion of nutritional quality or interact with it through individual metabolism. In this regard, the experimental part of this thesis focused on the water flea Daphnia magna, a key organism in aquatic food webs, particularly sensitive to the quality of its food resources. We first determine how the rise in temperatures could modulate the notion of nutritional quality for the consumer. Secondly, the development of a method based on microcalorimetry allows to establish the existing links between nutritional quality and consumer's metabolic rate. Finally, we explored the interactions between nutritional quality, metabolic rate and osmotic stress on Daphnia life traits in order to understand how an environmental factor (here salinity) could affect or be affected by quality-metabolism links.Our results first demonstrated the strong thermal dependence of stoichiometric nutritional requirements in Daphnia as well as the resulting potential consequences on producer-consumer decoupling in a context of global change. We then demonstrated the consequences of this decoupling (i.e. nutritional quality) on the resting metabolic rate (RMR) of consumers. We have demonstrated a systematic rise in RMR when decreasing nutritional quality. This additional energy cost ultimately having repercussions on the growth of consumers, measuring the RMR here seems to allow the quantification of the energy cost of nutritional constraints (stoichiometric but also biochemical). Finally, we were able to highlight the interactions between nutritional quality and tolerance to salinity as well as their repercussions at the metabolic level. In general, this thesis demonstrated the central role of RMR in the response of organisms to environmental stresses. Thus, measuring the RMR could constitute an essential indicator for predicting the structure and functioning of ecosystems in a context of global change.
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https://tel.archives-ouvertes.fr/tel-03071628
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Submitted on : Wednesday, December 16, 2020 - 9:46:07 AM
Last modification on : Thursday, December 17, 2020 - 3:37:57 AM

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Thomas Ruiz. Nutritional constraints on growth and metabolic rate of an ectotherm consumers (Daphnia magna) in a context of global change : Experimental approach by microcalorimetry. Ecology, environment. Université Clermont Auvergne, 2020. English. ⟨NNT : 2020CLFAC029⟩. ⟨tel-03071628⟩

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