With climatic changes, there is a predicted increase in the frequency and amplitude of extreme weather events, with local climates becoming more variable. Temperature is one of the most important factors affecting thermoregulation and therefore the energetic budget of homeotherms and it could play a determinant role in their fitness. Thus, the rapid temperature fluctuations associated with an energetically constraining winter could severely affect animal species. To cope with environmental constraints, organisms have the capacity to adjust their behavior, their morphology and/or their physiology, via the phenotypic flexibility. This ability for adjustment should theoretically allow species to buffer, up to a certain limit, the effects of climatic disruptions. However, phenotypic flexibility is only rarely quantified (or in an incomplete way), which restricts our understanding about the capacity of species to adjust to environmental disturbance. Considering the potential negative impacts of climatic change on species’ energetic budget, it became essential to study the limits of phenotypic to understand how and at which speed species can adjust their physiology to track the rapid variations of climate. Furthermore, because the individual energetic condition plays a determining role on fitness, it is also important to consider the long-term consequences of climatic variations on the reproductive capacity of animal species. My project aims to determine the direct effects of different temperature variations on the phenotypic flexibility of parameters associated to thermal acclimation and to estimate the long-term impacts of physiological constraints imposed by thermal variation on reproductive capacities. More precisely, my objectives are to determine (1) whether the thermal variation frequency (stable, fast, slow) affects the speed of individual metabolic adjustments, and (2) if this thermal variation frequency produces delayed effects on adult’s reproductive capacity and offspring’s condition during growth.