Variation in oxidative status, but not structural and physiological development, associated with changing ontogenetic environments

Despite the potential for temporally-dependent relationships between trait values and fitness (e.g., as juveniles approach life-stage transitions such as fledging), how developmental stage affects canalization (a measure of robustness to environmental variation) of morphological and physiological traits is rarely considered. To test the sensitivity of morphological and physiological traits to environmental variation in two developmental stages, we manipulated brood size at hatch in European starlings (Sturnus vulgaris) and cross-fostered chicks between enlarged and reduced broods approaching fledging. We measured body size (mass, tarsus, wing length) and physiological state (aerobic capacity, oxidative status) at asymptotic mass on day 15, then cross-fostered chicks between ‘high’ and ‘low’ quality environments and assessed the same traits again on day 20, after five days of pre-fledging mass recession. Chicks in reduced broods were heavier at asymptotic mass and had lower reactive oxyg..., ,