Seasonal body composition remodeling reveals tissue maintenance during dormancy and selective reserve mobilization during reproduction in tegu lizards Salvator merianae.

Understanding how organisms allocate energy across competing physiological demands is central to predicting responses to environmental variation. In seasonal environments, shifts in resource availability and activity impose dynamic constraints on energy storage, maintenance and reproduction. Here, we investigated seasonal changes in body composition in the tegu lizard Salvator merianae using the minimally invasive dual-energy X-ray absorptiometry (DEXA) technique. After DEXA validation against direct chemical analysis for this species, male and female individuals were repeatedly scanned across key phases of the annual cycle, including hibernation, reproduction and transition phases between them. Body composition remained largely unchanged during prolonged dormancy, despite fasting and inactivity, with lean and mineral compartments comparatively maintained in both sexes. In contrast, reproduction was associated with the most pronounced seasonal shifts, including reductions in fat reserves and increases in protein- and water-related compartments in both sexes, together with mineral remodeling that was more evident in females. In subsequent months, several of these components shifted back toward pre-reproductive values. These patterns indicate a coordinated reorganization of energy and body resources across seasons, with fat reserves mobilized during reproduction while lean and mineral compartments followed distinct, phase-dependent trajectories. Our results suggest a partial decoupling between energy storage and structural maintenance, consistent with the idea that key functional compartments may be differentially buffered against seasonal constraints. By linking within-individual variation in energy reserves to shifts in physiological demands, this study provides an integrative physiological perspective on how life-history trade-offs are expressed in seasonal environments. More broadly, these findings contribute to understanding how physiological flexibility may influence organismal performance under changing environmental conditions. SUMMARY STATEMENT: Validated DEXA measurements revealed broad maintenance of lean and mineral compartments during dormancy in both sexes, followed by fat mobilization during reproduction and sex-specific mineral remodeling, particularly in females.