Unpredictability and adaptive responses to dietary variability in Japanese quail

Understanding animals' molecular mechanisms of adaptation to unpredictable changes in dietary availability provides insights into how organisms optimize resource utilization and ensure survival under such conditions. The mechanistic target of rapamycin (mTOR) is a candidate nutrient-sensing pathway underpinning a form of adaptive plasticity when individuals encounter constraints in their energy budget. We exposed adult Japanese quails (Coturnix japonica) of both sexes to three dietary conditions: daily unpredictable feeding, constant restriction and full feeding for 16 days. Our study revealed that unpredictability reduced the body mass of female birds, whereas males remained unaffected. Egg production traits were not affected by unpredictable feeding. However, constant dietary restriction had a significant negative impact, suggesting resource reallocation to reproduction under unpredictable feeding conditions. We found sex-dependent gene expression patterns of mTOR pathway genes: while the unpredictable treatment did not affect gene expression in males, it downregulated MTOR and insulin-like growth factor-1 (IGF1) and its receptor (IGF1R) and upregulated Unc-51-like autophagy activating kinase-1 (ULK1) and autophagy-related genes (ATG9A and ATG5) in females. Additionally, variation in mTOR pathway gene expression was significantly associated with the effect of treatments on body mass and egg mass. Our study highlighted molecular mechanisms and adaptive responses towards dietary unpredictability and scarcity. This article is part of the theme issue 'Embracing variability in comparative physiology: why it matters and what to do with it'.