Food Restriction Reveals Individual Differences in Insulin-Like Growth Factor-1 Reaction Norms

Most organisms have to cope with unpredictable environmental challenges such as fluctuations in nutritional resources. Insulin-like growth factor-1 (IGF-1) is an evolutionarily conserved hormone that highly sensitive the individual status and regulates major life-history traits including lifespan reproduction across vertebrates. We investigated role of IGF-1 during periods food shortages by altering between two feeding regimes (110 70% daily intake) after a period ad libitum captive bearded reedlings ( Panurus biarmicus ). Each dietary treatment was repeated twice. Birds lost mass under restriction, but magnitude change depended on preceding conditions. Moreover, showed large, repeatable differences their reaction norms some individuals increasing levels response restricted diet, whereas others no responses or decreased levels. This variation explained average body mass: heavier had higher control were more likely decrease restriction than did lighter ones. result uncovers environment interaction (I × E) may important implications for evolution related hormonal phenotypes this species.