Whole nest food restriction has persistent physiological effects in developing zebra finches

In a rapidly changing world, food resources are becoming more limited, leading to unpredictable bouts and durations of nutritional stress. Many studies indicate that developmental nutritional stress can permanently alter a suite of physiological, morphological, or behavioral traits, yet the phenotypic effects of low food supply in the environment may vary depending on the mode and degree of parental care. For example, our previous work suggests that zebra finch (Taeniopygia guttata castanotis) parents can buffer offspring from food restriction, minimizing negative effects on offspring growth, at the cost of maintaining their own body mass. To evaluate the effects of whole nest food restriction on the offspring further, we investigated short- and long-term changes in physiological and morphological traits of zebra finch young exposed to either an ad libitum diet or a 40% restricted diet as nestlings and juveniles until 60 days post-hatch. Specifically, we measured furculum fat, the adrenocortical response, and glucose levels throughout development and into adulthood as well as body mass in adulthood to examine any latent or persistent effect. Young from the food-restricted nests overall had significantly higher baseline corticosterone and glucose compared to controls, suggesting that the previously observed parental buffering may not have been sufficient to mitigate the deleterious effects of food restriction. Furthermore, food-restricted birds had lower body mass compared to controls in adulthood, suggesting that there was a latent effect that manifested in adulthood, potentially due to the physiological costs observed during treatment and the later release of treatment. Furculum fat, the glucose response, and the adrenocortical response did not differ between experimental groups. There was also no difference in brood body size variance between treatment groups, and previously observed parental compensation in food-restricted nests did not correlate with offspring body mass in adulthood. Lastly, there was a significant negative relationship between body mass and baseline corticosterone in adulthood, suggesting that although growth and body mass were maintained during treatment, energy may have been redirected from growth and body mass maintenance to different processes in adulthood. This study further supports the need for measuring traits after treatment ends to determine persistent effects of stressors and highlights that parents cannot fully buffer their offspring from adverse environmental conditions.