ABS 2022
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The effects of nestling size and parental care on development of offspring physiology.
Zachary Laubach1, Sage Madden2, Aleea Pardue1, Kim Hoke3, Rebecca Safran1. 1University of Colorado, Boulder, Boulder, CO, United States; 2University of Califiornia, Davis, Davis, CA, United States; 3Colorado State University, Fort Collins, CO, United States

Size and growth early in life are important determinants of physiological development and offspring survival. In birds, asynchronous hatching can result in differences in nestling size, leaving smaller nestlings at a competitive disadvantage. Moreover, parental care, which is necessary for nestling growth, may modify the relationship between nestling size and physiology. We used data from n = 44 wild barn swallows (Hirundo rustica) from which we collected fasting blood glucose at baseline and in response to standardized stressor to test the hypothesis that smaller nestlings will have dysregulated glucose metabolism, and that this relationship will be most pronounced in nests with low parental care. We found that larger nestlings had a greater increase in blood glucose (β = 15.1, 95% CI: -2.76, 32.94 mg/dl glucose difference) than the smallest nestlings, which appear to exhibit a blunted glucose response. Given that glucose metabolism is essential for growth and considering that mobilization of glucose is a primary function of the vertebrate stress response, these results suggest that physiological costs may be part of the disadvantage of being small during early life.