TY - JOUR T1 - Maternal glucocorticoid levels during incubation predict breeding success, but not reproductive investment, in a free-ranging bird JF - bioRxiv DO - 10.1101/685891 SP - 685891 AU - Devin Fischer AU - Robby R. Marrotte AU - Eunice H. Chin AU - Smolly Coulson AU - Gary Burness Y1 - 2020/01/01 UR - http://biorxiv.org/content/early/2020/06/17/685891.abstract N2 - The hormone corticosterone (CORT)) has been hypothesized to be linked with fitness, but the directionality of the relationship is unclear. The “CORT-fitness hypothesis” proposes that high levels of CORT arise from challenging environmental conditions, resulting in lower reproductive success (a negative relationship). In contrast, the “CORT-adaptation hypothesis” suggests that, during energetically demanding periods, CORT will mediate physiological or behavioural changes that result in increased reproductive investment and success (a positive relationship). During two breeding seasons, we experimentally manipulated circulating CORT levels in female tree swallows (Tachycineta bicolor) prior to egg laying, and measured subsequent reproductive effort, breeding success, and maternal survival. When females were recaptured during egg incubation and again during the nestling stage, the CORT levels were similar among individuals in each treatment group, and maternal treatment had no effect on indices of fitness. By considering variation among females, we found support for the “CORT-adaptation hypothesis”; there was a significant positive relationship between CORT levels during incubation and hatching and fledging success. During the nestling stage CORT levels were unrelated to any measure of investment or success. Within the environmental context of our study, relationships between maternal glucocorticoid levels and indices fitness vary across reproductive stages.SUMMARY STATEMENT Maternal corticosterone levels predict breeding success of female tree swallows.Competing Interest StatementThe authors have declared no competing interest. ER -