Meeting Abstract
Most vertebrates respond to environmental and social stressors by increasing glucocorticoid secretion, which is expected to promote survival. However, when individuals are unable to evade stressors they can be exposed to chronically elevated glucocorticoids, which can have several negative long-term effects. One measure that may be a sensitive physiological indicator of chronic stress exposure is leukocyte counts, however this has seldom been experimentally tested. Here we experimentally manipulated chronic stress exposure in developing house sparrow (Passer domesticus) chicks and examined the effects on the heterophil to lymphocyte ratio (H:L ratio). After hatching, broods were split, and half of the chicks were randomly assigned to a control or chronic stress treatment. Chicks from both treatments were handled on days 2, 6, and 10 to measure growth. Blood samples were collected on day 10 to measure H:L ratios. Between days 2 and 10, chicks in the chronic stress treatment were also removed from the nest daily and exposed to restraint stress by placing them in a cloth bag for 30 minutes. We predicted that chicks in the chronic stress treatment would have a higher H:L ratio than their siblings in the control treatment. H:L ratios were analyzed blindly with respect to treatment using a compound microscope and were highly repeatable (R=.883, p=<.001). We found that although there was no effect of treatment on growth (F1,30.33=1.61, p=.21), H:L ratios were significantly higher in chicks in the chronic stress treatment than controls (F1,36=11.21, p=<.001). This study suggests that chronic stress increases the H:L ratio and that the H:L ratio may serve as a sensitive, minimally invasive tool to monitor chronic stress in developing chicks.
