Positive association between experimental cortisol increases and cage-measures of feeding behavior in wild-caught gerbils

Glucocorticoid hormone levels vary within a forager based upon environmental stressors such as illumination and riskier habitats, and a forager's response to environmental variables depends upon its glucocorticoid levels. Here, we report on a laboratory experiment in which we manipulated cortisol in Allenbyi's gerbils (Gerbillus andersoni allenbyi) to test the relationship between cortisol and behavior. We then quantified the resulting blood cortisol levels and feeding behavior in gerbils. Thirty gerbils were injected with 21-day slow-release cortisol pellets drawn from 5 different dosages. We quantified the physiological response to pellet implantation in gerbils by measuring cortisol level in blood serum using ELISA (Enzyme Linked Immunosorbent Assay). We fed gerbils daily by mixing millet seeds into the sand inside rodent cages and measured the remaining seeds the following day to quantify feeding efforts. Some evidence supports that subcutaneous supplementation of glucocorticoids (GCs) in the gerbils led to higher blood serum levels. Cortisol levels varied according to time period of measurement. Gerbils that received lower dosages consumed most of the food presented to them when compared to those receiving the highest doses. In this manner, we delineate a pattern on cortisol hormone level variation over time following dosing and consequences in feeding behavior.