Meeting Abstract
52.4 Saturday, Jan. 5 Learning about novel stressors: a role for acute corticosterone elevations in free-ranging lizards THAKER, M*; HEWS, DK; LIMA, SL; Indiana State Univ.; Indiana State Univ.; Indiana State Univ. mthaker@indstate.edu
Elevation in plasma corticosterone (CORT) during stressful events has been functionally linked to immediate changes in behaviors such as locomotion, foraging activity, and antipredator tactics in a variety of vertebrates. Lab studies indicate that acute CORT elevations mediate learning about stressors. Using wild male eastern fence lizards (Sceloporus undulatus), we provide the first field test of the hypothesis that an acute CORT elevation facilitates responding to and learning about a novel stressor. We used the enzyme inhibitor metyrapone to temporarily block stress-induced CORT synthesis, which we have demonstrated for this species. Immediately after capture, lizards were injected intracoelomically with either a metyrapone or control solution (polyethylene glycol) and were left undisturbed at site of capture for 20 min before the start of three sequential learning trials. Using a standardized protocol, each injected lizard was then exposed every 20 min for 1 hr to a novel stressor in the field � a rapidly approaching small red object. Each lizard, therefore, had three opportunities to learn about this novel stressor. Control lizards had greater flight-initiation distances (FID) and longer hiding durations than metyrapone lizards during the first presentation of the novel stressor. During the subsequent stressor encounters, control lizards progressively increased their FID and hid for shorter durations but metyrapone lizards did not change escape response tactics. A third set of lizards, exposed to the novel stressor for the first time 60 min after metyrapone or control injections, exhibited �uninformed� escape tactics similar to comparably-treated lizards that were first exposed to the stressor 20 min post injection. Our results suggest that inhibiting an acute corticosterone elevation with metyrapone impairs responding to and learning about novel stressors.
