Meeting Abstract
Plasma glucocorticoid (CORT) levels collected within 3 min of capture/handling are commonly believed to reflect pre-stressor CORT levels. Differences in these ‘baseline’ values are often interpreted as differences in the amount of social or environmental stress individuals have been exposed to prior to capture. However, many studies find inconsistent or absent relationships between ‘baseline’ CORT, health, and fitness. When interpreting ‘baseline’ values it is generally assumed that either 1) capture/handling stress did not influence CORT values prior to sampling or 2) any increase in CORT prior to sampling was both small enough, and consistent enough among individuals, not to obscure pre-capture differences. Yet, CORT increases in less than 3 min post-capture in most species in which timing has been carefully assessed, and the rate that stress-induced CORT levels increase can differ among individuals of the same species (e.g., stress-response phenotypes). In Florida scrub-jays (Aphelocoma coerulescens), plasma CORT levels begin to increase approximately 2 min post-capture, but the rate of increase between 2 and 3 min differs markedly between individuals with different stress-response phenotypes. Further, an individual’s stress responsiveness correlates with CORT levels collected within 1.5 min post-capture, suggesting that before capture there are intrinsic differences in basal CORT levels between the phenotypes. Together these data indicate that ‘baseline’ CORT values can be strongly influenced by an individual’s stress responsiveness. This influence can obscure, or entirely supersede, differences in basal CORT due to social or environmental stressors, thus complicating the interpretation of ‘baseline’ CORT values.
