Influence of Stressor Duration on Leukocyte and Hormonal Responses in Male Southeastern Five‐Lined Skinks (Plestiodon inexpectatus)

Abstract

Environmental stressors elicit elevations of plasma glucocorticoid hormones. Stressors also result in increases in the circulating heterophil to lymphocyte ratio (H:L ratio), which has been linked to increased glucocorticoids. Recently, there has been debate about the extent to which stress-induced elevations of corticosterone are tied to increases in the H:L ratio and about whether one measure of physiological stress might be used in lieu of the other. Few studies have examined the responses of both variables to standardized stressors in free-living animals, especially reptiles. Stressors may also affect levels of other hormones, such as prostaglandins or testosterone, that may influence leukocytes. Therefore, the H:L ratio, corticosterone, prostaglandin E(2) (PGE(2) ), and testosterone were monitored in free-living male southeastern five-lined skinks, Plestiodon inexpectatus, in response to various durations of confinement stress. Skinks confined for 1 hr had elevated H:L ratios and elevated corticosterone concentrations. In addition, corticosterone was positively correlated with the H:L ratio. In contrast, there were no effects of 2 hr of confinement on the H:L ratio, in spite of maximal corticosterone. Plasma PGE(2) was not affected by 15, 30, or 60 min of confinement but was positively correlated with monocytes and negatively correlated with lymphocytes in the 1 hr of confinement experiment. Consistent with many other studies of reptiles, confinement stress did not result in suppressed testosterone. Overall, the results indicate that, in reptiles at least, the H:L ratio and plasma corticosterone do not covary consistently and one measure of stress cannot be used in lieu of the other.