Evidence for a hormonal tactic maximizing green turtle reproduction in response to a pervasive ecological stressor

Mortality of breeding sea turtles due to excessive heat exposure after nest ing activities is an unusual feature of the Raine Island green turtle rooke ry. Breeding turtles that fail to return to the ocean after oviposition can experience increasing body temperatures that exceed lethal limits (>39 deg rees C) as ambient temperatures rise after sunrise. We investigated how acu te increases in body temperature influenced plasma corticosterone (B) conce ntrations of individual turtles. Furthermore, interactions between progeste rone (P) and testosterone (T) and increasing body temperature and the gluco corticoid corticosterone were examined for negative correlations. Breeding green turtles exhibited a 16-fold mean increase in plasma corticosterone co ncentration as body temperature (cloacal) rose from 28.2 to 40.7 degrees C in less than 6 h. However, the absolute increase in plasma B was small and much less than expected, despite the lethal stressor. Comparatively, the ma ximal B response to lethal heat stress was similar to plasma B concentratio ns obtained from breeding female turtles exposed to 8 h of capture stress. However, the maximal B response of breeding turtles exposed to heat and cap ture stressors was significantly less than the B response of nonbreeding ad ult female turtles subjected to an 8-h capture stressor. No negative correl ations were observed between plasma T and plasma B, between plasma T and bo dy temperature, between plasma P and plasma B, or between plasma P and body temperature. Our findings provide further evidence that reduced adrenocort ical function operates in breeding green turtles in the presence of even th e most pervasive of environmental stressors. (C) 2000 Academic Press.