Ts. Jessop et al., Evidence for a hormonal tactic maximizing green turtle reproduction in response to a pervasive ecological stressor, GEN C ENDOC, 118(3), 2000, pp. 407-417
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.