Basal and stress-induced corticosterone levels in olive ridley sea turtles(Lepidochelys olivacea) in relation to their mass nesting behavior

Adrenocortical responsiveness to turning stress was examined in wild, repro ductively-active olive ridley sea turtles (Lepidochelys olivacea) in relati on to their mass nesting (arribada) behavior. We hypothesized that the high sensitivity threshold (HST) observed in ovipositing sea turtles is associa ted with a diminished sensitivity of the hypothalamo-pituitary-adrenal (HPA ) axis to stressful stimuli in arribada females. We tested this hypothesis by determining whether arribada females exhibited an increased activation t hreshold of the HPA axis to an imposed stressor (turning stress). Mean basa l corticosterone (B) and glucose levels were below 1.0 ng/ml and 60 mg/dl, respectively. Basal B remained unchanged throughout, a 24-hr period in bask ing females. Most animals responded to turning stress with elevated mean B levels (up to 6.5 hg/ml after 6 hr) and no increase:in circulating glucose. Nearly 50% of females (and none of the males) were refractory to the stimu lation. Males exhibited the most rapid response, with B levels significantl y elevated by 20 min over basal levels. Among females, arribada and solitar y nesters exhibited a slower rate of response than basking, non-nesting ani mals. These results demonstrate that olive ridleys exhibit stress-induced c hanges in circulating B which are slower than those observed in most reptil ian and in mammalian, avian, and piscine species. Furthermore, the presence of refractory females and the relatively slower increase in B in arribada and solitary nesters indicate a hyporesponsiveness of the HPA axis to turni ng stress in nesting olive ridleys. The hyporesponsiveness may be part of a mechanism to facilitate arribada nesting. J. Exp. Zool. 284::652-662, 1999 . (C) 1999 Wiley-Liss,Inc.