Cyr Nicole E, Michael Romero L
Department of Biology, Tufts University, Medford, MA 02155, USA.
Gen Comp Endocrinol. 2007 Mar;151(1):82-9. doi: 10.1016/j.ygcen.2006.12.003. Epub 2006 Dec 22.
Chronic increases in stress hormones such as glucocorticoids are maladaptive, yet studies demonstrating a causal relationship among chronic stress, increases in glucocorticoid concentrations, and subsequent fitness costs in free-living animals are lacking. We experimentally induced chronic psychological stress in female European starlings (Sturnus vulgaris) by subjecting half of the females at our study site to a chronic stress protocol consisting of 4, 30 min stressors (loud radio, predator calls, a novel object, or predator decoys including a snake, rat, and owl) administered in random order daily for 8 days after clutch completion. Experimental females were captured at the end of the chronic stress protocol (9 days after the onset of the chronic stress protocol), and unstressed control females were captured at the same stage of the nesting cycle. Chronically stressed females had lower baseline corticosterone (CORT, the avian glucocorticoid) concentrations and lower reproductive success than unstressed females. Furthermore, surviving nestlings in experimentally stressed broods showed sensitization of the CORT response to acute stress, which is a physiological change that could persist to adulthood. Attenuation of baseline CORT concentrations in adult females is contrary to the general assumption that elevated CORT concentrations indicate stress, suggesting that more research is necessary before CORT concentrations can be used to accurately assess chronic stress in field studies.
长期增加诸如糖皮质激素等应激激素是适应不良的，但缺乏在自由生活的动物中证明慢性应激、糖皮质激素浓度增加和随后的适应性代价之间存在因果关系的研究。我们通过对研究地点一半的雌性欧洲椋鸟（Sturnus vulgaris）进行慢性应激实验，在产卵完成后，每天以随机顺序对其施加4次、每次30分钟的应激源（大声播放的收音机、捕食者叫声、一个新物体或包括蛇、老鼠和猫头鹰的捕食者诱饵），持续8天。在慢性应激实验结束时（慢性应激实验开始9天后）捕获实验雌性，在筑巢周期的同一阶段捕获无应激的对照雌性。长期受应激的雌性比无应激的雌性具有更低的基础皮质酮（CORT，鸟类糖皮质激素）浓度和更低的繁殖成功率。此外，实验应激巢中的存活雏鸟表现出对急性应激的CORT反应敏感化，这是一种可能持续到成年期的生理变化。成年雌性基础CORT浓度的降低与CORT浓度升高表明应激的一般假设相反，这表明在将CORT浓度用于野外研究中准确评估慢性应激之前，还需要更多的研究。
