Department of Ecology and Evolutionary Biology, Guyot Hall, Princeton University, Princeton, NJ 08540, USA.
Horm Behav. 2013 May;63(5):776-81. doi: 10.1016/j.yhbeh.2013.03.002. Epub 2013 Mar 19.
Correlative evidence from field studies has suggested that baseline concentrations of corticosterone, the main avian glucocorticoid hormone, affect reproductive strategies in vertebrate species. Such a role is conceivable in light of corticosterone's function as a metabolic hormone in regulating glucose and fat metabolism. From such correlational studies, however, the question has remained open whether glucocorticoid concentrations change in advance of reproductive activities or whether corticosterone concentrations vary passively as a consequence of the individual's reproductive investment and workload. To test such causal relationships, we manipulated corticosterone concentrations prior to the breeding season in adult great tits (Parus major) and quantified reproductive investment and success. Two weeks before egg-laying, we administered subcutaneous silastic implants filled with corticosterone that elevated circulating levels within the baseline range for approximately 30 days to adult males and females. Corticosterone manipulation did not affect lay date or yearly offspring production. However, reproductive behaviors were affected by corticosterone treatment: males fed their mates more often during incubation, and females increased incubation of eggs and brooding of nestlings compared to control individuals. Other behaviors during the nestling stage, when the implants were no longer effective, did not differ between the two treatment groups. Our findings do not support the view that baseline corticosterone concentrations, at least at the time of year when we administered implants, change reproductive strategies per se. The current data suggest that baseline corticosterone levels represent internal signals that causally mediate reproductive effort in individuals of a wild bird species. By increasing reproductive investment, baseline corticosterone concentrations may have functions during the breeding season that diverge from the suppressive effects of stress-induced concentrations.
来自野外研究的相关证据表明，皮质酮（主要的鸟类糖皮质激素）的基础浓度会影响脊椎动物物种的繁殖策略。鉴于皮质酮作为一种代谢激素在调节葡萄糖和脂肪代谢方面的作用，这种作用是可以想象的。然而，从这些相关性研究中，仍然存在一个问题，即糖皮质激素浓度是否会在繁殖活动之前发生变化，或者皮质酮浓度是否会被动地随着个体的繁殖投资和工作量而变化。为了检验这种因果关系，我们在繁殖季节前操纵了成年大山雀（Parus major）的皮质酮浓度，并量化了繁殖投资和成功。在产卵前两周，我们给成年雌雄鸟皮下植入了充满皮质酮的硅树脂植入物，使循环中的皮质酮水平在基础范围内升高，大约 30 天。皮质酮处理并没有影响产卵日期或每年的后代产量。然而，繁殖行为受到皮质酮处理的影响：雄性在孵化期间更频繁地给配偶喂食，而雌性与对照个体相比，增加了对卵的孵化和雏鸟的育雏。当植入物不再有效的育雏阶段的其他行为，两组之间没有差异。我们的研究结果不支持这样一种观点，即基础皮质酮浓度（至少在我们进行植入时的季节）本身会改变繁殖策略。目前的数据表明，基础皮质酮水平代表内部信号，在野生鸟类个体中因果地介导繁殖努力。通过增加繁殖投资，基础皮质酮浓度可能在繁殖季节具有与应激诱导浓度的抑制作用不同的功能。
