Loiseau Claire, Fellous Simon, Haussy Claudy, Chastel Olivier, Sorci Gabriele
Laboratoire de Parasitologie Evolutive, CNRS UMR 7103, Université Pierre et Marie Curie, Bât. A, 7ème étage, 7, quai St Bernard, Case 237, F-75252 Paris Cedex 05, France.
Horm Behav. 2008 Jan;53(1):266-73. doi: 10.1016/j.yhbeh.2007.10.006. Epub 2007 Oct 18.
Begging is a complex display involving a variety of different visual and auditory signals. Parents are thought to use these signals to adjust their investment in food provisioning. The mechanisms that ensure the honesty of begging displays as indicators of need have been recently investigated. It has been shown that levels of corticosterone (Cort), the hormone released during the stress response, increase during food shortage and are associated with an increased begging rate. In a recent study in house sparrows, although exogenous Cort increased begging rate, parents did not accordingly adjust their provisioning rate. Here, we tested the hypothesis that Cort might affect the expression of other components of begging displays, such as flange color (a carotenoid-based trait). We experimentally increased levels of circulating Cort and investigated the effects of the treatment on (1) the flange coloration of the nestlings, (2) the behavioral response and (3) the parental allocation of food and (4) nestling condition and cell-mediated immune response. We found that Cort affected flange coloration in a condition-dependent way. Cort-injected nestlings had less yellow flanges than controls only when in poor body condition. Parental feeding rate was also affected by the Cort treatment in interaction with flange color. Feeding rate of Cort-injected nestlings was negatively and significantly correlated with flange color (nestlings with yellower flanges receiving more food), whereas feeding rate and flange color were not correlated in control chicks. We also found that nestlings injected with Cort showed a weaker immune response than controls. These results suggest that, indeed, Cort has the potential to affect multiple components of the begging display. As Cort levels naturally raise during fasting, parents have to take into account these multiple components to take a decision as to optimally share their investment among competing nestlings.
乞食行为是一种复杂的表现，涉及多种不同的视觉和听觉信号。人们认为，亲鸟会利用这些信号来调整它们在食物供应方面的投入。最近，研究人员对确保乞食行为诚实性（作为需求指标）的机制进行了调查。研究表明，应激反应过程中释放的激素皮质酮（Cort）水平在食物短缺时会升高，并且与乞食率的增加有关。在最近一项针对家麻雀的研究中，尽管外源性皮质酮增加了乞食率，但亲鸟并没有相应地调整它们的喂食率。在此，我们检验了这样一个假设，即皮质酮可能会影响乞食行为其他组成部分的表现，比如翅斑颜色（一种基于类胡萝卜素的特征）。我们通过实验提高了循环皮质酮的水平，并研究了这种处理对以下方面的影响：（1）雏鸟的翅斑颜色；（2）行为反应；（3）亲鸟的食物分配；（4）雏鸟的身体状况和细胞介导的免疫反应。我们发现，皮质酮对翅斑颜色的影响取决于身体状况。只有在身体状况较差时，注射了皮质酮的雏鸟的翅斑黄色程度才比对照组低。皮质酮处理还与翅斑颜色相互作用，影响了亲鸟的喂食率。注射了皮质酮的雏鸟的喂食率与翅斑颜色呈负相关且显著相关（翅斑颜色更黄的雏鸟获得的食物更多），而在对照雏鸟中，喂食率与翅斑颜色没有相关性。我们还发现，注射了皮质酮的雏鸟的免疫反应比对照组弱。这些结果表明，皮质酮确实有可能影响乞食行为的多个组成部分。由于禁食期间皮质酮水平会自然升高，亲鸟在决定如何在相互竞争的雏鸟之间最优地分配投入时，必须考虑到这些多个组成部分。
