Gil Diego, Bulmer Elena, Celis Patricia, López-Rull Isabel
Departamento de Ecología Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), José Gutierrez Abascal 2, 28006, Madrid, Spain.
Proc Biol Sci. 2008 Mar 7;275(1634):549-54. doi: 10.1098/rspb.2007.1360.
Sibling competition has been shown to affect overall growth rates in birds. However, growth consists on the coordinated development of a multitude of structures, and there is ample scope for developmental plasticity and trade-offs among these structures. We would expect that the growth of structures that are used in sibling competition, such as the gape of altricial nestlings, should be prioritized under intense competition. We conducted an experiment in the spotless starling (Sturnus unicolor), cross-fostering nestlings to nests with different levels of sibling competition. We predicted that nestlings subjected to higher levels of sibling competition should develop larger gapes than control birds. We found that, halfway through the nestling period, overall size (a composite index of mass, wing, tarsus and bill) was reduced in nests with intense sibling competition, whereas gape width remained unaffected. At the end of the nestling period, experimental nestlings had wider gapes than controls. Additionally, a correlative study showed that nestling gape width increased when feeding conditions worsened and overall size decreased. These patterns could either be due to increased growth of gape flanges or to delayed reabsorption of this structure. Our results show that birds can invest differentially in the development of organs during growth, and that the growth of organs used in sibling competition is prioritized over structural growth.
同胞竞争已被证明会影响鸟类的整体生长速度。然而，生长是由众多结构的协调发育组成的，并且在这些结构之间存在着充分的发育可塑性和权衡取舍的空间。我们预计，在同胞竞争中使用的结构，如晚成雏鸟的嘴裂，在激烈竞争下其生长应被优先考虑。我们对纯色椋鸟（Sturnus unicolor）进行了一项实验，将雏鸟交叉寄养到具有不同同胞竞争水平的巢中。我们预测，受到更高水平同胞竞争的雏鸟应该比对照鸟发育出更大的嘴裂。我们发现，在雏鸟期过半时，同胞竞争激烈的巢中雏鸟的整体大小（体重、翅膀、跗跖和喙的综合指数）减小，而嘴裂宽度不受影响。在雏鸟期末期，实验雏鸟的嘴裂比对照雏鸟更宽。此外，一项相关性研究表明，当喂食条件变差且整体大小减小时，雏鸟的嘴裂宽度会增加。这些模式可能是由于嘴裂边缘的生长增加，或者是由于该结构的再吸收延迟。我们的结果表明，鸟类在生长过程中可以对器官发育进行不同的投入，并且在同胞竞争中使用的器官的生长比结构生长更受优先考虑。
