Eikenaar Cas, Hessler Sven, Ballstaedt Elmar, Schmaljohann Heiko, Kaiya Hiroyuki
Institute of Avian Research, An der Vogelwarte 21, 26386 Wilhelmshaven, Germany.
Institute of Avian Research, An der Vogelwarte 21, 26386 Wilhelmshaven, Germany.
Physiol Behav. 2018 Oct 1;194:450-455. doi: 10.1016/j.physbeh.2018.06.036. Epub 2018 Jun 26.
The spectacular natural phenomenon of avian migration is evidently shaped by physical factors, but we know little about the underlying physiological regulation. This contrast is especially apparent for the process of departure on a migratory flight. The decision to resume migration is shaped by a suite of departure cues from innate rhythms, and intrinsic and extrinsic factors. It currently appears that these departure cues are translated into actual departure by the hormone corticosterone, but other hormones may play a role too and probably interact with corticosterone. We captured this concept here by investigating the role of the hormone ghrelin and its interaction with corticosterone for the departure decision in a migratory songbird. Ghrelin functions as an appetite-regulating hormone. It has also been suggested to be involved in the regulation of departure by upregulating corticosterone in migrants ready to depart, and by facilitating the breakdown of lipids to fuel migratory flight. We measured plasmatic ghrelin and corticosterone levels in migrating common blackbirds (Turdus merula) at an autumnal stopover site, and determined their departure timing with the use of a fully-automated radio-telemetry system. Against our expectations, ghrelin level was not correlated with the birds' lipid stores or with corticosterone level. Furthermore, departure likelihood and nocturnal departure time were not associated with ghrelin levels. Our study thus does not support the idea that ghrelin is involved in the regulation of departure from stopover, at least not in common blackbirds. We discuss possible reasons for the lack of confirmation of our expectations.
鸟类迁徙这一壮观的自然现象显然受到物理因素的影响，但我们对其潜在的生理调节机制却知之甚少。这种反差在候鸟开始迁徙飞行的过程中尤为明显。重新开始迁徙的决定是由一系列来自内在节律、内在和外在因素的出发线索所决定的。目前看来，这些出发线索是通过激素皮质酮转化为实际出发行为的，但其他激素可能也发挥了作用，并且很可能与皮质酮相互作用。我们通过研究激素胃饥饿素及其与皮质酮在一种候鸟出发决定中的相互作用，捕捉到了这一概念。胃饥饿素作为一种调节食欲的激素。也有人提出它通过上调准备出发的候鸟体内的皮质酮，并促进脂质分解以提供迁徙飞行所需能量，从而参与出发调节。我们在秋季中途停留地测量了迁徙中的欧歌鸫（欧亚鸲）血浆中的胃饥饿素和皮质酮水平，并使用全自动无线电遥测系统确定了它们的出发时间。与我们的预期相反，胃饥饿素水平与鸟类的脂质储备或皮质酮水平并无关联。此外，出发可能性和夜间出发时间与胃饥饿素水平也没有关系。因此，我们的研究并不支持胃饥饿素参与中途停留出发调节的观点，至少在欧歌鸫中是这样。我们讨论了未证实我们预期结果的可能原因。
