Prost Stefan, Elbers Jean P, Slezacek Julia, Hykollari Alba, Fuselli Silvia, Smith Steve, Fusani Leonida
Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland.
Interdisciplinary Life Sciences, University of Veterinary Medicine, Vienna, Austria.
R Soc Open Sci. 2025 Mar 19;12(3):242107. doi: 10.1098/rsos.242107. eCollection 2025 Mar.
Migratory birds must accumulate large amounts of fat prior to migration to sustain long flights. In passerines, the small body size limits the amount of energy stores that can be transported, and therefore birds undergo cycles of extreme fattening and rapid exhaustion of reserves. Research on these physiological adaptations was rattled by the discovery that birds have lost the main vertebrate regulator of fat deposition, leptin. Recent studies have thus focused on ghrelin, known as 'hunger hormone', a peptide secreted by the gastrointestinal tract to regulate, e.g. food intake and body mass in vertebrates. Studies on domestic species showed that, in birds, ghrelin has effects opposite to those described in mammals such as inhibiting instead of promoting food intake. Furthermore, recent studies have shown that ghrelin administration influences migratory behaviour in passerine birds. Using comparative genomics and immunoaffinity chromatography, we show that ghrelin has been lost in Eupasseres after the basic split from Acanthisitti about 50 Ma. We found that the ghrelin receptor is still conserved in passerines. The maintenance of a functional receptor system suggests that in Eupasserines, another ligand has replaced ghrelin, perhaps to bypass the feedback system that would hinder the large pre-migratory accumulation of subcutaneous fat.
候鸟在迁徙前必须积累大量脂肪以维持长途飞行。在雀形目鸟类中，体型较小限制了可运输的能量储备量，因此鸟类会经历极度育肥和储备迅速耗尽的循环。鸟类失去了脂肪沉积的主要脊椎动物调节因子——瘦素，这一发现使对这些生理适应性的研究受到了冲击。因此，最近的研究集中在胃饥饿素上，它被称为“饥饿激素”，是一种由胃肠道分泌的肽，用于调节脊椎动物的食物摄入量和体重等。对家养物种的研究表明，在鸟类中，胃饥饿素的作用与在哺乳动物中描述的相反，例如它抑制而不是促进食物摄入。此外，最近的研究表明，施用胃饥饿素会影响雀形目鸟类的迁徙行为。通过比较基因组学和免疫亲和色谱法，我们发现大约在5000万年前从刺鹩亚目基本分化出来后，胃饥饿素在雀形目鸟类中已经消失。我们发现胃饥饿素受体在雀形目鸟类中仍然保守。功能性受体系统的维持表明，在雀形目鸟类中，另一种配体已经取代了胃饥饿素，这可能是为了绕过会阻碍迁徙前皮下脂肪大量积累的反馈系统。
