STOPOVER BIOLOGY: HOW DOES GHRELIN MEDIATE MIGRATORY DECISIONS?

Leonida Fusani 1,2, Silvia Fuselli 3, Wolfgang Goymann 4, Hiroyuki Kaiya 5, Steve Smith 1 1 University of Veterinary Medicine, Vienna; 2 University of Vienna; 3 University of Ferrara, Italy; 4 Max Planck Institute for Ornithology, Seewiesen, Germany; 5 National Cerebral and Cardiovascular Center Research Institute, Osaka, Japan Billions of migratory birds move across continents every year, performing long, non-stop flights over ecological barriers such as seas and deserts. During the journey, birds spend about 80% of their time at stopover sites, areas where birds can recover from the fatigue of long flights and refill their energy reserves. Atmospheric factors such as wind and rain influence migratory movements, but eventually the decision of staying longer at the stopover site or departing depends on the conditions of the birds. Surprisingly, the physiological mechanisms that control this decision are almost unknown. A recent study of our group showed that a recently discovered hormone, ghrelin, is involved in the regulation of stopover behaviour. Ghrelin is produced in the gastrointestinal tract, and in domestic birds appears to be important to regulate appetite and foraging. We hypothesized that ghrelin variations in the blood circulation tell the birds when it is time to go. We designed a series of experiments to test this hypothesis in wild garden warblers (Sylvia borin) during their passage at a stopover site in the Mediterranean Sea. We will study how ghrelin changes across phases of migration by simulating a long migratory flight and a refueling stopover. We will test the effects of drugs that mimic or counteract the action of ghrelin on migratory behaviour and food intake. In addition, we will investigate variation of the genes that control the production of ghrelin to understand why the relationships between condition, migratory behaviour, and food intake vary between individuals of the same species. Our methodology is innovative for several aspects. First, we will use the `overnight` approach that was developed in our lab to test wild animals during their real migratory journey: the birds are caught at the stopover site, kept in specially designed recording cages for a short time and then released. Second, we will study a `new` hormone whose role in avian biology is scarcely known. Third, we will deploy a multidisciplinary approach combining behavioural, physiological, and genetic studies of the same individuals, therefore reducing the number of animals required. Finally, because ghrelin is the end product of the metabolic pathway, we will be able to see how variability of the genes of the ghrelin system is reflected in changes of the active messenger and its effects, with a true gene-to-behaviour approach.