The unexpected loss of the ‘hunger hormone’ in songbirds – researchers stunned
The endocrine systems that regulate hunger, eating, and fat deposition are well conserved in vertebrates. For example, in mammals the hormone leptin produced by the fat cells reduces appetite, and disruption of this feedback system may result in metabolic diseases and obesity.
A few years ago however, it was discovered that birds have lost the leptin system during their evolution. Now, the new study discovered that songbirds have lost also the other main hormone of the system, ghrelin. The researchers were therefore very surprised to find out that most of Eupasserines, the largest group of birds comprising 60% of all avian species, have lost this hormone as well.
“A few studies of our team suggested that ghrelin could play a key role in controlling migratory behavior. Thus, we were stunned when we could not find ghrelin in the genome of garden warblers, one of our target species!” says Leonida Fusani whose research team led the study at the Konrad Lorenz Institute of Ethology, University of Veterinary Medicine, Vienna, and Department of Behavioral and Cognitive Biology, University of Vienna.
The team subsequently conducted an in-depth search for ghrelin both with bioinformatics tools, scanning through the genomes of other bird species, and with biochemical tools, analyzing samples from passerine birds and comparing them with those of quails and doves, which have ghrelin. “By using extensive sources and investigation methods, we were not able to find the genes coding for ghrelin in the DNA of any Eupasserine bird”, reports Stefan Prost, Assistant Professor at the University of Oulu, Finland, who conducted the genomic work.
The results of the study are a breakthrough in the study of avian physiology, and open important new avenues of research in biomedical science. “Passerine birds are unique in that they increase their body weight of 100% by accumulating enormous amount of fat before migration, yet they go easily back to their normal weight within days at the end of migration” says Fusani. “The loss of leptin and ghrelin appears to be linked to this extraordinary plasticity and understanding how birds manage to control their body fat could be very useful to address common health issues such as obesity and eating disorders”.
Read more about the ecology and genetics research at the University of Oulu