A surprising discovery: songbirds have lost the ”hunger hormone” ghrelin

The endocrine systems that regulate hunger, food intake and fat deposition are well conserved in vertebrates. In mammals, for example, the hormone leptin reduces appetite, and disruption of this feedback system can lead to metabolic disease and obesity. A few years ago, researchers discovered that birds have lost this leptin system in the course of evolution. Now, a study funded by the Austrian Science Fund FWF and led by Leonida Fusani from the Konrad Lorenz Institute of Ethology (KLIVV) at the University of Veterinary Medicine, Vienna and the Department of Behavioral and Cognitive Biology at the University of Vienna (lead author Stefan Prost) has found that songbirds have also lost the other main hormone of this system, ghrelin. A discovery that is also exciting for humans, especially in regard to obesity and eating disorders.

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In their study, the researchers focused on ghrelin. This peptide - also known as the “hunger hormone” - is secreted by the gastrointestinal tract to regulate food intake and body mass in vertebrates. However, studies on domestic birds had shown that ghrelin has the opposite effect in birds than in mammals, inhibiting food intake rather than promoting it. According to Leonida Fusani, “some of our team's studies also suggested that ghrelin might play a key role in the control of migratory behavior. We were therefore puzzled when we could not find ghrelin in the genome of the garden warbler, a passerine bird.”

Searching for the hunger hormone ghrelin in songbirds - and finding it nowhere

Based on this finding, the research team conducted a thorough search for ghrelin using both bioinformatic tools, by searching the genomes of other bird species, and biochemical tools, by analyzing samples from passerine birds and comparing them to those of quail and pigeons, which possess ghrelin. “We were very surprised to find that the Passerine birds, that is songbirds - the largest group of birds, comprising 60% of all bird species - have also lost this hormone,” says Fusani. Using all available sources and research methods, the scientists were unable to find the genes coding for ghrelin in the DNA of all songbirds for which information is available.

Groundbreaking work on bird physiology with important findings for humans

According to Fusani, these study results are a breakthrough in the study of bird physiology and open up important new avenues for biomedical research: “Songbirds are unique in that they can increase their body weight by up to 100% by accumulating enormous amounts of fat before migration, but return to their normal weight within a few days after the end of their long journeys,” explains Fusani. The loss of leptin and ghrelin seems to be related to this extraordinary plasticity, according to Fusani. Thus, “understanding how birds manage to control their body fat could be very useful for humans to tackle common health problems such as obesity and eating disorders,” emphasizes Fusani.

The article „The unexpected loss of the ‚hunger hormone‘ ghrelin in true passerines: a game changer in migration physiology“ by Stefan Prost, Jean P. Elbers, Julia Slezacek, Alba Hykollari, Silvia Fuselli, Steve Smith andLeonida Fusani was published in „Royal Society Open Science“.

Scientific article

Scientific contact:

Univ.-Prof. Leonida Fusani
Konrad-Lorenz-Institut für Vergleichende Verhaltensforschung (KLIVV)
Veterinärmedizinische Universität Wien (Vetmeduni)
Leonida.Fusani@vetmeduni.ac.at

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