02.09.2024: A large number of animal species undergo long periods of fasting. During such periods of food deprivation, the animals have to suppress their appetite. The appetite-regulating gut hormone ghrelin has received a lot of attention in studies on mammalian systems in this context. In wild birds, however, knowledge about the ghrelin system and its role during prolonged periods of fasting is scarce.

An international study led by the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine, Vienna (KLIVV) has now investigated this hormone in a recently published study in rockhopper penguins. The researchers have thus made an important contribution to a better understanding of the ghrelin system in birds.

Together with leptin and insulin, ghrelin is one of three important metabolic hormones. In mammals such as humans, it is an appetite-stimulating peptide that is produced in the gastric mucosa and the pancreas. The hormone also has a number of other effects. Most bird species also have a gene that codes for ghrelin. In contrast to mammals, however, ghrelin inhibits food intake in birds. The study, which has just been published in the journal ‘Hormones and Behavior’, therefore took a closer look at the effect of ghrelin during prolonged periods of fasting in birds.

In focus: Ghrelin concentration during the moult of rockhopper penguins

In their study, the KLIVV-led research team collected plasma samples for measurements of circulating ghrelin concentrations in adult rockhopper penguins (Eudyptes chrysocome chrysocome) during the three- to four-week-long moult, which the penguins repeat annually to replace their plumage. ‘We also took samples from chicks before and after feeding and from non-moulting adults,’ explains Julia Slezacek from Vetmeduni Vienna's KLIVV.

Moulting and chicks: Significantly different ghrelin levels

Ghrelin levels did not differ significantly between fed and unfed chicks, but chicks had significantly lower plasma ghrelin levels compared to adults. In addition, penguins in late moult - i.e. individuals at the end of the extended fasting period - had higher ghrelin levels than non-moulting adults.

Julia Slezacek from the KLIVV of the Vetmeduni draws the following conclusion: ‘In penguins, ghrelin appears to be regulated differently at different developmental stages and in different phases of the annual cycle. The control of hunger by ghrelin during the later stages of the moult is very plausible and could represent a kind of “stop signal” that prevents penguins from returning to the sea too early when their plumage is not yet fully renewed and efficient thermoregulation is not yet possible.’ According to the researchers, the study results contribute significantly to the understanding of the ghrelin system in birds, given the little or no knowledge about the function of ghrelin in seabirds and in fasting birds in general.

The article „Circulating profile of the appetite-regulating hormone ghrelin during moult-fast and chick provisioning in southern rockhopper penguins (Eudyptes chrysocome chrysocome)“ by Julia Slezacek, Petra Quillfeldt, Hiroyuki Kaiya, Alba Hykollari and Leonida Fusani was published in „Hormones and Behavior“.

Scientific article