Slezacek, J. | bioRxiv Science

bioRxiv2023

The influence of diet on gut microbiome and body mass dynamics in a capital-breeding migratory bird

Gut-associated microbial communities are known to play a vital role in the health and fitness of their hosts. Though studies investigating the factors associated with among-individual variation in microbiome structure in wild animal species are increasing, knowledge of this variation at the individual level is scarce, despite the clear link between microbiome and nutritional status uncovered in humans and model organisms. Here, we combine detailed life history, foraging preference, and faecal microbiome data to investigate the relationship between diet, microbiome stability and rates of body mass gain in a migratory capital-breeding bird, the light-bellied Brent goose (Branta bernicla hrota). Our findings suggest that there is a significant relationship between foraging and the diversity, composition and stability of the faecal microbiome. We also suggest a link between foraging phenotype and the rates of mass gain during the spring staging of a capital breeder. This study offers rare insight into individual-level temporal dynamics of the gut microbiome of a wild host. Further work is needed to uncover the functional link between individual dietary choices, gut microbiome structure and stability, and the implications this has for the reproductive success of this capital breeder.

molecular biology↗

bioRxiv2023

The unexpected loss of the "hunger hormone" ghrelin in true passerines: A game changer in migration physiology

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 the "hunger hormone", a peptide secreted by the gastrointestinal tract to regulate food intake, body mass, and other important functions 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, a series of recent studies have shown that ghrelin administration influences migratory behaviour in passerine birds, suggesting an important role of this hormone in bird migration. However, using comparative genomic analyses we show that ghrelin has been lost in the largest avian taxon Eupasseres, after the basic split from Acanthisitti about 50 million years ago. Eupasserines, also known as True passerines, include all but two of the ca. 10,000 known passerine species. We further found that the ghrelin receptor (growth hormone secretagogue receptor, GHS-R) is still conserved in passerine birds, as indicated by sites under purifying selection and in line with the effects of ghrelin administration. Thus, ghrelin adds to a list of hormones highly conserved in vertebrates that have lost their main functions in specific taxa. The maintenance of a functional receptor system, however, suggests that in eupasserine birds another ligand has replaced ghrelin, perhaps to bypass the feedback system that would hinder large pre-migratory accumulation of subcutaneous fat.

evolutionary biology↗