Organisms are shaped by their environment: they must survive and thrive under current conditions, and they must anticipate future changes in these conditions. Usually the environment is understood as a combination of abiotic (e.g., weather, nesting opportunities) and biotic factors (e.g., social environment, food availability, predation pressure). But in addition, animals interact with a hidden environment or ecosystem, one comprising all sorts of microbial life. These microbial ecosystems can be a trait of the broader environment in which an animal lives, a trait of an animal hosting the microbial ecosystem, or some combination of the two.

The gut microbiome is one of the better studied host-associated microbial ecosystems. Gut microbiota have complex symbiotic relationships with their hosts, and exert many profound and beneficial effects on their host. Gut microbes are important for development, immune function, digestion and metabolism, and they even can influence behaviour (the gut-brain-axe). On its turn, the host influences its gut microbe community via genotype, phenotype, behaviour (e.g., hibernation) and especially diet.

The complex interactions between host and microbiome have led to the introduction of the ‘holobiont’ (host plus all associated microbiota) and ‘hologenome’ (collective microbiota plus host genome) concepts. These concepts assume that the holobiont is the unit upon which natural selection acts. Following this, microbiomes should vary among hosts, be consistent within individuals, and be heritable; all having important evolutionary implications.  

We aim to investigate how the gut microbiome impacts the ecology and life history of their hosts, with the focus on birds. Our main projects involve:

• Gut microbiome and the development of birds 
• Seasonal and latitudinal variation in host and microbiome

Gut microbiome and the development of birds

Birds hatch virtually sterile and obtain a gut microbiome during their development. Rapidly obtaining  a complete and appropriate gut microbe community is likely important, because only then chicks can profit from the benefits of the host-gut microbiome interactions, such as an increased resistance against pathogens and parasites, and an improved energy and nutrient uptake. However, the establishment of the gut microbiome may be influenced by many aspects, such as diet and food intake (transfer of microbes, sources available for the microbes, etc.) and the environment (transfer of microbes from e.g. soil or nest material, food availability, weather, etc.).

We combine work on captive and wild birds to investigate how the development of the gut  microbiome is correlated and affects the development and subsequent survival of the chicks. We focus hereby on the impact of food availability on the development of the gut microbiome, and on the effect of diet and timing (early of late broods) on the development of the gut microbiome.

Seasonal and latitudinal variation in host and microbiome

Seasonal variation in day length and temperature varies along a latitudinal gradient, being more extreme at higher latitudes. Therefore the seasonal phenotypic changes of birds will vary with latitude. We aim to investigate how much the host-microbe interactions are shaped by the physical environment (day length and temperature) and its seasonal changes, and how much this impacts the host. We also want to determine how much of the variation in host-microbe interactions is due to the environment and how much is due to inherited components of the holobiont.