Social relationships affect make-up of gut bacteria in horses, findings suggest

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Ponies graze the wilderness in the Northern Carneddau region in Wales. Photo: Ian Nadin CC BY-SA 2.0 via Wikimedia Commons
Ponies graze the wilderness in the Northern Carneddau region in Wales. Photo: Ian Nadin CC BY-SA 2.0 via Wikimedia Commons

The vast army of microbes in the gut of horses appear to be structured within equine groups, affected by not only dietary and environmental factors, but also social interactions.

That was the conclusion of researchers after studying the gut microbiomes of a group of semi-feral mountain ponies.

University of Salford researcher Rachael Antwis and her colleagues say the make-up of the gut microbiome is linked to functional traits such as metabolism and immune function.

The drivers of its composition are increasingly well-known, but evidence of group-level microbiome convergence is limited.

Equids provided an interesting test case for microbiome dynamics at the subpopulation level, they said. As hindgut fermenters, they were particularly reliant on microbial digestion for energy and nutrition.

Their study, reported in the journal Microbiome, focused on the semi-feral Welsh Carneddau ponies of Snowdonia National Park, which are direct descendants of the wild Welsh mountain pony.

The researchers describe the Carneddau ponies as being the closest to a wild unmanaged pony population in Britain. They range over an area of up to 40 square kilometres and, while used to seeing humans, are not used to physical contact with them.

The researchers collected data about the demographic make-up of the ponies over 10 days, as well as information on their groupings and spatial distribution.

For each band, faecal samples were collected from the stallion plus 4–7 mares and 2–5 juveniles for molecular-based analysis to learn about each individuals’ gut microbiomes.

The bacteria identified in the faeces primarily belonged to the Bacteroidia, Clostridia, Spirochaetes, and Fibrobacteria classes, with 52.6% of the variation identified in the microbiome attributable to individual variation.

They also identified significant effects of band (group) and life stage on total microbiome composition, but not sex. The variation attributed to band was assessed at 14.0%, and life stage was assessed at 10.4%.

The band and life stage were found to account for a slightly larger proportion of the variation when looking only at the core microbiome (19.4% and 16.6%, respectively).

Spatial structuring within bands was also identified as a factor, suggesting that despite communal living, social behaviours still influenced microbiome composition.

“Indeed, we show that specific interactions (i.e. mother-offspring and stallion-mare) lead to more similar microbiomes, further supporting the notion that individuals influence the microbiome composition of one another and ultimately the group.”

Foals exhibited different microbiome composition to sub-adults and adults, most likely related to differences in diet.

“We provide novel evidence that microbiome composition is structured at multiple levels within populations of social mammals and thus may form a unit on which selection can act.

“High levels of within-individual variation in microbiome composition, combined with the potential for social interactions to influence microbiome composition, suggest the direction of microbiome selection may be influenced by the individual members present in the group.

“Although the functional implications of this require further research, these results lend support to the idea that multi-level selection can act on microbiomes.”

They noted that dispersal of individuals between bands meant that subpopulations were not genetically isolated.

They said their findings showed that semi-feral ponies exhibited variation in microbiome composition between bands, which may relate to social, dietary, and environmental factors.

“Due to the high level of within-individual variation, the direction of group selection may be influenced by the individual members present in the band.

“Spatial structuring was also identified within bands, suggesting that despite communal living, social behaviours still influence microbiome composition.”

The full study team comprised Antwis and Bryony Unwin, from the University of Salford; and Jessica Lea and Susanne Shultz from the University of Manchester.

Gut microbiome composition is associated with spatial structuring and social interactions in semi-feral Welsh Mountain ponies
Rachael E. Antwis, Jessica M.D. Lea, Bryony Unwin and Susanne Shultz
Microbiome 2018 6:207 https://doi.org/10.1186/s40168-018-0593-2

The study, published under a Creative Commons License, can be read here

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