Out of the stable: Social disruption and concurrent shifts in the feral mare (Equus caballus) fecal microbiota

The disruption of animals symbiotic bacterial communities --theirmicrobiota-- has been associated with myriad factors including changes tothe diet, hormone levels, and various stressors. The maintenance ofhealthy bacterial communities may be especially challenging for socialspecies as their microbiotas are also affected by group membership,social relationships, microbial transfer between individuals, and socialstressors such as increased competition and rank maintenance. Weinvestigated the effects of increased social instability, as determined bythe number of group changes made by females, on the microbiota infree-living, feral horses, Equus caballus, on Shackleford Banks, a barrierisland off the North Carolina coast. Females leaving their groups to joinnew ones had fecal microbial communities that were similarly diverse butcompositionally different than those of females that did not changegroups. Changing groups was also associated with the increasedabundance of a several bacterial genera and families. These changesmay be significant as horses are heavily dependent upon their microbialcommunities for nutrient absorption. Though we cannot identify theparticular mechanism or mechanisms driving these changes, to our knowledge, ours is the first study to demonstrate an association between acute socialperturbations and the microbiota in a free-ranging mammal.