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

The disruption of animals' symbiotic bacterial communities (their microbiota) has been associated with myriad factors including changes to the diet, hormone levels, and various stressors. The maintenance of healthy bacterial communities may be especially challenging for social species as their microbiotas are also affected by group membership, social relationships, microbial transfer between individuals, and social stressors such as increased competition and rank maintenance. We investigated the effects of increased social instability, as determined by the number of group changes made by females, on the microbiota in free-living, feral horses (Equus caballus) on Shackleford Banks, a barrier island off the North Carolina coast. Females leaving their groups to join new ones had fecal microbial communities that were similarly diverse but compositionally different than those of females that did not change groups. Changing groups was also associated with the increased abundance of a several bacterial genera and families. These changes may be significant as horses are heavily dependent upon their microbial communities for nutrient absorption. Though we cannot identify the particular mechanism(s) driving these changes, to the best of our knowledge, ours is the first study to demonstrate an association between acute social perturbations and the microbiota in a free-ranging mammal.

Zebras of all stripes repel biting flies at close range

The best-supported hypothesis for why zebras have stripes is that stripes repel biting flies. While this effect is well-established, the mechanism behind it remains elusive. Myriad hypotheses have been suggested, but few experiments have helped narrow the field of possible explanations. In addition, the complex visual features of real zebra pelage and the natural range of stripe widths have been largely left out of experimental designs. In paired-choice field experiments in a Kenyan savannah, we found that hungry Stomoxys flies released in an enclosure strongly preferred to land on uniform tan impala pelts over striped zebra pelts but exhibited no preference between the pelts of the zebra species with the widest stripes and the narrowest stripes. Our findings confirm that zebra stripes repel biting flies under naturalistic conditions and do so at close range (suggesting that several of the mechanisms hypothesized to operate at a distance are unnecessary for the fly-repulsion effect) but indicate that interspecific variation in stripe width is associated with selection pressures other than biting flies.