Why Didn't the Sifaka Cross the Road? Divergence of Propithecus edwardsi Gut Microbiomes Across Geographic Barriers in Ranomafana National Park, Madagascar

This study uses a biogeographic framework to identify patterns of gut microbiome divergence in an endangered lemur species endemic to Madagascar's southeastern rainforests, the Milne-Edwards's sifaka (Propithecus edwardsi). Specifically, we tested the effects of (1) geographic barriers, (2) habitat disturbance, and (3) geographic distance on gut microbiome alpha and beta diversity. We selected 10 social groups from 4 sites in Ranomafana National Park with varied histories of selective logging. Sites were spaced between 4 and 17 km apart falling on either side of two parallel barriers to animal movement: the Namorona River and the RN25 highway. Using 16S rRNA metabarcoding, we found the greatest beta diversity differentiation to occur between social groups, with significant divisions on opposite sides of geographic barriers (road/river). Habitat disturbance had the most significant effect on alpha diversity, though, contrary to many other studies, disturbance was associated with higher microbial species richness. Without biomedical context, it is unclear whether microbiome differences observed herein are neutral, adaptive, or maladaptive. However, microbiome divergence associated with the road/river may be a symptom of reduced host gene flow, warranting further investigation and perhaps conservation action (e.g., construction of wildlife bridges). Finally, this work demonstrates that significant microbiome variation can accrue over small sampling areas, lending new insight into host-microbe-environmental interactions.