Abstract

Throughout their wide geographic range, koalas (Phascolarctos cinereus) always eat Eucalyptus leaves. Few animals can stomach, let alone survive, on these fibrous, toxic leaves, and koalas are thought to rely on their gut microbiomes to help them digest their nutritionally poor diets. Our research has revealed that the microbes that make up the koala’s gut microbiomes vary over their range, with koalas from proximate populations having more similar microbiomes compared to koalas from opposite ends of the continent. These patterns extend to the microbes’ ability to break down and make different compounds, thereby potentially influencing the koala’s nutrition. Our work suggests that climate and dispersal patterns play a role in shaping these patterns, but we don’t know how diet is involved.