Faecal inoculations alter the gastrointestinal microbiome and allow dietary expansion in a wild specialist herbivore, the koala

Abstract

Background: Differences between individuals in their gastrointestinal microbiomes can lead to variation in their ability to persist on particular diets. Koalas are dietary specialists, feeding almost exclusively on Eucalyptus foliage but many individuals will not feed on particular Eucalyptus species that are adequate food for other individuals, even when facing starvation. We undertook a faecal inoculation experiment to test whether a koala's gastrointestinal (GI) microbiome influences their diet. Wild-caught koalas that initially fed on the preferred manna gum (Eucalyptus viminalis) were brought into captivity and orally inoculated with encapsulated material derived from faeces from koalas feeding on either the less preferred messmate (E. obliqua; treatment) or manna gum (control). Results: The gastrointestinal microbiomes of wild koalas feeding primarily on manna gum were distinct from those feeding primarily on messmate. We found that the gastrointestinal microbiomes of koalas were unresponsive to dietary changes because the control koalas' GI microbiomes did not change even when the nocturnal koalas were fed exclusively on messmate overnight. We showed that faecal inoculations can assist the GI microbiomes of koalas to change as the treatment koalas' GI microbiomes became more similar to those of wild koalas feeding on messmate. There was no overall difference between the control and treatment koalas in the quantity of messmate they consumed. However, the greater the change in the koalas' GI microbiomes, the more messmate they consumed after the inoculations had established. Conclusions: The results suggest that dietary changes can only lead to changes in the GI microbiomes of koalas if the appropriate microbial species are present, and/or that the koala gastrointestinal microbiome influences diet selection.

Marsupial Gut Microbiome

“…Microbial richness and diversity were also found to be lower in the microbiome of koalas feeding on manna gum, likely to be linked to a greater energy harvest from this species of Eucalyptus compared to messmate (Brice et al, 2019). Therefore it has been hypothesized that the inability of the majority of koalas to shift diets to messmate is due to a lack appropriate gut microbial assemblage for optimal digestion (Blyton et al, 2019). With the continuous threat of habitat loss and limited resources, the ability to shift diet and utilize different food sources is crucial for the survival and persistence of koalas in the wild.…”

Conserving the holobiont

“…Researchers recently showed that koalas were unable to switch between food tree species without the help of a faecal transplant pellet, containing a live microbiome sample from koalas that regularly ate the target tree species. Koalas that received the transplant established a gut microbiome more similar to koalas that ate the target species regularly, and were able to transition their diet to consume more of the target tree species (Blyton et al, 2019). This is one of the first studies to experimentally investigate the use of faecal transplants for conservation purposes-in this case, allowing dietary expansion in a highly specialized wild herbivore.…”

When an iconic native animal is overabundant: The koala in southern Australia

“…Furthermore, koalas in these habitats exhibit high site fidelity and appear reluctant to move to alternate habitat types even when trees become completely defoliated (Whisson et al, ). Recent research into the koala's microbiome suggests that this may be due to koalas becoming highly specialized on a single food tree such that they may have limited ability to switch their diet to another food tree species (Blyton et al, ; Brice et al, ).…”