Think truffles and you’ll probably think of France. But Australia is actually a global hotspot for truffle-like fungi, boasting hundreds of different species. Like culinary truffles, these truffle-like fungi produce underground sporing bodies rather than send up mushrooms.

Living underground has its challenges. Fungi which form mushrooms above ground can easily disperse their spores (the fungal equivalent to a plant’s seed) on the wind. But truffle-like fungi can’t do this. Instead, they rely on native mammals to follow their pungent smells, dig up the underground sporing body, eat it and disperse their spores in their scat.

Australia is a global hotspot for truffle-like fungi, with hundreds of species. Pictured is a selection of their underground sporing bodies. Todd Elliott, Author provided (no reuse)

Many native mammals eat fungi when they are easily available, including common brushtail possums (Trichosurus vulpecula), swamp wallabies (Wallabia bicolor), bush rats (Rattus fuscipes), and greater bilbies (Macrotis lagotis), but they generally don’t rely on them for a large part of their diet in the same way as potoroos and bettongs do. Among these fungi fans, there’s one species which stands out.

Australia’s most specialised fungi-eater is the long-footed potoroo (Potorous longipes), which relies on these fungi for over 90% of its diet. It’s likely to be one of the most fungi-dependent mammals in the world. Their nocturnal work digging up and eating fungi supports forests in southeastern Australia by helping to maintain the fungi-tree symbiosis.

The long-footed potoroo has long been rare due to habitat loss and fox predation. It’s been endangered for decades. Once considered more widespread, their range is now restricted to two regions between Victoria and New South Wales, much of which burned during the 2019-2020 megafires.

But there’s a newer threat: climate change.

In our new research, we analyse a rare long-term collection of potoroo scats. We found that as conditions get hotter, these potoroos are eating a much smaller range of fungi. This has significant implications for potoroo diets, fungal dispersal, and the health of our forests.

What’s in that scat?

Many truffle-like fungi live in ectomycorrhizal symbiosis with native trees such as eucalypts. This means they trade nutrients between their threadlike hyphae and the tree’s root system, a remarkably ancient relationship which supports tree growth and health and provides their fungal partners with a source of energy.

To explore whether climate change has been affecting the truffle-like fungi consumed by the long-footed potoroo, we partnered with colleagues at the Royal Botanic Gardens Victoria, CSIRO and the Victorian Department of Energy, Environment and Climate Action. We then turned to an extensive and extremely rare collection of potoroo scats.

These scats have been painstakingly collected over 23 years (1993-2016) by department staff. Collections of scats are enormously valuable to researchers, as they give us clear evidence of what an animal has been eating – and if their diets have changed over time.

Long-footed potoroos forage for fungi at night. This potoroo was captured on a trail camera. Emily McIntyre, CC BY-NC

We used DNA analysis to track which species of truffle-like fungi these potoroos had eaten over time. This process involved sequencing fungal DNA present in potoroo scats, and matching these DNA sequences to a fungal species database. This left us with a list of fungal species that were present in each potoroo scat.

Overall, we found potoroos ate fewer species of truffle-like fungi in warmer conditions. This trend was visible from season to season, as well as between years. As temperatures continue to increase due to climate change, we expect that long-footed potoroos will continue to consume fewer species of truffle-like fungi.

More heat, less fungal variety

During warm conditions, potoroos ate less of some genera of truffle-like fungi and more of others such as Mesophellia, a genus of truffle-like fungi producing hard-cased sporing bodies between five and 40 cm underground.

We already know these fungi are eaten in abundance by hungry bettongs after a bushfire. As climate change brings warmer temperatures, we expect Mesophellia may increasingly act as an important food source for long-footed potoroos when other resources are scarce.

Overall, our findings suggest climate change may make it harder for potoroos to get as wide a range of fungi to eat, which might make it harder for these marsupials to get the nutrients they need. The nutrition in sporing bodies varies widely between species, so eating a narrower fungal diet may mean less diverse nutrients.

If this happens, it’s possible potoroos could shift their diets and eat more insects or plants. But it’s not a guarantee, given these animals are such specialised fungi-eaters.

This, in turn, could have wider flow-on effects. If potoroos consume fewer species of truffle-like fungi, some species may have fewer chances to spread around landscapes. If they become rarer, it could disrupt the long symbiosis between fungi and ectomycorrhizal forest trees in lowland coastal forests through to tall mountain forests.

This three-way relationship benefits long-footed potoroos, truffle-like fungi, and the native trees that form ectomycorrhizal partnerships with these fungi. Each member of this relationship depends on the others.

Ripple effects

Not many people have seen these shy potoroos. But they have an importance far beyond their modest size. The simple act of digging up and eating truffle-like fungi is vital for the potoroo, the fungi and the forests around them.

Many of Australia’s once-common digging marsupials have become rare or been driven to extinction since European colonisation. The long-footed potoroo, too, is endangered by historic and ongoing threats, ranging from habitat loss to fox predation to climate change.

We don’t know yet how climate change will affect the complex relationship between potoroo, fungi, and the forests around them. Understanding these complex relationships is essential if we are to protect them against an uncertain future.