The marsupials’ varied diet could help safeguard some of Australia’s fungi and forests
© Stephanie Todd
A small endangered marsupial with a taste for truffles may be a linchpin in one kind of Australian forest — and the evidence is in the animal’s poop.
Northern bettongs feast on truffles, the meaty, spore-producing parts of certain fungi. Plenty of animals eat a selection of these subterranean orbs from time to time. But analyses of the scat from northern bettongs (Bettongia tropica) reveal that the marsupials eat truffles from a wider diversity of fungi species than other critters, including some that no other animals appear to favor, researchers report November 22 in Molecular Ecology.
That’s an important role because these truffle-producing fungi form beneficial relationships with tree roots, helping trees pull nutrients and moisture from soil. “There's been a whole raft of published studies showing that those fungi give plants an edge,” says Andrew Claridge, an ecologist for the New South Wales National Parks and Wildlife Service in Queanbeyan who wasn’t part of the study.
Australia’s eucalyptus forests host hundreds, or possibly even thousands, of truffle fungi species, says study coauthor Susan Nuske, an ecologist at the Swedish University of Agricultural Sciences in Umeå. Different species seem to be specialized to associate with particular trees or perform certain roles, so maintaining that diversity is key. By spreading truffles’ spores via scat, bettongs help keep the fungal community diverse and, by extension, the forest healthy, say Nuske and her colleagues.
But bettongs, once so abundant that they were considered garden pests, are now at risk of extinction. The marsupials, which have kangaroo-like hind legs and prehensile tails, live only in a narrow band of habitat where dense rainforest transitions to a more open eucalyptus-dominated forest. That territory has shrunk over time. A World Wildlife Fund-Australia report published December 6 estimates that bettongs’ habitat has declined by 70 percent in the past decade. Fewer than 2,500 of the animals are left in the wild, the WWF estimates.
Wiping out bettongs in a particular area would probably lower the diversity of fungi, sending ripple effects through the whole forest, says Nuske.
Nuske and her colleagues set out traps at three sites in North Queensland, and then collected poop samples from captured bettongs and other small mammals. The team analyzed DNA in the scat to figure out what species of fungi the animals were eating, matching small pieces of DNA to online databases cataloging the fungi’s genetic information. The researchers also created a local genetic database by gathering and analyzing fungi from the area.
Bettongs ate a greater diversity of truffle fungi than any of the nine other species that the scientists trapped, which included bandicoots and native rats. Other animals in these ecosystems also eat truffles, but most eat them only seasonally or part time. Fungi (both truffle fungi and other kinds) are the main components of bettongs’ diet, and the marsupials appear to be filling an ecological niche that other species aren’t, the researchers say.
Still, the relationships between trees, their associated fungi and truffle-eating animals can be challenging to study in the wild. That’s because the fungi live underground and the web of associations is complex. It’s possible that if bettongs weren’t around, other animals would adjust their diets and eat more species of fungi. But it’s unlikely that the other creatures could fully compensate for these voracious fungivores, the researchers say. They now want to analyze truffle fungus diversity in areas where bettongs once lived but have disappeared to see how those ecosystems have changed over time.
Ecologists and conservationists have been championing the bettong’s importance in sustaining these marginal forests for decades, says Claridge, but the outlook hasn’t improved for the marsupial. The new work is “a modern take on an old story,” he says, using genetic techniques to confirm the bettong’s importance in more detail.
The work is part of a larger World Wildlife Fund project looking at the role that bettongs play in their ecosystems to figure out how to best protect them. The report also outlines strategies for using controlled burning to encourage native habitat restoration and keep rainforests from encroaching farther on bettongs’ turf.
S.J. Nuske et al. The endangered northern bettong, Bettongia tropica, performs a unique and potentially irreplaceable dispersal function for ectomycorrhizal truffle fungi. Molecular Ecology. Published online November 22, 2018. doi: 10.1111/MEC.14916.
WWF-Australia, Sydney NSW. Bettongia tropica population status, distribution, habitat use and impact of fire. Published online December 6, 2018.