A long-held theory about the life cycle of one of Australia's most beloved natural icons has been upended in a botanical whodunnit that has revealed an unlikely hero.
The native banksias, with their colourful flowering spikes, were long thought to have been pollinated by honeyeater birds and marsupials, which are rewarded with large quantities of nectar.
But a team of scientists, led by researchers at La Trobe University, has uncovered another suspect in the survival of some of Australia's more unconventional Banksia flowers, in a paper published in the Botanical Journal of the Linnean Society.
Motion-activated game cameras have revealed that the native ash grey mouse (noodji) regularly take nectar from certain Banksia, while experiments manipulating animal access confirmed their role in pollination. While pollination by rodents is known in several plants from Africa, this is the first evidence for an Australia plant primarily being pollinated by rodents.
Lead researcher Stanislaw Wawrzyczek said before this study, pollination by mammals in south-western Australia was thought to be primarily achieved by the honey possum – a unique marsupial that feeds only on pollen and nectar.
"While most people would be familiar with the tree-form banksias with large, showy inflorescences that attract birds, in the heathlands of Western Australia there are some remarkable species where the flowers sit just above the ground.
"These species tend to have strongly musky-scented flowers, which suggests they have adapted to pollination by animals using smell when foraging," Stanislaw said.
"While it has long been thought that these species might be mammal pollinated, collecting the experimental and observational data to test this has proven challenging."
Working in the Lesueur Sandplain, the epicentre of banksia diversity near Jurien Bay in Western Australia, the research team set up cameras on four species with contrasting floral characteristics, noting the flowers' position on the plant, colour and scent.
They discovered that while honeyeater birds visited all species with equal frequency, mammals showed a preference for those with dull-coloured and strongly scented flowers placed near the ground.
Dr Ryan Phillips, co-author of the study and senior lecturer in ecology at La Trobe University, said it was unexpected that honey possums, dunnarts and ash-grey mice all contributed to pollination of a wide range of banksias.
The most surprising finding was that ash-grey mice, along with the introduced house mice, were the primary pollinators of Banksia subulata, commonly known as the awled honeypot.
"We were surprised to discover that the most frequent visitors of this species were mice, not marsupials, which provides the first compelling evidence of primary pollination by rodents in Australia," Dr Ryan Phillips said.
"This isn't just a case of the mice inspecting the flowers for some other food source, such as small insects —they clearly lapped nectar from the flower. "Our study suggests that, while many banksias evolved to use a spectrum of bird and non-flying mammal pollinators, other unexpected pollination strategies may remain to be discovered." Link to paper: https://academic.oup.com/botlinnean/advancearticle/doi/10.1093/botlinnean/boae061/7818956?login=false DOI: 10.1093
