Research findings back up Aboriginal legend on origin of Central Australian palm trees

Wednesday, 7 March 2012

Anna Salleh ABC Science

These palms were not a relic from Gondwana and could have been brought to Central Australia by Aboriginal people, say researchers

(ABC/Wikimedia)

Australian scientists say an often-told tourist story about how an iconic Central Australia palm came to be is nothing but a lovely myth.

A team of Australian and Japanese researchers report their findings today in the Proceedings of the Royal Society B.

"We've just demolished a textbook story," says team member, Professor David Bowman an environmental change biologist at the University of Tasmania.

The red cabbage palm, Livistona mariae, is a threatened species that is unique to the Finke Gorge near Alice Springs in Central Australia.

Northern Territory government promotion describes the palm as "a survivor from our rainforest past" - a relic, left over from Gondwanan times when Australia was covered in rainforest.

But Bowman and colleagues have found otherwise.

In previous research they found Australian palms came from a Southeast Asian ancestor that was adapted to growing in dry environments, and only adapted to growing in rainforests later on.

Bowman and colleagues used a genetic analysis to conclude that L. mariae is actually the same species as another Livistona palm, L. rigida, which grows in two pockets some 1000 kilometres away in northern Australia.

The findings feed into a long-standing debate over whether the two are actually the same species or not.

In their most recent study Bowman and colleagues examined the genetic relationship between the L. mariae and L. rigida in more detail.

They compared genetic fingerprints called nuclear microsatellite loci in 14 populations of L. mariae and L. rigida.

The researchers looked at L. mariae from the Finke Gorge's Palm Valley oasis, and L. rigida from Mataranka, just south of Katherine, and from Lawn Hill near Mount Isa.

They found L. mariae was most closely related to the L. rigida from Mataranka, but the most surprising discovery was how recently the two diverged.

After checking and double checking for months, the final estimate was that the L. mariae and L. rigida became separated just 15,000 years ago, completely ruling out that the palms in Palm Valley oasis are relics from Gondwana.

"What was shocking for us is that divergence was so recent, within the time period humans have been in Australia. We thought, 'Yikes, that's amazing'," says Bowman.

"The results tell us something transported seeds from Mataranka which is just south of Katherine to Palm Valley 15,000 years ago."

Long-distance dispersal

Bowman says that genetics is repeatedly showing how often outlying populations are not relics, but a product of long-distance dispersal instead. Another dispersed plant which was mistakenly believed to be a Gondwanan relic is the baobab.

But what dispersed L. mariae to Finke Gorge?

Bowman says, while a river could have been responsible for dispersing the seeds of L. rigida from Mataranka to Mt Isa via the Gulf of Carpentaria, there are no rivers to connect Mataranka to Finke Gorge.

A bird could have spread the tree to Central Australia and yet there is no evidence birds spread L. rigida to jungles nearby current established populations.

Another possibility is that it was spread by Aboriginal people who eat parts of the palm and use other parts for weaving, says Bowman.

But why would take them 1000 kilometres and nowhere else?

"It's a beautiful mystery," muses Bowman.