Friday, 9 March 2012

On The Ancestry Of 'Ancient' Palm Trees

The red cabbage palm (Livistona mariae)
Australia is home to many strange animals and plants such as the duck billed platypus or the eucalyptus tree, which actually requires fire in order to spread its seeds. The continent is one of the oldest landmasses on Earth and has been part of many of the greatest biological and geological upheavals in our planet's evolutionary history. Over the course of its 3.5 billion year history, it has preserved many organisms from the past, such as the lungfish which provides insight into the evolution of the amphibians.

Another is the red cabbage palm tree (Livistona mariae), thought to be a remnant of a time when Australia's weather was far wetter and more temperate. Studies of the genomes of these palm trees has shown that their ancestry might not be as ancient as previously thought. 15 million years ago, Australia began to dry out and this was thought to have destroyed nearly all the populations of palm trees.

However the genomic study, led by Dr David Bowman from the University of Tasmania has shown that the red cabbage's palm may in fact be descended from seeds brought to the continent by humans migrating out of Africa and down through Asia and Northern Oceania. The palm's 'closest' relative is the Mataranka palm (Livistona rigida). They are separated by a distance of 1000 kilometres making it appear that they could only be distantly related.

Yet a previous genetic study led again by Bowman showed that the two species are almost genetically identical, meaning that they are not only closely related but that the red cabbage palm must have diverged from the Mataranka palm. They calculated that this divergence occurred around 15,000 to 30,000 years ago, making the species even younger than our own. The only remaining question was how the population spread to Australia?

There are no direct water ways connecting the landmasses, making transportation by rivers impossible. The only viable explanation left for Bowman was that seeds of the red cabbage palm were brought either intentionally or unintentionally by the early ancestors of the Aborigines. The dates of migration and the species origins are close, separated by no more than 15,000 years. This study is particularly interesting as, a few months ago, another genetic study showed that another plant group, the cycads, are also far younger than originally thought.

Plants are generally quite resistant to climate change and can easily adapt. It is for this reason that many different plant groups are thought to be very ancient indeed, barely changing over hundreds of millions of years. Yet it may be possible that we have been mistaken about their ancestry for decades. This study is a perfect example of how genetics has transformed the science of palaeontology and the way we think about the past.