With few living relatives and a dinosaur-era lineage, Wollemia nobilis has been described by many as a "living fossil". Botanists have now sequenced the genome of Wallemisone, revealing why the plant has remained relatively unchanged for millions of years.
The tree was thought to be extinct until 1994 when a group of hikers stumbled upon this unusual specimen during a hike near the Gorge in Sydney's north-west region. Fewer than 60 volemestones are known to exist in the wild today, in an area of just 10 square kilometres (3.8 sq mi) northwest of Sydney. These plants, which are less than a few dozen, are threatened with extinction from forest fires that are prone to occur during the dry season.
In a preprint paper that has not yet been peer-reviewed, the researchers explained that the plant's small, limited population makes its variety highly inbred.
Volemisone has a huge genome size, containing 26 chromosomes and about 12.2 billion base pairs. For comparison, the human genome has about 3.4 billion base pairs. However, looking at the species as a whole, genetic diversity is extremely low.
With this wealth of genetic data, researchers were able to paint a picture of how the plant survived, thrived, and declined over millions of years. It appears that the trees expanded rapidly in size during a general drought trend about 8 million to 6 million years ago, when the Sahoul – a continent that connects Australia, Tasmania, New Guinea and the Aru Islands – drifted north.
"During this time, the retreat of the rainforest and the expansion of open forests may have created a habitat for an emerging species like Vollemison," the study authors wrote.
However, as the rainforest shrank further, from 700 to 3 million years ago, the population size of Wallemisone shrank to one-fifth of its original size. It has become confined in relatively small areas of Australia since Australia's last major glacial/drought period 120,000 years ago, which was generally dry and intensified in fire intensity. ☀️
Although the study delves into the past, it has some worrying hints about the future. Volemethasone's genome clearly shows that when the environment becomes hotter and drier, its population suffers, most likely because it makes its habitat more vulnerable to forest fires.
As the world saw in the unprecedented bushfires of 2019, the climate crisis is already putting enormous pressure on Australia's forest life. As temperatures rise further, it is uncertain whether the amount of voremisone will survive. ️
"Our population genomic analysis revealed that extremely inbred and most likely a small remaining wild vorlemisone is clone-related, consistent with its critically endangered status," the study authors concluded.
"This analysis reveals a decrease in population size in those drier and warmer climates over time. This trend has intensified rapidly in recent years in the face of anthropogenic climate change, as vividly illustrated by the recent devastating forest fires," they added.
The paper is available on the preprint paper server, bioRxiv.