Australasian Science Magazine

Spot the differences. On top is the newly recognised Oedura luritja, while at the bottom is Oedura cincta, another distantly related species that lives nearby with which it was long confused. Credit: Peter McDonald

By Paul Oliver & Peter McDonald

The identification of an ancient gecko species discovered hiding in Central Australia has provided new insights into how and when Australia’s deserts began to form 10 million years ago.

“Soon after leaving his camp I had the gratification to discover a magnificent specimen of the fan palm growing in the channel of the watercourse, with the drift of floods washed against its stem; its dome-shaped frondage contrasting strangely with the paler green foliage of the gum trees that surrounded it. It was a perfectly new botanical feature to me, nor did I expect to have met it in this latitude.” – Ernest Giles, 30 August 1872

As someone familiar with the vegetation of the flat, dry and hot Australian deserts, the explorer Giles was surprised to discover a valley full of palms in the ranges of Central Australia. The nearest palms occurred hundreds of kilometres to the north, separated by vast expanses of unsuitable dry desert country.

Subsequent researchers have found dozens of similarly isolated species and populations of plants, snails, fish and other vertebrates in the ranges of Central Australia – “the Central Uplands”. Most are separated from their nearest relatives by hundreds or even thousands of kilometres.

How and when did these plants and animals become localised?

One idea is that, just at the Central Uplands have provided a critical refuge for animals and Aboriginal people during droughts, they have also provided a refuge from the great aridification of Australia over far longer timescales. While more than 70% of the island continent is a vast and climatically harsh arid zone, this has not always been the case. Palaeoclimatic data and fossils tell us that Australia has been progressively drying out over the past 10 million years.

This has had profound consequences for the plants and animals of Australia. Some adapted to the new environments, while others probably contracted to wetter areas along Australia’s coast or else died out completely.

Like the coastal areas, could the Central Uplands have also provided climatically buffered refugia from the extremes of this aridification? This is a logical hypothesis from the data.

The Central Uplands include the highest mountains west of the Great Dividing Range (to 1531 metres), and there are isolated populations of cooler climate plant species that only occur on their summits. Likewise, nearby deep gorges provide cool refugia and permanent water, and are home to localised populations of water-dependent species such as fish and frogs – and of course, palms!

Based on this, many scientists had a further idea: perhaps by estimating the time of separation between Central Uplands isolates and their nearest relatives elsewhere in Australia, it would be possible to understand when current deserts spread across central Australia. Do they date back to initial aridification, potentially as long as 10 million years ago, or are they linked to much more recent intensifications of aridity through the glacials of the past few hundred thousand years?

It’s only in the past couple of decades that we have gained the genetic tools that allow us to address these questions using information about levels of genetic divergence.

Surprisingly, a number of recent studies provide evidence that species endemic to the Central Uplands were not particularly divergent from their relatives found elsewhere in Australia, and certainly much younger than any estimate for the age of the deserts. Most remarkably, the iconic Livistona palms that Giles came across are actually the same as species occurring in northern Australia, and were probably transported by Aboriginal people. This is a fascinating story in itself, but also somewhat disappointing to the proponents of the ancient relicts story.

But what about other groups? Lizards in particular are a spectacularly successful group in Australia’s deserts. There are many endemic species in the Central Uplands, including several that have only been recognised in the past decade. Among the lizards of these ranges there was one, noticed decades ago, that cried out for further investigation.

The story of this lizard began with, Robert “Bob” Bustard, a Scotsman who had a remarkable career including work in documentary-making, ecology, conservation and commercialisation of wildlife. However, his research all began with work on gecko ecology at The Australian National University, where he first noticed marbled velvet geckos in the sandstones around Kings Canyon that did not quite “look right” – they had colour pattern and scale differences to other velvet geckos found elsewhere in Central Australia.

However, for 40 years this is where things lay. In the absence of fresh genetic material, we were unable to test how divergent Bustard’s velvet geckos really were.

Then, in 2014, Peter contacted Paul for an update on the taxonomic status of Central Australian lizards. The conversation turned to: “Are there any lizards from around Alice Springs that need further work?” Soon we had some tissues from Kings Canyon to finally understand how divergent the “funny velvet gecko” might be.

To our excitement it was most certainly not the same as the marbled velvet gecko, but instead a completely new, relatively large and quite colourful species that lives in some of the most visited parks in Central Australia. Peter was surprised to learn that the first velvet gecko he ever caught was, unknown to him at the time, a completely new species.

Even more exciting, further analyses of the genetic data suggest that it doesn’t appear to have any close relatives (at least in comparison to all other described velvet geckos). We estimated that it diverged around 10 million years ago – similar to the timeframe other researchers have generated for when Australia may have first been undergoing major aridification. Based on this we think our new species might be a relict from these first aridification events.

In consultation with local Indigenous rangers we decided to name the new species Oedura luritja (although their first suggestion was to name it after a footballer!). This is a reference to both the Luritja people on whose land it occurs, and also related to the Arrernte word “Ulerenye” meaning “stranger” – which seemed appropriate for such a deeply divergent lineage.

Our work is also showing that Oedura luritja is not alone. A number of other localised lizard species are showing evidence of similar deep splits from their nearest living relatives. We think this is underpinned by the rocks they live on.

The new velvet gecko in particular is specialised for a life on rock and has a flattened body that enables it to squeeze into crevices. The rocks themselves are hundreds of millions of years old and may have provided a stable habitat with deep and climatically buffered crevices.

As Australia initially dried out in the late Miocene about 10 million years ago, relatives – which probably lived on trees in the surrounding plains – died out or moved somewhere else (once the trees were gone there was basically nowhere for them to live). However, O. luritja and some other lizards that it shares its habitat with have been able to hang on in the rocks for millions of years. So while the Central Uplands may have lost an ancient palm, they appear to have gained a suite of ancient lizards.

But the work is only just beginning. We have not yet carried out proper genetic analyses to understand the history and diversity of the vast majority of species that live in this special area.

Perhaps the most important question to ask pertains to the future. Are these isolated relicts extremely vulnerable to future climatic change, or are they well buffered from extremes in their rocky refugia? At the moment we simply don’t have the answers to these questions.

More work seems certain to shed further light on how and when deserts spread across Australia, provide a better window into the conservation needs of these relict species, and no doubt result in a few more surprises!