Fishing in the Desert

29 August 2012

When you think of deserts you don't normally think of fishing, but that's exactly what Dr Steve Cooper and his collaborators are doing in the deserts of Western Australia. What they've caught could help to answer some of the biggest questions in evolutionary biology.

Dr Cooper, Principal Researcher with the South Australian Museum's Evolutionary Biology Unit, is fishing in calcretes – calcium carbonate or limestone rock formations full of crevices and caves that hold groundwater. The calcrete systems are not far below the surface and are quite shallow — some up to only ten metres deep — but they can range in area from 3 km² to over 200 km². The only way to access these calcretes is through wells or boreholes that have been drilled by landholders or miners.

''A colleague from the WA Museum, Bill Humphreys, had a hunch that there might be animals living in these calcrete systems. With stygobiologist Stefan Eberhard, he dropped plankton nets down boreholes in the middle of nowhere and pulled out an amazing collection of blind animals," says Dr Cooper.

The discovery changed the common perception that these calcretes were lifeless. The team is now studying the unique ecosystems to identify the species present and look at how they evolved and adapted to their environment.

To catch the animals, a plankton net is dropped from a fishing pole. The net acts like a sieve as it is pulled through the groundwater and funnels the creatures into a collecting tube. A range of beetles, crustaceans and worms are collected and more than 800 new species have been identified in the past 14 years.

Diving beetles have been found in 40 of the calcrete deposits and about 100 new species have been identified and described by South Australian Museum Honorary Research Associate, Dr Chris Watts. These beetles are related to those found on the surface of ponds and creeks and are the main focus of Dr Cooper's research.

''We've shown that the different beetle lineages have been in these calcrete systems for about three to eight million years. This coincides with the period when Australia became quite arid and groundwater became the only permanent source of water in the region," Dr Cooper says.

"It's likely that the ancestors of the diving beetles used to live on the surface and then colonised the groundwater systems, adapted to living underground and stayed there for millions of years.''

The organisms within the calcrete deposits have become completely adapted to living in the dark. Like most subterranean animals, many have lost their eyes as well as their pigment or colour.

"Our latest research investigates how the beetles lost their eyes and pigment over time. This is one of the big questions in evolutionary biology – why non-functioning traits like wings on birds living on islands, or the appendix in humans, get lost over time. There is quite a debate as to how that occurs," Dr Cooper says.

"We are using this beetle system to try and answer these questions, by looking at the changes that occur over millions of years in the genes that are involved in eye development. We're working to discover if these genes can still function. Can you re-evolve an eye or is it lost forever?''

New DNA sequencing techniques are used by the team to identify the different genes involved in eye development in surface and subterranean beetles and compare them to see how the genes have changed. If the different genes for eye development are found to be largely intact, then the process of evolution may be reversible.

As well as losing their eyes and colour, these diving beetles may have adapted to their underground environment in other ways. Normally, these beetles are air-breathing. Adult beetles dive down into the water while carrying an air bubble underneath their elytra (wings) that they use to breathe. They then come back up to the surface and pick up more air when they need it.

''We're starting to think that the beetles in calcrete systems are actually breathing from the water. They seem to have an ability to stay underwater for very long periods of time," says Dr Cooper.

With at least 800 new species of subterranean organisms collected so far and probably thousands more that haven't been discovered yet, it's likely that these new findings are just the tip of the iceberg.

Stygobiology, the study of organisms in underground waters, is a growing field within Australia. For Dr Cooper and his colleagues, the South Australian Museum offers a vital base to make exciting discoveries about life in these water worlds beneath our feet.