Do you DIG legless lizards?

By Paul Oliver and Jessica Worthington Wilmer.

This is a story about the about how the genes of obscure and rare animals can speak the history of our diverse landscapes.

The stars of the story are two species of very odd-looking geckos.

We typically think of geckos as big-eyed, soft-bodied lizards that run around on walls at night. But geckos are in fact a diverse worldwide group with over two thousand species, and coming in wide range of sizes, shapes and colours.

The two geckos we focus on here are particularly different. They are part of an ancient Australian lineage of geckos that are trying very hard to not be geckos. For example, they are often active during the day, and some of them burrow around in soil and leaf litter. One species is even specialised predator of other lizards.

But most strikingly of all – they effectively lack limbs. Hence the popular name of legless lizards.

We are not snakes! Believe it or not these two lizards are part of a radiation of legless geckos. On top is the Collared Delma (Delma torquata) and on the bottom is the Brigalow Scaly-foot (Paradelma orientalis). Both species only occur in Queensland. Images Steve Wilson.

The forty odd species of Australian legless lizards are very easy to mistake for snakes. They may have even evolved behaviours and colour patterns that mimic small venomous snakes, in an attempt to fool predators. But if you look closely there are a few give-away signs that you are not looking at a snake, but at a very (very) weird gecko.

First, they have tiny ear openings behind their eyes. Second, they don’t have a forked tongue. Third, their tails are as long or even longer than their bodies. And fourth, they squeak instead of hiss when scared…. and at that point the intimidating snake turns into a cute legless gecko!

Digging into the past

Through funds generously supplied by Project DIG and in collaboration with scientists from the Department of Environment and Science, Queensland Museum scientists have recently undertaken genetic investigations of two of the rarest legless lizard species, both only found in Queensland.

Both of these species have distributions centred around the Brigalow Belt Bioregion and nearby areas in south-east and central Queensland. Work on fossil deposits from this area is revealing remarkable histories of biotic change and species turnover in response to climate change over the last 300 thousand or so years.

Here we sought to ask the same question using different methods – namely, how have the environments and animals of Central Queensland responded to prehistoric climatic change?

Our results were published early in 2020, and point to the same basic story as the fossils – there have likely been big changes in the distributions of these legless lizards.

One species, the tiny little collared legless lizard Delma torquata, seems to consist of two genetically divergent and now isolated populations – one in the iconic uplands around the Carnarvon Ranges, and one in coastal areas. This points to a formerly wider range, with probable contraction into refugial areas as climates warmed over the last million odd years.

The spectacular Carnarvon Ranges may have provided a refugia from prehistoric climate change for many species including the Collared Delma and Brigalow Scalyfoot. Image Gary Cranitch.

The other species, the Brigalow Scaly-foot Paradelma orientalis, occurs in more lowland areas, and shows lower genetic diversity over most of its range. However, there is tantalising evidence that genetic diversity is higher in the north, and lower in the south. More work is required to test this, but it suggests that this species may have moved south quite recently, potentially as the last ice age ended in the last 10,000 odd years.

These results contribute to a growing picture that habitats and animals in eastern Queensland have undergone marked cycles of contraction, expansion and (sometimes) extinction through prehistoric climate change.

At more contemporary scales, they also suggest that in order to survive any rapid climatic change in the future, species may need to be able to move to new areas where climates remain suitable. What capacity they may have to do that in the extensively cleared landscapes of Central Queensland is an interesting and important question.

Relatively small areas of natural Brigalow remain (top picture), and remnant populations of native species may struggle to move across the intervening clearer areas (bottom picture), especially as climates change. Images Steve Wilson.

This work shows how building our understanding of the evolutionary history of Queensland animals and plants may be critical to help us preserve biodiversity for the future.

In short, within the genes of legless lizards lie big stories, and big questions.

Supported by Project DIG, a ground breaking five-year partnership between Queensland Museum Network and BHP to digitally unlock the knowledge held in our State Collection for visitors and researchers worldwide.