The physiology of biome shifts and macroevolutionary change: How did Australian skinks colonise the arid zone so successfully?

A project undertaken at the School of Earth and Enviornmental Sciences, University of Adelaide and supervised by Dr Brett Goodman


This research project examined how the thermal environment influences the evolution of the thermal ecology of ectotherms. Because the operative thermal environment influences the physiological performance of ectotherms, optimality models posit that individuals should thermoregulate to maintain body temperatures within optimal limits. Many species of limb reduced lizards are fossorial or cryptozoic, and rely on friable substrates, such as sand and/or surface cover objects (e.g., logs, leaf litter) for cover and refuge. This work identified that the degree of limb reduction was negatively correlation with the evolution of low preferred and critical temperatures, and high rates of water loss in non-Lerista fossorial or cryptozoic skink species. However, this pattern broke down when species of the genus Lerista were included. Further, when examined using environment (biome) as factor most skink genera tended to show thermal physiological traits that matched their contemporary environment, with species from cooler environments having lower preferred temperatures, lower critical temperatures, and high rates of water loss. Here, the exception was species of the genus Ctenotus and Lerista, which maintain high values for these traits regardless of their current environment. These results suggest that the evolution of these traits in the Ctenotus and Lerista lineage occurred relatively early and may have been a key aspect of their successful adaptive radiation and high species diversity in arid and semi-arid environments.

Modes of locomotion vary substantially among organismal groups, which in extreme cases (e.g., terrestrial vs. aquatic locomotion) can result in drastic departures from the typical vertebrate body plan. Lizards show a broad range of morphologies, with limb reduced species typically positioned along a continuum defined by two distinct ecomorphs: short-bodied, long-tailed species and long-bodied, short-tailed species. While theory and speculation has suggested putative adaptive functional benefits of these ecomorphs (e.g., grass vs. burrowing), comparative tests demonstrating a performance benefit remain unclear. This study examined the locomotor performance and functional kinematics of 23 lizard species spanning the full range of limb-reduced ecomorphs. We used high speed video of lizards as they underwent locomotion on three contrasting substrates (grass, loose sand and on an open surface) to tested the following hypotheses. That relative locomotor performance would be maximal: (i) in short bodied, long-tailed taxa moving on the grass substrates, and (ii) in long-bodied, short-tailed taxa moving on sand substrates. We demonstrate that limb-reduced species with long bodies had greater tail and body amplitude when moving on all three substrates, and had the fastest performance when moving on a “grass” substrate. Further, the relative reduction in locomotor performance on grass and sand was lower in long-bodied, limb-reduced species, with species with the highest relative limb lengths experiencing the greatest reduction in performance. These results provide evidence to suggest that the short-bodied, long-tailed ecomorph, which has evolved repeatedly in squamate reptiles, may have evolved as an adaptation for locomotion through grass and similar substrates.

Figure 1. Lerita arenicola.
© Mark Hutchinson

Figure 2. Lerista punctatovittata.
© Mark Hutchinson


Figure 3. Lerista ameles.
© Mark Hutchinson

Figure 4. Lersita edwardsae.
© Mark Hutchinson


Figure 5. Ctenotus taeniololatus. © Eric Vanderduys