Do lizards have enhanced inhibition? A test in two species differing in ecology and sociobiology

Waiting for the right moment to strike, avoiding the ingestion of harmful foods, or ignoring stimuli associated with ephemeral or depleted resources requires the inhibition of prepotent responses. Good response inhibition facilities flexibility in behaviour which is associated with survival in unpredictable environments. To investigate differences in behavioural flexibility in lizards, we tested reversal learning in the sleepy lizard (Tiliqua rugosa asper) and compared its performance to the relatively closely related eastern blue-tongue skink (Tiliqua scincoides scincoides). We presented both species with a choice between either a light and dark blue stimulus or a triangle and X shape. Both species were able to learn to discriminate between these stimuli and showed similar learning ability during the acquisition of the discrimination. Sleepy lizards, however, demonstrated a higher probability of making a correct choice at the start of the reversal, hinting towards enhanced stimulus response inhibition. Sleepy lizards and blue-tongue skinks inhabit different environments and show differences in ecology and sociobiology, all of which could possibly lead to adaptive specialisation in cognitive ability. Although further research is required, we propose that selection might have led to a change in stimulus response inhibition in the arid-adapted sleepy lizard, because better response inhibition may help them avoid the costs of repeated choices towards stimuli which no longer predict a beneficial outcome.