Conditional same/different discrimination learning in the short-beaked echidna (Tachyglossus aculeatus)

Echidnas have evolved separately from other mammalian groups for more than 200 million years and incorporate a mixture of reptilian and mammalian features. Because of these factors, they have historically been considered ‘primitive’ animals. However they have successfully adapted to a wide variety of ecological niches and their neurophysiology demonstrates a number of unusual and apparently advanced characteristics, including a relatively large brain and cerebral cortex and a comparatively massive frontal cortex. These attributes make the echidna an intrinsically compelling subject for cognitive testing. Studies of learning in the echidna have thus far been limited to only a handful of experiments. These have demonstrated that echidnas are capable of easily forming a position habit in a T-maze, show rapid improvement across a series of successive habitreversals, are capable of learning visual discriminations and perform well in instrumental discrimination tests. This study aims to expand on these results by conducting a number of cognitive tests of the echidna’s learning abilities, specifically its’ ability to learn colour, shape and conditional discriminations, as well as the presumptively ‘high-level’ relationally based tasks of same/different and conditional same/different categorisation. This thesis also examines the ongoing debate about the mental processes involved in relational categorisation and how commonly they occur in non-human animals. In a wider context, echidnas are an ideal candidate to explore competing theories of cognitive evolution by examining whether a phylogenetically and physiologically ‘primitive’ species can perform what are generally considered to be ‘advanced’ cognitive tasks and what role ecological factors might play in the development of those abilities. Using an echidna as a subject also increases the comparatively small number of species used for cognitive testing and its’ distinct evolutionary history means these results provide a valuable comparison to the cognitive development of more commonly studied species.