Cephalopod molluscs are among the most complex and highly derived invertebrates. In the early Cambrian cephalopods diverged into two parallel lineages that remained similar morphologically until the Tertiary, when coleoid cephalopods (octopuses, cuttlefish and squids) diversified into new forms and niches, but the remaining species of nautiloids retained mostly ancestral features and began to decline in diversity. The last remnants of the nautiloid lineage, the genera Nautilus and Allonautilus, have simple brains and a limited range of behaviour, and may represent an 'evolutionary snapshot' of ancient cephalopods. In contrast, the modern coleoid cephalopods demonstrate remarkable behavioural plasticity, and have developed specialised brains containing dedicated learning and memory centres. These features have made them valuable neurobiological models that help to inform general principles of complex brains and behaviours. In contrast, almost nothing is known about behaviour and neurobiology of nautiloids. Behavioural experiments on nautilus may provide insights into the evolution of the complex brains of modern cephalopods. This study investigated learning and memory in the chambered nautilus, Nautilus pompilius. A Pavlovian conditioning procedure produced temporally separated short- and long-term memory stores, resulting in a biphasic memory curve. Short-term memory duration in N. pompilius was comparable to short-term memory in cuttlefish, but long-term memory was considerably shorter. In contrast, performance in a spatial memory task produced memory that was stable for at least three weeks, comparable to or exceeding observed retention times in octopuses. These results show that despite differences in neurobiology, behaviour and ecology between nautilus and the coleoids, at least some aspects of memory profile and duration are similar in both groups. In a final experiment investigating navigational strategy, results showed nautiluses were capable of encoding and recalling the relationships of multiple, visual cues to a goal location, and were able to navigate successfully using several different strategies. Overall this study demonstrates that despite their simple brain and limited behavioural range, nautiluses were adept at learning and remembering associations and visual features of their environment, and their performance was comparable to that of coleoids tested under similar conditions.
|School||CITY UNIVERSITY OF NEW YORK|
|Subjects||Animal Physiology Biology; Zoology|
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