Habituation and sensitization learning in adult solitary ascidians.

The ability of organisms to learn and remember is crucial for their survival. This cognitive ability spans a wide range of organisms, including both vertebrates and invertebrates, yet has remained little studied in many taxonomical groups. Ascidians (sea squirts), are basal chordates closely related to vertebrates, making them a valuable model for investigating the evolutionary origins of learning and memory. Despite their phylogenetic significance as a sister group to vertebrates, the learning and memory abilities of adult solitary ascidians have remained largely unexplored. In this study, we investigated, for the first time, the ability for nonassociative learning in the solitary ascidian Polycarpa mytiligera, focusing on habituation and sensitization. We employed controlled mechanical and electrical stimuli to assess these two forms of learning, specifically examining short-term sensitization and long-term habituation. Our findings demonstrate that P. mytiligera exhibits both types of learning and retains memory over both short- and long-term periods, thereby establishing P. mytiligera as a promising model for investigating learning and memory mechanisms in chordates.