Comparison of numerosity concept in a freshwater turtle after a two-year retention interval

Abstract: Cognition and memory ability is pivotal for animal survival and is believed to be particularly adaptive for long-lived species. Numerosity discrimination, crucial for resource management and social interactions, provides a quantitative framework that allows us to compare the performance and the recovery of previously established concepts after a long-term retention interval. In this research, we investigated the capacity of freshwater turtles to remember the experimental process and gradually recall the abstract concept of “greater than”. Five striped-necked turtles (Mauremys sinensis), trained in 2019 to discriminate between quantities represented by red cubes, were retested after a two-year retention interval with no exposure to stimuli or human interaction. Three turtles remembered the training process to acquire food rewards from the stimuli within the first day of testing. However, regaining the concept of “greater than” required more time: one turtle reached 68% accuracy (P = 0.0669) on Day 1, another achieved 77% (P = 0.0085) on Day 2, and a third reached 82% (P = 0.0022) on Day 3. The latter two individuals retained this high accuracy until the end of the experiment. As the study continued, memory recall for each subject improved with greater efficiency than two years prior. Our study confirms that freshwater turtles retain long-term memory of abstract concepts learned two years earlier and reveals significant individual heterogeneity in their recall and decision-making processes. These findings underscore the need for more comprehensive research into the factors shaping animal cognition and behavior, particularly in understanding the ecological and evolutionary pressures that influence memory retention, individual variability, and decision-making strategies. Significance statement: This study provides compelling evidence that freshwater turtles possess the ability to retain and recall abstract cognitive concepts over extended periods without reinforcement, highlighting their advanced cognitive capacities. By demonstrating that striped-necked turtles (Mauremys sinensis) can remember training and discriminate based on the concept of "greater than" after a two-year hiatus, our research not only challenges existing assumptions about reptilian memory capabilities but also enriches our understanding of cognitive evolution in long-lived species. The found individual differences in memory recall and decision-making underscore the complexity of animal cognition and highlight the significance of individual variability in behavioral studies. These insights contribute to a deeper understanding of the mechanisms that support long-term memory in animals.