Feng-Chun Lin’s research while affiliated with University of Otago and other places

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.

Social interactions are inevitable in the lives of most animals, since most essential behaviours require interaction with conspecifics, such as mating and competing for resources. Non-avian reptiles are typically viewed as solitary animals that predominantly use their vision and olfaction to communicate with conspecifics. Nevertheless, in recent years, evidence is mounting that some reptiles can produce sounds and have the potential for acoustic communication. Reptiles that can produce sound have an additional communicative channel (in addition to visual/olfactory channels), which could suggest they have a higher communicative complexity, the evolution of which is assumed to be driven by the need of social interactions. Thus, acoustic reptiles may provide an opportunity to unveil the true social complexity of reptiles that are usually thought of as solitary. This review aims to reveal the hidden social interactions behind the use of sounds in non-avian reptiles. Our review suggests that the potential of vocal and acoustic communication and the complexity of social interactions may be underestimated in non-avian reptiles, and that acoustic reptiles may provide a great opportunity to uncover the coevolution between sociality and communication in non-avian reptiles. This article is part of the theme issue ‘The power of sound: unravelling how acoustic communication shapes group dynamics’.

Little is known about the behavioral and cognitive traits that best predict invasion success. Evidence is mounting that cognitive performance correlates with survival and fecundity, two pivotal factors for the successful establishment of invasive populations. We assessed the quantity discrimination ability of the globally invasive red-eared slider (Trachemys scripta elegans). We further compared it to that of the native stripe-necked turtle (Mauremys sinensis), which has been previously evaluated for its superior quantity discrimination ability. Specifically, our experimental designs aimed to quantify the learning ability as numerosity pairs increased in difficulty (termed fixed numerosity tests), and the immediate response when turtles were presented with varied challenges concurrently in the same tests (termed mixed numerosity tests). Our findings reaffirm the remarkable ability of freshwater turtles to discern numerical differences as close as 9 vs 10 (ratio = 0.9), which was comparable to the stripe-necked turtle’s performance. However, the red-eared slider exhibited a moderate decrease in performance in high ratio tests, indicating a potentially enhanced cognitive capacity to adapt to novel challenges. Our experimental design is repeatable and is adaptable to a range of freshwater turtles. These findings emphasize the potential importance of cognitive research to the underlying mechanisms of successful species invasions.

Background Quantity discrimination, the ability to discriminate a magnitude of difference or discrete numerical information, plays a key role in animal behavior. While quantitative ability has been well documented in fishes, birds, mammals, and even in previously unstudied invertebrates and amphibians, it is still poorly understood in reptiles and has never been tested in an aquatic turtle despite the fact that evidence is accumulating that reptiles possess cognitive skills and learning ability. To help address this deficiency in reptiles, we investigated the quantitative ability of an Asian freshwater turtle, Mauremys sinensis , using red cubes on a white background in a trained quantity discrimination task. While spontaneous quantity discrimination methods are thought to be more ecologically relevant, training animals on a quantity discrimination task allows more comparability across taxa. Results We assessed the turtles’ quantitative performance in a series of tests with increasing quantity ratios and numerosities. Surprisingly, the turtles were able to discriminate quantities of up to 9 versus 10 (ratio = 0.9), which shows a good quantitative ability that is comparable to some endotherms. Our results showed that the turtles’ quantitative performance followed Weber’s law, in which success rate decreased with increasing quantity ratio across a wide range of numerosities. Furthermore, the gradual improvement of their success rate across different experiments and phases suggested that the turtles possess learning ability. Conclusions Reptile quantitative ability has long been ignored and therefore is likely under-estimated. More comparative research on numerical cognition across a diversity of species will greatly contribute to a clearer understanding of quantitative ability in animals and whether it has evolved convergently in diverse taxa.