Life stage and interspecies variation in salamander quantity discrimination, and incipient learning

Quantity discrimination is essential for adaptive decision making and originated early in evolutionary history. However, little is known about this ability in amphibians, especially during their development. In this study, we explored relative numeric abilities in larvae and metamorphs of two salamander species, Hynobius leechii and Salamandrella tridactyla using a spontaneous food-choice task. We tested 32 larvae and 16 metamorphs. The metamorphs included six H. leechii individuals and ten S. tridactyla individuals that had previously been tested during their larval stage. Individuals were offered two different types of food: bloodworms for larvae and cockroaches for metamorphs, both in a 1:8 ratio, and the individuals had to make a choice. Each individual completed 10 successful trials, each lasting for 20 min. Across life-history stages, individuals did not exhibit a statistically significant preference for larger vs smaller food quantities. Choice was not affected by species or life-history stage. However, binomial tests revealed that only Hynobius leechii metamorphs showed a higher probability of selecting larger quantities above chance, while the remaining groups did not show reliable discrimination. The duration to make a choice decreased over time, indicating task-level learning or habituation rather than learning about food quantity per se, with S. tridactyla making choices more quickly than H. leechii. This study provides the first insights into how spontaneous quantity-related decision making may vary across life-history stages in salamanders, contributing to a broader understanding of amphibian cognition.