Microgeographical variability in long-term memory formation in the pond snail, Lymnaea stagnalis

The ability to learn and form long-term memory (LTM) can enhance an animal’s fitness, for example by allowing it to remember predators, food sources or conspecific interactions. Here we used the great pond snail, Lymnaea stagnalis, to assess whether variability among natural populations in memory-forming capabilities occurs on a microgeographical scale. We used four populations from two different habitat types separated by 1–20 km: two from large, permanent canals and two from small, fluctuating drainage ditches. Of the four populations tested, only one, from a small drainage ditch, formed LTM lasting 24 h after a 0.5 h operant training session to reduce aerial respiration in hypoxic conditions when trained in pond water alone. Each of the four populations demonstrated the same memory retention capability over 2 consecutive years, indicating temporal stability within each population tested. Despite this lack of a consistent ability for LTM formation among populations in pond water, all populations tested demonstrated LTM formation in the presence of predator kairomones, from both tench, Tinca tinca, a predatory fish present at the large canal sites, and crayfish, Pacifastacus leniusculus, known to extend memory in a Dutch L. stagnalis population. Therefore, while we found differences between populations in LTM retention after training in pond water, the response to predator kairomones during training, an ecologically relevant stressor, appears highly conserved in this species, enabling all populations to form LTM.