Experienced social partners hinder learning performance in naive clonal fish
Social learning is widely assumed to enhance individual learning efficiency, particularly when naive observers have access to skilled demonstrators, yet the conditions under which this assumption holds remain poorly understood. Here, we investigated how individual learning is influenced by the skill level of social partners. We predicted that naive individuals would benefit from observing experienced conspecifics, yet found the opposite: trained partners significantly impaired naive individuals learning performance, while trained individuals remained unaffected by their partners skill level. We conducted experiments in near-identical individuals, using the all-female clonal Amazon molly (Poecilia formosa) to test whether these fish can learn an operant foraging task, whether individuals differ consistently in learning ability, and whether partner skill level influences learning performance. Using an operant conditioning paradigm over five days, half of the fish were trained to locate food inside a cylinder, whereas the remaining individuals received food randomly dispersed within their tank. Trained individuals subsequently visited the cylinder more frequently than randomly fed individuals and exhibited consistent individual differences in learning performance. In a second phase, fish were allowed to observe a conspecific while individual training was either continued (for trained individuals) or initiated (for naive individuals). We found that trained individuals did not benefit from the presence of a partner, regardless of the partners proficiency, but consistently outperformed naive individuals. In contrast, naive individuals showed reduced learning performance when paired with experienced partners, but not with naive partners. Together, our results indicate that Amazon mollies achieve this foraging task through individual learning and exhibit stable differences in learning ability. Moreover, social learning depends on both the learners own skill level and that of the social partner, such that observing an experienced conspecific may, in some cases, impede rather than enhance learning.