Social information use about novel aposematic prey is not influenced by a predator's previous experience with toxins

1. Aposematism is an effective antipredator strategy. However, the initial evolution and maintenance of aposematism is paradoxical because conspicuous prey are vulnerable to attack by naïve predators. Consequently, the evolution of aposematic signal mimicry is also difficult to explain. 2. The cost of conspicuousness can be reduced if predators learn about novel aposematic prey by observing another predator’s response to that same prey. On the other hand, observing positive foraging events might also inform predators about the presence of undefended mimics, accelerating predation on both mimics and their defended models. 3. It is currently unknown, however, how personal and social information combine to affect the fitness of aposematic prey. For example, does social information become more useful when predators have already ingested toxins and need to minimise further consumption? 4. We investigated how toxin load influences great tits’ (Parus major) likelihood to use social information about novel aposematic prey, and how it alters predation risk for undefended mimics. Birds were first provided with mealworms injected with bitter-tasting chloroquine (or a water-injected control), before information about a novel unpalatable prey phenotype was provided via video playback (either prey alone, or of a great tit tasting the noxious prey). 5. An experimentally-increased toxin load made great tits warier to attack prey, but only if they lacked social information about unpalatable prey. Socially educated birds consumed fewer aposematic prey relative to a cryptic phenotype, regardless of toxin load. In contrast, after personally experiencing aposematic prey, birds ignored social information about palatable mimics and were hesitant to sample them. 6. Our results suggest that social information use by predators could be a powerful force in facilitating the evolution of aposematism as it reduces predation pressure on aposematic prey, regardless of a predator’s toxin load. Nevertheless, observing foraging events of others is unlikely to alter frequency-dependent dynamics among models and mimics, although this may depend on predators having recent personal experience of the model’s unpalatability.LH was funded by the Finnish Cultural Foundation and Emil Aaltonen Foundation. RT was supported by an Independent Research Fellowship from the Natural Environment Research Council UK (NE/K00929X/1) and a start-up grant from the Helsinki Institute of Life Science (HiLIFE), University of Helsinki. HMR was supported by a research fellowship from the Institute of Zoology, and is currently supported by the Max Plank Society. JM was supported by the Academy of Finland via the Finnish Centre of Excellence Program and the University of Jyväskyl