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

Abstract

Aposematism is an effective antipredator strategy. However, the initial evolution and maintenance of aposematism are paradoxical because conspicuous prey are vulnerable to attack by naïve predators. Consequently, the evolution of aposematic signal mimicry is also difficult to explain. 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. It is currently unknown, however, how personal and social information combines to affect the fitness of aposematic prey. For example, does social information become more useful when predators have already ingested toxins and need to minimize further consumption? 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). 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. 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. A free Plain Language Summary can be found within the Supporting Information of this article.

Predators’ consumption of unpalatable prey does not vary as a function of bitter taste perception

“…Nevertheless, the ability to detect bitter taste might be important when predators are sampling prey with weaker chemical defenses or when defenses are more variable, which can increase the risk of ingesting toxins (Skelhorn and Rowe 2005;Barnett et al 2014). Furthermore, predators can gather social information about prey unpalatability by observing the disgust responses of other predators (Mason and Reidinger 1982;Johnston et al 1998;Skelhorn 2011;Thorogood et al 2018;Hämäläinen et al 2019a). Our study indicates that individuals vary in how likely they are to show these responses, which could create heterogeneity in social information that is available for observing predators.…”

“…These chemical defenses are often described as bitter tasting (Brower and Fink 1985;Glendinning 1994) and they typically generate aversive responses in predators, including head shaking, bill/mouth cleaning, and spitting out of food. Avian predators learn to avoid aposematic prey based on bitter taste (e.g., Skelhorn and Rowe 2006;Skelhorn and Rowe 2010) and birds' responses to bitter tastes can also provide other predators with social information about prey quality (Johnston et al 1998;Skelhorn 2011;Thorogood et al 2018;Hämäläinen et al 2019a). Bitter taste perception is therefore assumed to be important when predators are gathering information about prey profitability.…”

Peer Review #1 of "The effect of social information from live demonstrators compared to video playback on blue tit foraging decisions (v0.1)"

“…This initial preference makes our results difficult to interpret, and different symbol choice might have provided us better evidence of social information use. Interestingly, the Manuscript to be reviewed preference for square symbols has not been found in great tits (Lindström et al, 2001;Hämäläinen et al, 2019), and artificial prey with cross and square symbols have been used in many avoidance learning experiments (e.g. Alatalo & Mappes, 1996;Lindström et al, 1999;Lindström et al, 2001;Thorogood, Kokko & Mappes, 2018).…”

“…We presented birds videos by placing an LCD monitor (Dell E198FPF, 19", resolution 1280 × 1024, 75 Hz refresh rate, 300 cd/m 2 ) against the plexiglass (Fig. 1c), following previously validated methods Manuscript to be reviewed (Hämäläinen et al, 2017;Thorogood, Kokko & Mappes, 2018;Hämäläinen et al, 2019). The size of the demonstrator on the screen was smaller than the size of the live bird (approximately % of the real size).…”

“…We found recently that blue tits' behaviour changed when they were presented with video playback of a conspecific, but social information from videos did not influence their foraging decisions in a later foraging task (Hämäläinen et al, 2017). In contrast, great tits (Parus major) have been demonstrated to respond to videos of a conspecific (Snijders, Naguib & van Oers, 2017), and use social information from videos in their foraging decisions (Thorogood, Kokko & Mappes, 2018;Smit & Oers, 2019;Hämäläinen et al, 2019), suggesting that video playback can be used successfully in other parid tit species. It is, however, possible that even closely related species differ in their response to video stimuli.…”