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Biology Letters (4)
Rowe, Candy (2)
Ruxton, Graeme D (1)
Ruxton, Graeme D. (1)
Year of Publication
Predators are less likely to misclassify masquerading prey when their models are present
Ruxton, Graeme D.
Masquerading animals have evolved striking visual resemblances to inanimate objects. These animals gain protection from their predators not simply by avoiding detection, but by causing their predators to misclassify them as the ‘models’ that they appear to resemble. Using domestic chicks as predators and twig-mimicking caterpillars as prey, we demonstrated that masquerading prey were more likely to be misclassified as their models when viewed in isolation from their models than when viewed alongside examples of their model, although they benefitted from masquerade to some extent in both conditions. From this, we predict a selection pressure on masqueraders to use microhabitats that reduce the risk of them being viewed simultaneously with examples of their model, and/or to more closely resemble their model in situations where simultaneous viewing is commonplace.
masquerade; camouflage; predation; predator–prey; detection; classification
Avian predators attack aposematic prey more forcefully when they are part of an aggregation
Ruxton, Graeme D
Defended insects often advertise their unprofitability to potential predators using conspicuous aposematic coloration. Many aposematic insects are also gregarious, and it has been suggested that the aggregation of defended prey may have facilitated the evolution of aposematic coloration. Empirical studies have demonstrated that birds are more wary of aggregated aposematic prey, and learn to avoid them more quickly than solitary prey. However, many aposematic insects survive being attacked by birds, and the effect of aggregation on post-attack survival has not previously been investigated. Using domestic chicks as predators and artificially manipulated mealworms as prey, we provide empirical evidence that predators attack aggregated aposematic prey more forcefully than solitary prey, reducing the likelihood of prey surviving an attack. Hence, we suggest that previous works concluding that aggregation was an important pre-requisite for the evolution of aposematism may have overestimated the fitness benefits of aggregation, since aggregated prey may be attacked less but are also less likely to survive an attack.
aposematism; receiver psychology; insects
Avian predators taste–reject aposematic prey on the basis of their chemical defence
Avian predators learn to avoid defended insects on the basis of their conspicuous warning coloration. In many aposematic species, the level of chemical defence varies, with some individuals being more defended than others. Sequestration and production of defence chemicals is often costly and therefore less defended individuals enjoy the benefits of the warning signal without paying the full costs of chemical production. This is a fundamental theoretical problem for the evolutionary stability of aposematism, since less defended individuals appear to be at a selective advantage. However, if predators sample aposematic prey and selectively reject individuals on the basis of their chemical investment, aposematism could become evolutionarily stable. Previous research aimed at testing whether birds can use taste to discriminate between palatable and unpalatable prey has been confounded by other experimental factors. Here, we show that birds can taste and reject prey entirely on the basis of an individual's level of chemical defence and more importantly, they can make decisions on whether or not to consume a defended individual based upon their level of chemical investment. We discuss these results in relation to the evolution of aposematism, mimicry and defence chemistry.
aposematism; automimicry; receiver psychology; insects; toxins
Frequency-dependent taste-rejection by avian predation may select for defence chemical polymorphisms in aposematic prey
Chemically defended insects advertise their unpalatability to avian predators using conspicuous aposematic coloration that predators learn to avoid. Insects utilize a wide variety of different compounds in their defences, and intraspecific variation in defence chemistry is common. We propose that polymorphisms in insect defence chemicals may be beneficial to insects by increasing survival from avian predators. Birds learn to avoid a colour signal faster when individual prey possesses one of two unpalatable chemicals rather than all prey having the same defence chemical. However, for chemical polymorphisms to evolve within a species, there must be benefits that allow rare chemical morphs to increase in frequency. Using domestic chicks as predators and coloured crumbs for prey, we provide evidence that birds taste and reject proportionally more of the individuals with rare defence chemicals than those with common defence chemicals. This indicates that the way in which birds attack and reject prey could enhance the survival of rare chemical morphs and select for chemical polymorphism in aposematic species. This is the first experiment to demonstrate that predators can directly influence the form taken by prey's chemical defences.
domestic chick; toxin; insect; warning signal; receiver psychology
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