Mullerian mimicry, where 2 unpalatable species share a warning pattern, is classically believed to be a form of mutualism, where the species involved share the cost of predator education. Birds learn to avoid a color signal faster when individual prey possesses 1 of 2 bitter-tasting chemicals rather than all having the same chemical, suggesting that Mullerian mimics that possess different defense chemicals are better protected than those that possess the same defense chemical. Using domestic chicks as predators and flavored, colored crumbs for prey, we investigated whether birds learn to avoid 2 visually distinct crumb types faster when each crumb type possesses a different defense chemical than when both crumb types share the same defense chemical. We found that birds learned to avoid 2 visually distinct color signals at a similar rate, irrespective of whether each color signal represented a different defense chemical or whether both color signals represented the same defense chemical. This experiment, therefore, indicates that in terms of predator avoidance learning, possessing 2 defense chemicals is more advantageous when prey look the same than when they look different. This suggests that Mullerian mimics with different defense chemicals not only are better protected than Mullerian mimics that share a single chemical but also benefit more from their mimetic resemblance. Copyright 2006.
Many prey species possess eyespots: paired markings that often consist of two or more concentric circles. Predators are wary of such prey because eyespots are conspicuous and/or mistaken for vertebrate eyes. Here we used naïve domestic chicks as predators of artificial moth-like prey to test the hypothesis that both eyespots configuration and predator approach direction affect the antipredator efficacy of eyespots. We found that when chicks approached prey straight on, eyespots configuration did not influence attack latency. Chicks that approached from either the left or the right, were slower to attack prey in which the central circle of the eyespot was centrally placed or shifted in the direction of the chick’s approach, compared to prey in which the central circle had been shifted away from the direction of approach. These findings suggest that eyespots composed of concentric circles may protect prey against predators approaching from a wider range of directions than eyespots composed of eccentric circles. They are also consistent with the idea that eyespots are mistaken for eyes, and are perceived to pose a lesser risk when their “gaze” is averted from the approaching predator.
These data are the latency for the model predators (domestic chicks, Gallus gallus domesticus) to attack prey after the activation of the prey display. The latencies were measured in milliseconds.
Masquerading organisms appear to closely resemble inedible and generally inanimate objects, such as twigs, leaves, stones, and bird droppings. It has recently been demonstrated that masquerading prey gain protection from predation by being misclassified as inedible objects by their predators. Here, we present the first experimental test of the requirements of effective masquerade. Specifically, we explore whether masquerading prey need to be very similar in size to the "model" objects that they appear to resemble. Using domestic chicks as predators of twig-mimicking caterpillars, we find that matching a model object in size increases protection from predation; however, similarity of appearance without size matching still affords some protection. This study helps to explain why masquerading prey often resemble objects that are inherently variable in size (e.g., twigs, leaves, and stones) and has important implications for the evolution of masquerade as an antipredator defense.
Deimatic behaviours, also referred to as startle behaviours, are used against predators and rivals. Although many are spectacular, their proximate and ultimate causes remain unclear. In this review we aim to synthesise what is known about deimatic behaviour and identify knowledge gaps. We propose a working hypothesis for deimatic behaviour, and discuss the available evidence for the evolution, ontogeny, causation, and survival value of deimatic behaviour using Tinbergen's Four Questions as a framework. Our overarching aim is to direct future research by suggesting ways to address the most pressing questions in this field.
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.
Masquerade describes the resemblance of an organism to an inedible object and is hypothesized to facilitate misidentification of that organism by its predators or its prey. To date, there has been no empirical demonstration of the benefits of masquerade. Here, we show that two species of caterpillar obtain protection from an avian predator by being misidentified as twigs. By manipulating predators' previous experience of the putative model but keeping their exposure to the masquerader the same, we determined that predators misidentify masquerading prey as their models, rather than simply failing to detect them.
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