Understanding the diversity of anti-predator defence

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INTRODUCTION: Go into most Canadian backyards and you are likely to see numerous examples of protective colour patterns: moths that resemble their backgrounds, warningly-coloured ladybugs, and harmless hover flies that gain protection by resembling stinging wasps or bees. Over the last century, researchers have come to understand precisely how these defensive traits serve to protect organisms from predators. However, in treating each of these defensive adaptations independently, more fundamental questions have been overlooked. In particular, why have some species evolved one form of defence, while other species have evolved another? Likewise, why have some mimetic species evolved an almost perfect resemblance to their aversive models, while other species have evolved only a crude similarity? Over the course of this research program, I propose to test a series of key hypotheses which will help us understand why species evolve the defences that they do. Each of these hypotheses arises directly from an appreciation that anti-predator defences are the outcome of co-evolution between predators and prey, and therefore depend on a fundamental understanding of not just prey life history, but also predator cognition. OBJECTIVES: I have three objectives. First, I shall characterize observed variation in defences, ranging from eyespots in caterpillars to mimicry in hover flies, within a phylogenetic framework. From here, I will test for predicted associations between the evolved mode of defence and other attributes such as body size, and phenology. Many of the predicted associations arise directly from untested assumptions as to how predators would react to a given defence. Therefore, my second objective will be to test specific hypotheses as to how predator behaviour shapes the observed variation in prey defence. Third, in seeking fundamental explanations for the observed predator behaviours, I will develop and evaluate adaptive explanations for established psychological phenomena that have hitherto been considered primarily at the proximate level.METHODS: I will utilise phylogenetic reconstruction of past events to elucidate evolutionary patterns, and to characterise transitions between different defensive strategies, such as the trait changes necessary for wasp mimicry to evolve into bee mimicry. I will support these analyses by investigating the nature of predator behaviour proposed to generate this diversity. For example, I will use field trials to quantify the selective advantage of eyespots in different types of caterpillar by monitoring the survivorship of artificial caterpillars of different size, and I will evaluate how and why wild birds tend to overlook potentially informative features when discriminating palatable from unpalatable prey. To complement this work, I will develop original optimization models to evaluate whether any of the observed behaviours (such as a fear of novel cues and the use of a restricted set of discriminative features) can be understood from an adaptive perspective.SIGNIFICANCE: Predation is one of the most universal and important agents of selection, responsible for a bewildering array of traits in the natural world. Here we will test clear hypotheses as to why different species have evolved different anti-predator defences, and examine the role of predator cognition in shaping these defences. After decades of research in which camouflage, warning signals and mimicry were viewed independently, here we adopt a far broader perspective aimed at understanding how adaptive predator behaviour and cognition shape the diversity of anti-predator traits in prey.