Masquerade: critical testing of the ecology of disguise.

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It is well known that the external appearance of many species is influenced by selection for reduced ability of predators to detect individuals (a mechanism called crypsis or camouflage). However, some species have their external appearance intensely selected through an entirely different mechanism, which we call masquerade. Whereas with crypsis, detection of the individual in the environment is reduced; with masquerade the predator detects the existence of the potential prey but then misidentifies it as something unattractive to eat. Thus with crypsis, the predator passes close to the prey without realising it; whereas with masquerade the predator realises that it is passing close to an entity but mistakenly classifies that entity as something uninteresting. Examples of masquerade include caterpillars the look like twigs, spiders that look like bird droppings, fish that look like dead leaves and mantids that look like orchids. Although such examples are relatively well known, there has been a lack of scientific enquiry into masquerade; in contrast to historical and recent strong research activity on crypsis. Hence, this project will represent the first substantial investigation of the ecology of masquerade. Specifically, we will provide answers to some fundamental aspects of this mechanism that have never been explored previously. Firstly, although the difference between crypsis and masquerade is clear conceptually, and it seems obvious that the level of visual matching between say twig-mimicking caterpillars and the twigs on their host tree is driven by selection for masquerade, there is currently no unequivocal empirical demonstration of the fitness benefit of masquerade. Hence we will focus on twig-mimicking caterpillars to answer the following question: can a species ever be demonstrated to benefit specifically from masquerade rather than crypsis? It is likely that species benefit through both crypsis and masquerade so we will use the same system to explore whether masquerade can occur in the absence of crypsis; and how much can survival be increased by the joint action of masquerade and crypsis. Of course, if you look closely at a twig-mimicking caterpillar (or it moves, as it must do sometimes to gather food) then it becomes clear that it is a caterpillar and not a twig. Thus masquerade may become less effective if predators learn through experience to see through the disguise. We will thus explore whether masquerade can still be effective if predators have recent experience that the masquerading species occurs locally and is palatable; and if effectiveness is influenced by the local density of the masquerading species and the density of things that they are masquerading as. As previously hinted, masquerade involves adopting the appearance of inanimate objects; yet for many species movement is required for their own foraging. It seems likely that the resolution of this conflict is that masqueraders avoid movement when visual predators are prevalent by day and move to forage only at night; this hypothesis too will be tested both by literature survey and by purpose designed experiments. It would appear that many species adopt masquerade only when they are young and small; switching to other appearance forms (principally warning coloration) when older and larger. Again by surveying available literature for cross-species comparison and through purposed designed experiments we will attempt to identify the reasons for this often-dramatic change in appearance.