As such, the most basic, yet fundamental prediction of camouflage theory, is still poorly validated 21.Ĭamouflage through colour change is commonplace in the animal kingdom and may be achieved over different time scales from responses of less than a minute, when individuals are moving through a patchy background, to ontogenetic shifts over months or years, accompanying the transition between nursery and adult habitats 21.
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However, while all these studies comprise important evidence that individuals are efficiently concealed against the substrate, no study has directly quantified how closely differently coloured individuals match their background to predator eyes, and then how matching effectively reduces predation rates in natural conditions.
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More recently, with a better understanding of the anatomy of predator eyes, spectral sensitivity and visual modelling, different studies have estimated how individuals are camouflaged based to the view of predators through the use of spectrometry 14, 15, 16, 17, 18 or digital imagery 19, 20. Other studies, such as the classic example of camouflage and industrial melanism in the peppered moth ( Biston betularia) 6, have used correlational evidence, often based on morph-specific recapture rates, or artifical prey targets 9 to support the hypothesis that better camouflaged individuals are less frequently attacked by predators. This is a fundamental prediction of camouflage theory but, despite several emblematic cases consensually considered key examples of natural selection 6, 7, 8, 9, appropriate experimental evidence of the adaptive function of camouflage remains remarkably rare.Ī substantial body of previous work has used artificial dummy prey 10, 11 or computer-generated stimuli 12, 13 to test the survival advantage of camouflage in the laboratory or in the field. In this type of camouflage, better concealed individuals are less frequently detected by visual predators and therefore their survival chances are higher 5. Furthermore, many animals spanning a wide array of taxonomic groups take advantage of their colour patterns for concealment against the surrounding environment 3, 4, mainly by adopting a camouflage strategy known as background matching 4. Colour attributes may modulate individual fitness in many different ways, playing a crucial role in behavioural processes ranging from courtship and mate selection to predator deterrence through visual warning cues 3. The study of animal coloration has fascinated evolutionary biologists for centuries and provided important evidence of adaptation and natural selection 1, 2. dependent on the specific background-morph combination). Our work provides some of the clearest direct evidence to date that colour polymorphism and colour change provides a clear adaptive advantage for camouflage, and also highlights how this can be asymmetric across morphs and habitats (i.e. Predation trials with captive seahorses ( Hippocampus reidi), coupled with high-speed video analyses, closely matched model predictions: predation rates were similar for brown prawns between seaweed types, but pink individuals were attacked significantly less on red than brown weed. Digital image analysis and visual modelling of a fish predator (seahorse) predicted that brown prawns would be imperfectly concealed against both brown and red seaweed respectively, whereas pink prawns should be well camouflaged only in red weed. Here, we show that the level of camouflage achieved through colour adjustments towards the appearance of seaweed habitats is adaptive in reducing predation pressure in the prawn Hippolyte obliquimanus. However, aside from correlational evidence and studies using artificial dummy prey, experiments directly showing that better camouflaged prey to predator vision are at reduced risk of attack are lacking. Camouflage has been a textbook example of natural selection and adaptation since the time of the earliest evolutionists.