Abstract
Camouflage is perhaps the most widespread anti-predator defense in nature, with many different types thought to exist. Of these, resembling the general color and pattern of the background (background matching) is likely to be the most common. Background matching can be achieved by adaptation of individual appearance to different habitats or substrates, behavioral choice, and color change. Although the ability to change coloration for camouflage over a period of hours or days is likely to be widely found among animals, few studies have quantified this against different backgrounds. Here, we test whether juvenile shore crabs (Carcinus maenas) are capable of color change for camouflage by placing them on either black or white (experiment 1) or red and green (experiment 2) backgrounds. We find that crabs are capable of significant changes in brightness, becoming lighter on white backgrounds and darker on black backgrounds. Using models of predator (avian) vision, we show that these differences are large enough in many individuals to lead to perceptible changes in appearance. Furthermore, comparisons of crabs with the backgrounds show that changes are likely to lead to significant improvements in camouflage and potentially reduced detection probabilities. Crabs underwent some changes on the red and green backgrounds, but visual modeling indicated that these changes were very small and unlikely to be detectable. Our experiment shows that crabs are able to adjust their camouflage by changes in brightness over a period of hours, and that this could influence detection probability by predators.
Highlights
Camouflage is perhaps the most widespread and common means to avoid predation in nature, and can be achieved through a variety of mechanisms (Wallace, 1889; Poulton, 1890; Thayer, 1909; Cott, 1940; Stevens and Merilaita, 2009, 2011)
Experimental work on background matching has lagged behind that of other camouflage types, it is clear that the degree of resemblance to the background is a fundamental factor in the likelihood of detection (e.g., Pietrewicz and Kamil, 1977; Stuart-Fox et al, 2003; Vignieri et al, 2010)
For the calculations of hue, we found that two principal components (PCs) explained 97.9% of the variance (PC1: 64.0% and PC2: 33.9%)
Summary
Camouflage is perhaps the most widespread and common means to avoid predation in nature, and can be achieved through a variety of mechanisms (Wallace, 1889; Poulton, 1890; Thayer, 1909; Cott, 1940; Stevens and Merilaita, 2009, 2011) It has long been a textbook example of evolution, from the famous example of the peppered moth, Biston betularia (Kettlewell, 1955a; Cook et al, 2012), through to more recent studies of the molecular basis of adaptation to different backgrounds in mice and reptiles (Nachman et al, 2003; Rosenblum, 2006; Rosenblum et al, 2010; Nunes et al, 2011). Animals can evolve the ability to change color, allowing them to tune their camouflage to the specific environment or background where they are found (Stuart-Fox and Moussalli, 2009)
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