Background matching and disruptive coloration as habitat-specific strategies for camouflage

Martin Stevens,Samuel Green,Natasha Price,Jolyon Troscianko,Tom Tregenza

doi:10.1038/s41598-019-44349-2

Abstract

Camouflage is a key defence across taxa and frequently critical to survival. A common strategy is background matching, resembling the colour and pattern of the environment. This approach, however, may be ineffective in complex habitats where matching one patch may lead to increased visibility in other patches. In contrast, disruptive coloration, which disguises body outlines, may be effective against complex backgrounds. These ideas have rarely been tested and previous work focuses on artificial systems. Here, we test the camouflage strategies of the shore crab (Carcinus maenas) in two habitats, being a species that is highly variable, capable of plastic changes in appearance, and lives in multiple environments. Using predator (bird and fish) vision modelling and image analysis, we quantified background matching and disruption in crabs from rock pools and mudflats, predicting that disruption would dominate in visually complex rock pools but background matching in more uniform mudflats. As expected, rock pool individuals had significantly higher edge disruption than mudflat crabs, whereas mudflat crabs more closely matched the substrate than rock pool crabs for colour, luminance, and pattern. Our study demonstrates facultative expression of camouflage strategies dependent on the visual environment, with implications for the evolution and interrelatedness of defensive strategies.

Highlights

Many animals exhibit visual similarities with their environment, commonly referred to as ‘phenotype-environment associations’[1,2]
To assess how well crabs matched the colour and luminance of their backgrounds, discrimination or just noticeable difference (JND) values were used to determine the deviation between the carapace of an individual and the background
The poorest match was in crabs collected from rock pools against a rock pool background

Summary

Introduction

Many animals exhibit visual similarities with their environment, commonly referred to as ‘phenotype-environment associations’[1,2]. Selection has driven correlations in appearance between individual phenotypes and backgrounds in a wide range of animals, from rodents and lizards in terrestrial habitats[6,7] to crabs in marine habitats[2,8,9], and even in plants[10] These examples of phenotype-environment associations are highly suggestive of a camouflage function, but past work has rarely demonstrated or quantified the actual camouflage resulting from any match to the local environment; that is, phenotype-environment matching (but see[1]). Considerable research on disruptive coloration has demonstrated how this works, using artificial (human-made) prey presented to either birds or humans (e.g.19–24) These studies have shown that disruptive coloration frequently provides a reduction in detection (and potentially identification too), over and above the benefits conferred by background matching, and works at least in part by creating false edge information and hiding true body outlines[18,25]. A similar earlier model showed evidence for disruptive coloration and false edges in frogs[29]

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Conclusion