Active background selection facilitates camouflage in shore crabs, Carcinus maenas

Camouflage plays a significant role in preventing and facilitating predation. A common method used by many species to avoid detection is to match aspects of the visual background. Behaviour can constitute a valuable component of camouflage by enabling animals to choose appropriate substrates, yet how widespread this is remains relatively underexplored. Through a series of substrate choice experiments we tested whether the highly phenotypically diverse common shore crab shows substrate preferences, and whether preferences reflect choices that actively improve individual camouflage. Using image analysis, we compared brightness and colour metrics of crabs to their chosen versus alternative substrates. Crabs tended to choose substrates with a brightness that better matched their own appearance. However, choices depended on the exact backgrounds offered, for example with crabs preferring backgrounds resembling native rock pool colour patterns over those resembling mudflats, but showing little difference in choice between red and green substrates. The results help explain observations that shore crabs and other animals show phenotype-environment associations at a microscale and demonstrate how individuals can maintain camouflage in highly variable visual environments. Our study shows that substrate preferences can be a key route to enabling camouflage in a broad spectrum of species. & COPY; 2023 The Author(s). Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY license (http://creativecommons.org/licenses/ by/4.0/).

Automated summary

Camouflage plays a vital role in preventing and facilitating predation. The behavior of animals in selecting appropriate substrates contributes to their camouflage. By conducting substrate choice experiments, we found that shore crabs tend to choose substrates matching their own appearance in terms of brightness. This study helps explain the phenotype-environment associations observed in shore crabs and sheds light on how individuals can maintain camouflage in visually variable environments.