Different ways to disappear: transparency extends camouflage beyond background matching in heterogeneous environments

Environmental heterogeneity challenges camouflage because no single phenotype is expected to maximise concealment across all backgrounds. While uniform pigmentation can provide effective background matching on specific substrates, transparency may offer a more generalist camouflage strategy by reducing conspicuousness across different visual backgrounds. However, the relative survival advantages and trade-offs of these alternative strategies, particularly when they coexist within the same species, remain poorly understood. Here, we investigated how camouflage performance varies between solid-coloured and transparent forms of the chameleon prawn (Hippolyte varians) across heterogeneous seaweed backgrounds. Using an online visual search experiment, 3,367 participants searched for realistic prawn models presented against photographs of four seaweed species, generating 45,888 prey presentations. Survival analyses revealed strong interactions between prawn colour type and background. Solid-coloured prawns performed as specialists, achieving their highest survival on matching seaweeds, particularly for green and brown individuals. By contrast, transparent prawns maintained relatively high survival across most backgrounds, consistent with a generalist strategy. However, transparency also involved important trade-offs: increasing levels of chromatic and achromatic mismatch made transparent prawns more readily detectable than solid-coloured individuals, while increasing body size had a negative effect on their survival. These findings reveal complementary advantages and limitations of specialist and generalist camouflage within a single species, suggesting that environmental heterogeneity may create conditions favouring the coexistence of alternative camouflage strategies in natural populations.