Abstract
Camouflage is driven by matching the visual environment, yet natural habitats are rarely uniform and comprise many backgrounds. Therefore, species often exhibit adaptive traits to maintain crypsis, including colour change and behavioural choice of substrates. However, previous work largely considered these solutions in isolation, whereas many species may use a combination of behaviour and appearance to facilitate concealment. Here we show that green and red chameleon prawns (Hippolyte varians) closely resemble their associated seaweed substrates to the vision of predatory fish, and that they can change colour to effectively match new backgrounds. Prawns also select colour-matching substrates when offered a choice. However, colour change occurs over weeks, consistent with seasonal changes in algal cover, whereas behavioural choice of matching substrates occurs in the short-term, facilitating matches within heterogeneous environments. We demonstrate how colour change and behaviour combine to facilitate camouflage against different substrates in environments varying spatially and temporally.
Highlights
Background matching in the brown shrimpCrangon crangon: adaptive camouflage and behavioural-plasticity
Our results show that the coloration of chameleon prawns provides effective visual camouflage to predator vision against their main seaweed substrates
In the case of chameleon prawns, our results indicate that colour change is unlikely to have evolved as response to the spatial heterogeneity of their habitat, as is the case for rapidly changing animals such as chameleons[16] and cuttlefish[32]
Summary
We modelled the coloration of both green and red prawns and natural seaweed substrates (green sea lettuce and red dulse) to predator vision using the spectral sensitivity data of the dichromatic pollack (Pollachius pollachius)[45] and the trichromatic twospotted goby (Gobiusculus flavescens)[46]. In order to assess the level of camouflage between prawn colour types and seaweed species from the modelled perspectives of fish vision we used the widely implemented noise model for colour discrimination of Vorobyev and Osorio[49], which predicts chromatic signal discriminability as units of just noticeable differences (JNDs). Colour contrasts of green prawns against green sea lettuce (mean ± SE = 1.73 ± 0.15 for pollack, and 1.91 ± 0.17 for goby vision) were around the threshold of discriminability and much lower than against red dulse (6.66 ± 0.34 for pollack, and 6.38 ± 0.36 for goby vision).
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