Camouflage in heterogeneous intertidal habitats: background choice, colour change, and polyphenic crypsis in the chameleon prawn (Hippolyte varians).

Abstract

A core concept of camouflage is that strong phenotype–environment associations are essential, i.e., a relationship between animal coloration and elements of the visual environment. However, the visual composition of natural habitats is highly variable, both in time and space. To overcome the challenge of maintaining camouflage across multiple backgrounds, animals utilising camouflage are thought to have evolved a variety of strategies, for example, polyphenic coloration, colour change, and behaviours integrating colour patterns with the environment. Studies investigating these flexible camouflage traits, particularly in species displaying multiple colour forms, can facilitate a better understanding of the drivers and trade-offs of camouflage strategies. Camouflage traits are often investigated in isolation but are likely closely associated in an animal’s overall cryptic stratagem. In this thesis I explored the camouflage strategies used by highly variable chameleon prawns (Hippolyte varians; primarily the green and red colour forms) within heterogeneous intertidal habitats. Digital photography and image analysis were used to quantify colour patterns to models of predator (fish) vision to gain an ecologically valid assessment of camouflage. My findings demonstrate that polyphenic coloration can enable seaweed-specialist camouflage, and that longer-duration colour change can improve camouflage against mismatching substrates. I also show that prawns display strong behavioural preferences that actively maintain camouflage; the importance of vision for these decisions has also been explored. Furthermore, I demonstrate that chameleon prawns can adjust behavioural preferences in tandem with colour change. My investigation of the daily colour change rhythm of chameleon prawns establishes that these shifts are driven primarily by environmental light cues; the potential adaptive benefits are also discussed. I explored how the transparent-type colour patterns of prawns may allow for a more generalist camouflage strategy and found that these prawns have no distinct behavioural seaweed preference but are also able to change colour, the colour changes being influenced by uniform and mixed seaweed backgrounds. Overall, in this thesis I demonstrate how plastic camouflage traits, acting individually or in unison, can facilitate camouflage in the face of both rhythmic and stochastic, spatial and temporal, heterogeneity within the visual environment.