Colour Change and Camouflage in Rockpool Fish
Thesis or dissertation
University of Exeter
Camouflage is one of the most widespread anti-predator strategies in nature. Many animals use a combination of both morphological and behavioural means. Camouflage can be particularly challenging in heterogeneous environments, and as such some animals have evolved under selection to change colour to enable them to camouflage on a range of different background types. One such species is the rock goby (Gobius paganellus), a common rockpool fish capable of rapidly (within one minute) changing its colour and luminance (perceived lightness) when placed on different backgrounds. The rock goby provides a good model for studying rapid colour change in fish inhabiting habitats such as rocky shores that tend to be highly heterogeneous, and where fish may be exposed to both terrestrial and marine predators depending on tidal level. I used digital image analysis and a model of predator vision to quantify changes in colour, luminance, pattern, and camouflage. In chapter 2 I investigate the ability of rock gobies to match the colour of sand and algae covered rock, and test whether a fish’s previous background affects their ability to match a new one. I also tested their ability to match a range of different background brightness. Finally, I ask whether rock gobies exhibit behavioural background matching in addition to adaptive colour change. In chapter 3 I ask whether rock gobies change their body pattern in response to their visual background, and then whether the spatial frequency of more natural backgrounds influences pattern change. I found that the gobies rapidly changed colour and luminance in response to the different backgrounds and an individual’s previous background had no effect on its ability to change colour and camouflage on a new background. The level of camouflage did however differ between backgrounds whereby some colours and brightness appeared easier to match than others. Rock gobies also showed a behavioural preference for darker backgrounds over lighter ones. Moreover, gobies are capable of rapidly changing their body pattern in response to their background, with high spatial frequency substrates such as sand inducing the greatest change in pattern. This thesis shows that small rockpool fish use a combination of rapid colour and pattern change, and behaviour background choice, to camouflage themselves against their background.
MbyRes in Biosciences