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Abstract:
Camouflage, and in particular background-matching, is one of the most common
anti-predator strategies observed in nature. Animals can improve their match to the
colour/pattern of their surroundings through background selection, and/or by plastic
colour change. Colour change can occur rapidly (a few seconds), or it may be slow,
taking hours to days. Many studies have explored the cues and mechanisms behind
rapid colour change, but there is a considerable lack of information about slow colour
change in the context of predation: the cues that initiate it, and the range of phenotypes
that are produced. Here we show that peppered moth (Biston betularia) larvae respond
to colour and luminance of the twigs they rest on, and exhibit a continuous reaction
norm of phenotypes. When presented with a heterogeneous environment of mixed twig
colours, individual larvae specialise crypsis towards one colour rather than developing
an intermediate colour. Flexible colour change in this species has likely evolved in
association with wind dispersal and polyphagy, which result in caterpillars settling and
feeding in a diverse range of visual environments. This is the first example of visually
induced slow colour change in Lepidoptera that has been objectively quantified and
measured from the visual perspective of natural predators.
