Colour change of twig-mimicking peppered moth larvae is a continuous reaction norm that increases camouflage against avian predators

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.

The adaptive value of camouflage and colour change in a polymorphic prawn

“…The results we obtained represent a fundamental starting point for understanding the adaptive value of camouflage – one of the most common anti-predator strategies observed in nature – for many different species. In addition, colour change for camouflage is widespread in nature, being common in animals from both terrestrial and aquatic habitats 21 , which permits the generalization of our findings to different species living on heterogeneous habitats, such as many insects 53 , crabs 54 – 56 , fish 25 , 57 and lizards 58 . It is important to appreciate, however, that both colour change and camouflage may differentially affect the survival of individuals in each of the different habitats where they live, since each background type will exhibit specific requirements that may change the close relationship between animal and substrate coloration.…”

Imperfect camouflage: how to hide in a variable world?

“…This has the advantage that it can be done in controlled laboratory settings but can also use realistic background types to investigate natural coloration strategies. Peppered moth larvae change their colour in response to the twig that they are resting on, but in a heterogeneous environment with multiple twig colours, they seem to adopt a specialist strategy rather than developing an intermediate colour [35]. By contrast, shore crabs adjust their appearance over moults and can change from pale and dark forms to converge on a more dark green/brown generalist appearance, regardless of the background they are placed upon, and these forms are highly camouflaged to human observers across a range of habitats [31].…”

Improved camouflage through ontogenetic colour change confers reduced detection risk in shore crabs

“…For instance, many crustaceans can change their appearance depending on the habitat for increased similarity with the visual environment over a period of hours and days (Brown & Sandeen, 1948;Powell, 1964;Rao, Fingerman, & Bartell, 1967;Stevens, Lown, & Wood, 2014a;Stevens, Rong, & Todd., 2013). Similar changes for camouflage tuning over days and weeks occur both within and between moults in other groups, such as grasshoppers (Burtt, 1951;Edelaar, Baños-Villalba, Escudero, & Rodríguez-Bernal, 2017;Peralta-Rincon, Escudero, & Edelaar, 2017) and caterpillars (Eacock et al, 2017). Not only can individuals change their coloration over multiple time-scales to facilitate camouflage, but many also undergo changes in appearance as a result of ontogeny (Duarte et al, 2017;Iampietro, 1999;Jensen & Egnotovich, 2015;Reid, Abello, Kaiser, & Warman, 1997;Stevens, 2016;Styrishave, Rewitz, & Andersen, 2004;Todd, Qiu, & Chong, 2009).…”

“…Colour change is commonplace in nature, occurring both in invertebrates (e.g., insects, crustaceans and molluscs; Bedini, ; Barbosa et al, ; Eacock, Rowland, Edmonds, & Saccheri, ; Valkonen et al, ) and in vertebrates (e.g., fish, amphibians, reptiles and mammals; Akkaynak, Siemann, Barbosa, & Mäthger, ; Booth, ; Kang, Kim, & Jang, ). For instance, many crustaceans can change their appearance depending on the habitat for increased similarity with the visual environment over a period of hours and days (Brown & Sandeen, ; Powell, ; Rao, Fingerman, & Bartell, ; Stevens, Lown, & Wood, ; Stevens, Rong, & Todd., ).…”