The effect of predator appetite, prey warning coloration and luminance on predator foraging decisions

Abstract

Aposematic prey advertise their defence to visually hunting predators using conspicuous warning colouration. Established theory predicts that aposematic signals should evolve towards increased conspicuousness and similarity to enhance predator education. Contrary to theoretical expectations, there is often considerable within- and between-species variation in aposematic signals of animals sharing the same ecological niche, phylogeny and predators. This may be explained by varying responses of predators that weaken the selection pressure for a consistent signal. By presenting painted mealworm larvae as prey to great tits as predators we tested if different aposematic colour patterns have different values as a means of initial protection and learnt avoidance from predators, and how widely birds generalise their learnt avoidance to other colour patterns. We also investigated how the colour and luminance of the pattern elements affect predator attack decisions. Finally, we studied if hunger affects the predators' reaction to differently coloured prey. We found that similarity in colour was not crucial to the survival of aposematic prey, since learnt avoidance was not influenced by colour, and predators remembered and generalised widely in their learnt avoidance to other colours. We found that initial avoidance was, however, apparently influenced by luminance contrast. Interestingly, the predators' level of hunger was more important than the colour of the aposematic signal in determining birds' decisions to attack chemically-defended insect larvae. We discuss the implications of visual properties of prey colour pattern and predator appetite for the evolution of insect defences and warning signals. In addition we propose a methodological approach to effectively control for predator appetite in laboratory experiments.

Trade-off between warning signal efficacy and mating success in the wood tiger moth

“…In concordance, our results showed that increased colour contrast was beneficial for P. plantaginis males, with yellow males benefitting the most because of their greater conspicuousness. In addition to colour contrast, greater prey luminance contrast may increase the detection of prey, but also facilitate predator aversion [54] and memory retention of an invertebrate predator [55]. Our data showed that despite white P. plantaginis males having stronger luminosity contrast compared with the yellow males, it did not increase the survival of white males.…”

The Role of Life-History and Ecology in the Evolution of Color Patterns in Australian Chrysomeline Beetles

“…As the spectral sensitivities of chrysomelids appear to be limited to UV, blue and green but not red (Sharkey et al, 2017), active background matching may not fully explain color pattern differences of beetles with their host plant. Most studies that investigate the antipredator function of color patterns in insects focus predominantly on avian predators (e.g., Greenwood et al, 1981;Roper and Cook, 1989;Roper, 1990;Gamberale and Tullberg, 1996a;Marples et al, 1998;GamberaleStille and Tullberg, 1999;Lindström et al, 2001;Thomas et al, 2003;Forsman and Herrström, 2004;Exnerová et al, 2006;Rowland et al, 2007;Sandre et al, 2010;Ihalainen and Lindstedt, 2012). Yet, insect prey species such as chrysomeline beetles, may also be subject to predation by much smaller animals, including spiders and predatory insects.…”

Experimental evidence suggests that specular reflectance and glossy appearance help amplify warning signals

“…The possible importance of luminance contrast in predator learning and initial avoidance of defensive signalling has been suggested (e.g. refs 6, 7 and 8). For example, Prudic et al 9 tested the effect of luminance on invertebrate predators by painting milkweed bugs different tones of grey and found that a contrast in luminance was capable of being an effective warning signal.…”