Importance of colour in the reaction of passerine predators to aposematic prey: experiments with mutants of Pyrrhocoris apterus (Heteroptera)

Abstract

Persistent questions concerning the warning coloration of unpalatable insects address whether the bright aposematic colour itself or its combination with a species-specific dark pattern is the key factor in their protection against insectivorous birds, and how chromatic polymorphism originates and is maintained in aposematics. In the present study, these questions were tested experimentally, using the birds Parus major , Parus caeruleus , Erithacus rubecula , and Sylvia atricapilla as predators, and chromatically polymorphic firebug Pyrrhocoris apterus : red wild form, white, yellow, and orange mutants (all four of them with the same black melanin pattern, the mutants differing in colour of pteridine pigments only) and the nonaposematic brown-painted wild form as prey. The results show that a specific colour is essential for the birds to recognize the specific aposematic prey; the melanin pattern is not sufficient. White mutants were no better protected than nonaposematic firebugs; red wild-type and orange mutants were equally well protected against all bird species; and the reaction of birds to yellow mutants was species-specific. An evolutionary scenario of 'recurrent recessive mutations' is formulated to explain the origin of colour polymorphism in some aposematics.

Size-dependent colouration in larvae of Orgyia antiqua (Lepidoptera: Lymantriidae): A trade-off between warning effect and detectability?

“…This leads to the conclusion that detectability might be a more important determinant of survival rate than acceptability, even for a larva whose appearance allows one to expect the opposite. In particular, aposematic larvae are not safe because bird species differ in their ability to discriminate between aposematic and nonaposematic prey (Exnerová et al, 2003), also the threshold signal strength that creates the aversion appears to vary (Exnerová et al, 2006). The birds' willingness to consume aposematic prey also strongly depends on their hunger level as the results of the current and some other studies show (Chai, 1986;Sandre & Mappes, in prep.).…”

“…Quite obviously, detectability is higher if the body is larger, and, somewhat less obviously, there is some evidence that aposematic prey has a steeper size dependent detectability function, as compared to cryptic objects (Mänd et al, 2007;this study). This is biologically relevant because warning colouration rarely offers complete protection to the aposematic prey (Stimson & Berman, 1990;Geffeney et al, 2002;this study), and high detectability may thus be highly detrimental (Exnerová et al, 2003(Exnerová et al, , 2006Endler & Mappes, 2004). Such a trade-off situation may imply that warning colouration is the optimal solution for some intermediate body sizes, while most animals smaller and larger than that are selected to be cryptic, i.e.…”

Color contrast and stability as key elements for effective warning signals

“…Achromatic signals (black and white) (C) have great variation, indicating that these colors should not be considered a reliable warning signal. and orange stimuli (Exnerová et al, 2006b). However, these studies do not determine why these associations are made with such color types (i.e., the underlying mechanism for what makes such colors effective signals).…”

“…However, Aronsson and Gamberalle-Stille (2008) showed that the pattern of a warning signal may not be as important as the color component. Moreover, a completely black prey may not elicit an avoidance response from an avian predator (Exnerová et al, 2006b). Our analyses show that black signals are highly variable both during the day and between weather conditions.…”

“…Our results suggest that this might be due to the low contrast of black colors, which could potentially be interpreted as edible prey. Several studies on aposematic coloration in firebugs (Pyrrhocoris apterus: Heteroptera) have shown that predators pay more attention to the "main" color of the signal, rather than the patterns it may have (Exnerová et al, 2003(Exnerová et al, , 2006b). Moreover, a few studies have discussed the maximization of conspicuousness by achieving the greatest mismatch to the background, rather than just color contrast (Poulton, 1890;Cott, 1940;Endler, 1988).…”