Warning coloration can be disruptive: aposematic marginal wing patterning in the wood tiger moth - PubMed (original) (raw)

. 2015 Oct 12;5(21):4863-74.

doi: 10.1002/ece3.1736. eCollection 2015 Nov.

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Warning coloration can be disruptive: aposematic marginal wing patterning in the wood tiger moth

Atsushi Honma et al. Ecol Evol. 2015.

Abstract

Warning (aposematic) and cryptic colorations appear to be mutually incompatible because the primary function of the former is to increase detectability, whereas the function of the latter is to decrease it. Disruptive coloration is a type of crypsis in which the color pattern breaks up the outline of the prey, thus hindering its detection. This delusion can work even when the prey's pattern elements are highly contrasting; thus, it is possible for an animal's coloration to combine both warning and disruptive functions. The coloration of the wood tiger moth (Parasemia plantaginis) is such that the moth is conspicuous when it rests on vegetation, but when it feigns death and drops to the grass- and litter-covered ground, it is hard to detect. This death-feigning behavior therefore immediately switches the function of its coloration from signaling to camouflage. We experimentally tested whether the forewing patterning of wood tiger moths could function as disruptive coloration against certain backgrounds. Using actual forewing patterns of wood tiger moths, we crafted artificial paper moths and placed them on a background image resembling a natural litter and grass background. We manipulated the disruptiveness of the wing pattern so that all (marginal pattern) or none (nonmarginal pattern) of the markings extended to the edge of the wing. Paper moths, each with a hidden palatable food item, were offered to great tits (Parus major) in a large aviary where the birds could search for and attack the "moths" according to their detectability. The results showed that prey items with the disruptive marginal pattern were attacked less often than prey without it. However, the disruptive function was apparent only when the prey was brighter than the background. These results suggest that warning coloration and disruptive coloration can work in concert and that the moth, by feigning death, can switch the function of its coloration from warning to disruptive.

Keywords: Aposematism; camouflage; crypsis; defense; disruptive coloration; predation.

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Figures

Figure 1

Figure 1

(A) A Parasemia plantaginis individual is highly conspicuous resting on a plant. (B) The same individual feigned death and dropped to the ground when the observer approached it, becoming highly cryptic (the moth is in the center of the photo). (C) Geographic variation in forewing patterns (only right forewings are shown). The Regular pattern (rightmost) is common in central and northern Europe, and the Hash pattern (second from the left) is found mainly in North America.

Figure 2

Figure 2

(A) Mean brightness values of gray tone pixels (range, 0–255) of artificial prey and the background (

BG

) used in the detectability experiment. The eight prey types are Normal marginal Hash, Normal nonmarginal Hash, Normal marginal Regular, Normal nonmarginal Regular, Reversed marginal Regular, Reversed nonmarginal Regular, Reversed marginal Hash, and Reversed nonmarginal Hash. The prey items were created from two natural forewing patterns of P. plantaginis (see Materials and Methods). The brightness of the pale and dark gray patches was 236 and 34, respectively. (B) The background used in the detectability test. A Normal marginal Regular prey item is located near the top and slightly to the right of the centerline.

Figure 3

Figure 3

The order in which prey were attacked (mean and 95%

CI

) in the preference test. The prey items are arranged from left to right according to their brightness value. marginal and nonmarginal members of each pair have the same brightness.

Figure 4

Figure 4

Survival curves of each pair of prey items along the time (sec) from the start of the trial in the detectability test: (A) Normal Regular, (B) Reversed Regular, (C) Normal Hash, and (D) Reversed Hash. The four pairs were analyzed separately because the preference test showed a significant effect of the interaction between prey type and mean prey brightness.

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