Aposematism and crypsis combined as a result of distance dependence: functional versatility of the colour pattern in the swallowtail butterfly larva - PubMed (original) (raw)

Comparative Study

Aposematism and crypsis combined as a result of distance dependence: functional versatility of the colour pattern in the swallowtail butterfly larva

Birgitta S Tullberg et al. Proc Biol Sci. 2005.

Abstract

The idea that an aposematic prey combines crypsis at a distance with conspicuousness close up was tested in an experiment using human subjects. We estimated detectability of the aposematic larva of the swallowtail butterfly, Papilio machaon, in two habitats, by presenting, on a touch screen, photographs taken at four different distances and measuring the time elapsed to discovery. The detectability of larvae in these images was compared with images that were manipulated, using existing colours either to increase or decrease conspicuousness. Detection time increased with distance for all colourations. However, at the closest distance, detection time was longer for the larvae manipulated to be more cryptic than for the natural and more conspicuous forms. This indicates that the natural colouration is not maximally cryptic at a short distance. Further, smaller increments in distance were needed to increase detection time for the natural than for the conspicuous larva. This indicates that the natural colouration is not maximally conspicuous at longer distances. Taken together, we present the first empirical support for the idea that some colour patterns may combine warning colouration at a close range with crypsis at a longer range. The implications of this result for the evolution of aposematism are discussed.

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Figures

Figure 1

Figure 1

A fifth instar larva of the swallowtail butterfly, Papilio machaon with the colour patterns used in the experiment. Images (a)–(c) on Angelica archangelica in the shore habitat and images (d)–(f) on Peusedanum palustre in the fen habitat. The three larval colourations used were the normal, unmanipulated colour pattern (black and green bands and orange dots; (a) and (d)), the manipulated, uniformly green colour pattern (b) and (e) and the manipulated, black colouration with enlarged orange spots (c) and (f).

Figure 2

Figure 2

Two rare, natural colouration variants of the fifth instar P. machaon larvae. These individuals are offspring of two different females that were wild-caught in southern Sweden. (a) A uniformly green larva (but with orange spots present) that has lost the ability to synthesize the black pigment, (b) a black larva in which the black, orange-studded stripes are so broad that the normally green area is completely covered by black.

Figure 3

Figure 3

Time to detection by human subjects of the larva of P. machaon from photographs taken at four distances in a shore habitat (a)–(c) and in a fen habitat (d)–(f). Detection time increased with increasing distance for the normal larva (a) and (d), as well as for manipulated images of the larva (green: (b) and (e); black/orange: (c) and (f)).

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