Visual predators select for crypticity and polymorphism in virtual prey


Cryptically coloured animals commonly occur in several distinct pattern variants. Such phenotypic diversity may be promoted by frequency-dependent predation, in which more abundant variants are attacked disproportionately often, but the hypothesis has never been explicitly tested. Here we report the first controlled experiment on the effects of visual predators on prey crypticity and phenotypic variance, in which blue jays (Cyanocitta cristata) searched for digital moths on computer monitors. Moth phenotypes evolved via a genetic algorithm in which individuals detected by the jays were much less likely to reproduce. Jays often failed to detect atypical cryptic moths, confirming frequency-dependent selection and suggesting the use of searching images, which enhance the detection of common prey. Over successive generations, the moths evolved to become significantly harder to detect, and they showed significantly greater phenotypic variance than non-selected or frequency-independent selected controls.

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Figure 1: Samples of digital moths, shown on uniform grey (left) and cryptically textured (right) backgrounds, from the parental population, P0 (a), and from the F100 generations from the non-selected lines (b), the frequency-independent selection lines (c), and the experimental lines selected by the jays (d).
Figure 2: Detection accuracy of blocks of 100 trials as a function of crypticity of the target moth and dissimilarity between the target and the last previous correctly detected moth.
Figure 3: Changes in mean crypticity across successive generations in the three experimental lines (plotted with symbols), contrasted with the distribution of values from the two sets of control lines.
Figure 4: Changes in phenotypic variance of the digital moth population in the three experimental lines (plotted with symbols), contrasted with the distribution of values from the two sets of control lines.


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We thank J. Allen, R. Balda, J. Endler, T. Getty, L. Harshman, S. Louda, D. Pilson and S. Shettleworth for their comments and suggestions. This research was supported by a grant from the National Science Foundation.

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Correspondence to Alan B. Bond.

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Bond, A., Kamil, A. Visual predators select for crypticity and polymorphism in virtual prey. Nature 415, 609–613 (2002).

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