The antipredator benefits of postural camouflage in peppered moth caterpillars

Hannah M Rowland,Robert P Burriss,John Skelhorn

doi:10.1038/s41598-020-78686-4

Abstract

Camouflage is the most common form of antipredator defense, and is a textbook example of natural selection. How animals’ appearances prevent detection or recognition is well studied, but the role of prey behavior has received much less attention. Here we report a series of experiments with twig-mimicking larvae of the American peppered moth Biston betularia that test the long-held view that prey have evolved postures that enhance their camouflage, and establish how food availability and ambient temperature affect these postures. We found that predators took longer to attack larvae that were resting in a twig-like posture than larvae resting flat against a branch. Larvae that were chilled or food restricted (manipulations intended to energetically stress larvae) adopted a less twig-like posture than larvae that were fed ad libitum. Our findings provide clear evidence that animals gain antipredator benefits from postural camouflage, and suggest that benefits may come at an energetic cost that animals are unwilling or unable to pay under some conditions.

Highlights

This may be because the posture enhances caterpillars’ resemblance to bird d roppings[26], other interpretations of these data have been p roposed[4], and it remains unclear to what degree the model larvae accurately reflected either the appearance or the posture of real caterpillars
We exploit natural variation in the tendency of American peppered moth larvae to utilize twig-like postures to test whether naïve avian predators take longer to find and attack larvae when they are in these postures than when they are not
We show that American peppered moth larvae gain antipredator benefits from postural camouflage: chicks took longer to attack caterpillars resting at an angle than those resting flat against a branch

Summary

Introduction

This may be because the posture enhances caterpillars’ resemblance to bird d roppings[26], other interpretations of these data have been p roposed[4], and it remains unclear to what degree the model larvae accurately reflected either the appearance or the posture of real caterpillars. We exploit natural variation in the tendency of American peppered moth larvae to utilize twig-like postures (see SI experiment 2) to test whether naïve avian predators take longer to find and attack larvae when they are in these postures than when they are not (i.e., whether they benefit from postural camouflage).

Results

Conclusion