Abstract
Animal defensive coloration has long provided many important examples of evolution and adaptation. Of these, industrial melanism in the peppered moth is the classic textbook example of evolution in action, whereby dark and pale morphs suffer differential predation in polluted and unpolluted woodland based on their camouflage. Despite extensive work, a striking gap remains in that no study has ever objectively quantified their camouflage or related this directly to predation risk. Here we use image analysis and avian vision models to show that pale individuals more closely match lichen backgrounds than dark morphs. Artificial predation experiments in unpolluted woodland show 21% higher survival rates of pale than melanic individuals. Overall, we provide the strongest direct evidence to date that peppered moth morph frequencies stem from differential camouflage and avian predation, providing key support for this iconic example of natural selection.
Highlights
Animal defensive coloration has long provided many important examples of evolution and adaptation
The most important example of evolution in action is that of industrial melanism and the peppered moth (Biston betularia)
We expected that typica would share greater similarities with crustose lichen backgrounds in comparison to plain bark backgrounds, whereas the reverse should be seen with carbonaria
Summary
Animal defensive coloration has long provided many important examples of evolution and adaptation. 1760–1840), there was a rise of a new dark melanic (carbonaria) form in conjunction with a corresponding decline of the pale (typica) morph[4] The former is widely thought to have been well camouflaged against birds on trees where atmospheric pollution had killed off the lichen and soot particulates coated the bark, with typica effectively hidden on lichen-covered trunks and branches in unpolluted woodland. These claims have been firmly rebutted[14,15], but more importantly, the publication of scientific criticisms[4,16,17] led to some doubts in the scientific community and furthered the promotion of an anti-evolution agenda from the non-scientific community[18] Most of these criticisms and uncertainties have since been largely addressed (for example, natural resting sites), and the validity of the original studies confirmed through further experiments providing reliable evidence indicating bird predation is the most important selective factor driving camouflage in Biston betularia[11]. These differences translate into a strong survival advantage of typica individuals in unpolluted woodland
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