Mimicking multiple models: polyphenetic masqueraders gain additional benefits from crypsis

Many prey organisms avoid predation by mimicking inanimate objects: a phenomenon known as masquerade. It is expected that masquerade will show a frequency-dependent advantage such that masquerading species benefit more from their appearance when they are rare in comparison with their models. In such circumstances, selection may favor the coexistence of different phenotypes ( polyphenism or polymorphism). The American peppered moth caterpillar Biston betularia cognataria appears to show polyphenetic masquerade: caterpillars found on birch trees look like birch twigs; those on willow trees look like willow twigs. Here, we show in laboratory experiments that the caterpillar does benefit from masquerade and that polyphenism is key to this benefit: avian predators misclassified birch-fed larvae as birch twigs and willow-fed larvae as willow twigs. In a second experiment where the benefits of masquerade were excluded, we show that larvae are less likely to be attacked when located on the host species whose twigs they resemble than when found on an alternative species whose twigs they do not resemble; thus, the polyphenism provides antipredatory benefits through crypsis as well as through masquerade. This is the first time that a species has been demonstrated to have the capacity to benefit both from masquerade and from crypsis, and the first time, polyphenism has been demonstrated to benefit masquerade.