Swallowtail butterflies practice
Batesian mimicry, a
behavior in which the butterflies' appearance closely resemble that of distasteful species that prevents predation. Swallowtails differ from many animals that practice
mimicry. The tiger swallowtail butterfly (
Papilio glaucus), exhibits a female-limited
polymorphism for Batesian mimicry and others, such as the Canadian tiger swallowtail (
Papilio canadensis) do not display any form of mimicry. Predators include the
red-winged blackbird,
Pennsylvania firefly,
five-lined skink,
green darner,
goldenrod spider,
Chinese mantis,
fiery searcher, and
striped skunk.
Biological basis for polymorphisms in mimicry Not all individuals in some species are identical in appearance. For example,
Papilio glaucus (eastern tiger swallowtail), Y-linkage determines whether the females are either
wild-type (yellow and black) or melanic (dark
melanin replaces the yellow background). This genetic difference stems from the fact that
melanism is controlled by a single
gene, which controls the level of
dopamine in the organism. The
enzyme BAS, which assists dopamine in producing the yellow
pigmentation, normally found on the wings' background, is suppressed. Without the pigmentation, the butterfly appears mostly black (the melanic form) and is a Batesian mimic of
Battus philenor, the pipevine swallowtail. There are also
Papilio glaucus that are not wholly black; several possess an intermediate "sooty" color and are sensitive to
temperature. Given that the males of the species, which do not have Batesian mimicry, are preyed upon much more frequently by
predators than the females, an ongoing question is why females would exhibit the non-mimetic wing pattern, which would seemingly lower their fitness compared to the mimicry form. The
pipevine swallowtail exhibits Batesian mimicry as well. Several
hypotheses for this phenomenon were made, the two noteworthy being the pseudosexual selection hypothesis and the male avoidance hypothesis. In the pseudosexual hypothesis, male butterflies aggressively approached the
male-looking females and then mellowed their behavior into sexual behavior when they were close enough to identify them as females. In the male avoidance hypothesis, female butterflies disguise themselves in an attempt to evade male harassment, as courtship can be harmful, time-consuming, and attract predators. One study recorded male responses to females of each morphs and found that the males consistently favored the Batesian mimics, then the black and yellow, and then the morph with orange patches. The scientists concluded that
frequency-dependent selection did lead to equal success for all three alternative strategies: the Batesian females suffered the fewest predators but their fitness was reduced the most by sexual harassment, while the other two faced lower sexual harassment but also lost fitness from predators' attacks. == Mating and young ==