In butterflies, color and color patterns are essential for mate recognition and are used in defenses such as crypsis, warning coloration, disruption of visual tracking and mimicry. In the Eastern Tiger Swallowtail, Papilio glaucus, males and females exhibit drastically different color patterns, with the female mimicking the unpalatable Pipeline Swallowtail. In a close relative, Canadian Tiger Swallowtail, Papilio canadensis both the male and female display a color pattern similar to the Eastern Tiger Swallowtail male.
Wing color is under genetic control. In some point in its evolution, the female Eastern Tiger Swallowtails changed their color pattern from yellow to black. How did this happen? The black color of swallowtail wings is due to melanin, the most common type of pigment in insects. Females but not males produce melanin in the areas of the wing that in the males are yellow. Males do not produce melanin in these areas. The melanin production is controlled both by genes for proteins active in melanin synthesis and genes that suppress the melanin synthesis pathway. These genes are linked to the sex determining chromosome which is why only the females have the black coloration. These genes are present in Papilio glaucus but not Papilio canadensis and are the reason why P. glaucus, but not P. canadensis has black females.