D3490: Ontogenetic shifts in ultraviolet patterning among swallowtails (Papilionidae)

Animal color patterns are involved in key ecological interactions, from conspecific communication to predator avoidance. These functions, the organisms themselves, and their environments are rarely static. Many organisms exhibit plasticity in coloration in response to dynamic conditions. Some species change color in predictable sequences over the course of development, also known as ontogenetic color change (or OCC). OCC is both taxonomically widespread and diverse in its expression. However, few studies of OCC document colors that are invisible to humans: e.g., ultraviolet. While UV is not detectable to humans, it is visible to many arthropods and birds. Among insects, then, UV markings are likely involved in inter- and intraspecific signaling – and may also change over the course of development. In this study, we investigated UV coloration in three species of North American swallowtail butterflies (family Papilonidae): Papilio troilus, P. glaucus, and Battus philenor. We UV-photographed live caterpillars, live pupae, and preserved adults to answer three key questions about swallowtail UV: (1) Do swallowtail caterpillars, pupae, and/or adults reflect UV? (2) Is there OCC in UV patterns? and (3) Do UV patterns vary across species? Overall, we find that the larvae and adults of all three species possess unique UV markings, while pupae do not. While there are many possible adaptive hypotheses for these markings, we predict that size, mobility, and toxicity shape UV patterns in larvae and pupae, while sexual signaling and/or or mimicry are key drivers of UV in adults.