Mimicry-related Variation in Wing Color of Viceroy Butterflies (<i>Limenitis archippus</i>): a Test of the Model-Switching Hypothesis (Lepidoptera: Nymphalidae).
Keywords:Basilarchia, clinal change, Danaus, geographic variation, hybrid zone, introgression, monarch, Nearctic
AbstractThe viceroy butterfly (Limenitis archippus) is well known as a superb mimic of its chemically defended model, the monarch (Danaus plexippus). However, viceroy populations in both the southeastern and southwestern United States appear to have switched phenotypically from mimicking the tawny-orange monarch to mimicking two subspecies of a darker mahogany-brown model, the queen (Danaus gilippus). This paper, combining field censuses and computer-assisted wing-color analyses, supports the hypothesis of "model-switching" by the viceroy. Specifically, we demonstrate that in the southeastern United States, a latitudinal cline in viceroy wing color (darkening from orange to mahogany southward from Georgia through Florida) is geographically correlated with a latitudinal shift in relative abundance of monarchs and queens, with the latter becoming more prevalent southward. We therefore view the cline in viceroy coloration as an adaptive adjustment to a latitudinal selective gradient associated with danaine relative abundance. This work supports the hypothesis that the viceroy's mimetic wing-color pattern is regionally "fine-tuned," phenotypically tracking different models in different areas.