© Mike Quinn, Texas Parks & Wildlife
Researchers have identified a molecular pathway possibly linking the Monarch butterfly's central circadian clock to photoreceptors involved in its "sun compass," which is used to orient its flight during migration.1 Steven Reppert and colleagues at the University of Massachusetts Medical School performed three experiments focusing on polarized light inputs.
They first characterized a specialized dorsal rim area of the Monarch eye that is monochromatic for ultraviolet (UV) opsins. Next they performed behavioral studies with a polarized light filter and observed that in the absence of direct sunlight, the butterflies still adapted their orientation to that of the moving filter. "But when UV inputs were blocked, the butterflies started flying in circles," Reppert says. Finally, the team identified the presence of the