Flocks of fluttering gold and orange winged monarch butterflies use their antennae and not their brains to migrate from eastern North America to Mexico every year, authors of a new study published in Science suggest.
During their fall migration, monarch butterflies use the position of the sun to calculate where they should be going and an internal clock to adjust their calculations as the sun's position changes during the day.
Migrating monarch butterflies on the move. [Image courtesy of Dennis Curtin]
"We've known that the insect antenna is a remarkable organ, responsible for sensing not only olfactory cues but wind direction and even sound vibration," said senior study author Steven M. Reppert, M.D., professor and chair of neurobiology at the University of Massachusetts Medical School. "But its role in precise orientation over the course of butterfly migration is an intriguing new discovery, one that may spark a new line of investigation into neural connections between the antennae and the sun compass, and navigation mechanisms in other insects."
Monarchs do have a circadian clock in their brains, and it's generally been assumed this clock is the primary timekeeper for the butterflies' navigation, but some observations from 50 years ago suggested the antennae played a more important role.
To investigate, Christine Merlin of the UMass Medical School and colleagues surgically removed some monarchs' antennae, tethered the butterflies and then flew them outdoors in a flight simulator. The butterflies' lost their normal southwestern orientation, even though the clock molecules in their brains were keeping normal time.
Further experiments, which involved covering other monarchs' antennae with either black or clear enamel paint, indicated that the circadian clock in the antennae provide the primary timing mechanism for sun-compass orientation. As a related Perspective notes, the exact nature of the connection between the clocks in the antennae and brain is still unclear. Merlin and coauthors say that other insects that navigate by the sun may use their antennae in the same way.