Sun compass neurons are tuned to migratory orientation in monarch butterflies

Every autumn, monarch butterflies migrate from North America to their
overwintering sites in Central Mexico. To maintain their southward
direction, these butterflies rely on celestial cues as orientation
references. The position of the sun combined with additional skylight cues
are integrated in the central complex, a region in the butterfly’s brain
that acts as an internal compass. However, the central complex does not
solely guide the butterflies on their migration but helps monarchs in
their non-migratory form manoeuvre on foraging trips through their
habitat. By comparing the activity of input neurons of the central complex
between migratory and non-migratory butterflies, we investigated how a
different lifestyle affects the coding of orientation information in the
brain. During recording, we presented the animals with different simulated
celestial cues and found that the encoding of the sun was narrower in
migratory compared to non-migratory butterflies. This feature might
reflect the need of the migratory monarchs to rely on a precise sun
compass to keep their direction during their journey. Taken together, our
study sheds light on the neural coding of celestial cues and provides
insights into how a compass is adapted in migratory animals to
successfully steer them to their destination.