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Abstract
Recent studies of the iconic fall migration of monarch butterflies have illuminated
the mechanisms behind their southward navigation while using a time-compensated sun
compass. Skylight cues, such as the sun itself and polarized light, are processed
through both eyes and are probably integrated in the brain's central complex, the
presumed site of the sun compass. Time compensation is provided by circadian clocks
that have a distinctive molecular mechanism and that reside in the antennae. Monarchs
might also use a magnetic compass because they possess two cryptochromes that have
the molecular capability for light-dependent magnetoreception. Multiple genomic approaches
are now being used with the aim of identifying navigation genes. Monarch butterflies
are thus emerging as an excellent model organism in which to study the molecular and
neural basis of long-distance migration.