Visual experience affects both behavioral and neuronal aspects in the individual life history of the desert ant Cataglyphis fortis

The individual life history of the desert ant Cataglyphis fortis is characterized by a fast transition from interior tasks to mainly visually guided foraging. Previous studies revealed a remarkable structural synaptic plasticity in visual and olfactory input regions within the mushroom bodies of the ants' brain centers involved in learning and memory. Reorganization of synaptic complexes (microglomeruli) was shown to be triggered by sensory exposure rather than an internal program. Using video analyses at the natural nest site and activity recordings after artificial light treatments we investigated whether the ants get exposed to light before onset of foraging and whether this changes the ants' activity levels. We asked whether synaptic reorganization occurs in a similar time window by immunolabeling and quantification of pre- and postsynaptic compartments of visual and olfactory microglomeruli after periods of light-exposure. Ants reverted back to dark nest conditions were used to investigate whether synaptic reorganization is reversible. The behavior analyses revealed that late-interior ants (diggers) are exposed to light and perform exploration runs up to 2 days before they start foraging. This corresponds well with the result that artificial light treatment over more than 2-3 days significantly increased the ants' locomotor activities. At the neuronal level, visual exposure of more than 1 day was necessary to trigger reorganization of microglomeruli, and light-induced changes were only partly reversible in the dark. We conclude that visual preexposure is an important and flexible means to prepare the ants' visual pathway for orientation capabilities essential during foraging.