Morphologic representation of visual and antennal information in the ant brain

Ants in general are primarily olfactory animals, but many species also express visual behaviors. We analyze in 14 species, which range from purely olfactory to predominantly visually behaving ants, how the brains are equipped to control such behavior. We take the size and manifestation of the eyes as an indicator for the prevalence of vision in a given species, and we correlate it with the size of particular brain regions. Our morphometric data show that the size of the eyes generally correlates well with that of the optic lobes. The antennal lobes and the mushroom bodies have a surprisingly constant relative volume whereas, as expected, the relative size of the optic lobes varies strongly across species. Males of different species are more similar. Compared with workers, they all have large eyes, relatively larger optic lobes, smaller mushroom bodies, and similarly sized antennal lobes. The input regions of the mushroom bodies, the lip and the collar, generally correlate with the size of the optic and antennal lobe, respectively. Accordingly, the composition of the calyx reflects the importance of vision for the animal. We present data supporting the view that the mushroom bodies may participate in spatial orientation, landmark recognition, and visual information storage.