Modality-specific segregation of input to ant mushroom bodies.

The mushroom bodies are central brain neuropils involved in the control of complex behavior. In ants, the mushroom bodies are relatively large compared to those of honey bees, whereas the optic lobes of ants are considerably smaller. The general morphology of ant mushroom bodies is similar to that of honey bees. As in other Hymenoptera, the main input region of the mushroom bodies, the calyx, is subdivided into three compartments: the lip, the collar, and the basal ring. In many ant species this compartmentalization is not obvious and can only be visualized using neuronal tracers. The lip region receives antennal input and is large in all ant species. It appears to be composed of at least two different regions that have not yet been characterized in detail. The collar is large in other Hymenoptera, yet in ant workers it varies in size and is always much smaller than the lip region. The collar receives visual input and is relatively larger in males, which generally are more dependant on vision than are workers. The basal ring receives input from both the optic and antennal lobes. In one ant tribe, the Ponerini, the collar region appears to have changed its position, but based on afferent input it appears to be homologous to the hymenopteran collar. Generally, the composition of the mushroom body calyx correlates with the living conditions of ants, reflecting the great importance of olfaction and the lesser and more variable significance of vision for workers of the observed ant species.