Delayed Axonal Pruning in the Ant Brain: A Study of Developmental Trajectories

The coordination of neuronal maturation and behavioral development is a vital component of survival. The degradation of excessive axonal processes and neuronal networks is a ubiquitous developmental process. In Drosophila, a great portion of axonal pruning occurs during metamorphosis and transpires within hours after pupation. In contrast, we show, using EM-serial sectioning and 3D-reconstructions, that axonal pruning occurs after eclosion and over the course of 60 days in Cataglyphis albicans. Using the mushroom bodies of the brains of Cataglyphis, which have well-developed lip (olfactory integrator) and collar (visual integrator) regions, we show that axonal pruning is dependent upon the differences in the developmental trajectory of the lip and the collar brain regions and happens after eclosion. The elimination of the axonal boutons is most delayed in the collar region, where it is postponed until the ant has had extensive visual experience. We found that individual brain components within a single neuropil can develop at different rates that correlate with the behavioral ecology of these ants and suggest that glia may be mediating the axonal pruning. Our study provides evidence that adult ants may have relatively neotenous brains, and thus more flexibility, allowing them to neuronally adapt to the environment. This neoteny may, in part, explain the neural basis for age-dependent division of labor and the amazing behavioral flexibility exhibited by ants. (C) 2009 Wiley Periodicals, Inc. Develop Neurobiol 69: 350-364, 2009