Caste- and sex-specific adaptations within the olfactory pathway in the brain of the ant Camponotus floridanus

Olfaction plays a key role in mediating ant behavior, and ant societies are characterized by caste- and sex-specific division of labor. We propose that caste- and sex-specific adaptations in the olfactory pathway promote differences in olfactory behavior. This study compares olfactory centers in the brain of large (major) workers, small (minor) workers, virgin queens, and males of the carpenter ant Camponotus floridanus. The number of glomeruli in the antennal lobe was similar in the female castes, although the glomerular volumes differed. Males had ∼45% fewer glomeruli compared to females (∼258 and ∼434) and one antennal sensory tract was absent. A dual output pathway to the mushroom bodies was present in males. In contrast to females, however, the number of glomeruli connected to the medial antennocerebral tract was substantially smaller than those associated with the lateral tract. All glomeruli in the male antennal lobe contained serotonergic processes, whereas in the female castes glomeruli in the large tract six cluster lacked serotonergic innervations. We conclude that differences in general glomerular organization are subtle among the female castes, but sex-specific differences in the number, connectivity and neuromodulatory innervation of glomeruli are substantial and likely to underlie differences in olfactory processing and learning.