Phenotypic Plasticity in Number of Glomeruli and Sensory Innervation of the Antennal Lobe in Leaf-Cutting Ant Workers (A. vollenweideri)

In the leaft-cutting ant Atta vollenweideri, the worker caste exhibits a pronounced size-polymorphism, and divisions of lobor is dependent on worker size (alloethism). Behavior is largely guided by olfaction, and the olfactory system is highly developed. In a recent study, two different phenotypes of the antennal lobe of Atta vollenweideri workers were found: MG- and RG-phenotype (with/without a macroglomerulus). Here we ask whether the glomerular numbers are related to worker size. We found that the antennal lobes of small workers contain similar to 390 glomeruli (low-number; LN-phenotype), and in large workers we found a substantially higher number of similar to 440 glomeruli (high-number; HN-phenotype). All LN-phenotype workers and some small HN-phenotype workers do not possess and MG (LN-RG-phenotype and HN-RG-phenotype), and the remaining majority of HN-phenotype workers do possess an MG (HN-MG-phenotype). Using mass-staining of antennal olfactory receptor neurons we found that the sensory tracts divide the antennal lobe into six clusters of glomeruli (T1-T6.). In LN-phenotype workers. similar to 50 glomeruli are missing in the T4-cluster. Selective staining of single sensilla and their associated receptor neurons revealed that T4-glomeruli are innervated by receptor neurons from the main type of olfactory sensilla, the Sensilla trichodea curvata. The other type of olfactory sensilla (Sensilla basiconica) exclusively innervates T6-glomeruli. Quantitative analyses of differently sized workers revealed that the volume of T6 glomeruli scales with the power of 234 to file number of Sensilla basiconica. The results suggest that developmental plasticity leading to antennal-lobe phenotypes promotes differences in olfactory-guided behavior and may underlie task specialization within ant colonies. (C) 2009 Wiley Periodicals Inc, Develop Neurobiol 70 222-234 2010