Caste-specific expression patterns of olfactory related genes in the leaf-cutting ant, Atta vollenweideri

Leaf-cutting ants are evolutionary derived social insects with elaborated division of labor and tremendous colony sizes with millions of workers. Their social organization is mainly based on olfactory communication with different pheromones and is promoted by a pronounced size-polymorphism of workers that perform different tasks within the colony. The size polymorphism and associated behaviors are correlated to distinct antennal lobe phenotypes. Two worker phenotypes differ in number of olfactory glomeruli in the AL and the presence or absence of an extremely large glomerulus (macroglomerulus) involved in trail-pheromone reception. The males' AL contains three macroglomeruli which are presumably involved in detection of sex-pheromone components. We investigated the antennal transcripts of all major castes (males,queens and workers) and two worker subcastes (large and tiny workers). Furthermore, we analyzed differential gene expression using custom microarrays. A large number of genes involved in metabolism, immune defense and reproduction are differentially expressed in the three different castes, and some genes even between the two worker subcastes. In order to identify putative odorant receptor genes involved in pheromone detection, we identified differentially expressed olfactory receptor (OR) coding genes. In total, we found 185 OR coding genes. Among them one differs in relative expression between the two worker subcastes by a factor of >3. Thus, we now have a very promising candidate gene for trail-pheromone reception. With the same strategy, we identified three candidates for sex-pheromone receptor genes in males. In addition we identified genes from all other olfactory related gene families (17 chemosensory protein coding genes, 13 odorant binding protein coding genes, 2 sensory-neuron membrane protein coding genes, 9 ionotropic receptor coding genes, 2 gustatory receptor coding genes) and found ant-specific expansions, e.g. in the chemosensory protein gene family.