Sensitivity to Cuticular Hydrocarbons Across the Odorant Receptor Family in the Indian Jumping Ant

Eusocial insects rely on the olfactory detection of cuticular hydrocarbons (CHCs) to mediate fundamental eusocial behaviors, such as nestmate recognition, and reproductive division of labor. In the ponerine ant Harpegnathos saltator, highly expanded odorant receptor (OR) families detect CHCs and mediate these eusocial behaviors at the molecular level. Previous studies have characterized H. saltator OR (HsOr) genes within the 9-exon and other large subfamilies, but it remains unclear how other HsOr subfamilies may contribute to CHC detection. Using heterologous expression in Drosophila melanogaster olfactory neurons, we characterized HsOr sensitivity more broadly across the gene family, outside the 9-exon subfamily, to a panel of hydrocarbons (HC). Twenty-three HsOrs across sixteen subfamilies were screened, and several were found to be broadly tuned and weakly responsive to the HCs tested, except for HsOr152 which showed narrow tuning to a single HC found on the H. saltator cuticle. Lastly, we compiled and analyzed the HC responses from the 70 HsOrs from this and previous studies. This analysis suggests a combinatorial coding model of CHC detection, where several receptors across different subfamilies can contribute to the detection and discrimination of different CHCs. Our characterization of HsOrs provides functional insights into the molecular mechanisms of chemical communication among eusocial insects.