Genome-Wide Analysis of the Odorant Receptor Gene Family in , , and (Hymenoptera: Formicidae).

Olfactory systems in eusocial insects play a vital role in the discrimination of various chemical cues. Odorant receptors (ORs) are critical for odorant detection, and this family has undergone extensive expansion in ants. In this study, we re-annotated the genes from the most destructive invasive ant species and 2 other Formicidae species, and , with the aim of systematically comparing and analyzing the evolution and the functions of the in ant species, identifying 356, 298, and 306 potential functional , respectively. The evolutionary analysis of these showed that ants had undergone chromosomal rearrangements and that tandem duplication may be the main contributor to the expansion of the gene family in . Our further analysis revealed that 9-exon had biased chromosome localization patterns in all three ant species and that a 9-exon cluster () in was under strong positive selection (Ka/Ks = 1.32). Moreover, we identified 5 genes, namely , , , , and , with high sequence similarity (>70%) to the orthologs in and . An RT-PCR analysis was used to verify the antennal expression levels of these , which showed caste-specific expression. The subsequent analysis of the antennal expression profiles of the of the workers from the polygyne and monogyne social forms indicated that and were expressed at much higher levels in the monogyne workers than in the polygyne workers and that was expressed at higher levels in polygyne workers. Our study has contributed to the identification and analysis of the gene family in ants and expanded the understanding of the evolution and functions of the ORs in Formicidae species.