title: Diversification of the ant odorant receptor gene family and positive selection on candidate cuticular hydrocarbon receptors.
abstract: BACKGROUND
  Chemical communication plays important roles in the social behavior of ants making them one of the most successful groups of animals on earth. However, the molecular evolutionary process responsible for their chemosensory adaptation is still elusive. Recent advances in genomic studies have led to the identification of large odorant receptor (Or) gene repertoires from ant genomes providing fruitful materials for molecular evolution analysis. The aim of this study was to test the hypothesis that diversification of this gene family is involved in olfactory adaptation of each species.
  
  
  RESULTS
  We annotated the Or genes from the genome sequences of two leaf-cutter ants, Acromyrmex echinatior and Atta cephalotes (385 and 376 putative functional genes, respectively). These were used, together with Or genes from Camponotus floridanus, Harpegnathos saltator, Pogonomyrmex barbatus, Linepithema humile, Cerapachys biroi, Solenopsis invicta and Apis mellifera, in molecular evolution analysis. Like the Or family in other insects, ant Or genes evolve by the birth-and-death model of gene family evolution. Large gene family expansions involving tandem gene duplications, and gene gains outnumbering losses, are observed. Codon analysis of genes in lineage-specific expansion clades revealed signatures of positive selection on the candidate cuticular hydrocarbon receptor genes (9-exon subfamily) of Cerapachys biroi, Camponotus floridanus, Acromyrmex echinatior and Atta cephalotes. Positively selected amino acid positions are primarily in transmembrane domains 3 and 6, which are hypothesized to contribute to the odor-binding pocket, presumably mediating changing ligand specificity.
  
  
  CONCLUSIONS
  This study provides support for the hypothesis that some ant lineage-specific Or genes have evolved under positive selection. Newly duplicated genes particularly in the candidate cuticular hydrocarbon receptor clade that have evolved under positive selection may contribute to the highly sophisticated lineage-specific chemical communication in each ant species.
authors: Molecular Ecology and Evolution Research Unit, Prince of Songkla University, Songkla, 90112, Thailand. patamarerk.e@psu.ac.th.|Department of Biology, Faculty of Science, Prince of Songkla University, Songkla, 90112, Thailand. patamarerk.e@psu.ac.th.
authors: Patamarerk
authors: P
authors: Engsontia
authors: Department of Molecular Biotechnology and Bioinformatics, Faculty of Science, The Center for Genomics and Bioinformatics Research, Prince of Songkla University, Songkla, 90112, Thailand. unitsa.s@psu.ac.th.
authors: Unitsa
authors: U
authors: Sangket
authors: Department of Entomology, University of Illinois at Urbana-Champaign, 505 South Goodwin Avenue, Urbana, IL, 61801, USA. hughrobe@life.illinois.edu.
authors: Hugh M
authors: HM
authors: Robertson
authors: Department of Biology, Faculty of Science, Prince of Songkla University, Songkla, 90112, Thailand. chutamas.p@psu.ac.th.
authors: Chutamas
authors: C
authors: Satasook
mesh_terms: D000818:Animals; D001000:Ants / Q000235:genetics*; D019143:Evolution, Molecular; D005091:Exons; D006838:Hydrocarbons / Q000378:metabolism*; D010802:Phylogeny; D018035:Receptors, Odorant / Q000235:genetics*; D012641:Selection, Genetic
chemical_list: D006838:Hydrocarbons; D018035:Receptors, Odorant