The origin of the insect odorant receptor (OR) gene family has been hypothesized to have coincided with the evolution of terrestriality in insects. Missbach et al. (2014) suggested that ORs instead evolved with an ancestral OR co-receptor (Orco) after the origin of terrestriality and the OR/Orco system is an adaptation to winged flight in insects. We investigated genomes of the Collembola, Diplura, Archaeognatha, Zygentoma, Odonata, and Ephemeroptera, and find ORs present in all insect genomes but absent from lineages predating the evolution of insects. Orco is absent only in the ancestrally wingless insect lineage Archaeognatha. Our new genome sequence of the zygentoman firebrat Thermobia domestica reveals a full OR/Orco system. We conclude that ORs evolved before winged flight, perhaps as an adaptation to terrestriality, representing a key evolutionary novelty in the ancestor of all insects, and hence a molecular synapomorphy for the Class Insecta.
Raw genome sequence reads are being submitted to the Sequence Read Archive at the NCBI. The Thermobia domestica genome assembly is available from Dryad under doi:10.5061/dryad.p2t8170. All other data generated and analysed during this study, including all Odorant Receptor protein sequences, are included in the manuscript and supporting file. A detailed version of Figure 2 is provided in the supporting file. All Odorant Receptor protein sequences and the amino acid alignment used for the phylogenetic analysis have also been uploaded to Dryad.
Thermobia domestica genome assembly v 1.0Available at Dryad Digital Repository under a CC0 Public Domain Dedication.
- Juan Luis Jurat-Fuentes
- Brian R Johnson
- Brian R Johnson
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Richard Benton, University of Lausanne, Switzerland
© 2018, Brand et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.