Identification of Odorant Binding Proteins and Chemosensory Proteins in Antennal Transcriptomes of the Jumping Bristletail Lepismachilis y-signata and the Firebrat Thermobia domestica: Evidence for an Independent OBP-OR Origin.

Chemosensory protein (CSP) and gustatory receptor genes have been identified in all major arthropod groups. However, odorant binding proteins (OBP) and olfactory receptor genes are insect specific, suggesting that both gene families originated after the Hexapoda-Crustacea split (~470 million years ago). The seemingly parallel diversification of OBP and olfactory receptors has been suggested as coevolution between these genes after insect terrestrialization. To test this hypothesis we used the recently published transcriptomes of the jumping bristletail Lepismachilis y-signata and the firebrat Thermobia domestica to search for putative OBP and CSP sequences and analyzed their relationship to binding proteins of other insects and crustaceans. Our results suggest an evolution and expansion of OBPs as an adaptation to a terrestrial insect lifestyle, independently from the emergence of olfactory receptors.