ORigin

• Applicant: Dr. Michael Thoma
• Subject Area: Sensory and Behavioural Biology ; Animal Physiology and Biochemistry ; Evolution, Anthropology
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 319280168

Insects sense their chemical environment using members of three families of chemoreceptors, ionotropic receptors (IRs), gustatory receptors (GRs) and odorant receptors (ORs). Whereas IRs are of protostome origin and distant relatives of GRs have been described in the Placozoan Trichoplax adherens and in plants, ORs represent an insect-specific expansion with up to 400 OR genes present in some species. Because - in Drosophila melanogaster, where they were first described - IRs mainly detect water-soluble compounds such as acids and amines and most GRs are considered to be contact chemoreceptors, ORs have been suggested to be an adaptation to a terrestrial lifestyle by facilitating the detection of hydrophobic volatiles. However, this hypothesis has been recently challenged by the observation that ORs are absent in Archaeognatha, which suggests that ORs represent an adaptation to flight. The functional OR signaling complex in pterygote insects is a heteromultimer of tuning ORs, which convey ligand specificity, and a highly conserved co-receptor termed ORCo, which does not display any known ligand-binding function but is always co-expressed with all tuning receptors. Although tuning ORs have not been found in the firebrat Thermobia domestica, three ORCo paralogues were detected in antennal transcriptomes of this species. Hence, the common ancestor of zygentomes and winged insects probably had at least one copy of what was to become the ubiquitous co-receptor without having any tuning receptors. To resolve this paradox, we will obtain antennal transcriptomes of representatives of all four zygentome families to reconstruct the evolutionary scenario leading to the triplication of the ORCo ancestor in T. domestica. Because ORs including ORCo are considered to be a subfamily of GRs, it is likely that the ancestral ORCo also served a ligand-binding chemosensory function, which was lost in pterygote insects but could be conserved in zygentomes. To test this hypothesis, we will express identified zygentome ORCo paralogues in cell culture and test for a chemosensory function by exposing them to a large panel of odorants likely to be present in the zygentomes´ natural habitat. By combining transcriptomic profiling and functional examination, we hope to understand the first steps in the evolution of one of the largest multigene families in insects and one of the key innovations enabling insects to use chemical information for navigation whilst in flight.

• DFG Programme: Research Fellowships
• International Connection: New Zealand
• Host: Professor Richard David Newcomb, Ph.D.