Inheritance of olfactory preferences II. Olfactory receptor neuron responses from Heliothis subflexa x Heliothis...

Single-cell electrophysiological recordings were obtained from olfactory receptor neurons (ORNs) in sensilla trichodea on male antennae of hybrids formed mainly by crossing female Heliothis subflexa with male Heliothis virescens ('SV hybrids'). We recorded from the A-, B-, and C-type sensilla trichodea, with the latter two types housing ORNs exhibiting response profiles to different pheromone components that we had previously found to be characteristic for each species. For both the B- and the C-type SV hybrid sensilla, most of the ORNs exhibited a spike amplitude and ORN co-compartmentalization within sensilla that more strongly resembled the ORNs of parental H. subflexa rather than those of H. virescens. The overall mean dose-response profiles of the ORNs in hybrid C- and B-type sensilla were intermediate between those of the H. virescens and H. subflexa parental type ORNs. However, not all hybrid ORNs were intermediate in their tuning spectra, but rather ranged from those that closely resembled H. subflexa or H. virescens parental types to those that were intermediate, even on the same antenna. The most noteworthy shift in ORN responsiveness in hybrid males was an overall increase in sensitivity to Z9-14:Ald exhibited by Z9-16:Ald-responsive ORNs. Heightened cross-responsiveness to Z9-14:Ald by hybrid ORNs correlates well with observed behavioral cross-responsiveness of hybrids in which Z9-14:Ald could substitute for Z9-16:Ald in the pheromone blend, a behavior not observed in parental types. The hybrid ORN shifts involving greater sensitivity to Z9- 14:Ald also correlate well with studies of hybrid male antennal lobe interneurons that exhibited a shift toward greater cross-responsiveness to Z9-14:Ald and Z9- 16:Ald. We propose that the differences between parental H. virescens, H. subflexa, and SV hybrid male pheromone ORN responsiveness to Z9-16:Ald and Z9-14:Ald are most logically explained by an increased or decreased co-expression of two different odorant receptors for each of these compounds on the same ORN.