UNCORRECTED PROOF Homology of olfactory receptor neuron response characteristics inferred from hybrids between Asian and European corn borer moths (Lepidoptera: Crambidae) Michael J. Domingue a, *, Callie J. Musto b , Charles E. Linn Jr. b , Wendell L. Roelofs b , Thomas C. Baker a a Department of Entomology, Chemical Ecology Lab, Penn State University, University Park, PA 16802, USA b Department of Entomology, Barton Lab, New York State Agricultural Experiment Station, 630 W. North St., Cornell University, Geneva, NY 14456, USA 1. Introduction Reproductive traits have often been given a primary role in assessing the evolutionary relationships among populations and species as they provide strong evidence of reproductive isolation, the cornerstone of the Biological Species Concept (Mayr, 1963; Dobzhansky, 1970). Despite the role reproductive isolation is presumed to have played in creating phylogenetic patterns, understanding the mechanisms by which reproductive traits evolve during speciation events continues to be a challenge (Marshall et al., 2008; Smadja and Butlin, 2009). Furthermore, there is ongoing debate as to the relative importance of sexual traits versus ecological forces in the speciation process (Rundle and Nosil, 2005; Sueur et al., 2007; Seehausen et al., 2008). Ostrinia moths represent a group that has been studied in the context of such multiple evolutionarily significant traits. There are conflicting phylogenies for the group constructed from analyses of morphological traits (Mutuura and Munroe, 1970) and mitochon- drial DNA sequences (Kim, 1997). Patterns inferred from such analyses are also difficult to fully reconcile with patterns of reproductive isolating traits across the genus such as pheromone biology, host plant preference differentiation, or the ability to hybridize (Ishikawa et al., 1999; Frolov et al., 2007). Two species within the trilobed uncus group, the European corn borer (ECB), Ostrinia nubilalis, and the Asian corn borer (ACB), Ostrinia furnacalis, have been most intensely studied with respect to the biochemical and physiological mechanisms of sex pheromone differentiation. Like most other Ostrinia species, ECB uses (Z)-11-tetradecenyl acetate (Z11-14:OAc) and (E)-11-tetradecenyl acetate (E11-14:OAc) in its pheromone blend (Ishikawa et al., 1999). There are two ECB strains. The E-strain [ECB(E)] has 99% E11-14:OAc and 1% Z11- 14:OAc in its blend, whereas the Z-strain [ECB(Z)] uses a reverse 97:3 ratio of Z11- and E11-14:OAc (Kochansky et al., 1975; Glover et al., 1987). The ACB pheromone stands out as unusual among all Ostrinia, consisting of variable blends of (E)-12-tetradecenyl acetate (E12- 14:OAc) and (Z)-12-tetradecenyl acetate (Z12-14:OAc) (Klun et al., 1980; Ando et al., 1980; Boo and Park, 1998; Linn et al., 2007). Thus, the lineage leading to the ACB clearly experienced a shift in the production from the D-11-tetradecenyl acetates to the D-12- tetradecenyl acetates, which appears to have involved the activation of a desaturase gene used by ACB that is present but not active in ECB pheromone production (Roelofs et al., 2002). Several aspects of the olfactory processing of sex pheromones in these species also have been investigated. Both species have two olfactory receptor neurons (ORNs) that respond to their own pheromone components. The ORNs of ACB and ECB(E) have been shown to regularly respond to the opposing species’ pheromone components (Takanashi et al., 2006; Domingue et al., 2007a,b, Journal of Insect Physiology xxx (2009) xxx–xxx 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 ARTICLE INFO Article history: Received 24 July 2009 Received in revised form 14 September 2009 Accepted 15 September 2009 Keywords: Flight tunnels Olfaction Ostrinia Single-cell electrophysiology Sex pheromones ABSTRACT First generation hybrid males from crosses between the Asian corn borer (ACB), Ostrinia furnacalis, and the ‘‘univoltine Z-strain’’ European corn borer (ECB), Ostrinia nubilalis, were examined with respect to behavioral and physiological responses to ACB and ECB pheromones. The hybrid males often flew to the pheromone of ECB Z-strain, but very rarely to the ACB pheromone. We mapped the tuning profiles of each ORN of the F 1 hybrids with respect to the relevant pheromone components and a common behavioral antagonist by employing differential cross-adaptation and varying doses of the ligands. In the trichoid sensilla of F 1 hybrid males, the three co-compartmentalized ORNs produced spikes that were very difficult to distinguish by size, unlike the parental populations. Comparing the responses to ACB and ECB components at different doses reveals overlapping profiles similar to males of both parental types, but more responsiveness to the ECB pheromone components. We were unable to detect any differences in the ORN tuning profiles when comparing males with different behavioral phenotypes. While the two ECB pheromone races have similar ORN tuning properties that are different from those in ACB, the spike- amplitude patterns of ECB E-strain and ACB have greater homology when compared to ECB Z-strain. ß 2009 Published by Elsevier Ltd. * Corresponding Q1 author. Tel.: +1 814 863 1768; fax: +1 814 863 4439. E-mail address: mjdomingue@gmail.com (M.J. Domingue). G Model IP 2340 1–8 Please cite this article in press as: Domingue, M.J., et al., Homology of olfactory receptor neuron response characteristics inferred from hybrids between Asian and European corn borer moths (Lepidoptera: Crambidae). J. Insect Physiol. (2009), doi:10.1016/ j.jinsphys.2009.09.005 Contents lists available at ScienceDirect Journal of Insect Physiology journal homepage: www.elsevier.com/locate/jinsphys 0022-1910/$ – see front matter ß 2009 Published by Elsevier Ltd. doi:10.1016/j.jinsphys.2009.09.005