Genetics of Sex Pheromones: Mapping Desaturase Genes in Heliothis Species.

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Title: Genetics of Sex Pheromones: Mapping Desaturase Genes in Heliothis Species.
Author: Ward, Michael Duane Jr.
Advisors: Christina Grozinger, Committee Member
Coby Schal, Committee Member
Fred Gould, Committee Chair
Abstract: Many moths use a pheromone based sexual communication system where the female emits a precise mixture of volatile chemicals and only males who are physiologically tuned to that specific blend, respond. In order for the female to maintain her fitness, she must only attract conspecific males. If there were a mutation that caused a change in her pheromone blend it might be costly to the female’s fitness. In the species Trichoplusia ni. and Ostrinia nubilalis, normal males have been shown to discriminate between normal and mutant pheromone blends. Therefore a species pheromone blend is likely maintained by strong stabilizing selection. However, it seems contradictory given the action of stabilizing selection that thousands of unique pheromone blends have evolved in Lepidoptera. One useful approach to understanding how this diversity may have arisen is to examine the steps in the biosynthetic pathways of pheromone production and to look for ways that changes in the pheromone blend may have had limited fitness cost. Two closely related species of moth in the Noctuidae family, Heliothis virescens (Hv) and Heliothis subflexa (Hs), have been used for studying the genetics of pheromone blend because, while they remain reproductively isolated in the wild, they can be crossed to produce hybrids with altered pheromone blends. Both species produce a multicomponent pheromone blend that is comprised of a precise ratio of 7 compounds including: tetradecanal (14:Ald), (Z)-9-tetradecenal (Z9-14:Ald), hexadecanal (16:Ald), (Z)- 11-hexadecenal (Z11-16:Ald), (Z)-11-hexadecen-1-ol (Z11–16:OH), (Z)-9-hexadecenal (Z9-16:Ald), and (Z)-7-hexadecenal (Z7-16:Ald). With Hs and Hv producing different amounts of the individual components. Additionally, Hs produces 3 acetates that are not produced by Hv; (Z)-11, (Z)-9 and (Z)-7-hexadecanyl acetate. Our specific interest has been in the genes and enzymes that cause differences between the pheromone blends of these two species and the fact that the ratio of 16:Ald to Z9-16:Ald in Hv is greater than it is in Hs. Two pathways have been suggested that could produce this result, one where a Ά9 desaturase converts 16:CoA to Z9-16:Ald and another where a Ά11 desaturase produces Z11-18:Ald by desaturation of 18:CoA, which is then chain shortened to Z9-16:Ald. Previous experiments, using stable isotope labeled precursors, have shown no incorporation of 16:CoA into Z9-16:Ald in Hv suggesting that it is instead produced from 18:CoA. Here we take a slightly different approach where we look specifically for enzymes related to changes in pheromone components. Previous experiments in our lab have revealed 11 quantitative trait loci (QTL) that coded for differences between Hs and Hv in the proportions of 10 pheromone components. In this experiment, we combined previously obtained QTL information with heterologous probes designed using Helicoverpa zea and Helicoverpa assulta Ά9 and Ά11 desaturase genes respectively. We first probe for the desaturase genes in each species and then determine if these genes are found on any of the chromosomes that contain QTLs for changes in the ratio of 16:Ald to Z9-16:Ald. Based on our results, we conclude that the Ά11 desaturase appears to be the only desaturase involved in the difference in the level of Z9-16:Ald between H. virescens and H. subflexa.
Date: 2009-11-30
Degree: MS
Discipline: Entomology

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