Evolution of moth sex pheromones via ancestral genes

Abstract

Mate finding in most moth species involves long-distance signaling via female-emitted sex pheromones. There is a great diversity of pheromone structures used throughout the Lepidoptera, even among closely related species. The conundrum is how signal divergence has occurred. With strong normalizing selection pressure on blend composition and response preferences, it is improbable that shifts to pheromones of diverse structures occur through adaptive changes in small steps. Here, we present data supporting the hypothesis that a major shift in the pheromone of an Ostrinia species occurred by activation of a nonfunctional desaturase gene transcript present in the pheromone gland. We also demonstrate the existence of rare males that respond to the new pheromone blend. Their presence would allow for asymmetric tracking of male response to the new blend and, thus, evolution of an Ostrinia species with structurally different sex pheromone components.

Figure 1

Pheromone biosynthetic pathways for ACB and ECB from hexadecanoic acid (16:Acid) and proceeding through different routes to the 14-carbon acetate pheromone components.

Figure 2

Comparison of deduced amino acid sequences of Onu-Z9¹⁶, Onu-Z9¹⁸, Onu-Z/E11, Onu-Z/E14, and Ofu-Z/E14 to the Z11-desaturase from the cabbage looper moth (T. ni-Z11) and the redbanded leafroller moth (RBLR-Z/E11). The consensus residues are shaded with solid gray. Ofu-Z/E14 has an AA different from Onu-Z/E14 at amino acid 9 denoted with an asterisk.

Figure 3

Z/Ell desaturase expression in pYES2 system-GC/MS analyses of methyl esters (DMDS adducts) with the ion 245 m/z displayed. (A) Control INVSc1 cells with 0.5 mM myristic acid methyl ester (MAME) added. Z11-16 and Z11-18:Acids produced by chain elongation of Z9-14 and Z9-16:Acids. (B) INVSc1 cells transformed with pYES2-ECBG-PG2-ORF complemented with 0.5 mM MAME. New products are Z11- and E11-14:Acid along with additional Z11-16:Acid (amount above dotted line).

Figure 4

Z/E14-desaturase expression in a Baculovirus System. GC/MS analyses of methyl esters (DMDS adducts) with ion 217 and 287 displayed. (A) Control Sf21 cells that produce Z9-16, Z9-17, and Z9-18:Acids. (B) Sf21 insect cells infected with Bacmid-pFastBac1-ECBG-PG3-ORF and shown to produce additional Z14-16 and E14-16:Acids.

Figure 5

Phylogeny of insect desaturases. Numbers along branches represent bootstrap (in front of slash) and quartet-puzzling (behind slash) values greater than 50%. Because the ML and NJ trees were highly similar, only the NJ tree is shown here.