Advancement of DNA sequencing technology allows the routine use of genome sequences in the various fields of microbiology. The information held in genome sequences proved to provide objective and reliable means in the taxonomy of prokaryotes. Here, we describe the minimal standards for the quality of genome sequences and how they can be applied for taxonomic purposes.

Until around 1990, most multigene families were thought to be subject to concerted evolution, in which all member genes of a family evolve as a unit in concert. However, phylogenetic analysis of MHC and other immune system genes showed a quite different evolutionary pattern, and a new model called birth-and-death evolution was proposed. In this model, new genes are created by gene duplication and some duplicate genes stay in the genome for a long time, whereas others are inactivated or deleted from the genome. Later investigations have shown that most non-rRNA genes including highly conserved histone or ubiquitin genes are subject to this type of evolution. However, the controversy over the two models is still continuing because the distinction between the two models becomes difficult when sequence differences are small. Unlike concerted evolution, the model of birth-and-death evolution can give some insights into the origins of new genetic systems or new phenotypic characters.

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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.M ate finding in most moth species involves the use of long-distance sex pheromones, which are emitted by females (Arn, H. The Pherolist, www.nysaes.cornell.edu͞fst͞ faculty͞acree͞pheronet͞index.html). These chemical communication systems are highly canalized, with strong selection pressure against novel blends and response preferences. Thus, it is unlikely that shifts to pheromones of diverse structures occur through adaptive changes in small steps (1); rather, structural changes in the signaling system may require a major shift. In moth species studied to date, pheromone production (female) and response (male) are not genetically linked (2), but a model for the evolution of new pheromones based on asymmetric tracking (3, 4) predicts that a large mutational effect in female pheromone production can subsequently be tracked by male response. This model can explain how the Asian corn borer (ACB), Ostrinia furnacalis, evolved to use (Z)-and (E)-12-tetradecenyl acetate (Z͞E12-14:OAc) pheromone components (5), whereas all other analyzed Ostrinia species use Z͞E11-14:OAcs (6) (Fig. 1). What has been difficult to understand is how a major shift in a pheromone blend like this could occur.Moth sex pheromones are produced in specialized female abdominal glands, generally via unsaturated fatty-acid precursors produced by desaturases that exhibit a range of stereo-and regiospecificities (7). In an attempt to understand how these diverse desaturases evolved, we have characterized desaturase genes from various moth species. These include genes for desaturases producing Z9-(8-12), Z10-(10), Z11-(11-13), and E11-isomers (9, 12) of C14 and C16 unsaturated acids. In the course of these studies, we discovered that, in female European corn borer (ECB), O. nubilalis, the pheromone gland contains three different transcripts (cDNA) of desaturase genes, only one of which appears to result in a functional protein product. The functional transcript in ECB is for a ⌬11-desaturase used for production of its pheromone components. One of the nonfunctional transcripts is for a ⌬14-desaturase, which is use...