Progress 10/01/08 to 09/30/09
Outputs
OUTPUTS: This project focuses on understanding patterns of divergence and gene exchange between two pheromone strains (E and Z) of the European corn borer (ECB). Over the life of this project we have done the following: (1) Characterized patterns of variation at genomic regions surrounding the gene Tpi, the only gene that revealed fixed differences between E and Z strains. (2) Screened a BAC library with Tpi and identified an array of 11 overlapping BAC clones that await Illumina sequencing. This will allow us to gain insights into patterns of variation across a 500 mb region surrounding Tpi. (3) Typed pheromone trapped males using Tpi to ask whether males caught in E traps are indeed exclusively E, and vice versa for Z traps. The answer is that pheromone traps provide reliable indicators of the strain of trapped males. (4) Typed moths of both E and Z strain from Delaware, demonstrating that moths show less differentiation between strains at these localities (relative to upstate NY) suggesting the possibility of greater gene exchange. (5) Produced gene genealogies for a D11-desaturase and for a set of reductases, searching for genes/proteins that reveal the two strains to be exclusive groups. Part of the focus was to identify the fatty acid reductase (FAR) that is responsible (through allelic differences) for the difference in pheromone production between E and Z strains. This enzyme was ultimately identified by a group in Japan and confirmed by a lab in Sweden. We have now followed up to show that this reductase does show many fixed differences between the strains. The D11-desaturase genealogy does not distinguish E and Z ECB, but contains two very divergent clades. (6) Carried out intra-strain crosses and backcrosses to produce within strain mapping families. (7) Developed additional Z chromosome linked markers. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Our more recent data confirm that the genome of ECB (like that of many other organisms) is a mosaic of evolutionary histories, due in part to different selective pressures (leading to local selective sweeps) and to different levels of gene exchange (less gene exchange in the vicinity. So the extent of gene flow between strains varies across the genome and also varies among different geographic localities. The clear pattern of differentiation for Tpi (and surrounding region) may be due to a fixed inversion difference between the strains, a hypothesis that is being tested by our new mapping families. The observation that gene flow between strains varies across the genome has important consequences for managing natural populations, because the genome regions in which a gene resides will be an important predictor of whether mutations appearing in one strain will easily move into the other.
Publications
- Geiler, K.A. and Harrison, R.G. 2009. A Delta 11 desaturase gene genealogy reveals two divergent allelic classes within the European corn borer (Ostrinia nubilalis) BMC (Pending).
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Progress 10/01/07 to 09/30/08
Outputs
OUTPUTS: In the context of a genetic linkage map for European Corn Borer (ECB), we are examining gene genealogies in order to characterize regions in the ECB genome for which one or both of the two-pheromone strains (Z and E) show fixed differences (are exclusive groups). We have continued to examine genealogies in the region of the gene encoding TPI, the only region in the corn borer genome that appears to distinguish the two-pheromone strains. Using a BAC library, we have shown that the size of the region is greater than 300 kb. We have also continued to refine our genetic mapping and characterization of fatty acid reductases and desaturases, candidate barrier genes (involved in specificity of pheromone production). We are also: (1) examining the genotypes of male ECB which have been pheromone-trapped using either the E or Z pheromone blend; (2) expanding our sample of field-collected females for which we have data on genotypes of Z-linked genes. PARTICIPANTS: Steve Bogdanowicz oversees the technical aspects of this project and helps to mentor undergraduates who have contributed substantially to sequencing of gene regions in the vicinity of TPI. Ben Hamilton is a graduate student who is surveying pheromone trapped males and field collected females. In this project he has mentored an undergraduate, Larry Du. Ben has also set up crosses for further mapping work. TARGET AUDIENCES: Entomologists, evolutionary biologists, population geneticists. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
European Corn Borers are introduced pests that have had significant economic impacts in the United States (they are among the most important pests of maize). The nature of pheromone races of ECB influences patterns of gene exchange and how these populations evolve. These are issues that will be of increasing importance as resistant inbred and transgenic plants are used in the field. Our approach has shown that the genome is a mosaic of different histories, potentially reflecting different levels of gene exchange across the genome, with gene exchange occurring freely for some parts of the genome and being limited or prevented for other genomic regions. The work on FARs represents an attempt to identify a candidate barrier gene involved in the specificity of pheromone production.
Publications
- No publications reported this period
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Progress 10/01/06 to 09/30/07
Outputs
OUTPUTS: In the context of a genetic linkage map for European Corn Borer (ECB), we are examining gene genealogies in order to characterize regions in the ECB genome for which one or both of the two pheromone strains (Z and E) show fixed differences (are exclusive groups or are monophyletic). We have continued to examine genealogies in the region of the gene encoding TPI, the only region in the corn borer genome that appears to distinguish the two-pheromone strains. In spite of difficulties with the BAC library, we have shown that the size of the region is >200 kb. We have also continued to refine our genetic mapping and characterization of fatty acid reductases (FARS), which are candidate barrier genes (involved in specificity of pheromone production). We are also examining the Tpi genotype of male ECB, which have been pheromone-trapped using either the E or Z pheromone blend. Finally, we have also set up crosses within the Z strain to determine whether the linkage map generated
within strains is the same as that from crosses of Z x E.
PARTICIPANTS: Steve Bogdanowicz oversees the technical aspects of this project and helps to mentor Lee Stein, an undergraduate who has contributed substantially to sequencing of gene regions in the vicinity of Tpi. Ben Hamilton is a graduate student who is surveying pheromone-trapped males and also setting up crosses for further mapping work.
TARGET AUDIENCES: Entomologists, evolutionary biologists, and population geneticists.
Impacts
European Corn Borers are introduced pests that have had significant economic impacts in the United States (they are among the most important pests of maize). The nature of pheromone races of ECB influences patterns of gene exchange and how these populations evolve. These are issues that will be of increasing importance as resistant inbred and transgenic plants are used in the field. Our approach has shown that the genome is a mosaic of different histories, potentially reflecting different levels of gene exchange across the genome, with gene exchange occurring freely for some parts of the genome and being limited or prevented for other genomic regions. The work on FARs represents an attempt to identify a candidate barrier gene involved in the specificity of pheromone production.
Publications
- Malausa, T., Leniaud, L., Martin, J. F., Audiot, P., Bourguet, D., Ponsard, S., Lee, S. F., Harrison, R. G., and Dopman, E. 2007. Molecular Differentiation at Nuclear Loci in French Host Races of the European Corn Borer (Ostrinia nubilalis). Genetics 176(4):2343-2355.
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Progress 01/01/06 to 12/31/06
Outputs
In the context of a genetic linkage map for European corn borer (ECB), we are examining gene genealogies in order to characterize regions in the ECB genome for which one or both of the two-pheromone strains (Z and E) are exclusive groups (i.e., that they are monophyletic). To date, we have obtained data for six gene regions, only one of which (the sex-lined gene Tpi) shows the two-pheromone strains to be exclusive groups. We have used a BAC library for ECB to identify the larger gene region in which Tpi is embedded and to examine gene genealogies at known distances from Tpi. We have characterized four gene regions on either side of Tpi, extending as far as 100kb. Using this approach, we have shown that the pattern of exclusivity persists as one moves away from the Tpi coding region in both directions. We have cloned and sequenced a group of paralogous fatty acid reductases (FARs), an enzyme in the pheromone biosynthetic pathway that is responsible for the specificity
of E and Z strain pheromone production (and therefore a candidate Barrier or speciation gene). Using degenerate primers based on Bombyx and Drosophila sequences, we have amplified eight distinct FARs, all of which are expressed in ECB pheromone gland. From most of these FARs we now have full coding region sequences. We have mapped seven of these genes, none of which map to the chromosome on which the Pher (pheromone production) gene is located. Interestingly, however, the gene for FAR D is expressed in Z strain females but not in E stain females. Also interesting is that the gene encoding FAR G maps to a position that is indistinguishable from the position of Tpi.
Impacts
European Corn Borers are introduced pests that have had significant economic impacts in the United States (they are among the most important pests of maize). The status of pheromone and voltinism races of ECB influences patterns of gene exchange and how these populations evolve. These are issues that will be of increasing importance as resistant inbred and transgenic plants are used in the field. Our approach provides an opportunity to examine the possibility that gene exchange occurs freely for some parts of the genome and is limited or prevented for other genomic regions. This may have important consequences if (when) Bt resistance appears in natural populations. For example, if a gene locus that affects insecticide resistance resides in a part of the genome for which gene flow is limited, then expectations about the spread of resistance will be very different than for the case in which the locus is in a genomic region that experiences free gene exchange.
Publications
- Dalecky, A., Bogdanowicz, S.M., Dopman, E.B., Bourguet, D. and Harrison, R.G. 2006. Two multiplex sets of eight and five microsatellite markers for the European corn borer, Ostrinia nubilalis Hubner (Lepidoptera: Crambidae). Molecular Ecology Notes 6(3):945-947.
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Progress 01/01/05 to 12/31/05
Outputs
In the context of a genetic linkage map for European Corn Borer (ECB), we are examining gene genealogies in order to characterize regions in the ECB genome for which one or both of the two pheromone strains (Z and E) are exclusive groups (i.e., that they are monophyletic). To date, we have obtained data for six gene regions, only one of which (the sex-lined gene Tpi) shows the two-pheromone strains to be exclusive groups. We are using a BAC library for ECB to identify the larger gene region in which Tpi is embedded and to examine gene genealogies at known distances from Tpi. Initial screening of the BAC library identified a single clone in which Tpi resides. Using this approach, we have shown that the pattern of exclusivity persists as one moves away from the Tpi coding region in both directions. Using 12 micro satellite loci, we have shown that there is little evidence of differentiation between sympatric E and Z ECB at Geneva, NY (a focal population for our study).
However, at several loci, the presence of private alleles in one or both strains suggests that gene flow between strains may be limited. We have also embarked on a project to clone and sequence a candidate speciation gene that encodes a reductase, an enzyme in the pheromone biosynthetic pathway that is responsible for the specificity of E and Z strain pheromone production. Using degenerate primers based on Bombyx and Drosophila sequences, we have amplified fragments from ECB pheromone gland cDNA, which from sequence analysis appear to be reductases. Four different reductases have been identified and we are currently characterizing these genes and mapping their location on the linkage map.
Impacts
European Corn Borers are introduced pests that have had significant economic impacts in the United States (they are among the most important pests of maize). The status of pheromone and voltinism races of ECB influences patterns of gene exchange and how these populations evolve. These are issues that will be of increasing importance as resistant inbred and transgenic plants are used in the field. Our approach provides an opportunity to examine the possibility that gene exchange occurs freely for some parts of the genome and is limited or prevented for other genomic regions. This may have important consequences if (when) Bt resistance appears in natural populations. For example, if a gene locus that affects insecticide resistance resides in a part of the genome for which gene flow is limited, then expectations about the spread of resistance will be very different than for the case in which the locus is in a genomic region that experiences free gene exchange.
Publications
- Dopman, E.B., Perez, L., Bogdanowicz, S.M. and Harrison, R.G. 2005. Consequences of reproductive barriers for genealogical discordance in the European corn borer. Proceedings of the National Academy of Science 102(41):14706-14711.
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Progress 01/01/04 to 12/31/04
Outputs
This is a new project (start date Oct. 1, 2004). An initial focus is on studying the evolutionary genomics of European corn borer (ECB), on developing new markers for genealogical analysis, and on expanding the panel of moths that we sample for the five genes that we have already sequenced. The goal is to understand the history of divergence of the two ECB pheromone strains (E and Z) and to determine current patterns of gene exchange between the two strains. This fall we collected additional material from a population in Geneva, NY that we know harbors both pheromone strains of the ECB. In October, we obtained a large sample of moths from a mixed population in Northern Italy and these will arrive once an import permit is issued. The Geneva moths have already been sequenced for 5 genes - and we are currently working to develop primers for several other gene loci. We also carried out three generations of inbreeding to produce an inbred line, pupae from which were
shipped to the Clemson University Genomics Institute, where a BAC library for ECB is being constructed. The initial steps in the library construction have been completed successfully.
Impacts
European Corn Borers are introduced pests that have had significant economic impacts in the United States (they are among the most important pests of maize). The status of pheromone and voltinism 'races' of ECB influences patterns of gene exchange and how these populations evolve. These are issues that will be of increasing importance as resistant inbred and transgenic plants are used in the field. Our approach provides an opportunity to examine the possibility that gene exchange occurs freely for some parts of the genome and is limited or prevented for other genomic regions. This may have important consequences if (when) Bt resistance appears in natural populations. For example, if a gene locus that affects insecticide resistance resides in a part of the genome for which gene flow is limited, then expectations about the spread of resistance will be very different than for the case in which the locus is in a genomic region that experiences free gene exchange.
Publications
- No publications reported this period
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