Two sex-chromosome-linked microsatellite loci show geographic variance among North American Ostrinia nubilalis

摘要

PCR-based O. nubilalis population and pedigree analysis indicated female specificity of a (GAAAAT)n microsatellite, and male specificity of a CAYCARCGTCACTAA repeat unit marker. These loci were respectively named Ostrinia nubilalis W-chromosome 1 (ONW1) and O. nubilalis Z-chromosome 1 (ONZ1). Intact repeats of three, four, or five GAAAAT units are present among ONW1 alleles, and biallelic variation exists at the ONZ1 locus. Screening of 493 male at ONZ1 and 448 heterogametic females at ONZ1 and ONW1 loci from eleven North American sample sites was used to construct genotypic data. Analysis of molecular variance (AMOVA) and F-statistics indicated no female haplotype or male ONZ1 allele frequency differentiation between voltinism ecotypes. Four subpopulations from northern latitudes, Minnesota and South Dakota, showed the absence of a single female haplotype, a significant deviation of ONZ1 data from Hardy-Weinberg expectation, and low-level geographic divergence from other subpopulations. Low ONZ1 and ONW1 allele diversity could be attributed either to large repeat unit sizes, low repeat number, reduced effective population (Ne) size of sex chromosomes, or the result of recent O. nubilalis introduction and population expansion, but likely could not be due to inbreeding. These sequences have been deposited in GenBank , and .

>Abbreviation:

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ONW1

Ostrinia nubilalis W-chromosome marker number 1

ONZ1

Ostrinia nubilalis Z-chromosome marker number 1

class="kwd-title">Keywords: Ostrinia, Pyraloidea, microsatellite, sex-linked genetic markers class="head no_bottom_margin" id="s1title" style="text-transform: uppercase;">IntroductionMicrosatellites are repetitive nucleotide elements that have a core repeat structure of 2 to 6 nucleotides (). Microsatellite allele mutations predominantly occur via strand slippage during chromosome replication at a rate of 10⁻⁶ to 10⁻² (), and is influenced by repeat unit length, number of repeat units in the array, microsatellite flanking sequence, and recombination ().Ostrinia nubilalis (Hübner), the European corn borer, is an invasive agricultural pest in North America introduced from Europe around 1917. The herbivorous O. nubilalis larvae are adapted to feeding on cultivated Zea mays (L.) and annually cause major economic losses (). Phenotypic diversity in the North American population is present in two sex pheromone races, and three voltinism types (). Females of the two sex pheromone races are differentiated by their emission of either E- or Z-11-tetradecenyl acetate as the dominant pheromone component. Pheromone races show little allozyme marker differentiation (; ; ). They interbreed in the laboratory and under natural conditions continual gene flow between the races apparently occurs (; ). In contrast, diapause ecotypes differ in the number of degree days required prior to adult emergence (), and the resultant asynchrony of adult mating cycles between voltinism types was suggested to minimize genetic exchange (). Reduced gene flow between voltinism ecotypes was supported by RAPD-PCR marker data (), but not by allozyme marker () or mitochondrial RFLP data (href="#i1536-2442-003-29-0001-marcon1" rid="i1536-2442-003-29-0001-marcon1" class=" bibr popnode tag_hotlink tag_tooltip" id="__tag_96702447">Marcon et al., 1999).To date, locus specific genetic markers used for O. nubilalis population analysis have inherent limitations that restrict the levels of variation detected, which might contribute to the conflicting evidence provided between O. nubilalis ecotypes. Intraspecific diversity of allozyme markers is reduced by negative selection on nonsynonymous changes and environmental influence on post translational modification pathways (href="#i1536-2442-003-29-0001-hartel1" rid="i1536-2442-003-29-0001-hartel1" class=" bibr popnode">Hartel 1988). Mitochondrial DNA is also prone to fixation by genetic drift due to a reduced effective population size of the molecule compared to chromosomes (href="#i1536-2442-003-29-0001-avise2" rid="i1536-2442-003-29-0001-avise2" class=" bibr popnode tag_hotlink tag_tooltip" id="__tag_96702453">Avise et al., 1988). Given the limitations of previously used markers, unresolved questions regarding gene flow among North American ecotypes, and our desire to estimate both male- and female-based population differentiation (movement), we developed sex-specific O. nubilalis nuclear microsatellite markers. In the following allele variation of the North American population is characterized at two such markers, ONW1 (Ostrinia nubilalis W-chromosome 1) and ONZ1 (Ostrinia nubilalis Z-chromosome 1). Genotypic and haplotypic data were used to evaluate intraspecies differences, infer the presence of any population subdivision, and estimate the levels of genetic exchange (migration) among O. nubilalis voltinism ecotypes and geographically distinct North American subpopulations.