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The European corn borer (Ostrinia nubilalis) is an agricultural pest and burgeoning model for research on speciation, seasonal adaptation and insect resistance management. Although previous work in O. nubilalis has identified genes associated with differences in life cycle, reproduction, and resistance to Bt toxins, the general lack of a robust gene‐editing protocol for O. nubilalis has been a barrier to functional validation of candidate genes. Here, we demonstrate an efficient and practical methodology for heritable gene mutagenesis in O. nubilalis using the CRISPR/Cas9 genome editing system. Precise loss‐of‐function (LOF) mutations were generated at two circadian clock genes, period (per) and pigment‐dispersing factor receptor (pdfr), and a developmental gene, prothoracicotropic hormone (ptth). Precluding the need for a visible genetic marker, gene‐editing efficiency remained high across different single guide RNAs (sgRNA) and germline transmission of mutations to F1 offspring approached 100%. When single or dual sgRNAs were injected at a high concentration, gene‐specific phenotypic differences in behaviour and development were identified in F0 mutants. Specifically, F0 gene mutants demonstrated that PER, but not PDFR, is essential for normal timing of eclosion. PTTH F0 mutants were significantly heavier and exhibited a higher incidence of diapause. This work will accelerate future studies of gene function in O. nubilalis and facilitate the development of similar screens in other Lepidopteran and non‐model insects. [ABSTRACT FROM AUTHOR]

BACKGROUND: Ostrinia furnacalis (ACB) and Ostrinia nubilalis (ECB) are devastating pests of the agricultural crop maize worldwide. However, little is known about their potential distribution and niche shifts during their global invasion. Since long‐term selection to past climate variability has shaped their historical niche breadth, such niche shifts may provide an alternative basis for understanding their responses to present and future climate change. By integrating the niche unfilling, stability, and expansion situations into a single framework, our study quantifies the patterns of niche shift in the spatial distribution of these two pests during the different periods. RESULTS: Our results show that the overall suitable habitats of ACB and ECB in the future decrease but highly and extremely suitable habitat will become more widespread, suggesting these two insects may occur more frequently in specific regions. Compared with Southeast Asia and Australia, the ACB niche in China exhibited expansion rather than unfilling. For ECB, initial niches have a tendency to be retained in Eurasia despite there also being potential for expansion in North America. The niche equivalency and similarity test results further indicate that niche shifts were common for both ACB and ECB in different survival regions during their colonization of new habitat and their suitable habitat changes during the paleoclimate were associated with climatic changes. CONCLUSIONS: These findings improve our understanding of the ecological characteristics of ACB and ECB worldwide, and will be useful in the development of prevention and control strategies for two insect pests worldwide. © 2024 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

The E and Z pheromone strains of the European corn borer (ECB) provide an exceptional model system for examining the genetic basis of sexual isolation. Differences at two major genes account for variation in female pheromone production and male behavioral response, components of the pheromone communication system known to be important for mate recognition and mate choice. Strains of ECB are morphologically indistinguishable, and surveys of allozyme and DNA sequence variation have revealed significant allele frequency differences at only a single sex-linked locus, Tpi. Here we present a detailed genetic linkage map of ECB using AFLP and microsatellite markers and map the factors responsible for pheromone production (Pher) and male response (Resp). Our map covers 1697 cM and identifies all 31 linkage groups in ECB. Both Resp and Tpi map to the Z (sex) chromosome, but the distance between these markers (>20 cM) argues against the hypothesis that patterns of variation at Tpi are explained by tight linkage to this 'speciation gene.' However, we show, through analysis of marker density, that Tpi is located in a region of low recombination and suggest that a second Z-linked reproductive barrier could be responsible for the origin and/or persistence of differentiation at Tpi.

Phenological shifts are well‐documented in the ecological literature. However, their significance for changes in demography and abundance is less clear. We used 27 years of citizen science monitoring to quantify trends in phenology and relative abundance across 89 butterfly species. We calculated shifts in phenology using quantile regression and shifts in relative abundance using list length analysis and counts from field trips. Elongated activity periods within a year were the strongest predictor of increases in relative abundance. These changes may be driven in part by changes in voltinism, as this association was stronger in multivoltine species. Some species appear to be adding a late‐season generation, whereas other species appear to be adding a spring generation, revealing a possible shift from vagrant to resident. Our results emphasise the importance of evaluating phenological changes throughout species' flight period and understanding the consequences for such climate‐related changes on viability or population dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Seminal fluid proteins (SFPs) produced in the male accessory glands and ejaculatory duct are subject to strong sexual selection, often evolve rapidly and therefore may play a key role in reproductive isolation and species formation. However, little is known about reproductive proteins for species in which males transfer ejaculate to females using a spermatophore package. By combining RNA sequencing and proteomics, we characterize putative SFPs, identify proteins transferred in the male spermatophore and identify candidate genes contributing to a one‐way gametic incompatibility between Z and E strains of the European corn borer moth Ostrinia nubilalis. We find that the accessory glands and ejaculatory duct secrete over 200 highly expressed gene products, including peptidases, peptidase regulators and odourant‐binding proteins. A comparison between Ostrinia strains reveals that accessory gland and ejaculatory duct sequences with hormone degradation and peptidase activity are among the most extremely differentially expressed. However, most spermatophore peptides lack reproductive tissue bias or canonical secretory signal motifs and aproximately one‐quarter may be produced elsewhere before being sequestered by the male accessory glands during spermatophore production. In addition, most potential gene candidates for postmating reproductive isolation do not meet standard criteria for predicted SFPs and almost three‐quarters are novel, suggesting that both postmating sexual interactions and gametic isolation likely involve molecular products beyond traditionally recognized SFPs. [ABSTRACT FROM AUTHOR]

Copy-number variants (CNVs) reshape gene structure, modulate gene expression, and contribute to significant phenotypic variation. Previous studies have revealed CNV patterns in natural populations of Drosophila melanogaster and suggested that selection and mutational bias shape genomic patterns of CNV. Although previous CNV studies focused on heterogeneous strains, here, we established a number of second-chromosome substitution lines to uncover CNV characteristics when homozygous. The percentage of genes harboring CNVs is higher than found in previous studies. More CNVs are detected in homozygous than heterozygous substitution strains, suggesting the comparative genomic hybridization arrays underestimate CNV owing to heterozygous masking. We incorporated previous gene expression data collected from some of the same substitution lines to investigate relationships between CNV gene dosage and expression. Most genes present in CNVs show no evidence of increased or diminished transcription, and the fraction of such dosage-insensitive CNVs is greater in heterozygotes. More than 70% of the dosage-sensitive CNVs are recessive with undetectable effects on transcription in heterozygotes. A deficiency of singletons in recessive dosage-sensitive CNVs supports the hypothesis that most CNVs are subject to negative selection. On the other hand, relaxed purifying selection might account for the higher number of protein–protein interactions in dosage-insensitive CNVs than in dosage-sensitive CNVs. Dosage-sensitive CNVs that are upregulated and downregulated coincide with copy-number increases and decreases. Our results help clarify the relation between CNV dosage and gene expression in the D. melanogaster genome. [ABSTRACT FROM AUTHOR]

Short-read sequencing techniques provide the opportunity to capture genome-wide sequence data in a single experiment. A current challenge is to identify questions that shallow-depth genomic data can address successfully and to develop corresponding analytical methods that are statistically sound. Here, we apply the Roche/454 platform to survey natural variation in strains of Drosophila melanogaster from an African (n = 3) and a North American (n = 6) population. Reads were aligned to the reference D. melanogaster genomic assembly, single nucleotide polymorphisms were identified, and nucleotide variation was quantified genome wide. Simulations and empirical results suggest that nucleotide diversity can be accurately estimated from sparse data with as little as 0.2× coverage per line. The unbiased genomic sampling provided by random short-read sequencing also allows insight into distributions of transposable elements and copy number polymorphisms found within populations and demonstrates that short-read sequencing methods provide an efficient means to quantify variation in genome organization and content. Continued development of methods for statistical inference of shallow-depth genome-wide sequencing data will allow such sparse, partial data sets to become the norm in the emerging field of population genomics., Organismic and Evolutionary Biology

Speciation often involves the coupling of multiple isolating barriers to produce reproductive isolation, but how coupling is generated among different premating barriers is unknown. We measure the degree of coupling between the daily mating time and seasonal mating time between strains of European corn borer (Ostrinia nubilalis) and evaluate the hypothesis that the coupling of different forms of allochrony is due to a shared genetic architecture, involving genes with pleiotropic effects on both timing phenotypes. We measure differences in gene expression at peak mating times and compare these genes to previously identified candidates that are associated with changes in seasonal mating time between the corn borer strains. We find that the E strain, which mates earlier in the season, also mates 2.7 h earlier in the night than the Z strain. Earlier daily mating is correlated with the differences in expression of the circadian clock genes cycle, slimb, and vrille. However, different circadian clock genes associate with daily and seasonal timing, suggesting that the coupling of timing traits is maintained by natural selection rather than pleiotropy. Juvenile hormone gene expression was associated with both types of timing, suggesting that circadian genes activate common downstream modules that may impose constraint on future evolution of these traits. [ABSTRACT FROM AUTHOR]

In hybrid zones, whether barrier loci experience selection mostly independently or as a unit depends on the ratio of selection to recombination as captured by the coupling coefficient. Theory predicts a sharper transition between an uncoupled and coupled system when more loci affect hybrid fitness. However, the extent of coupling in hybrid zones has rarely been quantified. Here, we use simulations to characterize the relationship between the coupling coefficient and variance in clines across genetic loci. We then reanalyze 25 hybrid zone data sets and find that cline variances and estimated coupling coefficients form a smooth continuum from high variance and weak coupling to low variance and strong coupling. Our results are consistent with low rates of hybridization and a strong genome-wide barrier to gene flow when the coupling coefficient is much greater than 1, but also suggest that this boundary might be approached gradually and at a near constant rate over time., (Copyright © 2023 Cold Spring Harbor Laboratory Press; all rights reserved.)