Biology subjects

Marec, F.

Publications and source records attributed to Marec, F..

8 recordsLinked to original sources

bioRxiv2026

Parallel evolution of industrial melanism in the peppered moth: one locus, many alleles

The extent to which adaptation to environmental change occurs via single or multiple advantageous mutations remains an open question, which we examined by studying the spread of melanic forms of the peppered moth in Britain and continental Europe, in response to industrial coal pollution. In Britain, the darkest melanic form is due to the insertion of a transposable element (carb-TE) into a genomic region called ivory. Here, we characterize the spread of melanic forms in continental Europe from historical records and uncover the genetic basis of European melanism using genomic analyses of modern and museum specimens. We show that European melanism is also associated with variants at ivory, but with multiple alleles featuring structural variants, including several transposable elements, though not carb-TE. The primary central European melanic allele is a genetically dominant 805 base pair deletion (sollichau). Interestingly, melanic individuals with either sollichau (deletion) or carb-TE (insertion) alleles show elevated expression of ivory and its effector micro-RNA (mir-193) compared to non-melanic (typica) individuals, suggesting that contrasting structural variants in ivory have similar regulatory effects. A functional role for sollichau was corroborated, serendipitously, by its presence in a typica individual which also contains a linked deletion of mir-193, which is predicted to cancel the melanizing effect of the sollichau deletion. Our results support the idea that there can be many genetic origins of the same adaptive trait within a species, particularly one with a large effective population size and heterogeneous natural habitat, and when many mutations can give rise to the same phenotype.

evolutionary biology↗

bioRxiv2023

Ghost W chromosomes and unique genome architecture in ghost moths of the family Hepialidae

The classical model of sex chromosome evolution has been recently challenged in moths and butterflies (Lepidoptera). According to the current hypothesis, the adoption of a supernumerary chromosome may have driven the transition from the Z0 to the WZ sex chromosome system in females. However, the evolutionary history of the W chromosome remains enigmatic, especially in the early-diverging lepidopteran lineages. In ghost moths of the family Hepialidae, one of the most basal lepidopteran clades, there is conflicting evidence regarding their sex chromosomes. In this study, we aimed to clarify the status of the hepialid W chromosome. Using cytogenetics and genomics, we investigated the karyotype, sex chromosomes, genome size and repeatome of multiple ghost moth species and reconstructed basic phylogenetic relationships in the group. Our data show that Hepialidae have unusually large genomes (reaching up to 1C = 3 Gb) and are the oldest known lepidopteran clade with a W chromosome. However, the W does not form a typical heterochromatin body in polyploid nuclei, known as sex chromatin, previously employed to detect the presence of W chromosomes across Lepidoptera. Moreover, in some species, the W does not exhibit distinct repeat content and can escape detection via methods that rely on W-specific sequences. Analysis of the Z chromosome confirmed highly conserved gene content, arguing for a possible origin of the hepialid W chromosome from a B chromosome. We hypothesize that the mechanism underlying the formation of sex chromatin could be used in future research to study the origin of the W chromosome.

genomics↗

bioRxiv2023

Multiple sex chromosomes of Yponomeuta ermine moths suggest a role of sexual antagonism in sex chromosome turnover in Lepidoptera

Sex chromosome-autosome fusions give rise to neo-sex chromosomes, which provide an insight into early evolution of sex chromosomes and drivers of chromosomal fusions. While sex chromosome-autosome fusions are scarce in vertebrates with female heterogamety ([female]ZW/[male]ZZ), they are common in moths and butterflies (Lepidoptera), the most species rich group with heterogametic females. This contradicts theoretical model that assumes chromosome fusions to be random and predicts them to be rare in taxa with high chromosome number such as Lepidoptera. In the present study we analyzed sex chromosomes in nine ermine moths of the genus Yponomeuta (Yponomeutidae) and their two outgroups, Teinoptila gutella (Yponomeutidae) and Plutella xylostella (Plutellidae). We employed genomic in situ hybridization to identify sex chromosomes and used a custom designed microarray to identify Z-linked genes. Our results confirmed a multiple sex chromosome system Z1Z2W to be present in T. gutella and all Yponomeuta spp. except for Y. tokyonella. The multiple sex chromosome system resulted from a fusion between the W chromosome and autosome homeologous to the Bombyx mori chromosome 2 (BmChr2). The BmChr2 bears a cluster of genes with ovary-specific expression which suggests that sexually antagonistic selection could have driven fixation of the fusion in a common ancestor of Yponomeuta and Teinoptila genera. We hypothesize that sex chromosome turnover in Lepidoptera could be driven by sexual antagonism.

evolutionary biology↗

bioRxiv2022

High quality genomes corroborate 29 chromosomes of the haploid Hyles (Lepidoptera: Sphingidae) karyotype

BackgroundMorphological and traditional genetic studies of the young Pliocene genus Hyles have led to the understanding that despite its importance for taxonomy, phenotypic similarity of wing patterns does not correlate with phylogenetic relationship. To gain insights into various aspects of speciation in the Spurge Hawkmoth (Hyles euphorbiae), we assembled a chromosome-level genome and investigated some of its characteristics. ResultsThe genome of a male H. euphorbiae was sequenced using PacBio and Hi-C data, yielding a 504 Mb assembly (scaffold N50 of 18.2 Mb) with 99.9% of data represented by the 29 largest scaffolds forming the haploid chromosome set. Consistent with this, FISH analysis of the karyotype revealed n = 29 chromosomes and a WZ/ZZ (female/male) sex chromosome system. Estimates of chromosome length based on the karyotype image provided an additional quality metric of assembled chromosome size. Rescaffolding the published male H. vespertilio genome resulted in a high-quality assembly (651 Mb, scaffold N50 of 22 Mb) with 98% of sequence data in the 29 chromosomes. The larger genome size of H. vespertilio (average 1C DNA value of 562 Mb) was accompanied by a proportional increase in repeats from 45% in H. euphorbiae (measured as 472 Mb) to almost 55% in H. vespertilio. Several wing pattern genes were found on the same chromosomes in the two species, with varying amounts and positions of repetitive elements and inversions possibly corrupting their function. ConclusionsOur two-fold comparative genomics approach revealed high gene synteny of the Hyles genomes to other Sphingidae and high correspondence to intact Merian elements, the ancestral linkage groups of Lepidoptera, with the exception of three simple fusion events. We propose a standardized approach for genome taxonomy using nucleotide homology via scaffold chaining as the primary tool combined with Oxford plots based on Merian elements to infer and visualize directionality of chromosomal rearrangements. The identification of wing pattern genes promises future understanding of the evolution of forewing patterns in the genus Hyles, although further sequencing data from more individuals are needed. The genomic data obtained provide additional reliable references for further comparative studies in hawkmoths (Sphingidae).

genomics↗

bioRxiv2021

A conserved role of the duplicated Masculinizer gene in sex determination of the Mediterranean flour moth, Ephestia kuehniella

Sex determination in the silkworm, Bombyx mori, is based on Feminizer (Fem), a W-linked Fem piRNA that triggers female development in WZ individuals, and the Z-linked Masculinizer (Masc), which initiates male development and dosage compensation in ZZ individuals. While Fem piRNA is missing in a close relative of B. mori, Masc determines sex in several representatives of distant lepidopteran lineages. We studied the molecular mechanisms of sex determination in the Mediterranean flour moth, Ephestia kuehniella (Pyralidae). We identified an E. kuehniella Masc ortholog, EkMasc, and its paralog resulting from a recent duplication, EkMascB. Both genes are located on the Z chromosome and encode a similar Masc protein that contains two conserved domains but has lost the conserved double zinc finger domain. We developed PCR-based genetic sexing and demonstrated a peak in the expression of EkMasc and EkMascB genes only in early male embryos. Simultaneous knock-down experiments of both EkMasc and EkMascB using RNAi during early embryogenesis led to a shift from male- to female-specific splicing of the E. kuehniella doublesex gene (Ekdsx), their downstream effector, in ZZ embryos and resulted in a strong female-biased sex-ratio. Our results thus confirmed the conserved role of both EkMasc and EkMascB genes in masculinization. We suggest that the C-terminal proline-rich domain, we have identified in all functionally confirmed Masc proteins, in conjunction with the masculinizing domain, is important for transcriptional regulation of sex determination in Lepidoptera. The function of the Masc double zinc finger domain is still unknown, but appears to have been lost in E. kuehniella. Author summaryThe sex-determining cascade in the silkworm, Bombyx mori, differs greatly from those of other insects. In B. mori, female development is initiated by Fem piRNA expressed from the W chromosome during early embryogenesis. Fem piRNA silences Masculinizer (Masc) thereby blocking the male pathway resulting in female development. It is currently unknown whether this cascade is conserved across Lepidoptera. In the Mediterranean flour moth, Ephestia kuehniella, we identified an ortholog of Masc and discovered its functional duplication on the Z chromosome, which has not yet been found in any other lepidopteran species. We provide two lines of evidence that both the EkMasc and EkMascB genes play an essential role in masculinization: (i) they show a peak of expression during early embryogenesis in ZZ but not in WZ embryos and (ii) their silencing by RNAi results in female-specific splicing of the E. kuehniella doublesex gene (Ekdsx) in ZZ embryos and in a female-biased sex ratio. Our results suggest a conserved role of the duplicated Masc gene in sex determination of E. kuehniella.

genetics↗

bioRxiv2020

White pupae genes in the Tephritids Ceratitis capitata, Bactrocera dorsalis and Zeugodacus cucurbitae: a story of parallel mutations

Mass releases of sterilized male insects, in the frame of sterile insect technique programs, have helped suppress insect pest populations since the 1950s. In the major horticultural pests Bactrocera dorsalis, Ceratitis capitata, and Zeugodacus cucurbitae, a key phenotype white pupae (wp) has been used for decades to selectively remove females before releases, yet the gene responsible remained unknown. Here we use classical and modern genetic approaches to identify and functionally characterize causal wp− mutations in these distantly related fruit fly species. We find that the wp phenotype is produced by parallel mutations in a single, conserved gene. CRISPR/Cas9-mediated knockout of the wp gene leads to the rapid generation of novel white pupae strains in C. capitata and B. tryoni. The conserved phenotype and independent nature of the wp− mutations suggest that this technique can provide a generic approach to produce sexing strains in other major medical and agricultural insect pests.Competing Interest StatementThe authors have declared no competing interest.View Full Text

genetics↗

bioRxiv2020

Jekyll or Hyde? The genome (and more) of Nesidiocoris tenuis, a zoophytophagous predatory bug that is both a biological control agent and a pest

Nesidiocoris tenuis (Reuter) is an efficient predatory biological control agent used throughout the Mediterranean Basin in tomato crops but regarded as a pest in northern European countries. Belonging to the family Miridae, it is an economically important insect yet very little is known in terms of genetic information - no published genome, population studies, or RNA transcripts. It is a relatively small and long-lived diploid insect, characteristics that complicate genome sequencing. Here, we circumvent these issues by using a linked-read sequencing strategy on a single female N. tenuis. From this, we assembled the 355 Mbp genome and delivered an ab initio, homology-based, and evidence-based annotation. Along the way, the bacterial "contamination" was removed from the assembly, which also revealed potential symbionts. Additionally, bacterial lateral gene transfer (LGT) candidates were detected in the N. tenuis genome. The complete gene set is composed of 24,688 genes; the associated proteins were compared to other hemipterans (Cimex lectularis, Halyomorpha halys, and Acyrthosiphon pisum), resulting in an initial assessment of unique and shared protein clusters. We visualised the genome using various cytogenetic techniques, such as karyotyping, CGH and GISH, indicating a karyotype of 2n=32 with a male-heterogametic XX/XY system. Additional analyses include the localization of 18S rDNA and unique satellite probes via FISH techniques. Finally, population genomics via pooled sequencing further showed the utility of this genome. This is one of the first mirid genomes to be released and the first of a mirid biological control agent, representing a step forward in integrating genome sequencing strategies with biological control research.

genomics↗

bioRxiv2019

Maleness-on-the-Y (MoY) orchestrates male sex determination in major agricultural fruit fly pests

In insects, rapidly evolving primary sex-determining signals are transduced by a conserved regulatory module producing sex-specific proteins that direct sex determination and sexual differentiation1-4. In the agricultural pest Ceratitis capitata (medfly), a Y-linked maleness factor (M) is thought to repress the autoregulatory splicing of transformer (Cctra), which is required in XX individuals to establish and maintain female sex determination5,6. Despite previous attempts of isolating Y-linked genes using the medfly whole genome, the M factor has remained elusive7. Here, we report the identification of a Y-linked gene, Maleness-on the-Y (MoY), and show that it encodes a small novel protein which is both necessary and sufficient for medfly male sex determination. Transient silencing of MoY in XY individuals leads to the development of fertile females while transient expression of MoY in XX individuals results in fertile males. Notably, a cross between these sex reverted individuals gives rise to both fertile males and females indicating that a functional MoY can be maternally transmitted. In contrast to the diversity of M factors found in dipteran species8-11, we discovered MoY orthologues in seven other Tephritid species spanning [~]111 millions of years of evolution (Mya). We confirmed their male determining function in the olive fly (Bactrocera oleae) and the oriental fruit fly (Bactrocera dorsalis). This unexpected conservation of the primary MoY signal in a large number of important agricultural pests12 will facilitate the development of transferable genetic control strategies in these species, for example sterile male releases or sex-ratio-distorting gene drives.

genetics↗