Biology subjects

Dreau, A.

Publications and source records attributed to Dreau, A..

5 recordsLinked to original sources

bioRxiv2025

Benchmarking long-read genome assemblers for three sequencing protocols and three agricultural species

Today, long read technologies make it possible to produce telomere-to-telomere genome assemblies. These assemblies permit more accurate whole genome analyses, including on repeated regions. The genome assembly process can chain several steps such as read correction, contigs assembly, contig polishing, scaffolding and gap filling, among others. Each step usually requires at least one software package, and input sequences. For the end user, it is not necessarily clear which combination of tools, together with read types, will work best for a given genome. In this work, we will focus on contig production, which is a central and complex task of the assembly process. It aims at producing the longest, errorless, sequences, called contigs, from reads. While it is possible to produce contigs from short reads, long reads are now widely preferred, since they produce much longer contigs. In this work, we evaluate several contig producing software packages (usually named assemblers), on long reads generated by two sequencers using three protocols, for three eukaryotic, complex species with different characteristics. Our aim is twofold. First, we would like to give readers insight on the impact of sequencing technology and assembler combinations, in order to help them make their choice for a given genome. Second, we would like to present different assembly metrics and provide a critical view on their interpretation.

bioinformatics↗

bioRxiv2023

Fine-scale contemporary recombination variation and its fitness consequences in adaptively diverging stickleback fish

Despite deep evolutionary conservation, recombination varies greatly across the genome, among individuals, sexes, and populations and can be a major evolutionary force in the wild. Yet this variation in recombination and its impact on adaptively diverging populations is not well understood. To elucidate the nature and potential consequences of recombination rate variation, we characterized fine-scale recombination landscapes by combining pedigrees, functional genomics and field fitness measurements in an adaptively divergent pair of marine and freshwater threespine stickleback populations from River Tyne, Scotland. Through whole-genome sequencing of large nuclear families, we identified the genomic location of almost 50,000 crossovers and built recombination maps for 36 marine, freshwater, and hybrid individuals at 3.8 kilobase resolution. Using these maps, we quantified the factors driving variation in recombination rate: we find strong heterochiasmy between sexes (68% of the variation) but also differences among ecotypes (21.8%). Hybrids show evidence of significant recombination suppression, both in overall map length and in individual loci. We further tested and found reduced recombination rates both within single marine-freshwater adaptive loci and between loci on the same chromosome, suggestive of selection on linked cassettes . We tested theory supporting the evolution of linked selection using temporal sampling along a natural hybrid zone, and found that recombinants with shuffled alleles across loci show traits associated with reduced fitness. Our results support predictions that divergence in cis-acting recombination modifiers whose mechanisms are disrupted in hybrids, may have an important role to play in the maintenance of differences among adaptively diverging populations.

evolutionary biology↗

bioRxiv2020

Haplotype tagging reveals parallel formation of hybrid races in two butterfly species

Genetic variation segregates as linked sets of variants, or haplotypes. Haplotypes and linkage are central to genetics and underpin virtually all genetic and selection analysis. And yet, genomic data often lack haplotype information, due to constraints in sequencing technologies. Here we present "haplotagging", a simple, low-cost linked-read sequencing technique that allows sequencing of hundreds of individuals while retaining linkage information. We apply haplotagging to construct megabase-size haplotypes for over 600 individual butterflies (Heliconius erato and H. melpomene), which form overlapping hybrid zones across an elevational gradient in Ecuador. Haplotagging identifies loci controlling distinctive high- and lowland wing color patterns. Divergent haplotypes are found at the same major loci in both species, while chromosome rearrangements show no parallelism. Remarkably, in both species the geographic clines for the major wing pattern loci are displaced by 18 km, leading to the rise of a novel hybrid morph in the centre of the hybrid zone. We propose that shared warning signalling (Mullerian mimicry) may couple the cline shifts seen in both species, and facilitate the parallel co-emergence of a novel hybrid morph in both co-mimetic species. Our results show the power of efficient haplotyping methods when combined with large-scale sequencing data from natural populations. One-sentence summaryHaplotagging, a novel linked-read sequencing technique that enables whole genome haplotyping in large populations, reveals the formation of a novel hybrid race in parallel hybrid zones of two co-mimicking Heliconius butterfly species through strikingly parallel divergences in their genomes.

evolutionary biology↗

bioRxiv2020

Museum phylogenomics of extinct Oryctes beetles from the Mascarene Islands

The evolution of island systems is characterized by processes that result in extreme morphological diversity, high endemism and high extinction rates. These dynamics can make phylogenetic reconstruction difficult, i.e. the extinct flightless Dodo from Mauritius was assigned to the family of doves only through DNA analysis of subfossils. Many insect species on islands have gone extinct through habitat loss, and face similar challenges to decipher their evolutionary history, however historical specimens have not yet been harnessed for phylogenomic reconstructions. Here, we employed historical museum specimens from the Mascarene Islands to generate the first whole-genome based phylogeny of three presumably extinct species of the rhinoceros beetle genus Oryctes. We compared their genomes with those of an extant Oryctes species from the island of Reunion, as well as a flightless Reunion-based species previously placed into the supposedly unrelated genus Marronus. We found that Marronus borbonicus belongs instead to the genus Oryctes and that the two Reunion-based species (O. borbonicus and M. borbonicus) are not sister taxa, suggesting two independent colonizations. The divergence time between them (<3Myr) overlaps with the volcanic formation of Reunion, likely indicating that M. borbonicus became flightless in situ. Our study showcases the power of genomes from insect museum specimens to address evolutionary questions in light of increasing extinction rates.

evolutionary biology↗

bioRxiv2018

Genome-wide recombination map construction from single individuals using linked-read sequencing

Meiotic recombination is a major molecular mechanism generating genomic diversity. Recombination rates vary across the genome, often involving localized crossover \"hotspots\" and \"coldspots\". Studying the molecular basis and mechanism underlying this variation within and among individuals has been challenging due to the high cost and effort required to construct individualized genome-wide maps of recombination crossovers. In this study we introduce a new method to detect recombination crossovers across the genome from sperm DNA using Illumina sequencing of linked-read libraries produced using 10X Genomics technology. We leverage the long range information provided by the linked short reads to phase and assign haplotype states to each DNA molecule. When applied to DNA from gametes of a diploid organism, the majority of linked-read molecules can be used to faithfully reconstruct an individuals two haplotypes present at each location in the genome. A valuable rare fraction of molecules that span meiotic crossovers between the two chromosome haplotypes can then be isolated from the broader population of nonrecombinant molecules. Our pipeline, called ReMIX, allows us to characterize the genomic location and intensity of meiotic crossovers in a single individual and faithfully detects previously described recombination hotspots discovered by studies using mapping panels in mice. With a median crossover resolution of the mouse and stickleback being 15kb and 23kb respectively, ReMIX provides a powerful, high-throughput, low-cost approach to quantify recombination variation across the genome opening up numerous opportunities to study recombination variation with high genomic resolution in multiple individuals. ReMIX source code is available at at https://github.com/adreau/ReMIX.

genomics↗