Biology subjects

Lavanchy, E.

Publications and source records attributed to Lavanchy, E..

6 recordsLinked to original sources

bioRxiv2025

Benchmarking imputation accuracy in the presence or absence of a reference panel

Whole genome sequencing (WGS) of a large number of samples is costly. Solutions to reduce this cost include targeting a proportion of the genome (e.g. SNP arrays) or lowering the sequencing depth (low-coverage WGS, lcWGS) but both solutions suffer from either genotype missingness or uncertainty. Genomic imputation addresses this problem by inferring missing or uncertain genotypes using a collection of high quality genomic data (a reference panel). However, certain methods can impute a lcWGS dataset without a reference panel. Because the investment into generating a reference panel can be prohibitively expensive in non-model species, a benchmarking of the accuracy of these alternative methods of imputation can help inform study design. Here, we imputed a dataset of 2800 lcWGS in the presence and absence of a reference panel of 502 samples. We used 32 individuals sequenced at both high and low coverage to estimate the accuracy of each method and explored the limitations of lcWGS sample size and reference panel size. Although the best results were achieved with a large reference panel, using only a lcWGS dataset showed accurate imputation, when over 500 samples were used and we account for missing data and low frequency alleles. In addition, imputing with or without a reference panel gave similar results in a GWAS for a polygenic trait but required some quality control in the identification of homozygous-by-descent segments. Thus, while using a reference panel remains the ideal approach, imputation in suitably large lcWGS datasets can provide sufficient accuracy given proper quality control.

genomics↗

bioRxiv2025

Genomic bases of short-term evolution in the wild revealed by long-term monitoring and population-scale sequencing

Understanding how wild populations adapt to rapid environmental change requires linking phenotypic evolution to its genomic basis over contemporary timescales. This remains challenging because genetic and environmental effects are often intertwined. Here, we leverage a 30-year study of Swiss barn owls (Tyto alba) to explore this process. During this period, owls have evolved darker plumage and increased spottiness, two melanin-based traits associated with fitness. Whole-genome sequencing of 3,102 individuals reveals that these traits are largely controlled by few loci of major effect with partially overlapping architectures. Temporal allele frequency analyses show subtle but consistent shifts at these loci. Simulations indicate that genetic drift alone cannot explain these changes, whereas models incorporating selection do. Our findings demonstrate that selection on a small number of loci can drive rapid phenotypic evolution in the wild. This work underscores the adaptive potential of natural populations and the value of long-term genomic monitoring under accelerating climate change.

evolutionary biology↗

bioRxiv2024

The recombination landscape of the barn owl, from families to populations

Homologous recombination is a meiotic process that generates diversity along the genome and interacts with all evolutionary forces. Despite its importance, studies of recombination landscapes are lacking due to methodological limitations and a dearth of appropriate data. Linkage mapping based on familial data gives unbiased sex-specific broad-scale estimates of recombination while linkage disequilibrium (LD) based inference based on population data provides finer resolution data albeit depending on the effective population size and acting selective forces. In this study, we use a combination of these two methods, using a dataset of whole genome sequences and elucidate the recombination landscape for the Afro-European barn owl (Tyto alba). Linkage mapping allows us to refine the genome assembly to a chromosome-level quality. We find subtle differences in crossover placement between sexes that leads to differential effective shuffling of alleles. LD based estimates of recombination are concordant with family-based estimates and identify large variation in recombination rates within and among linkage groups. Larger chromosomes show variation in recombination rates while smaller chromosomes have a universally high rate which shapes the diversity landscape. We also identify local recombination hotspots in accordance with other studies in birds lacking the PRDM9 gene. However these hotspots show very little evolutionary stability when compared among populations with shallow genetic differentiation. Overall, this comprehensive analysis enhances our understanding of recombination dynamics, genomic architecture, and sex-specific variation in the barn owl, contributing valuable insights to the broader field of avian genomics. Article summaryTo study recombination events we look either in family data or in population data, with each method having advantages over the other. In this study we use both approaches to quantify the barn owl recombination landscape. We find that differences exist between sexes, populations and chromosomes.

genomics↗

bioRxiv2023

Detecting inbreeding depression in structured populations

Measuring inbreeding as well as its consequences on fitness is central for many areas in biology including human genetics and the conservation of endangered species. However, there is no consensus on the most appropriate method, neither for quantification of inbreeding itself nor for the model to estimate its effect on specific traits. In this project, we simulated traits based on simulated genomes from a large pedigree and empirical whole-genome sequences of human data from populations with various sizes and structure (from the 1,000 Genomes project). We compare the ability of various inbreeding coefficients (F) to quantify the strength of inbreeding depression: allele sharing, two versions of the correlation of uniting gametes which differ in the weight they attribute to each locus and two identical-by-descent segments-based estimators. We also compare two models: the standard linear model and a linear mixed model including a genetic relatedness matrix (GRM) as random effect to account for the non-independence of observations. We find linear mixed models give better results in scenarios with population or family structure. Within the mixed models, we compare three different GRM matrices and show that in homogeneous populations, there is little difference among the different F and GRM for inbreeding depression quantification. However, as soon as strong population or family structure is present, the strength of inbreeding depression can be most efficiently estimated only if (i) the phenotypes are regressed on inbreeding coefficient based on a weighted version of the correlation of uniting gametes, which gives more weight to common alleles and (ii) with the GRM obtained from an allele sharing relatedness estimator.

genomics↗

bioRxiv2022

Effect of reduced genomic representation on using runs of homozygosity for inbreeding characterization

Runs of homozygosity (ROHs) are proxy for genomic Identical-by-Descent segments and are increasingly used to measure individual inbreeding. ROHs analyses are mostly carried out on SNPs-arrays and whole-genome-sequencing data. Softwares recurrently used for their detection usually assume that genomic positions which have not been genotyped are non-variant. This might be true for whole-genome-sequencing data, but not for reduced genomic representations and can lead to spurious ROHs detection. We simulated the outputs of whole-genome-sequencing, two SNP-arrays and RAD-sequencing for three populations with different sizes. We compare the results of ROHs calling with two softwares: PLINK and RZooRoH. We demonstrate that to obtain meaningful estimates of inbreeding coefficients, RZooRoH requires fraction of genome seven times smaller compared to PLINK. When the SNP density is above 20 SNPs/Mb for PLINK and 3 SNPs/Mb for RZooRoH, ranks of ROHs-based inbreeding coefficients are conserved among individuals. With reduced genomic representations, ROHs distributions are consistently biased towards an underestimation of the total numbers of small and an overestimation of the total numbers of large ROHs, except for RZooRoH and high-density SNPs-arrays. We conclude that both ROHs-based inbreeding coefficients and ROHs distributions exact quantification are highly dependent on the fraction of genome sequenced and should thus be treated with caution. However, relative inbreeding estimates, such as comparison between individuals or populations, are reliable with reduced genomic representations providing that the fraction of genome sequenced is large enough. Consequently, we advise researchers working with reduced genomic data to use SNPs-independent measures or model-based ROHs calling methods for inbreeding estimations.

genomics↗

bioRxiv2021

Genomic consequences of colonisation, migration and genetic drift in barn owl insular populations of the eastern Mediterranean

The study of insular populations was key in the development of evolutionary theory. The successful colonisation of an island depends on the geographic context, and specific characteristics of the organism and the island, but also on stochastic processes. As a result, apparently identical islands may harbour populations with contrasting histories. Here, we use whole genome sequences of 65 barn owls to investigate the patterns of inbreeding and genetic diversity of insular populations in the eastern Mediterranean Sea. We focus on Crete and Cyprus, islands with similar size, climate and distance to mainland, that provide natural replicates for a comparative analysis of the impacts of microevolutionary processes on isolated populations. We show that barn owl populations from each island have a separate origin, Crete being genetically more similar to other Greek islands and mainland Greece, and Cyprus more similar to the Levant. Further, our data show that their respective demographic histories following colonisation were also distinct. On the one hand, Crete harbours a small population and maintains very low levels of gene flow with neighbouring populations. This has resulted in low genetic diversity, strong genetic drift, increased relatedness in the population and remote inbreeding. Cyprus, on the other hand, appears to maintain enough gene flow with the mainland to avoid such an outcome. Our work provides a comparative population genomic analysis of the effects of neutral processes on a classical island-mainland model system. It provides empirical evidence for the role of stochastic processes in determining the fate of diverging isolated populations.

evolutionary biology↗