Biology subjects

Chevalier, F.

Publications and source records attributed to Chevalier, F..

16 recordsLinked to original sources

bioRxiv2026

An Advanced Mobile Laboratory to enable field-based microbial ecology and cell biology across scales

Microbial biodiversity is central to ecosystem function, yet mechanistic insights into the cell biology of environmental organisms remain limited. The underlying challenges are twofold: most microbes remain uncultivable, and a persistent gap exists between field sampling and laboratory analyses. Here, we introduce the Advanced Mobile Laboratory (AML), a field-deployable platform that integrates confocal microscopy, image-enabled cell sorting, and cryo-preparation for expansion and electron microscopy. This setup enables immediate, standardized processing and analysis of environmental communities directly at the sampling site. We demonstrate its capability using marine eukaryotic plankton, showing how the AML enables multiscale investigations, from live imaging of natural communities to enabling ultrastructural and single-cell omics analyses, while minimizing sample degradation and enabling on-site experimentation. By bringing high-end sample preparation and analytical capacity into the field, the AML enables studying life in its natural context to mechanistically understand lifes diversity in the environment.

cell biology↗

bioRxiv2024

Abundant genetic variation is retained in many laboratory schistosome populations

Schistosomes are obligately sexual blood flukes that can be maintained in the laboratory using freshwater snails as intermediate and rodents as definitive hosts. The genetic composition of laboratory schistosome populations is poorly understood: whether genetic variation has been purged due to serial inbreeding or retained is unclear. We sequenced 19 - 24 parasites from each of five laboratory Schistosoma mansoni populations and compared their genomes with published exome data from four S. mansoni field populations. We found abundant genomic variation (0.897 - 1.22 million variants) within laboratory populations: these retained on average 49% ({pi} = 3.27e-04 - 8.94e-04) of the nucleotide diversity observed in the four field parasite populations ({pi} = 1.08e-03 - 2.2e-03). However, the pattern of variation was very different in laboratory and field populations. Tajimas D was positive in all laboratory populations except SmBRE, indicative of recent population bottlenecks, but negative in all field populations. Current effective population size estimates of laboratory populations were lower (2 - 258) compared to field populations (3,174 - infinity). The distance between markers at which linkage disequilibrium (LD) decayed to 0.5 was longer in laboratory populations (59 bp - 180 kb) compared to field populations (9 bp - 9.5 kb). SmBRE was the least variable; this parasite also shows low fitness across the lifecycle, consistent with inbreeding depression. The abundant genetic variation present in most laboratory schistosome populations has several important implications: (i) measurement of parasite phenotypes, such as drug resistance, using laboratory parasite populations will determine average values and underestimate trait variation; (ii) genome-wide association studies (GWAS) can be conducted in laboratory schistosome populations by measuring phenotypes and genotypes of individual worms; (iii) genetic drift may lead to divergence in schistosome populations maintained in different laboratories. We conclude that the abundant genetic variation retained within many laboratory schistosome populations can provide valuable, untapped opportunities for schistosome research.

genomics↗

bioRxiv2024

Hijacking and Integration of Algal Plastids andMitochondria in a Polar Planktonic Host

In oceanic plankton, various host organisms are capable of engulfing and temporarily integrating microalgae (photosymbiosis) or just their photosynthetic plastids (kleptoplastidy) as a solar-powered energy source. These cellular interactions can be considered to be representative of evolutionary steps in plastid acquisition in eukaryotes, but the underlying cellular mechanisms and dynamics are not fully understood. Here, we studied a kleptoplastidic dinoflagellate (RSD: Ross Sea Dinoflagellate), which is known to steal plastids of the microalga Phaeocystis antarctica. We tracked the morphology and activity of stolen plastids over several months by combining multimodal subcellular imaging and photophysiology. Upon integration inside a host vacuole, the volume of plastids and pyrenoids significantly increased and photosynthetic activity was boosted along with carbon fixation and transfer to the host. This may be supported by the retention of a 50-fold larger algal nucleus for [~]1 week. Once the algal nucleus was lost, there was a decrease in plastid volume and photosynthesis, but plastids were still beneficial for the host after > 2 months. Unlike other kleptoplastidic interactions, we showed that the algal mitochondrion was also stolen and retained for several months, transforming into an extensive network in close proximity with plastids. This highlights a new strategy in plankton along the continuum of plastid symbioses where both the energy-producing plastid and mitochondrion of a microalga are hijacked for several months by a host. This symbiosis that we found to be widely-distributed in polar regions suggests that plastid-mitochondrion interaction may have played a role in the evolution of plastid acquisition.

ecology↗

bioRxiv2024

Rapid phenotypic and genotypic change in a laboratory schistosome population

BackgroundGenomic analysis has revealed extensive contamination among laboratory-maintained microbes including malaria parasites, Mycobacterium tuberculosis and Salmonella spp. Here, we provide direct evidence for recent contamination of a laboratory schistosome parasite population, and we investigate its genomic consequences. The Brazilian Schistosoma mansoni population SmBRE has several distinctive phenotypes, showing poor infectivity, reduced sporocysts number, low levels of cercarial shedding and low virulence in the intermediate snail host, and low worm burden and low fecundity in the vertebrate rodent host. In 2021 we observed a rapid change in SmBRE parasite phenotypes, with a [~]10x increase in cercarial production and [~]4x increase in worm burden. MethodsTo determine the underlying genomic cause of these changes, we sequenced pools of SmBRE adults collected during parasite maintenance between 2015 and 2023. We also sequenced another parasite population (SmLE) maintained alongside SmBRE without phenotypic changes. ResultsWhile SmLE allele frequencies remained stable over the eight-year period, we observed sudden changes in allele frequency across the genome in SmBRE between July 2021 and February 2023, consistent with expectations of laboratory contamination. (i) SmLE-specific alleles rose in the SmBRE population from 0 to 41-46% across the genome between September and October 2021, documenting the timing and magnitude of the contamination event. (ii) After contamination, strong selection (s = [~]0.23) drove replacement of low fitness SmBRE with high fitness SmLE alleles. (iii) Allele frequency changed rapidly across the whole genome, except for a region on chromosome 4 where SmBRE alleles remained at high frequency. ConclusionsWe were able to detect contamination in this case because SmBRE shows distinctive phenotypes. However, this would likely have been missed with phenotypically similar parasites. These results provide a cautionary tale about the importance of tracking the identity of parasite populations, but also showcase a simple approach to monitor changes within populations using molecular profiling of pooled population samples to characterize fixed single nucleotide polymorphisms. We also show that genetic drift results in continuous change even in the absence of contamination, causing parasites maintained in different labs (or sampled from the same lab at different times) to diverge.

genomics↗

bioRxiv2024

Life Cycle and Morphogenetic Differentiation in Heteromorphic Cell Types of a Cosmopolitan Marine Microalga

O_LIGephyrocapsa huxleyi is a prevalent, bloom-forming phytoplankton species in the oceans. It exhibits a complex haplo-diplontic life cycle, featuring a diploid-calcified phase, a haploid phase, and a third decoupled phase produced during viral infection. Decoupled cells display a haploid-like phenotype, but are diploid. C_LIO_LIHere, we investigated the fate of decoupled cells during culture observations and we compared the transcriptome profiles and the cellular ultrastructure of the three cell types. C_LIO_LIWe found that decoupled cells can revert to the calcified form in the absence of viral pressure, revealing the transient nature of this cell type. Ultrastructural analyses showed distinct nuclear organisation with variations in chromatin volume. Transcriptomic analyses revealed gene expression patterns specific to each life phase. These included multiple regulatory functions in chromatin remodelling, broader epigenetic mechanisms and life cycling, which likely contributed to cell differentiation. Finally, the exploration of available host-virus transcriptomes supports life cycle transition during viral infection. C_LIO_LIThis study provides cellular and molecular foundations for nuclear remodelling and cell differentiation in coccolithophores and the identification of gene markers for studying coccolithophore life cycles in natural populations. C_LI

plant biology↗

bioRxiv2024

Interferon signaling is enhanced by ATR inhibition in glioblastoma cells irradiated with X-rays, protons or carbon ions

Background and purposeInterferon signaling plays an important role in antitumor immune responses. Inhibitors of the DNA damage response, such as ATR inhibitors, can increase interferon signaling upon conventional radiotherapy with X-rays. However, whether such inhibitors also increase interferon (IFN) signaling after high linear energy transfer (LET) particle irradiation is not known. Materials and methodsHuman glioblastoma U-251 and T98G cells were treated with X-rays, protons (linear energy transfer (LET): 7 and 38 keV/m) and carbon ions (LET: 28 and 73 keV/m), with and without ATR inhibitor (VE822) or ATM inhibitor (AZD1390). DNA damage signaling and cell cycle distribution were assayed by immunoblotting and flow cytometry, and radiosensitivity by clonogenic survival. IFN-{beta} secretion was measured by ELISA and STAT1 activation by immunoblotting. ResultsHigh-LET protons and carbon ions caused stronger activation of the DNA damage response compared to low-LET protons andX-rays at similar radiation dose. G2 checkpoint arrest was abrogated by the ATR inhibitor and prolonged by the ATM inhibitor after all radiation types. The inhibitors increased radiosensitivity, as measured after X- and carbon-ion-irradiation. ATR inhibition increased IFN signaling after both low-LET and high-LET irradiation in both cell lines. In T98G, IFN signaling was also enhanced by ATM inhibition. Notably, T98G cells secreted markedly more IFN-{beta} when the inhibitors were combined with high-LET compared to low-LET irradiation. ConclusionOur results show that ATR inhibition can increase IFN signaling after both X-, proton- and carbon-ion-irradiation. Additionally, IFN induction is strongly dependent on LET in one of the tested cell lines.

cancer biology↗

bioRxiv2024

Transportome remodeling of a symbiotic microalga inside a planktonic host

Metabolic exchange is one of the foundations of symbiotic associations between organisms and is a driving force in evolution. In the ocean, photosymbiosis between heterotrophic host and microalgae is powered by photosynthesis and relies on the transfer of organic carbon to the host (e.g. sugars). Yet, the identity of transferred carbohydrates as well as the molecular mechanisms that drive this exchange remain largely unknown, especially in unicellular photosymbioses that are widespread in the open ocean. Combining genomics, single-holobiont transcriptomics and environmental metatranscriptomics, we revealed the transportome of the marine microalga Phaeocystis in symbiosis within acantharia, with a focus on sugar transporters. At the genomic level, the sugar transportome of Phaeocystis is comparable to non-symbiotic haptophytes. By contrast, we found significant remodeling of the expression of the transportome in symbiotic microalgae compared to the free-living stage. More particularly, 32% of sugar transporter genes were differentially expressed. Several of them, such as GLUTs, TPTs and aquaporins, with glucose, triose-phosphate sugars and glycerol as potential substrates, were upregulated at the holobiont and community level. We also showed that algal sugar transporter genes exhibit distinct temporal expression patterns during the day. This reprogrammed transportome indicates that symbiosis has a major impact on sugar fluxes within and outside the algal cell, and highlights the complexity and the dynamics of metabolic exchanges between partners. This study improves our understanding of the molecular players of the metabolic connectivity underlying the ecological success of planktonic photosymbiosis and paves the way for more studies on transporters across photosymbiotic models.

cell biology↗

bioRxiv2023

Sweet and fatty symbionts: photosynthetic productivity and carbon storage boosted in microalgae within a host

Symbiosis between a host and intracellular eukaryotic microalgae is a widespread life strategy in aquatic ecosystems. This partnership is considered to be mainly energized by the photosynthetically-derived carbon energy of microalgal symbionts. A major question is whether microalgae increase their photosynthetic production and decrease carbon storage in order to maximize carbon translocation to their host. By combining three-dimensional subcellular imaging and physiological analyses, we show that the photosynthetic machinery (chloroplast and CO2-fixing pyrenoid) of the symbiotic microalga Micractinium conductrix significantly expands inside their host (the ciliate Paramecium bursaria) compared to the free-living state. This is accompanied by a 13-fold higher quantity of Rubisco enzymes and 16-fold higher carbon fixation rate. Time-resolved subcellular imaging revealed that photosynthetically-derived carbon is first allocated to starch during the day, with five times higher production in symbiosis despite low growth. Nearly half of the carbon stored in starch is consumed overnight and some accumulates in lipid droplets, which are 20-fold more voluminous in symbiotic microalgae. We also show that carbon is transferred to the host and hypothesize that much of this is respired by the high density of surrounding host mitochondria. We provide evidence that the boosted photosynthetic production of symbiotic microalgae could be explained by the energetic demands of the host. Overall, this study provides an unprecedented view of the subcellular remodeling and dynamics of carbon metabolism of microalgae inside a host, highlighting the potentially key role of the source-sink relationship in aquatic photosymbiosis. Significance statementSymbiotic interactions between a heterotrophic host and intracellular microalgae are widespread in aquatic ecosystems and are considered to be energized by the photosynthetically-derived carbon energy. However, little is known on the impact of symbiosis on the algal bioenergetics (e.g. carbon production and storage). This study reveals the morphological and physiological changes of a microalga inside a host at the subcellular scale over the day. We show that the photosynthetic machinery expands and carbon fixation and storage are boosted in symbiotic microalgae beyond their growth needs. This high photosynthetic production is very likely enhanced by the host energetic demands. Our findings advance our basic understanding of photosymbiosis and open new perspectives on the mechanisms and drivers of metabolic exchange between partners.

physiology↗

bioRxiv2023

Targeted volume Correlative Light and Electron Microscopy of an environmental marine microorganism

Photosynthetic microalgae are responsible for an important fraction of CO2 fixation and O2 production on Earth. Three-dimensional ultrastructural characterization of these organisms in their natural environment can contribute to a deeper understanding of their cell biology. However, the low throughput of volume electron microscopy (vEM) methods, along with the complexity and heterogeneity of environmental samples, pose great technical challenges. In the present study, we used a workflow based on a specific EM sample preparation, compatible with both light and vEM imaging in order to target one cell among a complex natural community. This method revealed the 3D subcellular landscape of a photosynthetic dinoflagellate with quantitative characterization of multiple organelles. We could show that this cell contains a single convoluted chloroplast and the arrangement of the flagellar apparatus with its associated photosensitive elements. Moreover, we observed chromatin features that could shed light on how transcriptional activity takes place in organisms where chromosomes are permanently condensed. Together with providing insights in dinoflagellates biology, this proof-of-principle study illustrates an efficient tool for the targeted ultrastructural analysis of environmental microorganisms in heterogeneous mixes.

cell biology↗

bioRxiv2022

Tailoring confocal microscopy for in-cell photophysiology studies

Photoautotrophs environmental responses have been extensively studied at the organism and ecosystem level. However, less is known about their photosynthesis at the single cell level. This information is needed to understand photosynthetic acclimation processes, as light changes as it penetrates cells, layers of cells or organs. Furthermore, cells within the same tissue may behave differently, being at different developmental/physiological stages. Here we describe a new approach for single-cell and subcellular photophysiology based on the customisation of confocal microscopy to assess chlorophyll fluorescence quenching by the saturation pulse method. We exploit this setup to: i. reassess the specialisation of photosynthetic activities in developing tissues of non-vascular plants; ii. identify a specific subpopulation of phytoplankton cells in marine photosymbiosis, which are consolidating metabolic connections with their animal hosts, and iii. testify to the link between light penetration and photoprotection responses inside the different tissues that constitute a plant leaf anatomy. MotivationVisualising photosynthetic responses in 3D is essential for understanding most acclimation processes, as light changes within photosynthetic tissues as it penetrates the absorbing/diffusing layers of the cells. To achieve this goal, we developed a new imaging workflow merging confocal microscopy and saturating pulse chlorophyll fluorescence detection. This method applies to samples characterised by increasing complexity and its simplicity will contribute to its widespread use in plant and microalgae photoacclimation studies.

plant biology↗

bioRxiv2021

Intracellular development and impact of a eukaryotic parasite on its zombified microalgal host in the marine plankton

Parasites are widespread and diverse in the oceanic plankton, and many of them infect single-celled algae for survival. How these parasites develop and scavenge energy within the host and whether the cellular organization and metabolism of the host is altered remain open questions. Combining quantitative structural and chemical imaging with time-resolved transcriptomics, we unveil dramatic morphological and metabolic changes of the parasite Amoebophrya (Syndiniales) during intracellular infection (e.g. 200-fold increase of mitochondrion volume), particularly following digestion of nutrient-rich host chromosomes. Some of these changes are also found in the apicomplexan parasites (e.g. sequential acristate and cristate mitochondrion, switch from glycolysis to TCA), thus underlining key evolutionary-conserved mechanisms. In the algal host, energy-producing organelles (chloroplast) remain intact during most of the infection, but sugar reserves diminish while lipid droplets increase. Thus, rapid infection of the host nucleus could be a zombifying strategy to digest nutrient-rich chromosomes and escape cytoplasmic defense while benefiting from the maintained C-energy production of the host cell.

cell biology↗

bioRxiv2021

Subcellular architecture and metabolic connection in the planktonic photosymbiosis between Collodaria (radiolarians) and their microalgae

Photosymbiosis is widespread and ecologically important in the oceanic plankton but remains poorly studied. Here, we used multimodal subcellular imaging to investigate the photosymbiosis between colonial Collodaria and their microalga dinoflagellate (Brandtodinium) collected in surface seawaters. We showed that this symbiosis is a very dynamic system whereby symbionts interact with different host cells via extracellular vesicles within the "greenhouse-like" colony. 3D electron microscopy revealed that the volume of the photosynthetic apparatus (plastid and pyrenoid) of the microalgae increased in symbiosis compared to free-living while the mitochondria volume was similar. Stable isotope probing coupled with NanoSIMS showed that carbon and nitrogen were assimilated and stored in the symbiotic microalga in starch granules and purine crystals, respectively. Nitrogen was also allocated to the algal nucleus (nucleolus). After 3 hours, low 13C and 15N transfer was detected in the host Golgi. Metal mapping revealed that intracellular iron concentration was similar in free-living and symbiotic microalgae (ca 40 ppm) and two-fold higher in the host, whereas copper concentration increased in symbiotic microalgae (up to 6900 ppm) and was detected in the host cell and extracellular vesicles. Sulfur mapping also pinpointed the importance of this nutrient for the algal metabolism. This study, which revealed subcellular changes of the morphology and nutrient homeostasis in symbiotic microalgae, improves our understanding on the metabolism of this widespread and abundant oceanic symbiosis and paves the way for more studies to investigate the metabolites exchanged.

ecology↗

bioRxiv2020

Cytoklepty in the plankton: a host strategy to optimize the bioenergetic machinery of endosymbiotic algae

Endosymbioses have shaped the evolutionary trajectory of life and remain widespread and ecologically important. Investigating modern oceanic photosymbioses can illuminate how algal endosymbionts are energetically exploited by their heterotrophic hosts, and inform on putative initial steps of plastid acquisition in eukaryotes. By combining 3D subcellular imaging with photophysiology, carbon flux imaging and transcriptomics, we show that cell division of algal endosymbionts (Phaeocystis) is blocked within hosts (Acantharia), and that their cellular architecture and bioenergetic machinery are radically altered. Transcriptional evidence indicates that a nutrient-independent mechanism prevents symbiont cell division and decouples nuclear and plastid division. As endosymbiont plastids proliferate, the volume of the photosynthetic machinery volume increases 100-fold in correlation with expansion of a reticular mitochondrial network in close proximity to plastids. Photosynthetic efficiency tends to increase with cell size and photon propagation modeling indicates that the networked mitochondrial architecture enhances light capture. This is accompanied by 150-fold higher carbon uptake and upregulation of genes involved in photosynthesis and carbon fixation, which, in conjunction with a ca.15-fold size increase of pyrenoids demonstrates enhanced primary production in symbiosis. NanoSIMS analysis revealed major carbon allocation to plastids and transfer to the host cell. Invagination of the symbiosome into endosymbionts to optimize metabolic exchanges is strong evidence that the algal metamorphosis is irreversible. Hosts therefore trigger and unambiguously benefit from major bioenergetic remodeling of symbiotic microalgae with important consequences for the oceanic carbon cycle. Unlike other photosymbioses, this interaction represents a so-called cytoklepty, which is a putative initial step towards plastid acquisition.

physiology↗

bioRxiv2020

In-cell quantitative structural imaging of phytoplankton using 3D electron microscopy

Phytoplankton is a minor fraction of the global biomass playing a major role in primary production and climate. Despite improved understanding of phytoplankton diversity and genomics, we lack nanoscale subcellular imaging approaches to understand their physiology and cell biology. Here, we present a complete Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) workflow (from sample preparation to image processing) to generate nanometric 3D phytoplankton models. Tomograms of entire cells, representatives of six ecologically-successful phytoplankton unicellular eukaryotes, were used for quantitative morphometric analysis. Besides lineage-specific cellular architectures, we observed common features related to cellular energy management: i) conserved cell-volume fractions occupied by the different organelles; ii) consistent plastid-mitochondria interactions, iii) constant volumetric ratios in these energy-producing organelles. We revealed detailed subcellular features related to chromatin organization and to biomineralization. Overall, this approach opens new perspectives to study phytoplankton acclimation responses to abiotic and biotic factors at a relevant biological scale.

plant biology↗

bioRxiv2020

Nucleo-plastidic PAP8/pTAC6 couples chloroplast formation with photomorphogenesis

The initial greening of angiosperm occurs upon light-activation of photoreceptors that trigger photomorphogenesis followed with the development of chloroplasts. In these semi-autonomous organelles, the construction of the photosynthetic apparatus depends on the coordination of nuclear and plastid gene expression. Here we show that PAP8, as an essential subunit of the plastid-encoded RNA polymerase, is under the control of a regulatory element recognized by the photomorphogenic factor HY5. PAP8 is localized and active in both plastids and the nucleus and particularly essential for the formation of late photobodies. In the albino pap8 mutant, phytochrome-mediated signalling is altered, PIFs are maintained, HY5 is not stabilized, and GLK1 expression is impaired. PAP8 translocates into plastids losing its pre-sequence, interacts with the PEP, and using an unknown route or a retrograde transport, reaches the nucleus where it has the ability to interact with pTAC12/HMR/PAP5. Since PAP8 is required for the phytochrome-B-mediated signalling cascade and the reshaping of the PEP, it may coordinate nuclear gene expression with the PEP-driven chloroplastic gene expression during chloroplast biogenesis.

plant biology↗

bioRxiv2019

Oxamniquine resistance alleles are widespread in Old World Schistosoma mansoni and predate drug deployment

Do mutations required for adaptation occur de novo, or are they segregating within populations as standing genetic variation? This question is key to understanding adaptive change in nature, and has important practical consequences for the evolution of drug resistance. We provide evidence that alleles conferring resistance to oxamniquine (OXA), an antischistosomal drug, are widespread in natural parasite populations under minimal drug pressure and predate OXA deployment. OXA has been used since the 1970s to treat Schistosoma mansoni infections in the New World where S. mansoni established during the slave trade. Recessive loss-of-function mutations within a parasite sulfotransferase (SmSULT-OR) underlie resistance, and several verified resistance mutations, including a deletion (p.E142del), have been identified in the New World. Here we investigate sequence variation in SmSULT-OR in S. mansoni from the Old World, where OXA has seen minimal usage. We sequenced exomes of 204 S. mansoni parasites from West Africa, East Africa and the Middle East, and scored variants in SmSULT-OR and flanking regions. We identified 39 non-synonymous SNPs, 4 deletions, 1 duplication and 1 premature stop codon in the SmSULT-OR coding sequence, including one confirmed resistance deletion (p.E142del). We expressed recombinant proteins and used an in vitro OXA activation assay to functionally validate the OXA-resistance phenotype for four predicted OXA-resistance mutations. Three aspects of the data are of particular interest: (i) segregating OXA-resistance alleles are widespread in Old World populations (4.29 - 14.91% frequency), despite minimal OXA usage, (ii) two OXA-resistance mutations (p.W120R, p.N171IfsX28) are particularly common (>5%) in East African and Middle-Eastern populations, (iii) the p.E142del allele has identical flanking SNPs in both West Africa and Puerto Rico, suggesting that parasites bearing this allele colonized the New World during the slave trade and therefore predate OXA deployment. We conclude that standing variation for OXA resistance is widespread in S. mansoni.\n\nAUTHOR SUMMARYIt has been argued that drug resistance is unlikely to spread rapidly in helminth parasites infecting humans. This is based, at least in part, on the premise that resistance mutations are rare or absent within populations prior to treatment, and take a long time to reach appreciable frequencies because helminth parasite generation time is long. This argument is critically dependent on the starting frequency of resistance alleles - if high levels of \"standing variation\" for resistance are present prior to deployment of treatment, resistance may spread rapidly. We examined frequencies of oxamniquine resistance alleles present in Schistosoma mansoni from Africa and the Middle East where oxamniquine has seen minimal use. We found that oxamniquine resistance alleles are widespread in the Old World, ranging from 4.29% in the Middle East to 14.91% in East African parasite populations. Furthermore, we show that resistance alleles from West African and the Caribbean schistosomes share a common origin, suggesting that these alleles travelled to the New World with S. mansoni during the transatlantic slave trade. Together, these results demonstrate extensive standing variation for oxamniquine resistance. Our results have important implications for both drug treatment policies and drug development efforts, and demonstrate the power of molecular surveillance approaches for guiding helminth control.

evolutionary biology↗