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Sicard, M.

Publications and source records attributed to Sicard, M..

10 recordsLinked to original sources
bioRxiv2026

The role of cognitivo-motor interaction in landmark reliance and navigational deficits in older adults

Declining spatial navigation abilities are a critical hallmark of aging, where the loss of spatial abilities precedes global cognitive impairment. While navigational decline is traditionally attributed to deficits in higher-order cognitive functions, emerging cognitive-motor frameworks suggest that age-related sensorimotor alterations play a significant, yet previously overlooked, role. Here, we investigate the coupling between locomotor integrity and navigation by combining an immersive virtual-reality path-integration paradigm with systematic manipulations of landmark availability and reliability, while recording gait kinematics alongside neural dynamics using high-density mobile-EEG from 30 young and 32 older adults. We demonstrate that older adults accumulate angular homing error more rapidly than younger adults, a deficit linked to altered gait dynamics. These age-dependent differences are reflected in increased mid-frontal theta activity, highlighting a robust coupling between gait-related sensorimotor alterations and decline in navigation. Older adults also exhibited increased reliance on visual landmarks, and particularly those with degraded gait, yet this compensatory reweighting of navigational cues remained less efficient and less precise than in younger adults. These findings highlight sensorimotor gait alterations as a central determinant of age-related navigation deficits, challenging the traditional separation of motor and cognitive domains and identifying locomotor integrity as a critical target for preserving spatial navigation abilities.

neuroscience↗
bioRxiv2026

Stranger Swings: Temperature-Dependent Upsides and Downsides of a Densovirus in Aedes albopictus

Vector-borne diseases remain a significant global health concern, with the invasive mosquito Aedes albopictus playing a key role in the transmission of arboviruses including dengue, chikungunya, and Zika viruses. As this species expands in novel territories, effective vector control strategies are increasingly critical. Densoviruses (DVs) have emerged as potential biological control agents, either through direct pathogenic effects on mosquito populations or via paratransgenesis. However, the influence of combined environmental factors, such as temperature and densovirus infection on mosquito life-history traits remains largely unexplored. In this study, we investigated the effects of different temperatures (28{degrees}C, 31{degrees}C, and 34{degrees}C) and exposure to the densovirus AalDV2 on the survival of Ae. albopictus and on several mosquito life-history traits including its development time, size and symmetry at adult stage. Larvae were individually reared under controlled conditions and exposed to AalDV2 or a control treatment. Temperature had a strong nonlinear effect on survival, with dramatic mortality increases at 34{degrees}C. Unexpectedly, AalDV2-infected larvae showed significantly higher survival than controls at this extreme temperature, suggesting a protective effect under thermal stress. Across all temperatures, viral infection delayed pupation in a sex-dependent manner, with females experiencing greater delays and reduced adult wing size. Quantitative PCR revealed high infection rates (>96%) across all conditions with a viral load increasing with higher temperature in a sex-dependent manner. Our findings reveal a paradoxical outcome: while AalDV2 imposes fitness costs through delayed development and reduced body size, it confers an unexpected survival advantage at the extreme temperature. This represents the first documentation of temperature-dependent protective effects by an entomopathogenic virus in mosquitoes, challenging conventional assumptions about pathogen impacts. These results have critical implications for vector biocontrol strategies in a warming climate, as densovirus deployment could inadvertently enhance mosquito resilience in heat-stressed regions. Further research is needed to elucidate the underlying mechanisms and assess the impact on mosquito population dynamics.

evolutionary biology↗
bioRxiv2025

Genomic Islands in Wolbachia Prophages Drive Amplification andDiversification of Cytoplasmic Incompatibility Genes in Culex pipiens

Wolbachia are maternally inherited endosymbiotic bacteria widespread among arthropods. They manipulate their host reproduction to enhance their prevalence in host populations. The most common manipulation is cytoplasmic incompatibility (CI), causing embryonic death in crosses between infected males and uninfected females, or between individuals carrying distinct incompatible Wolbachia. CI patterns are highly complex in the mosquito Culex pipiens, where the causal genes cidA and cidB are amplified and diversified, forming a "cid repertoire" within each Wolbachia wPip genome. Despite their central role in CI, the genomic mechanisms underlying such cid amplification and diversification remained poorly understood. This knowledge gap is largely due to the difficulty of assembling wPips genomes due to highly repeated genes and mobile elements, especially in WO prophages. Here, we directly annotated Illumina polished Nanopore-sequences to investigate the genomic flanking context of cid genes in three distinct wPip lineages. We assembled WO prophage regions of substantial length containing the entire cid repertoire previously described in these bacterial lineages. Within these WO regions, cid genes are consistently embedded in modular and rearrangeable islands composed of MutL, rnhA, and small mobile elements, all displaying hyperconserved nucleotide identity across islands. These genomic islands are probably drivers for major rearrangement and recombination events responsible for the amplification and diversification of cidwPip genes within and between the wPip genomes leading to CI complexity in C. pipiens.

evolutionary biology↗
bioRxiv2025

Recombination, truncation and horizontal transfer shape the diversity of cytoplasmic incompatibility patterns

Wolbachia are endosymbiotic bacteria inducing various reproductive manipulations of which cytoplasmic incompatibility (CI) is the most common. CI leads to reduced embryo viability in crosses between males carrying Wolbachia and uninfected females or those carrying an incompatible symbiont strain. In the mosquito Culex pipiens, the Wolbachia wPip causes highly complex crossing patterns. This complexity is linked to the amplification and diversification of the CI causal genes, cidA and cidB, with polymorphism located in the CidA-CidB interaction regions. We previously showed correlations between the identity of gene variants and CI patterns. However, these correlations were limited to specific crosses, and it is still unknown whether cid gene polymorphism in males and females Wolbachia can explain and predict the wide range of crossing types observed in C. pipiens. Taking advantage of a new method enabling full-gene acquisition, we sequenced complete cid repertoires from 45 wPip strains collected worldwide. We demonstrated that the extensive diversity of cid genes arises from recombination and horizontal transfers. We uncovered further cidB polymorphism outside the interface regions and strongly correlated with CI patterns. Most importantly, we showed that in every wPip genome, all but one cidB variant are truncated. Truncated cidBs located in palindromes are partially or completely deprived of their deubiquitinase domain, crucial for CI. The identity of the sole full-length cidB variant seems to dictate CI patterns, irrespective of the truncated cidBs present. Truncated CidBs exhibit reduced toxicity and stability in Drosophila cells, which potentially hinders their loading into sperm, essential for CI induction.

evolutionary biology↗
bioRxiv2023

Intra-lineage microevolution of Wolbachia leads to the emergence of new cytoplasmic incompatibility patterns

Mosquitoes of the Culex pipiens complex are worldwide vectors of arbovirus, filarial nematode, and avian malaria agents. In these hosts, the endosymbiotic bacteria Wolbachia induce cytoplasmic incompatibility (CI), that is, reduced embryo viability in so-called incompatible crosses. Wolbachia infecting Culex pipiens (wPip) cause CI patterns of unparalleled complexity, associated with the amplification and diversification of cidA and cidB genes, with up to six different gene copies described in a single wPip genome. By repeating crosses between Culex isofemale lines over 17 years, we documented the emergence of a new compatibility type. Using a new sequencing method adapted to multigene families to acquire cid genes, we showed that some wPip genomes lost specific cidA gene copies, thus giving rise to several sub-lineages segregating in the same cage. By linking phenotypic changes to their underlying genotypic bases, we showed that gene copies that are key for CI phenotypes originated from recombinations, not point mutations. We revealed how new CI patterns could emerge as part of a two-step process: first, local changes take place in the CI repertoires while maintaining compatibility with the surrounding mosquitoes, and then migration and secondary contact occur with the incompatible lines.

evolutionary biology↗
bioRxiv2022

Nanopore sequencing enables multigenic family reconstruction despite highly frequent PCR-induced recombination

This study developed a new bioinformatics pipeline to acquire all the different copies of multi-copy gene families based on Oxford Nanopore Technologies sequencing of PCR products. We used this pipeline to acquire the sequences of highly similar copies of the cidA and cidB genes present in the genomes of Wolbachia pipientis (wPip) bacteria infecting the cells of Culex pipiens mosquitoes. The approach is based on read mapping, SNP calling and haplotyping, using our already wide existing reference database for the cid genes obtained by cloning and Sanger sequencing. We addressed problems commonly faced when using mapping approaches for multi-copy gene families with highly similar variants (or haplotypes). In addition, we confirmed that PCR amplification causes frequent chimeras which have to be carefully considered when working on families of recombinant genes. We tested the robustness of the pipeline through a combination of analyses of simulated reads and of gene sequence acquisitions through cloning and Sanger sequencing. For genes of which the haplotype cannot be reconstructed from short reads sequencing, this pipeline confers a high throughput acquisition, gives reliable results as well as insights of the relative copy numbers of the different variants.

genomics↗
bioRxiv2022

Emergence and clonal expansion in Europe of Vibrio aestuarianus lineages pathogenic for oysters

Crassostrea gigas oysters represent a significant global food source, with 4.7 million tons harvested per year. In 2001, the bacterium V. aesturianus francensis emerged as a pathogen that causes adult oyster mortality in France and Ireland. Its impact on oyster aquaculture has increased in Europe since its reemergence in 2012. To better understand the evolutionary mechanisms leading to the emergence and persistence over time of this pathogen, we conducted a survey of mollusk diseases through national reference laboratories (NRLs) across Europe. We analyzed 54 new genomes of V. aestuarianus (Va) isolated from multiple environmental compartments since 2001, in areas with and without bivalve mortalities. We used a combination of comparative genomics and population genetics approaches to show that Va francensis lineages have undergone clonal expansion in Europe, likely after a recent selective bottleneck. Low mutation and recombination rates may have selected particular virulent genotypes. Furthermore, we identified a specific cus-cop-containing island conferring copper resistance to Va francensis whose acquisition may have favored the emergence of pathogenic lineages adapted to oysters.

microbiology↗
bioRxiv2021

The mosquito microbiome includes habitat-specific but rare symbionts

Microbial communities are known to influence mosquito lifestyles by modifying essential metabolic and behavioral processes that affect reproduction, development, immunity, digestion, egg survival, and ability to transmit pathogens. Many studies have used 16S rRNA gene amplicons to characterize mosquito microbiota and investigate factors that influence host-microbiota dynamics. However, a relatively low taxonomic resolution due to clustering methods based on arbitrary threshold and the overall dominance of Wolbachia or Asaia populations obscured the investigation of rare members of mosquito microbiota in previous studies. Here, we used high resolution Shannon entropy-based oligotyping approaches to analyze the microbiota of Culex pipiens, Culex quinquefasciatus and Aedes individuals from continental and overseas regions in Southern France and Guadeloupe as well as from laboratories with or without antibiotics treatment. Our experimental design that resulted in a series of mosquito samples with a gradient of Wolbachia density and relative abundance along with high-resolution analyses of amplicon sequences enabled the recovery of a robust signal from typically less accessible bacterial taxa. Our data confirm species-specific mosquito-bacteria associations with geography as a primary factor that influences bacterial community structure. But interestingly, they also reveal co-occurring symbiotic bacterial variants within single individuals for both Elizabethkingia and Erwinia genera, distinct and specific Asaia and Chryseobacterium in continental and overseas territories and a putative rare Wolbachia variant. Overall, our study reveals the presence of previously-overlooked microdiversity and multiple closely related symbiotic strains within mosquito individuals with a remarkable habitat-specificity.

microbiology↗
bioRxiv2018

Sharing cells with Wolbachia: the transovarian vertical transmission of Culex pipiens densovirus

Originality-Significance StatementThis contribution provides a window into the study of a densovirus called CpDV infecting Culex pipiens mosquitoes. The originality of the study lies in the fact that CpDV, a DNA virus, was to date almost unstudied, its interaction with its hosts and its transmission mode were unknown. Considering that all Cx. pipiens are infected with Wolbachia, we studied the influence of this bacterial endosymbiont on CpDV density and transmission. Although Wolbachia-RNA virus interactions, especially in non-native Wolbachia-host associations have been widely studied, Wolbachia-DNA virus interactions were rarely investigated.\n\nIn this natural tripartite Cx. pipiens-Wolbachia-CpDV system: O_LIWe revealed the wide prevalence of CpDV, mostly at low densities, in Cx. pipiens laboratory lines.\nC_LIO_LIWe monitored CpDV presence in several cell types in ovaries including the oocytes where they co-exist with the bacterial endosymbiont Wolbachia.\nC_LIO_LIWe demonstrated that CpDV density in ovaries was influenced by Wolbachia presence and strain variations\nC_LIO_LIWe studied CpDV vertical transmission depending on Wolbachia presence and strain variations\nC_LI\n\nWe report for the first time the occurrence of widely distributed covert CpDV infections in Cx. pipiens laboratory colonies. CpDV is maintained by both vertical and horizontal transmission and under the influence of the vertically transmitted bacterial endosymbiont Wolbachia. Taken together our results suggest that CpDV could be very prevalent in nature putatively influencing natural Cx. pipiens populations dynamics.\n\nSUMMARYCulex pipiens densovirus (CpDV), a single stranded DNA virus, has been isolated from Culex pipiens mosquitoes but differs from other mosquito densoviruses in terms of genome structure and sequence identity. Its transmission from host to host, the nature of its interactions with both its host and hosts endosymbiotic bacteria Wolbachia are not known. Here we report the presence of CpDV in the ovaries and eggs of Cx. pipiens mosquitoes in close encounters with Wolbachia. In the ovaries, CpDV quantity significantly differed between mosquito lines harboring different strains of Wolbachia and these differences were not linked to variations in Wolbachia densities. CpDV was vertically transmitted in all laboratory lines to 17%-20% of the offspring. For some females, however, the vertical transmission reached 90%. Antibiotic treatment that cured the host from Wolbachia also significantly affected both CpDV quantity and vertical transmission suggesting an impact of host microbiota, including Wolbachia, on CpDV transmission. Overall our results show that CpDV is transmitted vertically via transovarian path along with Wolbachia with which it shares the same cells. Our results are primordial to understand the dynamics of densovirus infection, their persistence and spread in populations considering their potential use in the regulation of mosquito vector populations.

microbiology↗