Biology subjects

duneau, d.

Publications and source records attributed to duneau, d..

5 recordsLinked to original sources

bioRxiv2024

Sex-specific sub-lethal effects of low virulence entomopathogenic fungi may boost the Sterile Insect Technique

BACKGROUNDThe Sterile Insect Technique (SIT) is a species-specific method for controlling insect pests. Recent studies have explored the combination of SIT with entomopathogenic microorganisms, known as boosted-SIT, to enhance its effectiveness. This study aimed to evaluate the potential of the entomopathogenic fungi, Metarhizium anisopliae, in boosting the SIT for managing the oriental fruit fly, Bactrocera dorsalis. METHODSAdult flies from a laboratory population of B. dorsalis were inoculated with one of eight strains of M. anisopliae to assess fungus virulence in each sex. Ideally, boosted-SIT should minimally impact sterile males and reduce female fecundity maximally. A brief exposure to fungal spores was efficient to infect males, and for them to transmit the fungus to females when hosted together for 24 hours. RESULTSOur results showed significant variations in the mortality induced by the strains in males, but not in females that exhibited low mortality. Strains varied in their sub-lethal effects on female fecundity, with almost a two-fold variation among strains. Furthermore, strains that had the lowest virulence on males tended to reduce female fecundity the most. CONCLUSIONOur study brings a proof of concept that it is possible to leverage boosted- SIT using carefully selected pathogen strains and their sub-lethal effects on both the male and female fruit fly.

ecology↗

bioRxiv2021

A within-host infection model to explore tolerance andresistance

How are some individuals surviving infections while others die? The answer lies in how infected individuals invest into controlling pathogen proliferation and mitigating damage, two strategies respectively called resistance and disease tolerance. Pathogen within-host dynamics (WHD), influenced by resistance, and its connection to host survival, determined by tolerance, decide the infection outcome. To grasp these intricate effects of resistance and tolerance, we used a deterministic theoretical model where pathogens interact with the immune system of a host. The model describes the positive and negative regulation of the immune response, consider the way damage accumulate during the infection and predicts WHD. When chronic, infections stabilize at a Set-Point Pathogen Load (SPPL). Our model predicts that this situation can be transient, the SPPL being then a predictor of life span which depends on initial condition (e.g. inoculum). When stable, the SPPL is rather diagnostic of non lethal chronic infections. In lethal infections, hosts die at a Pathogen Load Upon Death (PLUD) which is almost independent from the initial conditions. As the SPPL, the PLUD is affected by both resistance and tolerance but we demonstrate that it can be used in conjunction with mortality measurement to distinguish the effect of disease tolerance from that of resistance. We validate empirically this new approach, using Drosophila melanogaster and the pathogen Providencia rettgeri. We found that, as predicted by the model, hosts that were wounded or deficient of key antimicrobial peptides had a higher PLUD, while Catalase mutant hosts, likely to have a default in disease tolerance, had a lower PLUD.

evolutionary biology↗

bioRxiv2020

Gut cancer increases the risk for Drosophila to be preyed upon by hunting spiders in the laboratory

Predators are thought to prey on individuals that are in poor physical condition, although the evidence supporting this is ambiguous. We tested if sick individuals where more predated using Drosophila melanogaster flies as manipulable preys. We asked whether hunting spiders, trapped from the wild, would selectively prey upon flies with compromised health (i.e. chronically infected or cancerous) versus healthy flies under laboratory conditions. Flies chronically infected with the bacterium Providencia rettgeri, a natural Drosophila pathogen, were not selectively preyed upon by jumping spiders. We strengthened and confirmed our finding with another hunting spider species, small wolf spiders. We discuss that this result supports the hypothesis that chronic infection is associated with reduced symptoms notably to avoid the potentially deadly consequences of host predation on pathogens. We then induced colon cancer in some of the flies and asked whether the presence of cancer led to selective predation; there is little evidence for this, even in vertebrates. As the cancer developed, the incidence of predation by jumping spiders on the afflicted flies increased. We conclude that disease can have different lethal consequences through predation, even in invertebrate species, and that cancer is a factor in selective predation. Our results may explain why early tumours, but not metastasized cancers, are commonly detected in organisms in the wild, as cancer bearing individuals are rapidly eliminated due to the strong selective pressure against them.

ecology↗

bioRxiv2020

Step-specific adaptation and trade-off over the course of an infection by GASP-mutation small colony variants

During an infection, parasites face a succession of challenges, each decisive for disease outcome. The diversity of challenges requires a series of parasite adaptations to successfully multiply and transmit from host to host. Thus, the pathogen genotypes which succeed during one step might be counter-selected in later stages of the infection. Using the bacteria Xenorhabdus nematophila and adult Drosophila melanogaster as hosts, we showed that such step-specific adaptations, here linked to GASP mutations in the X. nematophila master gene regulator lrp, exist and can trade-off with each other. We found that nonsense lrp mutations had lowered ability to resist the host immune response, while all classes of mutations in lrp were associated with a decrease in the ability to proliferate during early infection. We demonstrate that reduced proliferation of X. nematophila best explains diminished virulence in this infection model. Finally, decreased proliferation during the first step of infection is accompanied with improved proliferation during late infection, suggesting a trade-off between the adaptations to each step. Step-specific adaptations could play a crucial role in the chronic phase of infections in any diseases that show similar small colony variants (also known as SCV) to X. nematophila. ImportanceWithin-host evolution has been described in many bacterial diseases, and the genetic basis behind the adaptations stimulated a lot of interest. Yet, the studied adaptations are generally focused on antibiotic resistance, rarely on the adaptation to the environment given by the host, and the potential trade-off hindering adaptations to each step of the infection are rarely considered. Those trade-offs are key to understand intra-host evolution, and thus the dynamics of the infection. However, the understanding of these trade-offs supposes a detailed study of host-pathogen interactions at each step of the infection process, with for each step an adapted methodology. Using Drosophila melanogaster as host and the bacteria Xenorhabdus nematophila, we investigated the bacterial adaptations resulting from GASP mutations known to induce small colony variant (SCV) phenotype positively selected within-the-host over the course of an infection, and the trade-off between step-specific adaptations.

evolutionary biology↗

bioRxiv2020

Evolution of sperm morphology in Daphnia

AO_SCPLOWBSTRACTC_SCPLOWSperm is the most fundamental male reproductive feature. It serves the fertilization of eggs and evolves under sexual selection. Two components of sperm are of particular interest, their number and their morphology. Mode of fertilization is believed to be a key determinant of sperm length across the animal kingdom. External fertilization, unlike internal, favors small and numerous sperm, since sperm density is thinned out in the environment. Here, we study the evolution of sperm morphology in the genus Daphnia, where fertilization occurs in a receptacle, the brood pouch, where sperm can constantly be flushed out by a water current. Based on microscopic observations of sperm morphologies mapped on a phylogeny with 15 Daphnia and 2 outgroup species, we found that despite the internal fertilization mode, Daphnia have among the smallest sperm recorded, as would be expected with external fertilization. Despite being all relatively small compared to other arthropods, sperm length diverged at least twice, once within each of the Daphnia subgenera Ctenodaphnia and Daphnia. Furthermore, species in the latter subgenus also lost the ability of cell compaction by extracellular encapsulation and have very polymorphic sperm with long, and often numerous, filopodia. We discuss the different strategies that Daphnia evolved to achieve fertilization success in the females brood pouch.

evolutionary biology↗