Biology subjects

Vale, P. F.

Publications and source records attributed to Vale, P. F..

At least 19 recordsLinked to original sources

bioRxiv2026

Fine-scale behavioural dynamics separates adaptive sickness behaviour from injury and infection pathology

Animals commonly reduce activity during infection, but it remains unclear when such "sickness behaviours" reflect adaptive host regulation versus injury responses or pathogen-driven pathology. We combined high-resolution behavioural phenotyping with experimental partitioning of injury, immune stimulation, and live bacterial infection to dissect these effects in Drosophila melanogaster. Using an outbred fly population, we tracked individual locomotor activity at 1 minute resolution for 400 hours in males and females subjected to one of four treatments: unhandled control, septic injury with buffer, immune stimulation with heat killed Pseudomonas entomophila, or septic infection with live P. entomophila. Across the early post-challenge window, total activity diverged most strongly between the unhandled control and the challenged treatments. Fine-scale analyses revealed that immune challenge primarily reshaped the microstructure of movement: the number of activity bouts changed little, whereas active bout lengths were shorter and inactive periods were modestly prolonged, especially in females. Among infected flies, individuals that died early exhibited a collapse of bout structure, showing prolonged inactivity punctuated by brief, sometimes intense, movements, whereas longer-lived infected flies maintained patterns closer to controls. These behavioural differences were detectable in the very early stages of infection: within the first 24-hours post-infection early-dying flies had both a reduced probability of initiating movement from rest and a reduced probability of sustaining on-going activity, consistent with pathogen-induced debilitation; longer-lived infected flies showed near-normal state-transition profiles. This early suppression of activity in acutely dying males was positively associated with subsequent survival time, suggesting a contribution of adaptive restraint alongside pathology. By resolving fine-scale behaviour and state-transition dynamics, our approach clarifies which aspects of "sickness behaviour" are likely adaptive and which signal pathology.

animal behavior and cognition↗

bioRxiv2025

Detecting infection-related mortality using dynamical statistical indicators of high-resolution activity time series

Predicting transitions between health, disease, and death across biological systems remains an important challenge with significant implications for both ecological management and medical intervention. Although the principles underlying these transitions are increasingly recognised, accurate and tractable dynamical indicators of health-to-disease transitions remain rare, especially at the level of individual organisms. Here, we use dynamical statistical indicators of high-resolution activity time series to predict infection-related mortality. By analysing locomotor activity data from infected Drosophila melanogaster flies, we find that individual dynamical indicators, such as the mean, variance, autocorrelation, and permutation entropy, differed between flies that survived and those that died during the experiment. When these indicators were used to train a Random Forest model, the classifier performed well (AUC = 0.94), demonstrating an accuracy of 87.9% in discriminating between infected flies that would die from infection and those that would survive, with the strongest discriminatory power detected over 12 hours prior to death. Our findings show that combining these easy-to-compute, dynamical statistical indicators with machine learning enhances the ability to predict health deterioration in the Drosophila model. Conceptually, our findings emphasize that the integration of dynamical statistical metrics from physiological or behavioural time-series with machine learning approaches may offer a promising avenue for real-time health monitoring in both ecological and clinical settings. HighlightsO_LIHigh-resolution locomotor activity time series distinguish infected flies that live or die C_LIO_LISimple dynamical indicators (mean, SD, CV, lag-1 autocorrelation) jointly improve outcome discrimination C_LIO_LIPermutation entropy declines over time and is reduced in flies approaching acute infection-related death C_LIO_LIRandom Forest models classify infection survival outcomes with high accuracy (AUC 0.94) C_LIO_LIDivergence in activity dynamics is detectable over 12-16 hours before death in flies that succumb to infection C_LI

ecology↗

bioRxiv2024

Genetic variation in trophic avoidance shows fruit flies are generally attracted to bacterial pathogens

Pathogen avoidance behaviours are often assumed to be an adaptive host defence from infection. However, there is limited experimental data on the prerequisite for this assumption: heritable, intrapopulation phenotypic variation for avoidance. We investigated trophic pathogen avoidance in 122 inbred Drosophila melanogaster lines, and in a derived outbred population. Using the FlyPAD system, we tracked the feeding choice that flies made between substrates that were either clean or contained a bacterial pathogen. We uncovered significant, but weakly heritable variation in the preference index among fly lines. However, instead of avoidance, most lines demonstrated a preference for several bacterial pathogens, showing avoidance only for extremely high bacterial concentrations. Bacterial preference was not associated with susceptibility to infection and was retained in flies with disrupted immune signalling. Phenotype-genotype association analysis indicated several novel genes (CG2321, CG2006, ptp99A) associated with increased preference for the bacterial substrate, while the amino-acid transporter sobremesa was associated with greater aversion. Together with previous work showing fitness benefits of consuming high-protein diets, our results suggest that bacterial attraction may instead reflect a dietary preference for protein over carbohydrate. More work quantifying intrapopulation variation in avoidance behaviours is needed to fully assess its importance in host-pathogen evolutionary ecology.

ecology↗

bioRxiv2024

Mitochondrial genome variation affects humoral and cell-mediated innate immune responses and infection outcomes

The role of mitochondria in both adaptive and innate immune responses is increasingly recognized, but the role of mitochondrial DNA (mtDNA) variation as an immunomodulatory factor has received less attention. One reason for this is the difficulty of separating the effect of mtDNA from that of the nuclear genome. By utilizing the fruit fly Drosophila melanogaster, a powerful model system, we created cytoplasmic hybrids, aka. cybrid lines, where unique mtDNAs (mitotypes) were introgressed into a controlled isogenic nuclear background. We harnessed a panel of cybrid lines to study the effect of mtDNA variation on humoral and cell-mediated innate immune responses. Mitotypes exhibited heterogeneity in infection outcomes upon bacterial, viral and parasitoid infections. One mitotype of note (mtKSA2) was more immunocompetent when compared to other mitotypes. We performed transcriptomic profiling of uninfected and infected flies to find the mechanistic basis of the immunocompetence of the mtKSA2 line. We found that in uninfected flies mtKSA2 caused an upregulation of oxidative phosphorylation (OXPHOS) and tricarboxylic acid cycle (TCA) related genes and a downregulation of a set of antimicrobial peptides (AMPs). Upon infection, mtKSA2 flies produced transcriptomic changes that were infection type and duration specific. When we examined immune cells (hemocytes) in mtKSA2 larvae, we noted an increase in hemocyte numbers. These hemocytes were activated in the absence of infection, increased their production of ROS, and showed evidence of increased encapsulation efficiency upon parasitoid wasp infection. Overall, our results show that mtDNA variation acts as an immunomodulatory factor in both humoral and cell-mediated innate immunity and that specific mitotypes can provide enhanced protection against various infections.

immunology↗

bioRxiv2023

Mitochondrial background can explain variable costs of immune deployment

Organismal health and survival depend on the ability to mount an effective immune response against infection. Yet, immune defence may be energy-demanding, resulting in fitness costs if investment in immune function deprives other physiological processes of resources. While evidence of costly immunity resulting in reduced longevity and reproduction is common, the role of energy-producing mitochondria on the magnitude of these costs is unknown. Here we employed Drosophila melanogaster cybrid lines, where several mitochondrial genotypes (mitotypes) were introgressed onto a single nuclear genetic background, to explicitly test the role of mitochondrial variation on the costs of immune stimulation. We exposed female flies carrying one of nine distinct mitotypes to either a benign, heat-killed bacterial pathogen (stimulating immune deployment while avoiding pathology), or to a sterile control, and measured lifespan, fecundity, and locomotor activity. We observed mitotype-specific costs of immune stimulation and identified a positive genetic correlation between lifespan and the proportion of time cybrids spent moving while alive. Our results suggests that costs of immunity are highly variable depending on the mitochondrial genome, adding to a growing body of work highlighting the important role of mitochondrial variation in host-pathogen interactions.

evolutionary biology↗

bioRxiv2023

The immune regulation and epidemiological consequences of immune priming in Drosophila

Invertebrates lack the immune machinery underlying vertebrate-like acquired immunity. However, in many insects past infection by the same pathogen can prime the immune response, resulting in improved survival upon reinfection. Here, we investigated the generality, specificity and mechanistic basis of innate immune priming in the fruit fly Drosophila melanogaster when infected with the gram-negative bacterial pathogen Providencia rettgeri. We find that priming in response to P. rettgeri infection is a long-lasting and pathogen-specific response. We further explore the epidemiological consequences of immune priming and find it has the potential to curtail pathogen transmission by reducing pathogen shedding and spread. The enhanced survival of individuals previously exposed to a non-lethal bacterial inoculum coincided with a transient decrease in bacterial loads, and we provide strong evidence that the effect of priming requires the IMD-responsive antimicrobial-peptide Diptericin-B in the fat body. Further, we show that while Diptericin B is the main effector of bacterial clearance, it is not sufficient for immune priming, which requires regulation of IMD by peptidoglycan recognition proteins. This work underscores the plasticity and complexity of invertebrate responses to infection, providing novel experimental evidence for the effects of innate immune priming on population-level epidemiological outcomes.

immunology↗

bioRxiv2022

Mitochondrial perturbations enhance cell-mediated innate immunity in Drosophila

Withdrawal StatementThe authors have withdrawn version 2 of this manuscript due to the erroneous revision with a related but different manuscript, which can now be found under doi: 10.1101/2024.03.28.587162. Note that version 1 of this preprint is correct and has now been published as doi: 10.1186/s12915-024-01858-5, which should be used for citation purposes. If you have any questions, please contact the corresponding author (Tiina S. Salminen, tiina.s.salminen@tuni.fi).

immunology↗

bioRxiv2022

Ageing leads to nonspecific antimicrobial peptide responses in Drosophila melanogaster

Evolutionary theory predicts a late-life decline in the force of natural selection, possibly leading to late-life deregulations of the immune system. A potential outcome of such immune-deregulation is the inability to produce specific immunity against target pathogens. We tested this possibility by infecting multiple Drosophila melanogaster lines (with bacterial pathogens) across age-groups, where either individual or different combinations of Imd- and Toll-inducible antimicrobial peptides (AMPs) were deleted using CRISPR gene editing. We show a high degree of non-redundancy and pathogen-specificity of AMPs in young flies: in some cases, even a single AMP could confer complete resistance. In contrast, ageing led to a complete loss of such specificity, warranting the action of multiple AMPs across Imd- and Toll-pathways during infections. Moreover, use of diverse AMPs either had no survival benefits, or even accompanied survival costs post-infection. These features were also sexually dimorphic: females expressed a larger repertoire of AMPs than males, but extracted equivalent survival benefits. Finally, age-specific expansion of the AMP-pool was associated with downregulation of negative-regulators of the Imd-pathway and a potential damage to renal function, as features of poorly-regulated immunity, Overall, we could establish ageing as an important driver of nonspecific AMP responses, across sexes and bacterial infections.

immunology↗

bioRxiv2022

The restriction factor pastrel is associated with host vigor, viral titer, and variation in disease tolerance during Drosophila C Virus infection

Genetic variation for both resistance and disease tolerance has been described in a range of species infected with bacterial, viral and fungal pathogens. In Drosophila melanogaster, genetic variation in mortality following systemic Drosophila C Virus (DCV) infection has been shown to be driven by large effect polymorphisms in the viral restriction factor pastrel (pst). However, it is unclear if pst impacts variation in DCV titres (i.e. resistance), or if it also contributes to disease tolerance. We investigated systemic infection across a range of DCV challenge doses spanning nine orders of magnitude, in males and females of ten Drosophila Genetic Reference Panel (DGRP) lines carrying either a susceptible (S) or resistant (R) pst allele. Our results uncover among-line variation in fly survival, viral titers, and disease tolerance measured both as the ability to maintain survival (mortality tolerance) and reproduction (fecundity tolerance). We confirm the role of pst in resistance, as fly lines with the resistant (R) pst allele experienced lower viral titers, and we uncover novel effects of pst on host vigor, as flies carrying the R allele exhibited higher survival and fecundity even in the absence of infection. Finally, we found significant variation in the expression of the JAK-STAT ligand upd3 and the epigenetic regulator of JAK-STAT G9a. While G9a has been previously shown to mediate tolerance of DCV infection, we found no correlation between the expression of either upd3 or G9a on fly tolerance or resistance. Our work highlights the importance of both resistance and tolerance in viral defence.

immunology↗

bioRxiv2022

Host and pathogen drivers of infection-induced changes in social aggregation behavior

Identifying how infection modifies host behaviours that determine social contact networks is important for understanding heterogeneity in infectious disease dynamics. Here, we investigate whether group social behaviour is modified during bacterial infection in Drosophila melanogaster, an established system for behavioural genetics, according to pathogen species, infectious dose, host genetic background and sex. We find that systemic infection with four different bacterial species results in a reduction in the mean pairwise distance within infected flies, and that the extent of this change depends on the infectious dose in a pathogen-specific way. In the presence of infected conspecifics, susceptible flies also tended to aggregate throughout time, but did not show any evidence of avoiding infected flies. We also observed genetic- and sex-based variation in social aggregation, with infected female flies aggregating more closely than infected males. In general, our results confirm that bacterial infection induces changes in fruit fly behaviour across a range of pathogen species, but also highlight that these effects vary between fly genetic backgrounds and can be sex-specific. We discuss possible explanations for sex differences in social aggregation and their consequences for individual variation in pathogen transmission.

animal behavior and cognition↗

bioRxiv2021

Mitonuclear interactions affect locomotor activity and sleep in Drosophila melanogaster

Mitochondria are organelles that produce cellular energy in the form of ATP through oxidative phosphorylation, and this primary function is conserved between many taxa. Locomotion is a trait that is highly reliant on metabolic function and expected to be greatly affected by disruptions to mitochondrial performance. To this end, we aimed to examine how activity and sleep vary between Drosophila melanogaster strains with different geographic origins, how these patterns are affected by mitochondrial DNA (mtDNA) variation, and how breaking up co-evolved mito-nuclear gene combinations affect the studied activity traits. The results demonstrate that Drosophila strains from different locations differ in sleep and activity, and the extent of variation differs between sexes, females in general being more active. By comparing activity and sleep of mtDNA variants introgressed onto a common nuclear background in cytoplasmic hybrid (cybrid) strains, we establish that mtDNA variation affects both traits, sex specifically. Furthermore, by using previously published mtDNA copy number data, we detected a positive correlation between mtDNA copy number and the activity levels of the cybrid flies. Altogether, our study shows that both mtDNA variation and mitonuclear interactions affect activity and sleep patterns, highlighting the important role that both genomes play on life-history trait evolution.

genetics↗

bioRxiv2021

Mechanisms of damage prevention, signalling, and repair impact the ability of Drosophila to tolerate enteric bacterial infection

The insect gut is frequently exposed to pathogenic threats and must not only clear these potential infections, but also tolerate relatively high microbe loads. In contrast to the mechanisms that eliminate pathogens, we currently know less about the mechanisms of disease tolerance. We investigated how well-described mechanisms that either prevent, signal, control, or repair damage during infection contribute to the phenotype of disease tolerance. We established enteric infections with the bacterial pathogen Pseudomonas entomophila in transgenic lines of Drosophila melanogaster fruit flies affecting dcy (a major component of the peritrophic matrix), upd3 (a cytokine-like molecule), irc (a negative regulator of reactive oxygen species) and egfr1 (epithelial growth factor receptor). Flies lacking dcy experienced the highest susceptibility, while loss of function of either irc or upd3 reduced tolerance in both sexes. The disruption of egfr1 resulted in a severe loss in tolerance in male flies but had no substantial effect on the ability of female flies to tolerate P. entomophila infection, despite carrying greater microbe loads than males. Together, our findings provide evidence for the role of damage limitation mechanisms in disease tolerance and highlight how sex differences in these mechanisms could generate sexual dimorphism in disease tolerance.

evolutionary biology↗

bioRxiv2021

Negative regulation of IMD contributes to disease tolerance during systemic bacterial infection in Drosophila

Disease tolerance is an infection phenotype where hosts show relatively high health despite harbouring elevated pathogen loads. Variation in the ability to reduce immunopathology may explain why some hosts can tolerate higher pathogen burdens with reduced pathology. Negative immune regulation would therefore appear to be a clear candidate for a mechanism underlying disease tolerance. Here, we examined how the negative regulation of the immune deficiency (IMD) pathway affects disease tolerance in Drosophila melanogaster when infected with four doses of the gram-negative bacterial pathogen Pseudomonas entomophila. We find that while flies unable to regulate the IMD response exhibited higher expression of antimicrobial peptides and lower bacterial loads as expected, this was not accompanied by a proportional reduction in mortality. Instead, UAS-RNAi knockdown of negative regulators of IMD (pirk and caudal) substantially increased the per-pathogen-mortality in both males and females across all tested infectious doses. Our results therefore highlight that in addition to regulating an efficient pathogen clearance response, negative regulators of IMD also contribute to disease tolerance.

evolutionary biology↗

bioRxiv2021

The Jak/Stat pathway mediates disease tolerance during systemic bacterial infection in Drosophila

Disease tolerance describes an infected hosts ability to maintain health independently of the ability to clear microbe loads. The Jak/Stat pathway plays a pivotal role in humoral innate immunity by detecting tissue damage and triggering cellular renewal, making it a candidate tolerance mechanism. Here, we find that in Drosophila melanogaster infected with Pseudomonas entomophila disrupting ROS-producing dual oxidase (duox) or the negative regulator of Jak/Stat Socs36E, render male flies less tolerant. Another negative regulator of Jak/Stat, G9a - which has previously been associated with variable tolerance of viral infections - did not affect the rate of mortality with increasing microbe loads compared to flies with functional G9a, suggesting it does not affect tolerance of bacterial infection as in viral infection. Our findings highlight that ROS production and Jak/Stat signalling influence the ability of flies to tolerate bacterial infection sex-specifically and may therefore contribute to sexually dimorphic infection outcomes in Drosophila.

evolutionary biology↗

bioRxiv2021

Epidemiological dynamics of viral infection in a marine pico-eukaryote

Ostreococcus tauri is a ubiquitous marine pico-eukaryote that is susceptible to lysis upon infection by its species specific Ostreococcus tauri viruses (OtVs). In natural populations of O. tauri, costs of resistance are usually invoked to explain the persistence or reappearance of susceptible individuals in resistant populations. Given the low costs of resistance measured in laboratory experiments with the O. tauri/OtV system to date, the question remains of why susceptible individuals persist in the wild at all. Epidemiological models of host and pathogen population dynamics are one useful approach to understand the conditions that can allow the coexistence of susceptible and resistant hosts. We used a SIR (Susceptible-Infected-Resistant) model to investigate epidemiological dynamics under different laboratory culturing regimes that are commonly used in the O.tauri/OtV system. When taking into account serial transfer (i.e. batchcycle lengths) and dilution rates as well as different resistance costs, our model predicts that no susceptible cells should be detected under any of the simulated conditions - this is consistent with laboratory findings. We thus considered an alternative model that is not used in laboratory experiments, but which incorporates one key process in natural populations: host populations are periodically re-seeded with new infective viruses. In this model, susceptible individuals re-occurred in the population, despite low costs of resistance. This suggests that periodic attack by new viruses, rather than (or in addition to) costs of resistance, may explain the high proportion of susceptible hosts in natural populations, and underlie the discrepancy between laboratory studies and observations of fresh isolates. ImportanceIn natural samples of Ostreococcus sp. and its associated viruses, susceptible hosts are common. However, in laboratory experiments, fully resistant host populations readily and irreversibly evolve. Laboratory experiments are powerful methods for studying process because they offer a stripped-down simplification of a complex system, but this simplification may be an oversimplification for some questions. For example, laboratory and field systems of marine microbes and their viruses differ in population sizes and dynamics, mixing or migration rates, and species diversity, all of which can dramatically alter process outcomes. We demonstrate the utility of using epidemiological models to explore experimental design and to understand mechanisms underlying host-virus population dynamics. We highlight that such models can be used to form strong, testable hypotheses about which key elements of natural systems need to be included in laboratory systems to make them simplified, rather than oversimplified, versions of the processes we use them to study.

microbiology↗

bioRxiv2020

Carry on caring: infected females maintain their level of parental care despite suffering high mortality

Parental care is a key component of an organisms reproductive strategy that is thought to trade-off with allocation towards immunity. Yet it is unclear how caring parents respond to pathogens: do infected parents reduce their amount of care as a sickness behaviour or simply from being ill, or do they prioritise their offspring by maintaining high levels of care? Here we explored the consequences of infection by the pathogen Serratia marcescens on mortality, time spent providing care, reproductive output, and expression of immune genes of female parents in the burying beetle Nicrophorus vespilloides. We compared untreated control females with infected females that were inoculated with live bacteria, immune-challenged females that were inoculated with heat-killed bacteria, and injured females that were injected with buffer. We found that infected and immune-challenged females mounted an immune response and that infected females suffered increased mortality. Nevertheless, infected and immune-challenged females maintained their normal level of care and reproductive output. There was thus no evidence that infection led to either a decrease or an increase in parental care or reproductive output. Our results show that parental care, which is generally highly flexible, can remain remarkably robust and consistent despite the elevated mortality caused by infection by pathogens. Overall, these findings suggest that infected females maintain a high level of parental care; a strategy that may ensure that offspring receive the necessary amount of care but that might be detrimental to the parents own survival or that may even facilitate disease transmission to offspring.

evolutionary biology↗

bioRxiv2019

Population-Level Disease Dynamics Reflect Individual Heterogeneities in Transmission

Host heterogeneity in disease transmission is widespread and presents a major hurdle to predicting and minimizing pathogen spread. Using the Drosophila melanogaster model system infected with Drosophila C virus, we integrate experimental measurements of individual host heterogeneity in social aggregation, virus shedding, and disease-induced mortality into an epidemiological framework that simulates outbreaks of infectious disease. We use these simulations to calculate individual variation in disease transmission and apportion this variation to specific components of transmission: social network degree distribution, infectiousness, and infection duration. The experimentally-observed variation produces substantial differences in individual transmission potential, providing evidence for genetic and sex-specific effects on disease dynamics at a population level. Manipulating variation in social network connectivity, infectiousness, and infection duration in simulated populations reveals that these components affect disease transmission in clear and distinct ways. We consider the implications of this genetic and sex-specific variation in disease transmission and discuss implications for appropriate control methods given the relative contributions made by social aggregation, virus shedding, and infection duration to transmission in other host-pathogen systems.

ecology↗

bioRxiv2019

Dissecting genetic and sex-specific host heterogeneity in pathogen transmission potential

Heterogeneity in disease transmission is widespread and, when not accounted for, can produce unpredictable outbreaks of infectious disease. Despite this, precisely how different sources of variation in host traits drive heterogeneity in disease transmission is poorly understood. Here we dissected the sources of variation in pathogen transmission using Drosophila melanogaster and Drosophila C Virus as a host-pathogen model system. We found that infected lifespan, viral growth, virus shedding, and viral load at death were all significantly influenced by fly genetic background, sex and female mating status. To understand how variation in each of these traits may generate heterogeneity in disease transmission, we estimated individual transmission potential by integrating data on virus shedding and lifespan alongside previously collected data on social aggregation. We found that [~]15% of between-individual heterogeneity in disease transmission was explained by a significant interaction between genetic and sex-specific variation. We also characterised the amount of variation in viral load, virus shedding, and lifespan following infection that could be explained by genetic background and sex. Amongst the determinants of individual variation in disease transmission these sources of host variation play roles of varying importance, with genetic background generally playing the largest role. Our results highlight the importance of characterising sources of variation in multiple host traits when studying disease transmission at the individual-level.

ecology↗