Biology subjects

Ben-Ami, F.

Publications and source records attributed to Ben-Ami, F..

10 recordsLinked to original sources

bioRxiv2025

Counterproductive: coinfection of a water flea by a fungus and a microsporidium reduces the reproductive outputs of all parties.

Organisms are often coinfected by more than one parasite species. These coinfections can alter the fitness of both host and its coinfecting parasites. Changes in host fitness are usually estimated by comparing parasite virulence under coinfection to the virulence of each parasite under single infection. While many studies focus on host survival as proxies of virulence, virulence can be expressed via reduced host fecundity. Here, we studied the outcome of coinfection of water fleas (Daphnia magna) by two microparasitic species, the fungus Metschnikowia bicuspidata and the microsporidium Hamiltosporidium tvaerminnensis. We found that Metschnikowia expressed its virulence mainly via host mortality and Hamiltosporidium expressed it mainly via host reproduction. Despite their competitive interaction, indicated by their reduced spore production, both parasites were able to fully express their virulence during coinfection. Host survival was dominated by Metschnikowia while clutch-size was dominated by Hamiltosporidium. Furthermore, coinfected hosts experienced increased virulence that was manifested only by additional reduction in reproduction (less clutches were released). Our results demonstrate that focusing only on the survival component of host fitness can miss important outcomes of coinfections. Since reduced host fecundity is a common outcome of parasitism, the influence of coinfection on host reproduction deserves more attention.

evolutionary biology↗

bioRxiv2025

Light pollution affects the behavior and life history traits of aquatic invertebrates

Circadian rhythms regulate essential biological processes, including behavior, reproduction and survival, across diverse organisms. Disruptions to this cycle, whether through artificial light at night (ALAN) or reduced exposure to full-spectrum daylight, can interfere with biological processes and ultimately threaten biodiversity. This concern is growing as ALAN spreads beyond urban areas through streetlights and skyglow. Aquatic ecosystems, in which zooplankton play a key role as primary consumers as well as prey for higher trophic levels, are particularly vulnerable. Despite growing research on the impact of ALAN on some zooplankton, rotifers remain largely understudied. Here, we conducted two experiments to assess the effects of light on Brachionus species. The first experiment examined how different ALAN wavelengths influenced life history traits in three Brachionus species, while the second one investigated the attachment behavior of B. rubens on a Daphnia host under four light conditions. Our findings reveal that ALAN has strong but species-specific effects on rotifers. Green light enhanced survival and reproductive output in B. calyciflorus sensu stricto, while suppressed reproduction in B. fernandoi. In B. rubens, white light particularly altered reproductive patterns and attachment behavior. These results highlight the complex and species-specific impacts that ALAN has on rotifers, emphasizing the need for further research to fully understand its broader ecological consequences.

ecology↗

bioRxiv2025

The legacy of past heatwaves on 'off-host' parasite stages: Reduced infection risk and costs in the Daphnia-Pasteuria system

Heatwaves challenge our understanding of how environmental stressors reshape host-parasite interactions, particularly during the critical "off-host" stages of endoparasites. These stages, often dismissed as inert and unaffected by environmental changes, remain a black box in ecological research despite their key role in parasites life cycle. Here, we examined how heatwaves affect the infectivity and progression of infection of Pasteuria ramosa, a bacterial parasite of the planktonic crustacean Daphnia magna. In order to measure the respective influences of the bacterial genotype and the heatwaves, we exposed the off-host stages (=spores) from four genetically distinct parasite clones to three temperature regimes (20{degrees}C, 30{degrees}C, 40{degrees}C), and tested their subsequent effects on host and parasite traits. Heatwaves reduced parasite infectivity, regardless of parasite genotype. Intriguingly, heat-stressed spores induced genotype-specific shifts in their host: one host clone increased castration rates at higher temperatures, while others experienced moderate to dramatic declines. Furthermore, individuals exposed to heat-stressed spores that remained uninfected, exhibited enhanced survival, suggesting reduced costs of resistance against damaged parasite spores. This study provides insights into how heatwaves, endured only by the parasite, can modulate various aspects of host-parasite interactions, underlying the importance of the parasites environmental history in evolutionary ecology and epidemiology. Open Research StatementAll data and code supporting the results of this study are provided here: https://github.com/JustineBoutry/HeatwaveSpores

evolutionary biology↗

bioRxiv2025

Transcriptomic landscape reveals immunity related trade-offs in an invertebrate-fungal host-parasite system

O_LIBy exploiting host resources, parasites impose significant fitness costs onto their hosts, thereby affecting their population dynamics. Hosts, in turn, employ a series of mechanism to resist or tolerate parasitic infections. Unlike vertebrates, which possess a sophisticated immune system, invertebrates rely solely on innate immunity to combat pathogens. Despite over 50 years of research, the molecular basis of innate immunity in non-insect invertebrates remains limited. C_LIO_LIWe used the Daphnia magna - Metschnikowia bicuspidata host-parasite system to shed light on conserved immune responses among Daphnia species and parasite-driven immunological shifts. We examined the transcriptomic landscape across infected, exposed-uninfected and unexposed individuals and identified candidate genes that might be involved in the haemocyte recruitment. Additionally, we identified genes that might encode for reinforcement of the gut epithelium, and thus confer resistance to the parasite. C_LIO_LIWe measured life-history traits and observed that shifts correlated with immune activation. Specifically, exposed-uninfected individuals exhibited a delay in reproductive maturation, likely a direct effect of immune activation. However, these shifts appeared temporal, as animals compensated in total reproductive output over time. C_LIO_LIUnlike exposed-uninfected animals, infected individuals exhibited metabolic shifts that are indicative of host metabolic exhaustion. This metabolic reallocation aligns with the terminal investment hypothesis, where hosts facing high mortality risk divert resources from somatic maintenance to immediate reproduction in order to maximize fitness before death. C_LIO_LIOur findings provide novel insights into the molecular and physiological mechanisms underlying invertebrate immune responses and life-history trade-offs in the context of parasitic infections. C_LI

evolutionary biology↗

bioRxiv2025

Decoding host responses: How a freshwater invertebrate defends against a parasitic bacterium

Host-parasite interactions drive coevolutionary dynamics, often leading to reciprocal adaptations between hosts and parasites, a process known as the Red Queen arms race. While the molecular mechanisms underlying vertebrate and insect immune responses have been studied extensively, those of aquatic invertebrates remain unexplored, despite their critical role in ecosystem stability and aquaculture. Here, we use the Daphnia magna-Pasteuria ramosa system to investigate the hosts immune response and the molecular mechanisms underlying host-parasite interactions. We inoculated 800 D. magna hosts with 20,000 mature spores of P. ramosa and tracked the progression of infection by measuring the proportion of infected individuals and the developmental stages of the parasite at multiple time points post-inoculation (hereafter p.i.). RNA sequencing was performed at key infection phases, early (Cauliflower stage), mid (Cauliflower and Grape stages), and terminal (Cauliflower, Grape, and Mature spore stages), to capture gene expression changes linked to infection dynamics. Our transcriptomic analyses revealed key immune genes involved in host defense, including genes involved in Toll signaling pathways, thereby revealing significant changes in pathways related to immune function, host metabolism, and resource allocation. Our findings suggest that iron sequestration may serve as a host defense strategy to restrict parasite growth, representing a form of nutritional immunity. Furthermore, pathways associated with infection-induced phenotypic traits, such as somatic growth, red coloration, and castration, were significantly upregulated, underscoring the impact of the infection on host physiology. Taken together, these findings provide new insights into the interplay between hosts and parasites at a molecular level in an ecologically relevant system, advancing our understanding of infection strategies in aquatic invertebrates.

evolutionary biology↗

bioRxiv2024

Threes a crowd: The relationship among endoparasites, an epibiont and their Daphnia host

In freshwater communities, organisms interact in a variety of ways, including predation, competition and parasitism. Parasites are ubiquitous, playing an important role in shaping freshwater communities. Endoparasites live within internal organs of their host, while ectoparasites, also known as epibionts, are confined to the external part of the hosts body. We conducted a series of experiments to examine the relationship between endoparasites and epibionts using the crustacean Daphnia magna as host, the rotifer Brachionus rubens as epibiont and three species of endoparasites. First, we tested host preference of the epibiont between Daphnia infected by endoparasites and uninfected Daphnia. Epibiont were found to attach more to uninfected Daphnia than to Daphnia infected by the yeast Metschnikowia bicuspidata. On the other hand, epibionts attached more to Daphnia infected by the microsporidium Hamiltosporidium tvaerminnensis than to uninfected Daphnia. Second, we examined the effect of epibionts on the infection of Daphnia by endoparasites. Infection prevalence tended to be higher, though not significantly, in the presence of epibionts. For two of the endoparasites, M. bicuspidata and H. tvaerminnensis, infection intensity (i.e., parasite spore production) was higher in the presence of epibionts. The infection intensity of M. bicuspidata and the bacterium Pasteuria ramosa was affected by the time of death of the Daphnia (i.e., virulence). Finally, we examined the effects of endoparasites and epibionts on the survival and offspring production of the Daphnia. Both host survival and offspring production were negatively affected by the endoparasites, while epibionts did not seem to affect the fitness of their host.

ecology↗

bioRxiv2024

Genome-wide allele frequency changes reveal that dynamic metapopulations evolve differently

BackgroundTwo important characteristics of metapopulations are extinction- (re)colonization dynamics and gene flow between subpopulations. These processes can cause strong shifts in genome-wide allele frequencies that are generally not observed in "classical" (large, stable, panmictic) populations. Subpopulations founded by one or a few individuals, the so-called propagule model, are initially expected to show intermediate allele frequencies at polymorphic sites until natural selection and genetic drift drive allele frequencies toward a mutation-selection-drift equilibrium characterized by a negative exponential-like distribution of the site frequency spectrum (SFS). ResultsWe followed changes in SFS distribution in a natural metapopulation of the cyclically parthenogenetic pond-dwelling microcrustacean Daphnia magna using biannual pool-seq samples collected over a five-year period from 118 ponds occupied by subpopulations of known age. As expected under the propagule model, SFSs in newly founded subpopulations trended toward intermediate allele frequencies and shifted toward right skewed distributions as the populations aged. Immigration and subsequent hybrid vigor altered this dynamic. ConclusionsThe analysis of SFS dynamics is a powerful approach to understand evolution in metapopulations. It allowed us to disentangle evolutionary processes occurring in a natural metapopulation, where many subpopulations evolve in parallel. Thereby, stochastic processes like founder and immigration events lead to a pattern of subpopulation divergence, while genetic drift, leads to converging SFS distributions in the persisting subpopulations. The observed processes are well explained by the propagule model and highlight that metapopulations evolve differently from classical populations.

evolutionary biology↗

bioRxiv2023

The gems of the Middle-East: Unveiling the biodiversity of Monogonont rotifers in temporary waterbodies of Israel

Temporary ponds represent ecologically important habitats that support high species diversity and provide essential ecosystem services, particularly in certain countries surrounding the Mediterranean Sea, where natural lakes are scarce. Israel is located along the southeastern Mediterranean coast and features Mediterranean and arid climatic zones that vary in a variety of meteorological parameters. Temporary ponds are prevalent throughout Israel, including the Mediterranean coast, Mediterranean mountain (i.e., Galilee region), and arid climatic zones. These temporal ponds harbor diverse invertebrate communities that exhibit significant spatial and temporal variations. Among these communities, Monogonont rotifers are notably one of the most diverse and abundant groups. Despite their significant role in aquatic food webs, rotifers are often overlooked in environmental studies, likely due to their small size and difficulties associated with their taxonomy. Resilient resting eggs produced by Monogonont rotifers during periods of unsuitable environmental conditions serve as significant source of propagules that drive the recolonization of temporary ponds upon rehydration, thereby influencing the dynamics of the pond community and metacommunity organization. Here, we examined the diversity of Monogonont rotifers by rehydrating sediment from 30 temporary ponds across Israel. Our analysis identified 39 species, with 25 (64%) of them being reported for the first time in Israel. We found the highest diversity of Monogonont rotifers in the Mediterranean coast region, which is characterized by low altitude, long hydroperiod, and relatively low mean summer daily maximum temperature, while the lowest diversity was found in the Arid region which is characterized by high altitude, short hydroperiod, and high mean summer daily maximum temperature. Our findings suggest that altitude, hydroperiod and mean summer daily maximum temperature are important parameters associated with the observed biodiversity patterns. Our metacommunity analysis further revealed a small contribution of geographic distance (2%) and environmental factors (1%) in shaping rotifer metacommunities. We also found a significant positive correlation among community composition, environmental distance (i.e., Gowers distance) and geographic distance, possibly due to a linearity in the sampling set-up. Overall, our study highlights the importance of temporary ponds as significant habitats for diverse rotifer communities and emphasizes the need to further study "micro" invertebrate diversity in these unique ecosystems.

ecology↗

bioRxiv2021

Causation without correlation: parasite-mediated frequency-dependent selection and infection prevalence

Parasite-mediated selection is thought to maintain host genetic diversity for resistance. We might thus expect to find a strong positive correlation between host genetic diversity and infection prevalence across natural populations. Here we used computer simulations to examine host-parasite coevolution in 20 simi-isolated clonal populations across a broad range of values for both parasite virulence and parasite fecundity. We found that the correlation between host genetic diversity and infection prevalence can be significantly positive for intermediate values of parasite virulence and fecundity. But the correlation can also be weak and statistically non-significant, even when parasite-mediated frequency-dependent selection is the sole force maintaining host diversity. Hence correlational analyses of field populations, while useful, might underestimate the role of parasites in maintaining host diversity. Subject Area. Evolution

evolutionary biology↗

bioRxiv2018

Disentangling unspecific and specific transgenerational immune priming components inhost-parasite interactions

Exposure to a pathogen primes many organisms to respond faster or more efficiently to subsequent exposures. Such priming can be unspecific or specific, and has been found to extend across generations. Disentangling and quantifying specific and unspecific effects is essential for understanding the genetic epidemiology of a system. By combining a large infection experiment and mathematical modeling, we disentangle different transgenerational effects in the crustacean model Daphnia magna exposed to different strains of the bacterial parasite Pasteuria ramosa. In the experiments, we exposed hosts to a high-dose of one of three parasite strains, and subsequently challenged their offspring with multiple doses of the same or a different strain, i. e. homologously or heterogously. We find that exposure to Pasteuria decreases the susceptibility of a hosts offspring by approximately 50%. This transgenerational protection is not larger for homologous than for heterologous parasite challenges. Our work represents an important contribution not only to the analysis of immune priming in ecological systems, but also to the experimental assessment of vaccines. We present for the first time an inference framework to investigate specific and unspecific effects of immune priming on the susceptibility distribution of hosts -- effects that are central to understanding immunity and the effect of vaccines.\n\nAuthor summaryImmune memory is a feature of immune systems that forms the basis of vaccination. In opposition to textbook accounts, the ability to specifically remember previous exposures has been found to extend to invertebrates and shown to be able to be passed on from mother to off-spring, i. e. to be transgenerational. In this paper, we investigate the extent of this specificity in unprecedented detail in water fleas. We exposed water flea mothers to different strains of a bacterial pathogen and challenged their offspring with a wide range of doses of a strain that were either identical to (homologous) or different from (heterologous) the strain, to which the mother had been exposed. We find that, while exposure of the mother reduces the susceptibility of the offspring, this effect is not specific. This work outlines the limits of specific transgenerational immune memory in this invertebrate system.

ecology↗