Fungal Epidemics Research Articles

A Review to Search Novel Antifungal Principles from Bioactive Plants: The Hidden Treasure

Now–a-days, fungal infections of the skin are very common in Bangladesh as like as the other countries in the world. Surprisingly, these infections have become very difficult to treat and cure permanently. We know that, skin takes part in many vital functions of the body as it is the largest organ. It maintains the temperature & salt-water balance and protects the internal organs from the external noxious environment. It is also involved in synthesis and excretion of many vital constituents of the body. Damage to the skin by various noxious stimuli like burns, injuries or infections are major concerns in Dermatology. At present, most of the health care providers in Bangladesh are facing serious problems due to the emergence of resistance to available anti-fungal drugs. The nature is considered as the hidden treasure of medicines. Innumerable natural compounds are used worldwide due to their acceptable margin of efficacy, safety & cost. The present review is involved to find out 24 (twenty four) bioactive plants used in rural Bangladesh as folklore medicines to treat various skin diseases including the fungal ones. Further researches are recommended immediately to identify, separate and assess the antifungal efficacy of bioactive principles present in these plants. Successful screening of the resistant fungal strains and their interaction with these bioactive compounds would also be an interesting era of study. Hopefully, the most promising compounds would be developed as newer medicines and manufactured commercially to combat the increasing burden of fungal epidemics. KYAMC Journal Vol. 13, No. 02, July 2022: 115-119

Virulent Disease Epidemics Can Increase Host Density by Depressing Foraging of Hosts.

AbstractAll else equal, parasites that harm host fitness should depress densities of their hosts. However, parasites that alter host traits may increase host density via indirect ecological interactions. Here, we show how depression of foraging rate of infected hosts can produce such a hydra effect. Using a foraging assay, we quantified reduced foraging rates of a zooplankton host infected with a virulent fungal parasite. We then parameterized a dynamical model of hosts, parasites, and resources with this foraging function, showing how foraging depression can create a hydra effect. Mathematically, the hydra arose when increased resource productivity exceeded any increase in resource consumption per host. Therefore, the foraging-mediated hydra effect more likely emerged (1) for hosts that strongly control logistic-like resources and (2) during larger epidemics of moderately virulent parasites. We then analyzed epidemics from 13 fungal epidemics in nature. We found evidence for a foraging-mediated hydra effect: large outbreaks depressed foraging rate and correlated with increased densities of both algal resources and Daphnia hosts. Therefore, depression of the foraging rate of infected hosts can produce higher host densities even during epidemics of parasites that increase host mortality. Such hydras might prevent the collapse of host populations but also could produce higher densities of infected hosts.

Parasitoid chytridiomycete Ericiomyces syringoforeus gen. et sp. nov. has unique cellular structures to infect the host

Many fungi have been identified as pathogens of marine algae. Among them, Chytridiomycota have been revealed as relatively highly abundant, but much of the diversity known within these groups is almost entirely based on environmental sequencing data. Here, we present a novel chytridiomycete genus and species, characterized by light microscopical observations, ultrastructure, and molecular phylogenetic analysis of the parasitic chytrid of brackish-water dinoflagellate Kryptoperidinium foliaceum from the Baltic Sea. Phylogenetic analysis of rDNA sequences and the ultrastructure of the strain reveals that it represents a new family in the order Rhizophydiales. Ericiomyces syringoforeus gen. et sp. nov. is a parasitoid with a life cycle composed by zoospores, which attach to the host, encyst, and produce a rhizoidal system (haustorium). Unlike typical Rhizophydiales chytrids, sporangium develops as a lateral outgrowth of the encysted zoospore. The ultrastructural study revealed at least two unique traits: the syringe-like organelle in the cyst, which supposed to paralyze the host, and funnel-shaped structure anchoring sporangium in the host wall. Sporangium matures and produces new zoospores within 3 days. Multiple infections are common and then the life cycle is 1–2 days shorter compared to the duration when a single infection occurred. Cross-infection experiments showed that E. syringoforeus could only infect dinoflagellates, being K. foliaceum highly susceptible to infection by the chytrid parasitoid. The effects of some fungal epidemics on populations of Kryptoperidinium are discussed.

Population of tetranychidae mites on apple trees and methods of restraining the number of resistant races in crimea

Analysis of apple tree phytosanitary state showed that the species composition of phytophage mites is labile and is subject to a constant shift of the share ratio. In 2012-2013, the apple orchards of Crimea were dominated by Amphytetranychus viennensis Zacher. Its share in the acarocomplex was 80%. Since 2014, the ratio has changed towards prevalence of Panonychus ulmi Koch. - 50%. With this, share of A. viennensis decreased to 25.0%. In some years there was mass reproduction of Tetranychus turkestani Ug et Nik and Tetranychus urticae Koch. The number of phytophage mites during the growing season depends on a number of factors: settlement to new areas, interspecies competition, reduction of feed base, occurrence of fungal diseases epidemics, increase in the number of natural enemies. The dependence of the phytophage mites population density on the numerical value of hydrothermal moisture index (HMI) was established: the higher the average daily air temperature in the absence of precipitation, the higher the population on the leaf apparatus. Appearance of resistant P. ulmi races to five acaricides belonging to different chemical classes was established with the following active substances: spirodiclofen, fenpyroximate, pyridaben, fenazaquin, tebufenpyrad. A. viennensisshowed the appearance of acaricide-resistant races with active substances pyridaben and tebufenpyrad. In connection with the decrease in acaricide effectiveness against spider mites in the industrial apple tree plantations of Crimea, an anti-resistant protection strategy has been developed using predatory Phytoseiidae mites - Phytoseiulus persimilis Ath. - H, Neoseiulus californicus McGregor, Amblyseius andersoni Chant.

Within-host priority effects and epidemic timing determine outbreak severity in co-infected populations.

Co-infections of hosts by multiple pathogen species are ubiquitous, but predicting their impact on disease remains challenging. Interactions between co-infecting pathogens within hosts can alter pathogen transmission, with the impact on transmission typically dependent on the relative arrival order of pathogens within hosts (within-host priority effects). However, it is unclear how these within-host priority effects influence multi-pathogen epidemics, particularly when the arrival order of pathogens at the host-population scale varies. Here, we combined models and experiments with zooplankton and their naturally co-occurring fungal and bacterial pathogens to examine how within-host priority effects influence multi-pathogen epidemics. Epidemiological models parametrized with within-host priority effects measured at the single-host scale predicted that advancing the start date of bacterial epidemics relative to fungal epidemics would decrease the mean bacterial prevalence in a multi-pathogen setting, while models without within-host priority effects predicted the opposite effect. We tested these predictions with experimental multi-pathogen epidemics. Empirical dynamics matched predictions from the model including within-host priority effects, providing evidence that within-host priority effects influenced epidemic dynamics. Overall, within-host priority effects may be a key element of predicting multi-pathogen epidemic dynamics in the future, particularly as shifting disease phenology alters the order of infection within hosts.

Viscosin-like lipopeptides from frog skin bacteria inhibit Aspergillus fumigatus and Batrachochytrium dendrobatidis detected by imaging mass spectrometry and molecular networking

Amphibian populations worldwide have declined and in some cases become extinct due to chytridiomycosis, a pandemic disease caused by the fungus Batrachochytrium dendrobatidis; however, some species have survived these fungal epidemics. Previous studies have suggested that the resistance of these species is due to the presence of cutaneous bacteria producing antifungal metabolites. As our understanding of these metabolites is still limited, we assessed the potential of such compounds against human-relevant fungi such as Aspergillus. In this work we isolated 201 bacterial strains from fifteen samples belonging to seven frog species collected in the highlands of Panama and tested them against Aspergillus fumigatus. Among the 29 bacterial isolates that exhibited antifungal activity, Pseudomonas cichorii showed the greatest inhibition. To visualize the distribution of compounds and identify them in the inhibition zone produced by P. cichorii, we employed MALDI imaging mass spectrometry (MALDI IMS) and MS/MS molecular networking. We identified viscosin and massetolides A, F, G and H in the inhibition zone. Furthermore, viscosin was isolated and evaluated in vitro against A. fumigatus and B. dendrobatidis showing MIC values of 62.50 µg/mL and 31.25 µg/mL, respectively. This is the first report of cyclic depsipeptides with antifungal activity isolated from frog cutaneous bacteria.

Expression of a Structural Protein of the Mycovirus FgV-ch9 Negatively Affects the Transcript Level of a Novel Symptom Alleviation Factor and Causes Virus Infection-Like Symptoms in Fusarium graminearum.

Infections of fungi by mycoviruses are often symptomless but sometimes also fatal, as they perturb sporulation, growth, and, if applicable, virulence of the fungal host. Hypovirulence-inducing mycoviruses, therefore, represent a powerful means to defeat fungal epidemics on crop plants. Infection with Fusarium graminearum virus China 9 (FgV-ch9), a double-stranded RNA (dsRNA) chrysovirus-like mycovirus, debilitates Fusarium graminearum, the causal agent of fusarium head blight. In search for potential symptom alleviation or aggravation factors in F. graminearum, we consecutively infected a custom-made F. graminearum mutant collection with FgV-ch9 and found a mutant with constantly elevated expression of a gene coding for a putative mRNA-binding protein that did not show any disease symptoms despite harboring large amounts of virus. Deletion of this gene, named virus response 1 (vr1), resulted in phenotypes identical to those observed in the virus-infected wild type with respect to growth, reproduction, and virulence. Similarly, the viral structural protein coded on segment 3 (P3) caused virus infection-like symptoms when expressed in the wild type but not in the vr1 overexpression mutant. Gene expression analysis revealed a drastic downregulation of vr1 in the presence of virus and in mutants expressing P3. We conclude that symptom development and severity correlate with gene expression levels of vr1 This was confirmed by comparative transcriptome analysis, showing a large transcriptional overlap between the virus-infected wild type, the vr1 deletion mutant, and the P3-expressing mutant. Hence, vr1 represents a fundamental host factor for the expression of virus-related symptoms and helps us understand the underlying mechanism of hypovirulence.IMPORTANCE Virus infections of phytopathogenic fungi occasionally impair growth, reproduction, and virulence, a phenomenon referred to as hypovirulence. Hypovirulence-inducing mycoviruses, therefore, represent a powerful means to defeat fungal epidemics on crop plants. However, the poor understanding of the molecular basis of hypovirulence induction limits their application. Using the devastating fungal pathogen on cereal crops, Fusarium graminearum, we identified an mRNA binding protein (named virus response 1, vr1) which is involved in symptom expression. Downregulation of vr1 in the virus-infected fungus and vr1 deletion evoke virus infection-like symptoms, while constitutive expression overrules the cytopathic effects of the virus infection. Intriguingly, the presence of a specific viral structural protein is sufficient to trigger the fungal response, i.e., vr1 downregulation, and symptom development similar to virus infection. The advancements in understanding fungal infection and response may aid biological pest control approaches using mycoviruses or viral proteins to prevent future Fusarium epidemics.

Allocation, not male resistance, increases male frequency during epidemics: a case study in facultatively sexual hosts.

Why do natural populations vary in the frequency of sexual reproduction? Virulent parasites may help explain why sex is favored during disease epidemics. To illustrate, we show a higher frequency of males and sexually produced offspring in natural populations of a facultative parthenogenetic host during fungal epidemics. In a multi-year survey of 32 lakes, the frequency of males (an index of sex) was higher in populations of zooplankton hosts with larger epidemics. A lake mesocosm experiment established causality: experimental epidemics produced a higher frequency of males relative to disease-free controls. One common explanation for such a pattern involves Red Queen (RQ) dynamics. However, this particular system lacks key genetic specificity mechanisms required for the RQ, so we evaluated two other hypotheses. First, individual females, when stressed by infection, could increase production of male offspring vs. female offspring (a tenant of the "Abandon Ship" theory). Data from a life table experiment supports this mechanism. Second, higher male frequency during epidemics could reflect a purely demographic process (illustrated with a demographic model): males could resist infection more than females (via size-based differences in resistance and mortality). However, we found no support for this resistance mechanism. A size-based model of resistance, parameterized with data, revealed why: higher male susceptibility negated the lower exposure (a size-based advantage) of males. These results suggest that parasite-mediated increases in allocation to sex by individual females, rather than male resistance, increased the frequency of sex during larger disease epidemics.

Crop Fertilization Impacts Epidemics and Optimal Latent Period of Biotrophic Fungal Pathogens.

Crop pathogens are known to rapidly adapt to agricultural practices. Although cultivar resistance breakdown and resistance to pesticides have been broadly studied, little is known about the adaptation of crop pathogens to fertilization regimes and no epidemiological model has addressed that question. However, this is a critical issue for developing sustainable low-input agriculture. In this article, we use a model of life history evolution of biotrophic wheat fungal pathogens in order to understand how they could adapt to changes in fertilization practices. We focus on a single pathogen life history trait, the latent period, which directly determines the amount of resources allocated to growth and reproduction along with the speed of canopy colonization. We implemented three fertilization scenarios, corresponding to major effects of increased nitrogen fertilization on crops: (i) increase in nutrient concentration in leaves, (ii) increase of leaf lifespan, and (iii) increase of leaf number (tillering) and size that leads to a bigger canopy size. For every scenario, we used two different fitness measures to identify putative evolutionary responses of latent period to changes in fertilization level. We observed that annual spore production increases with fertilization, because it results in more resources available to the pathogens. Thus, diminishing the use of fertilizers could reduce biotrophic fungal epidemics. We found a positive relationship between the optimal latent period and fertilization when maximizing total spore production over an entire season. In contrast, we found a negative relationship between the optimal latent period and fertilization when maximizing the within-season exponential growth rate of the pathogen. These contrasting results were consistent over the three tested fertilization scenarios. They suggest that between-strain diversity in the latent period, as has been observed in the field, may be due to diversifying selection in different cultural environments.

Nutritional effects on the mycelial growth and enzymatic activity of Isaria farinosa, and Hepialus larvae growth.

To investigate the nutritional requirements of the mycelial growth and pathogenesis-related enzymatic activity on Isaria farinosa and the nutritional effect of fungus on its host Hepialus larvae. Sixteen carbon sources, 16 nitrogen sources and 9 vitamin combinations were tested. The nutritional conditions that significantly prevented I.farinosa pathogenesis were selected as feed additives for rearing Hepialus larvae. Citric acid significantly inhibited the growth of I.farinosa and the activity of three enzymes. l-histidine and l-aspartic acid significantly reduced the dry weights of mycelia and their protease and lipase activities. Vitamin combination that lacked VB 1 significantly increased the growth of I.farinosa and enhanced its chitinase and lipase activities. l-aspartic acid, VB 1 or a combination of them were beneficial for maintaining the larvae survival rate and decreasing the disease rate. The result provides new insight to develop a nutrition-based strategy to control fungal epidemics during insect rearing. The ability of some specific nutrients to inhibit mycelial growth and enzymatic activity can prevent epidemics of fungal disease. These results will aid in the development of nutrition-based strategies to control entomopathogenic fungal epidemics during the large-scale rearing of insects.

A set of software components for the simulation of plant airborne diseases

Models to evaluate the impact of plant diseases on crop production under current and future climatic conditions are increasingly requested by different stakeholders. This paper presents four software components – InoculumPressure, DiseaseProgress, ImpactsOnPlants, AgromanagementDisease – which implement models to simulate the dynamics of generic polycyclic fungal epidemics and interactions with crop physiological processes. The software architecture adopted allows extending the components with alternate approaches to reproduce specific pathosystems or compare predictive capabilities. As proofs of concept, (i) the components are coupled with two crop simulators to reproduce wheat brown rust and rice blast epidemics and their impacts on leaf area and yield formation; (ii) spatially distributed sensitivity analyses are performed for rice in China and wheat in Europe to investigate model behaviour; (iii) a preliminary evaluation against observations of rice blast severity is performed in Northern Italy. The components are explicitly targeted to the modelling of crop–pathogen interactions to perform scenario analysis.

Resources, key traits and the size of fungal epidemics in Daphnia populations.

Parasites can profoundly affect host populations and ecological communities. Thus, it remains critical to identify mechanisms that drive variation in epidemics. Resource availability can drive epidemics via traits of hosts and parasites that govern disease spread. Here, we map resource-trait-epidemic connections to explain variation in fungal outbreaks (Metschnikowia bicuspidata) in a zooplankton host (Daphnia dentifera) among lakes. We predicted epidemics would grow larger in lakes with more phytoplankton via three energetic mechanisms. First, resources should stimulate Daphnia reproduction, potentially elevating host density. Secondly, resources should boost body size of hosts, enhancing exposure to environmentally distributed propagules through size-dependent feeding. Thirdly, resources should fuel parasite reproduction within hosts. To test these predictions, we sampled 12 natural epidemics and tracked edible algae, fungal infection prevalence, body size, fecundity and density of hosts, as well as within-host parasite loads. Epidemics grew larger in lakes with more algal resources. Structural equation modelling revealed that resource availability stimulated all three traits (host fecundity, host size and parasite load). However, only parasite load connected resources to epidemic size. Epidemics grew larger in more dense Daphnia populations, but host density was unrelated to host fecundity (thus breaking its link to resources). Thus, via energetic mechanisms, resource availability can stimulate key trait(s) governing epidemics in nature. A synthetic focus on resources and resource-trait links could yield powerful insights into epidemics.

A modelling framework to simulate foliar fungal epidemics using functional-structural plant models.

Sustainable agriculture requires the identification of new, environmentally responsible strategies of crop protection. Modelling of pathosystems can allow a better understanding of the major interactions inside these dynamic systems and may lead to innovative protection strategies. In particular, functional-structural plant models (FSPMs) have been identified as a means to optimize the use of architecture-related traits. A current limitation lies in the inherent complexity of this type of modelling, and thus the purpose of this paper is to provide a framework to both extend and simplify the modelling of pathosystems using FSPMs. Different entities and interactions occurring in pathosystems were formalized in a conceptual model. A framework based on these concepts was then implemented within the open-source OpenAlea modelling platform, using the platform's general strategy of modelling plant-environment interactions and extending it to handle plant interactions with pathogens. New developments include a generic data structure for representing lesions and dispersal units, and a series of generic protocols to communicate with objects representing the canopy and its microenvironment in the OpenAlea platform. Another development is the addition of a library of elementary models involved in pathosystem modelling. Several plant and physical models are already available in OpenAlea and can be combined in models of pathosystems using this framework approach. Two contrasting pathosystems are implemented using the framework and illustrate its generic utility. Simulations demonstrate the framework's ability to simulate multiscaled interactions within pathosystems, and also show that models are modular components within the framework and can be extended. This is illustrated by testing the impact of canopy architectural traits on fungal dispersal. This study provides a framework for modelling a large number of pathosystems using FSPMs. This structure can accommodate both previously developed models for individual aspects of pathosystems and new ones. Complex models are deconstructed into separate 'knowledge sources' originating from different specialist areas of expertise and these can be shared and reassembled into multidisciplinary models. The framework thus provides a beneficial tool for a potential diverse and dynamic research community.

Potassium stimulates fungal epidemics in Daphnia by increasing host and parasite reproduction

As natural enemies, parasites can dramatically harm host populations, and even catalyze their decline. Thus, identifying factors that promote disease spread is paramount. Environmental factors can drive epidemics by altering traits involved in disease spread. For example, nutrients (such as nitrogen and phosphorus) can stimulate reproduction of both hosts and parasites or alter rates of disease transmission by stimulating productivity and nutrition of food resources of hosts. Here, we demonstrate nutrient-trait-epidemic connections between the greatly understudied macronutrient potassium (K) and fungal disease (Metschnikowia bicuspidata) in a zooplankton host (Daphnia dentifera). In a three-year survey, epidemics grew larger in lakes with more potassium. In laboratory assays, potassium enrichment of low-K lake water enhanced both host and parasite reproduction. Parameterized with these data, a model predicted that potassium addition catalyzes disease spread. We confirmed this prediction with an experiment in large mesocosms (6000 L) in a low K-lake: potassium enrichment caused larger epidemics in replicated Daphnia populations. Consequently, the model--data combination mechanistically explained the field pattern and revealed a novel ecological role for the nutrient potassium. Furthermore, our findings highlight the need for further development of theory for nutrient limitation of epidemics. Such theory could help to explain heterogeneous eruptions of disease in space, connect these outbreaks to natural or anthropogenic enrichment of ecosystems, predict the ecological consequences of these outbreaks, and reveal novel strategies for disease management.

Chytrid infections and diatom spring blooms: paradoxical effects of climate warming on fungal epidemics in lakes

Summary1. We describe the dynamics of host–parasite interactions over a period of more than 30 years between the freshwater diatom Asterionella formosa and two highly virulent chytrid parasites (Rhizophydium planktonicum and Zygorhizidium planktonicum) in Lake Maarsseveen, The Netherlands. This period is characterised by a significant warming trend which is strongest in spring.2. The key spring event in lakes, the diatom bloom, was in many years dominated by Asterionella. We examine whether and how climate warming has affected the prevalence of infection in Asterionella by chytrids.3. In years with cold winters/early springs, a dense Asterionella bloom is followed by epidemic development of disease as high Asterionella densities greatly facilitate transmission of chytrid zoospores. This sequence of events is absent in milder winters.4. Earlier experimental studies have shown that the parasite is almost non‐infective at water temperatures below 3 °C, offering a disease‐free window of opportunity for growth of Asterionella. Climate warming has reduced periods in which water temperature remains <3 °C, narrowing the window of opportunity for uninfected growth. Consequently, Asterionella continuously suffers from infection, albeit at low levels.5. Population reduction as a result of low level infection allows other diatoms to take over as dominant species, possibly through priority effects.6. In mild winters, chytrid infections no longer reach epidemic levels, but remain at low prevalence since transmission is impaired at low host densities. Climate warming thus affects both host and parasite in intricate ways, with the host denied a bloom and consequently the parasite denied an epidemic.7. A shift from Asterionella to a mixed diatom community in years with mild winters may benefit the food web, because of the poor edibility of Asterionella, unless the numerous chytrid zoospores produced during epidemics significantly contribute to zooplankton nutrition.8. Our study demonstrates the potential complexity of climate change impacts on disease. A reduction in the likelihood of epidemic development of a virulent parasite would seem to be of great benefit to the host, but this was not the case. Unexpected, sometimes paradoxical consequences of climate change can be expected and suggest that the view of a ‘warmer hence sicker world’ may not always apply.

Wheat genes could help fight fungal epidemics

Wheat genes could help fight fungal epidemics

Quality matters: resource quality for hosts and the timing of epidemics

Epidemiologists increasingly realize that species interactions (e.g. selective predation) can determine when epidemics start and end. We hypothesize here that resource quality can also strongly influence disease dynamics: epidemics can be inhibited when resource quality for hosts is too poor and too good. In three lakes, resource quality for the zooplankton host (Daphnia dentifera) was poor when fungal epidemics (Metschnikowia bicuspidata) commenced and increased as epidemics waned. Experiments using variation in algal food showed that resource quality had conflicting effects on underlying epidemiology: high-quality food induced large production of infective propagules (spores) and high birth rate but also reduced transmission. A model then illustrated how these underlying correlations can inhibit the start of epidemics (when spore production/birth rate are too low) but also catalyse their end (when transmission becomes too low). This resource quality mechanism is likely to interface with other ones controlling disease dynamics and warrants closer evaluation.

Adaptation of the Fungal Parasite Zygorhizidium planktonicum During 200 Generations of Growth on Homogeneous and Heterogeneous Populations of Its Host, the Diatom Asterionella formosa1

We followed adaptation of the chytrid parasite Zygorhizidium planktonicum during 200 generations of growth on its host, the freshwater diatom Asterionella formosa, in a serial passage experiment. Evolution of parasite fitness was assessed both on a homogenous and heterogeneous host population, consisting of respectively a single new and ten different new host strains. These 10 host strains were genetically different and also varied in their initial susceptibility to the parasite. Parasite fitness increased significantly and rapidly on the new, genetically homogenous host population, but remained unaltered during 200 generations of growth on the heterogeneous host population. Enhanced parasite fitness was the result of faster and more efficient transmission, resulting in higher values of R0 (number of secondary infections). Consequently, parasites that evolved within the uniclonal host population infected significantly more of these hosts than did their ancestors. We thus provide experimental evidence for the widely held view that host genetic diversity restricts evolution of parasites and moderates their harmful effects. Genetically uniform host populations are not only at increased risk from fungal epidemics because they all share the same susceptibility, but also because new parasite strains are able to adapt quickly to new host environments and to improve their fitness.

Interactions between the bloom-forming dinoflagellate Peridinium gatunense and the chytrid fungus Phlyctochytrium sp.

Epidemic chytrid fungal infection of Peridinium gatunense, the major bloom-forming dinoflagellate in Lake Kinneret, Israel, is reported for the first time. The fungus, identified as Phlyctochytrium sp. based on morphological and life cycle characteristics, was first observed in December 2000. It rapidly developed into an epidemic, coinciding with a 1000-fold decline in Peridinium density within 9 days of the initial observation of the chytrid. In August 2001 a second fungal epidemic occurred, which was again associated with a Peridinium population crash. In 2002–2003 less dramatic fungal epidemics were recorded, infection prevalence was low and the Peridinium population did not crash. Laboratory experiments demonstrated that healthy Peridinium cells are not prone to fungal infection, mostly stressed or dead cells were infected. In other words, Phlyctochytrium is a saprophyte, possibly a facultative parasite of Peridinium. Probably another pathogen was responsible for the observed bloom crashes and the saprophytic Phlyctochytrium was a secondary parasite, infecting the already moribund cells. The emergence of fungal epidemics in Lake Kinneret could be interpreted as an early signal of ecosystem response to increasing anthropogenic stress.

WARMER DOES NOT HAVE TO MEAN SICKER: TEMPERATURE AND PREDATORS CAN JOINTLY DRIVE TIMING OF EPIDEMICS

Ecologists and epidemiologists worry that global warming will increase disease prevalence. These fears arise because several direct and indirect mechanisms link warming to disease, and because parasite outbreaks are increasing in many taxa. However, this outcome is not a foregone conclusion, as physiological and community-interaction-based mechanisms may inhibit epidemics at warmer temperatures. Here, we explore this thermal-community-ecology-based mechanism, centering on fish predators that selectively prey upon Daphnia infected with a fungal parasite. We used an interplay between a simple model built around this system's biology and laboratory experiments designed to parameterize the model. Through this data-model interaction, we found that a given density of predators can inhibit epidemics as temperatures rise when thermal physiology of the predator scales more steeply than that of the host. This case is met in our fish-Daphnia-fungus system. Furthermore, the combination of steeply scaling parasite physiology and predation-induced mortality can inhibit epidemics at lower temperatures. This effect may terminate fungal epidemics of Daphnia as lakes cool in autumn. Thus, predation and physiology could constrain epidemics to intermediate temperatures (a pattern that we see in our system). More generally, these results accentuate the possibility that warmer temperatures might actually enhance predator control of parasites.