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Periods of low host density impose a constraint on parasites with direct transmission, challenging their permanence in the system. The microsporidium Octosporea bayeri faces such constraint in a metapopulation of its host, the cladoceran Daphnia magna, where ponds frequently lose their host population due to ponds drying out in summer and freezing...
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The symptoms of Anopheles aquasalis larvae naturally infected by a microsporidium, and the ultrastructure of the infecting spores is described. The larvae were maintained under laboratory conditions in salt concentrations of 10 g/l and 20 g/l of water. Daily recordings of the mortality of the larvae were made and the dates of change of instar were...
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... An enhanced drift of infected individuals is likely to benefit horizontally transmitted parasites by favoring spore dispersal. Although drift might result in spore dilution and limit cannibalism, many spores persist in the environment even in the absence of suitable hosts 86 . Depending on the microsporidian species, spores can be more or less resistant. ...
In lotic freshwater ecosystems, the drift or downstream movement of animals (e.g., macroinvertebrates) constitutes a key dispersal pathway, thus shaping ecological and evolutionary patterns. There is evidence that macroinvertebrate drift may be modulated by parasites. However, most studies on parasite modulation of host drifting behavior have focused on acanthocephalans, whereas other parasites, such as microsporidians, have been largely neglected. This study provides new insight into possible seasonal and diurnal modulation of amphipod (Crustacea: Gammaridae) drift by microsporidian parasites. Three 72 h drift experiments were deployed in a German lowland stream in October 2021, April, and July 2022. The prevalence and composition of ten microsporidian parasites in Gammarus pulex clade E varied seasonally, diurnally, and between drifting and stationary specimens of G. pulex. Prevalence was generally higher in drifting amphipods than in stationary ones, mainly due to differences in host size. However, for two parasites, the prevalence in drift samples was highest during daytime suggesting changes in host phototaxis likely related to the parasite’s mode of transmission and site of infection. Alterations in drifting behavior may have important implications for G. pulex population dynamics and microsporidians’ dispersal. The underlying mechanisms are more complex than previously thought.
... On the other hand, observations from diverse taxa, ranging from bacteria to rodents, suggest that dormancy can provide prey with a refuge against organisms that infect or consume them [28][29][30]. Nevertheless, some parasites appear to have coopted host dormancy in a way that increases their survival and transmission [31][32][33]. While these observations have inspired theoretical work examining the interplay between dormancy and coevolution of host-parasite dynamics, empirical tests are lacking [34,35]. ...
Dormancy is an adaptation to living in fluctuating environments. It allows individuals to enter a reversible state of reduced metabolic activity when challenged by unfavorable conditions. Dormancy can also influence species interactions by providing organisms with a refuge from predators and parasites. Here we test the hypothesis that, by generating a seed bank of protected individuals, dormancy can modify the patterns and processes of antagonistic coevolution. We conducted a factorially designed experiment where we passaged a bacterial host ( Bacillus subtilis ) and its phage (SPO1) in the presence versus absence of a seed bank consisting of dormant endospores. Owing in part to the inability of phages to attach to spores, seed banks stabilized population dynamics and resulted in minimum host densities that were 30-fold higher compared to bacteria that were unable to engage in dormancy. By supplying a refuge to phage-sensitive strains, we show that seed banks retained phenotypic diversity that was otherwise lost to selection. Dormancy also stored genetic diversity. After characterizing allelic variation with pooled population sequencing, we found that seed banks retained twice as many host genes with mutations, whether phages were present or not. Based on mutational trajectories over the course of the experiment, we demonstrate that seed banks can dampen bacteria-phage coevolution. Not only does dormancy create structure and memory that buffers populations against environmental fluctuations, it also modifies species interactions in ways that can feed back onto the eco-evolutionary dynamics of microbial communities.
... These two parasites have different host exploitation and transmission strategies. While P. ramosa castrates its host and transmits horizontally upon host death (Ebert et al., 2004), H. tvaerminnensis can transmit both horizontally (upon host death) and vertically (from mother to parthenogenetic and sexual offspring) (Vizoso et al., 2005). Furthermore, in the laboratory, D. similis is resistant to P. ramosa, but it can become infected by H. tvaerminnensis at a low rate (S. ...
The competitive exclusion principle asserts that two species cannot stably coexist in the same habitat. However, the presence of a parasite can facilitate temporary coexistence between two host species occupying the same habitat. Studies of parasite-mediated interspecific competition typically use two host species that are both susceptible to a single parasite species, as it is rare to find a resistant host species that requires a parasite to enable coexistence with a competitively superior susceptible host. We therefore investigated how two host species characterized by different susceptibility profiles affect each other when they coexist in the same habitat, by conducting two long-term mesocosm experiments in the laboratory. We followed populations of Daphnia similis coexisting with Daphnia magna, in either the presence or absence of the microsporidium Hamiltosporidium tvaerminnensis and then the bacterium Pasteuria ramosa. We found that in the absence of parasites, D. magna competitively excluded D. similis within a short period of time. However, in the presence of either parasites, the competitive ability of D. magna decreased dramatically. Our results emphasize the importance of parasites in shaping community structure and composition, by allowing coexistence of a resistant host species that would otherwise become extinct.
... In Central Europe, where D. magna is summer-active (like in the north), its habitats rarely dry up in summer, as these ponds are neither small nor shallow as they are in the north; nor do they lack precipitation for several months, like the Mediterranean ponds (Table 1, Roulin et al. 2013;Seefeldt and Ebert 2019). When ponds dry up, D. magna avoid local extinction by producing drought-resistant resting stages that can also contain the parasite (Ebert 2005;Vizoso et al. 2005;Santos and Ebert 2022). The water temperature during the active (non-resting) phase of the host-parasite life cycle is thus influenced by variation in geographic location, and thus, climate, phenology (winteror summer-active) and pond size (Table 1). ...
... Hamiltosporidium tvaerminnensis (formerly called Octosporea bayeri) is an intracellular obligate microsporidia parasite specific to Daphnia magna (Ebert 2005;Haag et al. 2011). It infects the fat cells and the ovaries of the host, reducing its competitive ability, life expectancy and fecundity (Vizoso and Ebert 2004;Vizoso et al. 2005;Lass and Ebert 2006). Transmission is horizontal and vertical (through sexual and asexual host reproduction), and natural populations can reach almost 100% prevalence (Vizoso and Ebert 2004;Lass and Ebert 2006). ...
... Transmission is horizontal and vertical (through sexual and asexual host reproduction), and natural populations can reach almost 100% prevalence (Vizoso and Ebert 2004;Lass and Ebert 2006). The parasite is also able to survive in host resting stages, which allows for co-migration (Vizoso et al. 2005). ...
Although the outcome of parasitic infections can be explained by a combination of environmental and host/parasite genetic factors, these factors are often confounded by geography. Thus, linking temperature, a locally variable environmental factor, with host and parasite genetics can reveal complex spatial host-parasite interactions. We used Daphnia magna genotypes from Central Europe, where the Hamiltosporidium tvaerminnensis parasite has not yet been reported, and from two regions where it is frequently found, Northern Europe and Mediterranean basin. In Central Europe habitats are usually permanent and hosts are typically in their planktonic phase during summer – the hottest time of the year. In Northern Europe and the Mediterranean basin, on the other hand, hosts inhabit ponds that frequently dry-up in summer. We predicted that high temperatures during host and parasite active phases would prevent long-term parasite persistence. By exposing all hosts to two parasite isolates at ambient and stressfully high temperatures we tested this prediction. At ambient temperatures, we confirmed that long-term parasite persistence is only possible in Northern and Mediterranean host genotypes, while we observed reduced persistence at high temperature, but only for the Mediterranean hosts. Virulence was higher in Northern host genotypes only at ambient temperature. These results were consistent among the two parasites isolates. Our findings, thus, do not corroborate our hypotheses and suggest that predictions about responses to future climate change are highly complex in this host-parasite system.
... Other systems with multiple parasite entry sites are known (e.g. Raoult et al. 2005;Vizoso et al. 2005;Beyer and Turnbull 2009;Giordano et al. 2015), suggesting that a general model for host infection should include parallel steps. ...
Understanding how diversity is maintained in natural populations is a major goal of evolutionary biology. In coevolving hosts and parasites, negative frequency-dependent selection is one mechanism predicted to maintain genetic variation. While much is known about host diversity, parasite diversity remains understudied in coevolutionary research. Here, we survey natural diversity in a bacterial parasite by characterizing infection phenotypes for over 50 isolates in relation to 12 genotypes of their host, Daphnia magna. We find striking phenotypic variation among parasite isolates, and we discover the parasite can infect its host through at least five different attachment sites. Variation in attachment success at each site is explained to varying degrees by host and parasite genotypes. A spatial correlation analysis showed that infectivity of different isolates does not correlate with geographic distance, meaning isolates from widespread populations are equally able to infect the host. Overall, our results reveal that infection phenotypes of this parasite are highly diverse. Our results are consistent with the prediction that under Red Queen coevolutionary dynamics both the host and the parasite should show high genetic diversity for traits of functional importance in their interactions.
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... cdc.gov/anthrax/basics/how-people-are-infected.html). In the Daphnia system, the microsporidium Hamiltosporidium tvaerminnensis is able to enter the host by transovarial infections and through the ingestion of free spores with the food (Vizoso and Ebert 2005). Unless different infections routed are traded off with each other (Lipsitch et al. 1995), parasites generally benefit from having multiple ways to infect a host, as it increases their chances of infection and may reduce the chances for the host to evolve resistance. ...
To understand the mechanisms of antagonistic coevolution, it is crucial to identify the genetics of parasite resistance. In the Daphnia magna–Pasteuria ramosa host–parasite system, the most important step of the infection process is the one in which P. ramosa spores attach to the host’s foregut. A matching-allele model (MAM) describes the host–parasite genetic interactions underlying attachment success. Here we describe a new P. ramosa genotype, P15, which, unlike previously studied genotypes, attaches to the host’s hindgut, not to its foregut. Host resistance to P15 attachment shows great diversity across natural populations. In contrast to P. ramosa genotypes that use foregut attachment, P15 shows some quantitative variation in attachment success and does not always lead to successful infections, suggesting that hindgut attachment represents a less-efficient infection mechanism than foregut attachment. Using a Quantitative Trait Locus (QTL) approach, we detect two significant QTLs in the host genome: one that co-localizes with the previously described D. magna PR locus of resistance to foregut attachment, and a second, major QTL located in an unlinked genomic region. We find no evidence of epistasis. Fine mapping reveals a genomic region, the D locus, of ~13 kb. The discovery of a second P. ramosa attachment site and of a novel host-resistance locus increases the complexity of this system, with implications for both for the coevolutionary dynamics (e.g., Red Queen and the role of recombination), and for the evolution and epidemiology of the infection process.
... This new gammarid host and site finding might be explained by the same hypothesis, but here the distance from the seashore is much larger. It was previously described that some microsporidian species may persist outside their host and may still be horizontally transmitted after spore desiccation (Vizoso et al. 2005). We hypothesis that it should be the case for E. artemiae, also taking into account that the life cycle of the Artemia sp. ...
Title: Evolutionary histories of symbioses between microsporidia and their amphipod hosts : contribution of studying two hosts over their geographic ranges.Keywords: Symbioses, Phylogeny, Phylogeography, Amphipods, Host-Parasite, MicrosporidiaAbstract: Microsporidia are obligate endoparasites, exploiting their hosts with either vertical or horizontal transmission. While the former may promote co-speciation and host-specificity, the latter may promote shifts between host species. Freshwater amphipods are hosts for many microsporidian species, but no general pattern of host specificity and co-diversification is known.In my PhD work microsporidian infections, identified with SSU rDNA, were assessed in two Gammarus species complexes, G. roeselii and G. balcanicus , over their full geographic ranges (each c. 100 sites and 2000 individuals) in aim of (i) exploring the microsporidian diversity present in both hosts and their phylogenetic relationships; (ii) testing if the host phylogeographic history might have impacted host-parasite association (co-diversifications or recent host-shifts from local fauna); (iii) proposing the host-parasite evolutionary history scenarios to explain the diversity and co-bio-geographical pattern observed in the two host species between using N. granulosis as a model.The SSU rDNA marker revealed a high number of microsporidian variants (i.e. haplogroups, 24 and 54, respectively), clustered into 18 species-level taxa, almost all being shared between the two host species. However, many microsporidian haplogroups within a given parasite species are host-specific, suggesting host-parasite co-variation. Within each host species-complex, while the confrontation between hosts and parasites phylogeography suggested some degrees of co-diversification, these patterns remain to be confirmed, mainly as SSU rDNA reached its limits in phylogenetic information content in that matter.Strikingly, almost all of these microsporidia taxa were previously detected in other gammarids, mainly within the genus Gammarus, but also in other genera of Gammaridae. Some were already clearly recognised parasite taxa associated with amphipods: Nosema granulosis, Dictyocoela roeselum, D. muelleri, D. roeselum, D. duebenum, D. berillonum, Cucumispora roeselum, C. ornata, C. dikerogammari, Microsporidium sp 515 and Microsporidium sp 505). Many times, my results increased host taxonomic spectrums and extended geographic ranges (often widely). Some other taxa were known to be extremely rare, having scarce literature records often with few or even very few geographic records and being not fully described. My PhD work either extend host taxonomic spectrum and/or deeply extend geographic ranges for these taxa. It allowed a reappraisal for such taxa, changing their status from puzzling anecdotic association to potentially overlooked established associations for amphipods.
... H. tvaerminnensis transmits horizontally from dead individuals, as well as vertically from mother to parthenogenetic and sexual host offspring; therefore, the parasite reaches prevalence as high as 100% within a population by the end of the season (Lass & Ebert, 2006). By transmitting vertically to the host's resting eggs, H. tvaerminnensis is able to disperse along with its host to new populations and endure harsh environmental conditions such as summer droughts and winter freezing (Vizoso, Lass, & Ebert, 2005). ...
Parasite‐mediated selection varying across time and space in metapopulations is expected to result in host local adaptation and the maintenance of genetic diversity in disease‐related traits. However, non‐adaptive processes like migration and extinction‐(re)colonization dynamics might interfere with adaptive evolution. Understanding how adaptive and non‐adaptive processes interact to shape genetic variability in life‐history and disease‐related traits can provide important insights into their evolution in subdivided populations. Here we investigate signatures of spatially fluctuating, parasite‐mediated selection in a natural metapopulation of Daphnia magna. Host genotypes from infected and uninfected populations were genotyped at microsatellite markers, and phenotyped for life‐history and disease traits in common garden experiments. Combining phenotypic and genotypic data a QST‐FST‐like analysis was conducted to test for signatures of parasite mediated selection. We observed high variation within and among populations for phenotypic traits, but neither an indication of host local adaptation nor a cost of resistance. Infected populations have a higher gene diversity (Hs) than uninfected populations and Hs is strongly positively correlated with fitness. These results suggest a strong parasite effect on reducing population level inbreeding. We discuss how stochastic processes related to frequent extinction‐(re)colonization dynamics as well as host and parasite migration impede the evolution of resistance in the infected populations. We suggest that the genetic and phenotypic patterns of variation are a product of dynamic changes in the host gene pool caused by the interaction of colonization bottlenecks, inbreeding, immigration, hybrid vigor, rare host genotype advantage and parasitism. Our study highlights the effect of the parasite in ameliorating the negative fitness consequences caused by the high drift load in this metapopulation.
... Coccinellid beetle larvae become infected with Tubulinosema 561 hippodamiae when feeding on infected coccinellid eggs; 100% transmission occurred 562 between conspecifics but also between coccinellid species ( Saito and Bjornson, 2006 into the water immediately after death. Vizoso et al. (2005) assumed that bacterial or 581 detritivore activity may accelerate this process. Moreover, predators can play an important 582 role in spreading spores of microsporidia developing from the fat body of the infected hosts. ...
The discovery of microsporidia was a landmark in early insect pathology studies. Microsporidia are obligate intracellular parasites that have refined "the art of living together" with their hosts by minimizing damage in order to achieve optimum reproduction and transmission to new hosts. The assumption that the number of described microsporidia species is a minute portion of those actually existing was corroborated by a study in which 22 novel species were isolated from soil, sand, and compost. Microsporidia can be transmitted horizontally from one host individual to another, or vertically from parent to offspring. Microsporidia that partially or completely depend on vertical transmission need to be of relatively low virulence in order to be successfully transmitted to the next host generation. Vertical transmission should be an important trait supporting the persistence of a microsporidium in the host population, especially during the periods of low host density that are known to occur with this univoltine outbreak species.
... Spore morphology is especially important in considering the success of parasites (Salt, 1940;Wenner and Windsor, 1979;Poulin, 1995;Coop and Kyriazakis, 1999;Leonardos and Trilles, 2003;Tsotetsi et al., 2004;Kropf et al., 2005). For example, 3 different spore types of the microsporidian Octosporea bayeri, a parasite of the water flea Daphnia magna, have been observed, each with different spore shapes and sizes; while the exact roles of these different spore types are unknown, they may contribute to transmission or to protection against environmental stress (Vizoso et al., 2005). More generally, and similar to free-living organisms, larger parasite size typically implies higher fitness (Blueweiss et al., 1978;Moore, 1981;Peters, 1986). ...
Understanding host-parasite interactions is essential for ecological research, wildlife conservation and health management. While most studies focus on numerical traits of parasite groups, such as changes in parasite load, less focus is placed on the traits of individual parasites, such as parasite size and shape (parasite morphology). Parasite morphology has significant effects on parasite fitness, such as initial colonization of hosts, avoidance of host immune defenses, and the availability of resources for parasite replication. As such, understanding factors that affect parasite morphology is important in predicting the consequences of host-parasite interactions. Here, we studied how host diet affected the spore morphology of a protozoan parasite (Ophryocystis elektroscirrha), a specialist parasite of the monarch butterfly (Danaus plexippus). We found that different host plant species (milkweeds; Asclepias spp.) significantly affected parasite spore size. Previous studies have found that cardenolides, secondary chemicals in host plants of monarchs, can reduce parasite loads and increase the lifespan of infected butterflies. Adding to this benefit of high cardenolide milkweeds, we found here that infected monarchs reared on milkweeds of higher cardenolide concentrations yielded smaller parasites, a potentially hidden characteristic of cardenolides that may have important implications for monarch-parasite interactions.
