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Trichomonas vaginalis, a common sexually transmitted parasite that colonizes the human urogenital tract, secretes extracellular vesicles (TvEVs) that are taken up by human cells and are speculated to be taken up by parasites as well. While the crosstalk between TvEVs and human cells has led to insight into host:parasite interactions, roles for TvEVs in infection have largely been one-sided, with little known about the effect of TvEV uptake by T. vaginalis. Approximately 11% of infections are found to be coinfections of multiple T. vaginalis strains. Clinical isolates often differ in their adherence to and cytolysis of host cells, underscoring the importance of understanding the effects of TvEV uptake within the parasite population. To address this question, our lab tested the ability of a less adherent strain of T. vaginalis, G3, to take up fluorescently labeled TvEVs derived from both itself (G3-EVs) and TvEVs from a more adherent strain of the parasite (B7RC2-EVs). Here, we showed that TvEVs generated from the more adherent strain are internalized more efficiently compared to the less adherent strain. Additionally, preincubation of G3 parasites with B7RC2-EVs increases parasite aggregation and adherence to host cells. Transcriptomics revealed that TvEVs up-regulate expression of predicted parasite membrane proteins and identified an adherence factor, heteropolysaccharide binding protein (HPB2). Finally, using comparative proteomics and superresolution microscopy, we demonstrated direct transfer of an adherence factor, cadherin-like protein, from TvEVs to the recipient parasites surface. This work identifies TvEVs as a mediator of parasite:parasite communication that may impact pathogenesis during mixed infections.

Many insects have evolved the ability to manipulate plant growth to generate extraordinary structures called galls, in which insect larva can develop while being sheltered and feeding on the plant. In particular, cynipid (Hymenoptera: Cynipidae) wasps have evolved to form morphologically complex galls and generate an astonishing array of gall shapes, colors, and sizes. However, the biochemical basis underlying these remarkable cellular and developmental transformations remains poorly understood. A key determinant in plant cellular development is cell wall deposition that dictates the physical form and physiological function of newly developing cells, tissues, and organs. However, it is unclear to what degree cell walls are restructured to initiate and support the formation of new gall tissue. Here, we characterize the molecular alterations underlying gall development using a combination of metabolomic, histological, and biochemical techniques to elucidate how valley oak (Quercus lobata) leaf cells are reprogrammed to form galls. Strikingly, gall development involves an exceptionally coordinated spatial deposition of lignin and xylan to form de novo gall vasculature. Our results highlight how cynipid wasps can radically change the metabolite profile and restructure the cell wall to enable the formation of galls, providing insights into the mechanism of gall induction and the extent to which plants can be entirely reprogrammed to form unique structures and organs.

Genetic analyses of host‐specific parasites can elucidate the evolutionary histories and biological features of their hosts. Here, we used population‐genomic analyses of ectoparasitic seal lice (Echinophthirius horridus) to shed light on the postglacial history of seals in the Arctic Ocean and the Baltic Sea region. One key question was the enigmatic origin of relict landlocked ringed seal populations in lakes Saimaa and Ladoga in northern Europe. We found that that lice of four postglacially diverged subspecies of the ringed seal (Pusa hispida) and Baltic gray seal (Halichoerus grypus), like their hosts, form genetically differentiated entities. Using coalescent‐based demographic inference, we show that the sequence of divergences of the louse populations is consistent with the geological history of lake formation. In addition, local effective population sizes of the lice are generally proportional to the census sizes of their respective seal host populations. Genome‐based reconstructions of long‐term effective population sizes revealed clear differences among louse populations associated with gray versus ringed seals, with apparent links to Pleistocene and Holocene climatic variation as well as to the isolation histories of ringed seal subspecies. Interestingly, our analyses also revealed ancient gene flow between the lice of Baltic gray and ringed seals, suggesting that the distributions of Baltic seals overlapped to a greater extent in the past than is the case today. Taken together, our results demonstrate how genomic information from specialized parasites with higher mutation and substitution rates than their hosts can potentially illuminate finer scale population genetic patterns than similar data from their hosts. [ABSTRACT FROM AUTHOR]

Parasitism is increasingly seen as an ecological factor contributing to behavioural variation among individuals. Yet, the causal direction of the relationship between animal personality and parasites remains unclear. We measured behavioural traits (i.e. exploration, activity, boldness) in pumpkinseed sunfish, Lepomis gibbosus , before and after an experimental infection using cages in a lake where sunfish were naturally exposed to trematode and cestode infection for 1 month. Despite our initial assumptions (i.e. that all individuals would have the same risk of infection within a cage), we found that initial behavioural traits strongly influenced infection susceptibility: initially bolder and less active fish acquired a higher density of trematode and cestode parasites during the infection period. Following infection, fish body condition decreased with increasing cestode density, suggesting that infection is costly to hosts. Body condition was positively correlated with distance moved, a measure of activity, regardless of individual infection status. The repeatability of exploration and activity behaviour and the strength of the activity–exploration correlation (i.e. behavioural syndrome) were reduced following parasite exposure. Distance moved and trematode density were negatively correlated, suggesting that this infection decreases host activity levels. Since trematodes have a complex life cycle with piscivorous birds as a final host, a decrease in activity following infection may make infected fish more susceptible to bird predation, benefiting the parasite. Our results highlight the close links between behaviour and parasitism. We propose that two mechanisms may simultaneously operate: initial host behaviour influences their risk of infection, and infection introduces variation in the behavioural traits of infected hosts. • We infected pumpkinseed sunfish using cages in a lake with high parasite prevalence. • We measured exploration, activity and boldness before and after parasite exposure. • Less active and bolder fish were more susceptible to infection within cages. • Fish body condition decreased with high density of a parasite causing liver damage. • Fish activity was reduced with trematode infection causing black spot disease. [ABSTRACT FROM AUTHOR]

The 16th International Symposium on Schistosomiasis, held in Brazil, focused on disease control and elimination. Participants from 11 countries discussed various aspects of schistosomiasis, including the development of disease control tools and health education. The symposium featured keynote speeches, poster presentations, panel discussions, and abstract submissions. A Research Topic dedicated to the symposium aimed to disseminate selected studies presented during the event, covering topics such as diagnostic tests, host-parasite interactions, potential drug targets, and vaccine development. These studies contribute to the search for new strategies to combat schistosomiasis. The text also highlights the importance of education and diagnostic development in achieving the World Health Organization's guidelines for controlling and eliminating the disease. [Extracted from the article]

One of the fundamental aims of ecological, epidemiological and evolutionary studies of host–parasite interactions is to unravel which factors affect parasite virulence. Theory predicts that virulence and transmission are correlated by a trade-off, as too much virulence is expected to hamper transmission owing to excessive host damage. Coinfections may affect each of these traits and/or their correlation. Here, we used inbred lines of the spider mite Tetranychus urticae to test how coinfection with T. evansi impacted virulence–transmission relationships at different conspecific densities. The presence of T. evansi on a shared host did not change the relationship between virulence (leaf damage) and the number of transmitting stages (i.e. adult daughters). The relationship between these traits was hump-shaped across densities, both in single and coinfections, which corresponds to a trade-off. Moreover, transmission to adjacent hosts increased in coinfection, but only at low T. urticae densities. Finally, we tested whether virulence and the number of daughters were correlated with measures of transmission to adjacent hosts, in single and coinfections at different conspecific densities. Traits were mostly independent, meaning that interspecific competitors may increase transmission without affecting virulence. Thus, coinfections may impact epidemiology and parasite trait evolution, but not necessarily the virulence–transmission trade-off. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'. [ABSTRACT FROM AUTHOR]

Context-dependent dispersal allows organisms to seek and settle in habitats improving their fitness. Despite the importance of species interactions in determining fitness, a quantitative synthesis of how they affect dispersal is lacking. We present a meta-analysis asking (i) whether the interaction experienced and/or perceived by a focal species (detrimental interaction with predators, competitors, parasites or beneficial interaction with resources, hosts, mutualists) affects its dispersal; and (ii) how the species' ecological and biological background affects the direction and strength of this interaction-dependent dispersal. After a systematic search focusing on actively dispersing species, we extracted 397 effect sizes from 118 empirical studies encompassing 221 species pairs; arthropods were best represented, followed by vertebrates, protists and others. Detrimental species interactions increased the focal species' dispersal (adjusted effect: 0.33 [0.06, 0.60]), while beneficial interactions decreased it (−0.55 [−0.92, −0.17]). The effect depended on the dispersal phase, with detrimental interactors having opposite impacts on emigration and transience. Interaction-dependent dispersal was negatively related to species' interaction strength, and depended on the global community composition, with cues of presence having stronger effects than the presence of the interactor and the ecological complexity of the community. Our work demonstrates the importance of interspecific interactions on dispersal plasticity, with consequences for metacommunity dynamics. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'. [ABSTRACT FROM AUTHOR]

With the growth of the fashion and textile industries into the twenty-first century, associated pollution has become pervasive. Fibre-based microplastics are the most common types of plastics recovered from aquatic ecosystems encouraging the move towards organic fibre usage. Often marketed as biodegradable and 'environmentally friendly', organic textile fibres are seen as less harmful, but their impacts are understudied. Here, we assess the health effects of reconstituted bamboo-viscose fibres, processed bamboo-elastane fibres (both at 700 fibres/L) and their associated dye (Reactive Black-5, at 1 mg/L) on fish, with an emphasis on disease resistance utilising an established host-parasite system: the freshwater guppy host (Poecilia reticulata) and Gyrodactylus turnbulli (monogenean ectoparasite). Following 3 weeks exposure to the bamboo fibres and associated dye, half the experimental fish were infected with G. turnbulli, after which individual parasite trajectories were monitored for a further 17 days. Overall, exposures to reconstituted bamboo-viscose fibres, processed bamboo-elastane fibres or dye were not associated with any change in host mortality nor any significant changes in parasite infection burdens. When analysing the routine metabolic rate (RMR) of fish, uninfected fish had, on average, significantly impacted RMR when exposed to processed bamboo-elastane (increased RMR) and reconstituted bamboo-viscose (decreased RMR). Hosts exposed to reconstituted bamboo-viscose and the associated dye treatment showed significant changes in RMR pre- and post-infection. This study bolsters the growing and needed assessment of the potential environmental impacts of alternative non-plastic fibres; nevertheless, more research is needed in this field to prevent potential greenwashing. [ABSTRACT FROM AUTHOR]

Predators negatively affect prey outside of direct attack, and these nonconsumptive effects (NCEs) may cause over half the impacts of predators on prey populations. This "ecology of fear" framework has been extended to host–parasite interactions. The NCEs of parasites are thought to be small relative to those of predators. However, recent research shows ectoparasites exert NCEs on multiple life stages of Drosophila. In this study, we apply recent data to a matrix‐based model of fly populations experiencing infection/consumption and NCEs from an ectoparasitic mite. We found the NCEs of parasites on larvae, which are not actively parasitized, decreased the size of simulated host populations. By contrast, the NCEs on adult flies increased population size through compensatory egg production. The negative NCEs on larvae outweighed the positive effects on adults to reduce population size. This study suggests that parasitic NCEs can suppress host populations independent of infection. [ABSTRACT FROM AUTHOR]

Nematodes belonging to the genus Oesophagostomum frequently infect wild chimpanzees (Pan troglodytes) across widely separated field sites. Nodular lesions (granulomas) containing Oesophagostomum are commonly seen in the abdomen of infected chimpanzees post‐mortem. At Taï National Park, Côte d'Ivoire, previous studies have identified larvae of a variety of Oesophagostomum spp. in wild chimpanzee stool, based on sequencing of larval DNA, and nodular lesions associated with Oesophagostomum, identified morphologically to the genus level but not sequenced. Here we present three recent cases of parasitic granulomas found post‐mortem in chimpanzees at Taï. We complement descriptions of gross pathology, histopathology and parasitology with PCR and sequencing of DNA isolated from the parasitic nodules and from adult worms found inside the nodules. In all three cases, we identify Oesophagostomum stephanostomum as the causative agent. The sequences from this study were identical to the only other published sequences from nodules in nonhuman primates—those from the wild chimpanzees of Gombe, Tanzania. Research highlights: Chimpanzees in Taï National Park (Côte d'Ivoire) commonly have a small number of abdominal parasitic nodules, observed post‐mortem.A variety of Oesophagostum spp. has been found in the stool of Taï chimps.The nodules are caused by Oesophagostomum stephanostomum, and the ITS‐2 sequence is identical to the only other sequence obtained from chimp nodules (in Gombe, Tanzania). [ABSTRACT FROM AUTHOR]

The protozoan parasite Entamoeba histolytica is the causative agent of amebiasis, with clinical outcomes ranging from asymptomatic infections to severe invasive diseases. The innate immune system, particularly macrophages, is of paramount importance in resisting the invasion of host tissues and organs by the trophozoites of E. histolytica. Parasite-derived pathogenic factors, such as lectins, play a pivotal role in the promotion of macrophage polarization phenotypes that have undergone alteration. Nevertheless, the precise mechanisms by which E. histolytica modulates immune polarization remain largely unknown. The current study focused on the immunomodulatory effects of the Igl-C fragment of E. histolytica Gal/GalNAc lectin on macrophage polarization. These results demonstrated that Igl-C could induce the secretion of IL-1b, IL-6, and other cytokines, activating a mixed M1/M2 polarization state. M1 polarization of macrophages occurs in the early stages and gradually transitions to M2 polarization in the later stages, which may contribute to the persistence of the infection. Igl-C induces the macrophage M1 phenotype and causes the release of immune effector molecules, including iNOS and cytokines, by activating the NF-kB p65 and JAK-STAT1 transcription factor signaling pathways. Furthermore, Igl-C supports the macrophage M2 phenotype via JAK-STAT3 and IL-4-STAT6 pathways, which activate arginase expression in later stages, contributing to the tissue regeneration and persistence of the parasite. The involvement of distinct signaling pathways in mediating this response highlights the complex interplay between the parasite and the host immune system. These findings enhance our understanding of the Igl-Cmediated pathogenic mechanisms during E. histolytica infection. [ABSTRACT FROM AUTHOR]

Supplemental feeding can increase the overall health of animals but also can have variable effects on how animals defend themselves against parasites. However, the spatiotemporal effects of food supplementation on host–parasite interactions remain poorly understood, likely because large‐scale, coordinated efforts to investigate them are difficult. Here, we introduce the Nest Parasite Community Science Project, which is a community‐based science project that coordinates studies with bird nest box ‘stewards’ from the public and scientific community. This project was established to understand broad ecological patterns between hosts and their parasites. The goal of this study was to determine the effect of food supplementation on eastern bluebirds (Sialia sialis) and their nest parasite community across the geographic range of the bluebirds from 2018 to 2021. We received 674 nests from 69 stewards in 26 states in the eastern United States. Nest box stewards reported whether or not they provided mealworms or suet near nesting bluebirds, then they followed the nesting success of the birds (number of eggs laid and hatched, proportion that hatched, number and proportion of nestlings that successfully fledged). We then identified and quantified parasites in the nests. Overall, we found that food supplementation increased fledging success. The most common nest parasite taxon was the parasitic blow fly (Protocalliphora sialia), but a few nests contained fleas (Ceratophyllus idius, C. gallinae and Orchopeas leucopus) and mites (Dermanyssus spp. and Ornithonyssus spp.). Blow flies were primarily found at northern latitudes, where food supplementation affected blow fly prevalence. However, the direction of this effect varied substantially in direction and magnitude across years. More stewards fed bluebirds at southern latitudes than at northern latitudes, which contradicts the findings of other community‐based science projects. Overall, food supplementation of birds was associated with increased host fitness but did not appear to play a consistent role in defence against these parasites across all years. Our study demonstrates the importance of coordinated studies across years and locations to understand the effects of environmental heterogeneity, including human‐based food supplementation, on host–parasite dynamics. [ABSTRACT FROM AUTHOR]

Nematodes of the genus Trichinella are important pathogens of humans and animals. This study aimed to enhance the genomic and transcriptomic resources for T. pseudospiralis (non-encapsulated phenotype) and T. spiralis (encapsulated phenotype) and to explore transcriptional profiles. First, we improved the assemblies of the genomes of T. pseudospiralis (code ISS13) and T. spiralis (code ISS534), achieving genome sizes of 56.6 Mb (320 scaffolds, and an N50 of 1.02 Mb) and 63.5 Mb (568 scaffolds, and an N50 value of 0.44 Mb), respectively. Then, for each species, we produced RNA sequence data for three key developmental stages (first-stage muscle larvae [L1s], adults, and newborn larvae [NBLs]; three replicates for each stage), analysed differential transcription between stages, and explored enriched pathways and processes between species. Stage-specific upregulation was linked to cellular processes, metabolism, and host–parasite interactions, and pathway enrichment analysis showed distinctive biological processes and cellular localisations between species. Indeed, the secreted molecules calmodulin, calreticulin, and calsyntenin—with possible roles in modulating host immune responses and facilitating parasite survival—were unique to T. pseudospiralis and not detected in T. spiralis. These insights into the molecular mechanisms of Trichinella–host interactions might offer possible avenues for developing new interventions against trichinellosis. [ABSTRACT FROM AUTHOR]

Croziers paradox suggests that genetic kin recognition will not be evolutionarily stable. The problem is that more common tags (markers) are more likely to be recognized and helped. This causes common tags to increase in frequency, eliminating the genetic variability that is required for genetic kin recognition. Two potential solutions to this problem have been suggested: host-parasite coevolution and multiple social encounters. We show that the host-parasite coevolution hypothesis does not work as commonly assumed. Host-parasite coevolution only stabilizes kin recognition at a parasite resistance locus if parasites adapt rapidly to hosts and cause intermediate or high levels of damage (virulence). Additionally, when kin recognition is stabilized at a parasite resistance locus, this can have an additional cost of making hosts more susceptible to parasites. However, we show that if the genetic architecture is allowed to evolve, meaning natural selection can choose the recognition locus, genetic kin recognition is more likely to be stable. The reason for this is that host-parasite coevolution can maintain tag diversity at another (neutral) locus by genetic hitchhiking, allowing that other locus to be used for genetic kin recognition. These results suggest a way that host-parasite coevolution can resolve Croziers paradox, without making hosts more susceptible to parasites. However, the opportunity for multiple social encounters may provide a more robust resolution of Croziers paradox.

Some parasites manipulate their hosts phenotype to enhance predation rates by the next host in the parasites life cycle. Our understanding of this parasite-increased trophic transmission is often stymied by study-design challenges. A recurring difficulty has been obtaining uninfected hosts with a coevolutionary history with the parasites, and conducting experimental infections that mimic natural processes. In 1996, Lafferty and Morris provided what has become a classic example of parasite-increased trophic transmission; they reported a positive association between the intensity of a brain-infecting trematode (Euhaplorchis californiensis) in naturally infected California killifish (Fundulus parvipinnis) and the frequency of conspicuous behaviors, which was thought to explain the documented 10-30× increase in predation by the final host birds. Here, we address the primary gap in that study by using experimental infections to assess the causality of E. californiensis infection for increased conspicuous behaviors in F. parvipinnis. We hatched and reared uninfected F. parvipinnis from a population co-occurring with E. californiensis, and infected them 1-2 times/week over half their life span with E. californiensis and a small cyathocotylid trematode (SMCY) that targets the hosts muscle tissue. At 3 time points throughout the hosts lives, we quantified several conspicuous behaviors: contorting, darting, scratching, surfacing, and vertical positioning relative to the waters surface. Euhaplorchis californiensis and SMCY infection caused 1.8- and 2.5-fold overall increases in conspicuous behaviors, respectively. Each parasite was also associated with increases in specific conspicuous behaviors, particularly 1.9- and 1.4-fold more darting. These experimental findings help solidify E. californiensis-F. parvipinnis as a classic example of behavioral manipulation. Yet our findings for E. californiensis infection-induced behavioral change were less consistent and strong than those previously documented. We discuss potential explanations for this discrepancy, particularly the idea that behavioral manipulation may be most apparent when fish are actively attacked by predators. Our findings concerning the other studied trematode species, SMCY, highlight that trophically transmitted parasites infecting various host tissues are known to be associated with conspicuous behaviors, reinforcing calls for research examining how communities of trophically transmitted parasites influence host behavior.

Abstract Mounting evidence of the occurrence of direct and indirect interactions between the human blood fluke, Schistosoma mansoni, and the gut microbiota of rodent models raises questions on the potential role(s) of the latter in the pathophysiology of hepatointestinal schistosomiasis. However, substantial differences in both the composition and function between the gut microbiota of laboratory rodents and that of humans hinders an in-depth understanding of the significance of such interactions for human schistosomiasis. Taking advantage of the availability of a human microbiota-associated mouse model (HMA), we have previously highlighted differences in infection-associated changes in gut microbiota composition between HMA and wildtype (WT) mice. To further explore the dynamics of schistosome-microbiota relationships in HMA mice, in this study we (i) characterize qualitative and quantitative changes in gut microbiota composition of a distinct line of HMA mice (D2 HMA) infected with S. mansoni prior to and following the onset of parasite egg production; (ii) profile local and systemic immune responses against the parasite in HMA as well as WT mice and (iii) assess levels of faecal inflammatory markers and occult blood as indirect measures of gut tissue damage. We show that patent S. mansoni infection is associated with reduced bacterial alpha diversity in the gut of D2 HMA mice, alongside expansion of hydrogen sulphide-producing bacteria. Similar systemic humoral responses against S. mansoni in WT and D2 HMA mice, as well as levels of faecal lipocalin and markers of alternatively activated macrophages, suggest that these are independent of baseline gut microbiota composition. Qualitative comparative analyses between faecal microbial profiles of S. mansoni-infected WT and distinct lines of HMA mice reveal that, while infection-induced alterations of the gut microbiota composition are highly dependent on the baseline flora, bile acid composition and metabolism may represent key elements of schistosome-microbiota interactions through the gut-liver axis.

Abstract Seal lice (Echinophthirius horridus) are bloodsucking ectoparasites of phocid seals and vectors of pathogens like the heartworm, Acanthocheilonema spirocauda. Grey and harbour seal populations are recovering in German waters and wildlife health surveillance is crucial for wildlife conservation. A new, high effort sampling protocol for seal lice was applied for grey and harbour seals along the German North- and Baltic Sea coast. Freshly dead seals were systematically sampled within a health monitoring of stranded seals over 12 months. Prevalence, intensity and distribution patterns of seal lice were analysed. 58% of harbour seals (n = 71) and 70% of grey seals (n = 10) were infected with seal lice. A majority of harbour seals displayed mild levels of infection, while three were moderately and two were severely infected. The head was the preferred predilection site, indicating that E. horridus prefers body areas with frequent access to atmospheric oxygen. Nits and different developmental stages were recorded in all age classes in grey and harbour seals in all seasons. For the first time, copulating specimens of E. horridus were recorded on a dead harbour seal, highlighting that E. horridus reproduces throughout the year on seals of all age classes in German waters.

Mounting evidence of the occurrence of direct and indirect interactions between the human blood fluke, Schistosoma mansoni, and the gut microbiota of rodent models raises questions on the potential role(s) of the latter in the pathophysiology of hepatointestinal schistosomiasis. However, substantial differences in both the composition and function between the gut microbiota of laboratory rodents and that of humans hinders an in-depth understanding of the significance of such interactions for human schistosomiasis. Taking advantage of the availability of a human microbiota-associated mouse model (HMA), we have previously highlighted differences in infection-associated changes in gut microbiota composition between HMA and wildtype (WT) mice. To further explore the dynamics of schistosome-microbiota relationships in HMA mice, in this study we (i) characterize qualitative and quantitative changes in gut microbiota composition of a distinct line of HMA mice (D2 HMA) infected with S. mansoni prior to and following the onset of parasite egg production; (ii) profile local and systemic immune responses against the parasite in HMA as well as WT mice and (iii) assess levels of faecal inflammatory markers and occult blood as indirect measures of gut tissue damage. We show that patent S. mansoni infection is associated with reduced bacterial alpha diversity in the gut of D2 HMA mice, alongside expansion of hydrogen sulphide-producing bacteria. Similar systemic humoral responses against S. mansoni in WT and D2 HMA mice, as well as levels of faecal lipocalin and markers of alternatively activated macrophages, suggest that these are independent of baseline gut microbiota composition. Qualitative comparative analyses between faecal microbial profiles of S. mansoni-infected WT and distinct lines of HMA mice reveal that, while infection-induced alterations of the gut microbiota composition are highly dependent on the baseline flora, bile acid composition and metabolism may represent key elements of schistosome-microbiota interactions through the gut-liver axis. [ABSTRACT FROM AUTHOR]

Many genes and signalling pathways within plant and animal taxa drive the expression of multiple organismal traits. This form of genetic pleiotropy instigates trade-offs among life-history traits if a mutation in the pleiotropic gene improves the fitness contribution of one trait at the expense of another. Whether or not pleiotropy gives rise to conflict among traits, however, likely depends on the resource costs and timing of trait deployment during organismal development. To investigate factors that could influence the evolutionary maintenance of pleiotropy in gene networks, we developed an agent-based model of co-evolution between parasites and hosts. Hosts comprise signalling networks that must faithfully complete a developmental programme while also defending against parasites, and trait signalling networks could be independent or share a pleiotropic component as they evolved to improve host fitness. We found that hosts with independent developmental and immune networks were significantly more fit than hosts with pleiotropic networks when traits were deployed asynchronously during development. When host genotypes directly competed against each other, however, pleiotropic hosts were victorious regardless of trait synchrony because the pleiotropic networks were more robust to parasite manipulation, potentially explaining the abundance of pleiotropy in immune systems despite its contribution to life history trade-offs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Host contact zone dynamics can be influenced by parasites. • Luscinia nightingales have significantly different haemosporidian prevalence. • Differential prevalence did not change in sympatry versus allopatry. • Community structure was significantly different between hosts, even in sympatry. • Parasites are unlikely to drive contact zone dynamics in nightingales. Parasites are a key driving force behind many ecological and evolutionary processes. Prevalence and diversity of parasites, as well as their effects on hosts, are not uniform across host species. As such, the potential parasite spillover between species can significantly influence outcomes of interspecific interactions. We screened two species of Luscinia nightingales for haemosporidian blood parasites (Plasmodium, Leucocytozoon and Haemoproteus) along an approximately 3000 km transect in Europe, incorporating areas of host distant allopatry, close allopatry and sympatry. We found significant differences in infection rates between the two host species, with common nightingales having much lower parasite prevalence than thrush nightingales (36.7% versus 83.8%). This disparity was mostly driven by Haemoproteus prevalence, which was significantly higher in thrush nightingales while common nightingales had a small, but significantly higher, Plasmodium prevalence. Furthermore, we found no effect of proximity to the contact zone on infection rate in either host species. Despite having lower infection prevalence, common nightingales were infected with a significantly higher diversity of parasite lineages than thrush nightingales, and lineage assemblages differed considerably between the two species, even in sympatry. This pattern was mostly driven by the large diversity of comparatively rare lineages, while the most abundant lineages were shared between the two host species. This suggests that, despite the close evolutionary relationships between the two nightingales, there are significant differences in parasite prevalence and diversity, regardless of the distance from the contact zone. This suggests that spillover of haemosporidian blood parasites is unlikely to contribute towards interspecific interactions in this system. [ABSTRACT FROM AUTHOR]

Birds select breeding territories by assessing territory quality and considering predation pressure. However, in many small passerines, brood parasitism may also play an important role in territory occupancy. Settlement decisions are made under time pressure, especially for late migrants. An example of late migrants is the red-backed shrike Lanius collurio, a species wintering in sub-tropical Africa, which serves as a host for the common cuckoo Cuculus canorus and arrives in territories a few days later than their brood parasite. We expected that arriving red-backed shrikes avoided territories with common cuckoo presence. Then, we tested how experimentally provided artificial playback calls of the common cuckoo and woodpigeon (treated as control) affected the probability of red-backed shrike settlement. In the breeding season 2021, we observed 279 red-backed shrike territories to assess the effect of playback of common cuckoo calls on their host presence. Moreover, we adopt information on shrike territories collected in previous years to establish territory quality, measured by occupancy pattern over years. Each of these places was also checked for the presence of corvids, which are predators of shrike nests. We did not find difference with lower preference of shrikes towards cuckoo calls and to pigeon calls Columba columbus, what suggest the human presence and manipulation in the territories during experiments with recorders should be incorporated as an important factor to understanding shrikes' settlement behaviour. What is interesting we found no negative effect of corvids (jay Garrulus glandarius) in control territories. However, shrike territories where cuckoo calls were emitted and where the presence of corvids was found were less likely to be inhabited by shrikes. Therefore, territory quality, human presence enhanced by nest predators, is an important factor affecting host–parasite interactions. [ABSTRACT FROM AUTHOR]

The biodiversity of parasitic mites of the Demodecidae, infesting mammalian carnivorans, is poorly understood. To date, 18 host-specific species have been described, including four each from domestic dogs and cats, and only 10 from wild carnivores, known from single or duplicate reports. No data is available on the level of infestation of wild populations, or the co-occurrence of different demodecids in the same host, as only single species have been identified in individual hosts. A convenient model for such studies turned out to be the European polecat Mustela putorius, in which a new genus and species, Miridex putorii, was recently described in the vibrissae region of the skin of the head. Our study reveals that M. putorii co-occur with other species: Demodex putorii sp. nov. (associated with the hairless skin of the head) and Demodex foetorii sp. nov. (associated with hairy skin). Thus, the present study provides descriptions of species new to science. It also provides the first analysis of the occurrence of Demodecidae in wild mammalian carnivorans at the species and individual animal level based on the co-occurrence of three demodecid mite species in the skin of the head in M. putorius. Demodecid mites were found in 75.7% of 37 polecats; M. putorii showed the highest prevalence (56.8%), and D. putorii showed the highest abundance in the skin (mean 10.8 mites in 9 cm2). The three species co-occurred in 5.4% of the polecats, and two species in 27.0%. Despite the very high abundances, infestation was not associated with gross skin pathology (a feature of stable parasite–host systems formed by long-term co-evolution). The co-occurrence of several species and the separation of microhabitats are also typical of Demodecidae of other mammalian groups and illustrate the optimal use of the host body as a habitat and food source with limited impact. urn:lsid:zoobank.org:act:4D12FF6B-5A9E-4346-A496-52AC8448E7FE urn:lsid:zoobank.org:act:07C533F5-9392-4FD3-BF9A-E1058C0FC1D6 [ABSTRACT FROM AUTHOR]

The intricate relationships between parasites and hosts encompass a wide range of levels, from molecular interactions to population dynamics. Parasites influence not only the physiological processes in the host organism, but also the entire ecosystem, affecting mortality of individuals, the number of offspring through parasitic castration, and matter and energy cycles. Understanding the molecular mechanisms that govern host-parasite relationships and their impact on host physiology and environment remains challenging. In this study, we analyzed how infection with Microphallus trematodes affects the metabolome of two Littorina snail species inhabiting different intertidal zone shore levels. We applied non-targeted GC–MS-based metabolomics to analyze biochemical shifts induced by trematode infection in a host organism. We have identified changes in energy, amino acid, sugar, and lipid metabolism. In particular, we observed intensified amino acid catabolism and nitrogenous catabolites (glutamine, urea) production. These changes primarily correlated with infection and interspecies differences of the hosts rather than shore level. The changes detected in the host metabolism indicate that other aspects of life may have been affected, both within the host organism and at a supra-organismal level. Therefore, we explored changes in microbiota composition, deviations in the host molluscs behavior, and acetylcholinesterase activity (ACE, an enzyme involved in neuromuscular transmission) in relation to infection. Infected snails displayed changes in their microbiome composition. Decreased ACE activity in snails was associated with reduced mobility, but whether it is associated with trematode infection remains unclear. The authors suggest a connection between the identified biochemical changes and the deformation of the shell of molluscs, changes in their behavior, and the associated microbiome. The role of parasitic systems formed by microphallid trematodes and Littorina snails in the nitrogen cycle at the ecosystem level is also assumed. [ABSTRACT FROM AUTHOR]

We revisit the foundations of the Horsfall-Barratt (HB) scale, a widely cited and applied plant disease visual assessment tool introduced in 1945, a full 37 years prior to T. T. Hebert's 1982 critique that raised concerns regarding the scale's rationale, particularly its reliance on the Weber-Fechner law and visual perception assumptions. Although use of the HB scale and similar ordinal scales persists, comprehensive studies have revealed that direct visual estimation using percentage scales often proves more accurate and reliable. Challenges remain, such as biases due to estimator subjectivity and the potential for misclassification. The logarithmic assumptions of the HB scale have been debunked, and the importance of choosing appropriate interval sizes and numbers of classes in developing ordinal scales is emphasized. Analyzing ordinal scale data appropriately is crucial, and recent advances offer promising methods that reduce type II error rates. The closely related disease severity index is noted to have its shortcomings and potential for misuse. The letter underscores the need for continuous refinement and critical evaluation of disease assessment methodologies. [ABSTRACT FROM AUTHOR]

Host–parasite interactions can cause strong demographic fluctuations accompanied by selective sweeps of resistance/infectivity alleles. Both demographic bottlenecks and frequent sweeps are expected to reduce the amount of segregating genetic variation and therefore might constrain adaptation during co‐evolution. Recent studies, however, suggest that the interaction of demographic and selective processes is a key component of co‐evolutionary dynamics and may rather positively affect levels of genetic diversity available for adaptation. Here, we provide direct experimental testing of this hypothesis by disentangling the effects of demography, selection and their interaction in an experimental host–parasite system. We grew 12 populations of a unicellular, asexually reproducing algae (Chlorella variabilis) that experienced either growth followed by constant population sizes (three populations), demographic fluctuations (three populations), selection induced by exposure to a virus (three populations), or demographic fluctuations together with virus‐induced selection (three populations). After 50 days (~50 generations), we conducted whole‐genome sequencing of each algal host population. We observed more genetic diversity in populations that jointly experienced selection and demographic fluctuations than in populations where these processes were experimentally separated. In addition, in those three populations that jointly experienced selection and demographic fluctuations, experimentally measured diversity exceeds expected values of diversity that account for the cultures' population sizes. Our results suggest that eco‐evolutionary feedbacks can positively affect genetic diversity and provide the necessary empirical measures to guide further improvements of theoretical models of adaptation during host–parasite co‐evolution. [ABSTRACT FROM AUTHOR]

Most malaria (Plasmodium spp.) parasite species undergo asexual replication synchronously within the red blood cells of their vertebrate host. Rhythmicity in this intraerythrocytic developmental cycle (IDC) enables parasites to maximise exploitation of the host and align transmission activities with the time of day that mosquito vectors blood feed. The IDC is also responsible for the major pathologies associated with malaria, and plasticity in the parasite's rhythm can confer tolerance to antimalarial drugs. Both the severity of infection (virulence) and synchrony of the IDC vary across species and between genotypes of Plasmodium; however, this variation is poorly understood. The theory predicts that virulence and IDC synchrony are negatively correlated, and we tested this hypothesis using two closely related genotypes of the rodent malaria model Plasmodium chabaudi that differ markedly in virulence. We also test the predictions that, in response to perturbations to the timing (phase) of the IDC schedule relative to the phase of host rhythms (misalignment), the virulent parasite genotype recovers the correct phase relationship faster, incurs less fitness losses and so hosts benefit less from misalignment when infected with a virulent genotype. Our predictions are partially supported by results suggesting that the virulent parasite genotype is less synchronous in some circumstances and recovers faster from misalignment. While hosts were less anaemic when infected by misaligned parasites, the extent of this benefit did not depend on parasite virulence. Overall, our results suggest that interventions to perturb the alignment between the IDC schedule, and host rhythms and increase synchrony between parasites within each IDC, could alleviate disease symptoms. However, virulent parasites, which are better at withstanding conventional antimalarial treatment, would also be intrinsically better able to tolerate such interventions. [ABSTRACT FROM AUTHOR]

Melatonin is a pleiotropic neurohormone found in different animal, plant, and microorganism species. It is a product resulting from tryptophan metabolism in the pineal gland and is widely known for its ability to synchronize the circadian rhythm to antitumor functions in different types of cancers. The molecular mechanisms responsible for its immunomodulatory, antioxidant and cytoprotective effects involve binding to high-affinity G protein-coupled receptors and interactions with intracellular targets that modulate signal transduction pathways. In vitro and in vivo studies have reported the therapeutic potential of melatonin in different infectious and parasitic diseases. In this review, the protective and pathophysiological roles of melatonin in fighting protozoan and helminth infections and the possible mechanisms involved against these stressors will be discussed. • Melatonin is an indole hormone with different functions, from antioxidant activity to immunomodulation. • Melatonin has activity against protozoa by acting, above all, directly and indirectly in the infectious process. • Melatonin reduces the impact of the infectious process caused by helminths, especially by inducing protection against oxidative stress. [ABSTRACT FROM AUTHOR]

Abstract Predators negatively affect prey outside of direct attack, and these nonconsumptive effects (NCEs) may cause over half the impacts of predators on prey populations. This “ecology of fear” framework has been extended to host–parasite interactions. The NCEs of parasites are thought to be small relative to those of predators. However, recent research shows ectoparasites exert NCEs on multiple life stages of Drosophila. In this study, we apply recent data to a matrix‐based model of fly populations experiencing infection/consumption and NCEs from an ectoparasitic mite. We found the NCEs of parasites on larvae, which are not actively parasitized, decreased the size of simulated host populations. By contrast, the NCEs on adult flies increased population size through compensatory egg production. The negative NCEs on larvae outweighed the positive effects on adults to reduce population size. This study suggests that parasitic NCEs can suppress host populations independent of infection.

A key aspect of parasitic nematode infection is the nematodes' ability to evade and/or suppress host immunity. This immunomodulatory ability is likely driven by the release of hundreds of excretory/secretory proteins (ESPs) during infection. While ESPs have been shown to display immunosuppressive effects on various hosts, our understanding of the molecular interactions between individual proteins released and host immunity requires further study. We have recently identified a secreted phospholipase A2 (sPLA2) released from the entomopathogenic nematode (EPN) Steinernema carpocapsae we have named Sc-sPLA2. We report that Sc-sPLA2 increased mortality of Drosophila melanogaster infected with Streptococcus pneumoniae and promoted increased bacterial growth. Furthermore, our data showed that Sc-sPLA2 was able to downregulate both Toll and Imd pathway-associated antimicrobial peptides (AMPs) including drosomycin and defensin, in addition to suppressing phagocytosis in the hemolymph. Sc-sPLA2 was also found to be toxic to D. melanogaster with the severity being both dose- and time-dependent. Collectively, our data highlighted that Sc-sPLA2 possessed both toxic and immunosuppressive capabilities.

The biodiversity of parasitic mites of the Demodecidae, infesting mammalian carnivorans, is poorly understood. To date, 18 host-specific species have been described, including four each from domestic dogs and cats, and only 10 from wild carnivores, known from single or duplicate reports. No data is available on the level of infestation of wild populations, or the co-occurrence of different demodecids in the same host, as only single species have been identified in individual hosts. A convenient model for such studies turned out to be the European polecat Mustela putorius, in which a new genus and species, Miridex putorii, was recently described in the vibrissae region of the skin of the head. Our study reveals that M. putorii co-occur with other species: Demodex putorii sp. nov. (associated with the hairless skin of the head) and Demodex foetorii sp. nov. (associated with hairy skin). Thus, the present study provides descriptions of species new to science. It also provides the first analysis of the occurrence of Demodecidae in wild mammalian carnivorans at the species and individual animal level based on the co-occurrence of three demodecid mite species in the skin of the head in M. putorius. Demodecid mites were found in 75.7% of 37 polecats; M. putorii showed the highest prevalence (56.8%), and D. putorii showed the highest abundance in the skin (mean 10.8 mites in 9 cm2). The three species co-occurred in 5.4% of the polecats, and two species in 27.0%. Despite the very high abundances, infestation was not associated with gross skin pathology (a feature of stable parasite–host systems formed by long-term co-evolution). The co-occurrence of several species and the separation of microhabitats are also typical of Demodecidae of other mammalian groups and illustrate the optimal use of the host body as a habitat and food source with limited impact.urn:lsid:zoobank.org:act:4D12FF6B-5A9E-4346-A496-52AC8448E7FEhttps://zoobank.org/NomenclaturalActs/4D12FF6B-5A9E-4346-A496-52AC8448E7FEurn:lsid:zoobank.org:act:07C533F5-9392-4FD3-BF9A-E1058C0FC1D6https://zoobank.org/NomenclaturalActs/07C533F5-9392-4FD3-BF9A-E1058C0FC1D6

Birds select breeding territories by assessing territory quality and considering predation pressure. However, in many small passerines, brood parasitism may also play an important role in territory occupancy. Settlement decisions are made under time pressure, especially for late migrants. An example of late migrants is the red-backed shrike Lanius collurio, a species wintering in sub-tropical Africa, which serves as a host for the common cuckoo Cuculus canorus and arrives in territories a few days later than their brood parasite. We expected that arriving red-backed shrikes avoided territories with common cuckoo presence. Then, we tested how experimentally provided artificial playback calls of the common cuckoo and woodpigeon (treated as control) affected the probability of red-backed shrike settlement. In the breeding season 2021, we observed 279 red-backed shrike territories to assess the effect of playback of common cuckoo calls on their host presence. Moreover, we adopt information on shrike territories collected in previous years to establish territory quality, measured by occupancy pattern over years. Each of these places was also checked for the presence of corvids, which are predators of shrike nests. We did not find difference with lower preference of shrikes towards cuckoo calls and to pigeon calls Columba columbus, what suggest the human presence and manipulation in the territories during experiments with recorders should be incorporated as an important factor to understanding shrikes’ settlement behaviour. What is interesting we found no negative effect of corvids (jay Garrulus glandarius) in control territories. However, shrike territories where cuckoo calls were emitted and where the presence of corvids was found were less likely to be inhabited by shrikes. Therefore, territory quality, human presence enhanced by nest predators, is an important factor affecting host–parasite interactions.

Abstract Background The microbiome is known to play key roles in health and disease, including host susceptibility to parasite infections. The freshwater snail Galba truncatula is the intermediate host for many trematode species, including the liver and rumen flukes Fasciola hepatica and Calicophoron daubneyi, respectively. The snail-parasite system has previously been investigated. However, the specific interaction between the snail-associated microbiota and intra-snail developmental stages of trematodes has yet to be explored. Methods Galba truncatula snails were collected from farms in Northern Ireland and trematode infection was diagnosed using PCR. High-throughput sequencing analysis of the bacterial 16S ribosomal DNA V3-V4 hypervariable regions was subsequently applied to characterise the microbiota of both uninfected and infected snails. Results We first showed that the snail harboured microbiota that was distinct for its environment. The microbiota of infected snails was found to differ significantly from that of uninfected snails. In particular, the bacterial genera Mycoplasma and Methylotenera were significantly more abundant in infected snails, while genera Sphingomonas and Nocardioides were predominantly associated with uninfected snails. Conclusion These findings pave the way to future studies on the functional roles of bacteria in host-parasite relationships. Graphical Abstract

Abstract Background Cumulative malaria parasite exposure in endemic regions often results in the acquisition of partial immunity and asymptomatic infections. There is limited information on how host-parasite interactions mediate the maintenance of chronic symptomless infections that sustain malaria transmission. Methods Here, we determined the gene expression profiles of the parasite population and the corresponding host peripheral blood mononuclear cells (PBMCs) from 21 children (

Abstract Background Gyrodactylus is a lineage of monogenean flatworm ectoparasites exhibiting many features that make them a suitable model to study the host-parasite coevolutionary dynamics. Previous coevolutionary studies of this lineage mainly relied on low-power datasets (a small number of samples and a single molecular marker) and (now) outdated algorithms. Methods To investigate the coevolutionary relationship of gyrodactylids and their fish hosts in high resolution, we used complete mitogenomes (including two newly sequenced Gyrodactylus species), a large number of species in the single-gene dataset, and four different coevolutionary algorithms. Results The overall coevolutionary fit between the parasites and hosts was consistently significant. Multiple indicators confirmed that gyrodactylids are generally highly host-specific parasites, but several species could parasitize either multiple (more than 5) or phylogenetically distant fish hosts. The molecular dating results indicated that gyrodactylids tend to evolve towards high host specificity. Speciation by host switch was identified as a more important speciation mode than co-speciation. Assuming that the ancestral host belonged to Cypriniformes, we inferred four major host switch events to non-Cypriniformes hosts (mostly Salmoniformes), all of which occurred deep in the evolutionary history. Despite their relative rarity, these events had strong macroevolutionary consequences for gyrodactylid diversity. For example, in our dataset, 57.28% of all studied gyrodactylids parasitized only non-Cypriniformes hosts, which implies that the evolutionary history of more than half of all included lineages could be traced back to these major host switch events. The geographical co-occurrence of fishes and gyrodactylids determined the host use by these gyrodactylids, and geography accounted for most of the phylogenetic signal in host use. Conclusions Our findings suggest that the coevolution of Gyrodactylus flatworms and their hosts is largely driven by geography, phylogeny, and host switches. Graphical Abstract

The role of species interactions, as well as genetic and environmental factors, all likely contribute to the composition and structure of the gut microbiome; however, disentangling these independent factors under field conditions represents a challenge for a functional understanding of gut microbial ecology. Avian brood parasites provide unique opportunities to investigate these questions, as brood parasitism results in parasite and host nestlings being raised in the same nest, by the same parents. Here we utilized obligate brood parasite brown‐headed cowbird nestlings (BHCO; Molothrus ater) raised by several different host passerine species to better understand, via 16S rRNA sequencing, the microbial ecology of brood parasitism. First, we compared faecal microbial communities of prothonotary warbler nestlings (PROW; Protonotaria citrea) that were either parasitized or non‐parasitized by BHCO and communities among BHCO nestlings from PROW nests. We found that parasitism by BHCO significantly altered both the community membership and community structure of the PROW nestling microbiota, perhaps due to the stressful nest environment generated by brood parasitism. In a second dataset, we compared faecal microbiotas from BHCO nestlings raised by six different host passerine species. Here, we found that the microbiota of BHCO nestlings was significantly influenced by the parental host species and the presence of an inter‐specific nestmate. Thus, early rearing environment is important in determining the microbiota of brood parasite nestlings and their companion nestlings. Future work may aim to understand the functional effects of this microbiota variability on nestling performance and fitness. [ABSTRACT FROM AUTHOR]

By imposing novel selection pressures on both participants, biological invasions can modify evolutionary 'arms races' between hosts and parasites. A spatially replicated cross-infection experiment reveals strong spatial divergence in the ability of lungworms (Rhabdias pseudosphaerocephala) to infect invasive cane toads (Rhinella marina) in Australia. In areas colonized for longer than 20 years, toads are more resistant to infection by local strains of parasites than by allopatric strains. The situation reverses at the invasion front, where super-infective parasites have evolved. Invasion-induced shifts in genetic diversity and selective pressures may explain why hosts gain advantage over parasites in long-colonized areas, whereas parasites gain advantage at the invasion front. [ABSTRACT FROM AUTHOR]

Helminths use small microRNAs (miRNAs) to manipulate their host's immune responses by 'cross-kingdom' gene regulation, but the exact mechanisms remain unclear. Helminths communicate with their host cells by releasing miRNAs encapsulated in extracellular vesicles (EVs); this EV cargo is selectively packaged for specific microRNAs. Helminth miRNAs share structural similarities with mammalian miRNAs, allowing them to be loaded onto the host's argonaute (AGO) proteins. Helminth miRNAs use a multifaceted strategy, regulating host targets, mimicking host miRNAs to commandeer their biogenesis components, and potentially binding to other host miRNAs. Unravelling the complex mechanism of 'cross-kingdom' gene regulation could transform our approach to combating helminth infections and deepen our insight into host–parasite dynamics. MicroRNAs (miRNAs) are small noncoding RNAs that oversee gene modulation. They are integral to cellular functions and can migrate between species, leading to cross-kingdom gene suppression. Recent breakthroughs in helminth genome studies have sparked curiosity about helminth RNA regulators and their ability to regulate genes across species. Growing data indicate that helminth miRNAs have a significant impact on the host's immune system. Specific miRNAs from helminth parasites can merge with the host's miRNA system, implying that parasites could exploit their host's regulatory machinery and function. This review highlights the role of cross-kingdom helminth-derived miRNAs in the interplay between host and parasite, exploring potential routes for their uptake, processing, and consequences in host interaction. [ABSTRACT FROM AUTHOR]

Host–parasite coevolution is mediated by genetic interactions between the antagonists and may lead to reciprocal adaptation. In the black bean aphid, Aphis fabae fabae , resistance to parasitoids can be conferred by the heritable bacterial endosymbiont Hamiltonella defensa. H. defensa has been shown to be variably protective against different parasitoid species, and different genotypes of the black bean aphid's main parasitoid Lysiphlebus fabarum. However, these results were obtained using haphazard combinations of laboratory-reared insect lines with different origins, making it unclear how representative they are of natural, locally (co)adapted communities. We therefore comprehensively sampled the parasitoids of a natural A. f. fabae population and measured the ability of the five most abundant species to parasitize aphids carrying the locally prevalent H. defensa haplotypes. H. defensa provided resistance only against the dominant parasitoid L. fabarum (70% of all parasitoids), but not against less abundant parasitoids, and resistance to L. fabarum acted in a genotype-specific manner (G × G interactions between H. defensa and L. fabarum). These results confirm that strong species- and genotype-specificity of symbiont-conferred resistance is indeed a hallmark of wild A. f. fabae populations, and they are consistent with symbiont-mediated adaptation of aphids to the parasitoids posing the highest risk. [ABSTRACT FROM AUTHOR]

The study of host–parasite interactions is essential to understand the role of each host species in the parasitic transmission cycles in a given community. The use of ecological network highlights the patterns of interactions between hosts and parasites, allowing us to evaluate the underlying structural features and epidemiological roles of different species within this context. Through network analysis, we aimed to understand the epidemiological roles of mammalian hosts species (n = 67) and their parasites (n = 257) in the Pantanal biome. Our analysis revealed a modular pattern within the network, characterized by 14 distinct modules, as well as nestedness patterns within these modules. Some key nodes, such as the multi-host parasites Trypanosoma cruzi and T. evansi, connect different modules and species. These central nodes showed us that various hosts species, including those with high local abundances, contribute to parasite maintenance. Ectoparasites, such as ticks and fleas, exhibit connections that reflect their roles as vectors of certain parasites. Overall, our findings contribute to a comprehensive understanding of the structure of host–parasite interactions in the Pantanal ecosystem, highlighting the importance of network analysis as a tool to identifying the main transmission routes and maintenance of parasites pathways. Such insights are valuable for parasitic disease control and prevention strategies and shed light on the broader complexities of ecological communities. [ABSTRACT FROM AUTHOR]

Background and Aims Rhamphicarpa fistulosa (Hochst.) Benth. is an annual facultative parasitic plant adapted to hydromorphic soils. In sub-Saharan Africa it causes high crop losses as a weed in rainfed lowland rice (Oryza sativa L.). Fertilizers are often proposed as a control measure against hemiparasitic weeds, but an understanding of the nutrient effects on R. fistulosa is currently still elusive. Methods In two greenhouse pot experiments, conducted in 2016 in the Netherlands and in 2019 in the UK, host plants (O. sativa , cv IR64) and parasitic plants (R. fistulosa) were grown alone or combined and were subjected to different levels of nutrient availability. Biomass measurements were used to assess whether and how effects of nutrient availability are expressed in the host and parasite. Key Results Compared with parasite-free host plants, the biomass of parasite-infested plants was severely reduced, and nutrient effects on host plant biomass were less pronounced. Conversely, increased nutrient availability did not have an effect on parasitic plants when grown alone, but when grown with a host the parasitic plant biomass increased proportionally. Grown together, the combined biomass of host plant and parasite was substantially lower than that of the host plant grown alone. The ratio of biomass between host plant and parasite was unaffected by nutrient availability. Conclusions Fertilization benefits to rice plants are severely reduced but not completely nullified by R. fistulosa infection. The benefits to production and reproduction accrued by the parasite from increased nutrient availability are restricted to conditions in the presence of a host plant. Host presence and nutrient effects are thus observed to be synergetic; R. fistulosa plants parasitizing a suitable host respond strongly to increasing levels of nutrients. This is associated with an increased root biomass of the parasitic plant itself, but is more likely to result from exploitation of the nutrient uptake capacity of the host plant it parasitizes. [ABSTRACT FROM AUTHOR]

Background: Cumulative malaria parasite exposure in endemic regions often results in the acquisition of partial immunity and asymptomatic infections. There is limited information on how host-parasite interactions mediate the maintenance of chronic symptomless infections that sustain malaria transmission. Methods: Here, we determined the gene expression profiles of the parasite population and the corresponding host peripheral blood mononuclear cells (PBMCs) from 21 children (< 15 years). We compared children who were defined as uninfected, asymptomatic and those with febrile malaria. Results: Children with asymptomatic infections had a parasite transcriptional profile characterized by a bias toward trophozoite stage (~ 12 h-post invasion) parasites and low parasite levels, while early ring stage parasites were characteristic of febrile malaria. The host response of asymptomatic children was characterized by downregulated transcription of genes associated with inflammatory responses, compared with children with febrile malaria,. Interestingly, the host responses during febrile infections that followed an asymptomatic infection featured stronger inflammatory responses, whereas the febrile host responses from previously uninfected children featured increased humoral immune responses. Conclusions: The priming effect of prior asymptomatic infection may explain the blunted acquisition of antibody responses seen to malaria antigens following natural exposure or vaccination in malaria endemic areas. [ABSTRACT FROM AUTHOR]

Background: Gyrodactylus is a lineage of monogenean flatworm ectoparasites exhibiting many features that make them a suitable model to study the host-parasite coevolutionary dynamics. Previous coevolutionary studies of this lineage mainly relied on low-power datasets (a small number of samples and a single molecular marker) and (now) outdated algorithms. Methods: To investigate the coevolutionary relationship of gyrodactylids and their fish hosts in high resolution, we used complete mitogenomes (including two newly sequenced Gyrodactylus species), a large number of species in the single-gene dataset, and four different coevolutionary algorithms. Results: The overall coevolutionary fit between the parasites and hosts was consistently significant. Multiple indicators confirmed that gyrodactylids are generally highly host-specific parasites, but several species could parasitize either multiple (more than 5) or phylogenetically distant fish hosts. The molecular dating results indicated that gyrodactylids tend to evolve towards high host specificity. Speciation by host switch was identified as a more important speciation mode than co-speciation. Assuming that the ancestral host belonged to Cypriniformes, we inferred four major host switch events to non-Cypriniformes hosts (mostly Salmoniformes), all of which occurred deep in the evolutionary history. Despite their relative rarity, these events had strong macroevolutionary consequences for gyrodactylid diversity. For example, in our dataset, 57.28% of all studied gyrodactylids parasitized only non-Cypriniformes hosts, which implies that the evolutionary history of more than half of all included lineages could be traced back to these major host switch events. The geographical co-occurrence of fishes and gyrodactylids determined the host use by these gyrodactylids, and geography accounted for most of the phylogenetic signal in host use. Conclusions: Our findings suggest that the coevolution of Gyrodactylus flatworms and their hosts is largely driven by geography, phylogeny, and host switches. [ABSTRACT FROM AUTHOR]

Background: The microbiome is known to play key roles in health and disease, including host susceptibility to parasite infections. The freshwater snail Galba truncatula is the intermediate host for many trematode species, including the liver and rumen flukes Fasciola hepatica and Calicophoron daubneyi, respectively. The snail-parasite system has previously been investigated. However, the specific interaction between the snail-associated microbiota and intra-snail developmental stages of trematodes has yet to be explored. Methods: Galba truncatula snails were collected from farms in Northern Ireland and trematode infection was diagnosed using PCR. High-throughput sequencing analysis of the bacterial 16S ribosomal DNA V3-V4 hypervariable regions was subsequently applied to characterise the microbiota of both uninfected and infected snails. Results: We first showed that the snail harboured microbiota that was distinct for its environment. The microbiota of infected snails was found to differ significantly from that of uninfected snails. In particular, the bacterial genera Mycoplasma and Methylotenera were significantly more abundant in infected snails, while genera Sphingomonas and Nocardioides were predominantly associated with uninfected snails. Conclusion: These findings pave the way to future studies on the functional roles of bacteria in host-parasite relationships. [ABSTRACT FROM AUTHOR]

The study of microbiomes across organisms and environments has become a prominent focus in molecular ecology. This perspective article explores common challenges, methodological advancements, and future directions in the field. Key research areas include understanding the drivers of microbiome community assembly, linking microbiome composition to host genetics, exploring microbial functions, transience and spatial partitioning, and disentangling non‐bacterial components of the microbiome. Methodological advancements, such as quantifying absolute abundances, sequencing complete genomes, and utilizing novel statistical approaches, are also useful tools for understanding complex microbial diversity patterns. Our aims are to encourage robust practices in microbiome studies and inspire researchers to explore the next frontier of this rapidly changing field. [ABSTRACT FROM AUTHOR]

Reciprocal selection between symbiotic organisms and their hosts can generate variations in local adaptation between them. Symbionts often form species complexes with lineages partially adapted to various hosts. However, it is unclear how interactions among these lineages influences geographic variation in the extent of host‐symbiont local adaptation. We addressed this shortcoming with experiments on burying beetles Nicrophorus vespilloides and their specialist phoretic mite Poecilochirus carabi in two adjacent woodlands. Burying beetles transport these mites to vertebrate carrion upon which they both reproduce. P. carabi appears to be a species complex, with distinct lineages that specialise on breeding alongside different Nicrophorus species. We found that in one wood (Gamlingay Woods), N. vespilloides carries a mixture of mite lineages, with each lineage corresponding to one of the four Nicrophorus species that inhabits this wood. However, two burying beetle species coexist in neighbouring Waresley Woods and here N. vespilloides predominantly carries the mite lineage that favours N. vespilloides. Mite lineage mixing alters the degree of local adaptation for both N. vespilloides and the P. carabi mites, affecting reproductive success variably across different woodlands. In Gamlingay, mite lineage mixing reduced N. vespilloides reproductive success, while experimentally purifying mites lineage enhanced it. The near pure lineage of vespilloides mites negligibly affected Waresley N. vespilloides. Mite reproductive success varied with host specificity: Gamlingay mites had greatest reproductive success on Gamlingay beetles, and performed less well with Waresley beetles. By contrast, Waresley mites had consistent reproductive success, regardless of beetle's woodland of origin. We conclude that there is some evidence that N. vespilloides and its specific mite lineage have coadapted. However, neither N. vespilloides nor its mite lineage adapted to breed alongside other mite lineages. This, we suggest, causes variation between Waresley and Gaminglay Woods in the extent of local adaptation between N. vespilloides beetles and their P. carabi mites. [ABSTRACT FROM AUTHOR]

The relationship between pathogen proliferation and the cost of infection experienced by a host drives the ecology and evolution of host–pathogen dynamics. While environmental factors can shape this relationship, there is currently limited knowledge on the consequences of emerging contaminants, such as pharmaceutical pollutants, on the relationship between a pathogen's growth within the host and the damage it causes, termed its virulence. Here, we investigated how exposure to fluoxetine (Prozac), a commonly detected psychoactive pollutant, could alter this key relationship using the water flea Daphnia magna and its bacterial pathogen Pasteuria ramosa as a model system. Across a variety of fluoxetine concentrations, we found that fluoxetine shaped the damage a pathogen caused, such as the reduction in fecundity or intrinsic growth experienced by infected individuals, but with minimal change in average pathogen spore loads. Instead, fluoxetine modified the relationship between the degree of pathogen proliferation and its virulence, with both the strength of this trade-off and the component of host fitness most affected varying by fluoxetine concentration and host genotype. Our study underscores the potential for pharmaceutical pollution to modify the virulence of an invading pathogen, as well as the fundamental trade-off between host and pathogen fitness, even at the trace amounts increasingly found in natural waterways. [ABSTRACT FROM AUTHOR]

Australia has a highly endemic freshwater fish fauna, but basic biological knowledge for most is lacking. This includes an understanding, and description, of their parasite fauna. Additionally, the impacts of introduced fish species, and their parasites which have transferred across to native species, are also mostly unknown. This review provides the current level of knowledge of parasitic infection of the freshwater fish in Australia, both introduced and native. Only about a third of the native freshwater fish, but almost two‐thirds of introduced fish, have been reported as a host for a parasite. The majority of records occur along the eastern coastline of Australia and throughout the Murray Darling Basin; two drainage regions were yet to record any parasite infections. Of the 124 fish species, across 43 families, found as hosts in Australia, only 11 species had more than 10 reports of infection, with 31% of fish species only having single reports. A total of 13 different types of parasites were reported, with digeneans, protozoans, nematodes and monogeneans the most commonly reported. Significant gaps in the knowledge of parasites, and their potential impacts, of Australian freshwater fish still exist, and the need for fish biologists and fish parasitologists to work together is highlighted to ensure that as much information about each group can be obtained. [ABSTRACT FROM AUTHOR]

Toxoplasma gondii, a protozoan parasite with the ability to infect various warm-blooded vertebrates, including humans, is the causative agent of toxoplasmosis. This infection poses significant risks, leading to severe complications in immunocompromised individuals and potentially affecting the fetus through congenital transmission. A comprehensive understanding of the intricate molecular interactions between T. gondii and its host is pivotal for the development of effective therapeutic strategies. This review emphasizes the crucial role of proteomics in T. gondii research, with a specific focus on host–parasite interactions, post-translational modifications (PTMs), PTM crosstalk, and ongoing efforts in drug discovery. Additionally, we provide an overview of recent advancements in proteomics techniques, encompassing interactome sample preparation methods such as BioID (BirA*-mediated proximity-dependent biotin identification), APEX (ascorbate peroxidase-mediated proximity labeling), and Y2H (yeast two hybrid), as well as various proteomics approaches, including single-cell analysis, DIA (data-independent acquisition), targeted, top-down, and plasma proteomics. Furthermore, we discuss bioinformatics and the integration of proteomics with other omics technologies, highlighting its potential in unraveling the intricate mechanisms of T. gondii pathogenesis and identifying novel therapeutic targets. [ABSTRACT FROM AUTHOR]