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In the absence of chemical control with its negative side effects, fungal pathogens can cause large yield losses, requiring us to develop agroecosystems that are inherently disease resistant. Grassland biodiversity experiments often find plant species diversity to reduce pathogen pressure, but whether incorporating high biodiversity levels in agricultural fields have similar effects remains largely unknown. We tested if undersown plant species diversity could reduce barley disease, and whether the effect was mediated through above‐ or below‐ground mechanisms, by combining an agricultural field trial with a soil transplant experiment. As predicted, barley disease decreased in the presence of undersown plants. Undersown species richness had no effect, but their abundance led to early season disease reduction. Above‐ground mechanisms underpinned this disease reduction. Barley yield slightly decreased with increasing undersown species richness, and undersown species varied in their impact on yield. We identified two undersown species, Trifolium repens and T. hybridum, that contributed most to disease reduction and had the potential to increase barley yield. Furthermore, our results indicate that above‐ground mechanisms caused this. We show that agroecosystem functioning can be improved without trade‐offs on yield by targeted selection of undersown species. Read the free Plain Language Summary for this article on the Journal blog.

Invertebrate herbivores are important and diverse, and their abundance and impacts will likely shift under climate change. Yet, past studies of invertebrate herbivory have documented highly variable responses to changing temperature, making it challenging to predict the direction and magnitude of these shifts. One explanation for these responses is that changing environmental conditions drive concurrent changes in plant communities and herbivore traits. The impacts of changing temperature on herbivory might therefore depend on how temperature combines and interacts with characteristics of plant and herbivore communities. To test this, we surveyed damage to leaves by invertebrate herbivores on 4400 plant individuals in 220 sampling plots along a 1101 m elevational gradient. Increasing temperature drove community‐level herbivory via at least three overlapping mechanisms: increasing temperature directly reduced herbivory, indirectly affected herbivory by reducing plant‐community phylogenetic diversity, and indirectly affected herbivory by altering the effects of plant‐community functional and phylogenetic diversity on herbivory. Consequently, increasing plant functional diversity reduced herbivory in colder environments while increasing plant phylogenetic diversity increased herbivory in warmer environments. Moreover, different herbivore feeding guilds varied in their response to temperature and plant community composition. These results indicate that, even along a single elevation gradient in a single year, a variety of mechanisms can concurrently drive herbivory, thereby supporting the hypothesis that a universal response of herbivory to changing environmental conditions is unlikely to exist. Instead, our results highlight the importance of considering both plant and herbivore community context to predict how climate change will alter invertebrate herbivory.

Viral diversity has been discovered across scales from host individuals to populations. However, the drivers of viral community assembly are still largely unknown. Within-host viral communities are formed through co-infections, where the interval between the arrival times of viruses may vary. Priority effects describe the timing and order in which species arrive in an environment, and how early colonizers impact subsequent community assembly. To study the effect of the first-arriving virus on subsequent infection patterns of five focal viruses, we set up a field experiment using naïve Plantago lanceolata plants as sentinels during a seasonal virus epidemic. Using joint species distribution modelling, we find both positive and negative effects of early season viral infection on late season viral colonization patterns. The direction of the effect depends on both the host genotype and which virus colonized the host early in the season. It is well established that co-occurring viruses may change the virulence and transmission of viral infections. However, our results show that priority effects may also play an important, previously unquantified role in viral community assembly. The assessment of these temporal dynamics within a community ecological framework will improve our ability to understand and predict viral diversity in natural systems.

Predicting how climate change will affect disease risk is complicated by the fact that changing environmental conditions can affect disease through direct and indirect effects. Species with fast-paced life-history strategies often amplify disease, and changing climate can modify life-history composition of communities thereby altering disease risk. However, individuals within a species can also respond to changing conditions with intraspecific trait variation. To test the effect of temperature, as well as inter- and intraspecifc trait variation on community disease risk, we measured foliar disease and specific leaf area (SLA; a proxy for life-history strategy) on more than 2500 host (plant) individuals in 199 communities across a 1101 m elevational gradient in southeastern Switzerland. There was no direct effect of increasing temperature on disease. Instead, increasing temperature favoured species with higher SLA, fast-paced life-history strategies. This effect was balanced by intraspecific variation in SLA: on average, host individuals expressed lower SLA with increasing temperature, and this effect was stronger among species adapted to warmer temperatures and lower latitudes. These results demonstrate how impacts of changing temperature on disease may depend on how temperature combines and interacts with host community structure while indicating that evolutionary constraints can determine how these effects are manifested under global change. This article is part of the theme issue ‘Infectious disease ecology and evolution in a changing world’.

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural dines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale.

Invertebrate herbivores are important and diverse, and their abundance and impacts are expected to undergo unprecedented shifts under climate change. Yet, past studies of invertebrate herbivory have documented a wide variety of responses to changing temperature, making it challenging to predict the direction and magnitude of these shifts. One explanation for these idiosyncratic responses is that changing environmental conditions may drive concurrent changes in plant communities and herbivore traits. Thus, the impacts of changing temperature on herbivory might depend on how temperature combines and interacts with characteristics of plant communities and the herbivores that occupy them. Here, we test this hypothesis by surveying invertebrate herbivory in 220, 0.5 meter-diameter herbaceous plant communities along a 1101-meter elevational gradient. Our results suggest that increasing temperature can drive community-level herbivory via at least three overlapping mechanisms: increasing temperature directly reduced herbivory, indirectly affected herbivory by reducing phylogenetic diversity of the plant community, and indirectly affected herbivory by altering the effects of functional and phylogenetic diversity on herbivory. Consequently, increasing functional diversity of plant communities had a negative effect on herbivory, but only in colder environments while a positive effect of increasing phylogenetic diversity was observed in warmer environments. Moreover, accounting for differences among herbivore feeding guilds considerably improved model fit, because different herbivore feeding guilds varied in their response to temperature and plant community composition. Together, these results highlight the importance of considering both plant and herbivore community context in order to predict how climate change will alter invertebrate herbivory.

The inherently variable nature of epidemics renders predictions of when and where infection is expected to occur challenging. Differences in pathogen strain composition, diversity, fitness, and spatial distribution are generally ignored in epidemiological modeling and are rarely studied in natural populations, yet they may be important drivers of epidemic trajectories. To examine how these factors are linked to epidemics in natural host populations, we collected epidemiological and genetic data from 15 populations of the powdery mildew fungus, Podosphaera plantaginis, on Plantago lanceolata in the Åland Islands, Finland. In each population, we tracked spatiotemporal disease progression throughout one epidemic season and coupled our survey of infection with intensive field sampling of the pathogen. We found that strain composition varied greatly among populations in the landscape. Within populations, strain composition was driven by the sequence of strain activity: early-active strains reached higher abundances, leading to consistent strain compositions over time. Co-occurring strains also varied in their contribution to the growth of the local epidemic, and these fitness inequalities were linked to epidemic dynamics: a higher proportion of hosts became infected in populations containing strains that were more similar in fitness. Epidemic trajectories in the populations were also linked to strain diversity and spatial dynamics: higher infection rates occurred in populations containing higher strain diversity, while spatially clustered epidemics experienced lower infection rates. Together, our results suggest that spatial and/or temporal variation in the strain composition, diversity, and fitness of pathogen populations are important factors generating variation in epidemiological trajectories among infected host populations.

Identifying the ecological processes underlying community assembly remains an elusive goal in community ecology. We formalize assembly hypotheses as alternative models and apply each to predict 1,918 out-of-sample boreal forest understory communities to identify and separate the processes driving community assembly. Models are specified within a Bayesian joint species distribution framework that allows for the inclusion and separation of stochastic processes, environmental filtering, and two different species dependence structures. We found clear evidence that study communities are structured by both environmental filtering and compositional dependence highlighting the importance of selection in community assembly. The relative importance of environmental filtering was greater than compositional dependence in predicting both understory communities and the abundance of constituent species across broad suc-cessional and bioclimatic gradients. Contrary to ecological expectations, the inclusion of a flexible residual species dependence structure (accounting for more than compositional dependence) did not improve model predictions after accounting for the strong role of environmental filtering. Our results provide novel inference on the processes underlying community assembly facilitated by applying empirical approximations of alternative assembly processes to predict communities across a range of environmental conditions.

While the negative effects that pathogens have on their hosts are well-documented in humans and agricultural systems, direct evidence of pathogen-driven impacts in wild host populations is scarce and mixed. Here, to determine how the strength of pathogen-imposed selection depends on spatial structure, we analyze growth rates across approximately 4000 host populations of a perennial plant through time coupled with data on pathogen presence-absence. We find that infection decreases growth more in the isolated than well-connected host populations. Our inoculation study reveals isolated populations to be highly susceptible to disease while connected host populations support the highest levels of resistance diversity, regardless of their disease history. A spatial eco-evolutionary model predicts that non-linearity in the costs to resistance may be critical in determining this pattern. Overall, evolutionary feedbacks define the ecological impacts of disease in spatially structured systems with host gene flow being more important than disease history in determining the outcome.

While the positive relationship between plant biodiversity and ecosystem functioning (BEF) is well established, the extent to which this is mediated via belowground microbial processes is poorly understood. Growing evidence suggests that plant community structure influences soil microbial diversity, which in turn promotes functions desired for sustainable agriculture. Here, we outline the ‘plant-directed’ and soil microbe-mediated mechanisms expected to promote positive BEF. We identify how this knowledge can be utilized in plant diversification schemes to maximize ecosystem functioning in agroecosystems, which are typically species poor and sensitive to biotic and abiotic stressors. In the face of resource overexploitation and global change, bridging the gaps between biodiversity science and agricultural practices is crucial to meet food security in the Anthropocene.

The trade-off between within-host infection rate and transmission to new hosts is predicted to constrain pathogen evolution, and to maintain polymorphism in pathogen populations. Pathogen life-history stages and their correlations that underpin infection development may change under coinfection with other parasites as they compete for the same limited host resources. Cross-kingdom interactions are common among pathogens in both natural and cultivated systems, yet their impacts on disease ecology and evolution are rarely studied. The host plant Plantago lanceolata is naturally infected by both Phomopsis subordinaria, a seed killing fungus, as well as Plantago lanceolata latent virus (PlLV) in the Åland Islands, SW Finland. We performed an inoculation assay to test whether coinfection with PlLV affects performance of two P. subordinaria strains, and the correlation between within-host infection rate and transmission potential. The strains differed in the measured life-history traits and their correlations. Moreover, we found that under virus coinfection, within-host infection rate of P. subordinaria was smaller but transmission potential was higher compared to strains under single infection. The negative correlation between within-host infection rate and transmission potential detected under single infection became positive under coinfection with PlLV. To understand whether within-host and between-host dynamics are correlated in wild populations, we surveyed 260 natural populations of P. lanceolata for P. subordinaria infection occurrence. When infections were found, we estimated between-hosts dynamics by determining pathogen population size as the proportion of infected individuals, and within-host dynamics by counting the proportion of infected flower stalks in 10 infected plants. In wild populations, the proportion of infected flower stalks was positively associated with pathogen population size. Jointly, our results suggest that the trade-off between within-host i

Genetic differentiation and phenotypic plasticity jointly shape intraspecific trait variation, but their roles differ among traits. In short-lived plants, reproductive traits may be more genetically determined due to their impact on fitness, whereas vegetative traits may show higher plasticity to buffer short-term perturbations. Combining a multi-treatment greenhouse experiment with observational field data throughout the range of a widespread short-lived herb, Plantago lanceolata, we (1) disentangled genetic and plastic responses of functional traits to a set of environmental drivers and (2) assessed how genetic differentiation and plasticity shape observational trait–environment relationships. Reproductive traits showed distinct genetic differentiation that largely determined observational patterns, but only when correcting traits for differences in biomass. Vegetative traits showed higher plasticity and opposite genetic and plastic responses, masking the genetic component underlying field-observed trait variation. Our study suggests that genetic differentiation may be inferred from observational data only for the traits most closely related to fitness.

Human alteration of natural habitats may change the processes governing species interactions in wild communities. Wild populations are increasingly impacted by agricultural intensification, yet it is unknown whether this alters biodiversity mediation of disease dynamics. We investigated the association between plant diversity (species richness, diversity) and infection risk (virus richness, prevalence) in populations of Plantago lanceolata in natural landscapes as well as those occurring at the edges of cultivated fields. Altogether, 27 P. lanceolata populations were surveyed for population characteristics and sampled for PCR detection of five recently characterized viruses. We find that plant species richness and diversity correlated negatively with virus infection prevalence. Virus species richness declined with increasing plant diversity and richness in natural populations while in agricultural edge populations species richness was moderately higher, and not associated with plant richness. This difference was not explained by changes in host richness between these two habitats, suggesting potential pathogen spill‐over and increased transmission of viruses across the agro‐ecological interface. Host population connectivity significantly decreased virus infection prevalence. We conclude that human use of landscapes may change the ecological laws by which natural communities are formed with far reaching implications for ecosystem functioning and disease.

Aim The diversity and composition of natural communities are rapidly changing due to anthropogenic disturbances. Magnitude of this compositional reorganization varies across the globe, but reasons behind the variation remain largely unknown. Disturbances induce temporal turnover by stimulating species colonizations, causing local extinctions, altering dominance structure, or all of these. We test which of these processes drive temporal community changes, and whether they are constrained by natural environmental gradients. Moreover, we assess to what degree identity shifts translate to changes in dominance structure. Location Finland. Time period Observations 1985–2006, disturbance history > 140 years. Major taxa studied Vascular plants. Methods We investigated temporal turnover of boreal forest understorey in response to disturbance, here forest management, along a soil fertility gradient. We disentangle the roles of species gains, losses and abundance changes in driving temporal turnover in response to and after disturbance by comparing turnover rates in different forest age categories along a fertility gradient. We quantify temporal turnover using richness‐based complement of Jaccard’s similarity index and proportional‐abundance based dissimilarity index. We also test whether disturbance history or fertility influence the relationship between identity shifts and dominance structure. Results We found that the impact of disturbance on temporal turnover depends on soil fertility. The greatest turnover occurred in the most fertile forests immediately after disturbance. There, species gains and losses strongly altered dominance structure leading to high turnover, whereas undisturbed old forests and nutrient‐poor habitats were characterized by stable dominant species even when the majority of species shifted their identity. Main conclusions Our results suggest that human impacts on temporal biodiversity change vary along environmental gradients. In boreal forests, the f

Maternal effects of pathogen infection on progeny development and disease resistance may be adaptive and have important consequences for population dynamics. However, these effects are often context‐dependent and examples of adaptive transgenerational responses from perennials are scarce, although they may be a particularly important mechanism generating variation in the offspring of long‐lived species. Here, we studied the effect of maternal infection of Plantago lanceolata by Podosphaera plantaginis, a fungal parasite, on the growth, flower production and resistance of the progeny of six maternal genotypes in nutrient‐rich and nutrient‐poor environments. For this purpose, we combined a common garden study with automated phenotyping measurements of early life stages, and an inoculation experiment. Our results show that the effects of infection on the mother plants transcend to impact their progeny. Although maternal infection decreased total leaf and flower production of the progeny by the end of the growing season, it accelerated early growth and enhanced resistance to the pathogen P. plantaginis. We also discovered that the effects of maternal infection affected progeny development and resistance through a three way‐interaction between maternal genotype, maternal infection status and nutrient availability. Synthesis. Our results emphasize the importance of maternal effects mediated through genotypic and environmental factors in long‐living perennials and suggest that maternal infection can create a layer of phenotypic diversity in resistance. These results may have important implications for both epidemiological and evolutionary dynamics of host–parasite interactions in the wild.

When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata. Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area.

When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area.

When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata. Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area.

When plants establish outside their native range, their ability to adapt to the new environment is influenced by both demography and dispersal. However, the relative importance of these two factors is poorly understood. To quantify the influence of demography and dispersal on patterns of genetic diversity underlying adaptation, we used data from a globally distributed demographic research network comprising 35 native and 18 nonnative populations of Plantago lanceolata. Species-specific simulation experiments showed that dispersal would dilute demographic influences on genetic diversity at local scales. Populations in the native European range had strong spatial genetic structure associated with geographic distance and precipitation seasonality. In contrast, nonnative populations had weaker spatial genetic structure that was not associated with environmental gradients but with higher within-population genetic diversity. Our findings show that dispersal caused by repeated, long-distance, human-mediated introductions has allowed invasive plant populations to overcome environmental constraints on genetic diversity, even without strong demographic changes. The impact of invasive plants may, therefore, increase with repeated introductions, highlighting the need to constrain future introductions of species even if they already exist in an area.

The dynamics of ecological communities depend partly on species interactions within and among trophic levels. Experimental work has demonstrated the impact of species interactions on the species involved, but it remains unclear whether these effects can also be detected in long‐term time series across heterogeneous landscapes. We analyzed a 19‐yr time series of patch occupancy by the Glanville fritillary butterfly Melitaea cinxia, its specialist parasitoid wasp Cotesia melitaearum, and the specialist fungal pathogen Podosphaera plantaginis infecting Plantago lanceolata, a host plant of the Glanville fritillary. These species share a network of more than 4,000 habitat patches in the Åland islands, providing a metacommunity data set of unique spatial and temporal resolution. To assess the influence of interactions among the butterfly, parasitoid, and mildew on metacommunity dynamics, we modeled local colonization and extinction rates of each species while including or excluding the presence of potentially interacting species in the previous year as predictors. The metapopulation dynamics of all focal species varied both along a gradient in host plant abundance, and spatially as indicated by strong effects of local connectivity. Colonization and to a lesser extent extinction rates depended also on the presence of interacting species within patches. However, the directions of most effects differed from expectations based on previous experimental and modeling work, and the inferred influence of species interactions on observed metacommunity dynamics was limited. These results suggest that although local interactions among the butterfly, parasitoid, and mildew occur, their roles in metacommunity spatiotemporal dynamics are relatively weak. Instead, all species respond to variation in plant abundance, which may in turn fluctuate in response to variation in climate, land use, or other environmental factors.

Infection by multiple pathogens of the same host is ubiquitous in both natural and managed habitats. While intraspecific variation in disease resistance is known to affect pathogen occurrence, how differences among host genotypes affect the assembly of pathogen communities remains untested. In our experiment using cloned replicates of naive Plantago lanceolata plants as sentinels during a seasonal virus epidemic, we find non-random co-occurrence patterns of five focal viruses. Using joint species distribution modelling, we attribute the non-random virus occurrence patterns primarily to differences among host genotypes and local population context. Our results show that intraspecific variation among host genotypes may play a large, previously unquantified role in pathogen community structure.

Host individuals are often coinfected with diverse parasite assemblages, resulting in complex interactions among parasites within hosts. Within hosts, priority effects occur when the infection sequence alters the outcome of interactions among parasites. Yet, the role of host immunity in this process remains poorly understood. We hypothesized that the host response to first infection could generate priority effects among parasites, altering the assembly of later arriving strains during epidemics. We tested this by infecting sentinel host genotypes of Plantago lanceolata with strains of the fungal parasite, Podosphaera plantaginis, and measuring susceptibility to subsequent infection during experimental and natural epidemics. In these experiments, prior infection by one strain often increased susceptibility to other strains, and these facilitative priority effects altered the structure of parasite assemblages, but this effect depended on host genotype, host population, and parasite genotype. Thus, host genotype, spatial structure, and priority effects among strains all independently altered parasite assembly. Then, using a fine-scale survey and sampling of infections on wild hosts in several populations, we identified a signal of facilitative priority effects, which altered parasite assembly during natural epidemics. Together, these results provide evidence that within host priority effects by early arriving strains can drive parasite assembly, with implications for how strain diversity is spatially and temporally distributed during epidemics.

The dilution effect predicts increasing biodiversity to reduce the risk of infection, but the generality of this effect remains unresolved. Because biodiversity loss generates predictable changes in host community competence, we hypothesized that biodiversity loss might drive the dilution effect. We tested this hypothesis by reanalyzing four previously published meta-analyses that came to contradictory conclusions regarding generality of the dilution effect. In the context of biodiversity loss, our analyses revealed a unifying pattern: dilution effects were inconsistently observed for natural biodiversity gradients, but were commonly observed for biodiversity gradients generated by disturbances causing losses of native biodiversity. Incorporating biodiversity loss into tests of generality of the dilution effect further indicated that scale-dependency may strengthen the dilution effect only when biodiversity gradients are driven by biodiversity loss. Together, these results help to resolve one of the most contentious issues in disease ecology: the generality of the dilution effect.

The genus Capulavirus is a new genus in the family Geminiviridae that contains so far four species (Alfalfa leaf curl virus, Euphorbia caput-medusae latent virus, French bean severe leaf curl virus and Plantago lanceolata latent virus) that infect both cultivated and non-cultivated plants. Among them, plantago lanceolata latent virus (PlLV) infects ribwort plantain (Plantago lanceolata L.), a perennial herb that is native from Eurasia and is now widespread all over the world. PlLV is transmitted by the aphid Dysaphis plantaginea, which has a holocyclic lifestyle with two successive host plants: apple and plantain. Mechanical inoculation of sap using carborundum powder or syringe have also proved effective to infect various plants including P. lanceolata. Although plants naturally infected with PlLV displayed yellowing symptoms, agroinoculation in controlled conditions of an agroinfectious clone of PlLV in plantain did not reveal evidence of symptoms. In order to better decipher the prevalence and the diversity of PlLV, P. lanceolata plant samples were collected from four European countries (Finland, France, Italy and Spain), as well as from Iran and South Africa, and were tested by PCR for the presence of PlLV. While PlLV was initially reported from the Åland Islands (South-West Finland), we show that PlLV is also found from all sampled countries but South Africa. These results suggest that the geographic distribution of PlLV is larger than initially thought and that PlLV prevalence is probably relatively high in the Old World. Six complete genomes of PlLV from four distinct plant populations [Finland (2 genomes), France (1), Italy (1), Spain (1)] were amplified by RCA and/or PCR using a pair of abutting primers from infected samples, cloned and sequenced (Sanger). Partial nucleotidic sequences of the coat protein (cp) and replication-associated protein (rep) genes of PlLV were also obtained by PCR from samples collected in France (1) and Iran (2). The six PlLV comp

Wild plant populations may harbour a myriad of unknown viruses. As the majority of research efforts have targeted economically important plant species, the diversity and prevalence of viruses in the wild has remained largely unknown. However, the recent shift towards metagenomics-based sequencing methodologies, especially those targeting small RNAs, is finally enabling virus discovery from wild hosts. Understanding this diversity of potentially pathogenic microbes in the wild can offer insights into the components of natural biodiversity that promotes long-term coexistence between hosts and parasites in nature, and help predict when and where risks of disease emergence are highest. Here, we used small RNA deep sequencing to identify viruses in Plantago lanceolata populations, and to understand the variation in their prevalence and distribution across the Åland Islands, South-West Finland. By subsequent design of PCR primers, we screened the five most common viruses from two sets of P. lanceolata plants: 164 plants collected from 12 populations irrespective of symptoms, and 90 plants collected from five populations showing conspicuous viral symptoms. In addition to the previously reported species Plantago lanceolata latent virus (PlLV), we found four potentially novel virus species belonging to Caulimovirus, Betapartitivirus, Enamovirus, and Closterovirus genera. Our results show that virus prevalence and diversity varied among the sampled host populations. In six of the virus infected populations only a single virus species was detected, while five of the populations supported between two to five of the studied virus species. In 20% of the infected plants, viruses occurred as coinfections. When the relationship between conspicuous viral symptoms and virus infection was investigated, we found that plants showing symptoms were usually infected (84%), but virus infections were also detected from asymptomatic plants (44%). Jointly, these results reveal a diverse virus c

Background Understanding the mechanisms by which diversity is maintained in pathogen populations is critical for epidemiological predictions. Life-history trade-offs have been proposed as a hypothesis for explaining long-term maintenance of variation in pathogen populations, yet the empirical evidence supporting trade-offs has remained mixed. This is in part due to the challenges of documenting successive pathogen life-history stages in many pathosystems. Moreover, little is understood of the role of natural enemies of pathogens on their life-history evolution. Results We characterize life-history-trait variation and possible trade-offs in fungal pathogen Podosphaera plantaginis infecting the host plant Plantago lanceolata. We measured the timing of both asexual and sexual stages, as well as resistance to a hyperparasite of seven pathogen strains that vary in their prevalence in nature. We find significant variation among the strains in their life-history traits that constitute the infection cycle, but no evidence for trade-offs among pathogen development stages, apart from fast pathogen growth coninciding with fast hyperparasite growth. Also, the seemingly least fit pathogen strain was the most prevalent in the nature. Conclusions We conclude that in the nature environmental variation, and interactions with the antagonists of pathogens themselves may maintain variation in pathogen populations.

Many pathogens possess the capacity for sex through outcrossing, despite being able to reproduce also asexually and/or via selfing. Given that sex is assumed to come at a cost, these mixed reproductive strategies typical of pathogens have remained puzzling. While the ecological and evolutionary benefits of outcrossing are theoretically well-supported, support for such benefits in pathogen populations are still scarce. Here, we analyze the epidemiology and genetic structure of natural populations of an obligate fungal pathogen, Podosphaera plantaginis. We find that the opportunities for outcrossing vary spatially. Populations supporting high levels of coinfection –a prerequisite of sex – result in hotspots of novel genetic diversity. Pathogen populations supporting coinfection also have a higher probability of surviving winter. Jointly our results show that outcrossing has direct epidemiological consequences as well as a major impact on pathogen population genetic diversity, thereby providing evidence of ecological and evolutionary benefits of outcrossing in pathogens.

The genus Capulavirus is a new genus in the family Geminiviridae that contains so far four species (Alfalfa leaf curl virus, Euphorbia caput-medusae latent virus, French bean severe leaf curl virus and Plantago lanceolata latent virus) that infect both cultivated and non-cultivated plants. Among them, plantago lanceolata latent virus (PlLV) infects ribwort plantain (Plantago lanceolata L.), a perennial herb that is native from Eurasia and is now widespread all over the world. PlLV is transmitted by the aphid Dysaphis plantaginea, which has a holocyclic lifestyle with two successive host plants: apple and plantain. Mechanical inoculation of sap using carborundum powder or syringe have also proved effective to infect various plants including P. lanceolata. Although plants naturally infected with PlLV displayed yellowing symptoms, agroinoculation in controlled conditions of an agroinfectious clone of PlLV in plantain did not reveal evidence of symptoms. In order to better decipher the prevalence and the diversity of PlLV, P. lanceolata plant samples were collected from four European countries (Finland, France, Italy and Spain), as well as from Iran and South Africa, and were tested by PCR for the presence of PlLV. While PlLV was initially reported from the Åland Islands (South-West Finland), we show that PlLV is also found from all sampled countries but South Africa. These results suggest that the geographic distribution of PlLV is larger than initially thought and that PlLV prevalence is probably relatively high in the Old World. Six complete genomes of PlLV from four distinct plant populations [Finland (2 genomes), France (1), Italy (1), Spain (1)] were amplified by RCA and/or PCR using a pair of abutting primers from infected samples, cloned and sequenced (Sanger). Partial nucleotidic sequences of the coat protein (cp) and replication-associated protein (rep) genes of PlLV were also obtained by PCR from samples collected in France (1) and Iran (2). The six PlLV comp

Wild plant populations may harbour a myriad of unknown viruses. As the majority of research efforts have targeted economically important plant species, the diversity and prevalence of viruses in the wild has remained largely unknown. However, the recent shift towards metagenomics-based sequencing methodologies, especially those targeting small RNAs, is finally enabling virus discovery from wild hosts. Understanding this diversity of potentially pathogenic microbes in the wild can offer insights into the components of natural biodiversity that promotes long-term coexistence between hosts and parasites in nature, and help predict when and where risks of disease emergence are highest. Here, we used small RNA deep sequencing to identify viruses in Plantago lanceolata populations, and to understand the variation in their prevalence and distribution across the Åland Islands, South-West Finland. By subsequent design of PCR primers, we screened the five most common viruses from two sets of P. lanceolata plants: 164 plants collected from 12 populations irrespective of symptoms, and 90 plants collected from five populations showing conspicuous viral symptoms. In addition to the previously reported species Plantago lanceolata latent virus (PlLV), we found four potentially novel virus species belonging to Caulimovirus, Betapartitivirus, Enamovirus, and Closterovirus genera. Our results show that virus prevalence and diversity varied among the sampled host populations. In six of the virus infected populations only a single virus species was detected, while five of the populations supported between two to five of the studied virus species. In 20% of the infected plants, viruses occurred as coinfections. When the relationship between conspicuous viral symptoms and virus infection was investigated, we found that plants showing symptoms were usually infected (84%), but virus infections were also detected from asymptomatic plants (44%). Jointly, these results reveal a diverse virus c

Predicting the emergence, spread and evolution of parasites within and among host populations requires insight to both the spatial and temporal scales of adaptation, including an understanding of within-host up through community-level dynamics. Although there are very few pathosystems for which such extensive data exist, there has been a recent push to integrate studies performed over multiple scales or to simultaneously test for dynamics occurring across scales. Drawing on examples from the literature, with primary emphasis on three diverse host-parasite case studies, we first examine current understanding of the spatial structure of host and parasite populations, including patterns of local adaptation and spatial variation in host resistance and parasite infectivity. We then explore the ways to measure temporal variation and dynamics in host-parasite interactions and discuss the need to examine change over both ecological and evolutionary timescales. Finally, we highlight new approaches and syntheses that allow for simultaneous analysis of dynamics across scales. We argue that there is great value in examining interplay among scales in studies of host-parasite interactions.

Predicting the emergence, spread and evolution of parasites within and among host populations requires insight to both the spatial and temporal scales of adaptation, including an understanding of within-host up through community-level dynamics. Although there are very few pathosystems for which such extensive data exist, there has been a recent push to integrate studies performed over multiple scales or to simultaneously test for dynamics occurring across scales. Drawing on examples from the literature, with primary emphasis on three diverse host-parasite case studies, we first examine current understanding of the spatial structure of host and parasite populations, including patterns of local adaptation and spatial variation in host resistance and parasite infectivity. We then explore the ways to measure temporal variation and dynamics in host-parasite interactions and discuss the need to examine change over both ecological and evolutionary timescales. Finally, we highlight new approaches and syntheses that allow for simultaneous analysis of dynamics across scales. We argue that there is great value in examining interplay among scales in studies of host-parasite interactions.

Predicting the emergence, spread and evolution of parasites within and among host populations requires insight to both the spatial and temporal scales of adaptation, including an understanding of within-host up through community-level dynamics. Although there are very few pathosystems for which such extensive data exist, there has been a recent push to integrate studies performed over multiple scales or to simultaneously test for dynamics occurring across scales. Drawing on examples from the literature, with primary emphasis on three diverse host-parasite case studies, we first examine current understanding of the spatial structure of host and parasite populations, including patterns of local adaptation and spatial variation in host resistance and parasite infectivity. We then explore the ways to measure temporal variation and dynamics in host-parasite interactions and discuss the need to examine change over both ecological and evolutionary timescales. Finally, we highlight new approaches and syntheses that allow for simultaneous analysis of dynamics across scales. We argue that there is great value in examining interplay among scales in studies of host-parasite interactions.

We investigated the impact of below-ground and above-ground environmental heterogeneity on the ecology and evolution of a natural plant-pathogen interaction. We combined field measurements and a reciprocal inoculation experiment to investigate the potential for natural variation in abiotic and biotic factors to mediate infection outcomes in the association between the fungal pathogen Melampsora lini and its wild flax host, Linum marginale, where pathogen strains and plant lines originated from two ecologically distinct habitat types that occur in close proximity (bog' and hill'). The two habitat types differed strikingly in soil moisture and soil microbiota. Infection outcomes for different host-pathogen combinations were strongly affected by the habitat of origin of the plant lines and pathogen strains, the soil environment and their interactions. Our results suggested that tradeoffs play a key role in explaining the evolutionary divergence in interaction traits among the two habitat types. Overall, we demonstrate that soil heterogeneity, by mediating infection outcomes and evolutionary divergence, can contribute to the maintenance of variation in resistance and pathogenicity within a natural host-pathogen metapopulation.