Mixed infection,risk projection,and misdirection: Interactions among pathogens alter links between host resources and disease

A growing body of literature links resources of hosts to their risk of infectious disease. Yet most hosts encounter multiple pathogens, and projections of disease risk based on resource availability could be fundamentally wrong if they do not account for interactions among pathogens within hosts. Here, we measured infection risk of grass hosts (Avena sativa) exposed to three naturally co‐occurring viruses either singly or jointly (barley and cereal yellow dwarf viruses [B/CYDVs]: CYDV‐RPV, BYDV‐PAV, and BYDV‐SGV) along experimental gradients of nitrogen and phosphorus supply. We asked whether disease risk (i.e., infection prevalence) differed in single versus co‐inoculations, and whether these differences varied with rates and ratios of nitrogen and phosphorus supply. In single inoculations, the viruses did not respond strongly to nitrogen or phosphorus. However, in co‐inoculations, we detected illustrative cases of 1) resource‐dependent antagonism (lower prevalence of RPV with increasing N; possibly due to competition), 2) resource‐dependent facilitation (higher prevalence of SGV with decreasing N:P; possibly due to immunosuppression), and 3) weak or no interactions within hosts (for PAV). Together, these within‐host interactions created emergent patterns for co‐inoculated hosts, with both infection prevalence and viral richness increasing with the combination of low nitrogen and high phosphorus supply. We demonstrate that knowledge of multiple pathogens is essential for predicting disease risk from host resources and that projections of risk that fail to acknowledge resource‐dependent interactions within hosts could be qualitatively wrong. Expansions of theory from community ecology theory may help anticipate such relationships by linking host resources to diverse pathogen communities.     

Risk assessment for non-crop hosts of pea enation mosaic virus and the aphid vector Acyrthosiphon pisum

1. Viral insect-borne plant pathogens have devastating impacts in agroecosystems. Vector-borne pathogens are often transmitted by generalist insects that move between non-crop and crop hosts. Insect vectors can have wide diet breadths, but it is often unknown which hosts serve as pathogen reservoirs and which non-crop host harbours the highest density of vectors.
2. In the Pacific Northwest USA, the pea aphid (Acyrthosiphon pisum) is a key virus vector in pulse crops. Despite pea aphid having a large number of potential non-crop plant hosts occuring in the region, no reservoir has yet been identified for the economically-costly pathogen Pea Enation Mosaic Virus (PEMV).
3. We addressed these issues by linking field surveys of an aphid vector and plant virus with statistical models to develop risk assessments for common non-crop legumes; in 2018, we completed a 65-site survey where aphids were surveyed in weedy legumes within and outside dry pea fields.
4. We quantified the abundance of pea aphids on 17 hosts, and plant tissue was tested for PEMV. Relatively high densities of A. pisum were found in habitats dominated by hairy vetch (Vicia villosa), which was the only legume other than cultivated dry pea where PEMV was detected.
5. Our results indicate that V. villosa is a key alternative host for PEMV, and that pest management practices in this region should consider the distribution and abundance of this weedy host in viral disease mitigation efforts for pulses.

     

The influence of competing root symbionts on below‐ground plant resource allocation

1. Plants typically interact with multiple above‐ and below‐ground organisms simultaneously, with their symbiotic relationships spanning a continuum ranging from mutualism, such as with arbuscular mycorrhizal fungi (AMF), to parasitism, including symbioses with plant‐parasitic nematodes (PPN).
2. Although research is revealing the patterns of plant resource allocation to mutualistic AMF partners under different host and environmental constraints, the root ecosystem, with multiple competing symbionts, is often ignored. Such competition is likely to heavily influence resource allocation to symbionts.
3. Here, we outline and discuss the competition between AMF and PPN for the finite supply of host plant resources, highlighting the need for a more holistic understanding of the influence of below‐ground interactions on plant resource allocation. Based on recent developments in our understanding of other symbiotic systems such as legume–rhizobia and AMF‐aphid‐plant, we propose hypotheses for the distribution of plant resources between contrasting below‐ground symbionts and how such competition may affect the host.
4. We identify relevant knowledge gaps at the physiological and molecular scales which, if resolved, will improve our understanding of the true ecological significance and potential future exploitation of AMF‐PPN‐plant interactions in order to optimize plant growth. To resolve these outstanding knowledge gaps, we propose the application of well‐established methods in isotope tracing and nutrient budgeting to monitor the movement of nutrients between symbionts. By combining these approaches with novel time of arrival experiments and experimental systems involving multiple plant hosts interlinked by common mycelial networks, it may be possible to reveal the impact of multiple, simultaneous colonizations by competing symbionts on carbon and nutrient flows across ecologically important scales.

     

A field test of the dilution effect hypothesis in four avian multi-host pathogens

The Dilution Effect Hypothesis (DEH) argues that greater biodiversity lowers the risk of disease and reduces the rates of pathogen transmission since more diverse communities harbour fewer competent hosts for any given pathogen, thereby reducing host exposure to the pathogen. DEH is expected to operate most intensely in vector-borne pathogens and when species-rich communities are not associated with increased host density. Overall, dilution will occur if greater species diversity leads to a lower contact rate between infected vectors and susceptible hosts, and between infected hosts and susceptible vectors. Field-based tests simultaneously analysing the prevalence of several multi-host pathogens in relation to host and vector diversity are required to validate DEH. We tested the relationship between the prevalence in house sparrows (Passer domesticus) of four vector-borne pathogens–three avian haemosporidians (including the avian malaria parasite Plasmodium and the malaria-like parasites Haemoproteus and Leucocytozoon) and West Nile virus (WNV)–and vertebrate diversity. Birds were sampled at 45 localities in SW Spain for which extensive data on vector (mosquitoes) and vertebrate communities exist. Vertebrate censuses were conducted to quantify avian and mammal density, species richness and evenness. Contrary to the predictions of DEH, WNV seroprevalence and haemosporidian prevalence were not negatively associated with either vertebrate species richness or evenness. Indeed, the opposite pattern was found, with positive relationships between avian species richness and WNV seroprevalence, and Leucocytozoon prevalence being detected. When vector (mosquito) richness and evenness were incorporated into the models, all the previous associations between WNV prevalence and the vertebrate community variables remained unchanged. No significant association was found for Plasmodium prevalence and vertebrate community variables in any of the models tested. Despite the studied system having several characteristics that should favour the dilution effect (i.e., vector-borne pathogens, an area where vector and host densities are unrelated, and where host richness is not associated with an increase in host density), none of the relationships between host species diversity and species richness, and pathogen prevalence supported DEH and, in fact, amplification was found for three of the four pathogens tested. Consequently, the range of pathogens and communities studied needs to be broadened if we are to understand the ecological factors that favour dilution and how often these conditions occur in nature.     

Plant phylogeny drives arboreal caterpillar assemblages across the Holarctic

1. Assemblages of insect herbivores are structured by plant traits such as nutrient content, secondary metabolites, physical traits, and phenology. Many of these traits are phylogenetically conserved, implying a decrease in trait similarity with increasing phylogenetic distance of the host plant taxa. Thus, a metric of phylogenetic distances and relationships can be considered a proxy for phylogenetically conserved plant traits and used to predict variation in herbivorous insect assemblages among co‐occurring plant species.
2. Using a Holarctic dataset of exposed‐feeding and shelter‐building caterpillars, we aimed at showing how phylogenetic relationships among host plants explain compositional changes and characteristics of herbivore assemblages.
3. Our plant–caterpillar network data derived from plot‐based samplings at three different continents included >28,000 individual caterpillar–plant interactions. We tested whether increasing phylogenetic distance of the host plants leads to a decrease in caterpillar assemblage overlap. We further investigated to what degree phylogenetic isolation of a host tree species within the local community explains abundance, density, richness, and mean specialization of its associated caterpillar assemblage.
4. The overlap of caterpillar assemblages decreased with increasing phylogenetic distance among the host tree species. Phylogenetic isolation of a host plant within the local plant community was correlated with lower richness and mean specialization of the associated caterpillar assemblages. Phylogenetic isolation had no effect on caterpillar abundance or density. The effects of plant phylogeny were consistent across exposed‐feeding and shelter‐building caterpillars.
5. Our study reveals that distance metrics obtained from host plant phylogeny are useful predictors to explain compositional turnover among hosts and host‐specific variations in richness and mean specialization of associated insect herbivore assemblages in temperate broadleaf forests. As phylogenetic information of plant communities is becoming increasingly available, further large‐scale studies are needed to investigate to what degree plant phylogeny structures herbivore assemblages in other biomes and ecosystems.

     

Mixing tree species associated with arbuscular or ectotrophic mycorrhizae reveals dual mycorrhization and interactive effects on the fungal partners

1. Recent studies found that the majority of shrub and tree species are associated with both arbuscular mycorrhizal (AM) and ectomycorrhizal (EM) fungi. However, our knowledge on how different mycorrhizal types interact with each other is still limited. We asked whether the combination of hosts with a preferred association with either AM or EM fungi increases the host tree roots’ mycorrhization rate and affects AM and EM fungal richness and community composition.
2. We established a tree diversity experiment, where five tree species of each of the two mycorrhiza types were planted in monocultures, two‐species and four‐species mixtures. We applied morphological assessment to estimate mycorrhization rates and next‐generation molecular sequencing to quantify mycobiont richness.
3. Both the morphological and molecular assessment revealed dual‐mycorrhizal colonization in 79% and 100% of the samples, respectively. OTU community composition strongly differed between AM and EM trees. While host tree species richness did not affect mycorrhization rates, we observed significant effects of mixing AM‐ and EM‐associated hosts in AM mycorrhization rate. Glomeromycota richness was larger in monotypic AM tree combinations than in AM‐EM mixtures, pointing to a dilution or suppression effect of AM by EM trees. We found a strong match between morphological quantification of AM mycorrhization rate and Glomeromycota richness.
4. Synthesis. We provide evidence that the combination of hosts differing in their preferred mycorrhiza association affects the host''s fungal community composition, thus revealing important biotic interactions among trees and their associated fungi.

     

Pathogens manipulate the preference of vectors,slowing disease spread in a multi‐host system

The spread of vector‐borne pathogens depends on a complex set of interactions among pathogen, vector, and host. In single‐host systems, pathogens can induce changes in vector preferences for infected vs. healthy hosts. Yet it is unclear if pathogens also induce changes in vector preference among host species, and how changes in vector behaviour alter the ecological dynamics of disease spread. Here, we couple multi‐host preference experiments with a novel model of vector preference general to both single and multi‐host communities. We show that viruliferous aphids exhibit strong preferences for healthy and long‐lived hosts. Coupling experimental results with modelling to account for preference leads to a strong decrease in overall pathogen spread through multi‐host communities due to non‐random sorting of viruliferous vectors between preferred and non‐preferred host species. Our results demonstrate the importance of the interplay between vector behaviour and host diversity as a key mechanism in the spread of vectored‐diseases.     

Emerging zoonotic diseases originating in mammals: a systematic review of effects of anthropogenic land-use change

1. Zoonotic pathogens and parasites that are transmitted from vertebrates to humans are a major public health risk with high associated global economic costs. The spread of these pathogens and risk of transmission accelerate with recent anthropogenic land-use changes (LUC) such as deforestation, urbanisation, and agricultural intensification, factors that are expected to increase in the future due to human population expansion and increasing demand for resources.
2. We systematically review the literature on anthropogenic LUC and zoonotic diseases, highlighting the most prominent mammalian reservoirs and pathogens, and identifying avenues for future research.
3. The majority of studies were global reviews that did not focus on specific taxa. South America and Asia were the most-studied regions, while the most-studied LUC was urbanisation. Livestock were studied more within the context of agricultural intensification, carnivores with urbanisation and helminths, bats with deforestation and viruses, and primates with habitat fragmentation and protozoa.
4. Research into specific animal reservoirs has improved our understanding of how the spread of zoonotic diseases is affected by LUC. The behaviour of hosts can be altered when their habitats are changed, impacting the pathogens they carry and the probability of disease spreading to humans. Understanding this has enabled the identification of factors that alter the risk of emergence (such as virulence, pathogen diversity, and ease of transmission). Yet, many pathogens and impacts of LUC other than urbanisation have been understudied.
5. Predicting how zoonotic diseases emerge and spread in response to anthropogenic LUC requires more empirical and data synthesis studies that link host ecology and responses with pathogen ecology and disease spread. The link between anthropogenic impacts on the natural environment and the recent COVID-19 pandemic highlights the urgent need to understand how anthropogenic LUC affects the risk of spillover to humans and spread of zoonotic diseases originating in mammals.

     

Richness and Composition of Niche-Assembled Viral Pathogen Communities

The pathogen and parasite community that inhabits every free-living organism can control host vital rates including lifespan and reproductive output. To date, however, there have been few experiments examining pathogen community assembly replicated at large-enough spatial scales to inform our understanding of pathogen dynamics in natural systems. Pathogen community assembly may be driven by neutral stochastic colonization and extinction events or by niche differentiation that constrains pathogen distributions to particular environmental conditions, hosts, or vectors.Here, we present results from a regionally-replicated experiment investigating the community of barley and cereal yellow dwarf viruses (B/CYDV''s) in over 5000 experimentally planted individuals of six grass species along a 700 km latitudinal gradient along the Pacific coast of North America (USA) in response to experimentally manipulated nitrogen and phosphorus supplies. The composition of the virus community varied predictably among hosts and across nutrient-addition treatments, indicating niche differentiation among virus species. There were some concordant responses among the viral species. For example, the prevalence of most viral species increased consistently with perennial grass cover, leading to a 60% increase in the richness of the viral community within individual hosts (i.e., coinfection) in perennial-dominated plots. Furthermore, infection rates of the six host species in the field were highly correlated with vector preferences assessed in laboratory trials. Our results reveal the importance of niche differentiation in structuring virus assemblages. Virus species distributions reflected a combination of local host community composition, host species-specific vector preferences, and virus responses to host nutrition. In addition, our results suggest that heterogeneity among host species in their capacity to attract vectors or support pathogens between growing seasons can lead to positive covariation among virus species.     

Vector preference and host defense against infection interact to determine disease dynamics

Vector preference based on host infection status has long been recognized for its importance in disease dynamics. Prior theoretical work has assumed that all hosts are uniformly susceptible to the pathogen. Here we investigated disease dynamics when this assumption is relaxed using a series of vector–host epidemiological compartment models with variable levels of host resistance or tolerance to infection – collectively termed defense. In our models, vectors cannot acquire the infection from resistant hosts but can acquire from tolerant hosts. Specifically, we investigated the interacting effects of vector preference and host defense in a series of single‐ and two‐patch models. Results indicate that resistant host types generally reduce disease prevalence and pathogen spillover, independent of vector preference. The epidemiological consequences of host tolerance, however, depended on vector preference. When vectors preferred diseased hosts, tolerance reduced incidence compared to susceptible hosts; when vectors avoided diseased hosts, tolerance enhanced disease prevalence. Finally, a variation of the model that included preference‐based vector patch leaving rates suggests that both resistance and tolerance can promote pathogen spillover if vectors prefer diseased hosts, because of increased vector dispersal into susceptible patches. Collectively, we found complex, context‐dependent effects of vector preference and host defense on disease dynamics. In the context of management programs for vector‐borne diseases, managers should consider both the precise form of host defense present in a population, breed, or cultivar, as well as vector feeding behavior.     

Mechanisms of resistance and virulence in parasitic plant–host interactions

Parasitic plants pose a major biotic threat to plant growth and development and lead to losses in crop productivity of billions of USD annually. By comparison with “normal” autotrophic plants, parasitic plants live a heterotrophic lifestyle and rely on water, solutes and to a greater (holoparasitic plants) or lesser extent (hemiparasitic plants) on sugars from other host plants. Most hosts are unable to detect an infestation by plant parasites or unable to fend off these parasitic invaders. However, a few hosts have evolved defense strategies to avoid infestation or protect themselves actively post-attack often leading to full or partial resistance. Here, we review the current state of our understanding of the defense strategies to plant parasitism used by host plants with emphasis on the active molecular resistance mechanisms. Furthermore, we outline the perspectives and the potential of future studies that will be indispensable to develop and breed resistant crops.

Some plants are able to recognize parasitic plants as attacking pathogens and can fend them off by inducing defense responses.

Advances

• Receptor proteins have been discovered in host plants (i.e. sunflower, tomato, or cowpea) that detect parasitic plants as an invading pathogen and further induce plant immunity and resistance responses in hosts leading to a parasite rejection.
• Molecular patterns exist in parasitic plants that can be specifically detected by host plant receptors.
• The host plant receptors require co-receptors and signaling components (i.e. BAK1, SOBIR1, etc.) also known from plant immunity against microbes.
• Parasitic plants evolved strategies to circumvent and to suppress host plant immunity, i.e. by manipulating host cells with siRNAs or proteins that act as effectors.
• Similar to the interaction of plants with microbial pathogens, elements of PTI and ETI can be both observed in plant–parasitic plant interactions.

     

Enemies make you stronger: Coevolution between fruit fly host and bacterial pathogen increases postinfection survivorship in the host

Multiple laboratory studies have evolved hosts against a nonevolving pathogen to address questions about evolution of immune responses. However, an ecologically more relevant scenario is one where hosts and pathogens can coevolve. Such coevolution between the antagonists, depending on the mutual selection pressure and additive variance in the respective populations, can potentially lead to a different pattern of evolution in the hosts compared to a situation where the host evolves against a nonevolving pathogen. In the present study, we used Drosophila melanogaster as the host and Pseudomonas entomophila as the pathogen. We let the host populations either evolve against a nonevolving pathogen or coevolve with the same pathogen. We found that the coevolving hosts on average evolved higher survivorship against the coevolving pathogen and ancestral (nonevolving) pathogen relative to the hosts evolving against a nonevolving pathogen. The coevolving pathogens evolved greater ability to induce host mortality even in nonlocal (novel) hosts compared to infection by an ancestral (nonevolving) pathogen. Thus, our results clearly show that the evolved traits in the host and the pathogen under coevolution can be different from one‐sided adaptation. In addition, our results also show that the coevolving host–pathogen interactions can involve certain general mechanisms in the pathogen, leading to increased mortality induction in nonlocal or novel hosts.     

Nutrient trade‐offs mediated by ectomycorrhizal strategies in plants: Evidence from an Abies species in subalpine forests

1. Ectomycorrhizal (ECM) symbiosis is an evolutionary biological trait of higher plants for effective nutrient uptakes. However, little is known that how the formation and morphological differentiations of ECM roots mediate the nutrients of below‐ and aboveground plant tissues and the balance among nutrient elements across environmental gradients. Here, we investigated the effects of ECM foraging strategies on root and foliar N and P concentrations and N:P ratio Abies faxoniana under variations of climate and soil conditions.
2. The ECM symbionts preferentially mediated P uptake under both N and P limitations. The uptake efficiency of N and P was primarily associated with the ECM root traits, for example, ECM root tip density, superficial area of ECM root tips, and the ratio of living to dead root tips, and was affected by the ECM proliferations and morphological differentiations. The tissue N and P concentrations were positively associated with the abundance of the contact exploration type and negatively with that of the short‐distance exploration type.
3. Our findings indicate that the nutritional status of both below‐ and aboveground plant tissues can be strongly affected by ECM symbiosis in natural environments. Variations in the ECM strategies in response to varying environmental conditions significantly influence plant nutrient uptakes and trade‐offs.

     

Spread of an introduced parasite across the Hawaiian archipelago independent of its introduced host

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Relationships between nutrient enrichment,pleurocerid snail density and trematode infection rate in streams

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Tracking nutrients in space and time: Interactions between grazing lawns and drought drive abundances of tallgrass prairie grasshoppers

1. We contrast the response of arthropod abundance and composition to bison grazing lawns during a drought and non‐drought year, with an emphasis on acridid grasshoppers, an important grassland herbivore.
2. Grazing lawns are grassland areas where regular grazing by mammalian herbivores creates patches of short‐statured, high nutrient vegetation. Grazing lawns are predictable microsites that modify microclimate, plant structure, community composition, and nutrient availability, with likely repercussions for arthropod communities.
3. One year of our study occurred during an extreme drought. Drought mimics some of the effects of mammalian grazers: decreasing above‐ground plant biomass while increasing plant foliar percentage nitrogen.
4. We sampled arthropods and nutrient availability on and nearby (“off”) 10 bison‐grazed grazing lawns in a tallgrass prairie in NE Kansas. Total grasshopper abundance was higher on grazing lawns and the magnitude of this difference increased in the wetter year of 2019 compared to 2018, when drought led to high grass foliar nitrogen concentrations on and off grazing lawns. Mixed‐feeding grasshopper abundances were consistently higher on grazing lawns while grass‐feeder and forb‐feeder abundances were higher on lawns only in 2019, the wetter year. In contrast, the abundance of other arthropods (e.g., Hemiptera, Hymenoptera, and Araneae) did not differ on and off lawns, but increased overall in 2019, relative to the drought of 2018.
5. Understanding these local scale patterns of abundances and community composition improves predictability of arthropod responses to ongoing habitat change.

     

Ecosystem dynamics, biological diversity and emerging infectious diseases

In this article, we summarize the major scientific developments of the last decade on the transmission of infectious agents in multi-host systems. Almost sixty percent of the pathogens that have emerged in humans during the last 30-40 years are of animal origin and about sixty percent of them show an important variety of host species besides humans (3 or more possible host species). In this review, we focus on zoonotic infections with vector-borne transmission and dissect the contrasting effects that a multiplicity of host reservoirs and vectors can have on their disease dynamics. We discuss the effects exerted by host and vector species richness and composition on pathogen prevalence (i.e., reduction, including the dilution effect, or amplification). We emphasize that, in multiple host systems and for vector-borne zoonotic pathogens, host reservoir species and vector species can exert contrasting effect locally. The outcome on disease dynamics (reduced pathogen prevalence in vectors when the host reservoir species is rich and increased pathogen prevalence when the vector species richness increases) may be highly heterogeneous in both space and time. We then ask briefly how a shift towards a more systemic perspective in the study of emerging infectious diseases, which are driven by a multiplicity of hosts, may stimulate further research developments. Finally, we propose some research avenues that take better into account the multi-host species reality in the transmission of the most important emerging infectious diseases, and, particularly, suggest, as a possible orientation, the careful assessment of the life-history characteristics of hosts and vectors in a community ecology-based perspective.     

Fine‐scale variation within urban landscapes affects marking patterns and gastrointestinal parasite diversity in red foxes

1. Urban areas are often considered to be a hostile environment for wildlife as they are highly fragmented and frequently disturbed. However, these same habitats can contain abundant resources, while lacking many common competitors and predators. The urban environment can have a direct impact on the species living there but can also have indirect effects on their parasites and pathogens. To date, relatively few studies have measured how fine‐scale spatial heterogeneity within urban landscapes can affect parasite transmission and persistence.
2. Here, we surveyed 237 greenspaces across the urban environment of Edinburgh (UK) to investigate how fine‐scale variation in socio‐economic and ecological variables can affect red fox (Vulpes vulpes) marking behavior, gastrointestinal (GI) parasite prevalence, and parasite community diversity.
3. We found that the presence and abundance of red fox fecal markings were nonuniformly distributed across greenspaces and instead were dependent on the ecological characteristics of a site. Specifically, common foraging areas were left largely unmarked, which indicates that suitable resting and denning sites may be limiting factor in urban environments. In addition, the amount of greenspace around each site was positively correlated with overall GI parasite prevalence, species richness, and diversity, highlighting the importance of greenspace (a commonly used measure of landscape connectivity) in determining the composition of the parasite community in urban areas.
4. Our results suggest that fine‐scale variation within urban environments can be important for understanding the ecology of infectious diseases in urban wildlife and could have wider implication for the management of urban carnivores.

     

Niche‐based host extinction increases prevalence of an environmentally acquired pathogen

Understanding the ecology of environmentally acquired and multi‐host pathogens affecting humans and wildlife has been elusive in part because fluctuations in the abundance of host and pathogen species may feed back onto pathogen transmission. Complexity of pathogen‐host dynamics emerges from processes driving local extinction of the pathogen, its hosts and non‐hosts. While the extinction of species may entail losses in pathogen–host interactions and decrease the proportion of hosts infected by a pathogen (prevalence), some studies suggest the opposite pattern. Niche‐based extinction, based on the species tolerance to environmental conditions, may increase prevalence of infection because the pathogen and its hosts persist, while other species go extinct. Hence, understanding prevalence of infection requires disentangling random‐ and niche‐based extinction processes occurring simultaneously. To contribute to this exercise, we analysed the prevalence of an environmentally acquired, multi‐host pathogen, Mycobacterium ulcerans (MU), in a unique dataset of 16 communities of freshwater animals, surveyed during 12 months in Akonolinga, Cameroon in equatorial Africa. Two different ecosystems were identified: rivers (lotic) and swamps and flooded areas (lentic). Increased prevalence of MU infection was correlated with niche‐based extinction of aquatic host invertebrates and vertebrates in the lentic ecosystems, whereas decreased prevalence was associated with random disassembly of the lotic ecosystems. This finding suggests that random and niche‐based extinction of host taxa are key to assessing the effect of local extinction of species on the ecology of environmentally acquired and multi‐host pathogens.     

Vector preference for hosts differing in infection status: sharpshooter movement and Xylella fastidiosa transmission

1. Epidemiological theory predicts that vector preference for hosts differing in infection status (i.e. healthy or infected) affects disease dynamics. 2. Numerous studies have documented strong vector preference for or discrimination against infected hosts. However, the significance of these behaviours for pathogen transmission and spread has been poorly described. 3. We conducted a series of choice assays to evaluate orientation preference, feeding preference, and movement rates of an important group of vectors, the sharpshooter leafhoppers, based on host infection status for the generalist plant pathogen, Xylella fastidiosa Wells et al. 4. Sharpshooters did not discriminate between healthy versus infected‐but‐asymptomatic grapevines, but they oriented preferentially to healthy grapevines more frequently than either symptomatic vines or those artificially coloured to mimic disease symptoms. 5. In a field trial three sharpshooter species showed different movement rates and preferences for feeding site, but all species exhibited similar and significant preference for healthy hosts. 6. Although there was no significant difference in acquisition efficiency among vector species, those individuals that spent more time on healthy hosts tended to be less likely to acquire the pathogen. 7. These results suggest that sharpshooters discriminate against infected grapevines, which are likely to be of poorer quality, with visual cues playing a role in host selection. Preference by these vectors may affect pathogen acquisition, which could affect disease spread in the field.