Host Density Research Articles

Influence of Host and Landscape-Associated Factors in the Infection and Transmission of Pathogens: The Case of Directly Transmitted Virus in Mammals.

Among pathogens associated with mammals, numerous viruses with a direct transmission route impact human, domestic and wild species health. Host and landscape factors affect viral infection and transmission dynamics of these viruses, along with barriers to host dispersal and gene exchange. However, studies show biases toward certain locations, hosts and detected pathogens, with regional variations in similar host-virus associations. Using a systematic review, in two electronic repositories for articles published until December 2022, we analysed the available information on host- and landscape-associated factors influencing the infection and transmission of directly transmitted viruses in mammals. In the analysis, about 50% of papers examined either host traits, landscape composition or configuration measures, while approximately 24% combined host and landscape-associated factors. Additionally, approximately 17% of the articles included climatic data and 30% integrated factors related to anthropogenic impact, as these variables have a role in host density, distribution and virus persistence. The most significant and frequent host traits used as predictor variables were sex, age, body weight, host density and species identity. Land cover was the most evaluated landscape attribute, while some explored configuration variables like edge density and fragmentation indexes. Finally, temperature, precipitation and features such as human population density and human footprint index were also typically measured and found impactful. Given the many contributions host- and landscape-related factors have in pathogen dynamics, this systematic study contributes to a better knowledge of host-virus dynamics and the identification of variables and gaps that can be used for disease prevention.

Haemoparasite infection risk in multi-host avian system: an integrated analysis.

Avian blood parasites play a crucial role in wildlife health and ecosystem dynamics, exhibiting heterogeneous spatial distribution influenced by various factors. Although factors underlying heterogeneity in infection with blood parasites have been explored in many avian hosts, their importance in the context of host species and the parasite taxon remains poorly understood, particularly in cohabiting host species. Using next-generation sequencing for parasite screening, we investigate the association between Haemoproteus, Plasmodium and Trypanosoma infections in relation to individual parameters, host densities and landscape features in 3 cavity-nesting passerines: great tit (Parus major), blue tit (Cyanistes caeruleus) and collared flycatcher (Ficedula albicollis) in a highly fragmented forest habitat. Overall, Haemoproteus infections predominated, followed by Plasmodium and Trypanosoma, with great tits most and collared flycatchers least parasitized. There were no common patterns across host species in the probability of infection with locally transmitted parasites from each genus. Specifically, in all cases, the effect of particular parameters, if present, was observed only in 1 host species. Body condition influenced Haemoproteus and Plasmodium infections differently in tits. Host density, whether own species or all pooled, explained Haemoproteus infections in great tits and collared flycatchers, and Plasmodium in great tits. Landscape metrics, such as moisture index and distance to coast edge and pastures, affected infection probability in specific host–parasite combinations. Relative risk maps revealed infection risk gradients, but spatial variation repeatability over time was low. Our study highlights the complex dynamics of avian blood parasites in multi-host systems, shedding light on host–parasite interactions in natural ecosystems.

The on-Site Monitoring and Specimen-Making of Ectoparasites on Rodents and Other Small Mammals.

The ectoparasites of rodents and other small mammals usually involve five categories of arthropods-fleas, sucking lice, gamasid mites, chigger mites, and occasionally, ticks. These ectoparasites are medically important, serving as vectors for diseases such as plague, murine typhus, scrub typhus, forest encephalitis, Lyme disease, and other zoonoses. Field surveys, collection, and specimen preparation of ectoparasites are crucial for studying taxonomy, faunistics, ecology, and epidemiology. They are also essential for vector surveillance. The present protocol summarizes the on-site monitoring and specimen-making of ectoparasites of rodents and other sympatric small mammals. Besides the collection and specimen preparation of small mammal hosts, the protocol describes in detail the collection, fixation, specimen-making, and taxonomic identification of ectoparasites and provides some monitoring indices. The on-site monitoring indices include the host density index and the infestation indices of ectoparasites (prevalence, mean abundance, mean intensity). The methodologies outlined in this protocol provide technical guidance and references for vector monitoring (surveillance) and control. Key features • Collection and specimen preparation of small mammal hosts, including rodents (rats, mice, and voles) and other sympatric small mammals (shrews, tree shrews, and pikas). • Collection, fixation, specimen-making, and taxonomic identification of ectoparasites, including fleas, sucking lice, gamasid mites, chigger mites, and ticks. • On-site monitoring indices-host density index and infestation indices of ectoparasites: prevalence, mean abundance, and mean intensity. Graphical overview Flowchart for collection and specimen-making of ectoparasites and their hosts. A. Process for the collection and specimen preparation of small mammal hosts. B. Collection and fixation of ectoparasites. C. Process for specimen-making for different categories of ectoparasites.

Assessment of coral diseases in the shallow reefs of Aka-jima Marine Reserve (AMR), with a brief geographic perspective of disease occurrence throughout the larger Kerama-Shoto Marine National Park (KMNP), Okinawa, Japan

This study reports on the observation of coral diseases within the shallow/intertidal water habitat of the Akajima Marine Reserve (AMR), located within the Keramashoto Marine National Park (KMNP) of Japan. Major coral genera and species assessed during the survey included Montipora spp., Porites spp., Isopora palifera, Acropora spp., as well as others. Observed diseases and health conditions included Black Band Disease (BBD) in Montipora as well as in Goniopora, Skeletal Growth Anomalies (GAs) in Acropora, Montipora, Porites, Isopora and Astreopora, Terpios hoshinota covering Acropora, Montipora and Seriatopora, as well as bleaching, discoloration, and other compromised health signs. This field study recorded the presence of GAs in the genus Leptastrea for the first time within the Japanese Archipelago. The novelty in this study is reporting unreported genera to be infested with certain disease conditions, further this study demonstrates how surveys in previously poorly studied areas or habitats can reveal important information pertaining to coral diseases, thus helping to fill existing knowledge gaps. Another important aspect of this study is, we provide a review of the distribution of coral diseases within the KMNP based on our results and previous reports. Being a rapid survey, the dynamics of these diseases were not assessed, while the major cause(s) of the diseases remains to be identified. In general, climate change-related aspects including rises in sea surface temperature, as well as other factors such as host density may be responsible for disease prevalences in the region.

Emergence of black spot syndrome in Caribbean reefs: a century of fish collections reveal long-term increases in Scaphanocephalus infection.

Despite evidence that certain diseases of marine wildlife are increasing, long-term infection data are often lacking. Archived samples of hosts from natural history collections offer a powerful tool for evaluating temporal changes in parasitism. Using vouchered fish collections from the Southern Caribbean, we investigated long-term (1905-2022) shifts in infections by the trematode Scaphanocephalus spp., which causes black spot syndrome (BSS) in reef fishes. Examination of 190 museum-preserved fishes from Curaçao and Bonaire revealed that Scaphanocephalus infections are not new, with histologically confirmed detections from as early as 1948. However, Scaphanocephalus was rare among archival surgeonfish and parrotfishes, with an infection prevalence of <10% and an average abundance of 0.25 metacercariae per fish. Contemporary collections of 258 ocean surgeonfish and parrotfishes (7 species) supported a 7-fold higher prevalence (71%) and a 49-fold higher abundance (12.1). These findings offer evidence that infections by Scaphanocephalus spp. have increased substantially over the past century and underscore the value of biological repositories in the study of emerging parasites within marine ecosystems. We emphasize the need for additional research to evaluate the geographical extent of BSS emergence, test proposed hypotheses related to shifts in host density or environmental characteristics and assess the consequences for affected species.

5.C. Scientific session: Strengthen resilience against emerging vector-borne diseases through the ECDC Fellowship Programmes

Abstract Over the past decade, climate change has impacted the transmission of a wide range of vector-borne diseases (VBDs) in Europe, where locally transmitted outbreaks have occurred. It has been implicated in the observed expansion of competent disease vectors in Europe such as Aedes albopictus, which transmits diseases such as Zika, Dengue and Chikungunya. Climate may influence the life cycle of vectors, and the reproduction rate of viral particles inside vectors and human hosts, which means that upsurges in temperature can reduce the incubation period of these pathogens and the life cycle of vectors, thus boosting transmission risk through elevated vector populations. Moreover, globalization and international air travel contribute to pathogen and vector dispersion internationally. Risk mapping suggests further expansion of the species in northern Europe due to climate change. The above underscores the necessity for more proactive measures, such as developing an effective vector control program by monitoring the density and distribution of hosts and pathogens at urban, national, and cross-border levels. Additionally, establishing early warning systems based on integrated human and zoonotic and entomological surveillance is crucial to detect alerts promptly and comprehend where and when infections may emerge or spread. Furthermore, cross-border collaboration and harmonization of vector-borne surveillance systems across European countries may improve preparedness, control and response to mosquito-borne diseases. Preparedness and response require significant efforts from EU Member States and neighbouring countries. Only through a multidisciplinary approach, involving multiple sectors, can we truly prepare to address public health threats. To contribute to strengthening resilience against cross-border public health and emerging health threats in EU Member States and neighbouring countries, the European Centre of Disease Prevention and Control (ECDC) has established three fellowship training programmes. These programmes aim to create and maintain a network of highly qualified epidemiologists, microbiologists and public health professionals and strengthen the public health epidemiology workforce at EU and neighbor countries. This workshop will offer attendees a comprehensive overview of the ECDC’s fellowship programmes, describe how they function and explain their role in preparing for health threats. It will provide examples of three projects carried out by fellows on the implementation of preparedness, response and control measures for emerging vector-borne diseases in European countries at local, national and multinational levels. Those will set the scene for an in-depth analysis of the key challenges faced and can help promote awareness that integrated, multidisciplinary interventions are both feasible and effective in reducing the threat of vector-borne infectious diseases spreading in Europe and neighboring countries. Key messages • ECDC fellowship programmes aim to strengthen resilience against emerging public health threats in EU Member States and neighboring countries. • Fellows are engaged in national and cross-border integrated and multidisciplinary interventions to strengthen preparedness and mitigate the spread of emerging vector-borne diseases.

Realizing interfacial coupled electron/ion transport through reducing the interfacial oxygen density of carbon skeletons for high-performance lithium metal anodes

Lithium plating/stripping occurs at the anode/electrolyte interface which involves the flow of electrons from the current collector and the migration of lithium ions from the solid-electrolyte interphase (SEI). The dual continuous rapid transport of interfacial electron/ion is required for homogeneous Li deposition. Herein, we propose a strategy to improve the Li metal anode performance by rationally regulating the interfacial electron density and Li ion transport through the SEI film. This key technique involves decreasing the interfacial oxygen density of biomass-derived carbon host by regulating the arrangement of the celluloses precursor fibrils. The higher specific surface area and lower interfacial oxygen density decrease the local current density and ensure the formation of thin and even SEI film, which stabilized Li+ transfer through the Li/electrolyte interface. Moreover, the improved graphitization and the interconnected conducting network enhance the surface electronegativity of carbon and enable uninterruptible electron conduction. The result is continuous and rapid coupled interfacial electron/ion transport at the anode/electrolyte reaction interface, which facilitates uniform Li deposition and improves Li anode performance. The Li/C anode shows a high initial Coulombic efficiency of 98% and a long-term lifespan of over 150 cycles at a practical low N/P (negative-to-positive) ratio of 1.44 in full cells.

Characterizing the evolution of defense in a tripartite marine symbiosis using adaptive dynamics

Abstract The evolution and maintenance of symbiotic systems remains a fascinating puzzle. While the coevolutionary dynamics of bipartite (host–symbiont) systems are well-studied, the dynamics of more complex systems have only recently garnered attention with increasing technological advances. We model a tripartite system inspired by the marine symbiotic relationship between the alga Bryopsis sp., its intracellular defensive bacterial symbiont “Candidatus Endobryopsis kahalalidifaciens,” which produces a toxin that protects the alga against fish herbivores, and the sea-slug Elysia rufescens (Zan et al., 2019), which is not deterred by the toxin. We disentangle the role of selection on different actors within this system by investigating evolutionary scenarios where defense evolves as (i) a host-controlled trait that reduces algal reproductive ability; (ii) a symbiont-controlled trait that impacts symbiont transmission; and (iii) a trait jointly controlled by both host and symbiont. Optimal investment in defensive toxins varies based on the characteristics of the host, symbiont, and sea slug; and evolutionary trajectories are modulated by trade-off shape, i.e., a strongly decelerating trade-off between defense and symbiont transmission can drive symbiont diversification via evolutionary branching. Increasing slug herbivory reduces host investment in defense to favor reproduction, while symbiont investment in defense first declines and then increases as host density declines to the degree that horizontal symbiont transmission is no longer beneficial. Increasing vertical transmission selects for reduced defense by the host when it evolves as a jointly controlled trait, as a result of investment by the symbiont. Our theoretical exploration of the evolution of defensive symbiosis in scenarios involving interactions with multiple herbivores provides a first window into the origin and maintenance of the Bryopsis sp. system, and adds another piece to the puzzle of the evolution of symbiotic systems.

Comparing the differing effects of host species richness on metrics of disease

AbstractChanges in host species richness can alter infection risk and disease levels in multi‐host communities. I review theoretical predictions for direct and environmental transmission pathogens about the effects of host additions (or removals) on three commonly used disease metrics: the pathogen community reproduction number and infection prevalence and infected density in a focal host. To extend this prior work and explain why predictions differ between metrics, I analyze Susceptible Infected‐Recovered‐type models of an environmentally transmitted pathogen and multiple host species that compete for resources. Using local sensitivity analysis, I show how trait‐mediated and density‐mediated indirect effects drive each metric's response to variation in an added host's ability to transmit a pathogen, the added host's density, and the pathogen transmission mechanism. For each disease metric, the responses are typically predicted by the added host's ability to transmit the pathogen when interspecific competition is weak whereas the responses can be altered by shifts in host densities when interspecific competition is strong. In addition, the three metrics often respond in the same direction. However, the metrics can respond in different directions for three reasons: (1) differences between the ability of exposed individuals to transmit the pathogen over the length of time the individuals are infected (i.e., host competence) and a host population's instantaneous net rate of production of infectious propagules; (2) strong density‐mediated feedbacks driven by disease‐induced mortality; and (3) host additions or removals cause large changes in focal host density via competition or disease‐induced mortality. This study extends and unifies prior theoretical studies, and helps identify the rules governing the context‐dependent relationships between host species richness and the three metrics of disease.

A Parasite Plant Promotes the Coexistence of Two Annual Plants.

Consumers can influence the competitive outcomes of prey species in various ways. Modern coexistence theory predicts that consumers can promote prey coexistence by preferably targeting a competitively superior one, thereby reducing fitness differences. However, previous studies yielded mixed conclusions. In this study, we tested the hypothesis that a parasitic annual plant, Cuscuta campestris, facilitates the coexistence of two common annual plants. We performed field surveys and parasitism experiments to parameterize a plant competition dynamics model. The model suggested a competition-defence tradeoff: the legume Lespedeza striata was a better competitor than the grass Setaria faberi, while it was more susceptible to the parasite. Moreover, an empirical host-parasite dynamics model, extended from the plant competition model, predicted their coexistence within broad, biologically reasonable ranges of parameters. This work provides field evidence of the coexisting-promoting role of a parasitic plant, as caused by stabilising feedback between host and parasite densities.

Determining oviposition preferences to inform population reinforcement of the specialist chequered blue butterfly (Scolitantides orion)

Abstract Many Lepidoptera species are declining to the point that active measures such as reinforcements and reintroductions are necessary to maintain viable populations. To maximise success of such efforts, we need to understand the factors influencing habitat preferences for oviposition. In a Swedish island population of the red‐listed chequered blue butterfly (Scolitantides orion), we characterised oviposition preference by documenting whether the presence and abundance of eggs (i) increased with size and local density of its host plant, orpine (Hylotelephium telephium), and (ii) was associated with nectar plant abundance, degree of shading, and ground cover composition within small and large circular plots (1 m vs. 5 m radius) around focal plants. To reinforce a tiny population on a neighbouring island, we released 127 pupae and 46 imagos and recorded oviposition for two seasons. The probability of receiving eggs increased with focal host plant size, and also with mean size of other host plants and cover of lichens within the large plots. The abundance of eggs within large plots increased with host plant density and amount of lichen cover. Habitat characteristics of the large plots predicted oviposition better than did those of small plots, and both outperformed models including host plant size only. In the reinforcement population, all released pupae eclosed, and we found a total of 507 eggs on 272 host plants during the release season. Eggs were present on 5% of examined host plants, and median distance to a release spot was 19.3 m. In the following year, we found 420 eggs on 209 plants, and median distance to a release spot increased to 35.7 m, indicating diffusion through the habitat. Practical implication. The chequered blue butterfly prefers to oviposit on large host plants in patches with high host density and high cover of lichens. To identify suitable release habitats, environmental conditions should be considered in an area of ca 80 m2. The reinforcement shows that small releases can be successful and suggests that similar low‐effort approaches can be effective to boost local populations of many threatened butterflies, provided suitable habitats are available.

The occurrence patterns and alternative host use of the generalist parasitoid Parvilucifera infectans (Alveolata, Perkinsozoa) of marine dinoflagellates revealed by a high-frequency time series microscopic data at a temperate coastal site

Species belonging to the genus Parvilucifera (Alveolata, Perkinsozoa) are known as generalist parasitoids that can infect a variety of marine dinoflagellates and ultimately kill the host cell. Despite the accumulation of knowledge on Parvilucifera parasitoids over the last twenty years, the occurrence pattern and use of alternative hosts for persistent transmission within fluctuating natural dinoflagellate host communities have received relatively little attention. To address this, high-frequency (i.e., daily) time series protist monitoring was conducted for 411 days, from April 2020 to May 2021, at a temperate coastal site in Jinhae Bay, Republic of Korea. This site was characterized by frequent blooms of mixed dinoflagellates throughout most of the year. Nonetheless, Parvilucifera infections were detected only in the spring seasons, and its occurrence pattern was primarily governed by the presence and cell density of its primary dinoflagellate host, Akashiwo sanguinea. As long as the primary host was present at high densities (greater than 104 cells L-1), this primary host alone could support the transmission and persistence of the parasitoid. However, if the cell density of the primary host started to decline, then Parvilucifera searched for and exploited alternative hosts for its continued survival. Taken together, this study suggests that the presence and cell density of its preferred primary host species and the duration for which the density remains above the threshold level are key factors that regulate the timing of Parvilucifera occurrence and alternative host use.

Assessing potential for biological control of Japanese giant silkworm Caligula japonica using Anastatus gansuensis, a thelytokous parasitoid firstly reported in Eupelmidae.

Caligula japonica, commonly known as Japanese giant silkworm (JGS), is a serious defoliating pest of fruit and forest trees in East Asia. To develop eco-friendly and cost-effective control methods for this pest, we evaluated the potential for biological control of JGS using its egg parasitoid Anastatus gansuensis reared on the Chinese oak silkworm (COS) Antheraea pernyi. We compared the reproductive traits and population increase potential of the parasitoid on JGS and COS eggs, as well as its functional response to host egg densities and mutual interference at different parasitoid densities. Anastatus gansuensis was confirmed to be strictly synovigenic, with most eggs maturing post-emergence, and produced <1% male offspring on both host eggs. Although A. gansuensis females reared from COS eggs had longer longevity and oviposition period, and higher fecundity and net reproductive rate compared to those reared from JGS eggs, the parasitoid had a higher intrinsic rate of increase on JGS than COS eggs. The parasitoid exhibited a type II functional response to increasing host densities, with mutual interference among foraging female wasps occurred at higher parasitoid densities. Our results indicate a high potential for biological control of JGS using A. gansuensis. The parasitoid can be efficiently reared on COS eggs and used against JGS. It may be essential to provide food for emerging adult parasitoids allowing time for egg maturation prior to the rearing or augmentative release of the parasitoid. Some mutual interference at high parasitoid rearing densities likely reduces per capita parasitization efficiency of A. gansuensis. © 2024 Society of Chemical Industry.

Dispersal of optimal foragers in a patchy environment: Simulations with a mathematical model and tests of predictions in field experiments

To predict the effect of density on the dispersal of foraging parasitoids, we developed a spatially explicit individual-based model in which parasitoids move among host patches at random but use an optimal decision-rule about when to leave these patches. We used a simple decision rule where an individual forager exploits a patch as long as the instantaneous attack rate is higher than the average attack rate it has experienced in the environment. Such a rule implies that foragers compute and remember attack rates as they forage. Simulations with different combinations of patch distribution, host density, mutual interference, and parasitoid density predicted that dispersal distance should increase with parasitoid density. To test this prediction, we used data from two field experiments in which we released either few or many adults of the aphid parasitoid Aphelinus asychis in replicated sites, and subsequently assessed dispersal from the spatial distribution of parasitoid offspring. In the first experiment, we did not to detect a relation between the number released and dispersal distance, but in the second experiment, dispersal distance increased with initial density, as predicted by our model. We propose two hypotheses to explain the discrepancy between the experiments. Different levels of environmental variability among experiments, resulting from differences in experimental designs, could cause differences in statistical conclusions. However, there could be a threshold density below which dispersal is not density-dependent, and this threshold may have been exceeded in the second experiment where large releases involved many more individuals than in the first experiment. In any case, our approach linked individual behavior and spatial distribution, and our results show that the insect distributions in the field can be predicted, qualitatively, from theory about individual behavior.

Molecular Diversity of Ectomycorrhizal Fungi in Relation to the Diversity of Neighboring Plant Species.

(1) Background: Plant diversity has long been assumed to predict soil microbial diversity. The mutualistic symbiosis between forest trees and ectomycorrhizal (EM) fungi favors strong correlations of EM fungal diversity with host density in terrestrial ecosystems. Nevertheless, in contrast with host tree effects, neighboring plant effects are less well studied. (2) Methods: In the study presented herein, we examined the α-diversity, community composition, and co-occurrence patterns of EM fungi in Quercus acutissima across different forest types (pure forests, mixed forests with Pinus tabuliformis, and mixed forests with other broadleaved species) to ascertain how the EM fungi of focal trees are related to their neighboring plants and to identify the underlying mechanisms that contribute to this relationship. (3) Results: The EM fungal community exhibited an overall modest but positive correlation with neighboring plant richness, with the associations being more pronounced in mixed forests. This neighboring effect was mediated by altered abiotic (i.e., SOC, TN, LC, and LP) and biotic (i.e., bacterial community) factors in rhizosphere soil. Further analysis revealed that Tomentella_badia, Tomentella_galzinii, and Sebacina_incrustans exhibited the most significant correlations with plant and EM fungal diversity. These keystone taxa featured low relative abundance and clear habitat preferences and shared similar physiological traits that promote nutrient uptake through contact, short-distance and medium-distance smooth contact-based exploration types, thereby enhancing the potential correlations between EM fungi and the neighboring plant community. (4) Conclusions: Our findings contribute to the comprehension of the effect of neighboring plants on the EM fungal community of focal trees of different forest communities and the biodiversity sensitivity to environmental change.

Competition and edge effect in wildlife zoonotic agents

The Land-use change emerges as a fundamental factor in the increase in zoonotic diseases, affecting both ecosystems and human populations. The edge effect between forested areas and their surrounding environments, modifies species distribution, and consequently the dynamics zoonotic wildlife. Patches with high perimeter-to-area ratios may experience a more pronounced edge effect, justifying the relevance of studying patch shape in a disease dynamics. In addition, competition between species, especially between those that act as reservoirs and those that do not, plays a crucial role in eco-epidemiological dynamics. In this context, our study addresses competition dynamics between two species employ the Lotka–Volterra model. We introduce an internal classification in the host species with two compartments, susceptible and infected, and model the disease transmission rate using a function linked to parameters associated with the edge effect. Specifically, the transmission rate differentiates interactions between susceptible and infected individuals in the core area and the edge of the patch, being a function dependent on the shape index of the patch, and is of the edge effect and host density. We predicted that, although competition can decrease the spread of the disease among hosts, the edge effect can paradoxically increase it.

Reproductive Biology and Rearing Improvements of Apanteles opuntiarum, Potential Biocontrol Agent of the Argentine Cactus Moth, Cactoblastis cactorum.

The cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae) is native to South America and has been used as a biocontrol agent of Opuntia (Cactaceae) in Australia and South Africa. Its invasion in North America has raised concerns for the native Opuntia in the USA and Mexico. We investigated the reproductive biology and rearing procedures of a host-specific potential biocontrol agent, Apanteles opuntiarum Martínez and Berta (Hymenoptera: Braconidae). Given the gregarious nature of the parasitoid larvae, we studied the morphology of the immature stages and evaluated evidence of polyembryony and superparasitism. We also investigated the effects of host exposure arena and host density on parasitism rates and wasp production. The morphological descriptions provide a basis for comparison with other species. Early larval instars of A. opuntiarum are similar to other microgastrine immature stages. However, the mature larva exhibits placoid sensilla in the epistomal region, a unique character not previously reported. We provide evidence that A. opuntiarum eggs are not polyembryonic; females frequently superparasitize and have an oviposition preference for larvae parasitized 1-2 d previously. Exposing larvae of C. cactorum to wasps while inside the cactus resulted in lower parasitism and fewer offspring from each host than exposing larvae in the arena without the cactus. Parasitism and mortality rates were higher at lower host densities, possibly due to reduced host group defensive behavior. These results suggest that preference for superparasitism, host defensive behavior, and interactions with the cactus may play an important role in per-host wasp production under laboratory conditions.

GIS-ODE: linking dynamic population models with GIS to predict pathogen vector abundance across a country under climate change scenarios.

Mechanistic mathematical models such as ordinary differential equations (ODEs) have a long history for their use in describing population dynamics and determining estimates of key parameters that summarize the potential growth or decline of a population over time. More recently, geographic information systems (GIS) have become important tools to provide a visual representation of statistically determined parameters and environmental features over space. Here, we combine these tools to form a 'GIS-ODE' approach to generate spatiotemporal maps predicting how projected changes in thermal climate may affect population densities and, uniquely, population dynamics of Ixodes ricinus, an important tick vector of several human pathogens. Assuming habitat and host densities are not greatly affected by climate warming, the GIS-ODE model predicted that, even under the lowest projected temperature increase, I. ricinus nymph densities could increase by 26-99% in Scotland, depending on the habitat and climate of the location. Our GIS-ODE model provides the vector-borne disease research community with a framework option to produce predictive, spatially explicit risk maps based on a mechanistic understanding of vector and vector-borne disease transmission dynamics.

Potential effects of host competence and schooling behavior on parasite transmission in a host-pathogen system: a test of the dilution effect

High species diversity in a community may reduce the risk of infectious disease, termed the dilution effect. However, the generality of the dilution effect in different disease systems remains controversial as both host competence and behaviors of hosts may play roles in dilution or amplification of disease. Using the goldfish (Carassius auratus)-monogenean ectoparasite (Gyrodactylus kobayashii) system, effects of host competence and schooling behavior on parasite transmission were investigated while holding focal host density constant. Following competency tests of 12 fish species as potential hosts for the parasite, infection by G. kobayashii was determined on fins of goldfish mixed with each of three different species based on their level of host competence, including Prussian carp, Carassius gibelio (low competence), grass carp, Ctenopharyngodon idellus (non-competent), swordtail, Xiphophorus helleri (non-competent), and the four species combined. Compared with mean abundance (85.8 ± 25.1) on goldfish in the control group, the mean abundance on goldfish decreased significantly when paired with 10 Prussian carp (30.0 ± 16.5), but did not differ significantly when paired with 10 swordtail (70.0 ± 22.2), 10 grass carp (116.1 ± 33.2), or the multi-species of three Prussian carp, four grass carp and three swordtail (75.9 ± 30.8) during the 11-day experiment. The parasite was also found on the Prussian carp in the Prussian carp group and the multi-species group at a mean abundance of 7.1 and 10.9, respectively. Video recording showed that the school of goldfish mixed well with the Prussian carp, while they maintained separation from the grass carp and swordtail when mixed together. The distance between goldfish increased, and swimming speed and contact time decreased with the additional of other fish species for all groups. The results suggested that the presence of a low-competence host in sufficient numbers was a necessary condition for a dilution effect due to encounter reduction, and the dilution effect may also be enhanced by changes in schooling behavior of goldfish in the presence of low competence hosts. However, the presence of non-competent hosts did not result in any dilution effect owing to the specialist nature of the parasites and the lack of mixing with schools of goldfish.

Evolution of parasites in the Anthropocene: new pressures, new adaptive directions.

The Anthropocene is seeing the human footprint rapidly spreading to all of Earth's ecosystems. The fast-changing biotic and abiotic conditions experienced by all organisms are exerting new and strong selective pressures, and there is a growing list of examples of human-induced evolution in response to anthropogenic impacts. No organism is exempt from these novel selective pressures. Here, we synthesise current knowledge on human-induced evolution in eukaryotic parasites of animals, and present a multidisciplinary framework for its study and monitoring. Parasites generally have short generation times and huge fecundity, features that predispose them for rapid evolution. We begin by reviewing evidence that parasites often have substantial standing genetic variation, and examples of their rapid evolution both under conditions of livestock production and in serial passage experiments. We then present a two-step conceptual overview of the causal chain linking anthropogenic impacts to parasite evolution. First, we review the major anthropogenic factors impacting parasites, and identify the selective pressures they exert on parasites through increased mortality of either infective stages or adult parasites, or through changes in host density, quality or immunity. Second, we discuss what new phenotypic traits are likely to be favoured by the new selective pressures resulting from altered parasite mortality or host changes; we focus mostly on parasite virulence and basic life-history traits, as these most directly influence the transmission success of parasites and the pathology they induce. To illustrate the kinds of evolutionary changes in parasites anticipated in the Anthropocene, we present a few scenarios, either already documented or hypothetical but plausible, involving parasite taxa in livestock, aquaculture and natural systems. Finally, we offer several approaches for investigations and real-time monitoring of rapid, human-induced evolution in parasites, ranging from controlled experiments to the use of state-of-the-art genomic tools. The implications of fast-evolving parasites in the Anthropocene for disease emergence and the dynamics of infections in domestic animals and wildlife are concerning. Broader recognition that it is not only the conditions for parasite transmission that are changing, but the parasites themselves, is needed to meet better the challenges ahead.