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1
Boots, Michael, and Akira Sasaki. "Parasite‐Driven Extinction in Spatially Explicit Host‐Parasite Systems." American Naturalist 159, no. 6 (June 2002): 706–13. http://dx.doi.org/10.1086/339996.
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Kaltz, Oliver, and Jacqui A. Shykoff. "Local adaptation in host–parasite systems." Heredity 81, no. 4 (October 1998): 361–70. http://dx.doi.org/10.1046/j.1365-2540.1998.00435.x.
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Swann, Justine, Neema Jamshidi, Nathan E. Lewis, and Elizabeth A. Winzeler. "Systems analysis of host-parasite interactions." Wiley Interdisciplinary Reviews: Systems Biology and Medicine 7, no. 6 (August 26, 2015): 381–400. http://dx.doi.org/10.1002/wsbm.1311.
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Dallas, Tad, Shan Huang, Charles Nunn, Andrew W. Park, and John M. Drake. "Estimating parasite host range." Proceedings of the Royal Society B: Biological Sciences 284, no. 1861 (August 30, 2017): 20171250. http://dx.doi.org/10.1098/rspb.2017.1250.
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Estimating the number of host species that a parasite can infect (i.e. host range) provides key insights into the evolution of host specialism and is a central concept in disease ecology. Host range is rarely estimated in real systems, however, because variation in species relative abundance and the detection of rare species makes it challenging to confidently estimate host range. We applied a non-parametric richness indicator to estimate host range in simulated and empirical data, allowing us to assess the influence of sampling heterogeneity and data completeness. After validating our method on simulated data, we estimated parasite host range for a sparsely sampled global parasite occurrence database (Global Mammal Parasite Database) and a repeatedly sampled set of parasites of small mammals from New Mexico (Sevilleta Long Term Ecological Research Program). Estimation accuracy varied strongly with parasite taxonomy, number of parasite occurrence records, and the shape of host species-abundance distribution (i.e. the dominance and rareness of species in the host community). Our findings suggest that between 20% and 40% of parasite host ranges are currently unknown, highlighting a major gap in our understanding of parasite specificity, host–parasite network structure, and parasite burdens.
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Turner, Wendy C., Pauline L. Kamath, Henriette van Heerden, Yen-Hua Huang, Zoe R. Barandongo, Spencer A. Bruce, and Kyrre Kausrud. "The roles of environmental variation and parasite survival in virulence–transmission relationships." Royal Society Open Science 8, no. 6 (June 2021): 210088. http://dx.doi.org/10.1098/rsos.210088.
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Disease outbreaks are a consequence of interactions among the three components of a host–parasite system: the infectious agent, the host and the environment. While virulence and transmission are widely investigated, most studies of parasite life-history trade-offs are conducted with theoretical models or tractable experimental systems where transmission is standardized and the environment controlled. Yet, biotic and abiotic environmental factors can strongly affect disease dynamics, and ultimately, host–parasite coevolution. Here, we review research on how environmental context alters virulence–transmission relationships, focusing on the off-host portion of the parasite life cycle, and how variation in parasite survival affects the evolution of virulence and transmission. We review three inter-related ‘approaches’ that have dominated the study of the evolution of virulence and transmission for different host–parasite systems: (i) evolutionary trade-off theory, (ii) parasite local adaptation and (iii) parasite phylodynamics. These approaches consider the role of the environment in virulence and transmission evolution from different angles, which entail different advantages and potential biases. We suggest improvements to how to investigate virulence–transmission relationships, through conceptual and methodological developments and taking environmental context into consideration. By combining developments in life-history evolution, phylogenetics, adaptive dynamics and comparative genomics, we can improve our understanding of virulence–transmission relationships across a diversity of host–parasite systems that have eluded experimental study of parasite life history.
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McDevitt-Galles, Travis, Wynne E. Moss, Dana M. Calhoun, and Pieter T. J. Johnson. "Phenological synchrony shapes pathology in host–parasite systems." Proceedings of the Royal Society B: Biological Sciences 287, no. 1919 (January 22, 2020): 20192597. http://dx.doi.org/10.1098/rspb.2019.2597.
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A key challenge surrounding ongoing climate shifts is to identify how they alter species interactions, including those between hosts and parasites. Because transmission often occurs during critical time windows, shifts in the phenology of either taxa can alter the likelihood of interaction or the resulting pathology. We quantified how phenological synchrony between vulnerable stages of an amphibian host ( Pseudacris regilla ) and infection by a pathogenic trematode ( Ribeiroia ondatrae ) determined infection prevalence, parasite load and host pathology. By tracking hosts and parasite infection throughout development between low- and high-elevation regions (San Francisco Bay Area and the Southern Cascades (Mt Lassen)), we found that when phenological synchrony was high (Bay Area), each established parasite incurred a 33% higher probability of causing severe limb malformations relative to areas with less synchrony (Mt Lassen). As a result, hosts in the Bay Area had up to a 50% higher risk of pathology even while controlling for the mean infection load. Our results indicate that host–parasite interactions and the resulting pathology were the joint product of infection load and phenological synchrony, highlighting the sensitivity of disease outcomes to forecasted shifts in climate.
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Horn, Collin J., and Lien T. Luong. "Proximity to parasites reduces host fitness independent of infection in a Drosophila–Macrocheles system." Parasitology 145, no. 12 (March 13, 2018): 1564–69. http://dx.doi.org/10.1017/s0031182018000379.
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AbstractParasites are known to have direct negative effects on host fitness; however, the indirect effects of parasitism on host fitness sans infection are less well understood. Hosts undergo behavioural and physiological changes when in proximity to parasites. Yet, there is little experimental evidence showing that these changes lead to long-term decreases in host fitness. We aimed to determine if parasite exposure affects host fitness independent of contact, because current approaches to parasite ecology may underestimate the effect of parasites on host populations. We assayed the longevity and reproductive output of Drosophila nigrospiracula exposed or not exposed to ectoparasitic Macrocheles subbadius. In order to preclude contact and infection, mites and flies were permanently separated with a mesh screen. Exposed flies had shorter lives and lower fecundity relative to unexposed flies. Recent work in parasite ecology has argued that parasite–host systems show similar processes as predator–prey systems. Our findings mirror the non-consumptive effects observed in predator–prey systems, in which prey species suffer reduced fitness even if they never come into direct contact with predators. Our results support the perspective that there are analogous effects in parasite–host systems, and suggest new directions for research in both parasite ecology and the ecology of fear.
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Hovestadt, Thomas, Jeremy A. Thomas, Oliver Mitesser, and Karsten Schönrogge. "Multiple host use and the dynamics of host switching in host–parasite systems." Insect Conservation and Diversity 12, no. 6 (August 14, 2019): 511–22. http://dx.doi.org/10.1111/icad.12374.
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Medley, G. F. "Which comes first in host-parasite systems: Density dependence or parasite distribution?" Parasitology Today 8, no. 10 (October 1992): 321–22. http://dx.doi.org/10.1016/0169-4758(92)90061-6.
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Adda, P., J. L. Dimi, A. Iggidir, J. C. Kamgang, G. Sallet, and J. J. Tewa. "General models of host-parasite systems. Global analysis." Discrete & Continuous Dynamical Systems - B 8, no. 1 (2007): 1–17. http://dx.doi.org/10.3934/dcdsb.2007.8.1.
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Ekroth, Alice K. E., Charlotte Rafaluk-Mohr, and Kayla C. King. "Host genetic diversity limits parasite success beyond agricultural systems: a meta-analysis." Proceedings of the Royal Society B: Biological Sciences 286, no. 1911 (September 25, 2019): 20191811. http://dx.doi.org/10.1098/rspb.2019.1811.
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There is evidence that human activities are reducing the population genetic diversity of species worldwide. Given the prediction that parasites better exploit genetically homogeneous host populations, many species could be vulnerable to disease outbreaks. While agricultural studies have shown the devastating effects of infectious disease in crop monocultures, the widespread nature of this diversity–disease relationship remains unclear in natural systems. Here, we provide broad support that high population genetic diversity can protect against infectious disease by conducting a meta-analysis of 23 studies, with a total of 67 effect sizes. We found that parasite functional group (micro- or macroparasite) affects the presence of the effect and study setting (field or laboratory-based environment) influences the magnitude. Our study also suggests that host genetic diversity is overall a robust defence against infection regardless of host reproduction, parasite host range, parasite diversity, virulence and the method by which parasite success was recorded. Combined, these results highlight the importance of monitoring declines of host population genetic diversity as shifts in parasite distributions could have devastating effects on at-risk populations in nature.
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Wiser, Mark F. "Unique Endomembrane Systems and Virulence in Pathogenic Protozoa." Life 11, no. 8 (August 12, 2021): 822. http://dx.doi.org/10.3390/life11080822.
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Virulence in pathogenic protozoa is often tied to secretory processes such as the expression of adhesins on parasite surfaces or the secretion of proteases to assisted in tissue invasion and other proteins to avoid the immune system. This review is a broad overview of the endomembrane systems of pathogenic protozoa with a focus on Giardia, Trichomonas, Entamoeba, kinetoplastids, and apicomplexans. The focus is on unique features of these protozoa and how these features relate to virulence. In general, the basic elements of the endocytic and exocytic pathways are present in all protozoa. Some of these elements, especially the endosomal compartments, have been repurposed by the various species and quite often the repurposing is associated with virulence. The Apicomplexa exhibit the most unique endomembrane systems. This includes unique secretory organelles that play a central role in interactions between parasite and host and are involved in the invasion of host cells. Furthermore, as intracellular parasites, the apicomplexans extensively modify their host cells through the secretion of proteins and other material into the host cell. This includes a unique targeting motif for proteins destined for the host cell. Most notable among the apicomplexans is the malaria parasite, which extensively modifies and exports numerous proteins into the host erythrocyte. These modifications of the host erythrocyte include the formation of unique membranes and structures in the host erythrocyte cytoplasm and on the erythrocyte membrane. The transport of parasite proteins to the host erythrocyte involves several unique mechanisms and components, as well as the generation of compartments within the erythrocyte that participate in extraparasite trafficking.
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Stevens, J. "Computational aspects of host-parasite phylogenies." Briefings in Bioinformatics 5, no. 4 (January 1, 2004): 339–49. http://dx.doi.org/10.1093/bib/5.4.339.
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Granovitch, A. J. "Parasitic system reflects population structure of a parasite: conception and terms." Proceedings of the Zoological Institute RAS 313, no. 3 (September 25, 2009): 329–37. http://dx.doi.org/10.31610/trudyzin/2009.313.3.329.
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Population and community consequences of host–parasite interactions are considered. The special attention is given to the various aspects of population level of host-parasite interactions and to approaches to analysis of structure of parasitic systems (systems of populations of the various hosts united in community by interaction with population of a parasite). In the structure of parasitic systems it is allocated two essential architectonic components. The first is a consequence of the differentiated life cycle of a parasite and subdivision of its population onto phase groups (a metastructure of a parasitic system). The second is a consequence of environmental subdivision of parasites (parastructure of a parasitic system). As a whole the parasitic system is considered as a system of para- and metaelements. Importance of population and community levels consideration of the host-parasite interactions is underlined. The special attention is given to working out of a convenient and consistent terms framework for these purposes. The approach developed in the work can be considered as a methodological basis for the analysis of the hierarchical systems formed on the basis of any other type of mutual relations of organisms (others, than interaction of a host– parasite).
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de ROODE, J. C., L. R. GOLD, and S. ALTIZER. "Virulence determinants in a natural butterfly-parasite system." Parasitology 134, no. 5 (May 2006): 657–68. http://dx.doi.org/10.1017/s0031182006002009.
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SUMMARYMuch evolutionary theory assumes that parasite virulence (i.e. parasite-induced host mortality) is determined by within-host parasite reproduction and by the specific parasite genotypes causing infection. However, many other factors could influence the level of virulence experienced by hosts. We studied the protozoan parasite Ophryocystis elektroscirrha in its host, the monarch butterfly, Danaus plexippus. We exposed monarch larvae to wild-isolated parasites and assessed the effects of within-host replication and parasite genotype on host fitness measures, including pre-adult development time and adult weight and longevity. Per capita replication rates of parasites were high, and infection resulted in high parasite loads. Of all host fitness traits, adult longevity showed the clearest relationship with infection status, and decreased continuously with increasing parasite loads. Parasite genotypes differed in their virulence, and these differences were maintained across ecologically relevant variables, including inoculation dose, host sex and host age at infection. Thus, virulence appears to be a robust genetic parasite trait in this system. Although parasite loads and genotypes had strong effects on virulence, inoculation dose, host sex and age at infection were also important. These results have implications for virulence evolution and emphasize the need for a detailed understanding of specific host-parasite systems for addressing theory.
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Zinner, Dietmar, Filipa M. D. Paciência, and Christian Roos. "Host–Parasite Coevolution in Primates." Life 13, no. 3 (March 17, 2023): 823. http://dx.doi.org/10.3390/life13030823.
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Organisms adapt to their environment through evolutionary processes. Environments consist of abiotic factors, but also of other organisms. In many cases, two or more species interact over generations and adapt in a reciprocal way to evolutionary changes in the respective other species. Such coevolutionary processes are found in mutualistic and antagonistic systems, such as predator–prey and host–parasite (including pathogens) relationships. Coevolution often results in an “arms race” between pathogens and hosts and can significantly affect the virulence of pathogens and thus the severity of infectious diseases, a process that we are currently witnessing with SARS-CoV-2. Furthermore, it can lead to co-speciation, resulting in congruent phylogenies of, e.g., the host and parasite. Monkeys and other primates are no exception. They are hosts to a large number of pathogens that have shaped not only the primate immune system but also various ecological and behavioral adaptions. These pathogens can cause severe diseases and most likely also infect multiple primate species, including humans. Here, we briefly review general aspects of the coevolutionary process in its strict sense and highlight the value of cophylogenetic analyses as an indicator for coevolution.
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THIELTGES, D. W., M. D. BORDALO, A. CABALLERO HERNÁNDEZ, K. PRINZ, and K. T. JENSEN. "Ambient fauna impairs parasite transmission in a marine parasite-host system." Parasitology 135, no. 9 (June 19, 2008): 1111–16. http://dx.doi.org/10.1017/s0031182008004526.
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SUMMARYTo understand possible factors controlling transmission of trematode larvae between first and second intermediate hosts we examined the impact of ambient fauna on parasite transmission in a marine intertidal parasite-host association. Cockle hosts (Cerastoderma edule) kept together with selected co-occurring macrozoobenthic species in mesocosms acquired a lower parasite load compared to cockles kept alone, when targeted by cercariae of the trematodeHimasthla elongata. The reduction of parasite load in the cockles differed between the 7 macrozoobenthic species tested and was between 35 and 91%. Three different types of reduction could be distinguished: (1) predators (Carcinus maenas, Crangon crangon) actively preying upon cercariae, (2) non-host filter feeders (Crepidula fornicata,Mya arenaria, Crassostrea gigas) filtering cercariae but not becoming infected and (3) alternative hosts (Mytilus edulis, Macoma balthica) becoming infected by the cercariae and thus distracting cercariae from the target hosts. In addition, interference competition may occur in the form of disturbance of cockles by ambient organisms resulting in lower filtration rates and subsequently lower parasite loads. Our results suggest that the species composition and relative abundance of the ambient fauna of parasite-host systems play an important role in controlling trematode transmission rates in benthic marine systems.
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Gubbins, Simon, and Christopher A. Gilligan. "Biological control in a disturbed environment." Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences 352, no. 1364 (December 29, 1997): 1935–49. http://dx.doi.org/10.1098/rstb.1997.0180.
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Most ecological and epidemiological models describe systems with continuous uninterrupted interactions between populations. Many systems, though, have ecological disturbances, such as those associated with planting and harvesting of a seasonal crop. In this paper, we introduce host—parasite—hyperparasite systems as models of biological control in a disturbed environment, where the host—parasite interactions are discontinuous. One model is a parasite—hyperparasite system designed to capture the essence of biological control and the other is a host—parasite—hyperparasite system that incorporates many more features of the population dynamics. Two types of discontinuity are included in the models. One corresponds to a pulse of new parasites at harvest and the other reflects the discontinuous presence of the host due to planting and harvesting. Such discontinuities are characteristic of many ecosystems involving parasitism or other interactions with an annual host. The models are tested against data from an experiment investigating the persistent biological control of the fungal plant parasite of lettuce Sclerotinia minor by the fungal hyperparasite Sporidesmium sclerotivorum , over successive crops. Using a combination of mathematical analysis, model fitting and parameter estimation, the factors that contribute the observed persistence of the parasite are examined. Analytical results show that repeated planting and harvesting of the host allows the parasite to persist by maintaining a quantity of host tissue in the system on which the parasite can reproduce. When the host dynamics are not included explicitly in the model, we demonstrate that homogeneous mixing fails to predict the persistence of the parasite population, while incorporating spatial heterogeneity by allowing for heterogeneous mixing prevents fade–out. Including the host's dynamics lessens the effect of heterogeneous mixing on persistence, though the predicted values for the parasite population are closer to the observed values. An alternative hypothesis for persistence involving a stepped change in rates of infection is also tested and model fitting is used to show that changes in some environmental conditions may contribute to parasite persistence. The importance of disturbances and periodic forcing in models for interacting populations is discussed.
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Farrell, Maxwell J., Andrew W. Park, Clayton E. Cressler, Tad Dallas, Shan Huang, Nicole Mideo, Ignacio Morales-Castilla, T. Jonathan Davies, and Patrick Stephens. "The ghost of hosts past: impacts of host extinction on parasite specificity." Philosophical Transactions of the Royal Society B: Biological Sciences 376, no. 1837 (September 20, 2021): 20200351. http://dx.doi.org/10.1098/rstb.2020.0351.
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A growing body of research is focused on the extinction of parasite species in response to host endangerment and declines. Beyond the loss of parasite species richness, host extinction can impact apparent parasite host specificity, as measured by host richness or the phylogenetic distances among hosts. Such impacts on the distribution of parasites across the host phylogeny can have knock-on effects that may reshape the adaptation of both hosts and parasites, ultimately shifting the evolutionary landscape underlying the potential for emergence and the evolution of virulence across hosts. Here, we examine how the reshaping of host phylogenies through extinction may impact the host specificity of parasites, and offer examples from historical extinctions, present-day endangerment, and future projections of biodiversity loss. We suggest that an improved understanding of the impact of host extinction on contemporary host–parasite interactions may shed light on core aspects of disease ecology, including comparative studies of host specificity, virulence evolution in multi-host parasite systems, and future trajectories for host and parasite biodiversity. This article is part of the theme issue ‘Infectious disease macroecology: parasite diversity and dynamics across the globe’.
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GLEICHSNER, ALYSSA M., and DENNIS J. MINCHELLA. "Can host ecology and kin selection predict parasite virulence?" Parasitology 141, no. 8 (April 24, 2014): 1018–30. http://dx.doi.org/10.1017/s0031182014000389.
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SUMMARYParasite virulence, or the damage a parasite does to its host, is measured in terms of both host costs (reductions in host growth, reproduction and survival) and parasite benefits (increased transmission and parasite numbers) in the literature. Much work has shown that ecological and genetic factors can be strong selective forces in virulence evolution. This review uses kin selection theory to explore how variations in host ecological parameters impact the genetic relatedness of parasite populations and thus virulence. We provide a broad overview of virulence and population genetics studies and then draw connections to existing knowledge about natural parasite populations. The impact of host movement (transporting parasites) and host resistance (filtering parasites) on the genetic structure and virulence of parasite populations is explored, and empirical studies of these factors using Plasmodium and trematode systems are proposed.
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Byers, James E. "Effects of climate change on parasites and disease in estuarine and nearshore environments." PLOS Biology 18, no. 11 (November 24, 2020): e3000743. http://dx.doi.org/10.1371/journal.pbio.3000743.
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Information on parasites and disease in marine ecosystems lags behind terrestrial systems, increasing the challenge of predicting responses of marine host–parasite systems to climate change. However, here I examine several generalizable aspects and research priorities. First, I advocate that quantification and comparison of host and parasite thermal performance curves is a smart approach to improve predictions of temperature effects on disease. Marine invertebrate species are ectothermic and should be highly conducive to this approach given their generally short generation times. Second, in marine systems, shallow subtidal and intertidal areas will experience the biggest temperature swings and thus likely see the most changes to host–parasite dynamics. Third, for some responses like parasite intensity, as long as the lethal limit of the parasite is not crossed, on average, there may be a biological basis to expect temperature-dependent intensification of impacts on hosts. Fourth, because secondary mortality effects and indirect effects of parasites can be very important, we need to study temperature effects on host–parasite dynamics in a community context to truly know their bottom line effects. This includes examining climate-influenced effects of parasites on ecosystem engineers given their pivotal role in communities. Finally, other global change factors, especially hypoxia, salinity, and ocean acidity, covary with temperature change and need to be considered and evaluated when possible for their contributing effects on host–parasite systems. Climate change–disease interactions in nearshore marine environments are complex; however, generalities are possible and continued research, especially in the areas outlined here, will improve our understanding.
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Boots and Haraguchi. "The Evolution of Costly Resistance in Host-Parasite Systems." American Naturalist 153, no. 4 (1999): 359. http://dx.doi.org/10.2307/2463689.
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Boots, Michael, and Yoshihiro Haraguchi. "The Evolution of Costly Resistance in Host‐Parasite Systems." American Naturalist 153, no. 4 (April 1999): 359–70. http://dx.doi.org/10.1086/303181.
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Sorci, Gabriele, and Bruno Faivre. "Inflammation and oxidative stress in vertebrate host–parasite systems." Philosophical Transactions of the Royal Society B: Biological Sciences 364, no. 1513 (October 17, 2008): 71–83. http://dx.doi.org/10.1098/rstb.2008.0151.
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Innate, inflammation-based immunity is the first line of vertebrate defence against micro-organisms. Inflammation relies on a number of cellular and molecular effectors that can strike invading pathogens very shortly after the encounter between inflammatory cells and the intruder, but in a non-specific way. Owing to this non-specific response, inflammation can generate substantial costs for the host if the inflammatory response, and the associated oxygen-based damage, get out of control. This imposes strong selection pressure that acts to optimize two key features of the inflammatory response: the timing of activation and resolution (the process of downregulation of the response). In this paper, we review the benefits and costs of inflammation-driven immunity. Our aim is to emphasize the importance of resolution of inflammation as a way of maintaining homeostasis against oxidative stress and to prevent the ‘horror autotoxicus’ of chronic inflammation. Nevertheless, host immune regulation also opens the way to pathogens to subvert host defences. Therefore, quantifying inflammatory costs requires assessing (i) short-term negative effects, (ii) delayed inflammation-driven diseases, and (iii) parasitic strategies to subvert inflammation.
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LANGLAIS, M., and P. SILAN. "THEORETICAL AND MATHEMATICAL APPROACH OF SOME REGULATION MECHANISMS IN A MARINE HOST-PARASITE SYSTEM." Journal of Biological Systems 03, no. 02 (June 1995): 559–68. http://dx.doi.org/10.1142/s0218339095000514.
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Host-parasite systems offer such a complex behaviour that few quantitative analysis of their coupled dynamics have been performed. Many intertwinned factors play a role, such as intensity-dependent (intra or interspecific competition, pathogeny, immunological reactions) and/or intensity-independent (abiotic factors, host ethology). Most biomathematical approaches to host-parasite systems are concerned with infectious processes. Corresponding epidemiological models are not well-adapted to macroparasites whose demographical behaviour is quite specific: host mortality, parasite fertility and sometimes recruitment mechanisms depend on the amount of already fixed parasites on a given host and not on the mere existence of parasites. Overdispersion processes are fundamental and determine for a large part the regulation of both populations. A central issue is therefore a reliable description of these processes and their interactions with the global dynamics of the system. Our goal is to develop a mixed deterministic and stochastic model describing the dynamics of a host-parasite system (fish-helminth parasite) having a direct cycle within a marine environment. A dynamical analysis combining a deterministic approach and a stochastic one adapted to macroparasites allows the introduction of spatial and temporal heterogeneities. A particular effort is made towards the recruitment process.
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Rabajante, Jomar Fajardo. "On Spatiotemporal Overdispersion and Macroparasite Accumulation in Hosts Leading to Aggregation: A Quantitative Framework." Diseases 11, no. 1 (December 27, 2022): 4. http://dx.doi.org/10.3390/diseases11010004.
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In many host–parasite systems, overdispersion in the distribution of macroparasites leads to parasite aggregation in the host population. This overdispersed distribution is often characterized by the negative binomial or by the power law. The aggregation is shown by a clustering of parasites in certain hosts, while other hosts have few or none. Here, I present a theory behind the overdispersion in complex spatiotemporal systems as well as a computational analysis for tracking the behavior of transmissible diseases with this kind of dynamics. I present a framework where heterogeneity and complexity in host–parasite systems are related to aggregation. I discuss the problem of focusing only on the average parasite burden without observing the risk posed by the associated variance; the consequences of under- or overestimation of disease transmission in a heterogenous system and environment; the advantage of including the network of social interaction in epidemiological modeling; and the implication of overdispersion in the management of health systems during outbreaks.
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Gehman, Alyssa-Lois M., Richard J. Hall, and James E. Byers. "Host and parasite thermal ecology jointly determine the effect of climate warming on epidemic dynamics." Proceedings of the National Academy of Sciences 115, no. 4 (January 8, 2018): 744–49. http://dx.doi.org/10.1073/pnas.1705067115.
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Host–parasite systems have intricately coupled life cycles, but each interactor can respond differently to changes in environmental variables like temperature. Although vital to predicting how parasitism will respond to climate change, thermal responses of both host and parasite in key traits affecting infection dynamics have rarely been quantified. Through temperature-controlled experiments on an ectothermic host–parasite system, we demonstrate an offset in the thermal optima for survival of infected and uninfected hosts and parasite production. We combine experimentally derived thermal performance curves with field data on seasonal host abundance and parasite prevalence to parameterize an epidemiological model and forecast the dynamical responses to plausible future climate-warming scenarios. In warming scenarios within the coastal southeastern United States, the model predicts sharp declines in parasite prevalence, with local parasite extinction occurring with as little as 2 °C warming. The northern portion of the parasite’s current range could experience local increases in transmission, but assuming no thermal adaptation of the parasite, we find no evidence that the parasite will expand its range northward under warming. This work exemplifies that some host populations may experience reduced parasitism in a warming world and highlights the need to measure host and parasite thermal performance to predict infection responses to climate change.
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Morley, N. J., J. W. Lewis, and D. Hoole. "Pollutant-induced effects on immunological and physiological interactions in aquatic host–trematode systems: implications for parasite transmission." Journal of Helminthology 80, no. 2 (June 2006): 137–49. http://dx.doi.org/10.1079/joh2006345.
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AbstractUnder conditions of pollution both host and parasite are susceptible to the pathogenic effects of toxicants, which in turn may result in detrimental changes to their immunological and physiological processes. Digenetic trematodes, which encompass species of both medical and economic importance, possess complex life cycles and are common parasites of both vertebrates and molluscs. The combined stress induced by pollution and parasitism influences the physiology of the host which can have implications not only on host survival but also on the functional biology of resident parasite populations. The present paper reviews the effects of pollutants on the immunology and physiology in both vertebrate and molluscan host–trematode systems and the implications for parasite transmission.
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Robar, Nicholas, Dennis L. Murray, and Gary Burness. "Effects of parasites on host energy expenditure: the resting metabolic rate stalemate." Canadian Journal of Zoology 89, no. 11 (November 2011): 1146–55. http://dx.doi.org/10.1139/z11-084.
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Detrimental effects of parasitism on host fitness are frequently attributed to parasite-associated perturbations to host energy budgets. It has therefore been widely hypothesized that energetic costs of infection may be manifest as changes in host resting metabolic rate (RMR). Attempts to quantify these effects have yielded contradictory results across host–parasite systems. We used a meta-analysis of the literature to test the effects of parasites on mass-specific (n = 22) and whole-body (n = 15) host RMR. Parasites resulted in a qualitative increase in host RMR in the majority of studies; however, the overall effect of parasites on host RMR was small and statistically nonsignificant. Additionally, substantial among-study variation in host RMR could not be explained by any of the tested covariates. We conclude that the lack of an overall effect of parasites on host metabolism reflects inconsistent directionality and varying magnitudes of parasite-associated effects across studies, rather than an absence of system-specific effects. We contend that a general understanding of parasite effects on host energetics may be best achieved through identifying mechanisms underlying among-system variance in parasite effects on host RMR and relating parasite-associated perturbations of host energy budgets to robust estimates of host fitness.
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Strona, Giovanni, and Simone Fattorini. "A Few Good Reasons Why Species-Area Relationships Do Not Work for Parasites." BioMed Research International 2014 (2014): 1–5. http://dx.doi.org/10.1155/2014/271680.
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Several studies failed to find strong relationships between the biological and ecological features of a host and the number of parasite species it harbours. In particular, host body size and geographical range are generally only weak predictors of parasite species richness, especially when host phylogeny and sampling effort are taken into account. These results, however, have been recently challenged by a meta-analytic study that suggested a prominent role of host body size and range extent in determining parasite species richness (species-area relationships). Here we argue that, in general, results from meta-analyses should not discourage researchers from investigating the reasons for the lack of clear patterns, thus proposing a few tentative explanations to the fact that species-area relationships are infrequent or at least difficult to be detected in most host-parasite systems. The peculiar structure of host-parasite networks, the enemy release hypothesis, the possible discrepancy between host and parasite ranges, and the evolutionary tendency of parasites towards specialization may explain why the observed patterns often do not fit those predicted by species-area relationships.
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Vinson, John E., and Andrew W. Park. "Vector-borne parasite invasion in communities across space and time." Proceedings of the Royal Society B: Biological Sciences 286, no. 1917 (December 18, 2019): 20192614. http://dx.doi.org/10.1098/rspb.2019.2614.
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While vector-borne parasite transmission often operates via generalist-feeding vectors facilitating cross-species transmission in host communities, theory describing the relationship between host species diversity and parasite invasion in these systems is underdeveloped. Host community composition and abundance vary across space and time, generating opportunities for parasite invasion. To explore how host community variation can modify parasite invasion potential, we develop a model for vector-borne parasite transmission dynamics that includes a host community of arbitrary richness and species' abundance. To compare invasion potential across communities, we calculate the community basic reproductive ratio of the parasite. We compare communities comprising a set of host species to their subsets, which allows for flexible scenario building including the introduction of novel host species and species loss. We allow vector abundance to scale with, or be independent of, community size, capturing regulation by feeding opportunities and non-host effects such as limited oviposition sites. Motivated by equivocal data relating host species competency to abundance, we characterize plausible host communities via phenomenological relationships between host species abundance and competency. We identify an underappreciated mechanism whereby changes to communities simultaneously alter average competency and the vector to host ratio and demonstrate that the interaction can profoundly influence invasion potential.
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Williams, Paul D. "Unhealthy herds: Some epidemiological consequences of host heterogeneity in predator–host–parasite systems." Journal of Theoretical Biology 253, no. 3 (August 2008): 500–507. http://dx.doi.org/10.1016/j.jtbi.2008.03.022.
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KARVONEN, ANSSI, ANNA FALTÝNKOVÁ, JOCELYN MAH CHOO, and E. TELLERVO VALTONEN. "Infection, specificity and host manipulation of Australapatemon sp. (Trematoda, Strigeidae) in two sympatric species of leeches (Hirudinea)." Parasitology 144, no. 10 (May 15, 2017): 1346–55. http://dx.doi.org/10.1017/s0031182017000609.
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SUMMARYFactors that drive parasite specificity and differences in infection dynamics among alternative host species are important for ecology and evolution of host–parasite interactions, but still often poorly known in natural systems. Here, we investigated spatiotemporal dynamics of infection, host susceptibility and parasite-induced changes in host phenotype in a rarely explored host–parasite system, the Australapatemon sp. trematode infecting two sympatric species of freshwater leeches, Erpobdella octoculata and Helobdella stagnalis. We show significant variation in infection abundance between the host species in both space and time. Using experimental infections, we also show that most of this variation likely comes from interspecific differences in exposure rather than susceptibility. Moreover, we demonstrate that the hiding behaviour of E. octoculata, but not that of H. stagnalis, was impaired by the infection irrespective of the parasite abundance. This may increase susceptibility of E. octoculata to predation by the final avian host. We conclude that differences in patterns of infection and in behavioural alterations among alternative sympatric host species may arise in narrow spatial scales, which emphasises the importance of local infection and transmission dynamics for parasite life cycles.
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Ulrich, Yuko, and Paul Schmid-Hempel. "Host modulation of parasite competition in multiple infections." Proceedings of the Royal Society B: Biological Sciences 279, no. 1740 (April 4, 2012): 2982–89. http://dx.doi.org/10.1098/rspb.2012.0474.
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Parasite diversity is a constant challenge to host immune systems and has important clinical implications, but factors underpinning its emergence and maintenance are still poorly understood. Hosts typically harbour multiple parasite genotypes that share both host resources and immune responses. Parasite diversity is thus shaped not only by resource competition between co-infecting parasites but also by host-driven immune-mediated competition. We investigated these effects in an insect–trypanosome system, combining in vivo and in vitro single and double inoculations. In vivo , a non-pathogenic, general immune challenge was used to manipulate host immune condition and resulted in a reduced ability of hosts to defend against a subsequent exposure to the trypanosome parasites, illustrating the costs of immune activation. The associated increase in available host space benefited the weaker parasite strains of each pair as much as the otherwise more competitive strains, resulting in more frequent multiple infections in immune-challenged hosts. In vitro assays showed that in the absence of a host, overall parasite diversity was minimal because the outcome of competition was virtually fixed and resulted in strain extinction. Altogether, this shows that parasite competition is largely host-mediated and suggests a role for host immune condition in the maintenance of parasite diversity.
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Behrmann-Godel, J., and E. Yohannes. "Multiple isotope analyses of the pike tapeworm Triaenophorus nodulosus reveal peculiarities in consumer–diet discrimination patterns." Journal of Helminthology 89, no. 2 (January 22, 2014): 238–43. http://dx.doi.org/10.1017/s0022149x13000849.
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AbstractPrevious studies of dietary isotope discrimination have led to the general expectation that a consumer will exhibit enriched stable isotope levels relative to its diet. Parasite–host systems are specific consumer–diet pairs in which the consumer (parasite) feeds exclusively on one dietary source: host tissue. However, the small numbers of studies previously carried out on isotopic discrimination in parasite–host (ΔXP-HT) systems have yielded controversial results, showing some parasites to be isotopically depleted relative to their food source, while others are enriched or in equilibrium with their hosts. Although the mechanism for these deviations from expectations remains to be understood, possible influences of specific feeding niche or selection for only a few nutritional components by the parasite are discussed. ΔXP-HT for multiple isotopes (δ13C, δ15N, δ34S) were measured in the pike tapeworm Triaenophorus nodulosus and two of its life-cycle fish hosts, perch Perca fluviatilis and pike Esox lucius, within which T. nodulosus occupies different feeding locations. Variability in the value of ΔXP-HT calculated for the parasite and its different hosts indicates an influence of feeding location on isotopic discrimination. In perch liver ΔXP-HT was relatively more negative for all three stable isotopes. In pike gut ΔXP-HT was more positive for δ13C, as expected in conventional consumer–diet systems. For parasites feeding on pike gut, however, the δ15N and δ34S isotope values were comparable with those of the host. We discuss potential causes of these deviations from expectations, including the effect of specific parasite feeding niches, and conclude that ΔXP-HT should be critically evaluated for trophic interactions between parasite and host before general patterns are assumed.
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BELLAY, SYBELLE, DILERMANDO P. LIMA, RICARDO M. TAKEMOTO, and JOSÉ L. LUQUE. "A host-endoparasite network of Neotropical marine fish: are there organizational patterns?" Parasitology 138, no. 14 (August 19, 2011): 1945–52. http://dx.doi.org/10.1017/s0031182011001314.
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SUMMARYProperties of ecological networks facilitate the understanding of interaction patterns in host-parasite systems as well as the importance of each species in the interaction structure of a community. The present study evaluates the network structure, functional role of all species and patterns of parasite co-occurrence in a host-parasite network to determine the organization level of a host-parasite system consisting of 170 taxa of gastrointestinal metazoans of 39 marine fish species on the coast of Brazil. The network proved to be nested and modular, with a low degree of connectance. Host-parasite interactions were influenced by host phylogeny. Randomness in parasite co-occurrence was observed in most modules and component communities, although species segregation patterns were also observed. The low degree of connectance in the network may be the cause of properties such as nestedness and modularity, which indicate the presence of a high number of peripheral species. Segregation patterns among parasite species in modules underscore the role of host specificity. Knowledge of ecological networks allows detection of keystone species for the maintenance of biodiversity and the conduction of further studies on the stability of networks in relation to frequent environmental changes.
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Rodríguez, Sara M., and Nelson Valdivia. "Mesoscale spatiotemporal variability in a complex host-parasite system influenced by intermediate host body size." PeerJ 5 (August 17, 2017): e3675. http://dx.doi.org/10.7717/peerj.3675.
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Background Parasites are essential components of natural communities, but the factors that generate skewed distributions of parasite occurrences and abundances across host populations are not well understood. Methods Here, we analyse at a seascape scale the spatiotemporal relationships of parasite exposure and host body-size with the proportion of infected hosts (i.e., prevalence) and aggregation of parasite burden across ca. 150 km of the coast and over 22 months. We predicted that the effects of parasite exposure on prevalence and aggregation are dependent on host body-sizes. We used an indirect host-parasite interaction in which migratory seagulls, sandy-shore molecrabs, and an acanthocephalan worm constitute the definitive hosts, intermediate hosts, and endoparasite, respectively. In such complex systems, increments in the abundance of definitive hosts imply increments in intermediate hosts’ exposure to the parasite’s dispersive stages. Results Linear mixed-effects models showed a significant, albeit highly variable, positive relationship between seagull density and prevalence. This relationship was stronger for small (cephalothorax length >15 mm) than large molecrabs (<15 mm). Independently of seagull density, large molecrabs carried significantly more parasites than small molecrabs. The analysis of the variance-to-mean ratio of per capita parasite burden showed no relationship between seagull density and mean parasite aggregation across host populations. However, the amount of unexplained variability in aggregation was strikingly higher in larger than smaller intermediate hosts. This unexplained variability was driven by a decrease in the mean-variance scaling in heavily infected large molecrabs. Conclusions These results show complex interdependencies between extrinsic and intrinsic population attributes on the structure of host-parasite interactions. We suggest that parasite accumulation—a characteristic of indirect host-parasite interactions—and subsequent increasing mortality rates over ontogeny underpin size-dependent host-parasite dynamics.
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Dennehy, John J. "What Can Phages Tell Us about Host-Pathogen Coevolution?" International Journal of Evolutionary Biology 2012 (November 18, 2012): 1–12. http://dx.doi.org/10.1155/2012/396165.
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The outcomes of host-parasite interactions depend on the coevolutionary forces acting upon them, but because every host-parasite relation is enmeshed in a web of biotic and abiotic interactions across a heterogeneous landscape, host-parasite coevolution has proven difficult to study. Simple laboratory phage-bacteria microcosms can ameliorate this difficulty by allowing controlled, well-replicated experiments with a limited number of interactors. Genetic, population, and life history data obtained from these studies permit a closer examination of the fundamental correlates of host-parasite coevolution. In this paper, I describe the results of phage-bacteria coevolutionary studies and their implications for the study of host-parasite coevolution. Recent experimental studies have confirmed phage-host coevolutionary dynamics in the laboratory and have shown that coevolution can increase parasite virulence, specialization, adaptation, and diversity. Genetically, coevolution frequently proceeds in a manner best described by the Gene for Gene model, typified by arms race dynamics, but certain contexts can result in Red Queen dynamics according to the Matching Alleles model. Although some features appear to apply only to phage-bacteria systems, other results are broadly generalizable and apply to all instances of antagonistic coevolution. With laboratory host-parasite coevolutionary studies, we can better understand the perplexing array of interactions that characterize organismal diversity in the wild.
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TADIRI, C. P., M. E. SCOTT, and G. F. FUSSMANN. "Impact of host sex and group composition on parasite dynamics in experimental populations." Parasitology 143, no. 4 (February 18, 2016): 523–31. http://dx.doi.org/10.1017/s0031182016000172.
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SUMMARYTo better understand the spread of disease in nature, it is fundamentally important to have broadly applicable model systems with readily available species which can be replicated and controlled in the laboratory. Here we used an experimental model system of fish hosts and monogenean parasites to determine whether host sex, group size and group composition (single-sex or mixed-sex) influenced host-parasite dynamics at an individual and group level. Parasite populations reached higher densities and persisted longer in groups of fish compared with isolated hosts and reached higher densities on isolated females than on isolated males. However, individual fish within groups had similar burdens to isolated males regardless of sex, indicating that females may benefit more than males by being in a group. Relative condition was positively associated with high parasite loads for isolated males, but not for isolated females or grouped fish. No difference in parasite dynamics between mixed-sex groups and single-sex groups was detected. Overall, these findings suggest that while host sex influences dynamics on isolated fish, individual fish in groups have similar parasite burdens, regardless of sex. We believe our experimental results contribute to a mechanistic understanding of host-parasite dynamics, although we are cautious about directly extrapolating these results to other systems.
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Kirk, Kiaran. "Membrane Transport in the Malaria-Infected Erythrocyte." Physiological Reviews 81, no. 2 (April 1, 2001): 495–537. http://dx.doi.org/10.1152/physrev.2001.81.2.495.
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The malaria parasite is a unicellular eukaryotic organism which, during the course of its complex life cycle, invades the red blood cells of its vertebrate host. As it grows and multiplies within its host blood cell, the parasite modifies the membrane permeability and cytosolic composition of the host cell. The intracellular parasite is enclosed within a so-called parasitophorous vacuolar membrane, tubular extensions of which radiate out into the host cell compartment. Like all eukaryote cells, the parasite has at its surface a plasma membrane, as well as having a variety of internal membrane-bound organelles that perform a range of functions. This review focuses on the transport properties of the different membranes of the malaria-infected erythrocyte, as well as on the role played by the various membrane transport systems in the uptake of solutes from the extracellular medium, the disposal of metabolic wastes, and the origin and maintenance of electrochemical ion gradients. Such systems are of considerable interest from the point of view of antimalarial chemotherapy, both as drug targets in their own right and as routes for targeting cytotoxic agents into the intracellular parasite.
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Halliday, Fletcher W., Robert W. Heckman, Peter A. Wilfahrt, and Charles E. Mitchell. "A multivariate test of disease risk reveals conditions leading to disease amplification." Proceedings of the Royal Society B: Biological Sciences 284, no. 1865 (October 18, 2017): 20171340. http://dx.doi.org/10.1098/rspb.2017.1340.
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Theory predicts that increasing biodiversity will dilute the risk of infectious diseases under certain conditions and will amplify disease risk under others. Yet, few empirical studies demonstrate amplification. This contrast may occur because few studies have considered the multivariate nature of disease risk, which includes richness and abundance of parasites with different transmission modes. By combining a multivariate statistical model developed for biodiversity–ecosystem–multifunctionality with an extensive field manipulation of host (plant) richness, composition and resource supply to hosts, we reveal that (i) host richness alone could not explain most changes in disease risk, and (ii) shifting host composition allowed disease amplification, depending on parasite transmission mode. Specifically, as predicted from theory, the effect of host diversity on parasite abundance differed for microbes (more density-dependent transmission) and insects (more frequency-dependent transmission). Host diversity did not influence microbial parasite abundance, but nearly doubled insect parasite abundance, and this amplification effect was attributable to variation in host composition. Parasite richness was reduced by resource addition, but only in species-rich host communities. Overall, this study demonstrates that multiple drivers, related to both host community and parasite characteristics, can influence disease risk. Furthermore, it provides a framework for evaluating multivariate disease risk in other systems.
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Conrad, Bernard, Christian Iseli, and Magnus Pirovino. "Energy-harnessing problem solving of primordial life: Modeling the emergence of catalytic host-nested parasite life cycles." PLOS ONE 18, no. 3 (March 27, 2023): e0281661. http://dx.doi.org/10.1371/journal.pone.0281661.
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All life forms on earth ultimately descended from a primordial population dubbed the last universal common ancestor or LUCA via Darwinian evolution. Extant living systems share two salient functional features, a metabolism extracting and transforming energy required for survival, and an evolvable, informational polymer–the genome–conferring heredity. Genome replication invariably generates essential and ubiquitous genetic parasites. Here we model the energetic, replicative conditions of LUCA-like organisms and their parasites, as well as adaptive problem solving of host-parasite pairs. We show using an adapted Lotka-Volterra frame-work that three host-parasite pairs–individually a unit of a host and a parasite that is itself parasitized, therefore a nested parasite pair–are sufficient for robust and stable homeostasis, forming a life cycle. This nested parasitism model includes competition and habitat restriction. Its catalytic life cycle efficiently captures, channels and transforms energy, enabling dynamic host survival and adaptation. We propose a Malthusian fitness model for a quasispecies evolving through a host-nested parasite life cycle with two core features, rapid replacement of degenerate parasites and increasing evolutionary stability of host-nested parasite units from one to three pairs.
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Riascos, Jose M., Viviana Villegas, Ignacio Cáceres, Jorge E. Gonzalez, and Aldo S. Pacheco. "Patterns of a novel association between the scyphomedusa Chrysaora plocamia and the parasitic anemone Peachia chilensis." Journal of the Marine Biological Association of the United Kingdom 93, no. 4 (August 30, 2012): 919–23. http://dx.doi.org/10.1017/s002531541200094x.
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Jellyfish display strong population variability. Competitive interactions between fish and jellyfish have been depicted as a major mechanism controlling this variability. Biological associations involving jellyfish are, however, more diverse than predation–prey interactions and remain poorly understood. Parasitic associations in particular may have relevant effects on jellyfish host populations. We studied basic patterns (temporal patterns of parasite intensity–biomass and the distribution pattern of parasites among hosts) of the association between the parasitic anemone Peachia chilensis and its scyphozoan host, Chrysaora plocamia. The mean number of parasites per host (MI) was high (average = 465) and showed significant differences during the pelagic life phase of the medusa. The mean biomass of parasites per host was also significantly different among months but showed a different temporal pattern to that of MI, which may reflect recruitment pulses of parasitic larvae. The mean biomass of P. chilensis per host averaged 56.3 mg ash-free dry mass, which represents a trophic flow of energy probably linking pelagic and benthic food webs. The distribution of parasites among hosts was best fitted to the negative binomial distribution model, as typical for host–parasite systems. We concluded that the parasite-induced host mortality and reduction of fecundity, represented by parasitic castration, is restricted to a few hosts and is therefore under the expected levels that characterize the dynamic equilibrium of host–parasite systems.
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Baruš, Vlastimil, Andrea Šimková, Miroslav Prokeš, Milan Peňáz, and Lukáš Vetešník. "Heavy metals in two host-parasite systems: tapeworm vs. fish." Acta Veterinaria Brno 81, no. 3 (2012): 313–17. http://dx.doi.org/10.2754/avb201281030313.
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The tissue of two tapeworm species (Ligula intestinalis and Bathybothrium rectangulum) and body muscles of their fish host species were analyzed for heavy metal concentrations by standard methods using atomic absorption spectrometry. Regarding the values of accumulation ratio, the L. intestinalis accumulated 12.5–18.9 × more lead, 2.3–3 × more cadmium, and 4.4–14.1 × more chrome, compared to respective metal concentrations in muscles of cyprinid intermediate fish hosts. The gravid strobila biomass of the B. rectangulum accumulated 2.2 × more lead, 1.2 × more nickel, and 2.3 × more chrome compared with the respective concentrations in the muscles of the barbel Barbus barbus. Metal concentrations in the muscles of uninfected fish and by tapeworm infected barbels showed that the uninfected individuals exhibited 1.4 × more lead, 1.6 × more nickel and 1.7 × more chrome than the infected ones. Our study suggests that parasites are a useful bioindicator when evaluating environmental pollution of aquatic ecosystems by heavy metals.
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Milner, F. A., and C. A. Patton. "A new approach to mathematical modeling of host-parasite systems." Computers & Mathematics with Applications 37, no. 2 (January 1999): 93–110. http://dx.doi.org/10.1016/s0898-1221(98)00255-7.
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GILLIGAN, C. A., and S. A. SIMONS. "INOCULUM EFFICIENCY AND PATHOZONE WIDTH FOR TWO HOST-PARASITE SYSTEMS." New Phytologist 107, no. 3 (November 1987): 549–66. http://dx.doi.org/10.1111/j.1469-8137.1987.tb02926.x.
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Vaidyanathan, Rajeev, and Krishna Kodukula. "Using a systems biology approach to dissect parasite-host interactions." Drug Development Research 70, no. 4 (June 2009): 296–302. http://dx.doi.org/10.1002/ddr.20307.
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Blakeslee, April M. H., Darby L. Pochtar, Amy E. Fowler, Chris S. Moore, Timothy S. Lee, Rebecca B. Barnard, Kyle M. Swanson, et al. "Invasion of the body snatchers: the role of parasite introduction in host distribution and response to salinity in invaded estuaries." Proceedings of the Royal Society B: Biological Sciences 288, no. 1953 (June 23, 2021): 20210703. http://dx.doi.org/10.1098/rspb.2021.0703.
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In dynamic systems, organisms are faced with variable selective forces that may impose trade-offs. In estuaries, salinity is a strong driver of organismal diversity, while parasites shape species distributions and demography. We tested for trade-offs between low-salinity stress and parasitism in an invasive castrating parasite and its mud crab host along salinity gradients of two North Carolina rivers. We performed field surveys every six to eight weeks over 3 years to determine factors influencing parasite prevalence, host abundance, and associated taxa diversity. We also looked for signatures of low-salinity stress in the host by examining its response (time-to-right and gene expression) to salinity. We found salinity and temperature significantly affected parasite prevalence, with low-salinity sites (less than 10 practical salinity units (PSU)) lacking infection, and populations in moderate salinities at warmer temperatures reaching prevalence as high as 60%. Host abundance was negatively associated with parasite prevalence. Host gene expression was plastic to acclimation salinity, but several osmoregulatory and immune-related genes demonstrated source-dependent salinity response. We identified a genetic marker that was strongly associated with salinity against a backdrop of no neutral genetic structure, suggesting possible selection on standing variation. Our study illuminates how selective trade-offs in naturally dynamic systems may shape host evolutionary ecology.
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CIRTWILL, ALYSSA R., DANIEL B. STOUFFER, ROBERT POULIN, and CLÉMENT LAGRUE. "Are parasite richness and abundance linked to prey species richness and individual feeding preferences in fish hosts?" Parasitology 143, no. 1 (November 17, 2015): 75–86. http://dx.doi.org/10.1017/s003118201500150x.
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SUMMARYVariations in levels of parasitism among individuals in a population of hosts underpin the importance of parasites as an evolutionary or ecological force. Factors influencing parasite richness (number of parasite species) and load (abundance and biomass) at the individual host level ultimately form the basis of parasite infection patterns. In fish, diet range (number of prey taxa consumed) and prey selectivity (proportion of a particular prey taxon in the diet) have been shown to influence parasite infection levels. However, fish diet is most often characterized at the species or fish population level, thus ignoring variation among conspecific individuals and its potential effects on infection patterns among individuals. Here, we examined parasite infections and stomach contents of New Zealand freshwater fish at the individual level. We tested for potential links between the richness, abundance and biomass of helminth parasites and the diet range and prey selectivity of individual fish hosts. There was no obvious link between individual fish host diet and helminth infection levels. Our results were consistent across multiple fish host and parasite species and contrast with those of earlier studies in which fish diet and parasite infection were linked, hinting at a true disconnect between host diet and measures of parasite infections in our study systems. This absence of relationship between host diet and infection levels may be due to the relatively low richness of freshwater helminth parasites in New Zealand and high host–parasite specificity.
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Tao, Leiling, Camden D. Gowler, Aamina Ahmad, Mark D. Hunter, and Jacobus C. de Roode. "Disease ecology across soil boundaries: effects of below-ground fungi on above-ground host–parasite interactions." Proceedings of the Royal Society B: Biological Sciences 282, no. 1817 (October 22, 2015): 20151993. http://dx.doi.org/10.1098/rspb.2015.1993.
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Host–parasite interactions are subject to strong trait-mediated indirect effects from other species. However, it remains unexplored whether such indirect effects may occur across soil boundaries and connect spatially isolated organisms. Here, we demonstrate that, by changing plant (milkweed Asclepias sp.) traits, arbuscular mycorrhizal fungi (AMF) significantly affect interactions between a herbivore (the monarch butterfly Danaus plexippus ) and its protozoan parasite ( Ophryocystis elektroscirrha ), which represents an interaction across four biological kingdoms. In our experiment, AMF affected parasite virulence, host resistance and host tolerance to the parasite. These effects were dependent on both the density of AMF and the identity of milkweed species: AMF indirectly increased disease in monarchs reared on some species, while alleviating disease in monarchs reared on other species. The species-specificity was driven largely by the effects of AMF on both plant primary (phosphorus) and secondary (cardenolides; toxins in milkweeds) traits. Our study demonstrates that trait-mediated indirect effects in disease ecology are extensive, such that below-ground interactions between AMF and plant roots can alter host–parasite interactions above ground. In general, soil biota may play an underappreciated role in the ecology of many terrestrial host–parasite systems.