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Wilber MQ, DeMarchi JA, Briggs CJ, Streipert S. Rapid Evolution of Resistance and Tolerance Leads to Variable Host Recoveries following Disease-Induced Declines. Am Nat 2024; 203:535-550. [PMID: 38635360 DOI: 10.1086/729437] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/20/2024]
Abstract
AbstractRecoveries of populations that have suffered severe disease-induced declines are being observed across disparate taxa. Yet we lack theoretical understanding of the drivers and dynamics of recovery in host populations and communities impacted by infectious disease. Motivated by disease-induced declines and nascent recoveries in amphibians, we developed a model to ask the following question: How does the rapid evolution of different host defense strategies affect the transient recovery trajectories of hosts following pathogen invasion and disease-induced declines? We found that while host life history is predictably a major driver of variability in population recovery trajectories (including declines and recoveries), populations that use different host defense strategies (i.e., tolerance, avoidance resistance, and intensity-reduction resistance) experience notably different recoveries. In single-species host populations, populations evolving tolerance recovered on average four times slower than populations evolving resistance. Moreover, while populations using avoidance resistance strategies had the fastest potential recovery rates, these populations could get trapped in long transient states at low abundance prior to recovery. In contrast, the recovery of populations evolving intensity-reduction resistance strategies were more consistent across ecological contexts. Overall, host defense strategies strongly affect the transient dynamics of population recovery and may affect the ultimate fate of real populations recovering from disease-induced declines.
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2
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Buckingham LJ, Ashby B. Coevolution of Age-Structured Tolerance and Virulence. Bull Math Biol 2024; 86:62. [PMID: 38662120 PMCID: PMC11045647 DOI: 10.1007/s11538-024-01292-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Accepted: 04/03/2024] [Indexed: 04/26/2024]
Abstract
Hosts can evolve a variety of defences against parasitism, including resistance (which prevents or reduces the spread of infection) and tolerance (which protects against virulence). Some organisms have evolved different levels of tolerance at different life-stages, which is likely to be the result of coevolution with pathogens, and yet it is currently unclear how coevolution drives patterns of age-specific tolerance. Here, we use a model of tolerance-virulence coevolution to investigate how age structure influences coevolutionary dynamics. Specifically, we explore how coevolution unfolds when tolerance and virulence (disease-induced mortality) are age-specific compared to when these traits are uniform across the host lifespan. We find that coevolutionary cycling is relatively common when host tolerance is age-specific, but cycling does not occur when tolerance is the same across all ages. We also find that age-structured tolerance can lead to selection for higher virulence in shorter-lived than in longer-lived hosts, whereas non-age-structured tolerance always leads virulence to increase with host lifespan. Our findings therefore suggest that age structure can have substantial qualitative impacts on host-pathogen coevolution.
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Affiliation(s)
- Lydia J Buckingham
- Department of Mathematical Sciences, University of Bath, Bath, UK.
- Milner Centre for Evolution, University of Bath, Bath, UK.
| | - Ben Ashby
- Department of Mathematical Sciences, University of Bath, Bath, UK
- Milner Centre for Evolution, University of Bath, Bath, UK
- Department of Mathematics, Simon Fraser University, Burnaby, BC, Canada
- Pacific Institute on Pathogens, Pandemics and Society, Burnaby, BC, Canada
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3
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Kueneman JG, Bonadies E, Thomas D, Roubik DW, Wcislo WT. Neotropical bee microbiomes point to a fragmented social core and strong species-level effects. MICROBIOME 2023; 11:150. [PMID: 37452376 PMCID: PMC10347802 DOI: 10.1186/s40168-023-01593-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Accepted: 06/05/2023] [Indexed: 07/18/2023]
Abstract
BACKGROUND Individuals that band together create new ecological opportunities for microorganisms. In vertical transmission, theory predicts a conserved microbiota within lineages, especially social bees. Bees exhibit solitary to social behavior among and/or within species, while life cycles can be annual or perennial. Bee nests may be used over generations or only once, and foraging ecology varies widely. To assess which traits are associated with bee microbiomes, we analyzed microbial diversity within solitary and social bees of Apidae, Colletidae, and Halictidae, three bee families in Panama's tropical forests. Our analysis considered the microbiome of adult gut contents replicated through time, localities, and seasons (wet and dry) and included bee morphology and comparison to abdominal (dissected) microbiota. Diversity and distribution of tropical bee microbes (TBM) within the corbiculate bee clade were emphasized. RESULTS We found the eusocial corbiculate bees tended to possess a more conserved gut microbiome, attributable to vertical transmission, but microbial composition varied among closely related species. Euglossine bees (or orchid bees), corbiculates with mainly solitary behavior, had more variable gut microbiomes. Their shorter-tongued and highly seasonal species displayed greater diversity, attributable to flower-visiting habits. Surprisingly, many stingless bees, the oldest corbiculate clade, lacked bacterial genera thought to predate eusociality, while several facultatively social, and solitary bee species possessed those bacterial taxa. Indeed, nearly all bee species displayed a range of affinities for single or multiple variants of the "socially associated" bacterial taxa, which unexpectedly demonstrated high sequence variation. CONCLUSIONS Taken together, these results call into question whether specific bacterial associates facilitate eusocial behavior, or are subsequently adopted, or indicate frequent horizontal transmission between perennial eusocial colonies and other social, facultatively social, and solitary bees. Video Abstract.
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Affiliation(s)
- Jordan G Kueneman
- Smithsonian Tropical Research Institute, Panama City, Panama.
- Department of Entomology, Cornell University, Comstock Hall, 2126, Ithaca, NY, 14853, Czech Republic.
| | - Ernesto Bonadies
- Smithsonian Tropical Research Institute, Panama City, Panama
- Biology Centre of the Czech Academy of Sciences, Branisovska, České Budějovice, Czech Republic
| | | | - David W Roubik
- Smithsonian Tropical Research Institute, Panama City, Panama
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Kutzer MAM, Gupta V, Neophytou K, Doublet V, Monteith KM, Vale PF. Intraspecific genetic variation in host vigour, viral load and disease tolerance during Drosophila C virus infection. Open Biol 2023; 13:230025. [PMID: 36854375 PMCID: PMC9974301 DOI: 10.1098/rsob.230025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/02/2023] Open
Abstract
Genetic variation for resistance and disease tolerance has been described in a range of species. In Drosophila melanogaster, genetic variation in mortality following systemic Drosophila C virus (DCV) infection is driven by large-effect polymorphisms in the restriction factor pastrel (pst). However, it is unclear if pst contributes to disease tolerance. We investigated systemic DCV challenges spanning nine orders of magnitude, in males and females of 10 Drosophila Genetic Reference Panel lines carrying either a susceptible (S) or resistant (R) pst allele. We find among-line variation in fly survival, viral load and disease tolerance measured both as the ability to maintain survival (mortality tolerance) and reproduction (fecundity tolerance). We further uncover novel effects of pst on host vigour, as flies carrying the R allele exhibited higher survival and fecundity even in the absence of infection. Finally, we found significant genetic variation in the expression of the JAK-STAT ligand upd3 and the epigenetic regulator of JAK-STAT G9a. However, while G9a has been previously shown to mediate tolerance of DCV infection, we found no correlation between the expression of either upd3 or G9a on fly tolerance or resistance. Our work highlights the importance of both resistance and tolerance in viral defence.
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Affiliation(s)
- Megan A. M. Kutzer
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, UK
| | - Vanika Gupta
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, UK
| | - Kyriaki Neophytou
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, UK
| | - Vincent Doublet
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, UK
| | - Katy M. Monteith
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, UK
| | - Pedro F. Vale
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, UK
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A Sterility-Mortality Tolerance Trade-Off Leads to Within-Population Variation in Host Tolerance. Bull Math Biol 2023; 85:16. [PMID: 36670241 DOI: 10.1007/s11538-023-01119-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2022] [Accepted: 01/02/2023] [Indexed: 01/21/2023]
Abstract
While experimental studies have demonstrated within-population variation in host tolerance to parasitism, theoretical studies rarely predict for polymorphism to arise. However, most theoretical models do not consider the crucial distinction between tolerance to the effects of infection-induced deaths (mortality tolerance) and tolerance to the parasite-induced reduction in the reproduction of infected hosts (sterility tolerance). While some studies have examined trade-offs between host tolerance and resistance mechanisms, none has considered a correlation within different tolerance mechanisms. We assume that sterility tolerance and mortality tolerance are directly traded-off in a host population subjected to a pathogen and use adaptive dynamics to study their evolutionary behaviour. We find that such a trade-off between the two tolerance strategies can drive the host population to branch into dimorphic strains, leading to coexistence of strains with sterile hosts that have low mortality and fully fertile with high mortality rates. Further, we find that a wider range of trade-off shapes allows branching at intermediate- or high-infected population size. Our other significant finding is that sterility tolerance is maximised (and mortality tolerance minimised) at an intermediate disease-induced mortality rate. Additionally, evolution entirely reverses the disease prevalence pattern corresponding to the recovery rate, compared to when no strategies evolve. We provide novel predictions on the evolutionary behaviour of two tolerance strategies concerning such a trade-off.
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Paramasivam R, Gopal DR, Dhandapani R, Subbarayalu R, Elangovan MP, Prabhu B, Veerappan V, Nandheeswaran A, Paramasivam S, Muthupandian S. Is AMR in Dairy Products a Threat to Human Health? An Updated Review on the Origin, Prevention, Treatment, and Economic Impacts of Subclinical Mastitis. Infect Drug Resist 2023; 16:155-178. [PMID: 36636377 PMCID: PMC9831082 DOI: 10.2147/idr.s384776] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Accepted: 12/20/2022] [Indexed: 01/07/2023] Open
Abstract
Background Bovine mastitis is the most frequent and costly illness impacting dairy herds worldwide. The presence of subclinical mastitis in dairy cows has an impact on the decreased output of milk and milk quality, culling of affected cows, mortality rate, as well as mastitis-related treatment expenses, generating significant financial loss to the dairy industry. The pathogenic bacteria invade through the mammary gland, which then multiply in the milk-producing tissues causing infection, and the presence of pathogenic bacteria in milk is concerning, jeopardizes human health, and also has public health consequences. Intervention to promote herd health is essential to protect public health and the economy. Results This review attempts to provide an overview of subclinical mastitis, including mastitis in different species, the effect of mastitis on human health and its pathogenic mechanism, the prevalence and incidence of subclinical mastitis, and current preventive, diagnostic, and treatment methods for subclinical mastitis. It also elaborates on the management practices that should be followed by the farms to improve herd immunity and health. Conclusion This review brings the importance of the threat of antimicrobial resistance organisms to the dairy industry. Furthermore, this review gives a glimpse of the economic consequences faced by the farmers and a futuristic mastitis market analysis in the dairy industry.
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Affiliation(s)
- Ragul Paramasivam
- Research and Development Division, Chimertech Private Limited, Chennai, India
| | - Dhinakar Raj Gopal
- Department of Animal Biotechnology, Madras Veterinary College, Tamilnadu Veterinary and Animal Science University (TANUVAS), Chennai, 600007, India
| | | | | | | | - Bhavadharani Prabhu
- Research and Development Division, Chimertech Private Limited, Chennai, India
| | - Veeramani Veerappan
- Research and Development Division, Chimertech Private Limited, Chennai, India
| | | | | | - Saravanan Muthupandian
- AMR and Nanotherapeutics Lab, Centre for Transdisciplinary Research (CFTR), Department of Pharmacology, Saveetha Dental College, Saveetha Institute of Medical and Technical Sciences (SIMATS), Chennai, India,Division of Biomedical Science, College of Health Sciences, School of Medicine, Mekelle University, Mekelle, Ethiopia,Correspondence: Saravanan Muthupandian, Email
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Balard A, Heitlinger E. Shifting focus from resistance to disease tolerance: A review on hybrid house mice. Ecol Evol 2022; 12:e8889. [PMID: 35571751 PMCID: PMC9077717 DOI: 10.1002/ece3.8889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Revised: 04/11/2022] [Accepted: 04/14/2022] [Indexed: 11/10/2022] Open
Abstract
Parasites have been proposed to modulate the fitness of hybridizing hosts in part based on observations in the European house mouse hybrid zone (HMHZ), a tension zone in which hybrids show reduced fitness. We here review evidence (1) for parasite load differences in hybrid versus parental mice and (2) for health and fitness effects of parasites promoting or preventing introgression and hybridization. The question of relative resistance or susceptibility of hybrids to parasites in the HMHZ has long been controversial. Recent field studies found hybrids to be more resistant than mice from parental subspecies against infections with pinworms and protozoans (Eimeria spp.). We argue that the field studies underlying the contradictory impression of hybrid susceptibility have limitations in sample size, statistical analysis and scope, focusing only on macroparasites. We suggest that weighted evidence from field studies indicate hybrid resistance. Health is a fitness component through which resistance can modulate overall fitness. Resistance, however, should not be extrapolated directly to a fitness effect, as the relationship between resistance and health can be modulated by tolerance. In our own recent work, we found that the relationship between health and resistance (tolerance) differs between infections with the related species E. falciformis and E. ferrisi. Health and tolerance need to be assessed directly and the choice of parasite has made this difficult in previous experimental studies of house mice. We discuss how experimental Eimeria spp. infections in hybrid house mice can address resistance, health and tolerance in conjunction.
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Affiliation(s)
- Alice Balard
- Department of Molecular Parasitology Institute for Biology Humboldt University Berlin (HU) Berlin Germany
- Research Group Ecology and Evolution of Molecular Parasite‐Host Interactions Leibniz‐Institut for Zoo and Wildlife Research (IZW) im Forschungsverbund Berlin e.V. Berlin Germany
| | - Emanuel Heitlinger
- Department of Molecular Parasitology Institute for Biology Humboldt University Berlin (HU) Berlin Germany
- Research Group Ecology and Evolution of Molecular Parasite‐Host Interactions Leibniz‐Institut for Zoo and Wildlife Research (IZW) im Forschungsverbund Berlin e.V. Berlin Germany
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Paraskevopoulou S, Gattis S, Ben-Ami F. Parasite resistance and parasite tolerance: insights into transgenerational immune priming in an invertebrate host. Biol Lett 2022; 18:20220018. [PMID: 35382587 PMCID: PMC8984330 DOI: 10.1098/rsbl.2022.0018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Parasites impose different selection regimes on their hosts, which respond by increasing their resistance and/or tolerance. Parental challenge with parasites can enhance the immune response of their offspring, a phenomenon documented in invertebrates and termed transgenerational immune priming. We exposed two parental generations of the model organism Daphnia magna to the horizontally transmitted parasitic yeast Metschnikowia bicuspidata and recorded resistance- and tolerance-related traits in the offspring generation. We hypothesized that parentally primed offspring will increase either their resistance or their tolerance to the parasite. Our susceptibility assays revealed no impact of parental exposure on offspring resistance. Nonetheless, different fitness-related traits, which are indicative of tolerance, were altered. Specifically, maternal priming increased offspring production and decreased survival. Grandmaternal priming positively affected age at first reproduction and negatively affected brood size at first reproduction. Interestingly, both maternal and grandmaternal priming significantly reduced within-host–parasite proliferation. Nevertheless, Daphnia primed for two consecutive generations had no competitive advantage in comparison to unprimed ones, implying additive maternal and grandmaternal effects. Our findings do not support evidence of transgenerational immune priming from bacterial infections in the same host species, thus, emphasizing that transgenerational immune responses may not be consistent even within the same host species.
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Affiliation(s)
- Sofia Paraskevopoulou
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Sabrina Gattis
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Frida Ben-Ami
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel
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9
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Tamisier L, Szadkowski M, Girardot G, Djian‐Caporalino C, Palloix A, Hirsch J, Moury B. Concurrent evolution of resistance and tolerance to potato virus Y in Capsicum annuum revealed by genome-wide association. MOLECULAR PLANT PATHOLOGY 2022; 23:254-264. [PMID: 34729890 PMCID: PMC8743019 DOI: 10.1111/mpp.13157] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 10/19/2021] [Accepted: 10/20/2021] [Indexed: 05/21/2023]
Abstract
We performed a genome-wide association study of pepper (Capsicum annuum) tolerance to potato virus Y (PVY). For 254 pepper accessions, we estimated the tolerance to PVY as the coefficient of regression of the fresh weight (or height) of PVY-infected and mock-inoculated plants against within-plant virus load. Small (strongly negative) coefficients of regression indicate low tolerance because plant biomass or growth decreases sharply as virus load increases. The tolerance level varied largely, with some pepper accessions showing no symptoms or fairly mild mosaics, whereas about half (48%) of the accessions showed necrotic symptoms. We found two adjacent single-nucleotide polymorphisms (SNPs) at one extremity of chromosome 9 that were significantly associated with tolerance to PVY. Similarly, in three biparental pepper progenies, we showed that the induction of necrosis on PVY systemic infection segregated as a monogenic trait determined by a locus on chromosome 9. Our results also demonstrate the existence of a negative correlation between resistance and tolerance among the cultivated pepper accessions at both the phenotypic and genetic levels. By comparing the distributions of the tolerance-associated SNP alleles and previously identified PVY resistance-associated SNP alleles, we showed that cultivated pepper accessions possess favourable alleles for both resistance and tolerance less frequently than expected under random associations, while the minority of wild pepper accessions frequently combined resistance and tolerance alleles. This divergent evolution of PVY resistance and tolerance could be related to pepper domestication or farmer's selection.
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Affiliation(s)
- Lucie Tamisier
- Pathologie VégétaleINRAEMontfavetFrance
- GAFLINRAEMontfavetFrance
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10
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Prakash A, Khan I. Why do insects evolve immune priming? A search for crossroads. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2022; 126:104246. [PMID: 34453994 DOI: 10.1016/j.dci.2021.104246] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 08/25/2021] [Indexed: 06/13/2023]
Abstract
Until recently, it was assumed that insects lack immune memory since they do not have vertebrate-like specialized memory cells. Therefore, their most well studied evolutionary response against pathogens was increased basal immunity. However, growing evidence suggests that many insects also exhibit a form of immune memory (immune priming), where prior exposure to a low dose of infection confers protection against subsequent infection by the same pathogen that acts both within and across generations. Most strikingly, they can rapidly evolve as a highly parallel and mutually exclusive strategy from basal immunity, under different selective conditions and with divergent evolutionary trade-offs. However, the relative importance of priming as an optimal immune strategy also has contradictions, primarily because supporting mechanisms are still unclear. In this review, we adopt a comparative approach to highlight several emerging evolutionary, ecological and mechanistic features of priming vs basal immune responses that warrant immediate attention for future research.
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Affiliation(s)
- Arun Prakash
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, EH9 3FL, United Kingdom.
| | - Imroze Khan
- Department of Biology, Ashoka University, Plot No. 2, Rajiv Gandhi Education City, P.O. Rai, Sonepat, Haryana, 131029, India.
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11
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Singh P, Best A. Simultaneous evolution of host resistance and tolerance to parasitism. J Evol Biol 2021; 34:1932-1943. [PMID: 34704334 DOI: 10.1111/jeb.13947] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 09/17/2021] [Accepted: 10/11/2021] [Indexed: 12/22/2022]
Abstract
Tolerance and resistance are two modes of defence mechanisms used by hosts when faced with parasites. Here, we assume tolerance reduces infection-induced mortality rate and resistance reduces the susceptibility of getting infected. Importantly, a negative association between these two strategies has often been found experimentally. We study the simultaneous evolution of resistance and tolerance in a host population where they are related by such a trade-off. Using evolutionary invasion theory, we examine the patterns of optimal investment in each defence strategy, under different ecological scenarios. Our focus is on predicting which of the two strategies is favoured under various epidemiological and ecological conditions. Our key findings surround the impact of recovery and sterility of infected hosts. As the rate at which infected hosts recover from the infection, that is the recovery rate increases, the investment in tolerance increases (resistance decreases) when infected hosts are sterile, but this pattern reverses when infected hosts can reproduce. We further found that a change in the parameter determining the intraspecies competition for resources leading to a reduction in birth rate, that is the crowding factor affects investments in tolerance and resistance only when infected hosts can reproduce. These results emphasize the role of fecundity in driving the evolutionary dynamics of a host. We also find that disease prevalence can increase or decrease depending on whether or not the host evolves: prevalence is highest at low recovery rates when the host does not evolve, but the feedback of a change in tolerance and resistance reverses this pattern, leading to lower prevalence at low recovery rates as host evolves.
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Affiliation(s)
- Prerna Singh
- School of Mathematics and Statistics, University of Sheffield, Sheffield, UK
| | - Alex Best
- School of Mathematics and Statistics, University of Sheffield, Sheffield, UK
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Seal S, Dharmarajan G, Khan I. Evolution of pathogen tolerance and emerging infections: A missing experimental paradigm. eLife 2021; 10:e68874. [PMID: 34544548 PMCID: PMC8455132 DOI: 10.7554/elife.68874] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 08/23/2021] [Indexed: 12/11/2022] Open
Abstract
Researchers worldwide are repeatedly warning us against future zoonotic diseases resulting from humankind's insurgence into natural ecosystems. The same zoonotic pathogens that cause severe infections in a human host frequently fail to produce any disease outcome in their natural hosts. What precise features of the immune system enable natural reservoirs to carry these pathogens so efficiently? To understand these effects, we highlight the importance of tracing the evolutionary basis of pathogen tolerance in reservoir hosts, while drawing implications from their diverse physiological and life-history traits, and ecological contexts of host-pathogen interactions. Long-term co-evolution might allow reservoir hosts to modulate immunity and evolve tolerance to zoonotic pathogens, increasing their circulation and infectious period. Such processes can also create a genetically diverse pathogen pool by allowing more mutations and genetic exchanges between circulating strains, thereby harboring rare alive-on-arrival variants with extended infectivity to new hosts (i.e., spillover). Finally, we end by underscoring the indispensability of a large multidisciplinary empirical framework to explore the proposed link between evolved tolerance, pathogen prevalence, and spillover in the wild.
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Affiliation(s)
| | - Guha Dharmarajan
- Savannah River Ecology Laboratory, University of GeorgiaAikenUnited States
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13
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Montes N, Vijayan V, Pagán I. Host population structure for tolerance determines the evolution of plant-virus interactions. THE NEW PHYTOLOGIST 2021; 231:1570-1585. [PMID: 33997993 PMCID: PMC8362011 DOI: 10.1111/nph.17466] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Accepted: 05/02/2021] [Indexed: 06/12/2023]
Abstract
Heterogeneity for plant defences determines both the capacity of host populations to buffer the effect of infection and the pathogen´s fitness. However, little information is known on how host population structure for tolerance, a major plant defence, impacts the evolution of plant-pathogen interactions. By performing 10 serial passages of Turnip mosaic virus (TuMV) in Arabidopsis thaliana populations with varying proportion of tolerant genotypes simulating different structures for this trait, we analysed how host heterogeneity for this defence shapes the evolution of both virus multiplication, the effect of infection on plant fecundity and mortality, and plant tolerance and resistance. Results indicated that a higher proportion of tolerant genotypes in the host population promotes virus multiplication and reduces the effect of infection on plant mortality, but not on plant fecundity. These changes resulted in more effective plant tolerance to virus infection. Conversely, a lower proportion of tolerant genotypes reduced virus multiplication, boosting plant resistance. Our work for the first time provides evidence of the main role of host population structure for tolerance on pathogen evolution and on the subsequent feedback loops on plant defences.
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Affiliation(s)
- Nuria Montes
- Fisiología VegetalDepartamento Ciencias Farmacéuticas y de la SaludFacultad de FarmaciaUniversidad San Pablo‐CEU UniversitiesBoadilla del Monte (Madrid)28668Spain
- Servicio de ReumatologíaHospital Universitario de la PrincesaInstituto de Investigación Sanitaria (IIS‐IP)Madrid28008Spain
| | - Viji Vijayan
- Centro de Biotecnología y Genómica de Plantas UPM‐INIA and ETS Ingeniería Agronómica, Alimentaria y de BiosistemasUniversidad Politécnica de MadridMadrid28223Spain
| | - Israel Pagán
- Centro de Biotecnología y Genómica de Plantas UPM‐INIA and ETS Ingeniería Agronómica, Alimentaria y de BiosistemasUniversidad Politécnica de MadridMadrid28223Spain
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Sorci G, Léchenault-Bergerot C, Faivre B. Age reduces resistance and tolerance in malaria-infected mice. INFECTION GENETICS AND EVOLUTION 2020; 88:104698. [PMID: 33370596 DOI: 10.1016/j.meegid.2020.104698] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 12/16/2020] [Accepted: 12/23/2020] [Indexed: 12/30/2022]
Abstract
Once infected, hosts can rely on two strategies to cope with parasites: fight them (resist the infection) or minimize the damage they induce (tolerate the infection). While there is evidence that aging reduces resistance, how tolerance varies as hosts become old has been barely studied. Here, we used a rodent malaria parasite (Plasmodium yoelii) to investigate whether 2- and 12-month old house mice differ in their capacity to resist and tolerate the infection. We found that 12-month old mice harbored higher parasitemia, showing that age reduces resistance to malaria. Infection-induced deterioration of host health was assessed using red blood cell and body mass loss. Using both traits, the rate of decline in host health, as parasitemia increased, was more pronounced in 12- than in 2-month old mice, showing that age is also associated with impaired tolerance to malaria. Overall, resistance and tolerance positively covaried; however, this was only due to the age effect, since, within age classes, the two traits were not correlated. These results show that senescing individuals might be both more susceptible to infectious diseases and less able to cope with the damage that infection induces.
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Affiliation(s)
- Gabriele Sorci
- Biogéosciences, CNRS UMR 6282, Université de Bourgogne Franche-Comté, 6 Boulevard Gabriel, 21000 Dijon, France.
| | | | - Bruno Faivre
- Biogéosciences, CNRS UMR 6282, Université de Bourgogne Franche-Comté, 6 Boulevard Gabriel, 21000 Dijon, France
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Jiao J, Gilchrist MA, Fefferman NH. The impact of host metapopulation structure on short-term evolutionary rescue in the face of a novel pathogenic threat. Glob Ecol Conserv 2020. [DOI: 10.1016/j.gecco.2020.e01174] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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Abstract
Increasing evidence indicates that tolerance is a host defense strategy against pathogens as widespread and successful as resistance. Since the concept of tolerance was proposed more than a century ago, it has been in continuous evolution. In parallel, our understanding of its mechanistic bases and its consequences for host and pathogen interactions, ecology, and evolution has grown. This review aims at summarizing the conceptual changes in the meaning of tolerance inside and outside the field of phytopathology, emphasizing difficulties in demonstrating and quantifying this trait. We also discuss evidence of tolerance and current knowledge on its genetic regulation, mechanisms, and role in host-pathogen coevolution, highlighting common patterns across hosts and pathogens. We hope that this comprehensive review attracts more plant pathologists to the study of this key plant defense response.
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Affiliation(s)
- Israel Pagán
- Centro de Biotecnología y Genómica de Plantas (CBGP), Universidad Politécnica de Madrid (UPM) and Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), and E.T.S.I. Agronómica, Alimentaria y de Biosistemas, Campus de Montegancedo, UPM, 28223 Pozuelo de Alarcón, Madrid, Spain;
| | - Fernando García-Arenal
- Centro de Biotecnología y Genómica de Plantas (CBGP), Universidad Politécnica de Madrid (UPM) and Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), and E.T.S.I. Agronómica, Alimentaria y de Biosistemas, Campus de Montegancedo, UPM, 28223 Pozuelo de Alarcón, Madrid, Spain;
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17
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Mikaberidze A, McDonald BA. A tradeoff between tolerance and resistance to a major fungal pathogen in elite wheat cultivars. THE NEW PHYTOLOGIST 2020; 226:879-890. [PMID: 31917858 DOI: 10.1111/nph.16418] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2019] [Accepted: 12/12/2019] [Indexed: 06/10/2023]
Abstract
Tolerance and resistance represent two strategies that hosts evolved to protect themselves from pathogens. Tolerance alleviates the reduction in host fitness due to infection without reducing a pathogen's growth, whereas resistance reduces pathogen growth. We investigated the tolerance of wheat to the major fungal pathogen Zymoseptoria tritici in 335 elite wheat cultivars. We used a novel digital phenotyping approach that included 11 152 infected leaves and counted 2069 048 pathogen fruiting bodies. We discovered a new component of tolerance that is based on the relationship between the green area remaining on a leaf and the number of pathogen fruiting bodies. We found a negative correlation between tolerance and resistance among intolerant cultivars, presenting the first compelling evidence for a tradeoff between tolerance and resistance to plant pathogens. Surprisingly, the tradeoff arises due to limits in the host resources available to the pathogen and not due to metabolic constraints, contrary to what ecological theory suggests. The mechanism underlying this tradeoff may be relevant for many plant diseases in which the amount of host resources available to the pathogen can limit the pathogen population. Our analysis indicates that European wheat breeders may have selected for tolerance instead of resistance to an important pathogen.
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Affiliation(s)
- Alexey Mikaberidze
- School of Agriculture, Policy and Development, University of Reading, Whiteknights, Reading, RG6 6AR, UK
| | - Bruce A McDonald
- Plant Pathology, Institute of Integrative Biology, LFW, ETH Zurich, 8092, Zurich, Switzerland
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18
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Henschen AE, Adelman JS. What Does Tolerance Mean for Animal Disease Dynamics When Pathology Enhances Transmission? Integr Comp Biol 2020; 59:1220-1230. [PMID: 31141137 DOI: 10.1093/icb/icz065] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Host competence, or how well an individual transmits pathogens, varies substantially within and among animal populations. As this variation can alter the course of epidemics and epizootics, revealing its underlying causes will help predict and control the spread of disease. One host trait that could drive heterogeneity in competence is host tolerance, which minimizes fitness losses during infection without decreasing pathogen load. In many cases, tolerance should increase competence by extending infectious periods and enabling behaviors that facilitate contact among hosts. However, we argue that the links between tolerance and competence are more varied. Specifically, the different physiological and behavioral mechanisms by which hosts achieve tolerance should have a range of effects on competence, enhancing the ability to transmit pathogens in some circumstances and impeding it in others. Because tissue-based pathology (damage) that reduces host fitness is often critical for pathogen transmission, we focus on two mechanisms that can underlie tolerance at the tissue level: damage-avoidance and damage-repair. As damage-avoidance reduces transmission-enhancing pathology, this mechanism is likely to decrease host competence and pathogen transmission. In contrast, damage-repair does not prevent transmission-relevant pathology from occurring. Rather, damage-repair provides new, healthy tissues that pathogens can exploit, likely extending the infectious period and increasing host competence. We explore these concepts through graphical models and present three disease systems in which damage-avoidance and damage-repair alter host competence in the predicted directions. Finally, we suggest that by incorporating these links, future theoretical studies could provide new insights into infectious disease dynamics and host-pathogen coevolution.
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Affiliation(s)
- Amberleigh E Henschen
- Department of Natural Resource Ecology and Management, Iowa State University, 339 Science Hall II, 2310 Pammel Drive, Ames, IA 50011, USA
| | - James S Adelman
- Department of Natural Resource Ecology and Management, Iowa State University, 339 Science Hall II, 2310 Pammel Drive, Ames, IA 50011, USA
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19
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Oliveira JH, Bahia AC, Vale PF. How are arbovirus vectors able to tolerate infection? DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2020; 103:103514. [PMID: 31585195 DOI: 10.1016/j.dci.2019.103514] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 09/20/2019] [Accepted: 10/01/2019] [Indexed: 06/10/2023]
Abstract
One of the defining features of mosquito vectors of arboviruses such as Dengue and Zika is their ability to tolerate high levels of virus proliferation without suffering significant pathology. This adaptation is central to vector competence and disease spread. The molecular mechanisms, pathways, cellular and metabolic adaptations responsible for mosquito disease tolerance are still largely unknown and may represent effective ways to control mosquito populations and prevent arboviral diseases. In this review article, we describe the key link between disease tolerance and pathogen transmission, and how vector control methods may benefit by focusing efforts on dissecting the mechanisms underlying mosquito tolerance of arboviral infections. We briefly review recent work investigating tolerance mechanisms in other insects, describe the state of the art regarding the mechanisms of disease tolerance in mosquitos, and highlight the emerging role of gut microbiota in mosquito immunity and disease tolerance.
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Affiliation(s)
- José Henrique Oliveira
- Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de Santa Catarina, Florianopolis, SC, Brazil.
| | - Ana Cristina Bahia
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
| | - Pedro F Vale
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom.
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20
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Martín JA, Sobrino-Plata J, Coira B, Medel D, Collada C, Gil L. Growth resilience and oxidative burst control as tolerance factors to Ophiostoma novo-ulmi in Ulmus minor. TREE PHYSIOLOGY 2019; 39:1512-1524. [PMID: 31211377 DOI: 10.1093/treephys/tpz067] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 04/10/2019] [Accepted: 05/17/2019] [Indexed: 06/09/2023]
Abstract
The Dutch elm disease (DED) pathogens, Ophiostoma ulmi (Buisman) Nannf. and the more aggressive Ophiostoma novo-ulmi Brasier, have decimated European elm populations in the last 100 years. Today, the number of tolerant elm varieties available on the market is limited, partly due to the long breeding cycles and expensive facilities they require. Developing a low-cost technique to allow early screening of elm tolerance based on simple morphological and/or biochemical traits would considerably boost elm breeding and research. Within this general aim, we developed an in vitro plant culture system to (i) characterize stress responses to O. novo-ulmi-root inoculation in two Ulmus minor Mill. clones of contrasting susceptibility level to DED (termed 'tolerant' and 'susceptible') and (ii) compare the upward dispersal rate of the pathogen in the two clones. Constitutive xylem anatomy was similar in both clones, indicating that differences in plant responses to the pathogen are not attributable to anatomical factors (e.g., conduit size). Susceptible plantlets suffered a significant delay in apical growth and a decrease in chlorophyll content at 21 days post-inoculation (dpi). The rate of pathogen dispersal from roots to aerial tissues was similar in both clones. However, the tolerant clone showed a marked increase in lipid peroxidation at 1 dpi, while the susceptible clone showed enhanced values of lipid peroxidation during most of the experimental period (1-21 dpi). Despite wide stem colonization by the pathogen, the tolerant clone effectively regulated the oxidative stress levels and showed remarkable resilience to inoculation. These results extend current knowledge on elm defense mechanisms, and the proposed in vitro plant culture system emerges as a promising early screening method for tolerance to improve elm breeding.
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Affiliation(s)
- Juan A Martín
- Departamento de Sistemas y Recursos Naturales, ETSI Montes, Forestal y del Medio Natural, Universidad Politécnica de Madrid
| | - Juan Sobrino-Plata
- Departamento de Sistemas y Recursos Naturales, ETSI Montes, Forestal y del Medio Natural, Universidad Politécnica de Madrid
| | - Begoña Coira
- Departamento de Sistemas y Recursos Naturales, ETSI Montes, Forestal y del Medio Natural, Universidad Politécnica de Madrid
| | - David Medel
- Departamento de Sistemas y Recursos Naturales, ETSI Montes, Forestal y del Medio Natural, Universidad Politécnica de Madrid
| | - Carmen Collada
- Departamento de Sistemas y Recursos Naturales, ETSI Montes, Forestal y del Medio Natural, Universidad Politécnica de Madrid
| | - Luis Gil
- Departamento de Sistemas y Recursos Naturales, ETSI Montes, Forestal y del Medio Natural, Universidad Politécnica de Madrid
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21
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Bonneaud C, Tardy L, Giraudeau M, Hill GE, McGraw KJ, Wilson AJ. Evolution of both host resistance and tolerance to an emerging bacterial pathogen. Evol Lett 2019. [DOI: 10.1002/evl3.133] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Affiliation(s)
- Camille Bonneaud
- Centre for Ecology and Conservation; University of Exeter; Penryn Cornwall TR10 9FE United Kingdom
| | - Luc Tardy
- Centre for Ecology and Conservation; University of Exeter; Penryn Cornwall TR10 9FE United Kingdom
| | - Mathieu Giraudeau
- Centre for Ecology and Conservation; University of Exeter; Penryn Cornwall TR10 9FE United Kingdom
- School of Life Sciences; Arizona State University; Tempe Arizona 85287
- Current address: Centre for Ecological and Evolutionary Research on Cancer; UMR CNRS/IRD/UM 5290 MIVEGEC; 34394 Montpellier France
| | - Geoffrey E. Hill
- Department of Biological Sciences; Auburn University; Auburn Alabama 36849
| | - Kevin J. McGraw
- School of Life Sciences; Arizona State University; Tempe Arizona 85287
| | - Alastair J. Wilson
- Centre for Ecology and Conservation; University of Exeter; Penryn Cornwall TR10 9FE United Kingdom
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22
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Ferris C, Best A. The effect of temporal fluctuations on the evolution of host tolerance to parasitism. Theor Popul Biol 2019; 130:182-190. [PMID: 31415775 DOI: 10.1016/j.tpb.2019.07.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Revised: 05/29/2019] [Accepted: 07/29/2019] [Indexed: 11/19/2022]
Abstract
There are many mechanisms that hosts can evolve to defend against parasites, two of which are resistance and tolerance. These defences often have different evolutionary behaviours, and it is important to consider how each individual mechanism may respond to changes in environment. In particular, host defence through tolerance is predicted to be unlikely to lead to variation, despite many observations of diversity in both animal and plant systems. Hence understanding the drivers of diversity in host defence and parasite virulence is vital for predicting future evolutionary changes in infectious disease dynamics. It has been suggested that heterogeneous environments might generally promote diversity, but the effect of temporal fluctuations has received little attention theoretically or empirically, and there has been no examination of how temporal fluctuations affects the evolution of host tolerance. In this study, we use a mathematical model to investigate the evolution of host tolerance in a temporally fluctuating environment. We show that investment in tolerance increases in more variable environments, giving qualitatively different evolutionary behaviours when compared to resistance. Once seasonality is introduced evolutionary branching though tolerance can occur and create diversity within the population, although potentially only temporarily. This branching behaviour arises due to the emergence of a negative feedback with the maximum infected density on a cycle, which is strongest when the infected population is large. This work reinforces the qualitative differences between tolerance and resistance evolution, but also provides theoretical evidence for the theory that heterogeneous environments promote host-parasite diversity, hence constant environment assumptions may omit important evolutionary outcomes.
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Affiliation(s)
- Charlotte Ferris
- School of Mathematics and Statistics, University of Sheffield, Sheffield, S3 7RH, UK.
| | - Alex Best
- School of Mathematics and Statistics, University of Sheffield, Sheffield, S3 7RH, UK
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23
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Montes N, Alonso-Blanco C, García-Arenal F. Cucumber mosaic virus infection as a potential selective pressure on Arabidopsis thaliana populations. PLoS Pathog 2019; 15:e1007810. [PMID: 31136630 PMCID: PMC6555541 DOI: 10.1371/journal.ppat.1007810] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2019] [Revised: 06/07/2019] [Accepted: 05/01/2019] [Indexed: 02/07/2023] Open
Abstract
It has been proposed that in wild ecosystems viruses are often plant mutualists, whereas agroecosystems favour pathogenicity. We seek evidence for virus pathogenicity in wild ecosystems through the analysis of plant-virus coevolution, which requires a negative effect of infection on the host fitness. We focus on the interaction between Arabidopsis thaliana and Cucumber mosaic virus (CMV), which is significant in nature. We studied the genetic diversity of A. thaliana for two defence traits, resistance and tolerance, to CMV. A set of 185 individuals collected in 76 A. thaliana Iberian wild populations were inoculated with different CMV strains. Resistance was estimated from the level of virus multiplication in infected plants, and tolerance from the effect of infection on host progeny production. Resistance and tolerance to CMV showed substantial genetic variation within and between host populations, and depended on the virus x host genotype interaction, two conditions for coevolution. Resistance and tolerance were co-occurring independent traits that have evolved independently from related life-history traits involved in adaptation to climate. The comparison of the genetic structure for resistance and tolerance with that for neutral traits (QST/FST analyses) indicated that both defence traits are likely under uniform selection. These results strongly suggest that CMV infection selects for defence on A. thaliana populations, and support plant-virus coevolution. Thus, we propose that CMV infection reduces host fitness under the field conditions of the wild A. thaliana populations studied.
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Affiliation(s)
- Nuria Montes
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA), and E.T.S.I. Agronómica, Alimentaria y de Biosistemas, Campus de Montegancedo, Universidad Politécnica de Madrid, Pozuelo de Alarcón (Madrid), Spain
| | - Carlos Alonso-Blanco
- Departamento de Genética Molecular de Plantas, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas (CNB-CSIC), Campus Universidad Autónoma, Cantoblanco, Madrid, Spain
| | - Fernando García-Arenal
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA), and E.T.S.I. Agronómica, Alimentaria y de Biosistemas, Campus de Montegancedo, Universidad Politécnica de Madrid, Pozuelo de Alarcón (Madrid), Spain
- * E-mail:
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24
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Vitale C, Best A. The paradox of tolerance: Parasite extinction due to the evolution of host defence. J Theor Biol 2019; 474:78-87. [PMID: 31051178 DOI: 10.1016/j.jtbi.2019.04.024] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 04/24/2019] [Accepted: 04/29/2019] [Indexed: 10/26/2022]
Abstract
Host defence against parasite infection can rely on two broad strategies: resistance and tolerance. The spread of resistance traits usually lowers parasite prevalence and decreases selection for higher defence. Conversely, tolerance mechanisms increase parasite prevalence and foster selection for more tolerance. Here we examine the potential for the host to drive parasites to extinction through the evolution of one or other defence mechanism. We analysed theoretical models of resistance and tolerance evolution in both the absence and the presence of a trade-off between defence and reproduction. In the absence of costs, resistance evolves towards maximisation and, consequently, parasite extinction. Tolerance also evolves towards maximisation but the positive feedback between tolerance and disease prevents the disappearance of the parasite. On the contrary, when defence comes with costs it is impossible for the host to eliminate the infection through resistance, because costly resistance is selected against when parasites are at low prevalence. We uncover that the only path to disease clearance in the presence of costs is through tolerance. Paradoxically, however, it is by lowering tolerance -and hence increasing disease-induced mortality- that extinction can occur. We also show that such extinction can occur even in the case of parasite counter-adaptation. Our results emphasise the importance of tolerance as a defence strategy, and identify key questions for future research.
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Affiliation(s)
- Caterina Vitale
- School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, United Kingdom.
| | - Alex Best
- School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, United Kingdom.
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25
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Stutz WE, Calhoun DM, Johnson PTJ. Resistance and tolerance: A hierarchical framework to compare individual versus family-level host contributions in an experimental amphibian-trematode system. Exp Parasitol 2019; 199:80-91. [PMID: 30862495 DOI: 10.1016/j.exppara.2019.03.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 01/22/2019] [Accepted: 03/06/2019] [Indexed: 11/18/2022]
Abstract
Hosts have two general strategies for mitigating the fitness costs of parasite exposure and infection: resistance and tolerance. The resistance-tolerance framework has been well developed in plant systems, but only recently has it been applied to animal-parasite interactions. However, difficulties associated with estimating fitness, controlling parasite exposure, and quantifying parasite burden have limited application of this framework to animal systems. Here, we used an experimental approach to quantify the relative influence of variation among host individuals and genetic families in determining resistance and tolerance within an amphibian-trematode system. Importantly, we used multiple, alternative metrics to assess each strategy, and employed a Bayesian analytical framework to compare among responses while incorporating uncertainty. Relative to unexposed hosts, exposure to the pathogenic trematode (Ribeiroia ondatrae) reduced the survival and growth of California newts (Taricha torosa) (survival: 93% vs. 74%; growth: 0.29 vs. -0.5 vs mm day -1). Similarly, parasite infection success (the inverse of resistance) ranged from 8% to 100%. Yet despite this broad variation in host resistance and tolerance among individual newts, we found no evidence for transmissable, among-family variation in any of the resistance or tolerance metrics. This suggests that opportunities for evolution of these traits is limited, likely requiring significant increases in mutation, gene flow, or environmental heterogeneity. Our study provides a quantitative framework for evaluating the importance of alternative metrics of resistance and tolerance across multiple time points in the study of host-parasite interactions in animal systems.
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Affiliation(s)
- William E Stutz
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, 80309, USA
| | - Dana M Calhoun
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, 80309, USA.
| | - Pieter T J Johnson
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, 80309, USA
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26
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McNew SM, Knutie SA, Goodman GB, Theodosopoulos A, Saulsberry A, Yépez R. J, Bush SE, Clayton DH. Annual environmental variation influences host tolerance to parasites. Proc Biol Sci 2019; 286:20190049. [PMID: 30963843 PMCID: PMC6408884 DOI: 10.1098/rspb.2019.0049] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 02/06/2019] [Indexed: 12/16/2022] Open
Abstract
When confronted with a parasite or pathogen, hosts can defend themselves by resisting or tolerating the attack. While resistance can be diminished when resources are limited, it is unclear how robust tolerance is to changes in environmental conditions. Here, we investigate the sensitivity of tolerance in a single host population living in a highly variable environment. We manipulated the abundance of an invasive parasitic fly, Philornis downsi, in nests of Galápagos mockingbirds ( Mimus parvulus) over four field seasons and measured host fitness in response to parasitism. Mockingbird tolerance to P. downsi varied significantly among years and decreased when rainfall was limited. Video observations indicate that parental provisioning of nestlings appears key to tolerance: in drought years, mockingbirds likely do not have sufficient resources to compensate for the effects of P. downsi. These results indicate that host tolerance is a labile trait and suggest that environmental variation plays a major role in mediating the consequences of host-parasite interactions.
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Affiliation(s)
- Sabrina M. McNew
- Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Sarah A. Knutie
- Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Graham B. Goodman
- Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
| | | | - Ashley Saulsberry
- Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Janai Yépez R.
- Charles Darwin Research Station, Santa Cruz Island, Galápagos, Ecuador
| | - Sarah E. Bush
- Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
| | - Dale H. Clayton
- Department of Biology, University of Utah, Salt Lake City, UT 84112-0840, USA
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27
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Tavalire HF, Beechler BR, Buss PE, Gorsich EE, Hoal EG, le Roex N, Spaan JM, Spaan RS, van Helden PD, Ezenwa VO, Jolles AE. Context-dependent costs and benefits of tuberculosis resistance traits in a wild mammalian host. Ecol Evol 2018; 8:12712-12726. [PMID: 30619576 PMCID: PMC6308860 DOI: 10.1002/ece3.4699] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2018] [Revised: 10/02/2018] [Accepted: 10/12/2018] [Indexed: 12/24/2022] Open
Abstract
Disease acts as a powerful driver of evolution in natural host populations, yet individuals in a population often vary in their susceptibility to infection. Energetic trade-offs between immune and reproductive investment lead to the evolution of distinct life history strategies, driven by the relative fitness costs and benefits of resisting infection. However, examples quantifying the cost of resistance outside of the laboratory are rare. Here, we observe two distinct forms of resistance to bovine tuberculosis (bTB), an important zoonotic pathogen, in a free-ranging African buffalo (Syncerus caffer) population. We characterize these phenotypes as "infection resistance," in which hosts delay or prevent infection, and "proliferation resistance," in which the host limits the spread of lesions caused by the pathogen after infection has occurred. We found weak evidence that infection resistance to bTB may be heritable in this buffalo population (h 2 = 0.10) and comes at the cost of reduced body condition and marginally reduced survival once infected, but also associates with an overall higher reproductive rate. Infection-resistant animals thus appear to follow a "fast" pace-of-life syndrome, in that they reproduce more quickly but die upon infection. In contrast, proliferation resistance had no apparent costs and was associated with measures of positive host health-such as having a higher body condition and reproductive rate. This study quantifies striking phenotypic variation in pathogen resistance and provides evidence for a link between life history variation and a disease resistance trait in a wild mammalian host population.
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Affiliation(s)
- Hannah F. Tavalire
- Department of Integrative BiologyOregon State UniversityCorvallisOregon
- The Institute of Ecology and EvolutionUniversity of OregonEugeneOregon
- Present address:
Prevention Science InstituteUniversity of OregonEugeneOregon
- Present address:
Institute of Ecology and EvolutionUniversity of OregonEugeneOregon
| | | | | | - Erin E. Gorsich
- College of Veterinary MedicineOregon State UniversityCorvallisOregon
- Present address:
Erin E. Gorsich, Zeeman Institute: Systems Biology and Infectious Disease Epidemiology Research (SBIDER)University of WarwickCoventryUK
- Present address:
School of Life SciencesUniversity of WarwickCoventryUK
| | - Eileen G. Hoal
- South African Medical Research Council, DST/NRF Centre of Excellence for Biomedical TB Research, Division of Molecular Biology and Human Genetics, Faculty of Health SciencesStellenbosch UniversityTygerbergSouth Africa
| | - Nikki le Roex
- South African Medical Research Council, DST/NRF Centre of Excellence for Biomedical TB Research, Division of Molecular Biology and Human Genetics, Faculty of Health SciencesStellenbosch UniversityTygerbergSouth Africa
| | - Johannie M. Spaan
- Department of Integrative BiologyOregon State UniversityCorvallisOregon
| | - Robert S. Spaan
- Department of Fisheries and WildlifeOregon State UniversityCorvallisOregon
| | - Paul D. van Helden
- South African Medical Research Council, DST/NRF Centre of Excellence for Biomedical TB Research, Division of Molecular Biology and Human Genetics, Faculty of Health SciencesStellenbosch UniversityTygerbergSouth Africa
| | - Vanessa O. Ezenwa
- Odum School of Ecology and Department of Infectious Diseases, College of Veterinary MedicineUniversity of GeorgiaAthensGeorgia
| | - Anna E. Jolles
- Department of Integrative BiologyOregon State UniversityCorvallisOregon
- College of Veterinary MedicineOregon State UniversityCorvallisOregon
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28
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Budischak SA, Cressler CE. Fueling Defense: Effects of Resources on the Ecology and Evolution of Tolerance to Parasite Infection. Front Immunol 2018; 9:2453. [PMID: 30429848 PMCID: PMC6220035 DOI: 10.3389/fimmu.2018.02453] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2018] [Accepted: 10/04/2018] [Indexed: 12/29/2022] Open
Abstract
Resource availability is a key environmental constraint affecting the ecology and evolution of species. Resources have strong effects on disease resistance, but they can also affect the other main parasite defense strategy, tolerance. A small but growing number of animal studies are beginning to investigate the effects of resources on tolerance phenotypes. Here, we review how resources affect tolerance strategies across animal taxa ranging from fruit flies to frogs to mice. Surprisingly, resources (quality and quantity) can increase or reduce tolerance, dependent upon the particular host-parasite system. To explore this seeming contradiction, we recast predictions of models of sterility tolerance and mortality tolerance in a resource-dependent context. Doing so reveals that resources can have very different epidemiological and evolutionary effects, depending on what aspects of the tolerance phenotype are affected. Thus, it is critical to consider both sterility and mortality in future empirical studies of how behavioral and environmental resource availability affect tolerance to infection.
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Affiliation(s)
- Sarah A. Budischak
- W. M. Keck Science Department of Claremont McKenna, Pitzer, and Scripps Colleges, Claremont, CA, United States
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, United States
| | - Clayton E. Cressler
- School of Biological Sciences, University of Nebraska, Lincoln, NE, United States
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29
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Cohen C, Shemesh M, Garrido M, Messika I, Einav M, Khokhlova I, Tasker S, Hawlena H. Haemoplasmas in wild rodents: Routes of transmission and infection dynamics. Mol Ecol 2018; 27:3714-3726. [PMID: 30074652 DOI: 10.1111/mec.14826] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Revised: 07/04/2018] [Accepted: 07/19/2018] [Indexed: 01/06/2023]
Abstract
The way that some parasites and pathogens persist in the hostile environment of their host for long periods remains to be resolved. Here, longitudinal field surveys were combined with laboratory experiments to investigate the routes of transmission and infection dynamics of such a pathogen-a wild rodent haemotropic bacterium, specifically a Mycoplasma haemomuris-like bacterium. Fleaborne transmission, direct rodent-to-rodent transmission and vertical transmission from fleas or rodents to their offspring were experimentally quantified, and indications were found that the main route of bacterial transmission is direct, although its rate of successful transmission is low (~20%). The bacterium's temporal dynamics was then compared in the field to that observed under a controlled infection experiment in field-infected and laboratory-infected rodents, and indications were found, under all conditions, that the bacterium reached its peak infection level after 25-45 days and then decreased to low bacterial loads, which persist for the rodent's lifetime. These findings suggest that the bacterium relies on persistency with low bacterial loads for long-term coexistence with its rodent host, having both conceptual and applied implications.
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Affiliation(s)
- Carmit Cohen
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Merav Shemesh
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Mario Garrido
- Mitrani Department of Desert Ecology, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel
| | - Irit Messika
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Monica Einav
- Department of Life Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel
| | - Irina Khokhlova
- Wyler Department of Dryland Agriculture, French Associates Institute for Agriculture and Biotechnology of Drylands, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel
| | - Séverine Tasker
- School of Veterinary Sciences, University of Bristol, Langford, UK
| | - Hadas Hawlena
- Mitrani Department of Desert Ecology, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel
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Boots M, Best A. The evolution of constitutive and induced defences to infectious disease. Proc Biol Sci 2018; 285:rspb.2018.0658. [PMID: 30051865 PMCID: PMC6083258 DOI: 10.1098/rspb.2018.0658] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 06/21/2018] [Indexed: 01/15/2023] Open
Abstract
In response to infectious disease, hosts typically mount both constitutive and induced defences. Constitutive defence prevents infection in the first place, while induced defence typically shortens the infectious period. The two routes to defence, therefore, have very different implications not only to individuals but also to the epidemiology of the disease. Moreover, the costs of constitutive defences are likely to be paid even in the absence of disease, while induced defences are likely to incur the most substantial costs when they are used in response to infection. We examine theoretically the evolutionary implications of these fundamental differences. A key result is that high virulence in the parasite typically selects for higher induced defences even if they result in immunopathology leading to very high disease mortality. Disease impacts on fecundity are critical to the relative investment in constitutive and induced defence with important differences found when parasites castrate their hosts. The trade-off between constitutive and induced defence has been cited as a cause of the diversity in defence, but we show that the trade-off alone is unlikely to lead to diversity. Our models provide a framework to examine relative investment in different defence components both experimentally and in the field.
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Affiliation(s)
- Mike Boots
- Department of Integrative Biology, University of California, Berkeley, Berkeley CA, USA .,Department of Biosciences, University of Exeter, Penryn Campus, Penryn TR11 9FE, UK
| | - Alex Best
- School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH, UK
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Abstract
The two major mechanisms of plant defense against pathogens are resistance (the host's ability to limit pathogen multiplication) and tolerance (the host's ability to reduce the effect of infection on its fitness regardless of the level of pathogen multiplication). There is abundant literature on virtually every aspect of plant resistance to pathogens. Although tolerance to plant pathogens is comparatively less understood, studies on this plant defense strategy have led to major insights into its evolution, mechanistic basis and genetic determinants. This review aims at summarizing current theories and experimental evidence on the evolutionary causes and consequences of plant tolerance to pathogens, as well as the existing knowledge on the genetic determinants and mechanisms of tolerance. Our review reveals that (i) in plant-pathogen systems, resistance and tolerance generally coexist, i.e., are not mutually exclusive; (ii) evidence of tolerance polymorphisms is abundant regardless of the pathogen considered; (iii) tolerance is an efficient strategy to reduce the damage on the infected host; and (iv) there is no evidence that tolerance results in increased pathogen multiplication. Taken together, the work discussed in this review indicates that tolerance may be as important as resistance in determining the dynamics of plant-pathogen interactions. Several aspects of plant tolerance to pathogens that still remain unclear and which should be explored in the future, are also outlined.
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Affiliation(s)
- Israel Pagán
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA) and E.T.S. Ingeniería Agronómica, Alimentaria y de Biosistemas, Universidad Politécnica de Madrid, 28223 Madrid, Spain.
| | - Fernando García-Arenal
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA) and E.T.S. Ingeniería Agronómica, Alimentaria y de Biosistemas, Universidad Politécnica de Madrid, 28223 Madrid, Spain.
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32
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Ferris C, Best A. The evolution of host defence to parasitism in fluctuating environments. J Theor Biol 2017; 440:58-65. [PMID: 29221891 DOI: 10.1016/j.jtbi.2017.12.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Revised: 11/08/2017] [Accepted: 12/04/2017] [Indexed: 11/30/2022]
Abstract
Given rapidly changing environments, it is important for us to understand how the evolution of host defence responds to fluctuating environments. Here we present the first theoretical study of evolution of host resistance to parasitism in a classic epidemiological model where the host birth rate varies seasonally. We show that this form of seasonality has clear qualitative and quantitative impacts on the evolution of resistance. When the host can recover from infection, it evolves a lower level of defence when the amplitude is high. However, when recovery is absent, the host increases its defence for higher amplitudes. Between these different behaviours we find a region of parameter space that allows evolutionary bistability. When this occurs, the level of defence the host evolves depends on initial conditions, and in some cases a switch between attractors can lead to different periods in the population dynamics at each of the evolutionary stable strategies. Crucially, we find that evolutionary behaviour found in a constant environment for this model doesn't always hold for hosts with highly variable birth rates. Hence we argue that seasonality must be taken into account if we want to make predictions about evolutionary trends in real-world host-parasite systems.
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Affiliation(s)
- Charlotte Ferris
- School of Mathematics and Statistics, University of Sheffield, Sheffield, S3 7RH, UK.
| | - Alex Best
- School of Mathematics and Statistics, University of Sheffield, Sheffield, S3 7RH, UK
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Mesquita AFC, Lambertini C, Lyra M, Malagoli LR, James TY, Toledo LF, Haddad CFB, Becker CG. Low resistance to chytridiomycosis in direct-developing amphibians. Sci Rep 2017; 7:16605. [PMID: 29192210 PMCID: PMC5709405 DOI: 10.1038/s41598-017-16425-y] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Accepted: 10/31/2017] [Indexed: 12/13/2022] Open
Abstract
Host-generalist pathogens sporadically infect naive hosts, potentially triggering epizootics. The waterborne fungus Batrachochytrium dendrobatidis (Bd) is linked to declines of hundreds of amphibian species with aquatic larvae. Although several population declines and extinctions attributed to Bd have been reported among cryptic species undergoing direct development away from water, epidemiological studies focused on these terrestrial frogs are lacking. Our field data support that terrestrial direct-developing hosts are less exposed to Bd during their ontogeny than species with aquatic larvae, and thus they might lack adaptive responses against waterborne chytrids. Using controlled laboratory experiments, we exposed wild-caught amphibian species with terrestrial and aquatic life histories to Bd and found that direct developers showed more rapid increases in infection loads and experienced higher mortality rates than species with aquatic larvae. Our findings provide novel information about host responses to generalist pathogens and specifically show that our focal direct developing species have low resistance to Bd infections. Finally, our results underscore that we should not ignore Bd as a potential threat to direct developing species simply because they are less exposed to Bd in nature; instead future amphibian conservation plans should include efforts to safeguard hundreds of direct-developing amphibian species globally.
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Affiliation(s)
- Andréa F C Mesquita
- Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Zoologia, and Centro de Aquicultura (CAUNESP), 13506-900, Rio Claro, SP, Brazil
| | - Carolina Lambertini
- Departamento de Biologia Animal, I.B., Universidade Estadual de Campinas, 13083-862, Campinas, SP, Brazil
| | - Mariana Lyra
- Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Zoologia, and Centro de Aquicultura (CAUNESP), 13506-900, Rio Claro, SP, Brazil
| | - Leo R Malagoli
- Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Zoologia, and Centro de Aquicultura (CAUNESP), 13506-900, Rio Claro, SP, Brazil
| | - Timothy Y James
- Department of Ecology and Evolutionary Biology, University of Michigan, 48109, Ann Arbor, MI, USA
| | - Luís Felipe Toledo
- Departamento de Biologia Animal, I.B., Universidade Estadual de Campinas, 13083-862, Campinas, SP, Brazil
| | - Célio F B Haddad
- Universidade Estadual Paulista (UNESP), Instituto de Biociências, Departamento de Zoologia, and Centro de Aquicultura (CAUNESP), 13506-900, Rio Claro, SP, Brazil
| | - C Guilherme Becker
- Department of Biological Sciences, The University of Alabama, 35487, Tuscaloosa, AL, USA.
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34
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Zeller M, Koella JC. The Role of the Environment in the Evolution of Tolerance and Resistance to a Pathogen. Am Nat 2017; 190:389-397. [PMID: 28829641 DOI: 10.1086/692759] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Defense against parasites can be divided into resistance, which limits parasite burden, and tolerance, which reduces pathogenesis at a given parasite burden. Distinguishing between the two and understanding which defense is favored by evolution in different ecological settings are important, as they lead to fundamentally different evolutionary trajectories of host-parasite interactions. We let the mosquito Aedes aegypti evolve under different food levels and with either no parasite, a constant parasite, or a coevolving parasite (the microsporidian Vavraia culicis). We then tested tolerance and resistance of the evolved lines on a population level at the two food levels. Exposure to parasites during evolution increased resistance and tolerance, but there were no differences between the lines evolved with coevolving or constant parasites. Mosquitoes that had evolved with food restriction had higher resistance than those evolved with high food but similar tolerance. The mosquitoes that had restricted food when being tested had lower tolerance than those with normal food, but there was no difference in resistance. Our results emphasize the complexity and dependence on environmental conditions of the evolution and expression of resistance and tolerance and help to evaluate some of the predictions about the evolution of host defense against parasites.
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35
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Debes PV, Gross R, Vasemägi A. Quantitative Genetic Variation in, and Environmental Effects on, Pathogen Resistance and Temperature-Dependent Disease Severity in a Wild Trout. Am Nat 2017; 190:244-265. [PMID: 28731797 DOI: 10.1086/692536] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Health after pathogen contact varies among individuals because of differences in pathogen load (which is limited by resistance) and disease severity in response to pathogen load (which is limited by tolerance). To understand pathogen-induced host evolution, it is critical to know not only the relative contributions of nongenetic and genetic variation to resistance and tolerance but also how they change environmentally. We quantified nongenetic and genetic variation in parasite load and the associated temperature-dependent disease among trout siblings from two rivers. We detected a genetic variance for parasite load 6.6 times as large in the colder river. By contrast, genetic variance for disease traits tended to be larger in the warmer river, where the disease was manifested more severely. The relationships between disease severity and pathogen load (tolerance) exhibited plateaus at low pathogen load and stronger steepening slopes at high pathogen load in the warmer river. Our study demonstrates the environmental influence on disease severity, nongenetic and genetic variance for health-damage-limiting host abilities, and the shape of tolerance curves. Environmental variability is predicted to govern the presence and intensity of selection, change the relative contributions of nongenetic and genetic variance, and therefore hamper evolution toward more resistant and tolerant hosts.
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36
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37
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Martcheva M, Tuncer N, Kim Y. On the principle of host evolution in host-pathogen interactions. JOURNAL OF BIOLOGICAL DYNAMICS 2017; 11:102-119. [PMID: 26998890 DOI: 10.1080/17513758.2016.1161089] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
In this paper, we use a two-host one pathogen immuno-epidemiological model to argue that the principle for host evolution, when the host is subjected to a fatal disease, is minimization of the case fatality proportion [Formula: see text]. This principle is valid whether the disease is chronic or leads to recovery. In the case of continuum of hosts, stratified by their immune response stimulation rate a, we suggest that [Formula: see text] has a minimum because a trade-off exists between virulence to the host induced by the pathogen and virulence induced by the immune response. We find that the minimization of the case fatality proportion is an evolutionary stable strategy for the host.
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Affiliation(s)
- Maia Martcheva
- a Department of Mathematics , University of Florida , Gainesville , FL , USA
| | - Necibe Tuncer
- b Department of Mathematical Sciences , Florida Atlantic University , Boca Raton , FL , USA
| | - Yena Kim
- a Department of Mathematics , University of Florida , Gainesville , FL , USA
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38
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Willink B, Svensson EI. Intra- and intersexual differences in parasite resistance and female fitness tolerance in a polymorphic insect. Proc Biol Sci 2017; 284:20162407. [PMID: 28123090 PMCID: PMC5310041 DOI: 10.1098/rspb.2016.2407] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Accepted: 12/20/2016] [Indexed: 11/12/2022] Open
Abstract
To understand host-parasite interactions, it is necessary to quantify variation and covariation in defence traits. We quantified parasite resistance and fitness tolerance of a polymorphic damselfly (Ischnura elegans), an insect with three discrete female colour morphs but with monomorphic males. We quantified sex and morph differences in parasite resistance (prevalence and intensity of water mite infections) and morph-specific fitness tolerance in the females in natural populations for over a decade. There was no evidence for higher parasite susceptibility in males as a cost of sexual selection, whereas differences in defence mechanisms between female morphs are consistent with correlational selection operating on combinations of parasite resistance and tolerance. We suggest that tolerance differences between female morphs interact with frequency-dependent sexual conflict, which maintains the polymorphism locally. Host-parasite interactions can therefore shape intra- and intersexual phenotypic divergence and interfere with sexual selection and sexual conflict.
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Affiliation(s)
- Beatriz Willink
- Department of Biology, Evolutionary Ecology Unit, Lund University, Ecology Building, Lund 223-62, Sweden
| | - Erik I Svensson
- Department of Biology, Evolutionary Ecology Unit, Lund University, Ecology Building, Lund 223-62, Sweden
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39
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Sumoylation as an Integral Mechanism in Bacterial Infection and Disease Progression. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 963:389-408. [DOI: 10.1007/978-3-319-50044-7_22] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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40
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Klemme I, Karvonen A. Vertebrate defense against parasites: Interactions between avoidance, resistance, and tolerance. Ecol Evol 2016; 7:561-571. [PMID: 28116053 PMCID: PMC5243791 DOI: 10.1002/ece3.2645] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2016] [Revised: 11/08/2016] [Accepted: 11/13/2016] [Indexed: 12/03/2022] Open
Abstract
Hosts can utilize different types of defense against the effects of parasitism, including avoidance, resistance, and tolerance. Typically, there is tremendous heterogeneity among hosts in these defense mechanisms that may be rooted in the costs associated with defense and lead to trade‐offs with other life‐history traits. Trade‐offs may also exist between the defense mechanisms, but the relationships between avoidance, resistance, and tolerance have rarely been studied. Here, we assessed these three defense traits under common garden conditions in a natural host–parasite system, the trematode eye‐fluke Diplostomum pseudospathaceum and its second intermediate fish host. We looked at host individuals originating from four genetically distinct populations of two closely related salmonid species (Atlantic salmon, Salmo salar and sea trout, Salmo trutta trutta) to estimate the magnitude of variation in these defense traits and the relationships among them. We show species‐specific variation in resistance and tolerance and population‐specific variation in resistance. Further, we demonstrate evidence for a trade‐off between resistance and tolerance. Our results suggest that the variation in host defense can at least partly result from a compromise between different interacting defense traits, the relative importance of which is likely to be shaped by environmental components. Overall, this study emphasizes the importance of considering different components of the host defense system when making predictions on the outcome of host–parasite interactions.
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Affiliation(s)
- Ines Klemme
- Department of Biological and Environmental Science University of Jyvaskyla Jyvaskyla Finland
| | - Anssi Karvonen
- Department of Biological and Environmental Science University of Jyvaskyla Jyvaskyla Finland
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41
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Prediction and Prevention of Parasitic Diseases Using a Landscape Genomics Framework. Trends Parasitol 2016; 33:264-275. [PMID: 27863902 DOI: 10.1016/j.pt.2016.10.008] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2016] [Revised: 09/10/2016] [Accepted: 10/19/2016] [Indexed: 12/15/2022]
Abstract
Substantial heterogeneity exists in the dispersal, distribution and transmission of parasitic species. Understanding and predicting how such features are governed by the ecological variation of landscape they inhabit is the central goal of spatial epidemiology. Genetic data can further inform functional connectivity among parasite, host and vector populations in a landscape. Gene flow correlates with the spread of epidemiologically relevant phenotypes among parasite and vector populations (e.g., virulence, drug and pesticide resistance), as well as invasion and re-invasion risk where parasite transmission is absent due to current or past intervention measures. However, the formal integration of spatial and genetic data ('landscape genetics') is scarcely ever applied to parasites. Here, we discuss the specific challenges and practical prospects for the use of landscape genetics and genomics to understand the biology and control of parasitic disease and present a practical framework for doing so.
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42
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Toor J, Best A. Evolution of Host Defense against Multiple Enemy Populations. Am Nat 2016; 187:308-19. [DOI: 10.1086/684682] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
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43
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Garrido E, Llamas-Guzmán LP, Fornoni J. The effect of frequency-dependent selection on resistance and tolerance to herbivory. J Evol Biol 2015; 29:483-9. [PMID: 26411698 DOI: 10.1111/jeb.12768] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 09/22/2015] [Indexed: 12/01/2022]
Abstract
Negative frequency-dependent selection (FDS), where rare genotypes are favoured by selection, is commonly invoked as a mechanism explaining the maintenance of genetic variation in plant defences. However, empirical tests of FDS in plant-herbivore interactions are lacking. We evaluated whether the oviposition preference of the specialist herbivore Lema daturaphila is a mechanism through which this herbivore can exert FDS on its host plant Datura stramonium. The frequency of contrasting resistance-tolerance strategies was manipulated within experimental plots, and the plants were exposed to a similar initial density of their natural herbivore. Herbivore oviposition preference and final density, as well as plant damage and seed production, were estimated. Overall, we found that the high-resistant-low-tolerant genotypes produced four times more seeds when common than when rare, whereas the high-tolerant-low-resistant genotypes achieved twice its fitness when rare than when common. This pattern was the result of differential oviposition preferences. In addition, when the high-resistant-low-tolerant genotypes were common, there was a three-fold decreased in herbivore final density which led to a decrease in damage level by 10%. Thus, in our experiment positive FDS seems to favour resistance over tolerance. We discuss how this result would change if the extent of herbivore local adaptation and damage modify the pattern of positive FDS acting on resistance and the optimal allocation to tolerance.
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Affiliation(s)
- E Garrido
- Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, México, Distrito Federal, México
| | - L P Llamas-Guzmán
- Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, México, Distrito Federal, México
| | - J Fornoni
- Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, México, Distrito Federal, México
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44
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Izhar R, Ben-Ami F. Host age modulates parasite infectivity, virulence and reproduction. J Anim Ecol 2015; 84:1018-28. [PMID: 25661269 DOI: 10.1111/1365-2656.12352] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Accepted: 01/24/2015] [Indexed: 01/15/2023]
Abstract
Host age is one of the most striking differences among hosts within most populations, but there is very little data on how age-dependent effects impact ecological and evolutionary dynamics of both the host and the parasite. Here, we examined the influence of host age (juveniles, young and old adults) at parasite exposure on host susceptibility, fecundity and survival as well as parasite transmission, using two clones of the water flea Daphnia magna and two clones of its bacterial parasite Pasteuria ramosa. Younger D. magna were more susceptible to infection than older ones, regardless of host or parasite clone. Also, younger-infected D. magna became castrated faster than older hosts, but host and parasite clone effects contributed to this trait as well. Furthermore, the early-infected D. magna produced considerably more parasite transmission stages than late-infected ones, while host age at exposure did not affect virulence as it is defined in models (host mortality). When virulence is defined more broadly as the negative effects of infection on host fitness, by integrating the parasitic effects on host fecundity and mortality, then host age at exposure seems to slide along a negative relationship between host and parasite fitness. Thus, the virulence-transmission trade-off differs strongly among age classes, which in turn affects predictions of optimal virulence. Age-dependent effects on host susceptibility, virulence and parasite transmission could pose an important challenge for experimental and theoretical studies of infectious disease dynamics and disease ecology. Our results present a call for a more explicit stage-structured theory for disease, which will incorporate age-dependent epidemiological parameters.
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Affiliation(s)
- Rony Izhar
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Frida Ben-Ami
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 6997801, Israel
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45
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Medina I, Langmore NE. The evolution of acceptance and tolerance in hosts of avian brood parasites. Biol Rev Camb Philos Soc 2015; 91:569-77. [PMID: 25765722 DOI: 10.1111/brv.12181] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Revised: 01/26/2015] [Accepted: 02/12/2015] [Indexed: 11/29/2022]
Abstract
Avian brood parasites lay their eggs in the nests of their hosts, which rear the parasite's progeny. The costs of parasitism have selected for the evolution of defence strategies in many host species. Most research has focused on resistance strategies, where hosts minimize the number of successful parasitism events using defences such as mobbing of adult brood parasites or rejection of parasite eggs. However, many hosts do not exhibit resistance. Here we explore why some hosts accept parasite eggs in their nests and how this is related to the virulence of the parasite. We also explore the extent to which acceptance of parasites can be explained by the evolution of tolerance; a strategy in which the host accepts the parasite but adjusts its life history or other traits to minimize the costs of parasitism. We review examples of tolerance in hosts of brood parasites (such as modifications to clutch size and multi-broodedness), and utilize the literature on host-pathogen interactions and plant herbivory to analyse the prevalence of each type of defence (tolerance or resistance) and their evolution. We conclude that (i) the interactions between brood parasites and their hosts provide a highly tractable system for studying the evolution of tolerance, (ii) studies of host defences against brood parasites should investigate both resistance and tolerance, and (iii) tolerance and resistance can lead to contrasting evolutionary scenarios.
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Affiliation(s)
- Iliana Medina
- Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, Australia
| | - Naomi E Langmore
- Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, Canberra, Australia
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46
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Detilleux J, Kastelic JP, Barkema HW. Mediation analysis to estimate direct and indirect milk losses due to clinical mastitis in dairy cattle. Prev Vet Med 2015; 118:449-56. [PMID: 25638330 DOI: 10.1016/j.prevetmed.2015.01.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Revised: 11/17/2014] [Accepted: 01/07/2015] [Indexed: 11/17/2022]
Abstract
Milk losses associated with mastitis can be attributed to either effects of pathogens per se (i.e., direct losses) or effects of the immune response triggered by intramammary infection (indirect losses). The distinction is important in terms of mastitis prevention and treatment. Regardless, the number of pathogens is often unknown (particularly in field studies), making it difficult to estimate direct losses, whereas indirect losses can be approximated by measuring the association between increased somatic cell count (SCC) and milk production. An alternative is to perform a mediation analysis in which changes in milk yield are allocated into their direct and indirect components. We applied this method on data for clinical mastitis, milk and SCC test-day recordings, results of bacteriological cultures (Escherichia coli, Staphylococcus aureus, Streptococcus uberis, coagulase-negative staphylococci, Streptococcus dysgalactiae, and streptococci other than Strep. dysgalactiae and Strep. uberis), and cow characteristics. Following a diagnosis of clinical mastitis, the cow was treated and changes (increase or decrease) in milk production before and after a diagnosis were interpreted counterfactually. On a daily basis, indirect changes, mediated by SCC increase, were significantly different from zero for all bacterial species, with a milk yield decrease (ranging among species from 4 to 33g and mediated by an increase of 1000 SCC/mL/day) before and a daily milk increase (ranging among species from 2 to 12g and mediated by a decrease of 1000 SCC/mL/day) after detection. Direct changes, not mediated by SCC, were only different from zero for coagulase-negative staphylococci before diagnosis (72g per day). We concluded that mixed structural equation models were useful to estimate direct and indirect effects of the presence of clinical mastitis on milk yield.
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Affiliation(s)
- J Detilleux
- Department of Animal Production, Faculty of Veterinary Medicine, University of Liège, Liège, Belgium
| | - J P Kastelic
- Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta, Canada
| | - H W Barkema
- Department of Production Animal Health, Faculty of Veterinary Medicine, University of Calgary, Calgary, Alberta, Canada
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Toor J, Best A. The evolution of host resistance to disease in the presence of predators. J Theor Biol 2015; 365:104-11. [PMID: 25454010 DOI: 10.1016/j.jtbi.2014.10.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 08/15/2014] [Accepted: 10/05/2014] [Indexed: 11/18/2022]
Abstract
While theoretical models on the evolution of host defences against disease have been widely studied, the inclusion of predators and community interactions more generally, has often been overlooked. In this paper, we examine a host-parasite model with an additional predator and show that the predator changes the evolutionary behaviour of the host. We find that the hosts maximize their levels of resistance at intermediate predation rates, where the cost of infection and the risk of exposure to disease are both high. We show that this effect is heightened when parasites are highly virulent and when there is strong selective predation. We also show that the potential for evolutionary branching increases with the predation rate for regions where the susceptible and infected hosts coexist with the predator. Hence, our results reveal that there are considerable impacts of adding predators to a population.
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Affiliation(s)
- Jaspreet Toor
- School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH, UK.
| | - Alex Best
- School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH, UK
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Lion S, Gandon S. Evolution of spatially structured host-parasite interactions. J Evol Biol 2015; 28:10-28. [DOI: 10.1111/jeb.12551] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Revised: 11/06/2014] [Accepted: 11/10/2014] [Indexed: 01/19/2023]
Affiliation(s)
- S. Lion
- CEFE UMR 5175; CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE; Montpellier Cedex 5 France
| | - S. Gandon
- CEFE UMR 5175; CNRS - Université de Montpellier - Université Paul-Valéry Montpellier - EPHE; Montpellier Cedex 5 France
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Hily JM, García A, Moreno A, Plaza M, Wilkinson MD, Fereres A, Fraile A, García-Arenal F. The relationship between host lifespan and pathogen reservoir potential: an analysis in the system Arabidopsis thaliana--cucumber mosaic virus. PLoS Pathog 2014; 10:e1004492. [PMID: 25375140 PMCID: PMC4223077 DOI: 10.1371/journal.ppat.1004492] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2014] [Accepted: 09/29/2014] [Indexed: 11/18/2022] Open
Abstract
Identification of the determinants of pathogen reservoir potential is central to understand disease emergence. It has been proposed that host lifespan is one such determinant: short-lived hosts will invest less in costly defenses against pathogens, so that they will be more susceptible to infection, more competent as sources of infection and/or will sustain larger vector populations, thus being effective reservoirs for the infection of long-lived hosts. This hypothesis is sustained by analyses of different hosts of multihost pathogens, but not of different genotypes of the same host species. Here we examined this hypothesis by comparing two genotypes of the plant Arabidopsis thaliana that differ largely both in life-span and in tolerance to its natural pathogen Cucumber mosaic virus (CMV). Experiments with the aphid vector Myzus persicae showed that both genotypes were similarly competent as sources for virus transmission, but the short-lived genotype was more susceptible to infection and was able to sustain larger vector populations. To explore how differences in defense against CMV and its vector relate to reservoir potential, we developed a model that was run for a set of experimentally-determined parameters, and for a realistic range of host plant and vector population densities. Model simulations showed that the less efficient defenses of the short-lived genotype resulted in higher reservoir potential, which in heterogeneous host populations may be balanced by the longer infectious period of the long-lived genotype. This balance was modulated by the demography of both host and vector populations, and by the genetic composition of the host population. Thus, within-species genetic diversity for lifespan and defenses against pathogens will result in polymorphisms for pathogen reservoir potential, which will condition within-population infection dynamics. These results are relevant for a better understanding of host-pathogen co-evolution, and of the dynamics of pathogen emergence. Understanding pathogen emergence is a major goal of pathology, because of the high impact of emerging diseases. Pathogens emerge onto a new host from a reservoir, hence the relevance of identifying the determinants of host's reservoir potential. Host lifespan is considered as one such determinant: short-lived hosts will invest less in defenses, being more susceptible to infection, more competent as infection sources and/or will sustain larger vector populations, and thus, are effective reservoirs for long-lived host infection. Evidence for this hypothesis derives from analyses of different hosts of multihost pathogens, and here we examine whether it holds at the within-species level by comparing two genotypes of the plant Arabidopsis thaliana that differ in life-span and in tolerance to its natural pathogen Cucumber mosaic virus. Experiments showed that defenses to the virus and its aphid vector were less efficient in the short-lived genotype that, according to model simulations, was an effective reservoir under a large range of conditions. Reservoir potential, though, was modulated by the demography of host and vector and by the genetic composition of the host population. Thus, within-species genetic diversity for lifespan and pathogen defense will result in differences in reservoir potential, which will condition infection dynamics and host-pathogen co-evolution.
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Affiliation(s)
- Jean Michel Hily
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA), and E.T.S.I. Agrónomos, Campus de Montegancedo, Universidad Politécnica de Madrid, Madrid, Spain
| | - Adrián García
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA), Campus de Montegancedo, Universidad Politécnica de Madrid, Madrid, Spain
| | - Arancha Moreno
- Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas (ICA-CSIC), Madrid, Spain
| | - María Plaza
- Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas (ICA-CSIC), Madrid, Spain
| | - Mark D. Wilkinson
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA), Campus de Montegancedo, Universidad Politécnica de Madrid, Madrid, Spain
| | - Alberto Fereres
- Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas (ICA-CSIC), Madrid, Spain
| | - Aurora Fraile
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA), and E.T.S.I. Agrónomos, Campus de Montegancedo, Universidad Politécnica de Madrid, Madrid, Spain
| | - Fernando García-Arenal
- Centro de Biotecnología y Genómica de Plantas (UPM-INIA), and E.T.S.I. Agrónomos, Campus de Montegancedo, Universidad Politécnica de Madrid, Madrid, Spain
- * E-mail:
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Abstract
This Primer examines the phenomenon of infection tolerance and discusses three recent PLOS Biology research articles about the causes and consequences of variation in tolerance in natural populations. How do we defend ourselves against pathogenic microbes and other parasites infecting us? Research on defence against parasites has traditionally focused on resistance—the ability to prevent infection or limit parasite replication. The genetics, physiology, and evolutionary ecology of such traits are now relatively well understood. During the last few years it has been realized that another, conceptually different type of defence also plays an important role in animal host–parasite interactions. This type of defence is called tolerance, and can be defined as the ability to limit the health effects of parasites without preventing infection or controlling parasite replication. Our understanding of the causes and consequences of variation in tolerance is, however, still rudimentary. Three recent studies shed light on these questions. In a study of HIV in humans, Regoes et al. show that an MHC class I gene affects not only resistance (as previously known) but also tolerance. In a study of voles, Jackson et al. identify a transcription factor mediating age differences in tolerance to macroparasites. Finally, Hayward et al. demonstrate that tolerance to intestinal parasites in sheep is under positive directional selection, but that most of the variation is environmentally induced rather than heritable. These studies increase our knowledge of the genetic and physiological sources of variation in tolerance, and how this variation affects Darwinian fitness. In addition, they illustrate different approaches to untangle tolerance from other factors determining the health effects of infectious disease.
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Affiliation(s)
- Lars Råberg
- Functional Zoology, Department of Biology, Lund University, Lund, Sweden
- * E-mail:
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