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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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2
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Somé BM, Guissou E, Da DF, Richard Q, Choisy M, Yameogo KB, Hien DF, Yerbanga RS, Ouedraogo GA, Dabiré KR, Djidjou-Demasse R, Cohuet A, Lefèvre T. Mosquito ageing modulates the development, virulence and transmission potential of pathogens. Proc Biol Sci 2024; 291:20232097. [PMID: 38166422 PMCID: PMC10762442 DOI: 10.1098/rspb.2023.2097] [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: 09/15/2023] [Accepted: 11/27/2023] [Indexed: 01/04/2024] Open
Abstract
Host age variation is a striking source of heterogeneity that can shape the evolution and transmission dynamic of pathogens. Compared with vertebrate systems, our understanding of the impact of host age on invertebrate-pathogen interactions remains limited. We examined the influence of mosquito age on key life-history traits driving human malaria transmission. Females of Anopheles coluzzii, a major malaria vector, belonging to three age classes (4-, 8- and 12-day-old), were experimentally infected with Plasmodium falciparum field isolates. Our findings revealed reduced competence in 12-day-old mosquitoes, characterized by lower oocyst/sporozoite rates and intensities compared with younger mosquitoes. Despite shorter median longevities in older age classes, infected 12-day-old mosquitoes exhibited improved survival, suggesting that the infection might act as a fountain of youth for older mosquitoes specifically. The timing of sporozoite appearance in the salivary glands remained consistent across mosquito age classes, with an extrinsic incubation period of approximately 13 days. Integrating these results into an epidemiological model revealed a lower vectorial capacity for older mosquitoes compared with younger ones, albeit still substantial owing to extended longevity in the presence of infection. Considering age heterogeneity provides valuable insights for ecological and epidemiological studies, informing targeted control strategies to mitigate pathogen transmission.
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Affiliation(s)
- Bernard M. Somé
- Unité Paludisme et Maladies Tropicales Négligées, Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 545 Bobo Dioulasso, Burkina Faso
- Laboratoire Mixte International sur les Vecteurs (LAMIVECT), Bobo Dioulasso, Burkina Faso
- Département de Biochimie, Université Nazi Boni, 01 BP 1091 Bobo Dioulasso, Burkina Faso
| | - Edwige Guissou
- Unité Paludisme et Maladies Tropicales Négligées, Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 545 Bobo Dioulasso, Burkina Faso
- Laboratoire Mixte International sur les Vecteurs (LAMIVECT), Bobo Dioulasso, Burkina Faso
- Département de Biochimie, Université Nazi Boni, 01 BP 1091 Bobo Dioulasso, Burkina Faso
- MIVEGEC, IRD, CNRS, University of Montpellier, 34090 Montpellier cedex 5, France
- Ecole Normale Supérieure, BP 376 Koudougou, Burkina Faso
| | - Dari F. Da
- Unité Paludisme et Maladies Tropicales Négligées, Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 545 Bobo Dioulasso, Burkina Faso
| | - Quentin Richard
- IMAG, Université de Montpellier, CNRS, 34090 Montpellier, France
| | - Marc Choisy
- Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, 700000, Ho Chi Minh City, Vietnam
- Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7BN, UK
| | - Koudraogo B. Yameogo
- Unité Paludisme et Maladies Tropicales Négligées, Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 545 Bobo Dioulasso, Burkina Faso
- Laboratoire Mixte International sur les Vecteurs (LAMIVECT), Bobo Dioulasso, Burkina Faso
| | - Domombabele FdS. Hien
- Unité Paludisme et Maladies Tropicales Négligées, Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 545 Bobo Dioulasso, Burkina Faso
- Laboratoire Mixte International sur les Vecteurs (LAMIVECT), Bobo Dioulasso, Burkina Faso
| | - Rakiswende S. Yerbanga
- Unité Paludisme et Maladies Tropicales Négligées, Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 545 Bobo Dioulasso, Burkina Faso
- Laboratoire Mixte International sur les Vecteurs (LAMIVECT), Bobo Dioulasso, Burkina Faso
| | - Georges A. Ouedraogo
- Département de Biochimie, Université Nazi Boni, 01 BP 1091 Bobo Dioulasso, Burkina Faso
| | - Kounbobr R. Dabiré
- Unité Paludisme et Maladies Tropicales Négligées, Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 545 Bobo Dioulasso, Burkina Faso
- Laboratoire Mixte International sur les Vecteurs (LAMIVECT), Bobo Dioulasso, Burkina Faso
| | | | - Anna Cohuet
- Laboratoire Mixte International sur les Vecteurs (LAMIVECT), Bobo Dioulasso, Burkina Faso
- MIVEGEC, IRD, CNRS, University of Montpellier, 34090 Montpellier cedex 5, France
| | - Thierry Lefèvre
- Unité Paludisme et Maladies Tropicales Négligées, Institut de Recherche en Sciences de la Santé (IRSS), 01 BP 545 Bobo Dioulasso, Burkina Faso
- Laboratoire Mixte International sur les Vecteurs (LAMIVECT), Bobo Dioulasso, Burkina Faso
- MIVEGEC, IRD, CNRS, University of Montpellier, 34090 Montpellier cedex 5, France
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3
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Bruijning M, Metcalf CJE, Visser MD. Closing the gap in the Janzen-Connell hypothesis: What determines pathogen diversity? Ecol Lett 2024; 27:e14316. [PMID: 37787147 DOI: 10.1111/ele.14316] [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: 10/04/2022] [Revised: 09/11/2023] [Accepted: 09/17/2023] [Indexed: 10/04/2023]
Abstract
The high tree diversity in tropical forests has long been a puzzle to ecologists. In the 1970s, Janzen and Connell proposed that tree species (hosts) coexist due to the stabilizing actions of specialized enemies. This Janzen-Connell hypothesis was subsequently supported by theoretical studies. Yet, such studies have taken the presence of specialized pathogens for granted, overlooking that pathogen coexistence also requires an explanation. Moreover, stable ecological coexistence does not necessarily imply evolutionary stability. What are the conditions that allow Janzen-Connell effects to evolve? We link theory from community ecology, evolutionary biology and epidemiology to tackle this question, structuring our approach around five theoretical frameworks. Phenomenological Lotka-Volterra competition models provide the most basic framework, which can be restructured to include (single- or multi-)pathogen dynamics. This ecological foundation can be extended to include pathogen evolution. Hosts, of course, may also evolve, and we introduce a coevolutionary model, showing that host-pathogen coevolution can lead to highly diverse systems. Our work unpacks the assumptions underpinning Janzen-Connell and places theoretical bounds on pathogen and host ecology and evolution. The five theoretical frameworks taken together provide a stronger theoretical basis for Janzen-Connell, delivering a wider lens that can yield important insights into the maintenance of diversity in these increasingly threatened systems.
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Affiliation(s)
- Marjolein Bruijning
- Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
| | - C Jessica E Metcalf
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
| | - Marco D Visser
- Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA
- Institute of Environmental Sciences, Leiden University, Leiden, The Netherlands
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4
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Hite JL, Roos AMD. Pathogens stabilize or destabilize depending on host stage structure. MATHEMATICAL BIOSCIENCES AND ENGINEERING : MBE 2023; 20:20378-20404. [PMID: 38124557 DOI: 10.3934/mbe.2023901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
A common assumption is that pathogens more readily destabilize their host populations, leading to an elevated risk of driving both the host and pathogen to extinction. This logic underlies many strategies in conservation biology and pest and disease management. Yet, the interplay between pathogens and population stability likely varies across contexts, depending on the environment and traits of both the hosts and pathogens. This context-dependence may be particularly important in natural consumer-host populations where size- and stage-structured competition for resources strongly modulates population stability. Few studies, however, have examined how the interplay between size and stage structure and infectious disease shapes the stability of host populations. Here, we extend previously developed size-dependent theory for consumer-resource interactions to examine how pathogens influence the stability of host populations across a range of contexts. Specifically, we integrate a size- and stage-structured consumer-resource model and a standard epidemiological model of a directly transmitted pathogen. The model reveals surprisingly rich dynamics, including sustained oscillations, multiple steady states, biomass overcompensation, and hydra effects. Moreover, these results highlight how the stage structure and density of host populations interact to either enhance or constrain disease outbreaks. Our results suggest that accounting for these cross-scale and bidirectional feedbacks can provide key insight into the structuring role of pathogens in natural ecosystems while also improving our ability to understand how interventions targeting one may impact the other.
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Affiliation(s)
- Jessica L Hite
- University of Wisconsin-Madison, Department of Pathobiological Sciences, School of Veterinary Medicine, Madison, Wisconsin, USA
| | - André M de Roos
- Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, the Netherlands; Santa Fe Institute, Santa Fe, NM 87501, USA
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5
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Buckingham LJ, Bruns EL, Ashby B. The evolution of age-specific resistance to infectious disease. Proc Biol Sci 2023; 290:20222000. [PMID: 36695037 PMCID: PMC9874267 DOI: 10.1098/rspb.2022.2000] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Innate, infection-preventing resistance often varies between host life stages. Juveniles are more resistant than adults in some species, whereas the opposite pattern is true in others. This variation cannot always be explained by prior exposure or physiological constraints and so it has been hypothesized that trade-offs with other life-history traits may be involved. However, little is known about how trade-offs between various life-history traits and resistance at different life stages affect the evolution of age-specific resistance. Here, we use a mathematical model to explore how trade-offs with natural mortality, reproduction and maturation combine to affect the evolution of resistance at different life stages. Our results show that certain combinations of trade-offs have substantial effects on whether adults or juveniles are more resistant, with trade-offs between juvenile resistance and adult reproduction inherently more costly than trade-offs involving maturation or mortality (all else being equal), resulting in consistent evolution of lower resistance at the juvenile stage even when infection causes a lifelong fecundity reduction. Our model demonstrates how the differences between patterns of age-structured resistance seen in nature may be explained by variation in the trade-offs involved and our results suggest conditions under which trade-offs tend to select for lower resistance in juveniles than adults.
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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
| | - Emily L. Bruns
- Department of Biology, University of Maryland, College Park, MD 20742, USA
| | - 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, British Columbia, Canada
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6
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Simon MW, Barfield M, Holt RD. When growing pains and sick days collide: infectious disease can stabilize host population oscillations caused by stage structure. THEOR ECOL-NETH 2022. [DOI: 10.1007/s12080-022-00543-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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7
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Tate AT, Schulz NK. The within-host ecology of insects and their parasites: integrating experiments and mathematical models. CURRENT OPINION IN INSECT SCIENCE 2022; 49:37-41. [PMID: 34793990 DOI: 10.1016/j.cois.2021.11.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Revised: 11/03/2021] [Accepted: 11/11/2021] [Indexed: 06/13/2023]
Abstract
The within-host ecology of hosts and their microbes involves complex feedbacks between the host immune system, energetic resources, and microbial growth and virulence, which in turn affect the probability of transmission to new hosts. This complexity can be challenging to address with experiments alone, and mathematical models have traditionally played an essential role in disentangling these processes, making new predictions, and bridging gaps across biological scales. Insect hosts serve as uniquely powerful systems for the integration of experiments and theory in disease biology. In this review, we highlight recent studies in fruit flies, moths, beetles and other invertebrates that have inspired important mathematical models, and present open questions arising from recent modeling efforts that are ripe for testing in insects.
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Affiliation(s)
- Ann T Tate
- Department of Biological Sciences, Vanderbilt University, 465 21(st) Ave S., Nashville, TN, USA.
| | - Nora Ke Schulz
- Department of Biological Sciences, Vanderbilt University, 465 21(st) Ave S., Nashville, TN, USA
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8
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Phillips ZI, Reding L, Farrior CE. The early life of a leaf-cutter ant colony constrains symbiont vertical transmission and favors horizontal transmission. Ecol Evol 2021; 11:11718-11729. [PMID: 34522335 PMCID: PMC8427574 DOI: 10.1002/ece3.7900] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2021] [Revised: 05/24/2021] [Accepted: 06/22/2021] [Indexed: 01/05/2023] Open
Abstract
Colonial organisms host a large diversity of symbionts (collectively, parasites, mutualists, and commensals) that use vertical transmission (from parent colony to offspring colony) and/or horizontal transmission to disperse between host colonies. The early life of some colonies, characterized by the dispersal and establishment of solitary individuals, may constrain vertical transmission and favor horizontal transmission between large established colonies. We explore this possibility with the miniature cockroach Attaphila fungicola, a symbiont of leaf-cutter ants and the mutualist fungal gardens they cultivate. The early life of a leaf-cutter colony is characterized by the dispersal of a female alate (winged "queen") carrying a fungal pellet, and the subsequent establishment of a foundress (workerless "queen") raising her incipient fungal garden and colony. Roaches hitchhike on female alates during leaf-cutter nuptial flights, which strongly suggests that roaches are vertically transmitted to foundresses and their incipient colonies; however, weak compatibility between roaches and incipient gardens may constrain roach vertical transmission. Reciprocally, opportunities for horizontal transmission between large established colonies with abundant fungal gardens may weaken selection against roach-induced harm (virulence) of incipient gardens. We use a laboratory experiment, behavioral observations, field surveys, and a transmission model to estimate the effect roaches have on the survivorship of incipient gardens and the frequency of roach vertical transmission. Contrary to traditional assumptions, our results indicate that roaches harm incipient gardens and predominantly use horizontal transmission between established leaf-cutter colonies. Ultimately, "costs of generalism" associated with infecting disparate stages of a host's lifecycle (e.g., incipient vs. established colonies) may constrain the vertical transmission of roaches and a broad range of symbionts.
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Affiliation(s)
| | - Luke Reding
- Department of Integrative BiologyUniversity of TexasAustinTexasUSA
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9
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Hamley JID, Koella JC. Parasite evolution in an age-structured population. J Theor Biol 2021; 527:110732. [PMID: 33915143 DOI: 10.1016/j.jtbi.2021.110732] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 04/12/2021] [Accepted: 04/16/2021] [Indexed: 10/21/2022]
Abstract
Although mortality increases with age in most organisms, senescence is missing from models of parasite evolution. Since virulence evolves according to the host's mortality, and since virulence influences the intensity of transmission, which determines the average age at infection and thus the mortality rate of a senescing host, we expected that epi-evolutionary feedbacks would underlie the evolution of virulence in a population of senescing hosts. We tested this idea by extending an age-structured model of epidemiological dynamics with the parasite's evolution. A straightforward prediction of our model is that stronger senescence forces the evolution of higher virulence. However, the model also reveals that the evolved virulence depends on the average age at infection, giving an evolutionary feedback with the epidemiological situation, a prediction not found when assuming a constant mortality rate with age. Additionally, and in contrast to most models of parasite evolution, we found that the virulence at the evolutionary equilibrium is influenced by whether the force of infection depends on the density or on the frequency of infected hosts, due to changes in the average age at infection. Our findings suggest that ignoring age-specific effects, and in particular senescence, can give misleading predictions about parasite evolution.
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Affiliation(s)
- Jonathan I D Hamley
- Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland.
| | - Jacob C Koella
- Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland
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10
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Phillips ZI. Emigrating Together but Not Establishing Together: A Cockroach Rides Ants and Leaves. Am Nat 2021; 197:138-145. [PMID: 33417528 DOI: 10.1086/711876] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
AbstractSymbionts of ant colonies can hitchhike on winged ant reproductives (alates) during colony nuptial flights. Attaphila fungicola Wheeler, a miniature cockroach that lives in the nests of Texas leaf-cutter ants (Atta texana Buckley), hitchhikes on female alates (winged queens). Hitchhiking roaches are presumably vertically transmitted from leaf-cutter parent colonies to daughter colonies, remaining with female alates as they transition into foundresses (workerless queens); however, foundresses have limited resources and high mortality rates. Rather than remaining with foundresses likely to die (vertical transmission), roaches might abandon them during dispersal to infect higher-quality later stages of colony development (female alate-vectored transmission). In field experiments, I find evidence for female alate-vectored transmission and discover that roaches use a second hitchhiking step (riding foraged plant material) to infect established colonies. This work reveals a novel relationship between host dispersal and symbiont transmission and shows that colony development can be an important selection pressure on transmission.
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11
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Ben-Ami F. Host Age Effects in Invertebrates: Epidemiological, Ecological, and Evolutionary Implications. Trends Parasitol 2019; 35:466-480. [PMID: 31003758 DOI: 10.1016/j.pt.2019.03.008] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 03/19/2019] [Accepted: 03/21/2019] [Indexed: 12/26/2022]
Abstract
In most species, variation in age among individuals is the strongest and most visible form of phenotypic variation. Individual-level age effects on disease traits, caused by differences in the age at exposure of the host or its parents, have been widely documented in invertebrates. They can influence diverse traits, such as host susceptibility, virulence, parasite reproduction and further transmission, and may cascade to the population level, influencing disease prevalence and within-host competition. Here, I summarize what is known about the relationship between individual-level age/stage effects and infectious disease in invertebrates. I also attempt to link age effects to the theory of aging (senescence), and highlight the importance of population age structure to disease epidemiology and evolution. I conclude by identifying gaps in our understanding of individual- and population-level age effects in invertebrates. As the age structure of populations varies across space and time, age effects have strong epidemiological, ecological, and evolutionary implications for explaining variation in infectious diseases of invertebrates.
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Affiliation(s)
- Frida Ben-Ami
- School of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel.
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