1
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Vuorinen KEM, Oksanen T, Oksanen L, Vuorisalo T, Speed JDM. Why don't all species overexploit? OIKOS 2021. [DOI: 10.1111/oik.08358] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Katariina E. M. Vuorinen
- Dept of Natural History, NTNU Univ. Museum, Norwegian Univ. of Science and Technology Trondheim Norway
| | - Tarja Oksanen
- Dept of Arctic and Marine Biology, UiT, The Arctic Univ. of Norway, Campus Alta Alta Norway
- Dept of Biology, Ecology Section, Univ. of Turku Turku Finland
| | - Lauri Oksanen
- Dept of Arctic and Marine Biology, UiT, The Arctic Univ. of Norway, Campus Alta Alta Norway
- Dept of Biology, Ecology Section, Univ. of Turku Turku Finland
| | - Timo Vuorisalo
- Dept of Biology, Ecology Section, Univ. of Turku Turku Finland
| | - James D. M. Speed
- Dept of Natural History, NTNU Univ. Museum, Norwegian Univ. of Science and Technology Trondheim Norway
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2
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Nguyen VAT, Vural DC. Extinction in complex communities as driven by adaptive dynamics. J Evol Biol 2021; 34:1095-1109. [PMID: 33973303 DOI: 10.1111/jeb.13796] [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: 08/20/2020] [Revised: 04/08/2021] [Accepted: 04/20/2021] [Indexed: 11/30/2022]
Abstract
In a complex community, species continuously adapt to each other. On rare occasions, the adaptation of a species can lead to the extinction of others, and even its own. 'Adaptive dynamics' is the standard mathematical framework to describe evolutionary changes in community interactions, and in particular, predict adaptation driven extinction. Unfortunately, most authors implement the equations of adaptive dynamics through computer simulations that require assuming a large number of questionable parameters and fitness functions. In this study, we present analytical solutions to adaptive dynamics equations, thereby clarifying how outcomes depend on any computational input. We develop general formulas that predict equilibrium abundances over evolutionary time scales. Additionally, we predict which species will go extinct next, and when this will happen.
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3
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Parvinen K, Metz JAJ, Dieckmann U. Environmental dimensionality determines species coexistence. J Theor Biol 2020; 526:110280. [PMID: 32333978 DOI: 10.1016/j.jtbi.2020.110280] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Accepted: 04/14/2020] [Indexed: 10/24/2022]
Abstract
According to the competitive-exclusion principle, the number n of regulating variables describing a given community dynamics is an upper bound on the number of species (or types or morphs) that can coexist at equilibrium. On occasion, it is possible to reformulate a model with a lower number of regulating variables than appeared in the initial specification. We call the smallest number of such variables the dimension of the environmental feedback, or environmental dimension for short. For studying which species can invade a community, it is enough to know the sign of each species' long-term growth rate, i.e., invasion fitness. Therefore, different indicators of population growth - so-called fitness proxies, such as the basic reproduction number-are sometimes preferred. However, as we show, different fitness proxies may have different dimensions. Fundamental characteristics such as the environmental dimension should not depend on such arbitrary choices. Here, we resolve this difficulty by introducing a refined definition of environmental dimension that focuses on neutral fitness contours. On this basis, we show that this definition of environmental dimension is not only unambiguous, i.e., independent of the choice of fitness proxy, but also constructive, i.e., applicable without needing to assess an infinite number of possible fitness proxies. We then investigate how to determine environmental dimensions by analysing the two components of the environmental feedback: the impact map describing how a community's resident species affect the regulating variables and the sensitivity map describing how population growth depends on the regulating variables. The dimension of the impact map is lower than n when the set of feasible environments is of lower dimension than n, and the dimension of the sensitivity map is lower than n when not all n regulating variables affect the sign of population growth independently. While the minimum of the dimensions of the impact and sensitivity maps provides an upper bound on the environmental dimension, the combined effect of the two maps can result in an even lower environmental dimension, which happens when the sensitivity map is insensitive to some aspects of the impact map's image. To facilitate the applications of the framework introduced here, we illustrate all key concepts with detailed worked examples. In view of these results, we claim that the environmental dimension is the ultimate generalization of the traditional and widely used notions of the "number of regulating variables" or the "number of limiting factors", and is thus the sharpest generally applicable upper bound on the number of species that can robustly coexist in a community.
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Affiliation(s)
- Kalle Parvinen
- Department of Mathematics and Statistics, University of Turku, FI-20014, Finland; Evolution and Ecology Program, International Institute for Applied Systems Analysis (IIASA), Laxenburg A-2361, Austria.
| | - Johan A J Metz
- Evolution and Ecology Program, International Institute for Applied Systems Analysis (IIASA), Laxenburg A-2361, Austria; Institute of Biology and Mathematical Institute, Leiden University, NL-2333BE, the Netherlands; Netherlands Centre for Biodiversity, Naturalis, Leiden NL-2333CR, the Netherlands.
| | - Ulf Dieckmann
- Evolution and Ecology Program, International Institute for Applied Systems Analysis (IIASA), Laxenburg A-2361, Austria; Department of Evolutionary Studies of Biosystems, The Graduate University for Advanced Studies (Sokendai), Hayama, Kanagawa 240-0193, Japan.
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4
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Ecological changes with minor effect initiate evolution to delayed regime shifts. Nat Ecol Evol 2020; 4:412-418. [PMID: 32042123 PMCID: PMC7058421 DOI: 10.1038/s41559-020-1110-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Accepted: 01/13/2020] [Indexed: 11/08/2022]
Abstract
Regime shifts have been documented in a variety of natural and social systems. These abrupt transitions produce dramatic shifts in the composition and functioning of socioecological systems. Existing theory on ecosystem resilience has only considered regime shifts to be caused by changes in external conditions beyond a tipping point and therefore lacks an evolutionary perspective. In this study, we show how a change in external conditions has little ecological effect and does not push the system beyond a tipping point. The change therefore does not cause an immediate regime shift but instead triggers an evolutionary process that drives a phenotypic trait beyond a tipping point, thereby resulting (after a substantial delay) in a selection-induced regime shift. Our finding draws attention to the fact that regime shifts observed in the present may result from changes in the distant past, and highlights the need for integrating evolutionary dynamics into the theoretical foundation for ecosystem resilience.
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5
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Morozov A. Modelling Biological Evolution: Developing Novel Approaches. Bull Math Biol 2019; 81:4620-4624. [PMID: 31617043 DOI: 10.1007/s11538-019-00670-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Affiliation(s)
- Andrew Morozov
- Department of Mathematics, University of Leicester, University Road, Leicester, LE1 7RH, UK.
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6
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Abrams PA. How Does the Evolution of Universal Ecological Traits Affect Population Size? Lessons from Simple Models. Am Nat 2019; 193:814-829. [PMID: 31094600 DOI: 10.1086/703155] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
This article argues that adaptive evolutionary change in a consumer species should frequently decrease (and maladaptive change should increase) population size, producing adaptive decline. This conclusion is based on analysis of multiple consumer-resource models that examine evolutionary change in consumer traits affecting the universal ecological parameters of attack rate, conversion efficiency, and mortality. Two scenarios are investigated. In one, evolutionary equilibrium is initially maintained by opposing effects on the attack rate and other growth rate parameters; the environment or trait is perturbed, and the trait then evolves to a new (or back to a previous) equilibrium. Here evolution exhibits adaptive decline in up to one-half of all cases. The other scenario assumes a genetic perturbation having purely fitness-increasing effects. Here adaptive decline in the consumer requires that the resource be self-reproducing and overexploited and requires a sufficient increase in the attack rate. However, if the resource exhibits adaptive defense via behavior or evolution, adaptive decline may characterize consumer traits affecting all parameters. Favorable environmental change producing parameter shifts similar to those produced by adaptive evolution has similar counterintuitive effects on consumer population size. Many different food web models have already been shown to exhibit such counterintuitive changes in some species.
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7
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Govaert L, Fronhofer EA, Lion S, Eizaguirre C, Bonte D, Egas M, Hendry AP, De Brito Martins A, Melián CJ, Raeymaekers JAM, Ratikainen II, Saether B, Schweitzer JA, Matthews B. Eco‐evolutionary feedbacks—Theoretical models and perspectives. Funct Ecol 2018. [DOI: 10.1111/1365-2435.13241] [Citation(s) in RCA: 92] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Affiliation(s)
- Lynn Govaert
- Laboratory of Aquatic Ecology, Evolution and Conservation KU Leuven Leuven Belgium
- Department of Aquatic Ecology Eawag: Swiss Federal Institute of Aquatic Science and Technology Dübendorf Switzerland
- Department of Evolutionary Biology and Environmental Studies University of Zurich Zürich Switzerland
| | | | - Sébastien Lion
- Centre d'Ecologie Fonctionnelle et Evolutive CNRS, IRD, EPHE Université de Montpellier Montpellier France
| | | | - Dries Bonte
- Department of Biology Ghent University Ghent Belgium
| | - Martijn Egas
- Institute for Biodiversity and Ecosystem Dynamics University of Amsterdam Amsterdam The Netherlands
| | - Andrew P. Hendry
- Redpath Museum and Department of Biology McGill University Montreal Quebec Canada
| | - Ayana De Brito Martins
- Fish Ecology and Evolution DepartmentCenter for Ecology, Evolution and BiogeochemistryEawag: Swiss Federal Institute of Aquatic Science and Technology Dübendorf Switzerland
| | - Carlos J. Melián
- Fish Ecology and Evolution DepartmentCenter for Ecology, Evolution and BiogeochemistryEawag: Swiss Federal Institute of Aquatic Science and Technology Dübendorf Switzerland
| | | | - Irja I. Ratikainen
- Department of Biology Centre for Biodiversity Dynamics Norwegian University of Science and Technology Trondheim Norway
- Institute of Biodiversity, Animal Health and Comparative Medicine University of Glasgow Glasgow UK
| | - Bernt‐Erik Saether
- Department of Biology Centre for Biodiversity Dynamics Norwegian University of Science and Technology Trondheim Norway
| | - Jennifer A. Schweitzer
- Department of Ecology and Evolutionary Biology University of Tennessee Knoxville Tennessee
| | - Blake Matthews
- Department of Aquatic Ecology Eawag: Swiss Federal Institute of Aquatic Science and Technology Dübendorf Switzerland
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8
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Evolutionary Suicide of Prey: Matsuda and Abrams’ Model Revisited. Bull Math Biol 2018; 81:4778-4802. [DOI: 10.1007/s11538-018-0472-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Accepted: 07/16/2018] [Indexed: 10/28/2022]
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9
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Parvinen K, Dieckmann U. Environmental dimensionality. J Theor Biol 2018:S0022-5193(18)30122-X. [PMID: 29551543 DOI: 10.1016/j.jtbi.2018.03.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2017] [Revised: 03/04/2018] [Accepted: 03/07/2018] [Indexed: 11/26/2022]
Abstract
The number of regulating variables n in a given system is an upper bound to the number of coexisting species at equilibrium according to the competitive exclusion principle. However, it may be possible to formulate the model with a lower number of regulating variables, the smallest number of which is the dimension of the environmental feedback. Here we investigate how that dimension can be determined by analysing the two parts of environmental feedback: The impact map describes how the extant species affect the regulating variables, and the sensitivity map describes how population growth depends on the regulating variables. For the equilibrium condition it is enough to know the sign of each population growth rate, and therefore as the sensitivity map, different measures of population growth can be chosen, such as the basic reproduction number. The dimension of the environmental feedback must not depend on that choice. Different sensitivity maps can have different global dimensions, on which the definition thus cannot be based. Here we show that the local sensitivity dimension is independent of the choice, so that the concept is well-defined. The impact dimension is lower than n when the feasible set of environments is of lower dimension than n, and sensitivity dimension is lower than n when not all environmental variables affect the sign of population growth independently. Their combined effect can result in even lower environmental dimension. We illustrate such situations with examples. In conclusion, the dimension of environmental feedback gives valuable information about the potential coexistence of species.
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Affiliation(s)
- Kalle Parvinen
- Department of Mathematics and Statistics, University of Turku, FIN-20014 Finland.
| | - Ulf Dieckmann
- Department of Mathematics and Statistics, University of Turku, FIN-20014 Finland
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10
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Nurmi T, Parvinen K, Selonen V. The evolution of site-selection strategy during dispersal. J Theor Biol 2017; 425:11-22. [PMID: 28478118 DOI: 10.1016/j.jtbi.2017.05.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2016] [Revised: 04/19/2017] [Accepted: 05/03/2017] [Indexed: 11/16/2022]
Abstract
We propose a mathematical model that enables the evolutionary analysis of site-selection process of dispersing individuals that encounter sites of high or low quality. Since each site can be inhabited by at most one individual, all dispersers are not able to obtain a high-quality site. We study the evolutionary dynamics of the low-quality-site acceptance as a function of the time during the dispersal season using adaptive dynamics. We show that environmental changes affect the evolutionary dynamics in two ways: directly and indirectly via density-dependent factors. Direct evolutionary effects usually follow intuition, whereas indirect effects are often counter-intuitive and hence difficult to predict without mechanistic modeling. Therefore, the mechanistic derivation of the fitness function, with careful attention on density- and frequency dependence, is essential for predicting the consequences of environmental changes to site selection. For example, increasing fecundity in high-quality sites makes them more tempting for dispersers and hence the direct effect of this ecological change delays the acceptance of low-quality sites. However, increasing fecundity in high-quality sites also increases the population size, which makes the competition for sites more severe and thus, as an indirect effect, forces evolution to favor less picky individuals. Our results indicate that the indirect effects often dominate the intuitive effects, which emphasizes the need for mechanistic models of the immigration process.
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Affiliation(s)
- Tuomas Nurmi
- Department of Biology, University of Turku, FIN-20014, Finland.
| | - Kalle Parvinen
- Department of Mathematics and Statistics, University of Turku, FIN-20014, Finland; Evolution and Ecology Program, International Institute for Applied Systems Analysis, Laxenburg A-2361, Austria
| | - Vesa Selonen
- Department of Biology, University of Turku, FIN-20014, Finland
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11
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The evolution of parasitic and mutualistic plant-virus symbioses through transmission-virulence trade-offs. Virus Res 2017; 241:77-87. [PMID: 28434906 DOI: 10.1016/j.virusres.2017.04.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2016] [Revised: 04/11/2017] [Accepted: 04/12/2017] [Indexed: 12/21/2022]
Abstract
Virus-plant interactions range from parasitism to mutualism. Viruses have been shown to increase fecundity of infected plants in comparison with uninfected plants under certain environmental conditions. Increased fecundity of infected plants may benefit both the plant and the virus as seed transmission is one of the main virus transmission pathways, in addition to vector transmission. Trade-offs between vertical (seed) and horizontal (vector) transmission pathways may involve virulence, defined here as decreased fecundity in infected plants. To better understand plant-virus symbiosis evolution, we explore the ecological and evolutionary interplay of virus transmission modes when infection can lead to an increase in plant fecundity. We consider two possible trade-offs: vertical seed transmission vs infected plant fecundity, and horizontal vector transmission vs infected plant fecundity (virulence). Through mathematical models and numerical simulations, we show (1) that a trade-off between virulence and vertical transmission can lead to virus extinction during the course of evolution, (2) that evolutionary branching can occur with subsequent coexistence of mutualistic and parasitic virus strains, and (3) that mutualism can out-compete parasitism in the long-run. In passing, we show that ecological bi-stability is possible in a very simple discrete-time epidemic model. Possible extensions of this study include the evolution of conditional (environment-dependent) mutualism in plant viruses.
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12
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Evolution of Site-Selection Stabilizes Population Dynamics, Promotes Even Distribution of Individuals, and Occasionally Causes Evolutionary Suicide. Bull Math Biol 2016; 78:1749-72. [PMID: 27647007 PMCID: PMC5039230 DOI: 10.1007/s11538-016-0198-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2016] [Accepted: 08/16/2016] [Indexed: 12/03/2022]
Abstract
Species that compete for access to or use of sites, such as parasitic mites attaching to honey bees or apple maggots laying eggs in fruits, can potentially increase their fitness by carefully selecting sites at which they face little or no competition. Here, we systematically investigate the evolution of site-selection strategies among animals competing for discrete sites. By developing and analyzing a mechanistic and population-dynamical model of site selection in which searching individuals encounter sites sequentially and can choose to accept or continue to search based on how many conspecifics are already there, we give a complete characterization of the different site-selection strategies that can evolve. We find that evolution of site-selection stabilizes population dynamics, promotes even distribution of individuals among sites, and occasionally causes evolutionary suicide. We also discuss the broader implications of our findings and propose how they can be reconciled with an earlier study (Nonaka et al. in J Theor Biol 317:96–104, 2013) that reported selection toward ever higher levels of aggregation among sites as a consequence of site-selection.
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13
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Ferdy JB, Liu N, Sicard M. Transmission modes and the evolution of feminizing symbionts. J Evol Biol 2016; 29:2395-2409. [DOI: 10.1111/jeb.12963] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 06/18/2016] [Accepted: 07/26/2016] [Indexed: 11/28/2022]
Affiliation(s)
- J.-B. Ferdy
- Évolution et Diversité Biologique; UMR 5174 CNRS-UPS Université Paul Sabatier; Toulouse Cedex 9 France
| | - N. Liu
- Global Institute for Water Security; University of Saskatchewan; Saskatoon SK Canada
| | - M. Sicard
- Écologie et Biologie des Interactions; Équipe Écologie Évolution Symbiose; Université de Poitiers; UMR CNRS 7267; Poitiers Cedex France
- Institut des Sciences de l’Évolution; UMR 5554 CNRS-IRD-Université de Montpellier; Montpellier Cedex France
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14
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Hamelin FM, Allen LJS, Prendeville HR, Hajimorad MR, Jeger MJ. The evolution of plant virus transmission pathways. J Theor Biol 2016; 396:75-89. [PMID: 26908348 DOI: 10.1016/j.jtbi.2016.02.017] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Revised: 12/30/2015] [Accepted: 02/12/2016] [Indexed: 01/12/2023]
Abstract
The evolution of plant virus transmission pathways is studied through transmission via seed, pollen, or a vector. We address the questions: under what circumstances does vector transmission make pollen transmission redundant? Can evolution lead to the coexistence of multiple virus transmission pathways? We restrict the analysis to an annual plant population in which reproduction through seed is obligatory. A semi-discrete model with pollen, seed, and vector transmission is formulated to investigate these questions. We assume vector and pollen transmission rates are frequency-dependent and density-dependent, respectively. An ecological stability analysis is performed for the semi-discrete model and used to inform an evolutionary study of trade-offs between pollen and seed versus vector transmission. Evolutionary dynamics critically depend on the shape of the trade-off functions. Assuming a trade-off between pollen and vector transmission, evolution either leads to an evolutionarily stable mix of pollen and vector transmission (concave trade-off) or there is evolutionary bi-stability (convex trade-off); the presence of pollen transmission may prevent evolution of vector transmission. Considering a trade-off between seed and vector transmission, evolutionary branching and the subsequent coexistence of pollen-borne and vector-borne strains is possible. This study contributes to the theory behind the diversity of plant-virus transmission patterns observed in nature.
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Affiliation(s)
- Frédéric M Hamelin
- Department of Ecology, Agrocampus Ouest, UMR1349 IGEPP, F-35042 Rennes, France.
| | - Linda J S Allen
- Department of Mathematics and Statistics, Texas Tech University, Lubbock, TX 79409-1042, USA
| | - Holly R Prendeville
- USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR 97331, USA
| | - M Reza Hajimorad
- Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, TN 37996-4560, USA
| | - Michael J Jeger
- Division of Ecology and Evolution, Centre for Environmental Policy, Imperial College London, SL5 7PY, UK
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15
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Evolutionary suicide through a non-catastrophic bifurcation: adaptive dynamics of pathogens with frequency-dependent transmission. J Math Biol 2015; 72:1101-1124. [PMID: 26612110 DOI: 10.1007/s00285-015-0945-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 09/16/2015] [Indexed: 01/10/2023]
Abstract
Evolutionary suicide is a riveting phenomenon in which adaptive evolution drives a viable population to extinction. Gyllenberg and Parvinen (Bull Math Biol 63(5):981-993, 2001) showed that, in a wide class of deterministic population models, a discontinuous transition to extinction is a necessary condition for evolutionary suicide. An implicit assumption of their proof is that the invasion fitness of a rare strategy is well-defined also in the extinction state of the population. Epidemic models with frequency-dependent incidence, which are often used to model the spread of sexually transmitted infections or the dynamics of infectious diseases within herds, violate this assumption. In these models, evolutionary suicide can occur through a non-catastrophic bifurcation whereby pathogen adaptation leads to a continuous decline of host (and consequently pathogen) population size to zero. Evolutionary suicide of pathogens with frequency-dependent transmission can occur in two ways, with pathogen strains evolving either higher or lower virulence.
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16
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Zheng N, Whalen CC, Handel A. Modeling the potential impact of host population survival on the evolution of M. tuberculosis latency. PLoS One 2014; 9:e105721. [PMID: 25157958 PMCID: PMC4144956 DOI: 10.1371/journal.pone.0105721] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Accepted: 07/28/2014] [Indexed: 02/01/2023] Open
Abstract
Tuberculosis (TB) is an infectious disease with a peculiar feature: Upon infection with the causative agent, Mycobacterium Tuberculosis (MTB), most hosts enter a latent state during which no transmission of MTB to new hosts occurs. Only a fraction of latently infected hosts develop TB disease and can potentially infect new hosts. At first glance, this seems like a waste of transmission potential and therefore an evolutionary suboptimal strategy for MTB. It might be that the human immune response keeps MTB in check in most hosts, thereby preventing it from achieving its evolutionary optimum. Another possible explanation is that long latency and progression to disease in only a fraction of hosts are evolutionary beneficial to MTB by allowing it to persist better in small host populations. Given that MTB has co-evolved with human hosts for millenia or longer, it likely encountered small host populations for a large share of its evolutionary history and had to evolve strategies of persistence. Here, we use a mathematical model to show that indeed, MTB persistence is optimal for an intermediate duration of latency and level of activation. The predicted optimal level of activation is above the observed value, suggesting that human co-evolution has lead to host immunity, which keeps MTB below its evolutionary optimum.
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Affiliation(s)
- Nibiao Zheng
- Institute of Bioinformatics, University of Georgia, Athens, Georgia, United States of America
| | - Christopher C. Whalen
- Department of Epidemiology and Biostatistics, College of Public Health, University of Georgia, Athens, Georgia, United States of America
| | - Andreas Handel
- Department of Epidemiology and Biostatistics, College of Public Health, University of Georgia, Athens, Georgia, United States of America
- * E-mail:
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