1
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Penczykowski RM, Fearon ML, Hite JL, Shocket MS, Hall SR, Duffy MA. Pathways linking nutrient enrichment, habitat structure, and parasitism to host-resource interactions. Oecologia 2024; 204:439-449. [PMID: 37951848 DOI: 10.1007/s00442-023-05469-9] [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: 02/16/2023] [Accepted: 10/13/2023] [Indexed: 11/14/2023]
Abstract
Human activities simultaneously alter nutrient levels, habitat structure, and levels of parasitism. These activities likely have individual and joint impacts on food webs. Furthermore, there is particular concern that nutrient additions and changes to habitat structure might exacerbate the size of epidemics and impacts on host density. We used a well-studied zooplankton-fungus host-parasite system and experimental whole water column enclosures to factorially manipulate nutrient levels, habitat structure (specifically: mixing), and presence of parasites. Nutrient addition increased infection prevalence, density of infected hosts, and total host density. We hypothesized that nutrients, mixing, and parasitism were linked in multiple ways, including via their combined effects on phytoplankton (resource) abundance, and we used structural equation modeling to disentangle these pathways. In the absence of the parasite, both nutrients and mixing increased abundance of phytoplankton, whereas host density was negatively related to phytoplankton abundance, suggesting a mixture of bottom-up and top-down control of phytoplankton. In the presence of the parasite, nutrients still increased phytoplankton abundance but mixing no longer did, and there was no longer a significant relationship between host density and phytoplankton. This decoupling of host-resource dynamics may have resulted from reduced grazing due to illness-mediated changes in feeding behavior. Overall, our results show that the impact of one human activity (e.g., altered habitat structure) might depend on other human impacts (e.g., parasite introduction). Fortunately, carefully designed experiments and analyses can help tease apart these multifaceted relationships, allowing us to understand how human activities alter food webs, including interactions between hosts and their parasites and resources.
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Affiliation(s)
- Rachel M Penczykowski
- School of Biology, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
- Department of Biology, Washington University in St. Louis, St. Louis, MO, 63130, USA.
| | - Michelle L Fearon
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Jessica L Hite
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
- Department of Pathobiological Sciences, University of Wisconsin-Madison, Madison, WI, 53706, USA
| | - Marta S Shocket
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
- Department of Geography, University of Florida, Gainesville, FL, 32611, USA
| | - Spencer R Hall
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
| | - Meghan A Duffy
- School of Biology, Georgia Institute of Technology, Atlanta, GA, 30332, USA
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109, USA
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2
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Davenport ES, Dziuba MK, Jacobson LE, Calhoun SK, Monell KJ, Duffy MA. How does parasite environmental transmission stage concentration change before, during, and after disease outbreaks? Ecology 2024; 105:e4235. [PMID: 38185479 DOI: 10.1002/ecy.4235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Accepted: 11/09/2023] [Indexed: 01/09/2024]
Abstract
Outbreaks of environmentally transmitted parasites require that susceptible hosts encounter transmission stages in the environment and become infected, but we also know that transmission stages can be in the environment without triggering disease outbreaks. One challenge in understanding the relationship between environmental transmission stages and disease outbreaks is that the distribution and abundance of transmission stages outside of their hosts have been difficult to quantify. Thus, we have limited data about how changes in transmission stage abundance influence disease dynamics; moreover, we do not know whether the relationship between transmission stages and outbreaks differs among parasite species. We used digital PCR to quantify the environmental transmission stages of five parasites in six lakes in southeastern Michigan every 2 weeks from June to November 2021. At the same time, we quantified infection prevalence in hosts and host density. Our study focused on eight zooplankton host species (Daphnia spp. and Ceriodaphnia dubia) and five of their parasites from diverse taxonomic groups (bacteria, yeast, microsporidia, and oomycete) with different infection mechanisms. We found that parasite transmission stage concentration increased prior to disease outbreaks for all parasites. However, parasites differed significantly in the relative timing of peaks in transmission stage concentration and infection outbreaks. The "continuous shedder" parasites had transmission stage peaks at the same time as or slightly after the outbreak peaks. In contrast, parasites relying on host death for transmission ("obligate killers") had transmission stage peaks before outbreak peaks. For most parasites, lakes with outbreaks had higher spore concentrations than those without outbreaks, especially once an outbreak began; the exception was for a parasite, Pasteuria ramosa, with very strong genotypic specificity of infection. Overall, our results show that disease outbreaks are tightly linked to transmission stage concentration; outbreaks were preceded by increases in transmission stage concentration in the environment and then were fueled by the production of more transmission stages during the outbreak itself, with concentrations decreasing to pre-outbreak levels as outbreaks waned. Thus, tracking transmission stages in the environment improves our understanding of the drivers of disease outbreaks and reveals how parasite traits may affect these dynamics.
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Affiliation(s)
- Elizabeth S Davenport
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Marcin K Dziuba
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Logan E Jacobson
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Siobhan K Calhoun
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Kira J Monell
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Meghan A Duffy
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, USA
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3
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Shaw CL, Duffy MA. Rapid evolution of a bacterial parasite during outbreaks in two Daphnia populations. Ecol Evol 2023; 13:e9676. [PMID: 36694542 PMCID: PMC9843074 DOI: 10.1002/ece3.9676] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Revised: 12/09/2022] [Accepted: 12/10/2022] [Indexed: 01/18/2023] Open
Abstract
Myriad ecological and evolutionary factors can influence whether a particular parasite successfully transmits to a new host during a disease outbreak, with consequences for the structure and diversity of parasite populations. However, even though the diversity and evolution of parasite populations are of clear fundamental and applied importance, we have surprisingly few studies that track how genetic structure of parasites changes during naturally occurring outbreaks in non-human populations. Here, we used population genetic approaches to reveal how genotypes of a bacterial parasite, Pasteuria ramosa, change over time, focusing on how infecting P. ramosa genotypes change during the course of epidemics in Daphnia populations in two lakes. We found evidence for genetic change - and, therefore, evolution - of the parasite during outbreaks. In one lake, P. ramosa genotypes were structured by sampling date; in both lakes, genetic distance between groups of P. ramosa isolates increased with time between sampling. Diversity in parasite populations remained constant over epidemics, although one epidemic (which was large) had low genetic diversity while the other epidemic (which was small) had high genetic diversity. Our findings demonstrate that patterns of parasite evolution differ between outbreaks; future studies exploring the feedbacks among epidemic size, host diversity, and parasite genetic diversity would improve our understanding of parasite dynamics and evolution.
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Affiliation(s)
- Clara L. Shaw
- Department of Ecology & Evolutionary BiologyUniversity of MichiganAnn ArborMichiganUSA,Department of BiologyThe Pennsylvania State UniversityUniversity ParkPennsylvaniaUSA
| | - Meghan A. Duffy
- Department of Ecology & Evolutionary BiologyUniversity of MichiganAnn ArborMichiganUSA
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4
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Gutierrez SO, Minchella DJ, Bernal XE. Survival of the sickest: selective predation differentially modulates ecological and evolutionary disease dynamics. OIKOS 2022. [DOI: 10.1111/oik.09126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
| | | | - Ximena E. Bernal
- Dept of Biology, Purdue Univ. West Lafayette IN USA
- Smithsonian Tropical Research Inst. Panama Republic of Panama
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5
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Shaw CL, Bilich R, O'Brien B, Cáceres CE, Hall SR, James TY, Duffy MA. Genotypic variation in an ecologically important parasite is associated with host species, lake and spore size. Parasitology 2021; 148:1303-1312. [PMID: 34103104 PMCID: PMC8383271 DOI: 10.1017/s0031182021000949] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Revised: 05/11/2021] [Accepted: 05/31/2021] [Indexed: 11/10/2022]
Abstract
Genetic variation in parasites has important consequences for host–parasite interactions. Prior studies of the ecologically important parasite Metschnikowia bicuspidata have suggested low genetic variation in the species. Here, we collected M. bicuspidata from two host species (Daphnia dentifera and Ceriodaphnia dubia) and two regions (Michigan and Indiana, USA). Within a lake, outbreaks tended to occur in one host species but not the other. Using microsatellite markers, we identified six parasite genotypes grouped within three distinct clades, one of which was rare. Of the two main clades, one was generally associated with D. dentifera, with lakes in both regions containing a single genotype. The other M. bicuspidata clade was mainly associated with C. dubia, with a different genotype dominating in each region. Despite these associations, both D. dentifera- and C. dubia-associated genotypes were found infecting both hosts in lakes. However, in lab experiments, the D. dentifera-associated genotype infected both D. dentifera and C. dubia, but the C. dubia-associated genotype, which had spores that were approximately 30% smaller, did not infect D. dentifera. We hypothesize that variation in spore size might help explain patterns of cross-species transmission. Future studies exploring the causes and consequences of variation in spore size may help explain patterns of infection and the maintenance of genotypic diversity in this ecologically important system.
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Affiliation(s)
- Clara L. Shaw
- Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI48109, USA
| | - Rebecca Bilich
- Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI48109, USA
| | - Bruce O'Brien
- Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI48109, USA
| | - Carla E. Cáceres
- Department of Evolution, Ecology, & Behavior, School of Integrative Biology, University of Illinois Urbana-Champaign, Urbana, IL61801, USA
| | - Spencer R. Hall
- Department of Biology, Indiana University, Bloomington, IN47405, USA
| | - Timothy Y. James
- Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI48109, USA
| | - Meghan A. Duffy
- Department of Ecology & Evolutionary Biology, University of Michigan, Ann Arbor, MI48109, USA
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6
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Mechanisms by which predators mediate host-parasite interactions in aquatic systems. Trends Parasitol 2021; 37:890-906. [PMID: 34281798 DOI: 10.1016/j.pt.2021.06.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 06/21/2021] [Accepted: 06/28/2021] [Indexed: 02/08/2023]
Abstract
It is often assumed that predators reduce disease prevalence and transmission by lowering prey population density and/or by selectively feeding on infected individuals. However, recent studies, many of which come from aquatic systems, suggest numerous alternative mechanisms by which predators can influence disease dynamics in their prey. Here, we review the mechanisms by which predators can mediate host-parasite interactions in aquatic prey. We highlight how life histories of aquatic hosts and parasites influence transmission pathways and describe how such pathways intersect with predation to shape disease dynamics. We also provide recommendations for future studies; experiments that account for multiple effects of predators on host-parasite interactions, and that examine how predator-host-parasite interactions shift under changing environmental conditions, are particularly needed.
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7
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Hite JL, Pfenning‐Butterworth AC, Vetter RE, Cressler CE. A high-throughput method to quantify feeding rates in aquatic organisms: A case study with Daphnia. Ecol Evol 2020; 10:6239-6245. [PMID: 32724510 PMCID: PMC7381556 DOI: 10.1002/ece3.6352] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 04/13/2020] [Accepted: 04/14/2020] [Indexed: 11/17/2022] Open
Abstract
Food ingestion is one of the most basic features of all organisms. However, obtaining precise-and high-throughput-estimates of feeding rates remains challenging, particularly for small, aquatic herbivores such as zooplankton, snails, and tadpoles. These animals typically consume low volumes of food that are time-consuming to accurately measure.We extend a standard high-throughput fluorometry technique, which uses a microplate reader and 96-well plates, as a practical tool for studies in ecology, evolution, and disease biology. We outline technical and methodological details to optimize quantification of individual feeding rates, improve accuracy, and minimize sampling error.This high-throughput assay offers several advantages over previous methods, including i) substantially reduced time allotments per sample to facilitate larger, more efficient experiments; ii) technical replicates; and iii) conversion of in vivo measurements to units (mL-1 hr-1 ind-1) which enables broad-scale comparisons across an array of taxa and studies.To evaluate the accuracy and feasibility of our approach, we use the zooplankton, Daphnia dentifera, as a case study. Our results indicate that this procedure accurately quantifies feeding rates and highlights differences among seven genotypes.The method detailed here has broad applicability to a diverse array of aquatic taxa, their resources, environmental contaminants (e.g., plastics), and infectious agents. We discuss simple extensions to quantify epidemiologically relevant traits, such as pathogen exposure and transmission rates, for infectious agents with oral or trophic transmission.
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Affiliation(s)
- Jessica L. Hite
- School of Biological SciencesUniversity of NebraskaLincolnNebraskaUSA
| | | | - Rachel E. Vetter
- School of Biological SciencesUniversity of NebraskaLincolnNebraskaUSA
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8
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Shocket MS, Vergara D, Sickbert AJ, Walsman JM, Strauss AT, Hite JL, Duffy MA, Cáceres CE, Hall SR. Parasite rearing and infection temperatures jointly influence disease transmission and shape seasonality of epidemics. Ecology 2018; 99:1975-1987. [PMID: 29920661 DOI: 10.1002/ecy.2430] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/16/2017] [Revised: 04/03/2018] [Accepted: 05/19/2018] [Indexed: 11/07/2022]
Abstract
Seasonal epidemics erupt commonly in nature and are driven by numerous mechanisms. Here, we suggest a new mechanism that could determine the size and timing of seasonal epidemics: rearing environment changes the performance of parasites. This mechanism arises when the environmental conditions in which a parasite is produced impact its performance-independently from the current environment. To illustrate the potential for "rearing effects", we show how temperature influences infection risk (transmission rate) in a Daphnia-fungus disease system through both parasite rearing temperature and infection temperature. During autumnal epidemics, zooplankton hosts contact (eat) fungal parasites (spores) reared in a gradually cooling environment. To delineate the effect of rearing temperature from temperature at exposure and infection, we used lab experiments to parameterize a mechanistic model of transmission rate. We also evaluated the rearing effect using spores collected from epidemics in cooling lakes. We found that fungal spores were more infectious when reared at warmer temperatures (in the lab and in two of three lakes). Additionally, the exposure (foraging) rate of hosts increased with warmer infection temperatures. Thus, both mechanisms cause transmission rate to drop as temperature decreases over the autumnal epidemic season (from summer to winter). Simulations show how these temperature-driven changes in transmission rate can induce waning of epidemics as lakes cool. Furthermore, via thermally dependent transmission, variation in environmental cooling patterns can alter the size and shape of epidemics. Thus, the thermal environment drives seasonal epidemics through effects on hosts (exposure rate) and the infectivity of parasites (a rearing effect). Presently, the generality of parasite rearing effects remains unknown. Our results suggest that they may provide an important but underappreciated mechanism linking temperature to the seasonality of epidemics.
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Affiliation(s)
- Marta S Shocket
- Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA
| | - Daniela Vergara
- Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA
| | - Andrew J Sickbert
- Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA
| | - Jason M Walsman
- Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA
| | | | - Jessica L Hite
- Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA
| | - Meghan A Duffy
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan, 48109, USA
| | - Carla E Cáceres
- School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, USA
| | - Spencer R Hall
- Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA
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9
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Rossiter W, Davidson HM. Extrinsic and Intrinsic Predictors of Variation in Infection by Posthodiplostomum minimum MacCallum, 1921 (Trematoda) in Sunfishes ( Lepomis Rafinesque, 1819) from Eastern Ohio. J Parasitol 2018; 104:202-209. [PMID: 29553888 DOI: 10.1645/17-131] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The trematode Posthodiplostomum minimum MacCallum, 1921 (white grub) is a common parasite of centrarchid fishes, frequently reaching high prevalence and intensity in local populations. However, significant variation in infection has been observed across Lepomis Rafinesque, 1819 sunfish species, which are common and abundant hosts for this parasite. Previous observations suggest both extrinsic factors (e.g., habitat-specific characteristics and environmental parameters) and intrinsic factors (e.g., host size, behavior, and susceptibility) as important predictors of infection in this parasite-host system. In the present study, we evaluated the prevalence and intensity of P. minimum in 6 sympatric species of Lepomis sunfish (total of 563 individuals) across 9 lakes in eastern Ohio, U.S.A., that range in surface area from 5.6 to 1,448.7 hectares, and assessed the importance of both extrinsic and intrinsic factors as predictors of infection. We found that collection site (extrinsic factor) and host body mass and species identity (intrinsic factors) were the strongest predictors of infection intensity. Specifically, infection intensity was negatively associated with lake surface area and positively associated host body mass. Lepomis macrochirus (bluegill sunfish) and hybrid sunfish displayed the highest infection intensities, whereas Lepomis cyanellus (green sunfish) and Lepomis gulosus (warmouth sunfish) were significantly less burdened. We were unable to conclude if the observed variation among host species was due to host ecology or susceptibility. These general findings were supported by classification and regression tree (CART) analysis, which optimally partitioned variation in individual host infection intensities by using lake size and host body mass (but not host species identity). Although infection intensity was negatively associated with lake surface area (even among host individuals of the same size and species), the causal mechanisms involved remain unresolved and should be the impetus of future work on this parasite-host system.
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Affiliation(s)
- Wayne Rossiter
- Department of Biology, Waynesburg University, 51 W. College Street, Waynesburg, Pennsylvania 15370
| | - Harley M Davidson
- Department of Biology, Waynesburg University, 51 W. College Street, Waynesburg, Pennsylvania 15370
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10
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Linking host traits, interactions with competitors and disease: Mechanistic foundations for disease dilution. Funct Ecol 2018. [DOI: 10.1111/1365-2435.13066] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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11
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Shocket MS, Strauss AT, Hite JL, Šljivar M, Civitello DJ, Duffy MA, Cáceres CE, Hall SR. Temperature Drives Epidemics in a Zooplankton-Fungus Disease System: A Trait-Driven Approach Points to Transmission via Host Foraging. Am Nat 2018; 191:435-451. [PMID: 29570399 DOI: 10.1086/696096] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Climatic warming will likely have idiosyncratic impacts on infectious diseases, causing some to increase while others decrease or shift geographically. A mechanistic framework could better predict these different temperature-disease outcomes. However, such a framework remains challenging to develop, due to the nonlinear and (sometimes) opposing thermal responses of different host and parasite traits and due to the difficulty of validating model predictions with observations and experiments. We address these challenges in a zooplankton-fungus (Daphnia dentifera-Metschnikowia bicuspidata) system. We test the hypothesis that warmer temperatures promote disease spread and produce larger epidemics. In lakes, epidemics that start earlier and warmer in autumn grow much larger. In a mesocosm experiment, warmer temperatures produced larger epidemics. A mechanistic model parameterized with trait assays revealed that this pattern arose primarily from the temperature dependence of transmission rate (β), governed by the increasing foraging (and, hence, parasite exposure) rate of hosts (f). In the trait assays, parasite production seemed sufficiently responsive to shape epidemics as well; however, this trait proved too thermally insensitive in the mesocosm experiment and lake survey to matter much. Thus, in warmer environments, increased foraging of hosts raised transmission rate, yielding bigger epidemics through a potentially general, exposure-based mechanism for ectotherms. This mechanistic approach highlights how a trait-based framework will enhance predictive insight into responses of infectious disease to a warmer world.
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12
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Hite JL, Bosch J, Fernández-Beaskoetxea S, Medina D, Hall SR. Joint effects of habitat, zooplankton, host stage structure and diversity on amphibian chytrid. Proc Biol Sci 2017; 283:rspb.2016.0832. [PMID: 27466456 DOI: 10.1098/rspb.2016.0832] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 07/05/2016] [Indexed: 11/12/2022] Open
Abstract
Why does the severity of parasite infection differ dramatically across habitats? This question remains challenging to answer because multiple correlated pathways drive disease. Here, we examined habitat-disease links through direct effects on parasites and indirect effects on parasite predators (zooplankton), host diversity and key life stages of hosts. We used a case study of amphibian hosts and the chytrid fungus, Batrachochytrium dendrobatidis, in a set of permanent and ephemeral alpine ponds. A field experiment showed that ultraviolet radiation (UVR) killed the free-living infectious stage of the parasite. Yet, permanent ponds with more UVR exposure had higher infection prevalence. Two habitat-related indirect effects worked together to counteract parasite losses from UVR: (i) UVR reduced the density of parasite predators and (ii) permanent sites fostered multi-season host larvae that fuelled parasite production. Host diversity was unlinked to hydroperiod or UVR but counteracted parasite gains; sites with higher diversity of host species had lower prevalence of infection. Thus, while habitat structure explained considerable variation in infection prevalence through two indirect pathways, it could not account for everything. This study demonstrates the importance of creating mechanistic, food web-based links between multiple habitat dimensions and disease.
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Affiliation(s)
- Jessica L Hite
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
| | - Jaime Bosch
- Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, 28006 Madrid, Spain Centro de Investigación, Seguimiento y Evaluación, Parque Nacional de la Sierra de Guadarrama, Cta. M-604, Km. 27.6, 28740 Rascafría, Spain
| | | | - Daniel Medina
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, USA
| | - Spencer R Hall
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
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13
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Searle CL, Cortez MH, Hunsberger KK, Grippi DC, Oleksy IA, Shaw CL, de la Serna SB, Lash CL, Dhir KL, Duffy MA. Population Density, Not Host Competence, Drives Patterns of Disease in an Invaded Community. Am Nat 2016; 188:554-566. [PMID: 27788345 DOI: 10.1086/688402] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
Generalist parasites can strongly influence interactions between native and invasive species. Host competence can be used to predict how an invasive species will affect community disease dynamics; the addition of a highly competent, invasive host is predicted to increase disease. However, densities of invasive and native species can also influence the impacts of invasive species on community disease dynamics. We examined whether information on host competence alone could be used to accurately predict the effects of an invasive host on disease in native hosts. We first characterized the relative competence of an invasive species and a native host species to a native parasite. Next, we manipulated species composition in mesocosms and found that host competence results did not accurately predict community dynamics. While the invasive host was more competent than the native, the presence of the native (lower competence) host increased disease in the invasive (higher competence) host. To identify potential mechanisms driving these patterns, we analyzed a two-host, one-parasite model parameterized for our system. Our results demonstrate that patterns of disease were primarily driven by relative population densities, mediated by asymmetry in intra- and interspecific competition. Thus, information on host competence alone may not accurately predict how an invasive species will influence disease in native species.
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14
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Habitat, predators, and hosts regulate disease in
Daphnia
through direct and indirect pathways. ECOL MONOGR 2016. [DOI: 10.1002/ecm.1222] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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15
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Ebert D, Duneau D, Hall MD, Luijckx P, Andras JP, Du Pasquier L, Ben-Ami F. A Population Biology Perspective on the Stepwise Infection Process of the Bacterial Pathogen Pasteuria ramosa in Daphnia. ADVANCES IN PARASITOLOGY 2015; 91:265-310. [PMID: 27015951 DOI: 10.1016/bs.apar.2015.10.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The infection process of many diseases can be divided into series of steps, each one required to successfully complete the parasite's life and transmission cycle. This approach often reveals that the complex phenomenon of infection is composed of a series of more simple mechanisms. Here we demonstrate that a population biology approach, which takes into consideration the natural genetic and environmental variation at each step, can greatly aid our understanding of the evolutionary processes shaping disease traits. We focus in this review on the biology of the bacterial parasite Pasteuria ramosa and its aquatic crustacean host Daphnia, a model system for the evolutionary ecology of infectious disease. Our analysis reveals tremendous differences in the degree to which the environment, host genetics, parasite genetics and their interactions contribute to the expression of disease traits at each of seven different steps. This allows us to predict which steps may respond most readily to selection and which steps are evolutionarily constrained by an absence of variation. We show that the ability of Pasteuria to attach to the host's cuticle (attachment step) stands out as being strongly influenced by the interaction of host and parasite genotypes, but not by environmental factors, making it the prime candidate for coevolutionary interactions. Furthermore, the stepwise approach helps us understanding the evolution of resistance, virulence and host ranges. The population biological approach introduced here is a versatile tool that can be easily transferred to other systems of infectious disease.
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Affiliation(s)
- Dieter Ebert
- Zoological Institute, University of Basel, Basel, Switzerland
| | - David Duneau
- Zoological Institute, University of Basel, Basel, Switzerland; Department Ecologie et Diversité Biologique, University Paul Sabatier-Toulouse III, Toulouse, France
| | - Matthew D Hall
- Zoological Institute, University of Basel, Basel, Switzerland; Monash University, School of Biological Sciences, Clayton Campus, Melbourne, VIC, Australia
| | - Pepijn Luijckx
- Zoological Institute, University of Basel, Basel, Switzerland; Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON, Canada
| | - Jason P Andras
- Zoological Institute, University of Basel, Basel, Switzerland; Department of Biological Sciences, Mount Holyoke College, South Hadley, MA, USA
| | | | - Frida Ben-Ami
- Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
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16
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Strauss AT, Civitello DJ, Cáceres CE, Hall SR. Success, failure and ambiguity of the dilution effect among competitors. Ecol Lett 2015; 18:916-26. [PMID: 26119173 DOI: 10.1111/ele.12468] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2015] [Revised: 02/24/2015] [Accepted: 05/28/2015] [Indexed: 11/29/2022]
Abstract
It remains challenging to predict variation in the magnitude of disease outbreaks. The dilution effect seeks to explain this variation by linking multiple host species to disease transmission. It predicts that disease risk increases for a focal host when host species diversity declines. However, when an increase in species diversity does not reduce disease, we are often unable to diagnose why. Here, we increase mechanistic and predictive clarity of the dilution effect with a general trait-based model of disease transmission in multi-host communities. Then, we parameterise and empirically test our model with a multi-generational case study of planktonic disease. The model-experiment combination shows that hosts that vary in competitive ability (R*) and potential to spread disease (R0 ) can produce three qualitatively disparate outcomes of dilution on disease: the dilution effect can succeed, fail, or be ambiguous/irrelevant.
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Affiliation(s)
| | - David J Civitello
- Department of Integrative Biology, University of South Florida, Tampa, FL, 33620, USA
| | - Carla E Cáceres
- School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA
| | - Spencer R Hall
- Department of Biology, Indiana University, Bloomington, IN, 47401, USA
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17
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Civitello DJ, Penczykowski RM, Smith AN, Shocket MS, Duffy MA, Hall SR. Resources, key traits and the size of fungal epidemics in Daphnia populations. J Anim Ecol 2015; 84:1010-7. [PMID: 25733032 DOI: 10.1111/1365-2656.12363] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Accepted: 02/16/2015] [Indexed: 11/30/2022]
Abstract
Parasites can profoundly affect host populations and ecological communities. Thus, it remains critical to identify mechanisms that drive variation in epidemics. Resource availability can drive epidemics via traits of hosts and parasites that govern disease spread. Here, we map resource-trait-epidemic connections to explain variation in fungal outbreaks (Metschnikowia bicuspidata) in a zooplankton host (Daphnia dentifera) among lakes. We predicted epidemics would grow larger in lakes with more phytoplankton via three energetic mechanisms. First, resources should stimulate Daphnia reproduction, potentially elevating host density. Secondly, resources should boost body size of hosts, enhancing exposure to environmentally distributed propagules through size-dependent feeding. Thirdly, resources should fuel parasite reproduction within hosts. To test these predictions, we sampled 12 natural epidemics and tracked edible algae, fungal infection prevalence, body size, fecundity and density of hosts, as well as within-host parasite loads. Epidemics grew larger in lakes with more algal resources. Structural equation modelling revealed that resource availability stimulated all three traits (host fecundity, host size and parasite load). However, only parasite load connected resources to epidemic size. Epidemics grew larger in more dense Daphnia populations, but host density was unrelated to host fecundity (thus breaking its link to resources). Thus, via energetic mechanisms, resource availability can stimulate key trait(s) governing epidemics in nature. A synthetic focus on resources and resource-trait links could yield powerful insights into epidemics.
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Affiliation(s)
- David J Civitello
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
| | | | - Aimee N Smith
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
| | - Marta S Shocket
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
| | - Meghan A Duffy
- Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Spencer R Hall
- Department of Biology, Indiana University, Bloomington, IN, 47405, USA
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18
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Abstract
Hosts strongly influence parasite fitness. However, it is challenging to disentangle host effects on genetic vs plasticity-driven traits of parasites, since parasites can evolve quickly. It remains especially difficult to determine the causes and magnitude of parasite plasticity. In successive generations, parasites may respond plastically to better infect their current type of host, or hosts may produce generally 'good' or 'bad' quality parasites. Here, we characterized parasite plasticity by taking advantage of a system in which the parasite (the yeast Metschnikowia bicuspidata, which infects Daphnia) has no detectable heritable variation, preventing rapid evolution. In experimental infection assays, we found an effect of rearing host genotype on parasite infectivity, where host genotypes produced overall high or low quality parasite spores. Additionally, these plastically induced differences were gained or lost in just a single host generation. Together, these results demonstrate phenotypic plasticity in infectivity driven by the within-host rearing environment. Such plasticity is rarely investigated in parasites, but could shape epidemiologically important traits.
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19
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Cáceres CE, Davis G, Duple S, Hall SR, Koss A, Lee P, Rapti Z. Complex Daphnia interactions with parasites and competitors. Math Biosci 2014; 258:148-61. [PMID: 25445737 DOI: 10.1016/j.mbs.2014.10.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Revised: 10/01/2014] [Accepted: 10/07/2014] [Indexed: 10/24/2022]
Abstract
Species interactions can strongly influence the size and dynamics of epidemics in populations of focal hosts. The "dilution effect" provides a particularly interesting type of interaction from a biological standpoint. Diluters - other host species which resist infection but remove environmentally-distributed propagules of parasites (spores) - should reduce disease prevalence in focal hosts. However, diluters and focal hosts may compete for shared resources. This combination of positive (dilution) and negative (competition) effects could greatly complicate, even undermine, the benefits of dilution and diluter species from the perspective of the focal host. Motivated by an example from the plankton (i.e., zooplankton hosts, a fungal parasite, and algal resources), we study a model of dilution and competition. Our model reveals a suite of five results: • A diluter that is a superior competitor wipes out the host, regardless of parasitism. Although expected, this outcome is an ever-present danger in strategies that might use diluters to control disease. • If the diluter is an inferior competitor, it can reduce disease prevalence, despite the competition, as parameterized in our model. However, competition may also reduce density of susceptible hosts to levels below that seen in focal host-parasite systems alone. • As they decrease disease prevalence, diluters destabilize dynamics of the focal host and their resources. Thus, diluters undermine the stabilizing effects of disease. • The four species combination can generate very complex dynamics, including period-doubling bifurcations and torus (Neimark-Sacker) bifurcations. • At lower resource carrying capacity, the diluter’s dilution of spores is 'helpful' to the focal host, i.e., dilution can elevate host density by reducing disease. But, as the resource carrying capacity increases further, the equilibrium density of the diluter increases while the density of the focal host decreases, despite competition. Namely, the negative effects of competition start to outweigh the positive effects of dilution from the perspective of equilibrium density of the focal host.
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Affiliation(s)
- C E Cáceres
- School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - G Davis
- Department of Mathematics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - S Duple
- School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - S R Hall
- Department of Biology, Indiana University, Bloomington, IN 47405, United States
| | - A Koss
- Department of Mathematics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - P Lee
- School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States
| | - Z Rapti
- Department of Mathematics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, United States.
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20
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Abstract
Parasite virulence, or the damage a parasite does to its host, is measured in terms of both host costs (reductions in host growth, reproduction and survival) and parasite benefits (increased transmission and parasite numbers) in the literature. Much work has shown that ecological and genetic factors can be strong selective forces in virulence evolution. This review uses kin selection theory to explore how variations in host ecological parameters impact the genetic relatedness of parasite populations and thus virulence. We provide a broad overview of virulence and population genetics studies and then draw connections to existing knowledge about natural parasite populations. The impact of host movement (transporting parasites) and host resistance (filtering parasites) on the genetic structure and virulence of parasite populations is explored, and empirical studies of these factors using Plasmodium and trematode systems are proposed.
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21
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Hurtado PJ, Hall SR, Ellner SP. Infectious disease in consumer populations: dynamic consequences of resource-mediated transmission and infectiousness. THEOR ECOL-NETH 2014. [DOI: 10.1007/s12080-013-0208-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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22
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Civitello DJ, Penczykowski RM, Hite JL, Duffy MA, Hall SR. Potassium stimulates fungal epidemics in Daphnia by increasing host and parasite reproduction. Ecology 2013; 94:380-8. [PMID: 23691657 DOI: 10.1890/12-0883.1] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
As natural enemies, parasites can dramatically harm host populations, and even catalyze their decline. Thus, identifying factors that promote disease spread is paramount. Environmental factors can drive epidemics by altering traits involved in disease spread. For example, nutrients (such as nitrogen and phosphorus) can stimulate reproduction of both hosts and parasites or alter rates of disease transmission by stimulating productivity and nutrition of food resources of hosts. Here, we demonstrate nutrient-trait-epidemic connections between the greatly understudied macronutrient potassium (K) and fungal disease (Metschnikowia bicuspidata) in a zooplankton host (Daphnia dentifera). In a three-year survey, epidemics grew larger in lakes with more potassium. In laboratory assays, potassium enrichment of low-K lake water enhanced both host and parasite reproduction. Parameterized with these data, a model predicted that potassium addition catalyzes disease spread. We confirmed this prediction with an experiment in large mesocosms (6000 L) in a low K-lake: potassium enrichment caused larger epidemics in replicated Daphnia populations. Consequently, the model--data combination mechanistically explained the field pattern and revealed a novel ecological role for the nutrient potassium. Furthermore, our findings highlight the need for further development of theory for nutrient limitation of epidemics. Such theory could help to explain heterogeneous eruptions of disease in space, connect these outbreaks to natural or anthropogenic enrichment of ecosystems, predict the ecological consequences of these outbreaks, and reveal novel strategies for disease management.
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Affiliation(s)
- David J Civitello
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
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23
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Bertram CR, Pinkowski M, Hall SR, Duffy MA, Cáceres CE. Trait-mediated indirect effects, predators, and disease: test of a size-based model. Oecologia 2013; 173:1023-32. [DOI: 10.1007/s00442-013-2673-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2012] [Accepted: 04/22/2013] [Indexed: 10/26/2022]
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24
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Civitello DJ, Pearsall S, Duffy MA, Hall SR. Parasite consumption and host interference can inhibit disease spread in dense populations. Ecol Lett 2013; 16:626-34. [DOI: 10.1111/ele.12089] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Revised: 10/31/2012] [Accepted: 01/15/2013] [Indexed: 11/29/2022]
Affiliation(s)
- David J. Civitello
- Department of Biology; Indiana University; 1001 E. 3rd St.; Bloomington IN; 47405; USA
| | - Susan Pearsall
- Department of Biology; Indiana University; 1001 E. 3rd St.; Bloomington IN; 47405; USA
| | - Meghan A. Duffy
- School of Biology; Georgia Institute of Technology; Atlanta; GA 30332; USA
| | - Spencer R. Hall
- Department of Biology; Indiana University; 1001 E. 3rd St.; Bloomington IN; 47405; USA
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25
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Upstream-downstream gradient in infection levels by fish parasites: a common river pattern? Parasitology 2012; 140:266-74. [PMID: 23058079 DOI: 10.1017/s0031182012001527] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Physical habitat structure can influence the distribution and abundance of organisms. In rivers, stream drift, a common process originating from the unidirectional water flow, favours the displacement and downstream dispersion of invertebrates. This process could also generate a gradient in infection levels, leading to decreasing numbers of parasites per host as one moves upstream from the river mouth. We tested this hypothesis using 4 trematode species infecting the fish Gobiomorphus breviceps in the Manuherikia River (New Zealand). We analysed the abundance of each trematode infrapopulation as a function of distance from the river junction and fish size by generalized linear models. Our results supported the existence of a longitudinal gradient in trematode abundance along the river with a decreasing downstream-to-upstream continuum. This applied to 3 out of the 4 trematode species studied, suggesting that this might be a common pattern in river populations. Thus, the unidirectional river flow and a major process like drift in lotic systems, that influences the dynamics and distribution of invertebrate hosts, can also affect trematodes. Host properties like habitat preference, and parasite traits, particularly those related to transmission mode can influence the strength of the observed gradient, as may other environmental and biotic factors.
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26
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Duffy MA, Ochs JH, Penczykowski RM, Civitello DJ, Klausmeier CA, Hall SR. Ecological context influences epidemic size and parasite-driven evolution. Science 2012; 335:1636-8. [PMID: 22461614 DOI: 10.1126/science.1215429] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The occurrence and magnitude of disease outbreaks can strongly influence host evolution. In particular, when hosts face a resistance-fecundity trade-off, they might evolve increased resistance to infection during larger epidemics but increased susceptibility during smaller ones. We tested this theoretical prediction by using a zooplankton-yeast host-parasite system in which ecological factors determine epidemic size. Lakes with high productivity and low predation pressure had large yeast epidemics; during these outbreaks, hosts became more resistant to infection. However, with low productivity and high predation, epidemics remained small and hosts evolved increased susceptibility. Thus, by modulating disease outbreaks, ecological context (productivity and predation) shaped host evolution during epidemics. Consequently, anthropogenic alteration of productivity and predation might strongly influence both ecological and evolutionary outcomes of disease.
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Affiliation(s)
- Meghan A Duffy
- School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230, USA.
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27
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Tucker AJ, Williamson CE. Lakes in a New Light: Indirect Effects of Ultraviolet Radiation. ACTA ACUST UNITED AC 2011. [DOI: 10.1608/frj-4.2.474] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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28
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Overholt EP, Hall SR, Williamson CE, Meikle CK, Duffy MA, Cáceres CE. Solar radiation decreases parasitism in Daphnia. Ecol Lett 2011; 15:47-54. [PMID: 22034950 DOI: 10.1111/j.1461-0248.2011.01707.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Climate change and variation in atmospheric ozone are influencing the intensity of ultraviolet radiation (UVR) reaching ecosystems. Changing UVR regimes, in turn, may alter epidemics of infectious disease. This possibility hinges on the sensitivity of epidemiologically relevant traits of host and parasite to UVR. We address this issue using a planktonic system (a zooplankton host, Daphnia dentifera, and its virulent fungal parasite, Metschnikowia bicuspidata). Controlled laboratory experiments, coupled with in situ field incubations of spores, revealed that quite low levels of UVR (as well as longer wavelength light) sharply reduced the infectivity of fungal spores but did not affect host susceptibility to infection. The parasite's sensitivity to solar radiation may underlie patterns in a lake survey: higher penetration of solar radiation into lakes correlated with smaller epidemics that started later in autumn (as incident sunlight declined). Thus, solar radiation, by diminishing infectivity of the parasite, may potently reduce disease.
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Affiliation(s)
- Erin P Overholt
- Department of Zoology, Miami University, Oxford, OH 45056, USA.
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29
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Duffy MA, Housley JM, Penczykowski RM, Cáceres CE, Hall SR. Unhealthy herds: indirect effects of predators enhance two drivers of disease spread. Funct Ecol 2011. [DOI: 10.1111/j.1365-2435.2011.01872.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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30
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Epidemic size determines population-level effects of fungal parasites on Daphnia hosts. Oecologia 2011; 166:833-42. [PMID: 21305322 DOI: 10.1007/s00442-011-1905-4] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2010] [Accepted: 01/03/2011] [Indexed: 10/18/2022]
Abstract
Parasites frequently reduce the fecundity, growth, and survival of individual hosts. How often do these virulent effects reduce the density of host populations? Spectacular examples show that recently invaded parasites can severely impact host populations--but what about parasites persisting long-term in host populations? We have addressed this issue using a zooplankton host (Daphnia dentifera) that becomes infected with a fungal microparasite (Metschnikowia bicuspidata). We combined observations of epidemics in nine lakes over 6 years, fine-scale sampling of three epidemics, and a mesocosm experiment. Most epidemics remained small (<10% maximum prevalence) and exerted little influence on host densities. However, larger epidemics more severely depressed the populations of their hosts. These large/severe epidemics started and peaked earlier than smaller/benign ones. The larger epidemics also exerted particularly negative effects on host densities at certain lags, reflecting the delayed consequences of infection on fecundity reduction and host mortality. Notably, negative effects on the juvenile stage class manifested later than those on the adult stage class. The results of the experiment further emphasized depression of host density by the fungus, especially on the density of the juvenile stage class. Consequently, this common parasite reduces the density of host populations when conditions foster larger outbreaks characterized by an earlier start and earlier peak. Given these considerable effects on host density seen in a number of large epidemics, parasitism may sometimes rank highly among other factors (predation, resource availability) driving the population dynamics of these hosts.
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31
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Duffy MA, Cáceres CE, Hall SR, Tessier AJ, Ives AR. Temporal, spatial, and between-host comparisons of patterns of parasitism in lake zooplankton. Ecology 2010; 91:3322-31. [PMID: 21141193 DOI: 10.1890/09-1611.1] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In nature, multiple parasite species infect multiple host species and are influenced by processes operating across different spatial and temporal scales. Data sets incorporating these complexities offer exciting opportunities to examine factors that shape epidemics. We present a method using generalized linear mixed models in a multilevel modeling framework to analyze patterns of variances and correlations in binomially distributed prevalence data. We then apply it to a multi-lake, multiyear data set involving two Daphnia host species and nine microparasite species. We found that the largest source of variation in parasite prevalence was the species identities of host-parasite pairs, indicating strong host-parasite specificity. Within host-parasite combinations, spatial variation (among lakes) exceeded interannual variation. This suggests that factors promoting differences among lakes (e.g., habitat characteristics and species interactions) better explain variation in peak infection prevalence in our data set than factors driving differences among years (e.g., climate). Prevalences of parasites in D. dentifera were more positively correlated than those for D. pulicaria, suggesting that similar factors influenced epidemic size among parasites in D. dentifera. Overall, this study demonstrates a method for parsing patterns of variation and covariation in infection prevalence data, providing greater insight into the relative importance of different underlying drivers of parasitism.
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Affiliation(s)
- Meghan A Duffy
- School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332-0230, USA.
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32
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Schoebel CN, Wolinska J, Spaak P. Higher parasite resistance in Daphnia populations with recent epidemics. J Evol Biol 2010; 23:2370-6. [PMID: 20825550 DOI: 10.1111/j.1420-9101.2010.02097.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- C N Schoebel
- Eawag, Aquatic Ecology, Dübendorf, Switzerland & IBZ, ETH-Zürich, Switzerland.
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