1
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Greenspan SE, Roznik EA, Edwards L, Duffy R, Berger L, Bower DS, Pike DA, Schwarzkopf L, Alford RA. Constant-temperature predictions underestimate growth of a fungal amphibian pathogen under individual host thermal profiles. J Therm Biol 2023; 111:103394. [PMID: 36585075 DOI: 10.1016/j.jtherbio.2022.103394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2022] [Revised: 10/29/2022] [Accepted: 11/22/2022] [Indexed: 12/12/2022]
Abstract
Ectotherm body temperatures fluctuate with environmental variability and host behavior, which may influence host-pathogen interactions. Fungal pathogens are a major threat to ectotherms and may be highly responsive to the fluctuating thermal profiles of individual hosts, especially cool-loving fungi exposed to high host temperatures. However, most studies estimate pathogen thermal performance based on averages of host or surrogate environmental temperatures, potentially missing effects of short-term host temperature shifts such as daily or hourly heat spikes. We recorded individual thermal profiles of Australian rainforest frogs using temperature-sensitive radio-transmitters. We then reproduced a subset of individual thermal profiles in growth chambers containing cultures of the near-global amphibian pathogen Batrachochytrium dendrobatidis (Bd) to investigate how realistic host temperature profiles affect Bd growth. We focused on thermal profiles that exceed the thermal optimum of Bd because the effects of realistic heat spikes on Bd growth are unresolved. Our laboratory incubation experiment revealed that Bd growth varied in response to relatively small differences in heat spike characteristics of individual frog thermal profiles, such as a single degree or a few hours, highlighting the importance of individual host behaviors in predicting population-level disease dynamics. The fungus also grew better than predicted under the most extreme and unpredictable frog temperature profile, recovering from two days of extreme (nearly 32 °C) heat spikes without negative effects on overall growth, suggesting we are underestimating the growth potential of the pathogen in nature. Combined with the previous finding that Bd reduces host heat tolerance, our study suggests that this pathogen may carry a competitive edge over hosts in the face of anthropogenic climate change.
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Affiliation(s)
- Sasha E Greenspan
- College of Science and Engineering, James Cook University, Townsville, Queensland, 4811, Australia; Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, 35487, USA.
| | | | - Lexie Edwards
- College of Science and Engineering, James Cook University, Townsville, Queensland, 4811, Australia
| | - Richard Duffy
- College of Science and Engineering, James Cook University, Townsville, Queensland, 4811, Australia
| | - Lee Berger
- One Health Research Group, Melbourne Veterinary School, University of Melbourne, Werribee, Victoria, 3030, Australia
| | - Deborah S Bower
- Zoology Discipline, University of New England, Armidale, New South Wales, 2350, Australia
| | - David A Pike
- Department of Biology, Rhodes College, Memphis, TN, 38112, USA
| | - Lin Schwarzkopf
- College of Science and Engineering, James Cook University, Townsville, Queensland, 4811, Australia
| | - Ross A Alford
- College of Science and Engineering, James Cook University, Townsville, Queensland, 4811, Australia
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2
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McCaffery R, Russell RE, Hossack BR. Enigmatic Near‐Extirpation in a Boreal Toad Metapopulation in Northwestern Montana. J Wildl Manage 2021. [DOI: 10.1002/jwmg.22054] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Rebecca McCaffery
- U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center 600 East Park Ave Port Angeles WA 98362 USA
| | - Robin E. Russell
- U.S. Geological Survey, National Wildlife Health Center Madison WI 53711 USA
| | - Blake R. Hossack
- U.S. Geological Survey, Northern Rocky Mountain Science Center, Missoula, MT 59801, USA and Wildlife Biology Program, W. A. Franke College of Forestry and Conservation, University of Montana Missoula MT 59801 USA
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3
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Newcastle disease virus transmission dynamics in wild peridomestic birds in the United Arab Emirates. Sci Rep 2021; 11:3491. [PMID: 33568682 PMCID: PMC7876026 DOI: 10.1038/s41598-020-79184-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Accepted: 11/11/2020] [Indexed: 11/15/2022] Open
Abstract
To understand the dynamics of a pathogen in an animal population, one must assess how the infection status of individuals changes over time. With wild animals, this can be very challenging because individuals can be difficult to trap and sample, even more so since they are tested with imperfect diagnostic techniques. Multi-event capture-recapture models allow analysing longitudinal capture data of individuals whose infection status is assessed using imperfect tests. In this study, we used a two-year dataset from a longitudinal field study of peridomestic wild bird populations in the United Arab Emirates during which thousands of birds from various species were captured, sampled and tested for Newcastle disease virus exposure using a serological test. We developed a multi-event capture-recapture model to estimate important demographic and epidemiological parameters of the disease. The modelling outputs provided important insights into the understanding of Newcastle disease dynamics in peridomestics birds, which varies according to ecological and epidemiological parameters, and useful information in terms of surveillance strategies. To our knowledge, this study is the first attempt to model the dynamics of Newcastle disease in wild bird populations by combining longitudinal capture data and serological test results. Overall, it showcased that multi-event capture-recapture models represent a suitable method to analyse imperfect capture data and make reliable inferences on infectious disease dynamics in wild populations.
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4
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Brannelly LA, McCallum HI, Grogan LF, Briggs CJ, Ribas MP, Hollanders M, Sasso T, Familiar López M, Newell DA, Kilpatrick AM. Mechanisms underlying host persistence following amphibian disease emergence determine appropriate management strategies. Ecol Lett 2020; 24:130-148. [PMID: 33067922 DOI: 10.1111/ele.13621] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Revised: 06/18/2020] [Accepted: 09/08/2020] [Indexed: 12/19/2022]
Abstract
Emerging infectious diseases have caused many species declines, changes in communities and even extinctions. There are also many species that persist following devastating declines due to disease. The broad mechanisms that enable host persistence following declines include evolution of resistance or tolerance, changes in immunity and behaviour, compensatory recruitment, pathogen attenuation, environmental refugia, density-dependent transmission and changes in community composition. Here we examine the case of chytridiomycosis, the most important wildlife disease of the past century. We review the full breadth of mechanisms allowing host persistence, and synthesise research on host, pathogen, environmental and community factors driving persistence following chytridiomycosis-related declines and overview the current evidence and the information required to support each mechanism. We found that for most species the mechanisms facilitating persistence have not been identified. We illustrate how the mechanisms that drive long-term host population dynamics determine the most effective conservation management strategies. Therefore, understanding mechanisms of host persistence is important because many species continue to be threatened by disease, some of which will require intervention. The conceptual framework we describe is broadly applicable to other novel disease systems.
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Affiliation(s)
- Laura A Brannelly
- Veterinary BioSciences, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Werribee, Vic, 3030, Australia
| | - Hamish I McCallum
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, Qld., 4111, Australia
| | - Laura F Grogan
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, Qld., 4111, Australia.,Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia
| | - Cheryl J Briggs
- Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, 93106, USA
| | - Maria P Ribas
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia.,Wildlife Conservation Medicine Research Group, Departament de Medicina i Cirurgia Animals, Universitat Autònoma de Barcelona, Bellaterra, 08193, Spain
| | - Matthijs Hollanders
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia
| | - Thais Sasso
- Environmental Futures Research Institute and School of Environment and Science, Griffith University, Nathan, Qld., 4111, Australia
| | - Mariel Familiar López
- School of Environment and Sciences, Griffith University, Gold Coast, Qld., 4215, Australia
| | - David A Newell
- Forest Research Centre, School of Environment, Science and Engineering, Southern Cross University, Lismore, NSW, 2480, Australia
| | - Auston M Kilpatrick
- Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Santa Cruz, CA, 95064, USA
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5
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Meurling S, Kärvemo S, Chondrelli N, Cortazar Chinarro M, Åhlen D, Brookes L, Nyström P, Stenberg M, Garner TWJ, Höglund J, Laurila A. Occurrence of Batrachochytrium dendrobatidis in Sweden: higher infection prevalence in southern species. DISEASES OF AQUATIC ORGANISMS 2020; 140:209-218. [PMID: 32880378 DOI: 10.3354/dao03502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused worldwide declines in amphibian populations. While Bd is widespread in southern and central Europe, its occurrence and distribution in northernmost Europe is mostly unknown. We surveyed for Bd in breeding anurans in Sweden by sampling 1917 amphibians from 101 localities and 3 regions in Sweden (southern, northern and central). We found that Bd was widespread in southern and central Sweden, occurring in all 9 investigated species and in 45.5% of the 101 localities with an overall prevalence of 13.8%. No infected individuals were found in the 4 northern sites sampled. The records from central Sweden represent the northernmost records of Bd in Europe. While the proportion of sites positive for Bd was similar between the southern and central regions, prevalence was much higher in the southern region. This was because southern species with a distribution mainly restricted to southernmost Sweden had a higher prevalence than widespread generalist species. The nationally red-listed green toad Bufotes variabilis and the fire-bellied toad Bombina bombina had the highest prevalence (61.4 and 48.9%, respectively). Across species, Bd prevalence was strongly positively, correlated with water temperature at the start of egg laying. However, no individuals showing visual signs of chytridiomycosis were found in the field. These results indicate that Bd is widespread and common in southern and central Sweden with southern species, breeding in higher temperatures and with longer breeding periods, having higher prevalence. However, the impact of Bd on amphibian populations in northernmost Europe remains unknown.
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Affiliation(s)
- Sara Meurling
- Animal Ecology/ Department of Ecology and Genetics, Uppsala University, Norbyvägen 18D, 75236 Uppsala, Sweden
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6
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Rollins-Smith LA. Global Amphibian Declines, Disease, and the Ongoing Battle between Batrachochytrium Fungi and the Immune System. HERPETOLOGICA 2020. [DOI: 10.1655/0018-0831-76.2.178] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Louise A. Rollins-Smith
- Departments of Pathology, Microbiology and Immunology and Pediatrics, Vanderbilt University School of Medicine, Nashville, TN 37232, USA Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235, USA
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7
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Muths E, Hossack B, Campbell Grant E, Pilliod D, Mosher B. Effects of Snowpack, Temperature, and Disease on Demography in a Wild Population of Amphibians. HERPETOLOGICA 2020. [DOI: 10.1655/0018-0831-76.2.132] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- E. Muths
- US Geological Survey, Fort Collins Science Center, 2150 Centre Avenue, Building C, Fort Collins, CO 80526, USA
| | - B.R. Hossack
- US Geological Survey, Northern Rocky Mountain Science Center, Wildlife Biology Program, University of Montana, Missoula, MT 59812, USA
| | - E.H. Campbell Grant
- US Geological Survey, Patuxent Wildlife Research Center, SO Conte Anadromous Fish Laboratory, One Migratory Way, Turners Falls, MA 01376, USA
| | - D.S. Pilliod
- US Geological Survey, Forest and Rangeland Ecosystem Science Center, 970 Lusk Street, Boise, ID 83706, USA
| | - B.A. Mosher
- University of Vermont, Rubenstein School of Environment and Natural Resources, Aiken Center, 81 Carrigan Drive, Burlington, VT 05405, USA
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8
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Kärvemo S, Wikström G, Widenfalk L, Höglund J, Laurila A. Chytrid fungus dynamics and infections associated with movement distances in a red‐listed amphibian. J Zool (1987) 2020. [DOI: 10.1111/jzo.12773] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- S. Kärvemo
- Department of Ecology Swedish University of Agricultural Sciences Uppsala Sweden
- Department of Ecology and Genetics/Animal Ecology Uppsala University Uppsala Sweden
| | - G. Wikström
- Department of Ecology and Genetics/Animal Ecology Uppsala University Uppsala Sweden
| | - L.A. Widenfalk
- Department of Ecology Swedish University of Agricultural Sciences Uppsala Sweden
- Greensway AB Uppsala Sweden
| | - J. Höglund
- Department of Ecology and Genetics/Animal Ecology Uppsala University Uppsala Sweden
| | - A. Laurila
- Department of Ecology and Genetics/Animal Ecology Uppsala University Uppsala Sweden
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9
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Bolom‐Huet R, Pineda E, Díaz‐Fleischer F, Muñoz‐Alonso AL, Galindo‐González J. Known and estimated distribution in Mexico of
Batrachochytrium dendrobatidis,
a pathogenic fungus of amphibians. Biotropica 2019. [DOI: 10.1111/btp.12697] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
| | - Eduardo Pineda
- Red de Biología y Conservación de Vertebrados Instituto de Ecología A. C. Xalapa Veracruz México
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10
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Disease and climate effects on individuals drive post‐reintroduction population dynamics of an endangered amphibian. Ecosphere 2018. [DOI: 10.1002/ecs2.2499] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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11
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Daversa DR, Monsalve-Carcaño C, Carrascal LM, Bosch J. Seasonal migrations, body temperature fluctuations, and infection dynamics in adult amphibians. PeerJ 2018; 6:e4698. [PMID: 29761041 PMCID: PMC5947160 DOI: 10.7717/peerj.4698] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2017] [Accepted: 04/12/2018] [Indexed: 12/22/2022] Open
Abstract
Risks of parasitism vary over time, with infection prevalence often fluctuating with seasonal changes in the annual cycle. Identifying the biological mechanisms underlying seasonality in infection can enable better prediction and prevention of future infection peaks. Obtaining longitudinal data on individual infections and traits across seasons throughout the annual cycle is perhaps the most effective means of achieving this aim, yet few studies have obtained such information for wildlife. Here, we tracked spiny common toads (Bufo spinosus) within and across annual cycles to assess seasonal variation in movement, body temperatures and infection from the fungal parasite, Batrachochytrium dendrobatidis (Bd). Across annual cycles, toads did not consistently sustain infections but instead gained and lost infections from year to year. Radio-tracking showed that infected toads lose infections during post-breeding migrations, and no toads contracted infection following migration, which may be one explanation for the inter-annual variability in Bd infections. We also found pronounced seasonal variation in toad body temperatures. Body temperatures approached 0 °C during winter hibernation but remained largely within the thermal tolerance range of Bd. These findings provide direct documentation of migratory recovery (i.e., loss of infection during migration) and escape in a wild population. The body temperature reductions that we observed during hibernation warrant further consideration into the role that this period plays in seasonal Bd dynamics.
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Affiliation(s)
- David R Daversa
- Institute for Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Camino Monsalve-Carcaño
- Department of Biogeography and Global Change, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain
| | - Luis M Carrascal
- Department of Biogeography and Global Change, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain
| | - Jaime Bosch
- Department of Biogeography and Global Change, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain.,Centro de Investigación, Seguimiento y Evaluación, Parque Nacional de la Sierra de Guadarrama, Rascafría, Madrid, Spain
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12
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Valenzuela-Sánchez A, Schmidt BR, Uribe-Rivera DE, Costas F, Cunningham AA, Soto-Azat C. Cryptic disease-induced mortality may cause host extinction in an apparently stable host-parasite system. Proc Biol Sci 2018; 284:rspb.2017.1176. [PMID: 28954907 DOI: 10.1098/rspb.2017.1176] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 08/25/2017] [Indexed: 11/12/2022] Open
Abstract
The decline of wildlife populations due to emerging infectious disease often shows a common pattern: the parasite invades a naive host population, producing epidemic disease and a population decline, sometimes with extirpation. Some susceptible host populations can survive the epidemic phase and persist with endemic parasitic infection. Understanding host-parasite dynamics leading to persistence of the system is imperative to adequately inform conservation practice. Here we combine field data, statistical and mathematical modelling to explore the dynamics of the apparently stable Rhinoderma darwinii-Batrachochytrium dendrobatidis (Bd) system. Our results indicate that Bd-induced population extirpation may occur even in the absence of epidemics and where parasite prevalence is relatively low. These empirical findings are consistent with previous theoretical predictions showing that highly pathogenic parasites are able to regulate host populations even at extremely low prevalence, highlighting that disease threats should be investigated as a cause of population declines even in the absence of an overt increase in mortality.
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Affiliation(s)
- Andrés Valenzuela-Sánchez
- Centro de Investigación para la Sustentabilidad, Facultad de Ecología y Recursos Naturales, Universidad Andres Bello, República 440, Santiago, Chile .,ONG Ranita de Darwin, Nataniel Cox 152, Santiago, Chile.,Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK
| | - Benedikt R Schmidt
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland.,Info Fauna KARCH, Passage Maximilien-de-Meuron 6, 2000 Neuchâtel, Switzerland
| | | | | | - Andrew A Cunningham
- Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK
| | - Claudio Soto-Azat
- Centro de Investigación para la Sustentabilidad, Facultad de Ecología y Recursos Naturales, Universidad Andres Bello, República 440, Santiago, Chile
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13
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Greenspan SE, Bower DS, Webb RJ, Berger L, Rudd D, Schwarzkopf L, Alford RA. White blood cell profiles in amphibians help to explain disease susceptibility following temperature shifts. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2017; 77:280-286. [PMID: 28870450 DOI: 10.1016/j.dci.2017.08.018] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Revised: 08/30/2017] [Accepted: 08/30/2017] [Indexed: 06/07/2023]
Abstract
Temperature variability, and in particular temperature decreases, can increase susceptibility of amphibians to infections by the fungus Batrachochytrium dendrobatidis (Bd). However, the effects of temperature shifts on the immune systems of Bd-infected amphibians are unresolved. We acclimated frogs to 16 °C and 26 °C (baseline), simultaneously transferred them to an intermediate temperature (21 °C) and inoculated them with Bd (treatment), and tracked their infection levels and white blood cell profiles over six weeks. Average weekly infection loads were consistently higher in 26°C-history frogs, a group that experienced a 5 °C temperature decrease, than in 16°C-history frogs, a group that experienced a 5 °C temperature increase, but this pattern only approached statistical significance. The 16°C-acclimated frogs had high neutrophil:lymphocyte (N:L) ratios (suggestive of a hematopoietic stress response) at baseline, which were conserved post-treatment. In contrast, the 26°C-acclimated frogs had low N:L ratios at baseline which reversed to high N:L ratios post-treatment (suggestive of immune system activation). Our results suggest that infections were less physiologically taxing for the 16°C-history frogs than the 26°C-history frogs because they had already adjusted immune parameters in response to challenging conditions (cold). Our findings provide a possible mechanistic explanation for observations that amphibians are more susceptible to Bd infection following temperature decreases compared to increases and underscore the consensus that increased temperature variability associated with climate change may increase the impact of infectious diseases.
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Affiliation(s)
- Sasha E Greenspan
- College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia.
| | - Deborah S Bower
- College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia
| | - Rebecca J Webb
- One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland 4811, Australia
| | - Lee Berger
- One Health Research Group, College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland 4811, Australia
| | - Donna Rudd
- College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, Queensland 4811, Australia
| | - Lin Schwarzkopf
- College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia
| | - Ross A Alford
- College of Science and Engineering, James Cook University, Townsville, Queensland 4811, Australia
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14
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Bower DS, Mengersen K, Alford RA, Schwarzkopf L. Using a Bayesian network to clarify areas requiring research in a host-pathogen system. CONSERVATION BIOLOGY : THE JOURNAL OF THE SOCIETY FOR CONSERVATION BIOLOGY 2017; 31:1373-1382. [PMID: 28464282 DOI: 10.1111/cobi.12950] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Revised: 03/24/2017] [Accepted: 04/17/2017] [Indexed: 06/07/2023]
Abstract
Bayesian network analyses can be used to interactively change the strength of effect of variables in a model to explore complex relationships in new ways. In doing so, they allow one to identify influential nodes that are not well studied empirically so that future research can be prioritized. We identified relationships in host and pathogen biology to examine disease-driven declines of amphibians associated with amphibian chytrid fungus (Batrachochytrium dendrobatidis). We constructed a Bayesian network consisting of behavioral, genetic, physiological, and environmental variables that influence disease and used them to predict host population trends. We varied the impacts of specific variables in the model to reveal factors with the most influence on host population trend. The behavior of the nodes (the way in which the variables probabilistically responded to changes in states of the parents, which are the nodes or variables that directly influenced them in the graphical model) was consistent with published results. The frog population had a 49% probability of decline when all states were set at their original values, and this probability increased when body temperatures were cold, the immune system was not suppressing infection, and the ambient environment was conducive to growth of B. dendrobatidis. These findings suggest the construction of our model reflected the complex relationships characteristic of host-pathogen interactions. Changes to climatic variables alone did not strongly influence the probability of population decline, which suggests that climate interacts with other factors such as the capacity of the frog immune system to suppress disease. Changes to the adaptive immune system and disease reservoirs had a large effect on the population trend, but there was little empirical information available for model construction. Our model inputs can be used as a base to examine other systems, and our results show that such analyses are useful tools for reviewing existing literature, identifying links poorly supported by evidence, and understanding complexities in emerging infectious-disease systems.
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Affiliation(s)
- D S Bower
- College of Science and Engineering, James Cook University, 1 James Cook Drive, Douglas, QLD, 4811, Australia
| | - K Mengersen
- Faculty of Science and Engineering, Mathematical Sciences, Statistical Science, Queensland University of Technology, Brisbane, QLD, 4000, Australia
| | - R A Alford
- College of Science and Engineering, James Cook University, 1 James Cook Drive, Douglas, QLD, 4811, Australia
| | - L Schwarzkopf
- College of Science and Engineering, James Cook University, 1 James Cook Drive, Douglas, QLD, 4811, Australia
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15
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Greenberg DA, Palen WJ, Mooers AØ. Amphibian species traits, evolutionary history and environment predict Batrachochytrium dendrobatidis infection patterns, but not extinction risk. Evol Appl 2017; 10:1130-1145. [PMID: 29151866 PMCID: PMC5680631 DOI: 10.1111/eva.12520] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 07/18/2017] [Indexed: 12/17/2022] Open
Abstract
The fungal pathogen Batrachochytrium dendrobatidis (B. dendrobatidis) has emerged as a major agent of amphibian extinction, requiring conservation intervention for many susceptible species. Identifying susceptible species is challenging, but many aspects of species biology are predicted to influence the evolution of host resistance, tolerance, or avoidance strategies towards disease. In turn, we may expect species exhibiting these distinct strategies to differ in their ability to survive epizootic disease outbreaks. Here, we test for phylogenetic and trait-based patterns of B. dendrobatidis infection risk and infection intensity among 302 amphibian species by compiling a global data set of B. dendrobatidis infection surveys across 95 sites. We then use best-fit models that associate traits, taxonomy and environment with B. dendrobatidis infection risk and intensity to predict host disease mitigation strategies (tolerance, resistance, avoidance) for 122 Neotropical amphibian species that experienced epizootic B. dendrobatidis outbreaks, and noted species persistence or extinction from these events. Aspects of amphibian species life history, habitat use and climatic niche were consistently linked to variation in B. dendrobatidis infection patterns across sites around the world. However, predicted B. dendrobatidis infection risk and intensity based on site environment and species traits did not reveal a consistent pattern between the predicted host disease mitigation strategy and extinction outcome. This suggests that either tolerant or resistant species may have no advantage in ameliorating disease during epizootic events, or that other factors drive the persistence of amphibian populations during chytridiomycosis outbreaks. These results suggest that using a trait-based approach may allow us to identify species with resistance or tolerance to endemic B. dendrobatidis infections, but that this approach may be insufficient to ultimately identify species at risk of extinction from epizootics.
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Affiliation(s)
- Dan A. Greenberg
- Department of Biological Sciences and Crawford Laboratory of Evolutionary StudiesSimon Fraser UniversityBurnabyBCCanada
- Department of Biological Sciences and Earth to Ocean Research GroupSimon Fraser UniversityBurnabyBCCanada
| | - Wendy J. Palen
- Department of Biological Sciences and Earth to Ocean Research GroupSimon Fraser UniversityBurnabyBCCanada
| | - Arne Ø. Mooers
- Department of Biological Sciences and Crawford Laboratory of Evolutionary StudiesSimon Fraser UniversityBurnabyBCCanada
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16
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Whitfield SM, Alvarado G, Abarca J, Zumbado H, Zuñiga I, Wainwright M, Kerby J. Differential patterns of Batrachochytrium dendrobatidis infection in relict amphibian populations following severe disease-associated declines. DISEASES OF AQUATIC ORGANISMS 2017; 126:33-41. [PMID: 28930083 DOI: 10.3354/dao03154] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Global amphibian biodiversity has declined dramatically in the past 4 decades, and many amphibian species have declined to near extinction as a result of emergence of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). However, persistent or recovering populations of several amphibian species have recently been rediscovered, and such populations may illustrate how amphibian species that are highly susceptible to chytridiomycosis may survive in the presence of Bd. We conducted field surveys for Bd infection in 7 species of Costa Rican amphibians (all species that have declined to near extinction but for which isolated populations persist) to characterize infection profiles in highly Bd-susceptible amphibians post-decline. We found highly variable patterns in infection, with some species showing low prevalence (~10%) and low infection intensity and others showing high infection prevalence (>80%) and either low or high infection intensity. Across sites, infection rates were negatively associated with mean annual precipitation, and infection intensity across sites was negatively associated with mean average temperatures. Our results illustrate that even the most Bd-susceptible amphibians can persist in Bd-enzootic ecosystems, and that multiple ecological or evolutionary mechanisms likely exist for host-pathogen co-existence between Bd and the most Bd-susceptible amphibian species. Continued monitoring of these populations is necessary to evaluate population trends (continuing decline, stability, or population growth). These results should inform efforts to mitigate impacts of Bd on amphibians in the field.
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Scheele BC, Skerratt LF, Hunter DA, Banks SC, Pierson JC, Driscoll DA, Byrne PG, Berger L. Disease-associated change in an amphibian life-history trait. Oecologia 2017; 184:825-833. [DOI: 10.1007/s00442-017-3911-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Accepted: 07/06/2017] [Indexed: 11/30/2022]
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Greenspan SE, Roznik EA, Schwarzkopf L, Alford RA, Pike DA. Robust calling performance in frogs infected by a deadly fungal pathogen. Ecol Evol 2016; 6:5964-72. [PMID: 27547369 PMCID: PMC4983606 DOI: 10.1002/ece3.2256] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 05/25/2016] [Indexed: 11/11/2022] Open
Abstract
Reproduction is an energetically costly behavior for many organisms, including species with mating systems in which males call to attract females. In these species, calling males can often attract more females by displaying more often, with higher intensity, or at certain frequencies. Male frogs attract females almost exclusively by calling, and we know little about how pathogens, including the globally devastating fungus, Batrachochytrium dendrobatidis, influence calling effort and call traits. A previous study demonstrated that the nightly probability of calling by male treefrogs, Litoria rheocola, is elevated when they are in good body condition and are infected by B. dendrobatidis. This suggests that infections may cause males to increase their present investment in mate attraction to compensate for potential decreases in future reproduction. However, if infection by B. dendrobatidis decreases the attractiveness of their calls, infected males might experience decreased reproductive success despite increases in calling effort. We examined whether calls emitted by L. rheocola infected by B. dendrobatidis differed from those of uninfected individuals in duration, pulse rate, dominant frequency, call rate, or intercall interval, the attributes commonly linked to mate choice. We found no effects of fungal infection status or infection intensity on any call attribute. Our results indicate that infected males produce calls similar in all the qualities we measured to those of uninfected males. It is therefore likely that the calls of infected and uninfected males should be equally attractive to females. The increased nightly probability of calling previously demonstrated for infected males in good condition may therefore lead to greater reproductive success than that of uninfected males. This could reduce the effectiveness of natural selection for resistance to infection, but could increase the effectiveness of selection for infection tolerance, the ability to limit the harm caused by infection, such as reductions in body condition.
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Affiliation(s)
- Sasha E Greenspan
- College of Marine and Environmental Sciences James Cook University Townsville Queensland 4811 Australia
| | - Elizabeth A Roznik
- College of Marine and Environmental Sciences James Cook University Townsville Queensland 4811 Australia; Present address: Department of Integrative Biology University of South Florida Tampa Florida 33620
| | - Lin Schwarzkopf
- College of Marine and Environmental Sciences James Cook University Townsville Queensland 4811 Australia
| | - Ross A Alford
- College of Marine and Environmental Sciences James Cook University Townsville Queensland 4811 Australia
| | - David A Pike
- College of Marine and Environmental Sciences James Cook University Townsville Queensland 4811 Australia; Present address: Department of Integrative Biology University of South Florida Tampa Florida 33620
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