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Amphibian Declines


Chytridiomycosis. Ventral skin of upper hind limb of Atelopus varius from western Panama. Two sporangia (spore-containing bodies of Batrachochytrium sp.) containing numerous zoospores are visible within cells of the stratum corneum. Each flask-shaped sporangium has a single characteristic discharge tube (arrow) at the skin surface. Exiting zoospores are visible in the discharge tubes of both sporangia. (source: Daszak P, Berger L, Cunningham A, Hyatt A, Green D, Speare R. Emerging Infectious Diseases and Amphibian Population Declines. Emerg Infect Dis. 1999 Nov-Dec.)

Research and Publications 

Amphibians are the most threatened vertebrate taxon on the planet.  Nearly one-third of all amphibians are threatened with extinction.  There are many contributing factors to amphibian declines including habitat loss, disease (e.g. amphibian chytrid fungus, trematode, and ranaviral infections), climate change, and pollution.  We are attempting to understand and curb factors contributing to amphibian declines, as well as elucidate the importance of amphibians to ecosystems. In fact, the Rohr lab is actively researching the feasibility of developing a vaccination to curb chytrid fungal-related amphibian declines.

Sample Publications

Rumschlag, S.L., Halstead, N.T., Hoverman, J.T., Raffel, T.R., Carrick, H.J., Hudson, P.J., Rohr, J.R. 2019. Effects of pesticides on exposure and susceptibility to parasites can be generalized to pesticide class and type in aquatic communities. Ecology Letters 22: 962-972 Cover article


Cohen, J.M., McMahon, T.A., Ramsay, C., Roznik, E.A., Sauer, E.L., Bessler, S., Civitello, D.J., Delius, B.K., Halstead, N.T., Knutie, S.A., Nguyen, K., Ortega, C.N., Sears, B., Venesky, M.D., Young, S., Rohr, J.R. 2019. Impacts of thermal mismatches on chytrid fungus Batrachochytrium dendrobatidis prevalence are moderated by life stage, body size, elevation and latitude. Ecology Letters 22: 817-825 Cover article


Haggerty, C.J.E., Crisman, T.L., Rohr, J.R. 2019. Effects of forestry-driven changes to groundcover and soil moisture on amphibian desiccation, dispersal, and survival. Ecological Applications 29: e01870. 10.1002/eap.1870


Cohen, J.M., Civitello, D.J., Venesky, M.D.†, McMahon, T.A., Rohr, J.R. 2019. An interaction between climate change and infectious disease drove widespread amphibian declines. Global Change Biology 25: 927–937



Rumschlag, S.L., Rohr, J.R. 2018. The influence of pesticide use on amphibian chytrid fungal infections varies with host life stage across broad spatial scales. Global Ecology and Biogeography 27: 1277-1287


Sauer, E.L., Fuller, R.C., Richards-Zawacki, C.L., Sonn, J., Sperry, J.H., Rohr, J.R. 2018. Variation in individual temperature preferences, not behavioral fever, affects susceptibility to chytridiomycosis in amphibians. Proceedings of the Royal Society of London B 285: 20181111.


Rohr, J.R., Civitello, D.J., Cohen, J.M., Roznik, E.A., Sinervo, B., Dell, A.I. 2018. The complex drivers of thermal acclimation and breadth in ectotherms. Ecology Letters 21: 1425–1439 Cover article


Tornabene, B.J., Blaustein, A.R., Briggs, C.J., Rohr, J.R., Johnson, P.T.J., Hoverman, J.T. 2018. The influence of landscape and environmental factors on ranavirus epidemiology in a California amphibian assemblage. Freshwater Biology 63: 639–651


Stutz, W.E., Blaustein, A.R., Briggs, C.J., Hoverman, J.T., Rohr, J.R., Johnson, P.T.J. 2018. Using multi-response models to investigate pathogen coinfections across scales: insights from emerging diseases of amphibians. Methods in Ecology and Evolution 9: 1109–1120


Knutie, S.A., Gabor, C., Kohl, K.D., Rohr, J.R. 2018. Do host-associated gut microbiota mediate the effect of an herbicide on disease risk in frogs? Journal of Animal Ecology 87: 489-499


Gabor, C.R., Roznik, E.A., Knutie, S.A., Rohr, J.R. 2018. Are the adverse effects of stressors on amphibians mediated by their effects on stress hormones? Oecologia 186: 393-404


Rohr, J.R. 2018. Atrazine and amphibians: A story of profits, controversy and animus. In: Dominick A. DellaSala, and Michael I. Goldstein (eds.) The Encyclopedia of the Anthropocene 5: 141-148


Knutie, S.A., Shea, L.A., Kupselaitis, M., Wilkinson, C.L., Kohl, K.D., Rohr, J.R. 2017. Early-life diet affects host microbiota and later-life defenses against parasites in frogs. Integrative and Comparative Biology 57: 732-742


Rohr, J.R., Brown J., Battaglin, W.A., McMahon, T.A., Relyea, R.A. 2017. A pesticide paradox: Fungicides indirectly increase fungal infections. Ecological Applications 27: 2290-2302


Jayawardena, U.A., Rohr, J.R., Amerasinghe, P.H., Navaratne, A.N., Rajakaruna, R.S. 2017. Effects of agrochemicals on disease severity of Acanthostomum burminis infections (Digenea: Trematoda) in the Asian common toad, Duttaphrynus melanostictus. BMC Zoology 2: 13. doi: 10.1186/s40850-017-0022-1


Knutie, S.A., Wilkinson, C.L., Kohl, K.D., Rohr, J.R. 2017. Early-life disruption of amphibian microbiota decreases later-life resistance to parasites. Nature Communications 8: 86. doi:10.1038/s41467-017-00119-0 Altmetric score of 126, 97th percentile


Voyles, J., Johnson, L.R., Rochelle, K., Barron, C., Miller, D., Minster, J., Rohr. J.R., Rosenblum, E.B. 2017. Diversity in growth patterns among strains of the lethal fungal pathogen Batrachochytrium dendrobatidis across extended thermal optima. Oecologia 184: 363-373


McMahon, T.A., Rohr, J.R., Bernal, X. 2017. Light and noise pollution interact to disrupt interspecific interactions. Ecology 98: 1290–1299


McMahon, T.A., Boughton, R.K., Martin, L.B., Rohr. J.R. 2017. Exposure to an herbicide non-linearly affected corticosterone production in tadpoles. Journal of Herpetology 51: 270-273


Knutie, S.A., Wilkinson, C.L., Ortega, N., Rohr, J.R. 2017. Host resistance and tolerance of parasitic gut worms depend on resource availability. Oecologia 183: 1031-1040


Cohen, J.M., Venesky, M.D., Sauer, E.L., Civitello, D.J., McMahon, T.A., Roznik, E.A., Rohr, J.R. 2017. The thermal mismatch hypothesis explains outbreaks of an emerging infectious disease. Ecology Letters 20: 184–193 Cover Article, Featured in Nature: Sohn Hothouse of disease 543: S44–S46


Ehrsam, M., Knutie, S.A., Rohr, J.R. 2016. The herbicide atrazine induces hyperactivity and compromises tadpole detection of predator chemical cues. Environmental Toxicology and Chemistry 35: 2239-2244


Cohen, J., Civitello, D.J., Brace, A.J., Feichtinger, E., Ortega, N., Richardson, J.C., Sauer, E.L., Liu, X., Rohr, J.R. 2016. Spatial scale modulates the strength of ecological processes driving disease distributions. Proceedings of the National Academy of Sciences of the United States of America 113: E3359–E3364 doi:10.1073/pnas.1521657113 (this paper was a product of a graduate student project developed in a seminar course I taught with my postdoc on scale in ecology; Altmetric score of 53, 95th percentile)

         Awarded Best Graduate Student Paper by the Disease Ecology Section of the Ecological Society of America in 2016


Jayawardena, U.A., Rohr, J.R., Navaratne, A.N., Amerasinghe, P.H., Rajakaruna, R.S. 2016. Combined effects of pesticides and trematode infections on the hourglass tree frog Polypedates cruciger. EcoHealth 13: 111-122


Buck, J.C., Rohr, J.R., Blaustein, A.R. 2016. Effects of nutrient supplementation on host-pathogen dynamics of the amphibian chytrid fungus: a community approach. Freshwater Biology 61:110-120

McMahon, T.A., Rohr, J.R. 2015. Transition of chytrid fungus infection from mouthparts to hind limbs during amphibian metamorphosis. EcoHealth 12:188-193

Raffel, T.R., Halstead, N.T., McMahon, T.A., Davis, A.K., Rohr, J.R. 2015. Temperature variability and moisture synergistically interact to exacerbate an epizootic disease. Proceedings of the Royal Society of London B282:20142039

McMahon, T.A., Sears, B.F., Venesky, M.D., Brown, J.M., Deutsch, K., Halstead, N.T., Lentz, G., Tenouri, N., Young, S., Civitello, D.J., Ortega, N., Fites, J.S., Reinert, L.K., Rollins-Smith, L.A., Raffel, T.R., Rohr, J.R. 2014. Amphibians acquire resistance to live and dead fungus overcoming fungal immunosuppression. Nature 511:224-227 (cover photo and featured cover story; Altmetric score of 262, 99th percentile)

McMahon, T.A., Rohr, J.R. 2014. Trypan blue dye is an effective and inexpensive way to determine the viability of Batrachochytrium dendrobatidis zoospores. EcoHealth 11:164-167

Venesky, M.D., Liu, X., Sauer, E., Rohr, J.R. 2014. Linking manipulative experiments to field data to test the dilution effect. Journal of Animal Ecology 83:557-565

Venesky, M.D., Raffel, T.R, McMahon, T.A., Rohr, J.R. 2014. Confronting inconsistencies in the amphibian-chytridiomycosis system: implications for disease management. Biological Reviews 89:477-483

Rohr, J.R., Raffel, T.R., Halstead, N.T., McMahon, T.A., Johnson, S.A., Boughton, R.K., Martin, L.B. 2013. Early-life exposure to an herbicide has enduring effects on pathogen-induced mortality. Proceedings of the Royal Society of London B 280:20131502 (Altmetric score of 71)

McMahon, T.A., Romansic, J.M., Rohr, J.R. 2013. Non-monotonic and monotonic effects of pesticides on the pathogenic fungus Batrachochytrium dendrobatidis in culture and on tadpoles. Environmental Science and Technology 47:7958-7964

Rohr, J.R., Palmer, B.D. 2013. Climate change, multiple stressors, and the decline of ectotherms. Conservation Biology 27:741-751

Li, Y., Cohen, J.M., Rohr, J.R. 2013. A review and synthesis of the effects of climate change on amphibians. Integrative Zoology 8:145-161 Ranked as one of the four best papers published in the journal in 2013

Liu, X., Rohr, J.R., Li, Y. 2013. Climate, vegetation, introduced hosts and trade shape a global wildlife pandemic. Proceedings of the Royal Society of London B 280: 20122506double star recommendation by Faculty 1000

Raffel, T.R., Romansic, J.M., Halstead, N.T., McMahon, T.A., Venesky, M.D., Rohr, J.R. 2013. Disease and thermal acclimation in a more variable and unpredictable climate. Nature Climate Change 3: 146-151 (featured in News and Views, article by Ross Alford:; Altmetric score of 36, 97th percentile)

McMahon, T.A., Brannelly, L.A., Chatfield, M.W.H., Johnson, P.T.J., Joseph, M.B., McKenzie, V.J., Richards-Zawacki, C.L., Venesky, M.D., Rohr, J.R. 2013. Chytrid fungus Batrachochytrium dendrobatidis has nonamphibian hosts and releases chemicals that cause pathology in the absence of infection. Proceedings of the National Academy of Sciences of the United States of America 110: 210-215 (Altmetric score of 57, 98th percentile)

Venesky, M.D., Mendelson, J.R., Sears, B.F., Stiling, P.D., Rohr, J.R. 2012. Selecting for tolerance against pathogens and herbivores to enhance the success of reintroduction and translocation programs. Conservation Biology26: 586-592

McMahon, T.A., Halstead, N.T., Johnson, S., Raffel, T.R., Romansic, J.M., Crumrine, P.W., Boughton, R.K., Martin, L.B., Rohr, J.R. 2011. The fungicide chlorothalonil is nonlinearly associated with corticosterone levels, immunity, and mortality in amphibians. Environmental Health Perspectives 119: 1098-1103

Romansic, J.M., Johnson, P.T.J., Searle, C.L., Johnson, J.E., Tunstall, T., Han, B.A., Rohr, J.R., Blaustein, A.R. 2011. Individual and combined effects of multiple pathogens on Pacific treefrogs. Oecologia 166: 1029-1041

Schotthoefer, A.M., Rohr, J.R., Cole, R.A., Koehler, A.V., Johnson, C.M., Johnson, L.B., Beasley, V.R. 2011. Effects of wetland and landscape variables on parasite communities of Rana pipiens: links to anthropogenic changes. Ecological Applications 21: 1257-1271

Rohr, J.R., Halstead, N.T., Raffel, T.R. 2011. Modelling the future distribution of the amphibian chytrid fungus: The influence of climate and human-associated factors. Journal of Applied Ecology 48: 174-176 (invited submission)

Raffel, T.R., Michel, P.J., Sites, E.W., Rohr, J.R. 2010. Does temperature drive chytrid infections in newt populations?  Associations with leaf litter, vegetation and shade. EcoHealth 7: 526-536

Rohr, J.R., Raffel, T.R. 2010. Linking global climate and temperature variability to widespread amphibian declines putatively caused by disease. Proceedings of the National Academy of Sciences of the United States of America 107: 8269-8274

Rohr, J.R., McCoy, K.A. 2010. A qualitative meta-analysis reveals consistent effects of atrazine on freshwater fish and amphibians. Environmental Health Perspectives 118: 20-32

Rohr, J.R., Raffel, T.R., Sessions, S.K. 2009. Digenetic trematodes and their relationship to amphibian declines and deformities. In: Amphibian Biology. vol. 8. Amphibian Decline: Diseases, Parasites, Maladies, and Pollution. series editor Heatwole, H. & Wilkinson, J.W. Surrey Beatty & Sons, Chipping Norton, NSW, Australia, pp 3067-3088

Rohr, J.R., Raffel, T.R., Romansic, J., McCallum, H., Hudson, P.J. 2008. Evaluating the links between climate, disease spread, and amphibian declines. Proceedings of the National Academy of Sciences of the United States of America.105: 17436-17441

Rohr, J.R., Schotthoefer, A.M., Raffel, T.R., Carrick, H.J., Halstead, N., Hoverman, J.T., Johnson, C.M., Johnson, L.B., Lieske, C., Piwoni, M.D., Schoff, P.K., Beasley, V.R. 2008. Agrochemicals increase trematode infections in a declining amphibian species. Nature 455: 1235-1239 Featured on the cover

Rohr, J.R., Raffel, T.R., Sessions, S.K., Hudson, P.J. 2008. Understanding the net effects of pesticides on amphibian trematode infections. Ecological Applications 18: 1743-1753

Raffel, T.R., Rohr, J.R., Kiesecker, J.M., Hudson, P.J. 2006. Negative effects of changing temperature on amphibian immunity under field conditions. Functional Ecology 20: 819-828

Rohr, J.R., Sager, T., Sesterhenn, T., Palmer, B.D. 2006. Exposure, post-exposure, and density-mediated effects of atrazine on amphibians: Breaking down net effects into their parts. Environmental Health Perspectives 114: 46-50 Featured on the cover

Rohr, J.R., Palmer, B.D. 2005. Aquatic herbicide exposure increases salamander desiccation risk eight months later in a terrestrial environment. Environmental Toxicology and Chemistry 24: 1253-1258

Rohr, J.R., Elskus, A.A., Shepherd, B.S., Crowley, P.H., McCarthy, T.M., Niedzwiecki, J.H., Sager, T., Sih, A., Palmer, B.D. 2004. Multiple stressors and salamanders: Effects of an herbicide, food limitation, and hydroperiod. Ecological Applications 14: 1028-1040

Rohr, J.R., Elskus, A.A., Shepherd, B.S., Crowley, P.H., McCarthy, T.M., Niedzwiecki, J.H., Sager, T., Sih, A., Palmer, B.D. 2003. The lethal and sublethal effects of atrazine, carbaryl, endosulfan, and octylphenol on the streamside salamander, Ambystoma barbouri. Environmental Toxicology and Chemistry 22: 2385-2392

Rohr, J.R., Madison, D.M. 2003. Dryness increases predation risk in efts: Support for an amphibian decline hypothesis. Oecologia 135: 657-664

For a full list of publications, please see the Publications page on this website.

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