1
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Neely WJ, Souza KMC, Martins RA, Marshall VM, Buttimer SM, Brito de Assis A, Medina D, Whetstone RD, Lyra ML, Ribeiro JW, Greenspan SE, Haddad CFB, Alves dos Anjos L, Becker CG. Host-associated helminth diversity and microbiome composition contribute to anti-pathogen defences in tropical frogs impacted by forest fragmentation. ROYAL SOCIETY OPEN SCIENCE 2024; 11:240530. [PMID: 39100162 PMCID: PMC11296196 DOI: 10.1098/rsos.240530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 04/23/2024] [Indexed: 08/06/2024]
Abstract
Habitat fragmentation can negatively impact wildlife populations by simplification of ecological interactions, but little is known about how these impacts extend to host-associated symbiotic communities. The symbiotic communities of amphibians play important roles in anti-pathogen defences, particularly against the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). In this study, we analyse the role of macroparasitic helminth communities in concert with microbial communities in defending the host against Bd infection within the context of forest fragmentation. We found that skin microbial and helminth communities are disrupted at fragmented habitats, while gut microbiomes appear more resilient to environmental change. We also detected potential protective roles of helminth diversity and anti-pathogen microbial function in limiting Bd infection. Microbial network analysis revealed strong patterns of structure in both skin and gut communities, with helminths playing central roles in these networks. We reveal consistent roles of microbial and helminth diversity in driving host-pathogen interactions and the potential implications of fragmentation on host fitness.
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Affiliation(s)
- Wesley J. Neely
- Department of Biology, The University of Alabama, Tuscaloosa, AL35487, USA
- Department of Biology, Texas State University, San Marcos, TX78666, USA
| | - Kassia M. C. Souza
- Departamento de Biologia e Zootecnia, Universidade Estadual Paulista, Ilha Solteira, São Paulo 15385-000, Brazil
| | - Renato A. Martins
- Department of Biology, The Pennsylvania State University, University Park, PA16803, USA
| | | | - Shannon M. Buttimer
- Department of Biology, The Pennsylvania State University, University Park, PA16803, USA
| | - Ananda Brito de Assis
- Department of Biodiversity and Aquaculture Center, Universidade Estadual Paulista, Rio Claro, São Paulo 13506-900, Brazil
| | - Daniel Medina
- Department of Biology, The Pennsylvania State University, University Park, PA16803, USA
- Sistema Nacional de Investigación, SENACYT, City of Knowledge, Clayton, Panama, Republic of Panama
| | - Ross D. Whetstone
- Department of Biology, University of Massachusetts Boston, Boston, MA 02125, USA
| | - Mariana L. Lyra
- Department of Biodiversity and Aquaculture Center, Universidade Estadual Paulista, Rio Claro, São Paulo 13506-900, Brazil
- New York University Abu Dhabi, Abu Dhabi, UAE
| | - José Wagner Ribeiro
- Department of Biodiversity and Aquaculture Center, Universidade Estadual Paulista, Rio Claro, São Paulo 13506-900, Brazil
| | - Sasha E. Greenspan
- Department of Biology, The University of Alabama, Tuscaloosa, AL35487, USA
| | - Célio F. B. Haddad
- Department of Biodiversity and Aquaculture Center, Universidade Estadual Paulista, Rio Claro, São Paulo 13506-900, Brazil
| | - Luciano Alves dos Anjos
- Departamento de Biologia e Zootecnia, Universidade Estadual Paulista, Ilha Solteira, São Paulo 15385-000, Brazil
| | - C. Guilherme Becker
- Department of Biology, The Pennsylvania State University, University Park, PA16803, USA
- One Health Microbiome Center, Center for Infectious Disease Dynamics, Ecology Institute, Huch Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA16803, USA
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2
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O'Dwyer K, Milotic D, Milotic M, Koprivnikar J. Behave yourself: effects of exogenous-glucocorticoid exposure on larval amphibian anti-parasite behaviour and physiology. Oecologia 2024; 205:95-106. [PMID: 38689180 DOI: 10.1007/s00442-024-05547-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2022] [Accepted: 03/30/2024] [Indexed: 05/02/2024]
Abstract
Parasites represent a ubiquitous threat for most organisms, requiring potential hosts to invest in a range of strategies to defend against infection-these include both behavioural and physiological mechanisms. Avoidance is an essential first line of defence, but this behaviour may show a trade-off with host investment in physiological immunity. Importantly, while environmental stressors can lead to elevated hormones in vertebrates, such as glucocorticoids, that can reduce physiological immunity in certain contexts, behavioural defences may also be compromised. Here, we investigate anti-parasite behaviour and immune responses against a trematode (flatworm) parasite by larval amphibians (tadpoles) exposed or not to a simulated general stressor in the form of exogenous corticosterone. Tadpoles that were highly active in the presence of the trematode infectious stage (cercariae) had lower infection loads, and parasite loads from tadpoles treated only with dechlorinated water were significantly lower than those exposed to corticosterone or the solvent control. However, treatment did not affect immunity as measured through white blood-cell profiles, and there was no relationship between the latter and anti-parasite behaviour. Our results suggest that a broad range of stressors could increase host susceptibility to infection through altered anti-parasite behaviours if they elevate endogenous glucocorticoids, irrespective of physiological immunity effects. How hosts defend themselves against parasitism in the context of multiple challenges represents an important topic for future research, particularly as the risk posed by infectious diseases is predicted to increase in response to ongoing environmental change.
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Affiliation(s)
- Katie O'Dwyer
- Department of Chemistry and Biology, Toronto Metropolitan University, Toronto, ON, Canada.
- Marine and Freshwater Research Centre, Atlantic Technological University, Old Dublin Road, Co., Galway, Ireland.
| | - Dino Milotic
- Department of Chemistry and Biology, Toronto Metropolitan University, Toronto, ON, Canada
- Harry Butler Institute, Murdoch University, Perth, WA, Australia
| | - Marin Milotic
- Department of Chemistry and Biology, Toronto Metropolitan University, Toronto, ON, Canada
- Harry Butler Institute, Murdoch University, Perth, WA, Australia
| | - Janet Koprivnikar
- Department of Chemistry and Biology, Toronto Metropolitan University, Toronto, ON, Canada
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3
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Woodhams DC, McCartney J, Walke JB, Whetstone R. The adaptive microbiome hypothesis and immune interactions in amphibian mucus. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2023; 145:104690. [PMID: 37001710 PMCID: PMC10249470 DOI: 10.1016/j.dci.2023.104690] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2022] [Revised: 03/21/2023] [Accepted: 03/22/2023] [Indexed: 05/20/2023]
Abstract
The microbiome is known to provide benefits to hosts, including extension of immune function. Amphibians are a powerful immunological model for examining mucosal defenses because of an accessible epithelial mucosome throughout their developmental trajectory, their responsiveness to experimental treatments, and direct interactions with emerging infectious pathogens. We review amphibian skin mucus components and describe the adaptive microbiome as a novel process of disease resilience where competitive microbial interactions couple with host immune responses to select for functions beneficial to the host. We demonstrate microbiome diversity, specificity of function, and mechanisms for memory characteristic of an adaptive immune response. At a time when industrialization has been linked to losses in microbiota important for host health, applications of microbial therapies such as probiotics may contribute to immunotherapeutics and to conservation efforts for species currently threatened by emerging diseases.
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Affiliation(s)
- Douglas C Woodhams
- Department of Biology, University of Massachusetts Boston, Boston, MA, 02125, USA.
| | - Julia McCartney
- Department of Biology, University of Massachusetts Boston, Boston, MA, 02125, USA
| | - Jenifer B Walke
- Department of Biology, Eastern Washington University, Cheney, WA, 99004-2440, USA
| | - Ross Whetstone
- Department of Biology, University of Massachusetts Boston, Boston, MA, 02125, USA
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Davis AK, Maerz JC. Assessing Leukocyte Profiles of Salamanders and Other Amphibians: A Herpetologists' Guide. Methods Mol Biol 2023; 2562:443-458. [PMID: 36272093 DOI: 10.1007/978-1-0716-2659-7_29] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Assessing numbers of leukocytes in salamanders and other amphibians can be useful metrics for understanding health or stress levels of individuals in a population. In this chapter we describe the procedures for obtaining blood samples from amphibians, preparing blood films for microscopy, counting, and identifying cells. We also provide reference values for amphibian leukocytes for use in interpreting leukocyte data. From our assessment of the published and unpublished literature, "non-stressed" salamanders would have a leukocyte profile where 60-70% of cells are lymphocytes, 17-30% are neutrophils, 1-4% are eosinophils, 4-12% are basophils, and 2-6% are monocytes. In Ambystoma spp., the eosinophil abundance can be notably higher (30% of all white blood cells), for reasons unknown. Finally, the neutrophil-lymphocyte ratio of most non-stressed salamanders tends to be between 0.3 and 0.4 (sometimes less), while the ratios of stressed salamanders tend to be over 1.0.
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Affiliation(s)
- Andrew K Davis
- Odum School of Ecology, The University of Georgia, Athens, GA, USA
- D.B. Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, GA, USA
| | - John C Maerz
- D.B. Warnell School of Forestry and Natural Resources, The University of Georgia, Athens, GA, USA.
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5
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Rubenina I, Kirjusina M, Ceirans A, Gravele E, Gavarane I, Pupins M, Krasnov BR. Environmental, anthropogenic, and spatial factors affecting species composition and species associations in helminth communities of water frogs (Pelophylax esculentus complex) in Latvia. Parasitol Res 2021; 120:3461-3474. [PMID: 34476585 DOI: 10.1007/s00436-021-07303-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Accepted: 08/25/2021] [Indexed: 10/20/2022]
Abstract
We investigated factors affecting species composition and patterns of species associations in parasite communities of water frogs (Pelophylax esculentus complex), applying the distance-based redundancy analysis for component communities (assemblages harboured by host populations) and Markov random fields modelling for infracommunities (assemblages harboured by individual hosts), respectively. We asked (a) What are the relative effects of variation in environmental, land use (i.e., anthropogenic), and spatial factors on the variation in the species composition of component communities (i.e., in a locality)? and (b) What is the dominant pattern of species associations in infracommunities (in a host individual), and how do these associations vary along environmental and/or anthropogenic gradients? In component communities, the greatest portion of variation in helminth species composition was explained by the combined effects of space, anthropogenic pressure, and NDVI, with the pure effect of the spatial predictor being much stronger than the effects of the remaining predictors. In infracommunities, the probability of occurrence of some, but not all, helminth species depended on the occurrence of another species, with the numbers of negative and positive co-occurrences being equal. The strength and/or sign of associations of some species pairs were spatially stable, whereas interactions between other species pairs varied along the gradient of the amount of green vegetation, from negative to positive and vice versa. We conclude that the processes in parasite infracommunities and component communities in frogs are intertwined, with both bottom-up and top-down effects acting at different hierarchical scales.
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Affiliation(s)
- Ilze Rubenina
- Institute of Life Sciences and Technologies, Daugavpils University, Parades Street 1A, Daugavpils, 5401, Latvia.
| | - Muza Kirjusina
- Institute of Life Sciences and Technologies, Daugavpils University, Parades Street 1A, Daugavpils, 5401, Latvia
| | - Andris Ceirans
- Institute of Life Sciences and Technologies, Daugavpils University, Parades Street 1A, Daugavpils, 5401, Latvia
| | - Evita Gravele
- Institute of Life Sciences and Technologies, Daugavpils University, Parades Street 1A, Daugavpils, 5401, Latvia
| | - Inese Gavarane
- Institute of Life Sciences and Technologies, Daugavpils University, Parades Street 1A, Daugavpils, 5401, Latvia
| | - Mihails Pupins
- Institute of Life Sciences and Technologies, Daugavpils University, Parades Street 1A, Daugavpils, 5401, Latvia
| | - Boris R Krasnov
- Mitrani Department of Desert Ecology, Swiss Institute for Dryland Environmental and Energy Research, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Sede Boqer Campus, Midreshet Ben-Gurion, Israel
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6
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Gavel MJ, Young SD, Blais N, Forbes MR, Robinson SA. Trematodes coupled with neonicotinoids: effects on blood cell profiles of a model amphibian. Parasitol Res 2021; 120:2135-2148. [PMID: 33991246 DOI: 10.1007/s00436-021-07176-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Accepted: 04/27/2021] [Indexed: 11/30/2022]
Abstract
Habitat loss, climate change, environmental contaminants, and parasites and pathogens are among the main factors thought to act singly or together in causing amphibian declines. We tested for combined effects of neonicotinoid pesticides and parasites (versus parasites-only) on mortality, growth, and white blood cell profiles of a model amphibian: the northern leopard frog (Rana pipiens). We first exposed infectious stages of frog trematodes (cercariae of Echinostoma spp.) to low and high concentrations of thiamethoxam or clothianidin versus water-only controls. There were no differences in survival of trematode cercariae between treatments. For the main experiment, we exposed tadpoles to clean water versus high concentrations of clothianidin or thiamethoxam for 2 weeks and added trematode cercariae to all tanks after 1 week. Exposure of tadpoles and parasites to high concentrations of thiamethoxam or clothianidin did not affect parasite infection success. Tadpole survival was not different between treatments before or after parasite addition and there were no significant differences in tadpole snout-to-vent lengths or developmental stages between treatments. Tadpoles exposed to thiamethoxam + parasites had smaller widths than parasite-only tadpoles, whereas tadpoles exposed to clothianidin + parasites had higher eosinophil to leukocyte ratios compared to parasite-only tadpoles. Tadpoles of both neonicotinoid + parasite treatments had significantly lower monocyte to leukocyte ratios relative to parasite-only tadpoles. High concentrations of neonicotinoid combined with parasites appear to influence tadpole immune function important for further defense against parasites and pathogens. This work highlights the need for more holistic approaches to ecotoxicity studies, using multiple stressors.
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Affiliation(s)
- M J Gavel
- Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - S D Young
- Ecotoxicology and Wildlife Health Division, Wildlife and Landscape Science Directorate, Science and Technology Branch, National Wildlife Research Centre, Environment and Climate Change Canada, 1125 Colonel By Drive, Ottawa, Ontario, K1A 0H3, Canada
| | - N Blais
- Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - M R Forbes
- Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - Stacey A Robinson
- Ecotoxicology and Wildlife Health Division, Wildlife and Landscape Science Directorate, Science and Technology Branch, National Wildlife Research Centre, Environment and Climate Change Canada, 1125 Colonel By Drive, Ottawa, Ontario, K1A 0H3, Canada.
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7
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Brown SR, Flynn RW, Hoverman JT. Perfluoroalkyl Substances Increase Susceptibility of Northern Leopard Frog Tadpoles to Trematode Infection. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2021; 40:689-694. [PMID: 31995841 DOI: 10.1002/etc.4678] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Revised: 10/23/2019] [Accepted: 01/23/2020] [Indexed: 06/10/2023]
Abstract
Per/polyfluoroalkyl substances (PFAS) are contaminants of emerging concern that can impair immune function, yet few studies have tested whether exposure increases infection risk. Using laboratory experiments, we found that exposure to 10 ppb of perfluorohexanesulfonic acid increased trematode (Echinoparyphium lineage 3) infections in larval northern leopard frogs (Lithobates pipiens). However, there was no effect of perfluorooctanesulfonic acid. Our results demonstrate that PFAS can potentially enhance infection risk in natural systems. Environ Toxicol Chem 2021;40:689-694. © 2020 SETAC.
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Affiliation(s)
- Sophia R Brown
- Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana, USA
| | - R Wesley Flynn
- Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana, USA
| | - Jason T Hoverman
- Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana, USA
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8
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Timing and order of exposure to two echinostome species affect patterns of infection in larval amphibians. Parasitology 2020; 147:1515-1523. [PMID: 32660661 DOI: 10.1017/s0031182020001092] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The study of priority effects with respect to coinfections is still in its infancy. Moreover, existing coinfection studies typically focus on infection outcomes associated with exposure to distinct sets of parasite species, despite that functionally and morphologically similar parasite species commonly coexist in nature. Therefore, it is important to understand how interactions between similar parasites influence infection outcomes. Surveys at seven ponds in northwest Pennsylvania found that multiple species of echinostomes commonly co-occur. Using a larval anuran host (Rana pipiens) and the two most commonly identified echinostome species from our field surveys (Echinostoma trivolvis and Echinoparyphium lineage 3), we examined how species composition and timing of exposure affect patterns of infection. When tadpoles were exposed to both parasites simultaneously, infection loads were higher than when exposed to Echinoparyphium alone but similar to being exposed to Echinostoma alone. When tadpoles were sequentially exposed to the parasite species, tadpoles first exposed to Echinoparyphium had 23% lower infection loads than tadpoles first exposed to Echinostoma. These findings demonstrate that exposure timing and order, even with similar parasites, can influence coinfection outcomes, and emphasize the importance of using molecular methods to identify parasites for ecological studies.
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O’Dwyer K, Dargent F, Forbes MR, Koprivnikar J. Parasite infection leads to widespread glucocorticoid hormone increases in vertebrate hosts: A meta‐analysis. J Anim Ecol 2019; 89:519-529. [DOI: 10.1111/1365-2656.13123] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 09/18/2019] [Indexed: 11/28/2022]
Affiliation(s)
- Katie O’Dwyer
- Department of Chemistry and Biology Ryerson University Toronto ON Canada
| | - Felipe Dargent
- Department of Biology Carleton University Ottawa ON Canada
| | - Mark R. Forbes
- Department of Biology Carleton University Ottawa ON Canada
| | - Janet Koprivnikar
- Department of Chemistry and Biology Ryerson University Toronto ON Canada
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10
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Robinson SA, Gavel MJ, Richardson SD, Chlebak RJ, Milotic D, Koprivnikar J, Forbes MR. Sub-chronic exposure to a neonicotinoid does not affect susceptibility of larval leopard frogs to infection by trematode parasites, via either depressed cercarial performance or host immunity. Parasitol Res 2019; 118:2621-2633. [PMID: 31300888 DOI: 10.1007/s00436-019-06385-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Accepted: 06/24/2019] [Indexed: 12/26/2022]
Abstract
Little information is available on the effects of neonicotinoid insecticides on vertebrates. Previous work using amphibians found chronic exposure to some neonicotinoids had no detrimental effects on fitness-relevant traits. However, there is some evidence of more subtle effects of neonicotinoids on immune traits and evidence that other pesticides can suppress tadpole immunity resulting in elevated levels of parasitism in the exposed tadpoles. The objective of our study was to assess whether neonicotinoid exposure affected tadpole immunometrics and susceptibility to parasitic helminths. We assessed northern leopard frog tadpole (Lithobates pipiens) levels of parasitism and leukocyte profiles following exposure to environmentally relevant concentrations of clothianidin and free-living infective cercariae of a helminth parasite, an Echinostoma sp. trematode. When comparing tadpoles from controls to either 1 or 100 μg/L clothianidin treatments, we found similar measures of parasitism (i.e. prevalence, abundance and intensity of echinostome cysts) and similar leukocyte profiles. We also confirmed that clothianidin was not lethal for cercariae; however, slight reductions in swimming activity were detected at the lowest exposure concentration of 0.23 μg/L. Our results show that exposure to clothianidin during the larval amphibian stage does not affect leukocyte profiles or susceptibility to parasitism by larval trematodes in northern leopard frogs although other aspects such as length of host exposure require further study.
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Affiliation(s)
- Stacey A Robinson
- National Wildlife Research Centre, Wildlife and Landscape Science Directorate, Environment and Climate Change Canada, 1125 Colonel By Drive, Ottawa, ON, K1A 0H3, Canada.
| | - M J Gavel
- Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada
| | - S D Richardson
- National Wildlife Research Centre, Wildlife and Landscape Science Directorate, Environment and Climate Change Canada, 1125 Colonel By Drive, Ottawa, ON, K1A 0H3, Canada
| | - R J Chlebak
- National Wildlife Research Centre, Wildlife and Landscape Science Directorate, Environment and Climate Change Canada, 1125 Colonel By Drive, Ottawa, ON, K1A 0H3, Canada.,Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada
| | - D Milotic
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON, M5B 2K3, Canada
| | - J Koprivnikar
- Department of Chemistry and Biology, Ryerson University, 350 Victoria Street, Toronto, ON, M5B 2K3, Canada
| | - M R Forbes
- Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada
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11
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Gavel MJ, Richardson SD, Dalton RL, Soos C, Ashby B, McPhee L, Forbes MR, Robinson SA. Effects of 2 Neonicotinoid Insecticides on Blood Cell Profiles and Corticosterone Concentrations of Wood Frogs (Lithobates sylvaticus). ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY 2019; 38:1273-1284. [PMID: 30901102 DOI: 10.1002/etc.4418] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 01/19/2019] [Accepted: 03/14/2019] [Indexed: 06/09/2023]
Abstract
Neonicotinoids are widely used insecticides that are detectable in agricultural waterways. These insecticides are of concern due to their potential impacts on nontarget organisms. Pesticides can affect development of amphibians and suppress the immune system, which could impact disease susceptibility and tolerance. No previous studies on amphibians have examined the effects of these insecticides on differential blood cell proportions or concentrations of corticosterone (a general stress hormone). We investigated the effects of chronic exposure to 2 neonicotinoids, thiamethoxam and clothianidin, on immunometrics of wood frogs (Lithobates sylvaticus). Frogs were exposed to single, chronic treatments of 2.5 or 250 µg/L of clothianidin or thiamethoxam for 7 wk from Gosner stages 25 to 46. The juvenile frogs were then maintained for 3 wk post metamorphosis without exposure to neonicotinoids. We measured water-borne corticosterone twice: at 6 d and 8 wk after exposure in larval and juvenile frogs, respectively. We assessed differential blood cell profiles from juvenile frogs. Corticosterone was significantly lower in tadpoles exposed to 250 µg/L of thiamethoxam compared with other tadpole treatments, but no significant differences in corticosterone concentrations were found in treatments using juvenile frogs. Anemia was detected in all treatments compared with controls with the exception of tadpoles exposed to 2.5 µg/L of clothianidin. Neutrophil-to-leukocyte and neutrophil-to-lymphocyte ratios were elevated in frogs exposed to 250 µg/L of thiamethoxam. Collectively, these results indicate that chronic exposure to neonicotinoids has varied impacts on blood cell profiles and corticosterone concentrations of developing wood frogs, which are indicative of stress. Future studies should investigate whether exposure to neonicotinoids increases susceptibility to infection by parasites in both larval and adult wood frogs. Environ Toxicol Chem 2019;38:1273-1284. © 2019 Crown in the right of Canada. Published by Wiley Periodicals Inc. on behalf of SETAC.
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Affiliation(s)
- Melody J Gavel
- Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | | | - Rebecca L Dalton
- Department of Biology, Carleton University, Ottawa, Ontario, Canada
- Science and Technology Branch, Science and Risk Assessment Directorate, Ecological Assessment Division, Environment and Climate Change Canada, Gatineau, Quebec, Canada
| | - Catherine Soos
- Science and Technology Branch, Wildlife and Landscape Science Directorate, Ecotoxicology and Wildlife Health Division, Environment and Climate Change Canada, Saskatoon, Saskatchewan, Canada
- Department of Veterinary Pathology, University of Saskatchewan, Saskatoon, Canada
| | - Brendan Ashby
- Science and Technology Branch, Wildlife and Landscape Science Directorate, Ecotoxicology and Wildlife Health Division, Environment and Climate Change Canada, Saskatoon, Saskatchewan, Canada
| | - Landon McPhee
- Science and Technology Branch, Wildlife and Landscape Science Directorate, Ecotoxicology and Wildlife Health Division, Environment and Climate Change Canada, Saskatoon, Saskatchewan, Canada
| | - Mark R Forbes
- Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - Stacey A Robinson
- Science and Technology Branch, Wildlife and Landscape Science Directorate, Ecotoxicology and Wildlife Health Division, Environment and Climate Change Canada, Ottawa, Ontario, Canada
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