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Per- and polyfluoroalkyl substances (PFAS) are chemicals associated with adverse health effects. At aqueous film-forming foam sites, they occur as mixtures, with perfluorooctanesulfonic acid (PFOS) and perfluorohexanesulfonic acid (PFHxS) commonly co-occurring in the highest concentrations. Although PFOS and PFHxS toxicities have been studied, few studies have tested their potential interaction. Using Rana pipiens, the present study compared toxicities of a 1:1 PFOS:PFHxS mixture to PFOS and PFHxS individually with the prediction that responses would be additive. Gosner stage 25 (GS 25) tadpoles were exposed through metamorphosis (GS 46) to 0.5 and 1 ppb PFOS or PFHxS alone or to a mixture of 0.5 ppb PFOS and 0.5 ppb PFHxS. Tadpoles were weighed and measured (snout-vent length [SVL]) at day 31, metamorphic climax (GS 42), and GS 46. These values were used to calculate the scaled mass index (SMI), a measure of body condition. Body burdens were quantified on day 31 and at GS 46. The PFOS and PFHxS body burdens were elevated relative to controls at GS 46. No effects were observed on survival, SVL, or mass. Single PFAS effects included a 17% reduction in SMI at day 31 (0.5 ppb PFHxS) and a 1.1-day longer metamorphic period (1 ppb PFHxS) relative to controls. Mixture results deviated from additivity-SMIs were higher than expected on day 31 and lower than expected at GS 42. In addition, time to GS 42 in the PFAS mixture exceeded expected additivity by 12 days. Results from a chronic exposure to a 1:1 PFOS:PFHxS mixture resulted in changes in body condition and length of metamorphosis that deviated from additivity. More PFAS mixture toxicity studies conducted at relevant ratios and concentrations are needed. Environ Toxicol Chem 2022;41:3007-3016. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Per- and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants known to adversely affect health and development in many taxa. Although PFAS generally occur as mixtures in the environment, little is known about the effects of PFAS mixtures on organisms compared to single chemical exposures. Moreover, PFAS exposure in nature occurs alongside biotic factors such as parasitism. Even though host-parasite interactions are common in natural systems, there is little information about how PFAS affect these interactions. Here, we examined the effects of PFAS mixtures on the susceptibility of larval American bullfrogs (

Researchers have developed numerous per- and polyfluoroalkyl substances (PFAS)-free aqueous film-forming foam (AFFF) formulations to replace PFAS-containing AFFF used for fire suppression. As part of the Department of Defense's Strategic Environmental Research and Development Program (SERDP), we examined the direct lethal effects of seven PFAS-free AFFF and a PFAS-containing AFFF on 14 aquatic species using a series of lethal concentration (LC50) tests. We assessed the LC10, LC50, and LC90 values using log-logistic and logit analyses. Across all aquatic species tested, we discovered that exposure to at least one PFAS-free AFFF was more or as toxic as exposure to the PFAS-containing AFFF. For most cases, National Foam Avio F3 Green KHC 3% and Buckeye Platinum Plus C6MILSPEC 3% were the most and least toxic formulations, respectively. Moreover, we found consistency among results from multiple experiments using the same minnow species (

Freshwater systems are critical to life on earth, yet they are threatened by the increasing rate of synthetic chemical pollution. Current predictions of the effects of synthetic chemicals on freshwater ecosystems are hampered by the sheer number of chemical contaminants entering aquatic systems, the diversity of organisms inhabiting these systems, the myriad possible direct and indirect effects resulting from these combinations, and uncertainties concerning how contaminants might alter ecosystem metabolism via changes in biodiversity. To address these knowledge gaps, we conducted a mesocosm experiment that elucidated the responses of ponds composed of phytoplankton and zooplankton to standardized concentrations of 12 pesticides, nested within four pesticide classes, and two pesticide types. We show that the effects of the pesticides on algae were consistent within herbicides and insecticides and that responses of over 70 phytoplankton species and genera were consistent within broad taxonomic groups. Insecticides generated top-down effects on phytoplankton community composition and abundance, which were associated with persistent increases in ecosystem respiration. Insecticides had direct toxic effects on cladocerans, which led to competitive release of copepods. These changes in the zooplankton community led to a decrease in green algae and a modest increase in diatoms. Herbicides did not change phytoplankton composition but reduced total phytoplankton abundance. This reduction in phytoplankton led to short-term decreases in ecosystem respiration. Given that ponds release atmospheric carbon and that worldwide pesticide pollution continues to increase exponentially, scientists and policy makers should pay more attention to the ways pesticides alter the carbon cycle in ponds via changes in communities, as demonstrated by our results. Our results show that these predictions can be simplified by grouping pesticides into types and species into functional groups. Adopting this approach provides an opportunity to improve the efficiency of risk assessment and mitigation responses to global change.

Per- and polyfluoroalkyl substances (PFAS) are widespread, persistent environmental pollutants known to elicit a wide range of negative effects on wildlife species. There is scarce information regarding the toxicity of PFAS on amphibians, but amphibians may be highly susceptible because of their permeable skin and dependence on fresh water. Acute toxicity studies are a first step toward understanding responses to PFAS exposure, providing benchmarks for species-specific tolerances, informing ecological risk assessment (ERA), and designing chronic toxicity studies. We conducted standardized 96-h lethal concentration (LC50) toxicity tests for perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) with 9 widely distributed amphibian species native to eastern and central North America. We also conducted LC50 tests with perfluorohexane sulfonate (PFHxS) for 2 species and determined whether toxicity of PFOS and PFOA varied between life stages for 3 species. Acute toxicity varied among PFAS and species and between developmental stages within species. Across all species, toxicity of PFOS was more than 8× higher than PFOA. Salamanders in the genus Ambystoma were generally more sensitive to PFOS than were anurans (frogs and a toad). Toxicity of PFOA was highest for small-mouthed salamanders and gray tree frogs and lowest for Jefferson salamanders, American bullfrogs, green frogs, and wood frogs. Although only 2 species were exposed to PFHxS, survival was lower for green frogs than for American bullfrogs. Toxicity of PFAS also varied between developmental stages of larvae. Gray tree frogs were more sensitive at later developmental stages, and small-mouthed salamanders were more sensitive at earlier developmental stages. Our study is one of the first to report species-, developmental stage-, and compound-specific differences in sensitivity to PFAS across a wide range of amphibian species. The benchmarks for toxicity we determined can inform conservation and remediation efforts, guide chronic toxicity studies, and help predict influences on amphibian communities, thereby informing future ERAs for PFAS. Integr Environ Assess Manag 2021;17:684-689. © 2021 SETAC.

Predicting ecological effects of contaminants remains challenging because of the sheer number of chemicals and their ambiguous role in biodiversity-ecosystem function relationships. We evaluate responses of experimental pond ecosystems to standardized concentrations of 12 pesticides, nested in four pesticide classes and two pesticide types. We show consistent effects of herbicides and insecticides on ecosystem function, and slightly less consistent effects on community composition. Effects of pesticides on ecosystem function are mediated by alterations in the abundance and community composition of functional groups. Through bottom-up effects, herbicides reduce respiration and primary productivity by decreasing the abundance of phytoplankton. The effects of insecticides on respiration and primary productivity of phytoplankton are driven by top-down effects on zooplankton composition and abundance, but not richness. By demonstrating consistent effects of pesticides on communities and ecosystem functions and linking pesticide-induced changes in functional groups of organisms to ecosystem functions, the study suggests that ecological risk assessment of registered chemicals could be simplified to synthetic chemical classes or types and groups of organisms with similar functions and chemical toxicities.

Predicting ecological effects of contaminants remains challenging because of the sheer number of chemicals and their ambiguous role in biodiversity-ecosystem function relationships. We evaluate responses of experimental pond ecosystems to standardized concentrations of 12 pesticides, nested in four pesticide classes and two pesticide types. We show consistent effects of herbicides and insecticides on ecosystem function, and slightly less consistent effects on community composition. Effects of pesticides on ecosystem function are mediated by alterations in the abundance and community composition of functional groups. Through bottom-up effects, herbicides reduce respiration and primary productivity by decreasing the abundance of phytoplankton. The effects of insecticides on respiration and primary productivity of phytoplankton are driven by top-down effects on zooplankton composition and abundance, but not richness. By demonstrating consistent effects of pesticides on communities and ecosystem functions and linking pesticide-induced changes in functional groups of organisms to ecosystem functions, the study suggests that ecological risk assessment of registered chemicals could be simplified to synthetic chemical classes or types and groups of organisms with similar functions and chemical toxicities., The effects of pesticides on individual species could propagate into additional community-wide and ecosystem-level effects. Here the authors use a mesocosm experiment to test how a diverse array of herbicides and insecticides disrupt aquatic community structure and ecosystem function.

Increasing evidence suggests that phenotypic plasticity can play a critical role in ecotoxicology. More specifically, induced pesticide tolerance, in which populations exposed to a contaminant show increased tolerance to the contaminants later, has been documented in multiple taxa. However, the physiological mechanisms of induced tolerance remain unclear. We hypothesized that induced pesticide tolerance is the result of a generalized stress response based on previous studies showing that both natural stressors and anthropogenic stressors can induce tolerance to pesticides. We tested this hypothesis by first exposing larval wood frogs (Rana sylvatica) to either an anthropogenic stressor (sublethal carbaryl concentration), a natural stressor (cues from a caged predator), or a simulated stressor via exogenous exposure to the stress hormone corticosterone (125 nM). We also included treatments that inhibited corticosterone synthesis with the compound metyrapone (MTP). We then exposed the larvae to a lethal carbaryl treatment to assess time to death. We found that prior exposure to 125 nM of exogenous CORT and predator cues induced tolerance to a lethal concentration of carbaryl through a slight delay in time to death. Pre-exposure to sublethal carbaryl, as well as MTP alone or in combination with predator cues, did not induce tolerance to the lethal carbaryl concentration relative to the ethanol vehicle control treatment. Our study provides evidence that pesticide tolerance can be induced by a generalized stress response both in the presence and absence (exogenous CORT) of specific cues and highlights the importance of considering physiological ecology and environmental context in ecotoxicology.

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.

Per- and polyfluoroalkyl substances (PFAS) are contaminants of concern due to their widespread occurrence in the environment, persistence, and potential to elicit a range of negative health effects. Per- and polyfluoroalkyl substances are regularly detected in surface waters, but their effects on many aquatic organisms are still poorly understood. Species with thyroid-dependent development, like amphibians, can be especially susceptible to PFAS effects on thyroid hormone regulation. We examined sublethal effects of aquatic exposure to four commonly detected PFAS on larval northern leopard frogs (Rana [Lithobates] pipiens), American toads (Anaxyrus americanus), and eastern tiger salamanders (Ambystoma tigrinum). Animals were exposed for 30 days (frogs and salamanders) or until metamorphosis (toads) to 10, 100, or 1000 μg/L of perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS), or 6:2 fluorotelomer sulfonate (6:2 FTS). We determined that chronic exposure to common PFAS can negatively affect amphibian body condition and development at concentrations as low as 10 µg/L. These effects were highly species dependent, with species having prolonged larval development (frogs and salamanders) being more sensitive to PFAS than more rapidly developing species (toads). Our results demonstrate that some species could experience sublethal effects at sites with surface waters highly affected by PFAS. Our results also indicate that evaluating PFAS toxicity using a single species may not be sufficient for accurate amphibian risk assessment. Future studies are needed to determine whether these differences in susceptibility can be predicted from species' life histories and whether more commonly occurring environmental levels of PFAS could affect amphibians. Environ Toxicol Chem 2022;41:1407-1415. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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.

Recent climate-driven, physico-chemical changes documented in aquatic systems throughout the world are expected to intensify in the future. Specifically, changes in key environmental attributes of aquatic systems, such as water quantity, clarity, temperatures, ice cover, seasonal flow regimes, external loading, and oxygen content, will undoubtedly have a broad set of direct and indirect ecological consequences. Some anticipated impacts may be similar across different aquatic ecosystems, while others may be system-specific. Here, we review the potential effects of climatic changes for different freshwater habitats within the state of Indiana, USA, a Midwestern state with diverse land and water features. Given this heterogeneity and that the state is among the southernmost states of the US Midwest, evaluation of freshwater habitats of Indiana provides a useful perspective on potential impacts of climate change. In our study, we first review expected or anticipated changes to physico-chemical and habitat conditions in wetlands, lotic systems, small glacial lakes and Lake Michigan. We then highlight anticipated responses of select aquatic biota to these changes. We describe how climatic changes may interact with other anthropogenic stressors affecting freshwater habitats and consider the potential for evolutionary adaptation of freshwater aquatic organisms to mediate any responses. Given anticipated changes, we suggest aquatic ecosystem managers take a precautionary approach broadly applicable in temperate regions to (a) conserve a diversity of aquatic habitats, (b) enhance species diversity and both inter- and intra-population genetic variation, and (c) limit stressors which may exacerbate the risk of decline for aquatic biota.

Major histocompatibility complex (MHC) genes code for membrane-embedded proteins that are involved in parasite/pathogen recognition. The link between the MHC and immunity makes these genes important genetic markers to evaluate in systems where infectious disease is associated with population declines. As human impacts on wildlife populations continue to increase, it is also essential to evaluate the role of MHC and immunity in the context of anthropogenic change. Amphibians are an ideal model to test the role of the MHC in infectious disease resistance, as parasites and anthropogenic disturbances currently threaten populations worldwide. We characterized the diversity of MHC class IIβ peptide binding region alleles, 13 microsatellite loci, and population-level trematode resistance in 14 populations of wood frogs (Lithobates sylvaticus) in northwestern Pennsylvania with varying geographic distances to agriculture. To assess local adaptation in the MHC IIβ, we compared genetic differentiation of MHC IIβ and microsatellite markers (FST). We also tested for an effect of isolation by distance on genetic differentiation of MHC IIβ and microsatellite markers. In addition, we evaluated whether population-level MHC IIβ diversity and common allele frequencies correlate with distance to agriculture and trematode resistance. We found no evidence for genetic structure based on microsatellite analysis nor an effect of isolation by distance on neutral and immunogenetic markers. However, we did detect structure based on the MHC IIβ locus, suggesting that it is under local selection. The MHC IIβ allele Lisy-DAB*1 was more common in populations living near agricultural sites. Populations with higher MHC IIβ diversity showed increased resistance to trematodes. Our results suggest that wood frog populations experience immunogenetic differences at a small scale. In addition, agriculture may disturb natural associations between hosts and parasites through its influence on immunocompetence, underscoring the importance of examining the effects of environmental context on host-parasite interactions.

Host behaviour is known to influence disease dynamics. Additionally, hosts often change their behaviours in response to pathogen detection to resist and avoid disease. The capacity of wildlife populations to respond to pathogens using behavioural plasticity is critical for reducing the impacts of disease outbreaks. However, there is limited information regarding the ability of ectothermic vertebrates to resist diseases via behavioural plasticity. Here, we experimentally examine the effect of host behaviour on ranaviral infections, which affect at least 175 species of ectothermic vertebrates. We placed metamorphic (temporal block 1) or adult (block 2) southern toads (Anaxyrus terrestris) in thermal gradients, tested their temperature preferences before and after oral inoculation by measuring individual‐level body temperature over time, and measured ranaviral loads of viral‐exposed individuals. We found significant individual‐level variation in temperature preference and evidence for behavioural fever in both metamorphic and adult A. terrestris during the first 2 days after exposure. Additionally, we found that individual‐level change in temperature preference was negatively correlated with ranaviral load and a better predictor of load than average temperature preference or maximum temperature reached by an individual. In other words, an increase in baseline temperature preference was more important than simply reaching an absolute temperature. These results suggest that behavioural fever is an effective mechanism for resisting ranaviral infections. A free Plain Language Summary can be found within the Supporting Information of this article.

Neonicotinoids are a class of insecticide with global impacts on natural environments. Due to their high solubility, they are frequently found in stream ecosystems where they have the potential to impact non-target biota. While environmental concentrations are generally below lethal levels for most organisms, there are concerns that sublethal exposures can impact aquatic insects, particularly mayflies, which are highly sensitive to neonicotinoids. Because sublethal doses of neonicotinoids can reduce mobility in mayflies, exposure could indirectly increase mortality due to predation by impairing their ability to avoid initial detection or escape predators. We examined whether exposure to the neonicotinoid clothianidin at a concentration below the 96-h EC50 (7.5 µg/L), would increase the predation risk of Stenacron and Stenonema mayfly nymphs by larval southern two-lined salamanders (Eurycea cirrigera) or eastern dobsonfly nymphs (Corydalus cornutus) using a controlled laboratory experiment. For Stenacron, we found significant interactive effects between pesticide and dobsonfly exposure that increased the hazard ratio (HR). The HR assesses risk relative to a control population, in this case mayflies in similar experimental conditions but without exposure to neonicotinoids or predators. With the addition of clothianidin, the HR of mayflies exposed to a dobsonfly nymph significantly increased from 1.8 to 6.2 while the HR for those exposed to salamanders increased from 7.6 to 12.5. For Stenonema, the HR initially decreased due to dobsonfly exposure (1 to 0.3) but increased when clothianidin and dobsonflies were combined (0.3 to 1.6). Our study shows that aquatic exposure to clothianidin can increase mortality for aquatic insects through predator pressure. Such indirect effects associated with neonicotinoid exposure warrant further investigation to expand our understanding of pesticide impacts to aquatic systems.

Exposure to agrochemicals can drive rapid phenotypic and genetic changes in exposed populations. For instance, amphibian populations living far from agriculture (a proxy for agrochemical exposure) exhibit low pesticide tolerance, but they can be induced to possess high tolerance following a sublethal pesticide exposure. In contrast, amphibian populations close to agriculture exhibit high, constitutive tolerance to pesticides. A recent study has demonstrated that induced pesticide tolerance appears to have arisen from plastic responses to predator cues. As a result, we might expect that selection for constitutive pesticide tolerance in populations near agriculture (i.e., genetic assimilation) will lead to the evolution of constitutive responses to natural stressors. Using 15 wood frog (Rana sylvatica) populations from across an agricultural gradient, we conducted an outdoor mesocosm experiment to examine morphological (mass, body length, and tail depth) and behavioral responses (number of tadpoles observed and overall activity) of tadpoles exposed to three stressor environments (no-stressor, competitors, or predator cues). We discovered widespread differences in tadpole traits among populations and stressor environments, but no population-by-environment interaction. Subsequent linear models revealed that population distance to agriculture (DTA) was occasionally correlated with tadpole traits in a given environment and with magnitudes of plasticity, but none of the correlations were significant after Bonferroni adjustment. The magnitudes of predator and competitor plasticity were never correlated with the magnitude of pesticide-induced plasticity that we documented in a companion study. These results suggest that while predator-induced plasticity appears to have laid the foundation for the evolution of pesticide-induced plasticity and its subsequent genetic assimilation, inspection of population-level differences in plastic responses show that the evolution of pesticide-induced plasticity has not had a reciprocal effect on the evolved plastic responses to natural stressors.

Natural enemy ecology strives to unify predator-prey and host-pathogen interactions under a common framework to gain insights into community- and ecosystem-level processes. To address this goal, ecologists need a greater emphasis on: (1) quantifying pathogen-mediated effects on community structure to enable comparisons with predator-mediated effects and (2) determining the interactive effects of combined natural enemies on communities. We conducted a mesocosm experiment to assess the individual and combined effects of predators (dragonfly larvae and adult water bugs) and a pathogen (ranavirus) on the abundance and composition of a larval amphibian assemblage. We found that our three natural enemies structured victim assemblages in unique ways, producing distinct assemblages. Additionally, we found that in combination treatments, predators mainly drove assemblage structure such that the assemblages most closely resembled their respective predator treatments. We also found that predators reduced infection prevalence in combination treatments, and that the magnitude of this effect was dependent on predator identity. Compared to virus-alone treatments, the presence of dragonflies and water bugs reduced infection prevalence by 79% and 63%, respectively. Additionally, the presence of dragonflies eliminated ranavirus infection in two species, which demonstrates the prominent role of predators in disease dynamics in this system. Overall, this work demonstrates the importance of considering natural enemies in community ecology, as each enemy can elicit a unique structural change. Additionally, this study provides a unique empirical test of the healthy herds hypothesis for multi-species assemblages and underscores the importance of advancing our understanding of multi-enemy interactions within communities.

Spatio-temporal dynamics in habitat suitability and connectivity among mosaics of heterogeneous wetlands are critical for biological diversity and species persistence in aquatic patchy landscapes. Despite the recognized importance of stochastic hydroclimatic forcing in driving wetlandscape hydrological dynamics, linking such effects to emergent dynamics of metapopulation poses significant challenges. To fill this gap, we propose here a dynamic stochastic patch occupancy model (SPOM), which links parsimonious hydrological and ecological models to simulate spatio-temporal patterns in species occupancy in wetlandscapes. Our work aims to place ecological studies of patchy habitats into a proper hydrologic and climatic framework to improve the knowledge about metapopulation shifts in response to climate-driven changes in wetlandscapes. We applied the dynamic version of the SPOM (D-SPOM) framework in two wetlandscapes in the US with contrasting landscape and climate properties. Our results illustrate that explicit consideration of the temporal dimension proposed in the D-SPOM is important to interpret local- and landscape-scale patterns of habitat suitability and metapopulation occupancy. Our analyses show that spatio-temporal dynamics of patch suitability and accessibility, driven by the stochasticity in hydroclimatic forcing, influence metapopulation occupancy and the topological metrics of the emergent wetlandscape dispersal network. D-SPOM simulations also reveal that the extinction risk in dynamic wetlandscapes is exacerbated by extended dry periods when suitable habitat decreases, hence limiting successful patch colonization and exacerbating metapopulation extinction risks. The proposed framework is not restricted only to wetland studies but could also be applied to examine metapopulation dynamics in other types of patchy habitats subjected to stochastic external disturbances.

Current predictions of the effects of synthetic chemicals on freshwater ecosystems are hampered by the sheer number of chemical contaminants entering aquatic systems, the diversity of organisms inhabiting these systems, and uncertainties about how contaminants alter ecosystem metabolism. We conducted a mesocosm experiment that elucidated the responses of ponds composed of phytoplankton and zooplankton to standardized concentrations of 12 pesticides, nested within four pesticide classes and two pesticide types. We show that the effects of the pesticides on algae were consistent within herbicides and insecticides and responses of over 70 phytoplankton species and genera were consistent within broad taxonomic groups. Insecticides generated top-down effects on phytoplankton community composition and abundance, which were associated with persistent increases in ecosystem respiration. Herbicides reduced phytoplankton abundance, which was associated with decreases in primary productivity and ecosystem respiration. These results suggest that widespread pesticide use could have underexplored implications for the global carbon cycle. While these effects on ecosystem respiration were mediated through complex effects on communities, taxonomic groups of organisms responded similarly to pesticide types, suggesting opportunities to simplify ecological risk assessment.

Per- and polyfluoroalkyl substances (PFAS) are present in water and >99% of human serum. They are found in brains of wildlife; however, little is known about effects on the developing brain. To determine the effects of PFAS on brain and cardiac innervation, we conducted an outdoor mesocosm experiment with Northern leopard frog larvae (Rana pipiens) exposed to control, 10 ppb perfluorooctane sulfonate (PFOS), or a PFAS mixture totaling 10 ppb that mimicked aqueous film forming foam-impacted surface water (4 ppb PFOS, 3 ppb perfluorohexane sulfonate, 1.25 ppb perfluorooctanoate, 1.25 ppb perfluorohexanoate, and 0.5 ppb perfluoro-n-pentanoate). Water was spiked with PFAS and 25 larvae (Gosner stage (GS) 25) added to each mesocosm (n = 4 mesocosms per treatment). After 30 days, we harvested eight brains per mesocosm and remaining larvae developed to GS 46 (i.e. metamorphosis) before brains and hearts were collected. Weight, length, GS, and time to metamorphosis were recorded. Brain concentrations of all five PFAS were quantified using LC/MS/MS. Dopamine and metabolites, serotonin and its metabolite, norepinephrine, γ-aminobutyric acid, and glutamate were quantified using High Performance Liquid Chromatography with electrochemical detection while acetylcholine and acetylcholinesterase activity were quantified with the Invitrogen Amplex Red Acetylcholine Assay. PFOS accumulated in the brain time- and dose-dependently. After 30 days, the mixture decreased serotonin while both PFAS treatments decreased glutamate. Interestingly, acetylcholine increased in PFAS treatments at GS 46. This research shows that developmental environmentally relevant exposure to PFAS changes neurotransmitters, especially acetylcholine.

Dynamic internal feedbacks and stochastic external shocks drive the spatial organization and heterogeneity of patchy habitats, and thus the temporal variability of patch suitability and accessibility. Such spatiotemporal shifts impact species dispersal among patches and metapopulation persistence. Here, we extended the widely recognized concepts of patch-occupancy and metapopulation capacity from static to dynamic patchy habitats, with isolated wetlands embedded in uplands as the case study. We present a new metapopulation modeling approach by linking a hydrological model for wetland variability with a dynamic stochastic patch-occupancy model. In two case study wetlandscapes, we evaluate (1) spatiotemporal dynamics of wetland hydrologic regimes, and patch suitability and connectivity driven by stochastic hydroclimatic forcing, and (2) spatiotemporal patterns of patch occupancy and metapopulation dispersal dynamics. Our modeling results reveal the importance of specific connected patches that serve as persistent hubs and form the backbone of dispersal corridors to support species dispersal in fragmented dynamic landscapes. Our analyses reveal that the interplay between stochastic hydroclimatic forcing and patchy habitat structure could drive species to extinction when specific thresholds are crossed.

Global climate change is predicted to have significant impacts on ecological interactions such as host-parasite relationships. Increased temperatures may also interact with other anthropogenic stressors, such as chemical contaminants, to exacerbate or reduce parasite transmission. However, studies on the effects of pesticides on non-target species are typically conducted at one standard temperature, despite the toxicity of many agrochemicals being temperature-dependent. Furthermore, most studies assessing the effects of temperature on pesticide toxicity have been conducted on host organisms, limiting our understanding of how temperature affects the toxicity of pesticides to free-living parasite stages as they move through the environment in search of a host. Using the free-swimming cercariae stage of the trematode Echinostoma trivolvis, we examined how the toxicities of three different pesticides (a carbamate insecticide, strobilurin fungicide, and triazine herbicide) vary by temperature by monitoring cercarial swimming activity over time. Our three main findings were: 1) a strong main effect of temperature across all pesticide trials - higher temperatures caused cercariae to cease swimming activity earlier, likely due to an increased rate of energy expenditure, 2) atrazine, azoxystrobin, and carbaryl were directly toxic to cercariae to some degree, but not in a predictable dose-dependent manner, and 3) the temperature at which pesticide exposure occurs could affect its toxicity to cercariae. The interaction between pesticide and temperature was most evident in the azoxystrobin exposure; azoxystrobin caused cercariae to cease swimming activity earlier at 30 °C but caused cercariae to maintain swimming activity longer at 18 °C relative to their respective pesticide-free control treatments. These findings highlight the importance of conducting toxicity assays at multiple temperatures and suggest that the combined effects of pesticides and temperature on host-parasite interactions may be difficult to generalize.

Classical research on animal toxicity has focused on the role of toxins in protection against predators, but recent studies suggest these same compounds can offer a powerful defense against parasites and infectious diseases. Newts in the genus Taricha are brightly coloured and contain the potent neurotoxin, tetrodotoxin (TTX), which is hypothesized to have evolved as a defense against vertebrate predators such as garter snakes. However, newt populations often vary dramatically in toxicity, which is only partially explained by predation pressure. The primary aim of this study was to evaluate the relationships between TTX concentration and infection by parasites. By systematically assessing micro- and macroparasite infections among 345 adult newts (sympatric populations of Taricha granulosa and T. torosa), we detected 18 unique taxa of helminths, fungi, viruses and protozoans. For both newt species, per-host concentrations of TTX, which varied from undetectable to >60 μg/cm2 skin, negatively predicted overall parasite richness as well as the likelihood of infection by the chytrid fungus, Batrachochytrium dendrobatidis, and ranavirus. No such effect was found on infection load among infected hosts. Despite commonly occurring at the same wetlands, T. torosa supported higher parasite richness and average infection load than T. granulosa. Host body size and sex (females > males) tended to positively predict infection levels in both species. For hosts in which we quantified leucocyte profiles, total white blood cell count correlated positively with both parasite richness and total infection load. By coupling data on host toxicity and infection by a broad range of micro- and macroparasites, these results suggest that-alongside its effects on predators-tetrodotoxin may help protect newts against parasitic infections, highlighting the importance of integrative research on animal chemistry, immunological defenses and natural enemy ecology.

Environmental variation favors the evolution of phenotypic plasticity. For many species, we understand the costs and benefits of different phenotypes, but we lack a broad understanding of how plastic traits evolve across large clades. Using identical experiments conducted across North America, we examined prey responses to predator cues. We quantified five life-history traits and the magnitude of their plasticity for 23 amphibian species/populations (spanning three families and five genera) when exposed to no cues, crushed-egg cues, and predatory crayfish cues. Embryonic responses varied considerably among species and phylogenetic signal was common among the traits, whereas phylogenetic signal was rare for trait plasticities. Among trait-evolution models, the Ornstein-Uhlenbeck (OU) model provided the best fit or was essentially tied with Brownian motion. Using the best fitting model, evolutionary rates for plasticities were higher than traits for three life-history traits and lower for two. These data suggest that the evolution of life-history traits in amphibian embryos is more constrained by a species' position in the phylogeny than is the evolution of life history plasticities. The fact that an OU model of trait evolution was often a good fit to patterns of trait variation may indicate adaptive optima for traits and their plasticities.

Summary Coinfections are increasingly recognized as important drivers of disease dynamics. Consequently, greater emphasis has been placed on integrating principles from community ecology with disease ecology to understand within-host interactions among parasites. Using larval amphibians and two amphibian parasites (ranaviruses and the trematode Echinoparyphium sp.), we examined the influence of coinfection on disease outcomes. Our first objective was to examine how priority effects (the timing and sequence of parasite exposure) influence infection and disease outcomes in the laboratory. We found that interactions between the parasites were asymmetric; prior infection with Echinoparyphium reduced ranaviral loads by 9% but there was no reciprocal effect of prior ranavirus infection on Echinoparyphium load. Additionally, survival rates of hosts (larval gray treefrogs; Hyla versicolor) infected with Echinoparyphium 10 days prior to virus exposure were 25% greater compared to hosts only exposed to virus. Our second objective was to determine whether these patterns were generalizable to multiple amphibian species under more natural conditions. We conducted a semi-natural mesocosm experiment consisting of four larval amphibian hosts [gray treefrogs, American toads (Anaxyrus americanus), leopard frogs (Lithobates pipiens) and spring peepers (Pseudacris crucifer)] to examine how prior Echinoparyphium infection influenced ranavirus transmission within the community, using ranavirus-infected larval wood frogs (Lithobates sylvaticus) as source of ranavirus. Consistent with the laboratory experiment, we found that prior Echinoparyphium infection reduced ranaviral loads by 19 to 28% in three of the four species. Collectively, these results suggest that macroparasite infection can reduce microparasite replication rates across multiple amphibian species, possibly through cross-reactive immunity. Although the immunological mechanisms driving this outcome are in need of further study, trematode infections appear to benefit hosts that are exposed to ranaviruses. Additionally, these results suggest that consideration of priority effects and timing of exposure are vital for understanding parasite interactions within hosts and disease outcomes.

Novel outbreaks of emerging pathogens require rapid responses to enable successful mitigation. We simulated a 1‐day emergency meeting where experts were engaged to recommend mitigation strategies for a new outbreak of the amphibian fungal pathogen Batrachochytrium salamandrivorans. Despite the inevitable uncertainty, experts suggested and discussed several possible strategies. However, their recommendations were undermined by imperfect initial definitions of the objectives and scope of management. This problem is likely to arise in most real‐world emergency situations. The exercise thus highlighted the importance of clearly defining the context, objectives, and spatial–temporal scale of mitigation decisions. Managers are commonly under pressure to act immediately. However, an iterative process in which experts and managers cooperate to clarify objectives and uncertainties, while collecting more information and devising mitigation strategies, may be slightly more time consuming but ultimately lead to better outcomes.

Studies of the toxicity of poly- and perfluoroalkyl substances (PFAS) on amphibians, especially after metamorphosis, are limited. We examined effects of dermal PFAS exposure (30 d) on survival and growth of juvenile American toads (Anaxyrus americanus), eastern tiger salamanders (Ambystoma tigrinum), and northern leopard frogs (Rana pipiens). Chemicals included perfluorooctanoic acid, perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS), and 6:2 fluorotelomer sulfonate (6:2 FTS) at 0, 80, 800, or 8000 ppb on a moss dry weight basis. Exposure to PFAS influenced final snout-vent length (SVL) and scaled mass index (SMI), a measure of relative body condition. Observed effects depended on species and chemical, but not concentration. Anurans exposed to PFOS, PFHxS (frogs only), and 6:2 FTS demonstrated reduced SVL versus controls, whereas salamanders exposed to 6:2 FTS showed increased SVL. Frogs exposed to PFHxS and 6:2 FTS and toads exposed to PFOS had increased SMI compared to controls; salamanders did not demonstrate effects. Concentrations of 6:2 FTS in substrate decreased substantially by 30 d, likely driven by microbial action. Perfluorooctane sulfonate had notable biota-sediment accumulation factors, but was still

Per-/polyfluoroalkyl substances (PFAS) are pervasive in aquatic systems globally and capable of causing detrimental effects on human and wildlife health. However, most studies are conducted under artificial conditions that are not representative of environmental exposures. Environmental exposures are characterized by multiple routes of exposure, low aquatic PFAS levels, and greater environmental variability than laboratory tests. Determining whether these factors influence toxicity is critical for understanding the effects of PFAS on aquatic life, including amphibians. Our goal was to assess the impact of PFAS on an amphibian under semirealistic conditions. We reared northern leopard frog (Rana pipiens) larvae in outdoor mesocosms containing sediment spiked to low, medium, and high levels (nominally 10, 100, or 1000 ppb dry wt) of perfluorooctanesulfonic acid (PFOS) or perfluorooctanoic acid (PFOA) for 30 d. Larvae in all PFOS treatments and the medium-PFOA treatment were approximately 1.5 Gosner stages less developed than control animals after 30 d. Notably, these developmental delays were observed at PFOS concentrations in the water as low as 0.06 ppb, which is considerably lower than levels associated with developmental effects in laboratory studies. Our results suggest that deriving toxicity values from laboratory studies examining aquatic exposure only may underestimate the effects of environmental PFAS exposure. Environ Toxicol Chem 2021;40:711-716. © 2020 SETAC.

While parasites are fundamental components of ecological systems, emerging infectious diseases are a growing concern for conservation and management. Understanding the drivers and consequences of disease emergence in natural systems is complex because of the diverse array of factors associated with disease dynamics. Host behaviour plays an important role in disease dynamics across multiple scales (individuals to landscapes). Here, we synthesize our current understanding of the interplay between behaviour and disease in the context of conservation. We review the general importance of behaviour for determining the probability of exposure to parasites and the likelihood of infection once exposed. We also discuss the influence of infection on behaviours that affect disease transmission in populations and the potential trait-mediated indirect interactions that can influence disease risk within communities. Furthermore, we present several case studies demonstrating how the incorporation of behaviour into conservation and management strategies is critical for understanding emerging infectious diseases. Given the fundamental relationships between behaviour and infectious disease, there is a need for the development of practical methods for integrating this knowledge into conservation. Establishing a dialogue and forming collaborations between scientists and wildlife managers across multiple scales is an essential step. Ultimately, conservation practices that integrate knowledge of behaviour and infectious diseases will have a greater chance of success.

SUMMARYThe ubiquitous use of pesticides has increased concerns over their direct and indirect effects on disease dynamics. While studies examining the effects of pesticides on host–parasite interactions have largely focused on how pesticides influence the host, few studies have considered the effects of pesticides on parasites. We investigated the toxicity of six common insecticides at six environmentally-relevant concentrations to cercariae of the trematode Echinoparyphium from two populations. All six insecticides reduced the survival of cercariae (overall difference between mortality in control vs pesticide exposure = 86·2 ± 8·7%) but not in a predictable dose-dependent manner. These results suggest that Echinoparyphium are sensitive to a broad range of insecticides commonly used in the USA. The lack of a clear dose-dependent response in Echinoparyphium highlights the potential limitations of toxicity assays in predicting pesticide toxicity to parasites. Finally, population-level variation in cercarial susceptibility to pesticides underscores the importance of accounting for population variation as overlooking this variation can limit our ability to predict toxicity in nature. Collectively, this work demonstrates that consideration of pesticide toxicity to parasites is important to understanding how pesticides ultimately shape disease dynamics in nature.

Anthropogenic activities can have significant ecological and evolutionary consequences on populations and communities. In the United States, neonicotinoid insecticides are widespread across the agricultural Midwest and frequently detected in stream systems. Their effect on Heptageniidae mayflies is a major concern because they are highly sensitive to neonicotinoids and have some of the lowest reported tolerance values of any organism. Our objective was to evaluate population-level variation in neonicotinoid sensitivity. We did so by conducting 96 h half maximal effective concentration (EC5096-h) tests for the neonicotinoids clothianidin and thiamethoxam on populations of Stenacron, Stenonema, and Maccaffertium mayflies and testing for associations with agricultural landcover. Additionally, we collected water samples to assess temporal patterns of neonicotinoid presence in stream habitats. We found variation in neonicotinoid tolerance with EC50 values ranging from 4.9 μg/L to 32 μg/L and 19.8 μg/L to 86.5 μg/L for clothianidin and thiamethoxam, respectively. Agricultural landcover was associated with neonicotinoid tolerance for Stenacron and thiamethoxam but not for other comparisons. Moreover, water samples demonstrated that the amount of agricultural landcover was not a strong predictor of neonicotinoids presence in streams. Our data suggest that populations of Heptageniidae mayflies can vary substantially in neonicotinoid tolerance. Population-level variation should be considered in toxicity assessments and presents the potential for evolved tolerance.

Poly- and perfluoroalkyl substances (PFAS) are ubiquitous contaminants that can bioaccumulate in aquatic taxa. Amphibians are particularly vulnerable to contaminants and sensitive to endocrine disruptors during their aquatic larval stage. However, few studies have explored PFAS uptake rates in amphibians, which is critical for designing ecotoxicology studies and assessing the potential for bioaccumulation. Uptake rates of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were measured for larval northern leopard frogs (Rana pipiens), American toads (Anaxyrus americanus), and eastern tiger salamanders (Ambystoma tigrinum) during a 240-h exposure to 10 and 1000 μg/L concentrations. We measured body burden and calculated bioconcentration factor (BCF) every 48 h during the experiments. For all species and exposures, body burdens often reached steady state within 48–96 h of exposure. Steady-state body burdens for PFOA and PFOS ranged from 3819 to 16,481 ng/g dry weight (BCF = 0.46–2.5) and 6955–489,958 ng/g dry weight (47–259 BCFs), respectively. Therefore, PFAS steady state occurs rapidly in the larval amphibians we studied and particularly for PFOS. This result reflects a high potential for PFAS trophic transfer because amphibians are often low in trophic position and are important prey for many aquatic and terrestrial species.

Pesticide pollution can alter parasite transmission, but scientists are unaware if effects of pesticides on parasite exposure and host susceptibility (i.e. infection risk given exposure) can be generalised within a community context. Using replicated temperate pond communities, we evaluate effects of 12 pesticides, nested in four pesticide classes (chloroacetanilides, triazines, carbamates organophosphates) and two pesticide types (herbicides, insecticides) applied at standardised environmental concentrations on larval amphibian exposure and susceptibility to trematode parasites. Most of the variation in exposure and susceptibility occurred at the level of pesticide class and type, not individual compounds. The organophosphate class of insecticides increased snail abundance (first intermediate host) and thus trematode exposure by increasing mortality of snail predators (top-down mechanism). While a similar pattern in snail abundance and trematode exposure was observed with triazine herbicides, this effect was driven by increases in snail resources (periphytic algae, bottom-up mechanism). Additionally, herbicides indirectly increased host susceptibility and trematode infections by (1) increasing time spent in susceptible early developmental stages and (2) suppressing tadpole immunity. Understanding generalisable effects associated with contaminant class and type on transmission is critical in reducing complexities in predicting disease dynamics in at-risk host populations.

Indiana is home to many types of aquatic ecosystems, including lakes, rivers, streams, wetlands and temporary (ephemeral) pools, which provide habitats for a wide range of plants and animals. These ecosystems will experience changes in water quantity, water temperature, ice cover, water clarity and oxygen content as the state’s temperature and rainfall patterns shift. The plants and animals living in these aquatic ecosystems will undergo changes that will vary based on the species and the specific places they inhabit. It is challenging to know precisely how organisms will respond to changes in climate. Effects on one species create a difficult-to-predict chain reaction that potentially influences other species in the same ecosystem. Some organisms will adapt and evolve to survive, or even thrive, as the climate changes, but they will have to adjust to more than just the changes in climate. They will also respond to changes in a wide variety of other environmental factors that affect them, including invasive species, habitat destruction, contaminants, nutrient runoff, and land management decisions. While these complicated interactions make it challenging to predict the long-term fate of Indiana’s aquatic species, enough is known about climate-related stressors to help managers develop strategies to avoid the most critical outcomes, hopefully avoiding species loss. This report from the Indiana Climate Change Impacts Assessment (IN CCIA) uses climate projections for the state to explore the potential threats to Indiana’s aquatic ecosystems and describes potential management implications and opportunities.

1) Predators and pathogens are fundamental components of ecological communities that have the potential to influence each other via their interactions with victims and to initiate density- and trait-mediated effects, including trophic cascades. Despite this, experimental tests of the healthy herds hypothesis, wherein predators influence pathogen transmission, are rare. Moreover, no studies have separated effects mediated by density vs. traits. Using a semi-natural mesocosm experiment, we investigated the interactive effects of predatory dragonfly larvae (caged or lethal [free-ranging]) and a viral pathogen, ranavirus, on larval amphibians (gray treefrogs and northern leopard frogs). 2) We determined the influence of predators on ranavirus transmission and the relative importance of density- and trait-mediated effects on observed patterns. Lethal predators reduced ranavirus infection prevalence by 57–83% compared to no-predator and caged-predator treatments. The healthy-herds effect was more strongly associated with reductions in tadpole density than behavioral responses to predators. 3) We also assessed whether ranavirus altered the responses of tadpoles to predators. In the absence of virus, tadpoles reduced activity levels and developed deeper tails in the presence of predators. However, there was no evidence that virus presence or infection altered responses to predators. 4) Finally, we compared the magnitude of trophic cascades initiated by individual and combined natural enemies. Lethal predators initiated a trophic cascade by reducing tadpole density, but caged predators and ranavirus did not. The absence of a virus-induced trophic cascade is ostensibly the consequence of limited virus-induced mortality and the ability of infected individuals to continue interacting within the community. 5) Our results provide support for the healthy herds hypothesis in amphibian communities. We uniquely demonstrate that density-mediated effects of predators outweigh trait-mediated effects in driving this pattern. Moreover, this study was one of the first to directly compare trophic cascades caused by predators and pathogens. Our results underscore the importance of examining the interactions between predators and pathogens in ecology.

Summary 1.Associations among parasites affect many aspects of host-parasite dynamics, but a lack of analytical tools has limited investigations of parasite correlations in observational data that are often nested across spatial and biological scales. 2.Here we illustrate how hierarchical, multiresponse modeling can characterize parasite associations by allowing for hierarchical structuring, offering estimates of uncertainty, and incorporating correlational model structures. After introducing the general approach, we apply this framework to investigate coinfections among four amphibian parasites (the trematodes Ribeiroia ondatrae and Echinostoma spp., the chytrid fungus Batrachochytrium dendrobatidis, and ranaviruses) and among >2000 individual hosts, 90 study sites, and five amphibian host species. 3.Ninety-two percent of sites and 80% of hosts supported two or more pathogen species. Our results revealed strong correlations between parasite pairs that varied by scale (from among hosts to among sites) and classification (microparasite versus macroparasite), but were broadly consistent across taxonomically diverse host species. At the host-scale, infection by the trematode R. ondatrae correlated positively with the microparasites, B. dendrobatidis and ranavirus, which were themselves positively associated. However, infection by a second trematode (Echinostoma spp.) correlated negatively with B. dendrobatidis and ranavirus, both at the host- and site-level scales, highlighting the importance of differential relationships between micro- and macroparasites. 4.Given the extensive number of coinfecting symbiont combinations inherent to natural systems, particularly across multiple host species, multiresponse modeling of cross-sectional field data offers a valuable tool to identify a tractable number of hypothesized interactions for experimental testing while accounting for uncertainty and potential sources of co-exposure. For amphibians specifically, the high frequency of co-occurrence and coinfection among these pathogens – each of which is known to impair host fitness or survival – highlights the urgency of understanding parasite associations for conservation and disease management. This article is protected by copyright. All rights reserved.

1. A fundamental goal of disease ecology is to determine the landscape and environmental processes that drive disease dynamics at different biological levels to guide management and conservation. Although ranaviruses (family Iridoviridae) are emerging amphibian pathogens, few studies have conducted comprehensive field surveys to assess potential drivers of ranavirus disease dynamics. 2. We examined the factors underlying patterns in site-level ranavirus presence and individual-level ranavirus infection in 76 ponds and 1,088 individuals representing 5 amphibian species within the East Bay region of California. 3. Based on a competing-model approach followed by variance partitioning, landscape and biotic variables explained the most variation in site-level presence. However, biotic and individual-level variables explained the most variation in individual-level infection. 4. Distance to nearest ranavirus-infected pond (the landscape factor) was more important than biotic factors at the site-level; however, biotic factors were most influential at the individual-level. At the site level, the probability of ranavirus presence correlated negatively with distance to nearest ranavirus-positive pond, suggesting that the movement of water or mobile taxa (e.g., adult amphibians, birds, reptiles) may facilitate the movement of ranavirus between ponds and across the landscape. 5. Taxonomic richness associated positively with ranavirus presence at the site-level, but vertebrate richness associated negatively with infection prevalence in the host population. This might reflect the contrasting influences of diversity on pathogen colonization versus transmission among hosts. 6. Amphibian host species differed in their likelihood of ranavirus infection: American bullfrogs (Rana catesbeiana) had the weakest association with infection while rough-skinned newts (Taricha granulosa) had the strongest. After accounting for host species effects, hosts with greater snout-vent length had a lower probability of infection. 7. Our study demonstrates the array of landscape, environmental, and individual-level factors associated with ranavirus epidemiology. Moreover, our study helps illustrate that the importance of these factors varies with biological level.

There have been few attempts to synthesise the growing body of literature on phenotypic plasticity to reveal patterns and generalities about the extent and magnitude of plastic responses. Here, we conduct a review and meta-analysis of published literature on phenotypic plasticity in aquatic (marine and freshwater) gastropods, a common system for studying plasticity. We identified 96 studies, using pre-determined search terms, published between 1985 and November 2013. The literature was dominated by studies of predator-induced shell form, snail growth rates and life history parameters of a few model taxa, accounting for 67% of all studies reviewed. Meta-analyses indicated average plastic responses in shell thickness, shell shape, and growth and fecundity of freshwater species was at least three times larger than in marine species. Within marine gastropods, species with planktonic development had similar average plastic responses to species with benthic development. We discuss these findings in the context of the role of costs and limits of phenotypic plasticity and environmental heterogeneity as important constraints on the evolution of plasticity. We also consider potential publication biases and discuss areas for future research, indicating well-studied areas and important knowledge gaps.

While it is well documented that organisms can express phenotypic plasticity in response to single gradients of environmental variation, our understanding of how organisms integrate information along multiple environmental gradients is limited in many systems. Using the freshwater snail Helisoma trivolvis and two common predators (water bugs Belostoma flumineum and crayfish Orconectes rusticus), we explored how prey integrate information along multiple predation risk gradients (i.e. caged predators fed increasing amounts of prey biomass) that induce opposing phenotypes. When exposed to single predators fed increasing amounts of prey biomass, we detected threshold responses; intermediate amounts of consumed biomass induced phenotypic responses, but higher amounts induced little additional induction. This suggests that additional increases in predator-induced traits with greater predator risk offer minimal increases in fitness or that a limit in the response magnitude was reached. Additionally, the response thresholds were contingent on the predator and focal trait. For shell width, responses were generally detected at a lower amount of consumed biomass by water bugs compared to crayfish. Within the crayfish treatments, we found that the shell thickness response threshold was lower than the shell width response threshold. When we combined gradients of consumed biomass from both predators, we found that the magnitude of response to one predator was often reduced when the other predator was present. Interestingly, these effects were often detected at consumed biomass levels that were lower than the threshold concentration necessary to elicit a response in the single-predator treatments. Moreover, our combined predator treatments revealed that snails shifted from discrete responses to more continuous (i.e. graded) responses. Together, our results reveal that organisms experiencing multiple environmental gradients can integrate this information to make phenotypic decisions and demonstrate the novel result that an exposure to multiple species of predators can lower the response threshold of prey.

Understanding population responses to rapid environmental changes caused by anthropogenic activities, such as pesticides, is a research frontier. Genetic assimilation (GA), a process initiated by phenotypic plasticity, is one mechanism potentially influencing evolutionary responses to novel environments. While theoretical and laboratory research suggests that GA has the potential to influence evolutionary trajectories, few studies have assessed its role in the evolution of wild populations experiencing novel environments. Using the insecticide, carbaryl, and 15 wood frog populations distributed across an agricultural gradient, we tested whether GA contributed to the evolution of pesticide tolerance. First, we investigated the evidence for evolved tolerance to carbaryl and discovered that population-level patterns of tolerance were consistent with evolutionary responses to pesticides; wood frog populations living closer to agriculture were more tolerant than populations living far from agriculture. Next, we tested the potential role of GA in the evolution of pesticide tolerance by assessing whether patterns of tolerance were consistent with theoretical predictions. We found that populations close to agriculture displayed constitutive tolerance to carbaryl whereas populations far from agriculture had low naïve tolerance but high magnitudes of induced tolerance. These results suggest GA could play a role in evolutionary responses to novel environments in nature.

AimTo quantify the influence of a suite of landscape, abiotic, biotic, and host-level variables on ranavirus disease dynamics in amphibian assemblages at two biological levels (site and host-level).LocationWetlands within the East Bay region of California, USA.MethodsWe used competing models, multimodel inference, and variance partitioning to examine the influence of 16 landscape and environmental factors on patterns in site-level ranavirus presence and host-level ranavirus infection in 76 wetlands and 1,377 amphibian hosts representing five species.ResultsThe landscape factor explained more variation than any other factors in site-level ranavirus presence, but biotic and host-level factors explained more variation in host-level ranavirus infection. At both the site- and host-level, the probability of ranavirus presence correlated negatively with distance to nearest ranavirus-positive wetland. At the site-level, ranavirus presence was associated positively with taxonomic richness. However, infection prevalence within the amphibian population correlated negatively with vertebrate richness. Finally, amphibian host species differed in their likelihood of ranavirus infection: American Bullfrogs had the weakest association with infection while Western Toads had the strongest. After accounting for host species effects, hosts with greater snout-vent length had a lower probability of infection.Main conclusionsStrong spatial influences at both biological levels suggest that mobile taxa (e.g., adult amphibians, birds, reptiles) may facilitate the movement of ranavirus among hosts and across the landscape. Higher taxonomic richness at sites may provide more opportunities for colonization or the presence of reservoir hosts that may influence ranavirus presence. Higher host richness correlating with higher ranavirus infection is suggestive of a dilution effect that has been observed for other amphibian disease systems and warrants further investigation. Our study demonstrates that an array of landscape, environmental, and host-level factors were associated with ranavirus epidemiology and illustrates that their importance vary with biological level.