Rana Pipiens Research Articles

Healthy but smaller herds: Predators reduce pathogen transmission in an amphibian assemblage.

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 (grey treefrogs and northern leopard frogs). 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 behavioural responses to predators. 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. 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. 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.

Bioevaluation of Ranatuerin-2Pb from the Frog Skin Secretion of Rana pipiens and its Truncated Analogues.

Antimicrobial peptides (AMPs) are considered as a promising agent to overcome the drug-resistance of bacteria. Large numbers of AMPs have been identified from the skin secretion of Rana pipiens, including brevinins, ranatuerins, temporins and esculentins. In this study, the cDNA precursor of a broad-spectrum antimicrobial peptide, ranatuerin-2Pb, was cloned and identified. Additionally, two truncated analogues, RPa and RPb, were synthesised to investigate the structure-activity relationship of ranatuerin-2Pb. RPa lost antimicrobial activity against Candida albicans, MRSA, Enterococcus faecalis and Pseudomonas aeruginosa, while RPb retained its broad-spectrum antimicrobial activity. Additionally, ranatuerin-2Pb, RPa and RPb demonstrated inhibition and eradication effects against Staphylococcus aureus biofilm. RPb showed a rapid bacterial killing manner via membrane permeabilization without damaging the cell membrane of erythrocytes. Moreover, RPb decreased the mortality of S. aureus infected Galleria mellonella larvae. Collectively, our results suggested that RPb may pave a novel way for natural antimicrobial drug design.

Developmental exposure to perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) selectively decreases brain dopamine levels in Northern leopard frogs

Per- and polyfluoroalkyl substances (PFAS) are synthetic compounds that are a major public health concern due to widespread use, long environmental and biological half-lives, detection in most human plasma samples, and links to multiple adverse health outcomes. The literature suggests that some PFAS may be neurotoxic. However, there are major gaps in the literature with respect to how environmentally-relevant doses during development may influence the nervous system. To address this gap, we utilized a sentinel species, Northern leopard frogs (Lithobates pipiens) to determine the effects of developmental exposure to environmentally relevant perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) on major neurotransmitter systems. Frog larvae at Gosner stage 25 were exposed to 10, 100, or 1000 ppb PFOS or PFOA for 30 days before neurochemical analysis. High performance liquid chromatography (HPLC) with electrochemical detection or fluorescent detection assays was used to measure neurotransmitter levels, which were normalized to protein levels in each sample. Dopamine (DA) decreased significantly in the brains of frogs treated with PFOA (1000 ppb) and PFOS (100 and 1000 ppb). Significant increases in DA turnover also resulted from PFOA and PFOS treatment. Neither PFOS, nor PFOA produced detectable alterations in serotonin (nor its metabolite), norepinephrine, gamma-amino butyric acid (GABA), glutamate, or acetylcholine. PFAS body burdens showed that PFOS accumulated relative to dose, while PFOA did not. These data suggest that DArgic neurotransmission is selectively affected in developmentally exposed amphibians and that PFAS should be evaluated for a potential role in diseases that target the DA system.

MEMRI for visualizing brain activity after auditory stimulation in frogs.

Anuran amphibians are common model organisms in bioacoustics and neurobiology. To date, however, most available methods for studying auditory processing in frogs are highly invasive and thus do not allow for longitudinal study designs, nor do they provide a global view of the brain, which substantially limits the questions that can be addressed. The goal of this study was to identify areas in the frog brain that are responsible for auditory processing using in vivo manganese-enhanced MRI (MEMRI). We were interested in determining if the neural processing of socially relevant acoustic stimuli (e.g., species-specific calls) engages a specific pattern of brain activation that differs from patterns elicited by less- or nonrelevant acoustic signals. We thus designed an experiment, in which we presented three different types of acoustic stimuli (species-specific calls, band-limited noise, or silence) to fully awake northern leopard frogs (Rana pipiens) and then conducted MEMRI T1-weighted imaging to investigate differences in signal intensity due to manganese uptake as an indication of brain activity across all three conditions. We found the greatest change in signal intensity within the torus semicircularis (the principal central auditory region), the habenula, and the paraphysis of frogs that had been exposed to conspecific calls compared with noise or silence conditions. Stimulation with noise did not result in the same activation patterns, indicating that signals with contrasting social relevance are differentially processed in these areas of the amphibian brain. MEMRI provides a powerful approach to studying brain activity with high spatial resolution in frogs. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Amphibian Host and Skin Microbiota Response to a Common Agricultural Antimicrobial and Internal Parasite.

Holistic approaches that simultaneously characterize responses of both microbial symbionts and their hosts to environmental shifts are imperative to understanding the role of microbiotas on host health. Using the northern leopard frog (Lithobates pipiens) as our model, we investigated the effects of a common trematode (family Echinostomatidae), a common agricultural antimicrobial (Sulfadimethoxine; SDM), and their interaction on amphibian skin microbiota and amphibian health (growth metrics and susceptibility to parasites). In the trematode-exposed individuals, we noted an increase in alpha diversity and a shift in microbial communities. In the SDM-treated individuals, we found a change in the composition of the skin microbiota similar to those induced by the trematode treatment. Groups treated with SDM, echinostomes, or a combination of SDM and echinostomes, had higher relative abundances of OTUs assigned to Flavobacterium and Acinetobacter. Both of these genera have been associated with infectious disease in amphibians and the production of anti-pathogen metabolites. Similar changes in microbial community composition between SDM and trematode exposed individuals may have resulted from stress-related disruption of host immunity. Despite changes in the microbiota, we found no effect of echinostomes and SDM on host health. Given the current disease- and pollution-related threats facing amphibians, our study highlights the need to continue to evaluate the influence of natural and anthropogenic stressors on host-associated microbial communities.

Safeguarding Wetlands and Their Connections within Wetlandscapes to Improve Conservation Outcomes for Threatened Amphibian Species

AbstractWetlands should not be considered as independent objects but as dynamically connected objects, collectively known as wetlandscapes. We developed a framework that analyzes the influences of wetland suitability and connectivity on amphibian distributions. We defined two indices: a Wetland Suitability Index describing wetland quality and a Movement Permeability Index characterizing wetland connectivity for amphibian population dynamics. These indices were calculated from raster datasets and time‐varying inundation estimates. The indices were used to define a wetlandscape and an amphibian model was used to simulate population dynamics within the wetlandscape. The framework was applied to the Nose Creek watershed, a highly modified wetlandscape in Alberta, Canada. Two amphibian species were selected with different habitat preferences: the Northern Leopard Frog that prefers wet habitats and has high mobility over land, and the Great Plains Toad that prefers terrestrial habitats and has low mobility over land. We found each amphibian species had a “preferred” wetlandscape, reflecting their life cycle traits and migration strategies which in turn were dependent on the hydrological and ecological connections within the wetlandscape. This study highlights the importance of investigating both individual wetlands and the wetlandscape and considering both wetland habitat quality and connectivity as non‐substitutable properties that act jointly, but differently, on population dynamics.

Application of CNTF or FGF-2 increases the number of M2-like macrophages after optic nerve injury in adult Rana pipiens.

We have previously shown that a single application of the growth factors ciliary neurotrophic factor (CNTF) or fibroblast growth factor 2 (FGF-2) to the crushed optic nerve of the frog, Rana pipiens, increases the numbers and elongation rate of regenerating retinal ganglion cell axons. Here we investigate the effects of these factors on the numbers and types of macrophages that invade the regeneration zone. In control PBS-treated nerves, many macrophages are present 100 μm distal to the crush site at 1 week after injury; their numbers halve by 2 weeks. A single application of CNTF at the time of injury triples the numbers of macrophages at 1 week, with this increase compared to control being maintained at 2 weeks. Application of FGF-2 is equally effective at 1 week, but the macrophage numbers have fallen to control levels at 2 weeks. Immunostaining with a pan-macrophage marker, ED1, and a marker for M2-like macrophages, Arg-1, showed that the proportion of the putative M2 phenotype remained at approximately 80% with all treatments. Electron microscopy of the macrophages at 1 week shows strong phagocytic activity with all treatments, with many vacuoles containing axon fragments and membrane debris. At 2 weeks with PBS or FGF-2 treatment the remaining macrophages are less phagocytically active, containing mainly lipid inclusions. With CNTF treatment, at 2 weeks many of the more numerous macrophages are still phagocytosing axonal debris, although they also contain lipid inclusions. We conclude that the increase in macrophage influx seen after growth factor application is beneficial for the regenerating axons, probably due to more extensive removal of degenerating distal axons, but also perhaps to secretion of growth-promoting substances.

Larval amphibians rapidly bioaccumulate poly- and perfluoroalkyl substances

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.

Habitat selection by Common Gartersnakes (<i>Thamnophis sirtalis</i>) is affected by vegetation structure but not by location of Northern Leopard Frog (<i>Lithobates pipiens</i>) prey

Understanding the factors affecting habitat selection of species is important for effective management and for conservation because habitat selection affects fitness. We tested the competing, but not mutually exclusive, hypotheses that habitat selection of Common Gartersnakes (Thamnophis sirtalis) at a fine spatial scale is driven by vegetation structure or by Northern Leopard Frog (Lithobates pipiens) prey abundance. We conducted surveys for snakes and frogs in six, 1-ha study grids in eastern Ontario in 2014 and 2015. Common Gartersnakes used areas dominated by forbs more than expected based on availability, and used grassy areas less than expected based on availability. Gartersnakes showed no preference for sites with more frogs. Thus, vegetation structure is important in habitat selection of Common Gartersnakes, but Northern Leopard Frog abundance is not. Common Gartersnakes and Northern Leopard Frogs did have a preference for forbs, but gartersnakes do not appear to be using habitat specifically based on frog abundance at a fine scale. Future work should study habitat use by snakes over a longer period to account for high variability in frog abundance and for temporal changes in habitat structure. Future work should also examine the distribution of other prey items in relation to the distribution of snakes.

Artificial reproduction using leuprolide acetate in the frog Rana pipiens

Procuring offspring from captive animals can be important for research and conservation efforts. Yet, reliable methods for obtaining fertilised eggs are unavailable for many species. In this study, we examined the efficacy of one drug, leuprolide acetate, to induce reproduction (i.e. egg production, tadpole hatching) in the northern leopard frog, Rana pipiens. We found that leuprolide acetate successfully induced breeding and larval development in animals that were overwintered in the lab, but not in animals caught during the breeding season. These results indicate that leuprolide acetate can be successful in inducing breeding and fertilisation of frog eggs, but that its effectiveness might be contingent upon length of time in captivity and the animals having undergone an artificial overwintering period in the laboratory prior to induction. Artificial breeding success is species and context dependent; therefore, identifying additional methods effective across taxa will help support species in need of management intervention.

Artificial reproduction using leuprolide acetate in the frog Rana pipiens

Procuring offspring from captive animals can be important for research and conservation efforts. Yet, reliable methods for obtaining fertilised eggs are unavailable for many species. In this study, we examined the efficacy of one drug, leuprolide acetate, to induce reproduction (i.e. egg production, tadpole hatching) in the northern leopard frog, Rana pipiens. We found that leuprolide acetate successfully induced breeding and larval development in animals that were overwintered in the lab, but not in animals caught during the breeding season. These results indicate that leuprolide acetate can be successful in inducing breeding and fertilisation of frog eggs, but that its effectiveness might be contingent upon length of time in captivity and the animals having undergone an artificial overwintering period in the laboratory prior to induction. Artificial breeding success is species and context dependent; therefore, identifying additional methods effective across taxa will help support species in need of management intervention.

Retinoic acid application affects optic nerve microglia and macrophages after optic nerve injury in frog Rana pipiens

Retinoic acid (RA) plays major roles during nervous system development. We have previously shown that RA signaling pathway components are upregulated after optic nerve injury and that exogenous application of RA improves the long‐term survival of axotomized retinal ganglion cells to more than 90%. In addition, there is some evidence that RA may be a factor involved in the induction of phagocytic macrophages, promoting the production of pro‐repair chemokines that could play a role in successful regeneration. The objective of the present study is to determine the effects of RA application on the macrophage populations in the optic nerve after injury. We performed optic nerve crush and applied into the nerve either saline solution or retinoic acid. We examined the optic nerves at 48h, one week, and two weeks after axotomy with immunocytochemistry and electron microscopy. Electron microscope studies of the proximal, injury, and distal sites of the optic nerves show macrophages filled with secondary lysosomes and residual bodies. Immunocytochemistry of various macrophage subtypes was carried out followed by confocal microscopy. Our results indicate that application of RA to the optic nerve causes a significant increase in the number of macrophages and microglia present one week after optic nerve injury. Most cells were CD68‐positive in saline‐ and RA‐treated nerves. We also identified activated microglia (Iba1‐positive) and a sub‐population of anti‐inflammatory M2 macrophages (arginase‐positive) at the injury and distal sites. In conclusion, the application of RA affects the number and the distribution of macrophages after optic nerve injury and it may play a role in the success of optic nerve regeneration.Support or Funding InformationREB is supported by NIH grant GM116692, JMB by NIH grant NS081726This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Associations between environmental pollutants and larval amphibians in wetlands contaminated by energy-related brines are potentially mediated by feeding traits

Energy production in the Williston Basin, located in the Prairie Pothole Region of central North America, has increased rapidly over the last several decades. Advances in recycling and disposal practices of saline wastewaters (brines) co-produced during energy production have reduced ecological risks, but spills still occur often and legacy practices of releasing brines into the environment caused persistent salinization in many areas. Aside from sodium and chloride, these brines contain elevated concentrations of metals and metalloids (lead, selenium, strontium, antimony and vanadium), ammonium, volatile organic compounds, hydrocarbons, and radionuclides. Amphibians are especially sensitive to chloride and some metals, increasing potential effects in wetlands contaminated by brines. We collected bed sediment and larval amphibians (Ambystoma mavortium, Lithobates pipiens and Pseudacris maculata) from wetlands in Montana and North Dakota representing a range of brine contamination history and severity to determine if contamination was associated with metal concentrations in sediments and if metal accumulation in tissues varied by species. In wetland sediments, brine contamination was positively associated with the concentrations of sodium and strontium, both known to occur in oil and gas wastewater, but negatively correlated with mercury. In amphibian tissues, selenium and vanadium were associated with brine contamination. Metal tissue concentrations were higher in tadpoles that graze compared to predatory salamanders; this suggests frequent contact with the sediments could lead to greater ingestion of metal-laden materials. Although many of these metals may not be directly linked with energy development, the potential additive or synergistic effects of exposure along with elevated chloride from brines could have important consequences for aquatic organisms. To effectively manage amphibian populations in wetlands contaminated by saline wastewaters we need a better understanding of how life history traits, species-specific susceptibilities and the physical-chemical properties of metals co-occurring in wetland sediments interact with other stressors like chloride and wetland drying.

Landscape genetics reveal broad and fine-scale population structure due to landscape features and climate history in the northern leopard frog (Rana pipiens) in North Dakota.

Prehistoric climate and landscape features play large roles structuring wildlife populations. The amphibians of the northern Great Plains of North America present an opportunity to investigate how these factors affect colonization, migration, and current population genetic structure. This study used 11 microsatellite loci to genotype 1,230 northern leopard frogs (Rana pipiens) from 41 wetlands (30 samples/wetland) across North Dakota. Genetic structure of the sampled frogs was evaluated using Bayesian and multivariate clustering methods. All analyses produced concordant results, identifying a major east–west split between two R. pipiens population clusters separated by the Missouri River. Substructuring within the two major identified population clusters was also found. Spatial principal component analysis (sPCA) and variance partitioning analysis identified distance, river basins, and the Missouri River as the most important landscape factors differentiating R. pipiens populations across the state. Bayesian reconstruction of coalescence times suggested the major east–west split occurred ~13–18 kya during a period of glacial retreat in the northern Great Plains and substructuring largely occurred ~5–11 kya during a period of extreme drought cycles. A range‐wide species distribution model (SDM) for R. pipiens was developed and applied to prehistoric climate conditions during the Last Glacial Maximum (21 kya) and the mid‐Holocene (6 kya) from the CCSM4 climate model to identify potential refugia. The SDM indicated potential refugia existed in South Dakota or further south in Nebraska. The ancestral populations of R. pipiens in North Dakota may have inhabited these refugia, but more sampling outside the state is needed to reconstruct the route of colonization. Using microsatellite genotype data, this study determined that colonization from glacial refugia, drought dynamics in the northern Great Plains, and major rivers acting as barriers to gene flow were the defining forces shaping the regional population structure of R. pipiens in North Dakota.

Light-Induced Length Shrinkage of Rod Photoreceptor Outer Segments.

PurposeThis study was designed to verify light-induced outer segment (OS) length shrinkage of rod photoreceptors and to characterize its anatomic source at disc-level resolution.MethodsFrog (Rana pipiens) retinas were used for this study. Time-lapse light microscopy of freshly isolated OSs was employed to test transient rod OS changes at 10 ms temporal resolution. Histological light microscopy of dark- and light-adapted retinas was used to confirm light-induced rod OS length changes; and transmission electron microscopy (TEM) was used to quantify light-driven structural perturbation of rod OSs at disc level resolution.ResultsTime-lapse light microscopy images verified transient length shrinking responses in freshly isolated rod OSs. Histological light microscopy images confirmed reduced rod OS lengths in light-adapted retinas, compared to that of dark-adapted retinas. TEM images disclosed shortened inter-disc distances in light-adapted retinas compared to dark-adapted retinas.ConclusionsLight-induced rod OS length shrinkage was confirmed using time-lapse light microscopy of isolated rod OSs and histological light microscopy of dark- and light-adapted retinas. TEM revealed that the rod OS length shrinkage was correlated to the light-driven decrease of the space between individual discs, not the disc thickness itself.Translational RelevanceLight-induced transient rod response promises a noninvasive biomarker for early diagnosis of age-related macular degeneration and retinitis pigmentosa, in which the rod photoreceptors are known to be more vulnerable than cone photoreceptors.

Effects of persistent energy-related brine contamination on amphibian abundance in national wildlife refuge wetlands

To inform sustainable energy development, it is important to understand the ecological effects of historical and current production practices and the persistence of those effects. The Williston Basin is one of North America's largest oil production areas and overlaps the Prairie Pothole Region, an area densely populated with wetlands that provide important wildlife habitat. Although historical disposal practices that released chloride-rich waters (brines) produced during oil extraction into the environment are no longer used, brine spills still occur frequently. We sampled 33 wetlands for three amphibian species in Montana and North Dakota during 2015–2017, primarily on National Wildlife Refuges, and used N-mixture models to determine how abundance varied with evidence of brine contamination. To provide insight into effects of historical versus contemporary contamination, we also estimated the association of well density and age with water quality and amphibian abundance. Abundance of boreal chorus frog (Pseudacris maculata) larvae declined most rapidly in response to increased chloride (range: 0.04–17,500 mg/L), followed by the northern leopard frog (Lithobates [Rana] pipiens) and barred tiger salamander (Ambystoma mavortium). Water quality and population- and community-level abundance of amphibians were more strongly related to nearby wells (≤800 m) installed before 1982 than to wells installed since 1982. These results suggest historical brine management practices were the primary driver of contamination and reduced amphibian abundance in wetlands we sampled, reflecting multi-decadal ecological effects. These persistent effects also underscore the critical need for tools to restore landscapes affected by brine contamination.

Predator Effects on Metamorphosis: The Effects of Scaring Versus Thinning at High Prey Densities

Organisms with complex life cycles face the challenge of when to switch between habitats and foraging strategies over ontogeny in ways that improve their fitness. Metamorphosis is a well-studied life history event in animals, and ecologists have spent decades trying to understand how the size at and time to metamorphosis are altered by natural stressors such as competition and predation. The challenges in interpreting the effects of predators on metamorphic decisions include the need to compare predator species that pose different levels of risk, compare the roles of predators inducing fear versus thinning of the density of prey, and examine prey life history traits and behavior over ontogeny. We addressed these challenges in a mesocosm experiment in which we introduced a high initial density of hatchling Northern Leopard Frogs (Rana pipiens) and exposed them to three different species of caged predators (to induce three different levels of fear), three rates of hand-thinning (to mimic the thinning effect...

Interaction between invasive plant leaf litter and NaCl on two model amphibians

Human activities are rapidly changing natural environments, often with harmful consequences for native communities. The introduction of invasive species is particularly damaging to native communities, especially when invasive species alter the chemical environment and create novel, stressful conditions. These abiotic conditions are predicted to favor other stress-tolerant organisms, potentially shifting community abundance and diversity over time. However, few environments are free of other anthropogenic stressors (i.e., chemical contaminants), which can also influence patterns of abundance and diversity. Therefore, to understand the impacts of invasive species, we need to consider their potential interactions with other anthropogenic stressors. Towards this goal, we tested how leachates from invasive plants and road salt impacted a model amphibian that is native to the U.S. (northern leopard frog, Lithobates pipiens) and a model amphibian that is non-native to the U.S. and considered invasive in some localities (African clawed frog, Xenopus laevis). We examined the effects of native and invasive leaf litter leachate and sublethal NaCl concentrations on amphibian development, size, and tolerance to a lethal concentration of NaCl. Exposure to invasive leaf litter and sublethal NaCl both accelerated hatching time in leopard frogs, but neither affected hatching time in Xenopus. Exposure to invasive leaf litter also led to reduced mass and tolerance to lethal NaCl concentrations in the leopard frog, but had no effect on mass and led to increased tolerance to lethal NaCl concentrations in Xenopus. These findings suggest that invasive leaf litter leachate impacts these amphibian species differently, being more stressful to the leopard frog than Xenopus. Further, we demonstrate that the presence of a pollutant may augment the effect of invasive leaf litter on amphibians, highlighting the need to consider concurrent stressors in invasive species management.

Insecticide-induced changes in amphibian brains: How sublethal concentrations of chlorpyrifos directly affect neurodevelopment.

Widespread use of pesticides often contaminates natural habitats, exposing nontarget organisms to pesticides that were designed to control pest populations. Even low levels of pesticides can affect aquatic communities both directly and indirectly. Previous work has shown that trace amounts of the pesticide chlorpyrifos altered tadpole morphology and neurodevelopment in artificial ponds (mesocosms). To determine whether effects resulted from direct chlorpyrifos exposure or from disruption of the food web due to a pesticide-induced decline in zooplankton, we examined the impacts of chlorpyrifos on amphibian development in the presence of chlorpyrifos-resistant zooplankton, a key component of the aquatic trophic community. Northern leopard frog (Lithobates pipiens) tadpoles were reared through metamorphosis in mesocosms containing either 0 or 1 µg/L chlorpyrifos and either chlorpyrifos-resistant or chlorpyrifos-sensitive Daphnia pulex zooplankton. Developmental exposure to chlorpyrifos resulted in metamorphs with a relatively wider optic tectum, medulla, and diencephalon compared with controls, and this result was found regardless of the zooplankton population within the mesocosm. Thus, chlorpyrifos directly impacted brain development, independent of the effects on the trophic community. With respect to body shape, chlorpyrifos had no effect on body shape of metamorphs reared in mesocosms with chlorpyrifos-sensitive zooplankton, but body shape was sensitive to zooplankton population in the absence of chlorpyrifos. To conclude, low, ecologically relevant doses of organophosphorous pesticides can directly impact neurodevelopment in a vertebrate model. Environ Toxicol Chem 2018;37:2692-2698. © 2018 SETAC.

Exotic InvasivePomacea maculata(Giant Apple Snail) Will Depredate Eggs of Frog and Toad Species of the Southeastern US

Pomacea maculata (Giant Apple Snail) is a freshwater snail from South America that is an invasive species on the Gulf of Mexico coastal plain. A sister species has been shown to prey on amphibian eggs in Asia. To test whether the Giant Apple Snail will prey on amphibian eggs, we presented eggs of Lithobates palustris (Pickerel Frog), Lithobates pipiens (Northern Leopard Frog), and Anaxyrus americanus (American Toad) to Giant Apple Snails in a laboratory experiment. Giant Apple Snails ate the eggs of all 3 species.