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The manner in which parasite intensity and aggregation varies with host age can provide insights into parasite dynamics and help identify potential means of controlling infections in humans and wildlife. A significant challenge is to distinguish among competing mechanistic hypotheses for the relationship between age and parasite intensity or aggregation. Because different mechanisms can generate similar relationships, testing among competing hypotheses can be difficult, particularly in wildlife hosts, and often requires a combination of experimental and model fitting approaches. We used field data, experiments, and model fitting to distinguish among ten plausible drivers of a curvilinear age-intensity relationship and increasing aggregation with host age for echinostome trematode infections of green frogs. We found little support for most of these proposed drivers but did find that the parsimonious explanation for the observed age-intensity relationship was seasonal exposure to echinostomes. The parsimonious explanation for the aggregated distribution of parasites in this host population was heterogeneity in exposure. A predictive model incorporating seasonal exposure indicated that tadpoles hatching early or late in the breeding season should have lower trematode burdens at metamorphosis, particularly with simulated warmer climates. Application of this multi-pronged approach (field surveys, lab experiments, and modeling) to additional parasite-host systems could lead to discovery of general patterns in the drivers of parasite age-intensity and age-distribution relationships.

An important contribution to infectious disease emergence in wildlife is environmental degradation driven by pollution, habitat fragmentation, and eutrophication. Amphibians are a wildlife group that is particularly sensitive to land use change, infectious diseases, and their interactions. Residential suburban land use is now a dominant, and increasing, form of land cover in the USA and globally, contributing to increased pollutant and nutrient loading in freshwater systems. We examined how suburbanization affects the infection of green frog (Rana clamitans) tadpoles and metamorphs by parasitic flatworms (Echinostoma spp.) through the alteration of landscapes surrounding ponds and concomitant changes in water quality. Using sixteen small ponds along a forest-suburban land use gradient, we assessed how the extent of suburban land use surrounding ponds influenced echinostome infection in both primary snail and secondary frog hosts. Our results show that the degree of suburbanization and concurrent chemical loading are positively associated with the presence and burden of echinostome infection in both host populations. This work contributes to a broader understanding of how land use mediates wildlife parasitism and shows how human activities at the household scale can have similar consequences for wildlife health as seemingly more intensive land uses like agriculture or urbanization. [ABSTRACT FROM AUTHOR]

Preference-performance theory predicts that females should select breeding sites that maximize offspring performance. Amphibians have been a model system for investigating habitat selection, yet most studies have focused on habitat selection in response to predators and conspecifics. We investigated female oviposition site selection and larval performance in eastern gray treefrogs (Hyla versicolor) among pools with and without one of two ecologically distinct heterospecific larvae, the green frog (Rana clamitans) and the American bullfrog (Rana catesbeiana). Pools without heterospecifics were used on more nights and had more eggs deposited compared to pools with heterospecifics. In a competition experiment, treefrog larval performance matched this female preference: tadpoles developed faster and grew larger in the absence of either heterospecific. Although we hypothesized that bullfrogs would more strongly affect female treefrog preference and offspring performance because of previous work demonstrating that bullfrogs had stronger negative effects on other tadpoles, both heterospecifics elicited similar responses. The effects of heterospecifics on anuran breeding site selection are understudied and not well understood, and our results demonstrate that female selection of breeding sites is an adaptive behavior for offspring in the presence of heterospecific competitors., (© 2023 The Authors. Ecology published by Wiley Periodicals LLC on behalf of The Ecological Society of America.)

In the last several decades, amphibian populations have been declining worldwide. Many factors have been linked to global amphibian decline, including habitat destruction, pollution, introduced species, global environmental changes, and emerging infectious diseases. Recent studies of amphibian skin infections were mainly focused on the presence of chytridiomycosis, neglecting other members of the frogs' skin communities. The diversity pattern of fungal dwellers on the skin of green frogs (Pelophylax esculentus complex) was investigated. A total of 100 adults were sampled from three localities in South Banat (northern Serbia) over three consecutive years and detected fungal dwellers were identified using light microscopy and ITS and BenA gene sequencing. Structures belonging to fungi and fungus-like organisms including a variety of spores and different mycelia types were documented in the biofilm formed on amphibian skin, and are classified into 10 groups. In total, 42 fungal isolates were identified to species, section, or genus level. The difference in mycobiota composition between sampling points (localities and green frog taxa) was documented. The highest number of fungal structures and isolates was recorded on the hybrid taxon P. esculentus and locality Stevanove ravnice. Parental species showed a markedly lower diversity than the hybrid taxon and were more similar in diversity patterns and were placed in the same homogenous group. The locality Stevanove ravnice exhibited more pronounced differences in diversity pattern than the other two localities and was placed in a distinct and separate homogenous group. Among the fungal isolates, the highest isolation frequency was documented for Alternaria alternata, Aspergillus sp. sect. Nigri, Epicoccum nigrum, Fusarium proliferatum, and Trichoderma atroviride. Among the documented species, dematiaceous fungi, causative agents of chromomycosis in amphibians, were also recorded in this research with high isolation frequency. Also, some rare fungal species such as Quambalaria cyanescens and Pseudoteniolina globosa are documented for the first time in this research as microbial inhabitants of amphibian skin., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Global climate change is expected to alter patterns of temperature variability, which could influence species interactions including parasitism. Species interactions can be difficult to predict in variable-temperature environments because of thermal acclimation responses, i.e. physiological changes that allow organisms to adjust to a new temperature following a temperature shift., The goal of this study was to determine how thermal acclimation influences host resistance to infection and to test for parasite acclimation responses, which might differ from host responses in important ways., We tested predictions of three, non-mutually exclusive hypotheses regarding thermal acclimation effects on infection of green frog tadpoles ( Lithobates clamitans) by the trematode parasite Ribeiroia ondatrae with fully replicated controlled-temperature experiments. Trematodes or tadpoles were independently acclimated to a range of 'acclimation temperatures' prior to shifting them to new 'performance temperatures' for experimental infections., Trematodes that were acclimated to intermediate temperatures (19-22 °C) had greater encystment success across temperatures than either cold- or warm-acclimated trematodes. However, host acclimation responses varied depending on the stage of infection (encystment vs. clearance): warm- (22-28 °C) and cold-acclimated (13-19 °C) tadpoles had fewer parasites encyst at warm and cold performance temperatures, respectively, whereas intermediate-acclimated tadpoles (19-25 °C) cleared the greatest proportion of parasites in the week following exposure., These results suggest that tadpoles use different immune mechanisms to resist different stages of trematode infection, and that each set of mechanisms has unique responses to temperature variability. Our results highlight the importance of considering thermal responses of both parasites and hosts when predicting disease patterns in variable-temperature environments. [ABSTRACT FROM AUTHOR]

Suburban neighborhoods are a dominant type of human land use. Many housing regions globally rely on septic systems, rather than sanitary sewers, for wastewater management. There is evidence that septic systems may contaminate waterbodies more than sewer lines. There is also mounting evidence that human activities contaminate waterways with endocrine-disrupting chemicals (EDCs), which alter wildlife sexual development. While endocrine disruption is often associated with intense activities such as agriculture or wastewater treatment plant discharges, recent evidence indicates that endocrine disruption is pervasive in frogs from suburban neighborhoods. In conjunction with other putative EDC sources, one hypothesis is that wastewater is contaminating suburban waterways with EDCs derived from pharmaceuticals or personal care products. Here, we measure estradiol (E2) in metamorphosing green frogs ( Rana clamitans ) from forested ponds and suburban ponds adjacent to either septic tanks or sanitary sewers. We show that E2 is highest in male frogs from septic neighborhoods and that E2 concentrations are significantly lower in male frogs from forested ponds and from ponds near sewers. These results indicate that septic tanks may be contaminating aquatic ecosystems differently than sewer lines. This pattern contrasts prior work showing no difference in EDC contamination or morphological endocrine disruption between septic and sewer neighborhoods, implying that suburbanization may have varying effects at multiple biological scales like physiology and anatomy. [ABSTRACT FROM AUTHOR]

How parasites influence individual host traits and survival often depends on the ecological context of the host-parasite interaction, such as the presence of competitors or predators and trait variation among hosts., We examined the effects of three key components of ecological context - host density, size structure and predator cue - on interactions between larval frogs and trematode parasites (Digenea: Echinostomatidae) in mesocosms., We found that effects of parasites on host growth could be either negative or positive, depending on host size and overall growth rate, but not on predator presence. A surprising positive effect of parasites on host growth under some conditions could represent an adaptive host life history response, whereby enhanced growth allows escape from a smaller, less tolerant size class that experiences more negative fitness effects of infection., Notably, only host size class was a strong predictor of infection intensity, but not host density or predator cue., Overall, these results suggest that parasitism, competition and host size interact to influence host fitness. Ecological context thus mediates the interactions between parasites and their hosts, with implications for parasite effects in nature. [ABSTRACT FROM AUTHOR]

A pre-diabetes syndrome induced by endocrine disruptors (ED) was recently demonstrated in the model amphibian Silurana (Xenopus) tropicalis and was suggested to be a potential cause of amphibian population decline. However, such effects have not been found in wild type frogs exposed to ED and the capacity of amphibians to physiologically develop diabetes under natural conditions has not been confirmed. This study showed that a high fat diet (HFD) model displaying the important characteristics of mammal HFD models including glucose intolerance, insulin resistance and nonalcoholic fatty liver disease (NAFLD) can be developed with green frogs (Pelophylax spp.). Wild green frogs exposed to 10 μg L -1 benzo [a]pyrene (BaP) for 18 h also displayed several characteristics of the pre-diabetes phenotype previously observed in Xenopus including glucose intolerance, gluconeogenesis activation and insulin resistance. The study results confirmed that metabolic disorders induced by ED in wild green frogs are typical of the pre-diabetes phenotype and could serve as a starting point for field studies to determine the role of ED in the decline of amphibian populations. From an environmental perspective, the response of wild green frogs to different ED (10 μg L -1 ) suggests that a simple glucose-tolerance test could be used on wild anurans to identify bodies of water polluted with metabolic disruptors that could affect species fitness., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Parasites and predators can have complex, nonadditive effects on a shared group of victims, which can have important consequences for population dynamics. In particular, parasites can alter host traits that influence prédation risk, and predators can have nonconsumptive effects on prey traits which influence susceptibility (i.e., infection intensity and tolerance) to parasites. Here, we examined the combined effects of trematode parasites (Digenea: Echinostomatidae) and odonate ( Anax) predators on the survival of larval green frogs (Rana clamitans). First, in a large-scale mesocosm experiment, we manipulated the presence or absence of parasites in combination with the presence of no predator, caged predators, or free predators, and measured survival, traits, and infection. Parasites, caged predators, and free predators decreased survival, and we found a strong negative Synergistic effect of parasites in combination with free predators on survival. Importantly, we then examined the potential mechanisms that explain the observed synergistic effect of parasites and predators in a series of follow-up experiments. Results of the follow-up experiments suggest that increased prédation susceptibility due to elevated activity levels in the presence of free-swimming parasite infective stages (i.e., an avoidance response) is the most likely mechanism responsible for the observed synergism. These results suggest a potential trade-off in susceptibility to parasites and predators, which can drive nonadditive effects that may have important consequences for natural enemy interactions in natural populations and amphibian conservation. [ABSTRACT FROM AUTHOR]

The article discusses a study that reevaluated the use of toe clips to detect ranavirus infection in green frogs, and explored the potential use of blood onto filter paper and hepatic fine needle aspirates (FNA) as alternatives. The adequacy of using green frogs as a target-sampling species for ranavirus infection in the wild is investigated. Findings show low prevalence of Frog Virus 3 (FV3) in post-metamorphic green frogs, suggesting that green frogs are poor reservoirs for the virus.

Sexual reproduction of apicomplexan parasites in haematophagous arthropods requires that intracellular sexual stages of these protozoa escape vertebrate erythrocytes in the blood meal. Although cues that signal sexual stages of the human malaria parasite ( Plasmodium falciparum Welch, 1897) to emerge from erythrocytes are well documented, such signals are poorly known for other blood-dwelling Apicomplexa. The objective of this comparative study was to investigate conditions required to induce in vitro emergence of sexual stages of Hepatozoon clamatae (Stebbins, 1905) from frog erythrocytes. Blood was drawn from Green Frogs ( Rana clamitans Latreille in Sonnini de Manoncourt and Latreille, 1801 = Lithobates clamitans clamitans (Latreille in Sonnini de Manoncourt and Latreille, 1801)) infected with H. clamatae and treated with solutions of various concentrations of saline, pH, and xanthurenic acid at different temperatures. Hypertonic saline solutions of 200 and 222 mmol/L at pH 7.4 and 7.7 elicited emergence of nearly 100% of gamonts from frog erythrocytes, but at pH 8.0 resulted in decreased emergence. Solutions containing 1, 10, and 100 μmol/L xanthurenic acid increased gamont emergence at saline concentrations of 156, 178, and 244 mmol/L, but decreased emergence at 200 and 222 mmol/L. Gamont emergence increased as incubation temperatures increased from 18 to 26 °C. These results suggest that conditions necessary for emergence of sexual stages of bloodstream Apicomplexa from erythrocytes vary among genera. [ABSTRACT FROM AUTHOR]

A new species of hylid frog is described from Tapir Valley Nature Reserve, located on the Caribbean slope of Tenorio Volcano in Bijagua, Alajuela Province, Costa Rica. A molecular phylogenetic analysis supports its inclusion in the genus Tlalocohyla. Morphological, morphometric, larval, and acoustic characteristics further distinguish it from other species in the genus and support its uniqueness. The new species is closely related to T. picta and T. smithii, and is separated by at least 500 kilometers from the nearest known occurrence of a population of T. picta in southern Honduras. The new species is readily distinguished from all other Tlalocohyla by its brilliant green coloration marked with a pronounced, incomplete light dorsolateral stripe that is bordered above by a diffuse reddish-brown stripe. Its dorsum is marked with bold reddish brown spots and its ventral skin is fully transparent. This new Tlalocohyla is currently only known from the type locality, where it inhabits a lentic wetland system with an emergent herbaceous vegetation-dominated benthic zone, surrounded by tropical rainforest. A description of its bioacoustic repertoire and information on natural history, reproduction and habitat preference of this new species are provided.

Changes in percentage of forest cover can influence nutrient levels in aquatic systems and change abiotic conditions that may influence species. The authors examined how increasing amounts of leaf litter influenced toxicity of the insecticide carbaryl using larval green frogs ( Rana clamitans) in outdoor mesocosm ponds. Insecticides can have direct negative effects on individual physiology and behavior and indirect effects on the food web, which can result in trophic cascades. They predicted that direct effects of the insecticide would dominate when nutrients were low (resulting in negative impacts on amphibian development and survival), whereas indirect effects could offset direct effects when nutrients were more abundant through a trophic cascade that leads to more food for tadpoles (resulting in positive effects on amphibian development and survival). The authors found support for this hypothesis: first, total green frog survival was greatest with increased leaf litter input in the presence of carbaryl. Additionally, most green frogs that reached metamorphosis were from ponds with high leaf litter input and carbaryl. Second, the impact of carbaryl on developmental stage and tadpole mass varied depending on the amount of leaf litter present. With high amounts of leaf litter, carbaryl had a positive impact on development and growth; in contrast, with low amounts of leaf litter, carbaryl had negative or no effects on tadpole development and mass. The present study suggests that differences in nutrient levels between ponds exposed to pesticides could play a role in amphibian population dynamics. Environ. Toxicol. Chem. 2012; 31: 1518-1524. © 2012 SETAC [ABSTRACT FROM AUTHOR]

The majority of studies on the toxicity of glyphosate-based herbicides to amphibians have focused on larval life stages exposed in aqueous media. However, adult and juvenile amphibians may also be exposed directly or indirectly to herbicides. The potential for such exposures is of particular interest in the littoral zone surrounding wetlands as this is preferred habitat for many amphibian species. Moreover, it may be argued that potential herbicide effects on juvenile or adult amphibians could have comparatively greater influence on overall recruitment, reproductive potential and thus stability of local populations than effects on larvae. In this experiment, juvenile green frogs (Lithobates clamitans) were exposed to two concentrations (2.16 and 4.27kga.e./ha) of a glyphosate-based herbicide formulation (VisionMax®), which were based on typical application scenarios in Canadian forestry. The experimental design employed frogs inhabiting in situ enclosures established at the edge of small naturalized wetlands that were split in half using an impermeable plastic barrier. When analyzed using nominal target application rates, exposure to the glyphosate-based herbicide had no significant effect on survival, body condition, liver somatic index or the observed rate of Batrachochytrium dendrobatidis infection. However, there were marginal trends in both ANOVA analysis and post-hoc regressions regarding B. dendrobatidis infection rates and liver somatic index in relation to measured exposure estimates. Results from this study highlight the importance of field research and the need to include multiple endpoints when examining potential effects of a contaminant on non-target organisms. [Copyright &y& Elsevier]

1. Organisms can protect themselves against parasitism by reducing either parasite burden (resistance) or damage caused by parasites at a given burden (tolerance), but little is known about resistance and tolerance to multiple parasites among wild animal populations and species. The fitness effects of parasitism can be broken down into two components: (i) cost of parasite exposure, the difference in fitness between organisms that were not exposed to parasites and those that were exposed but not infected, and (ii) tolerance, the change in host fitness as a function of parasite burden. For amphibians, a taxon that is being decimated by disease, knowing which species and ontogenetic stages are least resistant or least tolerant to which parasites would help target research and management efforts. 2. We reared American toad ( Bufo americanus) and green frog ( Rana clamitans) tadpoles in a common garden environment and quantified survival and trematode burdens after exposure to 20 Echinostoma trivolvis, Ribeiroia ondatrae or plagiorchid trematode cercariae. 3. All three trematodes caused significant B. americanus mortality, but R. ondatrae was the only species to induce significant mortality of R. clamitans and was the most deadly of the parasites. Young tadpoles had greater parasite-induced mortality than older tadpoles. 4. Mortality patterns were driven by B. americanus having lower resistance and a higher cost of parasite exposure than R. clamitans, older tadpoles having higher tolerance than younger tadpoles, B. americanus and R. clamitans exhibiting lower resistance and a higher cost of parasite exposure, respectively, to R. ondatrae relative to the other tested trematodes, and skin-penetrating trematodes inducing a higher cost of parasite exposure than non-skin-penetrators. Host size was not predictive of resistance but was a positive predictor of the cost of resistance and tolerance; however, size alone could not fully account for host differences in tolerance. 5. Interactions among developmental stage and host and trematode species emphasize the plasticity and context-dependency of defence strategies and the importance of considering resistance and tolerance to multiple parasites in wild host species. [ABSTRACT FROM AUTHOR]

Developmental instability, measured as fluctuating asymmetry (FA), is often used as a tool to measure stress and the overall quality of organisms. Under FA, it is assumed that control of symmetry during development is costly and that under stress the trajectory of development is disturbed, resulting in asymmetric morphologies. Amphibian emergent infectious diseases (EIDs), such as Ranavirus and chytrid fungus, have been involved in several mortality events, which makes them stressors and allows for the study of FA. We analyzed nine populations of green frogs (Rana clamitans) for the presence or absence of Ranavirus and chytrid fungus. Individuals were measured to determine levels of FA in seven traits under the hypothesis that FA is more likely to be observed in individuals infected by the pathogens. Significantly higher levels of FA were found in individuals with Ranavirus compared with uninfected individuals among all populations and all traits. We did not observe FA in individuals infected with chytrid fungus for any of the traits measured. Additionally, we observed a significant association between Ranavirus infection and levels of FA in both males and females, which may indicate this viral disease is likely to affect both sexes during development. Altogether, our results indicate that some EIDs may have far-reaching and nonlethal effects on individual development and populations harboring such diseases and that FA can be used as a conservation tool to identify populations subject to such a stress. [ABSTRACT FROM AUTHOR]

Recent extensions of occupancy modeling have focused not only on the distribution of species over space, but also on additional state variables (e.g., reproducing or not, with or without disease organisms, relative abundance categories) that provide extra information about occupied sites. These biologist-driven extensions are characterized by ambiguity in both species presence and correct state classification, caused by imperfect detection. We first show the relationships between independently published approaches to the modeling of multistate occupancy. We then extend the pattern-based modeling to the case of sampling over multiple seasons or years in order to estimate state transition probabilities associated with system dynamics. The methodology and its potential for addressing relevant ecological questions are demonstrated using both maximum likelihood (occupancy and successful reproduction dynamics of California Spotted Owl) and Markov chain Monte Carlo estimation approaches (changes in relative abundance of green frogs in Maryland). Just as multistate capture-recapture modeling has revolutionized the study of individual marked animals, we believe that multistate occupancy modeling will dramatically increase our ability to address interesting questions about ecological processes underlying population-level dynamics. [ABSTRACT FROM AUTHOR]

Road traffic causes significant amphibian and reptile mortality, which could be mitigated through the installation of road crossing structures that facilitate safe passage, but only if reptiles and amphibians are willing to use them. Through a series of behavioral choice experiments with frogs and turtles, we examined how aperture diameter, substrate type, length, and light permeability influenced individuals’ preferences for specific attributes of crossing structures, and how individuals responded to various heights of barrier fences. Snapping turtles (Chelydra serpentina), green frogs (Rana clamitans), and leopard frogs (Rana pipiens) preferred larger diameter tunnels (>0.5m) whereas painted turtles (Chrysemys picta) preferred tunnels of intermediate (0.5–0.6m) diameter. Green frogs preferred soil- and gravel-lined tunnels to concrete- and PVC-lined tunnels. Painted turtles showed non-random choice of different lengths of tunnel, possibly indicating some avoidance of the longest tunnel (9.1m); although no species preferred to exit via the longest tunnels (9.1m), members of all four species used such tunnels. Green frogs preferred tunnels with the greatest light permeability. Fences 0.6m in height were effective barriers to green frogs, leopard frogs, and snapping turtles, whereas 0.3m fences excluded painted turtles. We conclude that tunnels>0.5m in diameter lined with soil or gravel and accompanied by 0.6–0.9m high guide fencing would best facilitate road crossing for these and likely other frog and turtle species. [Copyright &y& Elsevier]

Changes in host diversity and community structure have been linked to disease, but the mechanisms underlying such relationships and their applicability to non-vector-borne disease systems remain conjectural. Here we experimentally investigated how changes in host community structure affected the transmission and pathology of the multi-host parasite Ribeiroia ondatrae, which is a widespread cause of amphibian limb deformities. We exposed larval amphibians to parasites in monospecific or heterospecific communities, and varied host number to differentiate between density- and diversity-mediated effects on transmission. In monospecific communities, exposure to Ribeiroia significantly increased mortality (15%), malformations (40%) and time-to-metamorphosis in toads. However, the presence of tree frogs significantly reduced infection in toads, leading to fewer malformations and higher survival than observed in monospecific communities, providing evidence of parasite-mediated facilitation. Our results suggest that interspecific variation in parasite resistance can inhibit parasite transmission in multi-species communities, reducing infection and pathology in sensitive hosts. [ABSTRACT FROM AUTHOR]

Embryos of three aquatic breeding amphibian species, Ambystoma mexicanum, Hyla chrysoscelis, and Rana clamitans, were exposed to increasing levels (0, 5, 10, 30, 60, 100, 300, and 500 mg/L) of nitrate-N ( $$ {\text{NO}}^{ - }_{3} $$ ) in laboratory, static-renewal experiments. Lethal effects were recorded from Gosner stage 2 ( H. chrysoscelis and R. clamitans) or Harrison stage 2 ( A. mexicanum) to time of hatching. Date of hatching and length at hatching were also compared between treatments for A. mexicanum. No significant differences in mortality between treatments were found between the three species. A. mexicanum in the 300 and 500 mg/L treatments hatched significantly earlier than individuals in the other treatment groups and, consequently, were significantly shorter in length at hatching. However, no effect on length was detected when days until hatching was considered as a covariate in the analysis. This study supports other recent research showing little to no effect of $$ {\text{NO}}^{ - }_{3} $$ on amphibian embryos. The lack of effect at such high nitrate concentrations raises questions about the specific mechanisms responsible for protecting amphibians from $$ {\text{NO}}^{ - }_{3} $$ during embryonic development, especially when compared to other chemicals that have shown more deleterious effects. [ABSTRACT FROM AUTHOR]

Anurans undergo dramatic morphological and physiological changes at metamorphosis, accompanied by shifts in diet and habitat. Frogs provide an ideal model organism for studying ontogenetic shifts in diet due to their biphasic life history and widespread distribution throughout their range. Analysis of stable isotopes of carbon (C) and nitrogen (N) in green frog tadpoles and adult frogs was used to describe ontogenetic shifts in diet and habitat. Adult and larval green frogs were collected from four wetland locations in Nova Scotia, Canada and analyzed for stable isotopes. Differences in isotopic ratios were observed among tadpoles and adults. Tadpoles from wetlands with high nitrate concentrations exhibited greater δ15N values than adults, while tadpoles from wetlands without N enrichment had lower δ15N values. These enriched nitrogen signatures were probably the result of larval exposure to nitrogenous pollution originating from fertilizers and illustrate the difficulties in using isotope analysis to quantify trophic structure in biphasic organisms occupying dramatically different habitats. [ABSTRACT FROM AUTHOR]

Amphibian populations have been undergoing declines on a global scale. Among the many threats to these populations are emergent infectious diseases (EIDs). The Ranavirus in particular has been found within many declining amphibian populations. Although non-lethal sampling methods exist for some amphibian groups, such as salamanders, the anurans are traditionally tested using a lethal method. By comparing traditional liver samples and a new nonlethal method of toe clipping we prove that the Ranavirus can also be determined in frogs using a nonlethal method, a much needed tool in threatened populations. This method will allow for ranaviral detection without further impacting declining populations, and can further be used for other research questions. [ABSTRACT FROM AUTHOR]

Predators have been shown to alter the timing of switch points between life history stages, but few studies have addressed switch point plasticity in prey exposed simultaneously to conflicting predation pressure. We tested hatching responses of green frog ( Rana clamitans) embryos subject to perceived predation risk from chemical cues released by two stage-specific predators, predicting that these predators would elicit: (1) directional hatching responses when presented independently, and (2) intermediate phenotypic responses when presented simultaneously. R. clamitans embryos in outdoor exclosures were exposed to cues from an egg predator (freshwater leeches; Nephelopsis obscura), a larval predator (dragonfly nymphs, Aeschna canadensis), and both predators in a 2 × 2 factorial experiment, and changes in hatchling size, hatchling developmental stage, and hatching time were compared to those for control embryos. Leeches alone induced embryos to hatch at a smaller size and an earlier developmental stage than controls, while dragonfly nymphs elicited a delay in egg hatching time that was associated with larger size and later developmental stage at hatching. Embryos failed to respond to simultaneous exposure to both predators, implying that responses to each occurred concurrently and were therefore dampened. Our results indicate that prey under threat from conflicting predators may manifest intermediate defensive phenotypes. Such intermediate responses may result in elevated rates of prey mortality with possible consequences at the population level. [ABSTRACT FROM AUTHOR]

The increasing threat of emerging infectious diseases in both wildlife and humans has spurred interest in the causes of disease emergence, including the role of anthropogenic change. A prior field study of infection patterns in amphibians suggests that echinostome infection may be an emerging disease of green frogs Rana clamitans living in urbanized environments. We examined the impact of echinostome infection on green frog tadpoles at a wide range of developmental stages (Gosner stage 25–39). Echinostome infection was associated with green frog mortality rates of up to 40% in an early developmental stage, and none in later developmental stages. Tadpoles exposed to higher echinostome doses exhibited higher edema rates, a potential sign of compromised renal function. Histopathological analysis further supported the hypothesis that echinostome-induced tadpole mortality resulted from compromised renal function. Given that the timing of highest cercarial shedding can coincide with the most vulnerable stages of green frog tadpole development, echinostomes could significantly impact green frog survival in nature. [ABSTRACT FROM AUTHOR]

Assessing the success of created seasonal pools as mitigation for the loss of wooded wetlands is generally based on two or three years of monitoring. We monitored a wetland mitigation site in midcoast Maine, USA, from 1999 to 2004 to track populations of wood frogs (Rana sylvatica) and spotted salamanders (Ambystoma maculattum) in three created seasonal pools. Our goal was to study breeding patterns for six years to assess if presence of breeding animals in the first three years corresponded with long-term reproductive success and to track changes in vegetation development and hydrology in the mitigated pools. Breeding effort (egg masses/female) and reproductive success (juveniles/egg mass) were assessed using full enclosure drift fence/pitfall trap arrays and egg mass counts. Breeding effort was similar in all three pools for both species. However, for wood frogs, reproductive success was inversely related to hydroperiod and highest in the single pool that successfully replicated the desired seasonal water regime. The other two pools developed permanent and semi-permanent hydroperiods, thereby supporting populations of green frogs (Rana clamitans). Green frog tadpoles within these pools preyed upon wood frog eggs and embryos, causing almost complete losses in the last four years of the study. While spotted salamander reproductive success was also reduced in the permanent pool, spotted salamanders were more successful at producing metamorphs in the presence of green frogs. Over the study period, common cattail (Typha latifolia) dominated the pools, and although wetland vegetation did develop, it was not typical of forested seasonal pools. Our work shows that the presence of breeding amphibians characteristic of seasonal pools in the first three years is not sufficient to determine reproductive success of target species in created pools. Hydrology and canopy cover are elements of critical concern if created pools are to support native amphibian communities associated with seasonal pools. [ABSTRACT FROM AUTHOR]

Abstract: The triazine herbicide atrazine has been suggested to be a potential disruptor of normal sexual development in male frogs. The goals of this study were to collect native ranid frogs from sites in agricultural and non-agricultural areas and determine whether hypothesised atrazine effects on the gonads could be observed at the gross morphological and histological levels. Juvenile and adult green frogs (Rana clamitans), bullfrogs (R. catesbeiana) and leopard frogs (R. pipiens) were collected in the summers of 2002 and 2003. Atrazine concentrations were below the limit of quantification at non-agricultural sites, and concentrations did not exceed 2μg/L at most agricultural sites. One concentration greater than 200μg atrazine/L was measured once at one site in 2002. Hermaphroditic individuals with both male and female gonad tissue in either one or both gonads, were found at a low incidence at both non-agricultural and agricultural sites, and in both adults and juveniles. Testicular oocytes (TO) were found in male frogs at most of the sites, with the greatest incidence occurring in juvenile leopard frogs. TO incidence was not significantly different between agricultural and non-agricultural sites with the exception of juveniles collected in 2003. Atrazine concentrations were not significantly correlated with the incidence of hermaphroditism, but maximum atrazine concentrations were correlated with TO incidence in juvenile frogs in 2003. However, given the lack of a consistent relationship between atrazine concentrations and TO incidence, it is more likely the TOs observed in this study result from natural processes in development rather than atrazine exposure. [Copyright &y& Elsevier]

The application of road de-icing compounds during the winter has the potential to result in the contamination of nearby freshwater habitats and affect amphibians breeding in those habitats. We conducted a study of the effects of several de-icing and associated compounds (sodium chloride, magnesium chloride, calcium acetate, magnesium acetate, sodium ferrocyanide, and sodium formate) on the tadpoles of three species of anurans: African clawed frogs (Xenopus laevis), American toads (Bufo americanus), and green frogs (Rana clamitans). The survivorship of X. laevis tadpoles was negatively affected by MgCl2, but not by NaCl. The survivorship of R. clamitans tadpoles was negatively affected by both NaCl and MgCl2. The tadpoles of B. americanus were not affected by the concentrations of NaCl and MgCl2 used in this study. Our results suggest that contamination of freshwater habitats by de-icing and associated compounds could potentially adversely affect at least some anuran populations, but that this potential can vary from species to species, and from compound to compound. [ABSTRACT FROM AUTHOR]

We examined variation in aggressive responses within and among individuals in the green frog, Rana clamitans. We tested the hypothesis that resident males respond in a graded fashion to changes in perceived intruder proximity (stimulus intensity). We also investigated how response level varied with responder body size. We found that green frogs differentially alter aggressive responses (increasing movement and calling rates while decreasing the duration and dominant frequency of their calls) with an increase in stimulus intensity. Body size did not appear to be a significant influence on most response levels. We suggest that aggressive responses are graded, and advertisement and aggressive calls represent opposite ends of a continuum. Green frogs do not exhibit clearly defined thresholds for responses like those reported for some other frogs. By using graded responses rather than discrete “all-or-nothing” responses, males may reduce the potential costs of aggressive encounters. [ABSTRACT FROM AUTHOR]

The article focuses on the geographical distribution of animals. Ecologists have long attempted to explain animal distributions at fine spatial scales through mechanisms such as habitat selection. During the 1980s, however, interest has shifted to patterns at the landscape scale, and much of conservation-oriented research has since focused on predicting the spatial distribution and persistence of organisms through time and disturbances. Researchers strived to provide empirical support for various theories on patch dynamics in the landscape. Based on the life history of pond-breeding amphibians, it could be expected that spatial patterns at ponds depend on both patch (for example: pond site) and landscape characteristics (for example: proximity of terrestrial habitat). Indeed, pond-breeding amphibians have complex life cycles, as they use distinct components of the landscape at different developmental stages and periods of the year. Embryos and larvae are generally confined to ponds and their development is regulated by biotic and abiotic factors such as water chemistry and temperature.

Flow cytometry (FC) is a laboratory method used to detect genetic damage induced by environmental contaminants and other stressors in animals, including amphibians. We tested FC methods on three species of ranid frogs collected from farm ponds and natural wetlands in southeastern Minnesota. We compared FC metrics for Rana clamitans between ponds with direct exposure to agricultural contaminants and reference (unexposed) ponds. Concentrations of atrazine in water from our farm ponds ranged from 0.04 to 0.55 ppb. We found that R. clamitans from exposed ponds had DNA content similar to frogs from unexposed ponds. Pond-averaged C-values (a measure of DNA content) ranged from 6.53 to 7.08 for R. pipiens (n = 13), 6.55 to 6.60 for R. clamitans (n = 40) and 6.74 for R. palustris (n = 5). Among all species, the mean sample CVs ranged from 1.91 (R. palustris) to 6.31 (R. pipiens). Deformities were observed in only 2 of 796 individuals among all species and occurred in both reference and exposed ponds. Although we did not detect evidence of DNA damage associated with agriculture in our study, we demonstrated the potential of FC for screening amphibian populations for genetic damage. Metrics from a variety of amphibian species and locations as well as laboratory studies are needed to further assess the value of FC for monitoring amphibian genetic integrity in contaminated sites. [ABSTRACT FROM AUTHOR]

The majority of studies on pesticide impacts have evaluated the effects of single exposures. However, multiple exposures to a pesticide may be more prevalent. The objective of our study was to determine how multiple exposures versus single exposure at different times during development affected survival to metamorphosis, tadpole survival, tadpole mass, and tadpole developmental stage of green frog (Rana clamitans) tadpoles reared at low and high density in outdoor cattle tank ponds. Tadpoles were exposed to carbaryl zero, one, two, or three times at 14-d intervals. We applied single doses of carbaryl at one of three times, specifically during early, mid, or late development. Overall, we found that multiple exposures had a greater impact than single exposures during development. More individuals reached metamorphosis in ponds exposed to multiple doses of carbaryl compared with controls, indicating that the presence of carbaryl stimulated metamorphosis. The presence of carbaryl in the aquatic environment also resulted in more developed tadpoles compared with controls. Tadpoles in control ponds did not reach metamorphosis and were less developed than individuals exposed to carbaryl; this effect indicates that, under ideal conditions, green frogs could overwinter in ponds so that greater size could be attained before metamorphosis in the following spring or summer. Our study demonstrated the importance of including realistic application procedures when evaluating the effects of a pesticide and that multiple exposures to a... [ABSTRACT FROM AUTHOR]

Retinoids, which are Vitamin A derivatives, are important signaling molecules that regulate processes critical for development in all vertebrates. The objective of our study was to examine uptake and metabolism of the model retinoid, all-trans retinoic acid (all-trans RA), by three native North American anurans, Rana sylvatica, R. pipiens, and R. clamitans. Limb-bud stage tadpoles (stages 26-28) were exposed to all-trans RA concentrations of 0, 250, 500, 750, 1000, and 1250 ng/ml for 24 h. Water and tissue samples, collected at 0, 4, 12, and 24 h, were analyzed by high pressure liquid chromatography with diode-array detection (HPLC-DAD) to characterize aqueous exposure and all-trans RA uptake and metabolism. All-trans RA degraded rapidly in exposure water (i.e., with organisms), with over 70% of the parent compound gone in 4 h and none detected by 24 h. Consistent with this result, tadpoles from the three species showed the greatest accumulation of all-trans RA at 4 h followed by decreasing tissue concentrations at 12 and 24 h. In addition to all-trans RA, several other chromatographic peaks were observed in the tissue extracts indicating metabolism of the retinoid by the tadpoles. Identification of potential metabolites of all-trans RA and endogenous retinoids was conducted by comparing retention times and absorption spectra of available standards (i.e., 4-oxo-all-trans RA, 4-oxo-13-cis RA, 13-cis RA, 9-cis RA, all-trans retinol, all-trans retinal) to those in the tissue extracts. In all three species, all-trans RA was metabolized to 4-oxo-all trans RA and 13-cis RA. The RA isomer, 9-cis RA, was detected in two species,R. sylvatica and R. pipiens. All three species also had measurable levels of vitamin A (all-trans retinol), while the aldehyde form (all-trans retinal) was detected only in R. clamitans. Our results indicate that all-trans RA is rapidly metabolized by these Ranid species to a variety of retinoid derivatives, several of which are known ligands for RA and retinoid receptors, and are capable of activating this signaling transduction pathway. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the effects of an insecticide on larval amphibian communities experiencing natural stresses of competition for resources, predation, and pond drying. It explains that amphibian populations are often imbedded in agricultural landscapes and have the potential for habitat contamination. The study demonstrated that even short-lived contaminants can potentially change natural communities.

Within the last decade, there have been increasing reports of malformed amphibians across North America. Recently, it has been suggested that hind-limb malformations are a consequence of xenobiotic disruption of developmental pathways regulated by retinoids. To assess the validity of this hypothesis, the developmental toxicity of all-trans retinoic acid (RA) was examined in Xenopus laevis and four North American anurans, at several life stages. To determine the effects of RA on embryogenesis, mid-blastula stage embryos were exposed to 0, 6.25, 12.5, 25, or 50 ng RA/ml for 24 h. To evaluate the effects of RA on hind-limb development, early- and mid-limb bud stage tadpoles were exposed to RA concentrations of 0, 250, 500, 750, 1000, or 1250 ng RA/ml for 24 h. Mid-blastula RA exposure resulted in a concentration-dependent increase in dysmorphogenesis and mortality in the three species examined (R. clamitans, R. septentrionalis and X. laevis). RA exposure at stage 51 in X. laevis and stage 28 in R. sylvatica resulted in concentration-dependent increases in reductions and deletions of the hind limb. However, RA was ineffective at inducing hind-limb abnormalities in stages 26 and 28 of R. pipiens, stage 28 in R. clamitans, or stage 48 in X. laevis tadpoles. These results indicate that mid-blastula stage embryos are more sensitive to RA-induced dysmorphogenesis and mortality than limb-bud stage tadpoles. The significance of these findings is discussed in the context of the possible occurrence of retinoid mimics in the environment. [ABSTRACT FROM PUBLISHER]