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ABSTRACT Elevated ultraviolet radiation (UVR) is postulated as one of multiple, interrelated environmental stressors driving amphibian population declines globally. However, key knowledge gaps remain in elucidating the link between elevated UVR and amphibian declines in a changing climate, including whether timing and irradiance of UVR exposure in early life dictates the onset of detrimental carryover effects post‐metamorphosis. In this study, striped marsh frog larvae (Limnodynastes peronii) were exposed to UVR at one of two different irradiances for up to 7 days, either as hatchlings (Gosner stage 23) or as older larvae (Gosner stage 25−28). These animals were then reared to metamorphosis in the absence of UVR to examine independent and interactive carryover effects throughout development. Older larvae were more sensitive to UVR than hatchlings, with 53.1% and 15.6% mortality in larvae exposed to high and low irradiance respectively, compared with no mortality of hatchlings in either irradiance treatment. Irradiance and timing of UVR exposure had interactive effects on larval body length, causing stunted growth patterns and a lack of compensatory growth following UVR exposure, particularly in animals exposed to high irradiance UVR later in development. Timing of UVR exposure also determined the severity of carryover effects into metamorphosis, including delayed metamorphosis and the first published account (to our knowledge) of latent UVR‐induced depigmentation in an amphibian. These findings highlight how acute changes to the larval UVR exposure regime can impact on amphibian health later in life, with implications for our understanding of the effects of climate change on UVR‐related amphibian declines. [ABSTRACT FROM AUTHOR]

The article discusses the unique adaptation of Kurixalus eiffingeri frog larvae living in phytotelmata to not exhibit defecation behavior until metamorphosis. This sanitation strategy is hypothesized to prevent ammonia contamination in the closed aquatic environment where the larvae reside. The study shows that K. eiffingeri larvae excrete less ammonia into their environment, retain high concentrations of ammonia in their gut, and exhibit greater tolerance to ammonia compared to other frog species. The findings suggest that K. eiffingeri larvae have evolved a unique sanitation strategy to hold ammonia-containing feces in their gut and have developed an unusual tolerance to environmental ammonia. [Extracted from the article]

AbstractAquatic communities are increasingly exposed to complex mixtures of contaminants, mainly pesticides due to the impact of agricultural activity. The aim of this study was to evaluate the toxicity of an eight-pesticide cocktail on larvae of the South American common toad, Rinella arenarum. The cocktail represents a realistic mixture of insecticides (cypermethrin, chlorpyrifos and lambda-cyhalothrin), herbicides (glyphosate, glufosinate ammonium, prometryn and metolachlor), and a fungicide (pyraclostrobin) previously found in aquatic organisms (Prochilodus lineatus) from the Salado River Basin, an area with strong agricultural pressure. Computational simulations through the Density Functional Tight-Binding method indicated a strong spontaneous trend toward the formation of the cocktail, suggesting that it may act as a novel xenobiotic entity in the environment. The cocktail effects were evaluated in early-developing and premetamorphic larvae, at feasible concentrations found in real scenarios. The mixture led to high mortality and teratogenicity in early-developing larvae. Premetamorphic larvae showed endocrine disruption, oxidative stress, and impairments in detoxification and hepatic functioning. Neurotoxicity, genotoxicity, cardiotoxicity and high mortality under stress conditions were also observed in exposed larvae. This novel evaluation highlights the ecotoxicological risk for aquatic organisms exposed to complex mixtures and underscores the need to consider cocktail effects in studies regarding ecosystems health. [ABSTRACT FROM AUTHOR]

Amphibian larvae can affect the structure and functioning of freshwater ecosystems, but their effects have been little explored although amphibian biodiversity is rapidly declining. Given that larvae of different amphibian species belong to different trophic levels, their effects on freshwater communities and processes can be expected to differ, with herbivores likely having direct effects on algae and predators having indirect effects through trophic cascades. We explored this question through a mesocosm experiment conducted in montane ponds, using an anuran and a urodele species affected by emergent diseases. We used different scenarios of reduction and loss of one or both species, and compared them to a control scenario representing a typical amphibian community in the study area composed of four species, with total larval density held constant. Loss of the anuran resulted in lower chlorophyll concentration and algal density, likely due to replacement by more efficient grazers. Loss of the urodele produced similar trends but weaker, possibly due to an increase of invertebrate grazing activity in the absence of this predator. Our study shows how the loss of amphibian species can alter the structure of montane ponds, but also how the mechanisms involved and the intensity of effects differ for different species. [ABSTRACT FROM AUTHOR]

Ecologists strive to untangle the complex interplay of current and historical factors, along with evolutionary history of species, to understand communities' structure. However, this can be achieved by integrating different approaches to expanding our knowledge about the underlying processes connecting assemble rules of ecological communities. In order to better understand how ecological and/or evolutionary factors may affect the structure of communities, we assessed the phylogenetic and functional structure of 33 tadpole communities in the Atlantic Forest Southeastern Brazil and tested whether phylogenetic conservatism drives tadpole traits. We identified 19 communities which were significantly phylogenetic clustered and 10 which were significantly functional clustered. Trait diversity was skewed towards the root, indicating phylogenetic trait conservatism as an important driver of the structure of tadpole communities. The best explanatory model of the phylogenetic diversity included, in order of importance, presence of potential fish predators, water conductivity, external diversity of vegetation structure, canopy cover, internal diversity of vegetation structure and dissolved oxygen. Most variables were negatively correlated with phylogenetic diversity, but the presence of potential fish predators was positively correlated. For functional structure, external diversity of vegetation structure, canopy cover, area, dissolved oxygen and presence of potential fish predators were selected as the best explanatory model (presented in order of importance). Furthermore, of the 10 functionally structured communities, eight were also phylogenetically structured. In this sense, environmental variables could be filtering tadpole lineages interacting with phylogenetically conserved species traits, thus driving anura tadpole species' occurrence on communities. Our study provides evidence that anuran communities structure results from interacting ecological and evolutionary processes. [ABSTRACT FROM AUTHOR]

Amphibian larvae inhabiting temporary ponds often exhibit the capacity to accelerate development and undergo metamorphosis in challenging conditions like desiccation. However, not all species exhibit this ability, the yellow‐bellied toad (Bombina variegata) is one such example. The underlying mechanisms behind the inability to accelerate development under desiccation remain largely unexplored. The hypothalamic–pituitary–interrenal (HPI) axis and corticosterone (CORT), which act synergistically with thyroid hormone, are thought to facilitate metamorphosis in response to desiccation stress. In this study, we aimed to investigate whether modification in the HPI axis, particularly CORT levels, contributes to the absence of adaptive plasticity in B. variegata under desiccation stress. The study design included four treatments: high water level, high water level with exogenous CORT, low water level, and low water level with metyrapone (a CORT synthesis inhibitor). The main objective was to evaluate the effects of these treatments on whole‐body corticosterone levels, life history, morphological traits, and oxidative stress parameters during the prometamorphic and metamorphic climax developmental stages. While low water level had no effect on total corticosterone levels, larval period, body condition index, and metamorphic body shape, it negatively affected metamorph size, mass, and growth rate. Our findings suggest that constant exposure to desiccation stress over generations may have led to modifications in the HPI axis activity in B. variegata, resulting in adaptation to changes in water level, evident through the absence of stress response. Consequently, CORT may not be a relevant stress indicator in desiccation conditions for this species. Research Highlights: The pond drying conditions had no influence on the overall corticosterone levels.Inability of Bombina variegata to accelerate development in pond drying conditions could be explained by the modification of endocrine signaling pathways. [ABSTRACT FROM AUTHOR]

Chironomid (Diptera: Chironomidae) larvae play a key role in aquatic food webs as prey for predators like amphibian and dragonfly larvae. This trophic link may be disrupted by anthropogenic stressors such as Bacillus thuringiensis var. israelensis (Bti), a biocide widely used in mosquito control. In a companion study, we recorded a 41% reduction of non-target larval chironomids abundance in outdoor floodplain pond mesocosms (FPMs) treated with Bti. Therefore, we examined the diet of two top predators in the FPMs, larvae of the palmate newt (Salamandridae: Lissotriton helveticus) and dragonfly (Aeshnidae: predominantly Anax imperator), using bulk stable isotope analyses of carbon and nitrogen. Additionally, we determined neutral lipid fatty acids in newt larvae to assess diet-related effects on their physiological condition. We did not find any effects of Bti on the diet proportions of newt larvae and no significant effects on the fatty acid content. We observed a trend in Aeshnidae larvae from Bti-FPMs consuming a higher proportion of large prey (Aeshnidae, newt, damselfly larvae; ~42%), and similar parts of smaller prey (chironomid, mayfly, Libellulidae, and zooplankton), compared to controls. Our findings may suggest bottom-up effects of Bti on aquatic predators but should be further evaluated, for instance, by using compound-specific stable isotope analyses of fatty acids or metabarcoding approaches. [ABSTRACT FROM AUTHOR]

The intensification of livestock farming can pose risks to the environment due to the increased use of veterinary products and the generation of waste in confined areas. The quality of water bodies near livestock establishments (Areco River (A) and Doblado stream (D), San Antonio de Areco, Buenos Aires, Argentina) was studied by physicochemical parameters, metals, pesticides, emerging contaminants, and lethal and sublethal toxicity (neurotoxicity and oxidative stress) in larvae of the native amphibian Rhinella arenarum. Six sites were selected: upstream (S1A and S1D), at the level (S2A and S2D), and downstream (S3A and S3D) from the establishments. A low concentration of dissolved oxygen was observed in Doblado stream (< 2.34 mg/L). Cu, Mn, V, and Zn exceeded the limits for the protection of aquatic life at various sites. Between 24 and 34 pesticides were detected in all sites, with 2,4-D, atrazine, and metolachlor being the most recurrent. In water and sediment, the concentrations of ivermectin (S2A, 1.32 μg/L and 58.18 μg/kg; S2D, 0.8 μg/L and 85.22 μg/kg) and oxytetracycline (S2A, < 1 mg/L and < 1 mg/kg; S2D, 11.8 mg/L and 39 mg/kg) were higher at sites near the establishments. All sites caused between 30 and 38.3% of lethality and produced neurotoxicity and alterations in the reduced glutathione content. Moreover, larvae exposed to samples from all sites incorporated ivermectin. These results demonstrate the degradation of the studied sites in relation to the agricultural activities of the area, highlighting the need to take measures to protect and preserve aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Developmental plasticity evolves in heterogeneous environmental conditions as long as individuals can accurately perceive them. A paradigmatic example of developmental plasticity is the ability of amphibian larvae to alter growth and development in response to the risk of pond drying. Such responses are often found in amphibian species breeding in highly dynamic water bodies with high desiccation risk. The inselbergs of the Guianan Shield are rocky outcrops with extremely high and fluctuating temperatures and a marked seasonality in precipitation. During the rainy season, eroded depressions form precipitation-dependent pools with a high and variable risk of desiccation within the timeframe of a few days. The frog Leptodactylus lithonaetes specializes in breeding in this extreme environment, and its tadpoles are thus forced to cope with desiccation risk by adjusting their developmental trajectories and physiological performance. We experimentally assessed the effect of different levels of desiccation risk, under controlled temperature conditions, on developmental rate, growth, and temperature-dependent locomotor performance in tadpoles of Leptodactylus lithonaetes. We did not find an effect of desiccation risk on developmental rate, but under simulated drying conditions, tadpoles showed larger body size, greater body mass, and enhanced locomotor performance compared to constant (high or low) water levels. These results suggest that drying pools offer cues that trigger developmental and behavioral changes in these tadpoles, enabling them to enhance growth over a short time span without accelerating development. We discuss the potential compensatory mechanisms behind these responses and highlight the need for further investigations in species with semiterrestrial life histories in extreme environments. [ABSTRACT FROM AUTHOR]

Predators significantly impact the development process and subsequently influence the metamorphic decisions of amphibian larvae. Larvae often exhibit induced growth and metamorphic plasticity in response to the presence of predators. However, growth and development rates are not always perfectly correlated, growth responses can vary throughout ontogeny. It is crucial to consider the stage‐specific growth responses induced by predators. Here, we employ a critical windows experimental design and examine development‐related growth and metamorphic responses to predators in the endangered Chinhai spiny newt (Echinotriton chinhaiensis). Our findings reveal that predators constrain the development process of spiny newt larvae and also impact survival to metamorphosis. Inducible plasticity predominantly exhibits in the early and middle stages of larval development. Our results also suggest that diverse developmental plasticity has been adopted by larvae in response to predators. The presence of predators during early stage induces larvae to exhibit a same size at metamorphosis but a prolonged time to metamorphosis, while predators present during middle stage induce larvae to exhibit a large size at metamorphosis but a same time to metamorphosis. The presence of predators at the late developmental stage does not induce any plasticity in larval growth and metamorphosis. Moreover, these results also suggest that several stages of larval development are likely critical developmental windows for spiny newt larvae. This study not only provides basic biological information on predator‐induced developmental plasticity of the endangered Chinhai spiny newt but also likely provides biological insights for the implementation of in situ conservation and preservation efforts for endangered species. [ABSTRACT FROM AUTHOR]

Tonic immobility is an antipredator defence in which the prey animal remains motionless after physical contact with the predator, pretending to be dead. This behaviour has been observed among a variety of taxa but has received only little attention in amphibian larvae. During our field studies with fire salamander larvae, we observed that larvae from different habitats display tonic immobility after handling. In our study site, we find larvae in pond and stream habitats, that differ in several aspects such as their stress response and their risk‐taking behaviour, likely caused by the very different habitat conditions. We measured the time that the tonic immobility behaviour was displayed but found no difference between larvae from the two habitat types. Likewise, we also found no correlation between the size of the larvae and the duration of displaying the behaviour. In conclusion, we found that fire salamander larvae show tonic immobility, but found no evidence that the different habitat conditions influence the tonic immobility behaviour. [ABSTRACT FROM AUTHOR]

Amphibian declines are sometimes correlated with increasing levels of ultraviolet radiation (UVR). While disease is often implicated in declines, environmental factors such as temperature and UVR play an important role in disease epidemiology. The mutagenic effects of UVR exposure on amphibians are worse at low temperatures. Amphibians from cold environments may be more susceptible to increasing UVR. However, larvae of some species demonstrate cold acclimation, reducing UV‐induced DNA damage at low temperatures. Understanding of the mechanisms underpinning this response is lacking. We reared Limnodynastes peronii larvae in cool (15°C) or warm (25°C) waters before acutely exposing them to 1.5 h of high intensity (80 µW cm−2) UVBR. We measured the color of larvae and mRNA levels of a DNA repair enzyme. We reared larvae at 25°C in black or white containers to elicit a skin color response, and then measured DNA damage levels in the skin and remaining carcass following UVBR exposure. Cold‐acclimated larvae were darker and displayed lower levels of DNA damage than warm‐acclimated larvae. There was no difference in CPD‐photolyase mRNA levels between cold‐ and warm‐acclimated larvae. Skin darkening in larvae did not reduce their accumulation of DNA damage following UVR exposure. Our results showed that skin darkening does not explain cold‐induced reductions in UV‐associated DNA damage in L. peronii larvae. Beneficial cold‐acclimation is more likely underpinned by increased CPD‐photolyase abundance and/or increased photolyase activity at low temperatures. Research Highlights: Cold temperatures darken Limnodynastes peronii larvae.Darker larvae were not protected from UV‐induced DNA damage.Improved resilience to DNA damage following UV exposure in cold‐acclimated larvae is likely driven by acclimation of DNA repair enzymes. [ABSTRACT FROM AUTHOR]

Simple Summary: This study investigates the similarity of microplastic characteristics between amphibian larvae and their aquatic environment. Microplastics from water, sediment, and amphibian larvae were extracted and analyzed. This study focused on the shape, color, and chemical composition of the particles. The findings revealed a similarity in the microplastics' shapes and colors between those in water and amphibian larvae and, to a lesser extent, between those in larvae and sediment. However, no significant similarities were observed in their chemical composition. This study highlights the impact of microplastic pollution on freshwater ecosystems and its implications for amphibian larvae. Microplastics, pervasive environmental pollutants, are found across various ecosystems, including small inland water bodies. They are reported in different environmental media, yet little is known about the mutual relationships of microplastics' properties across components of small inland water bodies. Here, having extracted and analyzed these particles from water, sediment, and amphibian larvae from 23 sites, we test within-site similarities regarding shape (morphological type), color, and chemical composition (polymer type). We also provide a brief characterization of the microplastics extracted from water and sediment regarding these parameters. We observed a statistically significant similarity of microplastics' shapes and colors between those extracted from water and amphibian larvae. Such a similarity, though less pronounced, was also found between amphibian larvae and sediment. However, the chemical composition (polymer type) of the microplastics from water, sediment, and amphibian larvae did not exhibit any similarities beyond what would be expected by chance. The observed congruence in the colors and shapes of microplastics between amphibian larvae and their corresponding aquatic habitats underscores the profound interconnectedness among the constituents of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

In Mediterranean climates, amphibian larvae often occupy temporary ponds where they must avoid deleterious temperatures and develop before these ponds dry out. We measured thermal heterogeneity in one of these ponds and discussed its relationship with development time and thermal tolerance in three observed species. We found large daily thermoclines that may reach 14°C and persist into the early evening. To our knowledge, this is the first time that such a large degree of thermal heterogeneity has been reported in temporary ponds. Thus, we raise hypotheses linking thermoregulation, habitat use, and growth that Mediterranean amphibian larvae, or other aquatic larvae inhabiting water bodies with strong thermoclines, might exhibit. We argue that studies on thermoregulation of larvae are badly needed to help us understand the responses of Mediterranean amphibians to global warming. [ABSTRACT FROM AUTHOR]

Unmetabolized human pharmaceuticals may enter aquatic environments, and potentially exert adverse effects on the survival of non-target organisms. Here, Pelophylax nigromaculatus tadpoles were exposed to different concentrations of antidiabetic glibenclamide (GLB) for 30 days to evaluate its potential ecotoxicological effect in amphibians using intestinal microbiomic and metabolomic profiles. The mortality rate of GLB-exposed groups appeared to be lower than that of the control group. Despite not being statistically significant, there was a tendency for a decrease in intestinal microbial diversity after exposure. The relative abundance of bacteria phylum Firmicutes was shown to decrease, but those of other phyla did not in GLB-exposed tadpoles. Some potentially pathogenic bacteria (e.g., Clostridium, Bilophila, Hafnia) decrease unexpectedly, while some beneficial bacteria (e.g., Akkermansia, Faecalibacterium) increased in GLB-exposed tadpoles. Accordingly, GLB-induced changes in intestinal microbial compositions did not seem harmful to animal health. Moreover, minor changes in a few intestinal metabolites were observed after GLB exposure. Overall, our results suggested that exposure to low levels of GLB did not necessarily exert an adverse impact on amphibian larvae. [ABSTRACT FROM AUTHOR]

Turbidity represents an obstacle to visual acuity underwater that might entail considerable consequences for multiple faunal traits. Morphology, especially eye size, could be adjusted to cope with reduced visibility in turbid water. Moreover, turbidity could interfere with colour signals or crypsis. Turbid water may simultaneously impair the ability of prey and predators to detect each other, which may cause reduced speed, flight initiation distance, activity time, boldness, and exploratory behaviour by prey.In this work, we compared these traits in larvae of the newt Pleurodeles waltl from transparent and turbid ponds (around 100 and 300 FTU, respectively). Body size did not differ between pond types, but larvae from turbid ponds had smaller eyes, probably because visual acuity is structurally hindered by the environment. Colouration did not differ between transparent and turbid ponds on average, but it was more variable in larvae from transparent than turbid ponds, probably because transparent ponds trigger crypsis towards diverse background colours, whereas turbid ponds promote reduced pigmentation in all cases.In addition, behavioural traits were gauged in larvae from both types of ponds, in tests conducted in either transparent or turbid water. Speed was unaffected by turbidity, but larvae from turbid ponds increased their flight initiation distance when tested in transparent water. In all cases, larvae from transparent ponds were more active, and bolder in transparent water, and all larvae were more exploratory when tested in transparent water (regardless of which pond type they came from).Turbidity could trigger more cautious behaviours, probably because it makes predators harder to track. Alternatively, transparent water could stimulate a more expansive use of space through improved visibility, or it might encourage a more active search for shelter.These results shed light on the role of turbidity as a promotor of morphological and behavioural variability in amphibian larvae. These ecological consequences of water turbidity can be framed in terms of energy allocation and detectability in the context of predator–prey interactions. [ABSTRACT FROM AUTHOR]

In this work, we evaluated the subchronic toxicity of FeSe nanoparticles (NPs) in tadpoles of Rana saharica. Tadpoles were exposed for 1–3 weeks to FeSe NPs at 5 mg/L and 100 mg/L rates. Parameters of oxidative stress were measured in whole larvae, and the micronucleus test was performed on circulating blood erythrocytes. We noted a disturbance of the detoxification systems. Enzymatic and non-enzymatic data showed that exposure to FeSe NPs involved a highly significant depletion of GSH, a significant increase in GST activity, and a lipid peroxidation associated with a highly significant increase in MDA. We also noted a neurotoxic effect characterized by a significant inhibition of AChE activity. A micronucleus test showed concentration-dependent DNA damage. This research reveals that these trace elements, in their nanoform, can cause significant neurotoxicity, histopathologic degeneration, cellular and metabolic activity, and genotoxic consequences in Rana larvae. [ABSTRACT FROM AUTHOR]

Rising temperatures can facilitate epizootic outbreaks, but disease outbreaks may be suppressed if temperatures increase beyond the optimum of the pathogens while still within the temperature range that allows for effective immune function in hosts. The two most devastating pathogens of wild amphibians, Batrachochytrium dendrobatidis (Bd) and ranaviruses (Rv), co‐occur in large areas, yet little is known about the consequences of their co‐infection and how these consequences depend on temperature. Here we tested how exposure to Bd and subsequent exposure to Rv, followed by treatment at elevated temperatures (28 and 30°C versus 22°C) affected Bd and Rv prevalence, infection intensities, and resulting mortalities in larval agile frogs and common toads. We found multiple pieces of evidence that the presence of one pathogen influenced the prevalence and/or infection intensity of the other pathogen in both species, depending on temperature and initial Rv concentration. Generally, the 30°C treatment lowered the prevalence and infection intensity of both pathogens and, in agile frogs, this was mirrored by higher survival. These results suggest that if temperatures naturally increase or are artificially elevated beyond what is ideal for both Bd and Rv, amphibians may be able to control infections and survive even the simultaneous presence of their most dangerous pathogenic enemies. [ABSTRACT FROM AUTHOR]

The majority of the amphibian larvae spend their early life stage in aquatic medium. In such system, they respond to a broad array of stimuli (tactile, chemical and visual cues) and exhibit suitable behavioural responses. The ability of detection of food and predator was studied in the tadpoles of the Indian skipper frog Euphlyctis cyanophlyctis in the laboratory setup by using a rectangular glass test tank with end compartments (stimulus zones) providing exclusively visual and and (or) chemical food (either boiled spinach or tadpoles of Duttaphrynus melanostictus) and predator (tadpoles of Hoplobatrachus tigerinus). A test tadpole E. cyanophlyctis was held at the centre of the test tank for 5 min (acclimation) to perceive visual and (or) chemical food or predator cues. Then it was released from the centre of the test tank and allowed to associate or stay away from the caged stimulus subjects (food or predator), which were placed at one end of the test tank either in a glass beaker (visual cues) or in a mesh cage wrapped with cheese cloth (chemical cues) for a period of 10 min. The test tadpoles failed to detect either food or predator through visual cues. They spent almost an equal amount of time in the zone housing food or predator in a glass beaker as compared to the opposite zone, which was kept empty. However, they detected both food and predator solely through chemical cues. In tests with chemical food cues (either boiled spinach or tadpoles of D. melanostictus), they spent the majority of their time (67.25 % of total time) near chemical food cues rather than empty or visual food cues. In contrast, in tests with chemical predator cues (tadpoles of H. tigerinus), they spent the majority of their time (68.89 % of total time) away from the chemical predator cues. Therefore, the findings show that E. cyanophlyctis tadpoles detect both food and predator through chemical sensory mechanism rather than visual ones. [ABSTRACT FROM AUTHOR]

Organisms that shift their phenologies in response to global warming will experience novel photic environments, as photoperiod (daylength) continues to follow the same annual cycle. How different organisms respond to novel photoperiods could result in phenological mismatches and altered interspecific interactions. We conducted an outdoor mesocosm experiment exposing green frog (Rana clamitans) larvae, gray treefrog (Hyla versicolor) larvae, phytoplankton, periphyton, and zooplankton to a three‐month shift in photoperiod: an early‐season photoperiod (simulating April) and a late‐season photoperiod (simulating July). We manipulated photoperiod by covering and uncovering tanks with clear or light‐blocking lids to mimic realistic changes in daylength. We assessed amphibian life history traits and measured phytoplankton, periphyton, and zooplankton abundances. Green frog larvae and gray treefrog metamorphs were more developed under the early‐season photoperiod. Gray treefrog total length was also reduced, but photoperiod did not affect green frog total length. Although phytoplankton and periphyton abundances were not affected by photoperiod, copepod nauplii were in greater abundance under the early‐season photoperiod. Overall, this simplified aquatic community did not exhibit significant changes to structure when exposed to a three‐month shift in photoperiod. Temperate amphibians that breed earlier in the year may develop faster, which may have long‐term costs to post‐metamorphic growth and performance. Asynchronous shifts in zooplankton abundances in response to altered photoperiods could subsequently affect freshwater community structure. While photoperiod has been shown to individually affect freshwater organisms, our study using replicated outdoor wetland communities shows that the comprehensive effects of photoperiod may be less important than other cues such as temperature and precipitation. [ABSTRACT FROM AUTHOR]

Facultative colour change is widespread in the animal kingdom, and has been documented in many distantly related amphibians. However, experimental data testing the extent of facultative colour change, and associated physiological and morphological implications are comparatively scarce. Background matching in the face of spatial and temporal environmental variation is thought to be an important proximate function of colour change in aquatic amphibian larvae. This is particularly relevant for species with long larval periods such as the western spadefoot toad, Pelobates cultripes, whose tadpoles spend up to six months developing in temporary waterbodies with temporally variable vegetation. By rearing tadpoles on different coloured backgrounds, we show that P. cultripes larvae can regulate pigmentation to track fine-grained differences in background brightness, but not hue or saturation. We found that colour change is rapid, reversible, and primarily achieved through changes in the quantity of eumelanin in the skin. We show that this increased eumelanin production and/or maintenance is also correlated with changes in morphology and oxidative stress, with more pigmented tadpoles growing larger tail fins and having an improved redox status. [ABSTRACT FROM AUTHOR]

Several aquatic sampling techniques are commonly used to detect and quantify amphibian larvae. Although many techniques have been standardized, comparisons among methods have been poorly studied. We employed a removal design to investigate the detection rate of amphibian larvae using box enclosures and evaluated the reliability of timed dipnet sampling relative to the more quantitative box enclosure sampling across 13 vernal pools. For these comparisons, we studied larvae of the endangered California Tiger Salamander (Ambystoma californiense; CTS) and the smaller and more abundant tadpoles of the Pacific Treefrog (Pseudacris regilla; PTF). Based on N-mixture model estimates, box enclosure sampling captured only 5% more of the CTS larvae present than PTF tadpoles, despite disparities in their sizes and estimated abundances. Dipnet sampling was slightly more effective at detecting CTS larvae than was enclosure sampling, while both methods equally detected PTF tadpoles. We found a strong relationship (R2 = 0.92) between the densities of CTS larvae estimated from dipnet sampling and those calculated from the more quantitative enclosure sampling, indicating that dipnet sampling is a reliable measurement of relative abundance. We conclude that timed dipnet surveys can be an important tool for monitoring populations of CTS, and possibly other lenticbreeding amphibians, especially given its relative efficiency that can be replicated across both time and space. [ABSTRACT FROM AUTHOR]

Abstract Background Urban development results in habitat destruction, affecting populations of amphibians, the most fragile group of vertebrates. With changes in the environment, these animals become more exposed to light and predators. To enhance their chances of survival, they display plasticity of body coloration. Aside from adaptive benefits, animals exhibiting background matching meet the energetic costs and restrictions of changing body tones. To study the physiological consequences of Hyla arborea tadpole adaptation to background color, we followed oxidative stress parameters after rearing larvae on a constant background (black/white) and after changing the background color. Results Larvae cultivated for 20 days on constant substrate color exhibited differences in body coloration but without differences in lipid peroxidation (LPO) concentration between dark and pale individuals, suggesting that coloration investment during this period did not induce higher oxidative damage in darker tadpoles. Prolonged exposure of larvae (37 days) to a dark habitat increased antioxidative system defense and LPO concentrations, compared to animals reared permanently in the white surroundings. The positive correlation of oxidative damage with color intensity of individuals points to the physiological consequences of higher investment in the number of pigment cells necessary for dark pigmentation. In individuals faced with non-matching background and change in body coloration, defense system declined and LPO occurred relative to individuals cultivated in white habitat. Conclusion Here, we have pointed to consequences related to background matching and stress that amphibians experienced during chromatic adaptations. Background color change causes a complex physiological response affecting the antioxidative defense parameters. This investigation elucidates the accompanying cost of amphibiansʼ adjustment to an altered environment.

Freshwater ecosystems are threatened by climate change and invasive species. Amphibians are important members of freshwater communities and are susceptible to negative effects of climate change and invasion. Furthermore, both climate change and invasion can influence density of amphibian larvae at the microhabitat scale because of larval clustering. To understand the effects of climate change and invasion on Pacific Chorus Frog Pseudacris regilla (Baird and Girard, 1852) larvae, a 2 × 2 × 2 factorial experiment was carried out with a climate treatment (future/historical; simulated as changes in both temperature and hydroperiod), indirect exposure to the invasive Brook Stickleback Culaea inconstans (Kirtland, 1840) fish (chemical cues present/absent), and conspecific density (conspecific present/absent). We measured tadpole survival and development rate along with variables related to body shape, including mass, growth, growth rate, body mass index, tail fin depth, tail muscle depth, tail muscle width, and rear limb length. We assessed the effects of 3 common and important stressors (climate, invasive species, and density) alone and in combination with the other stressors to explore their interactions. Climate change, as simulated by our study, had large effects on Pacific Chorus Frog tadpole development and body shape. Brook Stickleback chemical cues had smaller but important effects on body shape and development rate when combined with additional stressors. Competition because of presence of a conspecific tadpole also reduced survival and had large effects on body shape. Pairwise interactions were largely additive or antagonistic. Three-way stressor interactions were most often antagonistic, resulting in less-than-additive effects of the 3 stressors together. However, 3 synergistic 3-way emergent interactions were detected. When all 3 stressors were present, development rate was faster than expected but rear limb length and tail muscle width were smaller than expected. Our results illustrate that climate change and conspecific density have wide-ranging effects on amphibian growth, development, and morphology—effects which may carry over into the terrestrial stage and reduce fitness. Furthermore, our findings reveal complex stressor interactions that were not predictable from single stressor effects or pairwise stressor effects, illustrating the difficulty in predicting multiple stressor interactions in freshwater systems. [ABSTRACT FROM AUTHOR]

Fungicide usage has increased globally in response to the rise in fungal pathogens, especially in the agricultural sector. However, research examining the toxicity of fungicides is still limited for many aquatic species. In this study, we examined the acute toxicity of two widely used fungicides, chlorothalonil and pyraclostrobin, on six North American larval amphibian species across multiple families using 96-h LC50 tests. We found that pyraclostrobin was approximately 3.5x more toxic than chlorothalonil; estimated LC50 values ranged from 5–18 µg/L for pyraclostrobin and 15–50 µg/L for chlorothalonil. Comparing across amphibian groups, we found that salamanders were 3x more sensitive to pyraclostrobin than anuran species and equally as sensitive to chlorothalonil. Notably, our estimated LC50 values within the range of the expected environmental concentration for these fungicides suggesting environmental exposures could lead to direct mortality in these species. Given the widespread and increasing usage of fungicides, additional work should be conducted to assess the general risk posed by these chemicals to amphibian and their associated aquatic habitats. [ABSTRACT FROM AUTHOR]

The impacts of landscape anthropization on mosquito abundance and diversity are already well studied, but the underlying ecological factors behind these effects are still poorly understood. One such underlying ecological factor may be related to the loss of amphibians in human‐modified landscapes, providing ideal habitats for several mosquito species. In this study, we conducted a mosquito and amphibian larvae survey in 77 ponds along a gradient of landscape anthropization in western Switzerland. We used structural equation models to investigate the direct and indirect effects of building footprints and several local pond parameters on mosquito abundance and composition through amphibian abundance. We highlighted that landscape anthropization increases the presence probability of mosquito larvae and the proportion of Culex pipiens in mosquito communities. Our results also suggested that one of the ecological mechanisms underlying these effects is a reduction in amphibian abundance, limiting competition and predation experienced by mosquitoes in human‐modified landscapes. In addition, we showed that several local pond characteristics prevent the presence and abundance of mosquito larvae. Indeed, deep ponds, which promote amphibian abundance, limit the probability of larval mosquito presence, and large and old ponds have a lower larval mosquito abundance. Amphibians appear to be effective control agents of natural mosquito populations. Therefore, the development of measures to protect amphibians in human‐modified landscapes could help to reduce both mosquito‐related nuisances and the risk of emergence of vector‐borne diseases in humans and wildlife. [ABSTRACT FROM AUTHOR]

Losses in biodiversity can alter disease risk through changes in host species composition. Host species vary in pathogen susceptibility and competence, yet how changes in diversity alter host–pathogen dynamics remains unclear in many systems, particularly with respect to generalist pathogens. Amphibians are experiencing worldwide population declines linked to generalist pathogens, such as ranavirus, and thus represent an ideal group to investigate how host species composition affects disease risk. We conducted experiments in which amphibian larvae of three native species (Pacific tree frogs, Pseudacris regilla; Cascades frogs, Rana cascadae; and Western toads, Anaxyrus boreas) were exposed to ranavirus individually (in the laboratory) or as assemblages (in outdoor mesocosms). In a laboratory experiment, we observed low survival and high viral loads in P. regilla compared to the other species, suggesting that this species was highly susceptible to the pathogen. In the mesocosm experiment, we observed 41% A. boreas mortality when alone and 98% mortality when maintained with P. regilla and R. cascadae. Our results suggest that the presence of highly susceptible species can alter disease dynamics across multiple species, potentially increasing infection risk and mortality in co‐occurring species. [ABSTRACT FROM AUTHOR]

Background: Urban development results in habitat destruction, affecting populations of amphibians, the most fragile group of vertebrates. With changes in the environment, these animals become more exposed to light and predators. To enhance their chances of survival, they display plasticity of body coloration. Aside from adaptive benefits, animals exhibiting background matching meet the energetic costs and restrictions of changing body tones. To study the physiological consequences of Hyla arborea tadpole adaptation to background color, we followed oxidative stress parameters after rearing larvae on a constant background (black/white) and after changing the background color. Results: Larvae cultivated for 20 days on constant substrate color exhibited differences in body coloration but without differences in lipid peroxidation (LPO) concentration between dark and pale individuals, suggesting that coloration investment during this period did not induce higher oxidative damage in darker tadpoles. Prolonged exposure of larvae (37 days) to a dark habitat increased antioxidative system defense and LPO concentrations, compared to animals reared permanently in the white surroundings. The positive correlation of oxidative damage with color intensity of individuals points to the physiological consequences of higher investment in the number of pigment cells necessary for dark pigmentation. In individuals faced with non-matching background and change in body coloration, defense system declined and LPO occurred relative to individuals cultivated in white habitat. Conclusion: Here, we have pointed to consequences related to background matching and stress that amphibians experienced during chromatic adaptations. Background color change causes a complex physiological response affecting the antioxidative defense parameters. This investigation elucidates the accompanying cost of amphibiansʼ adjustment to an altered environment. [ABSTRACT FROM AUTHOR]

Tropical savannas are globally extensive and ecologically invaluable ecosystems. As most ecosystems however, they are subject to serious anthropogenic stress. Defaunation, and especially the loss of large mammals, is pervasive in tropical savannas and known to trigger wide‐ranging ecological effects, from vegetation changes to the loss of ecosystem function. Despite what is currently known about the terrestrial consequences of defaunation, and the potential cross‐ecosystem influence of large mammals, virtually no research has investigated associated effects on small adjacent water bodies. This research gap persists because (1) tropical savannas have been historically neglected, (2) the ecological value of small water bodies (e.g. ponds) is only recently being recognized, and (3) empirical baseline data are often lacking. In this paper, we compared a rare pre‐change dataset with newly collected data on 213 freshwater assemblages, to investigate community structure and composition before and after a major defaunation event. Our research focused on a diverse species assemblage of amphibian larvae (i.e. tadpoles) in temporary savanna ponds. We found that pond vegetation cover increased from 16.0% to 45.6% post‐defaunation, that is, a near three‐fold increase. Such habitat changes seemed to have benefitted those species that use vegetation during reproduction (e.g. the leaf‐folding Afrixalus spp.), while others have declined. Interestingly, we found a strong correlation between tadpole community shifts and other freshwater organisms, which indicates that habitat changes have affected a wide variety of aquatic organisms. Given that organisms inhabiting temporary aquatic habitats often have complex life histories with terrestrial adult life stages, we propose that the terrestrial effects of defaunation have indirectly led to distinct aquatic communities, in addition to direct habitat effects. These results shed new light on the potential role of large‐bodied mammals in shaping adjacent ecosystems, and raise important questions concerning the functioning of temporary aquatic systems in the Anthropocene. [ABSTRACT FROM AUTHOR]

Ivermectin (IVM) is a broad-spectrum veterinary antiparasitic used worldwide in cattle breeding. The aim of this study was to evaluate the lethal effects of the active ingredient and a commercial formulation of IVM (1 % active ingredient) in the embryonic stage (S. 4–6) and larval stage (S. 25) of the South American amphibian Rhinella arenarum through chronic standardized bioassays. Also, behavior analysis and oxidative stress and cholinergic effects biomarkers were analyzed at 1, 10 and 100 μg IVM/L concentrations. For the embryonic stage, the active ingredient (96 h- LC 50 : 15900 μg/L) was more toxic than the commercial formulation (96 h-LC 50 : 51230 μg/L) during the acute period, while at chronic exposure the commercial formulation was more toxic (504 h-LC 50 : 10.25 μg/L), compared to the active ingredient (504 h-LC 50 : 312.80 μg/L). For the larval stage, in acute exposure, the active ingredient (96 h-LC 50 : 800 μg/L) was more toxic than the commercial formulation (96 h-LC 50 : 1550 μg/L). In the chronic exposure, the commercial formulation (504 h-LC 50 : 77.33 μg/L) was more toxic than the active ingredient (504 h-LC 50 : 195.25 μg/L). Overall, larvae exhibited greater sensitivity to both the active ingredient and the commercial formulation. However, during chronic exposure, embryos were more sensitive to the commercial formulation than larvae. The commercial formulation primarily induced oxidative stress, and both forms of the compound affected behavior and cholinergic effect biomarkers, even at low environmentally relevant concentrations (1 μg/L). These results highlight the potential impact of IVM on aquatic ecosystems. [Display omitted] • IVM caused lethal and sublethal effects on R. arenarum larvae at low concentrations. • Lethality was stage and time dependent, being the larval stage more sensitive. • Behavior and neurotoxicity biomarkers were altered at environmental concentrations. • Environmental concentrations of IVM caused negative effects on amphibian larvae. [ABSTRACT FROM AUTHOR]

Fish are significant predators of amphibian larvae in streams and larvae can detect these predators through both visual and olfactory cues. The ability to effectively recognize these cues may depend on the evolutionary history of predator and prey such that recently introduced predators may not be recognized as readily as those that have consistently coexisted with the prey species. As such, the relatively recent introduction of rainbow trout (Oncorhynchus mykiss) into Southern Appalachian headwater streams where the black-bellied salamander (Desmognathus quadramaculatus) and brook trout (Salvelinus fontinalis) naturally coexist has raised concern. The objective of this study was to determine whether black-bellied salamander larvae respond to cues from introduced rainbow trout. To evaluate this, salamander activity metrics (general activity and number of movements) were recorded before and after exposure to either native trout predator cue (brook), introduced trout predator cue (rainbow), or conditioned tap water (control). Larvae were collected from different stream reaches based on their cooccurrence with brook trout only, rainbow trout only, rainbow and brook trout, or no trout predators. Larvae that co-occur with trout reduced their activity when exposed to brook trout predator cue, but their response to rainbow trout predator cue depended on their previous co-occurrence. A follow-up test to determine the influence of alarm cue on predator response indicated that the alarm cue enhanced the response to the rainbow trout predator. [ABSTRACT FROM AUTHOR]

Understanding habitat availability and use patterns are essential in developing comprehensive conservation strategies for focal species. Studies on amphibian larval habitat use are limited, especially from modified habitats. We investigated the habitat availability and use patterns of overwintering tadpoles of the Nanorana frog in an anthropogenically modified stream in the western Himalaya. Habitat was assessed in terms of depth, velocity, substrate type, and instream cover. We quantified the microhabitat preference of the tadpoles to develop habitat suitability criteria (HSC) curves, the biological component of habitat simulation tools used in instream flow management. We analyzed the data covering winter and post‐winter seasons using cumulative link mixed models to understand the influence of check dams and seasons on the hydraulic properties of microhabitats used by the tadpoles. We confirm the influence of check dam and season on velocity and the influence of season on depth used by the tadpoles. Based on this, we generated HSCs for tadpoles occurring in natural and modified pools during both seasons. We recommend intermediate water depths (30–60 cm) during the low flow season to sustain the tadpole population in the study stream and other required habitat features. The study underlines the importance of spatial and temporal variation in the habitat suitability for Nanorana tadpoles. These HSCs can be used in hydrological models for estimating the minimum ecological flow for overwintering tadpoles in the study area. A large‐scale study based on the recommendations can lead to a better conservation plan in light of altered streamflow in the western Himalaya region. [ABSTRACT FROM AUTHOR]

The use of insecticides to control undesirable pest species in forestry has undergone a shift from broad spectrum to narrow spectrum insecticides to reduce the risk of effects on non-target species. However, there is still risk of direct effects on non-target species as some insecticides function as hormone mimics, or through indirect pathways as the insecticide is broken down in the environment. Tebufenozide, an ecdysone hormone mimic, is the active ingredient in insecticides used in a variety of large scale pest control programs. An oft cited reason for the safety of Tebufenozide is that it is rapidly broken down in the environment by microbes. We investigated the potential non-target effects of two Tebufenozide formulations used in Canada, Mimic 240LV and Limit 240, on aquatic communities using an outdoor mesocosm experiment. We focus on direct effects on amphibian larvae (wood frog, Rana sylvaticus), zooplankton communities, and effects on biofilm and phytoplanktonic microbial communities that could arise from either direct toxicity, or from breaking down the insecticide as a nutrient and/or carbon source. There was limited evidence for direct effects on amphibian larvae or zooplankton communities. There were small but non-significant shifts in biofilm microbial communities responsible for nutrient cycling. Beta diversity in the plankton community was slightly higher among tanks treated with insecticide indicating a community dispersion/disbiosis effect. Overall, we found limited evidence of negative effects, however, subtle changes to microbial communities did occur and could indicate changes to ecosystem function. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are critical emerging pollutants around the world. There is a growing interest in the effects of MP ingestion, non-digestion, and toxicity on aquatic organisms. Amphibian tadpoles are the vertebrate group that has received the least attention regarding this issue. The aim of the present study was to determine the ingestion of polyethylene MPs by Scinax squalirostris tadpoles by atomic force microscopy (AFM) and to evaluate the activities of carboxylesterase (CbE, using 4-naphthyl butyrate-NB-, and 1-naphthyl acetate –NA- as substrates) and alkaline phosphatase (ALP) under MP exposure. Enzyme activities were analyzed spectrophotometrically at 2 and 10 days of exposure. Tadpoles were exposed to two different treatments during 10 days: a negative control (CO, dechlorinated water) and MP (60 mg L−1). AFM images of the digestive contents of tadpoles revealed the presence of MPs. After 10 days of MP exposure, CbE (NB) activity was significantly higher and CbE (NA) activity was significantly lower in MP treatments than in controls. ALP activity decreased in MP treatments after 2 and 10 days of exposure. The detection of MP particles in the intestinal contents and the effects on metabolic enzymes in a common frog species evidenced the potential health risk of MP to aquatic vertebrates. Thus, the differential response in enzymes and substrates demonstrate the need for considering the complex effects of contaminants and nutrients on ecosystems for ecotoxicological risk characterization. [ABSTRACT FROM AUTHOR]

Due to their various properties as polymeric materials, plastics have been produced, used and ultimately discharged into the environment. Although some studies have shown their negative impacts on the marine environment, the effects of plastics on freshwater organisms are still poorly studied, while they could be widely in contact with this pollution. The current work aimed to better elucidate the impact and the toxicity mechanisms of two kinds of commercial functionalized nanoplastics, i.e., carboxylated polystyrene microspheres of, respectively, 350 and 50 nm (PS350 and PS50), and heteroaggregated PS50 with humic acid with an apparent size of 350 nm (PSHA), all used at environmental concentrations (0.1 to 100 µg L−1). For this purpose, two relevant biological and aquatic models—amphibian larvae, Xenopus laevis, and dipters, Chironomus riparius—were used under normalized exposure conditions. The acute, chronic, and genetic toxicity parameters were examined and discussed with regard to the fundamental characterization in media exposures and, especially, the aggregation state of the nanoplastics. The size of PS350 and PSHA remained similar in the Xenopus and Chironomus exposure media. Inversely, PS50 aggregated in both exposition media and finally appeared to be micrometric during the exposition tests. Interestingly, this work highlighted that PS350 has no significant effect on the tested species, while PS50 is the most prone to alter the growth of Xenopus but not of Chironomus. Finally, PSHA induced a significant genotoxicity in Xenopus. [ABSTRACT FROM AUTHOR]

Nitrite, as a part of nitrogen cycle, is one of the most common toxic compounds in aquatic ecosystems. Since skeletal development is an essential process during amphibian metamorphosis, exposure of larval amphibians to nitrite might disrupt skeletal development. To evaluate whether nitrite affects skeletal development of amphibian larvae, Bufo gargarizans larvae at Gs26 were exposed to 10, 100, 500 and 1000 μg/L nitrite–nitrogen (NO2-N) in the present study. The metamorphosis rate, body weight, body length, forelimb length and hindlimb length of B. gargarizans exposed to NO2-N were decreased. The microscopic structures of thyroid gland were altered under NO2-N exposure at Gs42. The skeletal lengths of the humerus, femur and fibulare of tadpole at Gs42 were significantly reduced under 100, 500 and 1000 μg/L NO2-N treatment groups, and the lengths of humerus, tibia-fibula and tibiale of tadpole at Gs46 were significantly reduced under 1000 μg/L NO2-N treatment groups. In addition, the expression levels of thyroid hormone (TH) and endochondral ossification-related genes of tadpoles at Gs42 and Gs46 were tested by qRT-PCR. Overall, NO2-N exposure could affect the expressions of these genes and then may influence the activity and function of thyroid gland, further disturbing the amphibian metamorphosis and skeletal development of amphibian larvae. [ABSTRACT FROM AUTHOR]

In addition to habitat loss and fragmentation, behavioral traits and the deterioration of water environments also contribute to the local extinction of amphibians. Abundant microflora in urban ponds may cause fatal diseases, whereas symbiotic bacteria may protect the host from pathogens; these effects may vary with group size. In this study, I monitored the growth of Japanese common toad (Bufo japonicus) larvae in Tokyo using three different group sizes: 1 (solitary), 2 (pair), and 15. Although there was no genetic bias in the major histocompatibility complex (MHC) class II genes or microsatellite loci to the survival of the larvae, the mortality risk of the larvae reared in pond water was higher than that of those reared in tap water. According to the survival analysis, the risk was more significant when the group size was 15. This result would be unwelcomed for the B. japonicus tadpoles, which have habits of social aggregation. Furthermore, larval metamorphosis took longer to complete in pond than tap water without any difference in body length or mass. These findings provide fundamental insight into the impact of the aquatic environment and the effect of the group size on animal health and conservation.

Global warming and environmental pollutants both pose a threat to the behavior and physiology of animals, but research on the combined effects of the two is limited. Atrazine, a widely used herbicide, has toxic effects on organisms. In this study, the effects of environmental concentrations of atrazine exposure (100 μg/L) for seven days on the movement, metabolism and gene expression related to motility of Pelophylax nigromaculatus larvae (GS8) were investigated under global warming. The results showed that compared to the optimal growth temperature (18 °C), atrazine treatment under global warming (21 °C) significantly increased the average speed (about 11.2 times) and maximum acceleration (about 1.98 times) of P. nigromaculatus larvae, altered the relative abundance of 539 metabolites, including Formyl-5-hydroxykynurenamine, 2,4-Dihydroxybenzophenone, and FAPy-adenine, and changed the nucleotide metabolism, pyrimidine metabolism, glycerophospholipid metabolism, and purine metabolism, as well as increased the gene expression of SPLA2 (about 6.46 times) and CHK (about 3.25 times). In summary, atrazine treatment under global warming caused metabolic disorders in amphibian larvae and increased the expression of some movement-related genes in the brain, resulting in abnormally active. [Display omitted] • Atrazine treatment under global warming increased movement active of tadpole. • Atrazine treatment under global warming caused metabolic disorders of tadpole. • Atrazine treatment under global warming increased movement-related gene expressions. [ABSTRACT FROM AUTHOR]

Monensin, an antibacterial commonly used in animal fattening, can enter aquatic ecosystems and harm non-target organisms. Since there are no previous studies about the effects of monensin on amphibians, the aim of the present study was to evaluate the lethal and sublethal toxicity of a commercial formulation of monensin (CFM) through standardized bioassays with embryos and larvae of the amphibian Rhinella arenarum. Oxidative stress (catalase and glutathione S-transferase activities, and reduced glutathione and lipid peroxidation levels), cholinesterasic effect (acetylcholinesterase and butyrylcholinesterase activities) and mutagenicity (micronuclei frequency) biomarkers were evaluated. The CFM produced teratogenic effects, with a teratogenic index of 6.21. Embryos (504 h-LC50: 273.33 µg/L) were more sensitive than larvae, as no significant mortality was observed on larvae exposed up to 3000 µg/L for 504 h. However, oxidative stress, cholinesterasic effect and mutagenicity biomarkers were altered on larvae exposed for 96 h to environmentally relevant concentrations (4, 12 and 20 µg/L of monensin active ingredient). The CFM caused adverse effects on the exposed organisms, primarily on embryos, leading to lethal and sublethal effects, which could impact the wildlife when it reaches aquatic ecosystems. • Mortality was stage and time dependent, with embryos being more sensitive. • Monensin produced teratogenicity for Rhinella arenarum embryos. • Oxidative stress and neurotoxicity biomarkers were altered at low concentrations. • Environmental concentrations caused genotoxicity. • The risk quotient indicated a risk of adverse effects on aquatic organisms. [ABSTRACT FROM AUTHOR]

Pathogens can alter species composition and ecosystem function by causing direct and indirect effects on communities. Zoospores of the chytrid fungus Batrachochytrium dendrobatidis (hereafter, Bd), a pathogen implicated in worldwide amphibian declines, can be consumed by filter‐feeding zooplankton and can damage mouthparts of infected amphibian larvae. Consequently, we hypothesized that this pathogen would affect the abundance of zooplankton and survival and feeding abilities of larval amphibian hosts. In turn, this could affect the algal food resources of zooplankton and tadpoles, which can include phytoplankton and periphyton. We tested these hypotheses by manipulating the presence of western toad (Anaxyrus boreas) larvae and Bd in outdoor mesocosms and quantifying the densities of amphibians, zooplankton, phytoplankton, and periphyton. Bd infections reduced amphibian larval densities, but this only weakly benefitted periphyton (a density‐mediated indirect effect). After controlling for larval densities, mesocosms with Bd‐exposed larvae had significantly more periphyton biomass than mesocosms with larvae but no Bd, consistent with infection‐induced mouthpart damage reducing larval feeding rates on attached algae (a trait‐mediated indirect effect). In fact, the estimated trait‐mediated effect of Bd on periphyton biomass was larger than the density‐mediated effect. However, we did not find evidence that Bd exposure triggered a switch to filter‐feeding phytoplankton. The presence of Bd was associated with increased copepod abundance, consistent with zooplankton consuming chytrid zoospores. These results suggest that Bd has the potential to cause both trait‐ and density‐mediated indirect effects that can alter community composition and perhaps the primary productivity of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Perceived predation risk to offspring may have similar ultimate community-level impacts to those of consumptive trophic interactions. The present study investigated the behavioral effects of common carp Cyprinus carpio–an omnivorous fish capable of triggering an ecosystem shift to an algae-dominated state–on anurans, using a natural experiment conducted in a system of fish-stocked ponds. We compared oviposition patterns and larval densities of anurans and abundance of zooplankton and phytoplankton in ponds where fish were virtually absent and ponds where common carp was dominant. All studied anuran species bred in fish-poor ponds, while in ponds with high fish densities most of them oviposited infrequently or virtually did not breed. Oviposition habitat selection coupled with fish trophic pressure resulted in diametrically different tadpole densities between fish-poor and fish-dominated ponds. The alimentary tract contents of tadpoles of three locally common anurans, Pelobates fuscus, Hyla orientalis, and Rana temporaria, contained large numbers of unicellular algae, but also significant numbers of zooplanktonic grazers. According to stable nitrogen isotope analyses, tadpoles occupied a trophic level similar to a primary consumer, snail Lymnaea stagnalis, indicating that they fed mainly on algae. While total biomass of crustacean zooplankton did not differ between pond types, chlorophyll a concentrations were low in fish-poor ponds compared to fish-dominated ponds and negatively related to total tadpole biomass. Our findings indicate that scarcity of anuran larvae, resulting mainly from the behavioral responses of breeding anurans to fish predation risk, may facilitate algal production, although ecosystem shifts in the presence of fish occur along more pathways than a top-down cascade.

Unpaved roads make up at least 14 million kilometers of the worldwide road network. Although investigations of road runoff often are focused on paved roads, unpaved roads contribute large volumes of runoff to roadside aquatic habitats and introduce unique constituents to runoff, such as chemical dust suppressants. At least 200 products across five chemical categories are commercially available for road dust suppression and are typically applied at rates up to 4.5 L/m2. Many of these products are poorly described and are lacking basic information on environmental transport, fate, and potential toxicity to roadside organisms. We characterized the aquatic toxicity of 27 commercially available dust control products, including 13 biobased products from the U.S. Department of Agriculture BioPreferred catalog, using juvenile rainbow trout. Acute toxicity varied by more than 1000-fold among products, with 96-h LC50 values ranging from 1.7 to > 16,000 mg/L. Toxicity was not well-predicted by product category. Testing with selected products after simulated weathering under UV radiation did not provide evidence of photoenhanced toxicity. Additional tests with freshwater mussels, juvenile crayfish, pond snails, and amphibian larvae indicated that juvenile rainbow trout were reasonable surrogates for these organisms for a subset of products. This effort represents one of the first comparative studies of dust suppressant toxicity and provides important information for assessing risk to aquatic resources from a widely used but understudied class of contaminants in road runoff. [ABSTRACT FROM AUTHOR]

Temporary water bodies are temporally variable ecosystems supported primarily by rainwater. The biota supported by such water bodies present a range of capacities to remain in this environment for all or part of their life cycles. During floods, temporary pools can connect with permanent streams, promoting changes in trophic networks in the aquatic food webs. The aim of this research was to analyse the feeding ecology of a fish community in a temporary pool near of Tlacotalpan, in the Mexican southeast, in order to understand the dynamics of the feeding habits. First, we identified feeding habits that can be interpreted as guilds of the fishes in the temporary pool: the annual killifish Millerichthys robustus (the only autochthonous species) is planktophagous; Cynodonichthys tenuis and Astyanax aeneus are insectivores; Dormitator maculatus and larvae of amphibians (Lithobates sp.) are mainly detritivorous; and Poecilia mexicana is planktophagous and insectivorous. We then estimated the effect of coexistence on niche breadth and overlap. The niches of M. robustus and P. mexicana evidenced overlap, but the breadth was adjusted inversely, suggesting feeding specialisation in M. robustus in response to competition. We documented the existence of two cohorts of M. robustus; the niche breadth of the first and second cohorts suggesting different strategies probably related to competition under variable conditions. The niche of C. tenuis and A. aeneus, and D. maculatus and tadpoles overlapped, following a pattern of feeding generalisation in response to competition. [ABSTRACT FROM AUTHOR]

Hydrology and dissolved oxygen (DO) availability drive wetland occupancy by zooplantivorous predators in the Prairie Pothole Region of the northeastern Great Plains, as follows. Permanent wetlands favor fishes, while the shallow waters of seasonal wetlands favor invertebrates and the larvae of the amphibian spring-breeding guild, including Tiger Salamanders (Ambystoma tigrinum). Semi-permanent wetlands fluctuate between these two extremities, holding water during wet years but drying during droughts, which means the aquatic vertebrate occupancy of these wetlands typically switches between fishes (wet periods) and amphibian larvae (droughts). Further, the shallow water of wetlands promotes hypoxic/anoxic conditions, creating "summerkills" and "winterkills," primarily of fishes, which obligately breathe DO. Spring-breeding amphibian larvae avoid summerkills by air gulping--using their lungs to access atmospheric oxygen--and avoid winterkills by metamorphosing. Zooplankton, in turn, have several responses to these wetland conditions and their predators. In reaction to visually mediated, size-selective fish predation, small and semi-transparent zooplankton are selected for, and they undertake daily vertical migrations; the literature on this ecological interaction is vast. In response to intense invertebrate predation pressure, zooplankton become large. In response to wetland hypoxia, zooplankton upregulate hemoglobin (i.e., create blood), which makes them conspicuously red. Nocturnally active Tiger Salamander larvae use senses other than vision (likely lateral line mechano- and electroreceptors) to detect prey, permitting zooplankton to be large and red. The presence or absence of fishes or amphibians, combined with zooplankton morphology (small/large, semi-transparent/red), therefore create hypotheses regarding recent wetland conditions. This variability, while characterizing semi-permanent wetlands, is much more dramatic and dynamic than has previously been reported for palustrine basins. As such, by this and other criteria, I offer a synthesis built upon an understanding of respiratory physiology to explain the ecological communities observed in prairie wetlands. [ABSTRACT FROM AUTHOR]

Microplastic pollution has become a pressing environmental concern globally, with its impact on various ecosystems increasingly studied. Among the affected ecosystems, aquatic environments play a crucial role, serving as habitats for diverse organisms, including amphibian larvae. This article aims to explore the similarity of microplastic characteristics between amphibian larvae and their aquatic environment. By examining the sources, distribution, ingestion and potential impacts of microplastics on amphibian larvae and their aquatic habitats, we can gain insights into the interconnectedness of these elements within ecosystems. Understanding these similarities is pivotal for devising effective mitigation strategies and safeguarding amphibian populations and their habitats. [ABSTRACT FROM AUTHOR]

During biotic invasions, native prey are abruptly exposed to novel predators and are faced with unprecedented predatory pressures. Under these circumstances, the lack of common evolutionary history may hamper predator recognition by native prey, undermining the expression of effective antipredator responses. Nonetheless, mechanisms allowing prey to overcome evolutionary naïveté exist. For instance, in naïve prey, history of coevolution with similar native predators or detection of general traits characterizing predators can favor the recognition of stimuli released by invasive predators. However, few studies have assessed how these mechanisms shape prey response at the community level. Here, we evaluated behavioral responses in naïve larvae of 13 amphibian species to chemical and visual cues associated with an invasive predator, the American red swamp crayfish (Procambarus clarkii). Moreover, we investigated how variation among species responses was related to their coexistence with similar native crayfish predators. Amphibian larvae altered their behavior in presence of visual stimuli of the alien crayfish, while chemical cues elicited feeble and contrasting behavioral shifts. Activity reduction was the most common and stronger response, whereas some species exhibited more heterogeneous strategies also involving distancing and rapid escape response. Interestingly, species sharing coevolutionary history with the native crayfish were able to finely tune their response to the invasive one, performing bursts to escape. These results suggest native prey can respond to invasive predators through recognition of generic risk cues (e.g. approaching large shapes), still the capability of modulating antipredator strategies may also depend on their coevolutionary history with similar native predators. [ABSTRACT FROM AUTHOR]

Nanotoxicity data for amphibians are limited compared to other taxonomic groups. The present study assessed toxicity of titanium dioxide nanoparticles (nanoTiO2, anatase form, particle size < 25 nm) on tadpoles of Duttaphrynus melanostictus after short term and chronic exposures. Exposure to nanoTiO2 (≤ 100 mg/L) for 96 h had no significant effect on survival but upon transfer to nanoTiO2 free water for another 21 days, survival of the tadpoles pre-exposed to nanoTiO2 was greatly reduced and their development was delayed. Chronic exposure to nanoTiO2 (0.1 to 10 mg/L) for 14 days had no significant effects on acetylcholinesterase activities but induced mortalities (up to 40%) and histological alterations in the intestine and liver tissues. The results indicate that release of nanoTiO2 to aquatic ecosystems could pose negative impacts to amphibian populations. [ABSTRACT FROM AUTHOR]

Amphibians show a high amount of species richness and endemism. Such diversity can be attributed to their microenvironment as amphibians display fine‐scale heterogeneity depending on the microhabitats they inhabit. Tadpoles are considered as good indicators for understanding microhabitat–species association as they reflect the breeding sites and signify species survival potential. In this study, we assessed the microhabitat factors influencing the distribution of tadpoles of three endemic frogs of the genus Nyctibatrachus namely N. jog, N. kempholeyensis, and N. kumbara from central Western Ghats, India. Forty‐three streams were sampled from three river basins, and stream characteristics were analyzed using generalized linear models. The results indicate that the tadpoles show specific microhabitat preferences and spatial niche partitioning. Among microhabitat variables, the slope significantly influenced the distribution of tadpoles of N. jog and N. kempholeyensis. The tadpoles of N. jog preferred steep slopes, while N. kempholeyensis tadpoles were found in gradual slopes with low water depth. For N. kumbara tadpoles, water temperature significantly influenced their distribution in the streams. Such spatial heterogeneity promotes the coexistence of these species supporting the niche theory. The study advances the understanding of how amphibian diversity from the Western Ghats is shaped at the microhabitat scale. The perennial streams that the Nyctibatrachus tadpoles inhabit are at risk due to anthropogenic activities. The findings of this study provide important baseline data that could be useful for the conservation of the endemic anurans in the Western Ghats, India. [ABSTRACT FROM AUTHOR]

Antibiotics such as Oxytetracycline (OTC) is widely used around the world and it caused serious environmental issues in China, especially in Yangtze delta area. However, its effects on amphibian gut morphology and intestinal microbiota are still unclear. In this study, tadpoles of Pelophylax nigromaculatus was exposed to 0, 5, 90 and 450 μg/L OTC of environmentally relevant concentrations from Gosner (Gs) 26 to Gs 38. The results showed that severe histopathological injuries including cytoplasmic damage, cell arrangement disorganisation and structure deformation were observed in the gut of larvae in 90 and 450 μg/L OTC exposure groups. Moreover, Tunel assay also revealed higher apoptotic ratio in the intestine of tadpoles in 90 and 450 μg/L OTC treatment groups. Furthermore, the relative abundance of dominant phyla and genera of gut microbial community in OTC exposure groups was significantly different from that of control though the richness and species diversity did not show remarkable changes. We concluded that OTC may pose potential health risks to amphibian larvae through inducing gut histopathological injury and intestinal microbiota dysbiosis. [ABSTRACT FROM AUTHOR]

Hexavalent chromium (Cr [VI]) is one of the major detrimental heavy metal pollutants. In the present study, Bufo gargarizans were exposed to 0, 52, 104, 208, and 416 μg/L Cr (VI) from Gosner stage 2 until metamorphosis; and growth, development, and histological characteristics of the thyroid gland and skeletal ossification were examined. The results demonstrated that the survival rate of larvae exposed to Cr (VI) was not different from that measured in animals from the control group. However, high levels of Cr (VI) (104, 208, and 416 μg/L) were associated with significantly delayed growth and development. The suppression of skeletal ossification was observed at high Cr (VI) levels. Besides, histological alterations of the thyroid gland, such as follicular cell hyperplasia, colloid depletion, and peripheral colloid vacuolation, were found in 52 to 416 μg/L Cr (VI) treatments. The results of the present study highlight reductions in growth and development as well as percent metamorphosis and skeletal ossification due to histological alteration of the thyroid gland during exposure to Cr (VI) in B. gargarizans larvae. The present investigation could provide a basis for understanding the detrimental effects of Cr (VI) in amphibian larvae. Environ Toxicol Chem 2021;40:2474–2483. © 2021 SETAC [ABSTRACT FROM AUTHOR]