Agrochemicals disrupt multiple endocrine axes in amphibians

Chemical contaminants and environmental stressors induced teratogenic effect in aquatic ecosystem - A comprehensive review

Aquatic environments, including marine and freshwater ecosystems, are vital for ecological balance and biodiversity. The rising global demand for aquaculture products necessitates increased production, with intensified aquaculture practices posing significant environmental risks. This review explores the pathways through which chemical pollutants, heavy metals, pharmaceuticals, and environmental stressors induce teratogenic effects in aquatic species. The review highlights the impact of pesticide include triazine herbicides, organophosphate and organochlorine insecticides, and carbamates on aquatic life, emphasizing their interference with endocrine systems and developmental processes. Heavy metals like mercury, lead, cadmium, arsenic, and chromium are noted for their persistence and bioaccumulative properties, disrupting cellular and hormonal functions. Pharmaceuticals, including NSAIDs, antibiotics, and chemotherapeutic agents, exert teratogenic effects by disrupting physiological and developmental pathways. Environmental stressors includes temperature fluctuations, salinity variations, pH changes, and oxygen level imbalances exacerbate the teratogenic impact of pollutants. This review highlights the importance of comprehensive environmental management and understanding these complex interactions is essential for formulating efficient strategies to safeguard the effective measures to protect aquatic ecosystems and the biodiversity.

Living in a multi-stressor world: nitrate pollution and thermal stress interact to affect amphibian larvae

The interaction of widespread stressors such as nitrate pollution and increasing temperatures associated with climate change is likely to affect aquatic ectotherms such as amphibians. The metamorphic and physiological traits of amphibian larvae during the critical onset of metamorphosis are particularly susceptible to these stressors. We used a crossed experimental design subjecting Rana temporaria larvae to four constant rearing temperatures (18, 22, 26, 28°C) crossed with three environmentally relevant nitrate concentrations (0, 50, 100 mg l-1) to investigate the interactive and individual effects of these stressors on metamorphic (i.e. growth and development) and physiological traits (i.e. metabolism and heat tolerance) at the onset of metamorphosis. Larvae exposed to elevated nitrate concentrations and thermal stress displayed increased metabolic rates but decreased developmental rate, highlighting interactive effects of these stressors. However, nitrate pollution alone had no effect on either metamorphic or physiological traits, suggesting that detoxification processes were sufficient to maintain homeostasis but not in combination with increased rearing temperatures. Furthermore, larvae exposed to nitrate displayed diminished abilities to exhibit temperature-induced plasticity in metamorphosis timing and heat tolerance, as well as reduced acclimation capacity in heat tolerance and an increased thermal sensitivity of metabolic rate to higher temperatures. These results highlight the importance of considering the exposure to multiple stressors when investigating how natural populations respond to global change.

Glyphosate formulations cause mortality and diverse sublethal defects during embryonic development of the amphibian Xenopuslaevis

The human impact on environmental landscapes, such as land use, climate change or pollution, is threatening global biodiversity and ecosystems maintenance. Pesticides like the herbicide glyphosate have garnered considerable attention due to their well-documented harmful effects on non-target species. During application, the active ingredient glyphosate is utilized in various formulations, each containing different additive adjuvants. However, the possible effects of these formulations on amphibians - the group with the highest decline rates among vertebrates - remain largely unknown. Therefore, the present study investigated the effects of four glyphosate formulations (Glyphosat TF, Durano TF, Helosate 450 TF, Kyleo) on the embryonic development of the model organism Xenopus laevis (South African clawed frog). Embryos at the 2-cell stage were exposed to various concentrations of glyphosate formulations (glyphosate: 0.01-100 mg/L), and mortality as well as sublethal effects on different organs and tissues were analyzed. The results indicated that the formulations had different effects, particularly on the mortality of Xenopus laevis embryos. At sublethal concentrations, the formulations altered the embryos' external appearance, leading to malformations such as reduced eye and head size. In addition, exposure to formulations impaired heart morphology and function, and the expression of heart-specific genes was altered at a molecular level. Our results confirmed that glyphosate formulations had a stronger effect on Xenopus laevis embryogenesis than pure glyphosate. Therefore, it is crucial to evaluate the active ingredient and the co-formulations independently, as well as the combined, commercially available products, during pesticide risk assessments and renewal procedures of agrochemicals. The severe global decline of amphibians, partly due to herbicide use, highlights the need for strict and efficient monitoring of environmental pesticide loads and application areas.

Microplastics and TiO2 nanoparticles mixture as an emerging threat to amphibians: A case study on bullfrog embryos

Emerging contaminants can act as contributing factors to the decline of amphibian populations worldwide. Recently, scientists have drawn attention to the potential ecotoxicity of microplastics and nanomaterials in amphibians, however, their possible effects on embryonic developmental stages are still absent. Thus, the present study analyzed the developmental toxicity of environmentally relevant concentrations of polyethylene microplastics (PE MPs; 60 mg/L) and titanium dioxide nanoparticles (TiO2 NPs; 10 μg/L), isolated or in combination (Mix group) on bullfrog embryos, Aquarana catesbeiana, adapting the Frog Embryo Teratogenesis Assay (FETAX, 96h). Allied to the FETAX protocol, we also analyzed the heart rate and morphometric data. The exposure reduced the survival and hatching rates in groups exposed to TiO2 NPs, and to a lesser extent, also affected the Mix group. TiO2 NPs possibly interacted with the hatching enzymes of the embryos, preventing hatching, and reducing their survival. The reduced effects in the Mix group are due to the agglomeration of both toxicants, making the NPs less available for the embryos. PE MPs got attached to the gelatinous capsule of the chorion (confirmed by fluorescence microscopy), which protected the embryos from eventual direct effects of the microplastics on the hatching and survival rates. Although there were no cardiotoxic effects nor morphometric alterations, there was a significant increase in abdominal edemas in the hatched embryos of the PE MPs group, which indicates that osmoregulation might have been affected by the attachment of the microplastics on the embryos' gelatinous capsule. This study presents the first evidence of developmental toxicity of environmental mixtures of microplastics and nanoparticles on amphibians and reinforces the need for more studies with other amphibian species, especially neotropical specimens that could present bigger sensibility. Our study also highlighted several features of the FETAX protocol as useful tools to evaluate the embryotoxicity of several pollutants on amphibians.

Population declines of a widespread amphibian in agricultural landscapes

Modern agricultural practices are suspected to play a major role in the ongoing erosion of biodiversity. In order to assess whether this biodiversity loss is linked to past habitat modifications (e.g. land consolidation) or to current consequences of modern agriculture (e.g. use of agrochemicals), it remains essential to monitor species that have persisted in agricultural landscapes to date. In this study, we assessed the presence, abundance and recent population trends of one such species, the spined toad (Bufo spinosus) along a gradient of habitats from preserved (forests) to highly agricultural sites in rural Western France. Our results showed that both presence and abundance of spined toads were markedly lower in reproductive ponds surrounded by intensive agriculture. The most salient result of our study is the ongoing decline of this species in farmland habitats. Indeed, this result suggests that unknown factors are currently affecting a widespread terrestrial amphibian previously thought to persist in agricultural landscapes. These factors have recently induced strong population declines over the course of a few years. Future investigations are required to identify these factors at a time when anthropogenic activities are currently leading to unprecedented rates of biodiversity loss.

Framework for multi-stressor physiological response evaluation in amphibian risk assessment and conservation

Controlled laboratory experiments are often performed on amphibians to establish causality between stressor presence and an adverse outcome. However, in the field, identification of lab-generated biomarkers from single stressors and the interactions of multiple impacts are difficult to discern in an ecological context. The ubiquity of some pesticides and anthropogenic contaminants results in potentially cryptic sublethal effects or synergistic effects among multiple stressors. Although biochemical pathways regulating physiological responses to toxic stressors are often well-conserved among vertebrates, different exposure regimes and life stage vulnerabilities can yield variable ecological risk among species. Here we examine stress-related biomarkers, highlight endpoints commonly linked to apical effects, and discuss differences in ontogeny and ecology that could limit interpretation of biomarkers across species. Further we identify promising field-based physiological measures indicative of potential impacts to health and development of amphibians that could be useful to anuran conservation. We outline the physiological responses to common stressors in the context of altered functional pathways, presenting useful stage-specific endpoints for anuran species, and discussing multi-stressor vulnerability in the larger framework of amphibian life history and ecology. This overview identifies points of physiological, ecological, and demographic vulnerability to provide context in evaluating the multiple stressors impacting amphibian populations worldwide for strategic conservation planning.

Colouration matters in dull toads: ultraviolet adornment for ladies and agrochemicals fading effects

Integument colouration can influence many aspects of fitness, and is under strong sexual selection. Amphibians often express sexual dichromatism, and ultra-violet (UV) colouration is usually biased toward males as a sexual signal. As an honest signal, colouration is related to several individual traits, but can also be related to environmental factors such as anthropogenic pollutants, to which amphibians are highly sensitive. In this study, we investigated sexual dichromatism and UV reflectance covering a large visual spectrum (wavelength ranging from 300 to 700 nm) on different body areas (throat, ventral and dorsal areas), in a widespread amphibian species, the spiny toad (Bufo spinosus). Then, we tested the impact of chronic exposure to two widespread herbicides (glyphosate's primary metabolite [AMPA] and Nicosulfuron) on their colouration. We found a strong but unexpected sexual dichromatism with females reflecting more in the UV spectrum (throat and ventral area) than males, suggesting these body parts might be critical in intra-specific signalling. Females with higher ventral UV reflectance were in better body condition, suggesting an honest signal role of UV reflectance which could influence male choice. Throat colouration was further differentially influenced by agrochemicals according to sexes. In AMPA-exposed males, throat was more saturated in yellow-orange than in control males, and Nicosulfuron exposure decreased the throat's reflectance hue in females, which can bear consequences on mate attractiveness. Future studies need to investigate the underlying mechanisms that are altered by agrochemical exposure.

Thyroid and reproduction in amphibians and reptiles

The relationship between the thyroid gland and reproduction in amphibians and reptiles has been studied for more than 100 years. Most studies suggest a positive involvement of thyroid hormones with some aspects of reproduction, but some studies support a negative role for thyroid hormones at certain life stages. Comprehensive studies of gene activation/suppression by thyroid hormones and their absence at various levels of the hypothalamo-pituitary-gonadal axis coupled with observations of adrenocorticoid activity, reproductive performance, and metabolic involvement are needed to understand this complex relationship.

Exploring the repairing mechanisms of reduced graphene oxide (rGo) on the dysregulation of Xenopus Laevis larva hypothalamus-pituitary-thyroid (HPT) axis caused by chiral triazole fungicide metconazole

Replacing chair fungicide racemate marketed product by its enantiomer with high activity and low environmental risk for application is a more environmentally friendly methods to control crop diseases. Moreover, carbon-based nanomaterials, with the desirable chemical and mechanical properties, exhibits latent reduce fungicide toxicity capability, while the mechanism is still poorly understood. Therefore, the present study characterized the toxicity of rac-metconazole (Mez; (1RS,5RS;1RS,5SR)-5-(4-chlorobenzyl)-2,2-dimethyl-1-(1H)) and its two cis-enantiomers as well as the repairing effect of reduced graphene oxide (rGo) on Xenopus Laevis larva by examining growth appearance indexes, Mez bioaccumulation, and hypothalamus-pituitary-thyroid (HPT) axis related hormone contents and gene expression after 14 and 28 days exposure. Compared with two cis-Mez, rac-Mez was preferentially bioaccumulated in tadpoles, and rac-Mez treatment showed a higher toxicity effect on tadpole including growth stage and body weight inhibition by dysregulating tadpole thyroid stimulating hormone (TSH) and thyroid hormone (TH) contents and related gene expression. Enantioselectivity was observed in two cis-Mez treatments. Compared with R,S-Mez, S,R-Mez treatment showed more severe damage on tadpole HPT axis related physiological and biochemical processes. rGo could effectively decrease the toxicity of Mez, especially shown the capacity of repairing the hormone dysregulation caused by R,S-Mez treatment. Moreover, the addition of rGo can decrease the bioaccumulation of Mez in tadpoles. Therefore, R,S-Mez is less toxic to Xenopus Laevis larva growth, and its toxicity could be effectively repaired by the addition of rGO.

A review of non-destructive biomonitoring techniques to assess the impacts of pollution on reproductive health in frogs and toads

In anuran amphibians (frogs and toads), evidence linking pollution to population declines is limited, in particular through impaired reproduction. Here we review the evidence for pollutant-induced alterations on reproductive endpoints in wild anurans with a particular focus on the application of non-destructive endpoints including on sex ratios, male reproductive phenotypes (data are too scarce for females) and reproductive outputs (reflective of mating success). Data evidencing alterations in sex ratio in wild anurans are scarce, however, both feminisation and masculinisation in response to pollution have been reported (seven studies). Male nuptial pad morphology and calling behaviour display high sensitivity to pollutant-exposure and are important features determining male breeding success, however there is considerable variation in these endpoints and inconsistencies in the responses of them to pollution are reported in wild anurans. Data for clutch size are insufficient to assess sensitivity to pollutants (five studies only). However, hatch success and offspring fitness (tadpole survival/development) are sensitive to pollution, with clear linkages to population stability. In conclusion, there are a wide range of non destructive measures with good potential for application to assess/monitor reproductive health in wild anurans, however, a greater understanding of pollutant effects on these endpoints is needed. There measures deserve wider application as they are relatively simple and inexpensive to implement, and as they can be applied non-destructively are widely applicable to our declining anuran populations.

Contributions of water-borne corticosterone as one non-invasive biomarker in assessing nitrate pollution stress in tadpoles of Rana temporaria

Among a multitude of stressors to which wildlife is exposed, environmental pollution is a pervasive one that poses a serious threat. The permeable skin of amphibians is likely to increase direct contact of the body with pollutants, making them a group worth studying to access environmental quality. Consequently, finding reliable and complementary biomarkers that will present detectable and predictable changes in response to pollutants is essential to identify pollution sublethal effects on amphibians and to investigate whether these are in part responsible for population declines. The glucocorticoid hormone corticosterone (CORT), involved in many metabolic functions, is often used to measure the physiological stress response to environmental stressors in amphibians. In this study, we evaluated whether water-borne CORT can serve as a non-invasive biomarker for nitrate pollution stress in the European common frog (Rana temporaria) by comparing the effect of nitrate exposure on hormone release rates and on other physiological downstream biomarkers, i.e., ultimate physiological effects of the stressor. Specifically, we investigated the effect of different nitrate concentrations (0, 10, 50, and 100 mg/L) on water-borne CORT release rates, age, size, and body condition. Exposure to nitrate pollution significantly increased age at metamorphosis and water-borne CORT release rates, and led to reduced mass and body condition, but only at higher nitrate concentrations (i.e., 50 and 100 mg/L). Considering this similar sensitivity to other acknowledged biomarkers, water-borne CORT was a reliable biomarker of physiological stress in R. temporaria exposed to nitrate pollution stress in a controlled single-stressor laboratory approach. Thus, water-borne CORT is a promising method to be included in more holistic approaches. We recommend that such approaches keep testing multiple biomarker combinations, as species are exposed to several stressors likely to interact and produce varied outcomes in different biomarkers in their natural habitats.

Atrazine alters early sexual development of the South American silverside, Odontesthes bonariensis

Atrazine (ATZ) is a frequent contaminant in freshwater ecosystems within agricultural regions. The capacity of this herbicide to interfere with the vertebrate endocrine system is broadly recognized, but the mechanisms and responses usually differ among species. In this study, ATZ effects on hypothalamus-pituitary-gonadal (HPG) axis key genes expression and early gonadal development were evaluated in Odontesthes bonariensis larvae waterborne exposed during the gonadal differentiation period. Fish were treated to 0, 0.7, 7.0, and 70 µg ATZ/L at 25 °C from the 2nd to 6th week after hatching (wah), and a group was kept in clean water until the 12th wah. Parallelly, a group was submitted to 0.05 µg/L of ethinylestradiol (EE₂) as a positive estrogenic control. From each treatment, eight larvae were sampled at 6 wah for gene expression analysis and twelve larvae at 12 wah for phenotypic sex histological determination. The expression of gnrh1, lhb, fshb, and cyp19a1b was assessed in the head, and the ones of amha, 11βhsd2, and cyp19a1a in the trunk. Fish growth was significantly higher in fish exposed to 7 and 70 µg ATZ/L in the 6 wah, but the effect vanished at the 12 wah. The expression of lhb was upregulated in both sex larvae exposed from 7 µg ATZ/L. However, a dimorphic effect was induced on cyp19a1a expression at 70 µg ATZ/L, up or downregulating mRNA transcription in males and females, respectively. Delayed ovarian development and increased number of testicular germ cells were histologically observed from 7 to 70 µg ATZ/L, respectively, and a sex inversion (genotypic male to phenotypic female) was found in one larva at 70 µg ATZ/L. The lhb expression was also upregulated by EE₂, but the cyp19a1a expression was not affected, and a complete male-to-female reversal was induced. Further, EE₂ upregulated gnrh1 in females and cyp19a1b in both sexes, but it did not alter any assessed gene in the trunk. In conclusion, ATZ disrupted HPG axis physiology and normal gonadal development in O. bonariensis larvae at environmentally relevant concentrations. The responses to ATZ only partially overlapped and were less active when compared to the model estrogenic compound EE₂.

Naphthenic acid fraction compounds reduce the reproductive success of wood frogs (Rana sylvatica) by affecting offspring viability

Understanding the toxicity of organic compounds in oil sands process-affected water (OSPW) is necessary to inform the development of environmental guidelines related to wastewater management in Canada's oil sands region. In the present study, we investigated the effects of naphthenic acid fraction compounds (NAFCs), one of the most toxic components of OSPW, on mating behaviour, fertility, and offspring viability in the wood frog (Rana sylvatica). Wild adult wood frogs were exposed separately from the opposite sex to 0, 5, or 10 mg/L of OSPW-derived NAFCs for 24 h and then combined in outdoor lake water mesocosms containing the same NAFC concentrations (n = 2 males and 1 female per mesocosm, n = 3 mesocosms per treatment). Mating events were recorded for 48 h and egg masses were measured to determine adult fertility. NAFC exposure had no significant effect on mating behaviour (probability of amplexus and oviposition, amplexus and oviposition latency, total duration of amplexus and number of amplectic events) or fertility (fertilization success and clutch size). Tadpoles (50 individuals per mesocosm at hatching, and 15 individuals per mesocosm from 42 d post-hatch) were reared in the same mesocosms under chronic NAFC exposure until metamorphic climax (61-85 d after hatching). Offspring exposed to 10 mg/L NAFCs during development were less likely to survive and complete metamorphosis, grew at a reduced rate, and displayed more frequent morphological abnormalities. These abnormalities included limb anomalies at metamorphosis, described for the first time after NAFC exposure. The results of this study suggest that NAFCs reduce wood frog reproductive success through declines in offspring viability and therefore raise the concern that exposure to NAFCs during reproduction and development may affect the recruitment of native amphibian populations in the oil sands region.

Effects of a Neonicotinoid Insecticide and Population Density on Behavior and Development of Wood Frogs (Rana sylvatica)

Amphibians have been facing global declines over the last decades from direct and indirect effects of anthropogenic activities. A contributor to declines is waterway contamination from agricultural runoffs of pesticides such as neonicotinoids. Beyond direct and indirect effects of the pesticide, few studies have investigated the possible interactions between neonicotinoids and natural environmental stressors across larval development, which could alter the strength and direction of observed neonicotinoid effects. The present study used a fully crossed design to investigate how a concentration of imidacloprid (a neonicotinoid; 10 µg/L) measured in surface waters interacted with low and high population densities (0.33 and 1 tadpole/L, respectively), an important environmental stressor, to influence behavior and development across metamorphosis in wood frogs (Rana sylvatica), known to breed in agricultural landscapes. Behaviors were measured in the absence and presence of predation cues using open-field tests at three distinct developmental stages, up to the metamorph stage. We found that imidacloprid did not interact with population density or independently affect behaviors in the absence of predation cues. However, individuals raised at high density compared with low density were more active at an early developmental stage but less active at metamorphic climax. Furthermore, both density and imidacloprid independently decreased the natural freezing response of tadpoles to predation cues. Finally, we found that distance traveled in the open-field test was weakly repeatable between aquatic stages but not repeatable across metamorphosis, a pattern that was not affected by treatments. The present study provides novel insights on the ecotoxicology of imidacloprid in the presence of a natural stressor, highlighting the importance of including behavioral assays and natural stressors in studies of amphibian ecotoxicology. Environ Toxicol Chem 2022;41:2968-2980. © 2022 SETAC.

Adverse Outcome Pathways for Chronic Copper Toxicity to Fish and Amphibians

In the present review, we synthesize information on the mechanisms of chronic copper (Cu) toxicity using an adverse outcome pathway framework and identify three primary pathways for chronic Cu toxicity: disruption of sodium homeostasis, effects on bioenergetics, and oxidative stress. Unlike acute Cu toxicity, disruption of sodium homeostasis is not a driving mechanism of chronic toxicity, but compensatory responses in this pathway contribute to effects on organism bioenergetics. Effects on bioenergetics clearly contribute to chronic Cu toxicity with impacts at multiple lower levels of biological organization. However, quantitatively translating these impacts into effects on apical endpoints such as growth, amphibian metamorphosis, and reproduction remains elusive and requires further study. Copper-induced oxidative stress occurs in most tissues of aquatic vertebrates and is clearly a significant driver of chronic Cu toxicity. Although antioxidant responses and capacities differ among tissues, there is no clear indication that specific tissues are more sensitive than others to oxidative stress. Oxidative stress leads to increased apoptosis and cellular damage in multiple tissues, including some that contribute to bioenergetic effects. This also includes oxidative damage to tissues involved in neuroendocrine axes and this damage likely alters the normal function of these tissues. Importantly, Cu-induced changes in hormone concentrations and gene expression in endocrine-mediated pathways such as reproductive steroidogenesis and amphibian metamorphosis are likely the result of oxidative stress-induced tissue damage and not endocrine disruption. Overall, we conclude that oxidative stress is likely the primary driver of chronic Cu toxicity in aquatic vertebrates, with bioenergetic effects and compensatory response to disruption of sodium homeostasis contributing to some degree to observed effects on apical endpoints. Environ Toxicol Chem 2022;41:2911-2927. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Long-term sex-dependent inflammatory response of adult frogs to ammonium exposure during the larval stage

Among others, the global change involves a worldwide increase in cropland area, with the concomitant rise in nitrogenous fertilizer supplementation and species range alterations, including parasites and pathogens. As most animals rely on their immune systems against these infectious agents, studying the potential effects of nitrogenous compounds on animal immune response is vital to understand their susceptibility to infections under these altered circumstances. Being subjected to an alarming process of global declines, amphibians are the object of particular attention, given their sensitivity to these compounds, especially to ammonium. Moreover, whereas adults can actively avoid polluted patches, larvae are confined within their waterbodies, thus exposed to contaminants in it. In this work, we test whether chronic exposure to a sublethal dose of ammonium during the larval stage of Pelophylax perezi frogs, released from all contamination after metamorphosis, leads to impaired inflammatory response to phytohemagglutinin in adults. We also test whether such a response differs between agrosystem individuals as compared with conspecifics from natural habitats. We found negative carryover effects of chronic exposure of larvae to ammonium on adult inflammatory response, which could imply a greater susceptibility to pathogens and parasites. However, this damage is only true for males, which, according to the immunocompetence handicap hypothesis, could be a consequence of a testosterone-triggered impairment of male immune function. In disagreement with our prediction, however, we detected no differences in the inflammatory response of agrosystem frogs to phytohemagglutinin as compared with natural habitat conspecifics.

An amphibian high fat diet model confirms that endocrine disruptors can induce a metabolic syndrome in wild green frogs (Pelophylax spp. complex)

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.

Did decades of glyphosate use have selected for resistant amphibians in agricultural habitats?

Glyphosate-based herbicides are used worldwide, and glyphosate's primary metabolite (aminomethylphosphonic acid: AMPA), is globally retrieved in surface waters. AMPA induces various adverse effects on aquatic wildlife, including selective mortality, which suggests that glyphosate exposure may have selected for AMPA-resistant individuals. We tested this hypothesis using spined toads (Bufo spinosus), an amphibian found in a variety of habitats, from AMPA-exposed agricultural lands to AMPA-free forested areas. We predicted that the offspring of individuals originating from agricultural habitats would develop AMPA-resistance - and be less prone to develop adverse effects from- AMPA exposure. To investigate this question, we performed a common garden brood-rearing experiment. The embryos and larvae of 40 spined toad pairs captured in agricultural and forest ponds were exposed either to an environmental relevant concentration of AMPA (0.4 μg L^-1) or to control conditions (n = 8160 embryos, n = 240 tadpoles). We monitored development durations, developmental abnormalities and morphology, measured across key developmental stages. Although we observed significant effects of AMPA on fitness parameters in each group, these effects were not exacerbated in individuals from AMPA-free habitats. We suggest that temporal and/or spatial dynamics of contamination, as well as gene flow between exposed and preserved populations, may hinder adaptive divergence between populations. Yet, we show strong adverse effects of AMPA exposure at early developmental stages. AMPA could therefore be one of the numerous causes of declining wild amphibian populations.

Mechanisms of Caspases 3/7/8/9 in the Degeneration of External Gills of Chinese Giant Salamanders (Andrias davidianus)

Metamorphosis is a critical stage in the adaptive development of amphibians from aquatic to terrestrial animals. Metamorphosis of the Chinese giant salamander is mainly manifested by the loss of external gills with consequent changes in the respiratory pattern. The loss of the external gill is regulated by the pathway of apoptosis in which caspase genes are the key factors. This study cloned and expressed the caspase 3/7/8/9 genes of the Chinese giant salamander. The main results were as follows: the complete open reading frames (ORFs) were 885 bp, 960 bp, 1461 bp and 1279 bp, respectively; caspase 3/7/8/9 genes all contained the CASc domain, and most of the motifs were located in CASc domain; and caspase 8 possessed two DED structural domains and caspase 9 possessed a CARD structural domain. Furthermore, results from the tissue distribution analysis indicated that caspase 3/7/8/9 genes were all significantly expressed in the external gill, and at 9 and 10 months of age (MOA), which is the peak time for the loss, the EXPRESSION level of caspase 3/7/8/9 genes was obviously high, which was consistent with the histological result. Moreover, the loss of external gills of the Chinese giant salamander may result from activation of both the apoptosis-related death receptor pathway and the mitochondrial pathway. Finally, it was discovered that thyroid hormone (TH) treatment could both advance the time point at which the external gills of the Chinese giant salamander began to degenerate and shorten this process. Interestingly, at the peak of its metamorphosis (9 MOA), the Chinese giant salamander further accelerated the metamorphosis rate of TH treatment, which suggested a promotive effect on the loss of external gills via the superimposition of the exogenous TH and caspase genes. The study of caspase genes in this experiment was conducive to understanding the mechanism of external gill loss in the Chinese giant salamander, as well as improving our understanding of the metamorphosis development of some Caudata species.

Chemometric modeling of acute toxicity of diverse aromatic compounds against Rana japonica

Chemicals used in our daily life show different toxic effects to the aquatic and terrestrial species and thus hamper the ecological balance. In the present time, amphibians are one of them, which are threatened to be extinct. Quantitative structure-activity relationship (QSAR) is an useful tool for prediction involving less time, money and manpower without requiring any animal experiments to assess the unavailable acute toxicity data for the untested molecules. In this study, we have developed QSAR models for ecotoxicity of some waterborne diverse aromatic compounds on an amphibian species Rana japonica (Japanese brown frog) employing Genetic Algorithm (GA) for variable selection followed by Partial Least Squares (PLS) regression method following recommendations of the Organization for Economic Co-operation and Development (OECD) for QSAR model development. Double cross-validation (DCV) followed by Best Subset Selection (BSS) were employed to select suitable models. The models displayed promising statistical quality in terms of R² (= 0.837-0.841), Q²_LOO (= 0.782-0.787), R²_pred or Q²_F1 (= 0.802-0.82) and some other internal and external validation metrics for tadpoles of Rana japonica (N_Training = 44, N_Test = 14). These models can be applied for data gap filling for a new untested compound falling within the applicability domain (AD) of the models.

Exposure to the synthetic phenolic antioxidant 4,4'-thiobis(6-t-butyl-m-cresol) disrupts early development in the frog Silurana tropicalis

Many chemicals in commonly used household and industrial products are being released into the environment, yet their toxicity is poorly understood. The synthetic phenolic antioxidant, 4,4'-thiobis(6-t-butyl-m-cresol) (CAS 96-69-5; TBBC) is present in many common products made of rubber and plastic. Yet, this phenolic antioxidant has not been tested for potential toxicity and developmental disruption in amphibians, a sensitive and susceptible class. We investigated whether acute and chronic exposure to TBBC would interfere with thyroid hormone-dependent developmental processes in the frog Silurana tropicalis and thus affect its early life-stage development. We exposed S. tropicalis embryos at the Nieuwkoop-Faber (NF) 9-10 stage to TBBC at nominal concentrations (0, 25, 50, 75, 100, 200 and 400 μg/L) to determine the 96h lethal concentrations and sublethal effects. We conducted a chronic exposure starting at stage NF47-48 to three sublethal TBBC nominal concentrations (0, 0.002, 0.1 and 5 μg/L) for 48-52 days to evaluate effects on growth and metamorphosis. The 96h lethal and effective (malformations) TBBC concentrations (LC₅₀ and EC₅₀) were 70.5 and 76.5 μg/L, respectively. Acute exposure to all TBBC concentrations affected S. tropicalis growth and was lethal at 200 and 400 μg/L. Chronic exposure to sublethal TBBC concentrations reduced body size by 8% at 5 μg/L and body mass by 17% at 0.002 μg/L when metamorphosis was completed. This study demonstrates that TBBC is toxic, induces malformations and inhibits tadpole growth after acute and chronic exposures. These findings call for further investigations on the mode of actions of TBBC and related antioxidants for developmental disruption in amphibians.

Effects of cadmium on the female reproductive axis of a Neotropical fish

Metals are one of the contaminants released from the increase of anthropic activities. They can be classified as endocrine disruptors once they can affect the reproductive parameters of different organisms. The aim of the study was to evaluate the potential effects of cadmium on regulatory reproduction axis (Hypothalamic-Pituitary-Gonadal-Liver, the HPGL axis) in females of Rhamdia quelen exposed to nominal concentrations of 0.1; 1; 10 and 100 μg.L^-1 of cadmium. After 15 days, tissues were collected for hormonal quantification, brain aromatase (cyp19a1b), hepatic vitellogenin (vtg) gene expression, and biomarkers analysis. Cadmium was quantified in water, gonad and liver samples. The plasma levels of estradiol, testosterone and gonad and hepatosomatic indexes did not changed after Cd exposure. The cyp19a1b was not different among the groups. Cadmium was detected at higher concentrations in the liver compared to the gonads. No genotoxicity was observed, only erythrocytes nuclear alterations. Metallothionein was reduced at 10 μg.L^-1 in the liver and 10 and 100 μg.L^-1 in the gonad. Hepatic superoxide dismutase activity increased and this can lead to a hydrogen peroxide increase, one of reactive oxygen species. This increase without a compensation of other enzymes of the antioxidant system can lead to lipoperoxidation, as occurred at 100 μg.L^-1. Hepatic vitellogenin gene expression increased as well as the injury index at 0,1 and 100 μg.L^-1. The tested cadmium concentrations have been found in the freshwater ecosystems and can affect the female reproductive regulation axis HPGL of the Neotropical species R. quelen.

Direct and indirect effects of chronic exposure to ammonium on anuran larvae survivorship, morphology, and swimming speed

Several constituents of the current global change are usually deemed accountable for the worldwide declines of amphibian populations. Among these, water contamination poses a major threat, especially to larval stages, which are unable to escape a polluted water body. This problem is remarkable in agrosystems, one of the main sources of water pollution and whose area is forecasted to increase in the forthcoming decades. However, pollutants represent a selective pressure that may result in tolerance in affected areas. In this work, we tested whether chronic exposure to a sublethal concentration of ammonium (10 mg/L), one of the most frequent agrochemicals, affects differently hatching success, survivorship, morphology and swimming performance of Pelophylax perezi tadpoles from agrosystem and pine grove habitats. Ammonium diminished survivorship at the earliest stages after hatching. Thus, lower density was a by-product of exposure to ammonium. Higher density slowed down development, reduced snout-vent length, and had a sharper negative effect on body mass and tail length and depth of ammonium treated individuals with respect to the control. In turn, ammonium accelerated development and increased body mass, SVL, and tail length and depth. These effects did not depend on provenance habitat. However, only pine grove tadpoles' swimming speed was negatively affected by ammonium, which supports the hypothesis that agrosystem tadpoles are more tolerant to ammonium. Finally, corroborating previous findings, tadpoles with larger bodies and tails were faster swimmers, whereas proportionally more massive individuals were slower, and tail depth was unrelated to swimming speed.

Exposure to a mixture of benzo[a]pyrene and triclosan induces multi-and transgenerational metabolic disorders associated with decreased female investment in reproduction in Silurana (Xenopus) tropicalis

Animals must partition limited resources between their own growth and subsequent reproduction. Endocrine disruptors (ED) may cause maternal metabolic disorders that decrease successful reproduction and might be responsible for multi- and transgenerational effects in amphibians. We found that the frog Silurana (Xenopus) tropicalis, exposed to environmentally relevant concentrations of benzo[a]pyrene and triclosan throughout its life cycle, produced F1 females with delayed sexual maturity and decreased size and weight. These F1 females displayed a marked metabolic syndrome associated with decreased fasting plasma cholesterol and triglyceride concentrations and decreased gonadal development. F1 females from F0 exposed animals also had decreased reproductive investment highlighted by a decrease of oocyte lipid reserves associated with significant F2-tadpole mortality. F2 females from F0 exposed animals also displayed a marked metabolic syndrome but were able to correctly direct liver lipid metabolism to the constitution of fat bodies and oocyte yolk stores. In addition, the F2 females produced progeny that had normal mortality levels at 5 days post hatching compared to the controls suggesting a good reproductive investment. Our data confirmed that these ED, at concentrations often found in natural ponds, can induce multi- and transgenerational metabolic disorders in the progeny of amphibians that are not directly exposed. We present a hypothesis to explain the transmission of the metabolic syndrome across generations through modification of egg reserves. However, when high mortality occurred at the tadpole stage, surviving females were able to cope with metabolic costs and produce viable progeny through sufficient investment in the contents of oocyte reserves.

Cylindrospermopsin directly disrupts spermatogenesis in isolated male zebrafish testis

Cylindrospermopsin (CYN) is a cytotoxin, and its documented effects in mammals include damage to several organs. CYN also has hormone-disrupting properties, including estrogenic activity, progesterone production inhibition, and apoptosis induction. While CYN has been reported to exert reproductive toxicity in mice, little is known about its effect on fish reproductive function. Using ex vivo organ culture, we investigated the direct action of CYN on the male reproductive system. Isolated zebrafish testis was exposed to 250, 500, and 1000 µg/L CYN for 24 h and 7 d, followed by histo-morphological analysis. The results demonstrate that exposure to CYN led to a decrease in cell types from all three phases of spermatogenesis in zebrafish testis. There were also significant changes in fshr, lhr, and igf3 transcript levels, as well as testosterone secretion following exposure to CYN. In summary, this study provides novel information on the adverse effects of CYN on testicular spermatogenesis and male reproduction in zebrafish. These results provide a framework for a better understanding of CYN toxicity and the mechanism underlying the adverse action of CYN on male reproduction in fish.

Nonylphenol and cyproterone acetate effects in the liver and gonads of Lithobates catesbeianus (Anura) tadpoles and juveniles

Environmental pollution plays an important role in amphibian population decline. Contamination with endocrine disrupting chemicals (EDCs) is particularly worrying due to their capacity to adversely affect organisms at low doses. We hypothesized that exposure to EDCs such as 4-nonylphenol (NP) and cyproterone acetate (CPA) could trigger responses in the liver and gonads, due to toxic and endocrine disrupting effects. Growth rate may also be impaired by contamination. We investigated sublethal effects of a 28-day exposure to three different concentrations of NP and CPA on liver pigmentation, gonadal morphology, body mass, and length of tadpoles and juveniles Lithobates catesbeianus. Liver pigmentation and the gonadal morphologies of treated tadpoles did not differ from control, but growth rate was impaired by both pollutants. Juveniles treated with 10 μg/L NP and 0.025 and 0.25 ng/L CPA displayed increased liver melanin pigmentation, but gonadal morphologies, sex ratios, and body mass were not affected after treatments. The increase in liver pigmentation may be related to defensive, cytoprotective role of melanomacrophages. The decreased growth rate in tadpoles indicates toxic effects of NP and CPA. Thus, contamination with NP and CPA remains a concern and sublethal effects of different dosages of the compounds on native species should be determined.

Interdependence of Thyroid and Corticosteroid Signaling in Vertebrate Developmental Transitions

Post-embryonic acute developmental processes mainly allow the transition from one life stage in a specific ecological niche to the next life stage in a different ecological niche. Metamorphosis, an emblematic type of these post-embryonic developmental processes, has occurred repeatedly and independently in various phylogenetic groups throughout metazoan evolution, such as in cnidarian, insects, molluscs, tunicates, or vertebrates. This review will focus on metamorphoses and developmental transitions in vertebrates, including typical larval metamorphosis in anuran amphibians, larval and secondary metamorphoses in teleost fishes, egg hatching in sauropsids and birth in mammals. Two neuroendocrine axes, the hypothalamic-pituitary-thyroid and the hypothalamic-pituitary-adrenal/interrenal axes, are central players in the regulation of these life transitions. The review will address the molecular and functional evolution of these axes and their interactions. Mechanisms of integration of internal and environmental cues, and activation of these neuroendocrine axes represent key questions in an “eco-evo-devo” perspective of metamorphosis. The roles played by developmental transitions in the innovation, adaptation, and plasticity of life cycles throughout vertebrates will be discussed. In the current context of global climate change and habitat destruction, the review will also address the impact of environmental factors, such as global warming and endocrine disruptors on hypothalamic-pituitary-thyroid and hypothalamic-pituitary-adrenal/interrenal axes, and regulation of developmental transitions.

Gaps in global wildlife trade monitoring leave amphibians vulnerable

As the biodiversity crisis continues, we must redouble efforts to understand and curb pressures pushing species closer to extinction. One major driver is the unsustainable trade of wildlife. Trade in internationally regulated species gains the most research attention, but this only accounts for a minority of traded species and we risk failing to appreciate the scale and impacts of unregulated legal trade. Despite being legal, trade puts pressure on wild species via direct collection, introduced pathogens, and invasive species. Smaller species-rich vertebrates, such as reptiles, fish, and amphibians, may be particularly vulnerable to trading because of gaps in regulations, small distributions, and demand of novel species. Here, we combine data from five sources: online web searches in six languages, Convention on International Trade in Endangered Species (CITES) trade database, Law Enforcement Management Information System (LEMIS) trade inventory, IUCN assessments, and a recent literature review, to characterise the global trade in amphibians, and also map use by purpose including meat, pets, medicinal, and for research. We show that 1215 species are being traded (17% of amphibian species), almost three times previous recorded numbers, 345 are threatened, and 100 Data Deficient or unassessed. Traded species origin hotspots include South America, China, and Central Africa; sources indicate 42% of amphibians are taken from the wild. Newly described species can be rapidly traded (mean time lag of 6.5 years), including threatened and unassessed species. The scale and limited regulation of the amphibian trade, paired with the triptych of connected pressures (collection, pathogens, invasive species), warrants a re-examination of the wildlife trade status quo, application of the precautionary principle in regard to wildlife trade, and a renewed push to achieve global biodiversity goals.

In the last few decades, exotic pets have become much more common. In the UK in 2008, reptiles and amphibians were more popular than dogs, with over eight million in captivity. But while almost all pet cats and dogs are born and bred in captivity, exotic pets are often taken from the wild, putting species and their habitats at risk.

An international trade agreement called the Convention on International Trade in Endangered Species (CITES) strives to prevent unsustainable animal trade. But to get CITES protection, species depend on data showing that wildlife trade threatens their survival. In addition, their range countries need to first propose them to be listed. For most wild animal species, there are no data on population size or population decline. In the case of amphibians, CITES regulates the trade of just 2.5% of species. This leaves the rest with no protection from overarching international trade regulations. To protect these animals, researchers need to find out which species are in trade, where they are coming from, and how many are already threatened.

To address this, Hughes, Marshall and Strine combined data from five sources, including official CITES trade records, recent research and an online search for amphibian sales in six languages. The data showed evidence of trade in at least 1,215 amphibian species, representing 17% of all amphibians. The figure is three times higher than previous estimates. Of the species in trade, more than one in five is vulnerable to extinction, endangered, or critically endangered. For a further 100 of the traded species, data on population were unavailable. Moreover, analysis of the origins of traded individuals showed that around 42% came from the wild. Tropical parts of the world had the highest number of species in trade, but the data showed exchanges happening across the globe.

Unsustainable wildlife trade can have devastating consequences for wild animals. It has already driven at least 21 reptile species to extinction, and data of amphibian species are unknown. To prevent further species going extinct, legal wildlife trade should follow the precautionary principle when it comes to wildlife trade. Rather than allowing people to trade a species until CITES regulates it, a blanket ban should come into force for species that have not been assessed or are threatened. Trade would be able to resume for a species only when assessments show that it would not cause major population decline, or secure, captive breeding facilities can be guaranteed.

A Review of the Effects of the Biopesticides Bacillus thuringiensis Serotypes israelensis (Bti) and kurstaki (Btk) in Amphibians

Insecticides are important in agriculture, to reduce human disease, and to decrease the nuisance of biting insects. Despite this, many have the potential for environmental impacts and toxicity in nontarget organisms. We reviewed data on the effects of insecticides based on toxins from Bacillus thuringiensis var. israelensis (Bti) and Bacillus thuringiensis var. kurstaki (Btk) on amphibians. The few peer-reviewed publications that are available for Bti provide variable conclusions, ranging from few observable effects to evidence of acute toxicity at high concentrations. We briefly highlight the current controversies and identify key areas for future investigation.

Effect of ethylenethiourea on metamorphosis and ovary development: A comparative study of three larval frogs

Amphibian endocrine systems interact with each other during normal development. Interference with one of the endocrine systems may influence others. We studied the effect of a thyroid inhibitor (ethylenethiourea [ETU]) on metamorphosis and ovary development of three species, Sphaerotheca pashchima, Indosylvirana caesari, and Euphlyctis cyanophlyctis with different larval durations. We treated the tadpoles of these species with 50, 100, and 200 mg/L concentrations of ETU and studied their larval duration, size at metamorphosis, and ovary development. The results revealed that ETU affects metamorphosis, depending on the species and concentration. ETU delayed metamorphosis of E. cyanophlyctis tadpoles and did not affect metamorphosis in S. pashchima tadpoles. Lower concentrations of ETU stimulated metamorphosis in I. caesari tadpoles while high concentration delayed metamorphosis. In the tadpoles (E. cyanophlyctis) treated with higher concentrations of ETU, ovary development was advanced with an increased size of the diplotene oocytes. Oocyte size was smaller in the tadpoles (of I. caesari) treated with lower concentrations of ETU. These results demonstrated that the tadpoles of these species show different responses to the thyroid inhibitor, possibly due to the differences in the larval duration and sensitivity. Inhibition or acceleration of metamorphosis did not interfere in the ovary development of E. cyanophlyctis and I. caesari. These results will be useful in understanding the impact of endocrine disruptors on the interaction between thyroid and sex steroid hormones.

Testicular morphometric changes in neotropical anurans from agroecosystems

One of the causes of the global decline of amphibians is agricultural activity, responsible for causing habitat fragmentation and bringing a range of agrochemicals and fertilizers in the environment, compounds with a potential disrupting effect on non-target organisms, such as frogs. Exposure to these compounds has numerous harmful effects on the testes of these animals, which can compromise reproduction and, consequently, the maintenance of their communities. In this context, we compared the morphology and morphometry of the testes of three species of neotropical anurans (Physalaemus cuvieri, Dendropsophus minutus, and Boana albopunctata) from an agricultural area and a conservation unit. Histologically, the testicular morphology of the species was similar for both environments; however, morphometrically, there was a difference in the measured testicular parameters (locular area and area of spermatogenic cysts). Physalaemus cuvieri presented higher averages of locular and spermatogonial area in the agricultural environment, whereas the area occupied by the spermatozoa was smaller. Additionally, the testicular pigmentation, which is only present in this species, was greater in animal from the agricultural area. In D. minutus, the locular, spermatogonial, and sperm areas showed lower values in the agricultural area, whereas in B. albopunctata, the opposite pattern was found, with the area of the locule, spermatocytes, and spermatozoids being higher. Agricultural activities influence the testicular metric parameters in different species, and our results suggest that D. minutus is most sensitive to anthropic pressures. The least sensitive species is B. albopunctata. We highlight the importance of evaluating different species, since each species responds differently to agricultural activities.

Developmental reproductive toxicity and endocrine activity of propiconazole in the Xenopus tropicalis model

Environmental pollutants and especially endocrine disrupting chemicals (EDCs) are implicated as one of the drivers of the amphibian declines. To advance the understanding of the risks of EDCs to amphibians, methods to determine endocrine-linked adverse effects are needed. The aims were to 1) develop a partial life-cycle assay with the model frog Xenopus tropicalis to determine endocrine perturbation and adverse developmental effects, and 2) determine effects of propiconazole in this assay. Propiconazole is a pesticide with multiple endocrine modes of action in vitro. Its potential endocrine activity and adverse effects in amphibians remain to be elucidated. Tadpoles were exposed to 0, 33 and 384 μg propiconazole/L during critical developmental windows until completed metamorphosis. At metamorphosis, a sub-sample of animals was analysed for endpoints for disruption of estrogen/androgen (sex ratio, brain aromatase activity) and thyroid pathways (time to metamorphosis). The remaining individuals were kept unexposed for 2 months post-metamorphosis to analyze effects on sexual development including gonadal and Müllerian duct maturity and gametogenesis. At metamorphosis, brain aromatase activity was significantly increased in the high-dose group compared to control. In both propiconazole groups, an increased proportion of individuals reached metamorphosis faster than the mean time for controls, suggesting a stimulatory effect on the thyroid system. At 2 months post-metamorphosis, testis size, sperm and Müllerian duct maturity were reduced in the low-dose males, and the liver somatic index in males was increased in both propiconazole groups, compared with controls. In conclusion, our results show that propiconazole exposure caused endocrine perturbations and subsequent hepatic and reproductive effects evident at puberty, indicating persistent disruption of metabolism and male reproductive function. Our findings advance the development of methodology to determine endocrine and adverse effects of EDCs. Moreover, they increase the understanding of endocrine perturbations and consequent risk of adverse effects of azoles in amphibians.

Tissues injury and pathological changes in Hyla intermedia juveniles after chronic larval exposure to tebuconazole

Tebuconazole (TBZ), an azole pesticide, is one of the most frequently detected fungicides in surface water. Despite its harmful effects, mainly related to endocrine disturbance, the consequences of TBZ exposure in amphibians remain poorly understood. Here, we investigated the adverse and delayed effects of TBZ chronic exposure on a native anuran species, often inhabiting cultivated areas, the Italian tree frog (Hyla intermedia). To disclose the multiple mechanisms of action through which TBZ exerts its toxicity we exposed tadpoles over the whole larval period to two sublethal TBZ concentrations (5 and 50 μg/L), and we evaluated histological alterations in three target organs highly susceptible to xenobiotics: liver, kidney, and gonads. We also assessed morphometric and gravimetric parameters: snout-vent length (SVL), body mass (BM), liver somatic index (LSI), and gonad-mesonephros complex index (GMCI) and determined sex ratio, gonadal development, and differentiation. Our results show that TBZ induces irreversible effects on multiple target organs in H. intermedia, exerting its harmful effects through several pathological pathways, including a massive inflammatory response. Moreover, TBZ markedly affects sexual differentiation also by inducing the appearance of sexually undetermined individuals and a general delay of germ cell maturation. Given the paucity of data on the effects of TBZ in amphibians, our results will contribute to a better understanding of the environmental risk posed by this fungicide to the most endangered group of vertebrates.