Integration of a battery of biomarkers to evaluate the health status of field-collected frogs of Leptodactylus luctator living in ecosystems with different anthropogenic disturbances

Amphibians are the most threatened group of vertebrates because they have certain biological and ecological characteristics that make them sensitive to environmental changes. The aim of this study was to evaluate the health status of field-collected adult frogs of Leptodactylus luctator (Amphibia, Anura) living in sites with different anthropogenic disturbances (florihorticulture, petrochemical industry and sewage discharges) and a reference site without any detectable influence of such activities. To this end, a battery of 21 biomarkers (hematological, biochemical and individual biomarkers) was studied using a multivariate approach that allows us to evaluate the relationship between them and provide information on their usefulness. The frogs at the florihorticulture, petrochemical and sewage discharges sites exhibited several biomarkers far from homeostasis. In addition, we identified 11 of 21 biomarkers that were useful indicators of the health status of the frogs and allowed discrimination between study sites in the following order: lymphocytes (98 %), neutrophils (45 %), hemoglobin (42 %), monocytes (41 %), fat body index (35 %), eosinophils (35 %), hepatosomatic index (33 %), mean corpuscular hemoglobin (32 %), thrombocytes (27 %), catalase in liver (26 %), and GST in liver (26 %). The results suggest that hematological biomarkers contribute the most to site separation, whereas biochemical biomarkers contribute the least. The integral interpretation of the results also allowed us to diagnose the different health status of L. luctator: The frogs from the petrochemical industry were the most negatively affected, followed by the frogs from the sewages discharges and finally the frogs from the florihorticulture and reference sites. This is the first field study with anurans in which so many biomarkers were examined.

How do different concentrations of aluminum and zinc affect the survival, body size, morphology and immune system of Physalaemus cuvieri (Fitzinger, 1826) tadpole?

The assessment of amphibian responses as bioindicators of exposure to chemical pollutants is an important tool for conservation of native species. This study aimed to investigate the effects of chronic aluminum (Al) and zinc (Zn) exposure on survival, body size, morphology (malformations), and immune system (leukocyte profile) in P. cuvieri tadpoles. Ecotoxicological analyses were performed utilizing chronic toxicity tests in which 210 tadpoles at the 25th Gosner developmental stage were exposed to Al and Zn. Individuals of P. cuvieri were maintained in glass containers containing various concentrations of aluminum sulfate (0.1, 0.2, or 0.3 mg/L) and zinc sulfate (0.18, 0.27 or 0.35 mg/L), and tests were performed in triplicate. After 14 days, amphibians were weighed, measured and survival rate, malformations in the oral and intestine apparatus, leukocyte profile, and ratio between neutrophils and lymphocytes determined. The differing concentrations of Al and Zn did not produce lethality in P. cuvieri where 95% of the animals survived 326 hr following metal exposure. Individuals exposed to Zn achieved greater body growth and weight gain compared to controls. Aluminum increased weight gain compared controls. These metals also produced malformations of the oral and intestine apparatus and enhanced occurrence of hemorrhages, especially at the highest doses. Lymphocytes were the predominant cells among leukocytes, with lymphopenia and neutrophilia observed following Al and Zn treatment, as evidenced by elevated neutrophil/lymphocyte ratio, an important indicator of stress in animals. Data suggest that further studies need to be carried out, even with metal concentrations higher than those prescribed by CONAMA, to ensure the conservation of this species.

Toxic, genotoxic, mutagenic, and bioaccumulative effects of metal mixture from settleable particulate matter on American bullfrog tadpoles (Lithobates catesbeianus)

Amphibians are more susceptible to environmental stressors than other vertebrates due to their semipermeable skin and physiological adaptations to living in very specific microhabitats. Therefore, the aim of the present study was to investigate the effects of a metal mixture from settleable particulate matter (SePM) released from metallurgical industries on Lithobates catesbeianus tadpoles. Endpoints analyzed included metal bioconcentration, morphological (biometrical indices), hematological parameters (hemoglobin and blood cell count), and erythrocyte DNA damage (genotoxicity and mutagenicity). American bullfrog tadpoles (Gosner's stage 25) were kept under control condition (no contaminant addition) or exposed to a sub-lethal and environmentally relevant concentration (1 g.L-1) of SePM for 96 h. Tadpoles exposed to SePM exhibited elevated whole blood levels of Fe56, AL, Sn, Pb, Zn, Cr, Cu, Ti, Rb, V, Ce, La, Ag, As. SePM-exposed tadpoles showed a significant decrease in condition factor (12%) and increases in hepatosomatic index (25%), hemoglobin concentration (17%), and total leukocytes (82%), thrombocytes (90%), and monocytes (78%) abundance. In addition, exposed tadpoles showed higher MN and ENAs (340 and 140%, respectively) frequencies, and erythrocyte DNA damage with approximately 1.2- to 1.8-fold increases in comet parameters. Taken together, these results suggest that the multimetal mixture found in SePM is potentially genotoxic and mutagenic to L. catesbeianus tadpoles, induces stress associated with hematological changes, and negatively affects growth. Although such contamination occurs at sublethal levels, regulatory standards are needed to control the emission of SePM and protect amphibian populations.

Curative Effects of Dianthus orientalis against Paracetamol Triggered Oxidative Stress, Hepatic and Renal Injuries in Rabbit as an Experimental Model

The aim of the present study investigates the hepatoprotective, nephroprotective and hematopoietic and antioxidant effects of Dianthus orientalis leaves aqueous extract (DO.AQ) in rabbits intoxicated with paracetamol. Different experimental groups were formed, i.e., group N, group T, group ELD, group EMD, group EHD and group SM. The groups with leaves aqueous extract of Dianthus orientalis of 200 and 400 mg/kg body weight, i.e., group EMD and group EHD, showed remedial effects; however, a high dose extract significantly (p < 0.05) reduced the elevated serum levels of alanine transaminase ALT, aspartate transaminase AST and alkaline phosphatase ALP and renal related indices such as serum creatinine, urea and uric acid, and serum electrolytes such as Ca, Mg, P, Na and K, as well as the total count of RBC, WBC, platelets and hemoglobin Hb concentration, mean corpuscular hemoglobin MCH concentration and hematocrit HCT values. Additionally, the extract showed positive effects on the lipid profile, i.e., decreasing levels of cholesterol, triglycerides and LDL and increasing levels of HDL. The levels of thiobarbituric acid reactive substances TBARS, glutathione GSH and radical scavenging activity were also evaluated in liver and kidney homogenates. Paracetamol fed animals had high levels of thiobarbituric acid reactive substances and low levels of glutathione GSH and radical scavenging activity (RSA). Extract ingestion caused a significant increase in glutathione and radical scavenging activity RSA levels, while reducing the (TBARS) levels, showing that the extracts have antioxidant potentials. The antioxidant capacity of the Dianthus orientalis leaves aqueous extract at various dosages demonstrated an increased inhibition of DPPH, i.e., 2, 2-diphenyl-1-picrylehydrazyle free radical. The histological study of the liver and kidney supports the protective activity of Dianthus orientalis leaves aqueous extract against paracetamol intoxication with optimistic effects regarding oxidative stress condition and serum electrolytes balance.

Changes in blood parameters and metabolism in bullfrog tadpoles, Lithobates catesbeianus, (Shaw, 1802) after exposure to the Sorocaba River (São Paulo, Brazil) water

This study evaluated the genetic damage, oxidative stress, neurotoxicity, and energy metabolism in bullfrog tadpoles (Lithobates catesbeianus) exposed to water from two sites of the Sorocaba River, Ibiúna (PI), and Itupararanga reservoir (PIR), in summer and winter. After 96-h exposure, the erythrocyte number decreased in PI and increase in PIR in summer. Bullfrogs show oxidative unbalance (liver, kidney, and muscle), with alterations in the nitric oxide synthase and glucose 6-phosphate dehydrogenase. Cholinesterase increased in the brain in PI and PIR in the summer and decreased in PI in the winter. It also increased in the muscle in both PI and PIR in the winter. Tadpoles show alterations in the activity of the metabolic enzymes (liver, kidney, and muscle), such as phosphofructokinase, pyruvatokinase, malate dehydrogenase, and lactate dehydrogenase; and in the amount of glucose and triglycerides metabolites. Exposure to the Sorocaba River reflected a stressful situation for L. catesbeianus as the changes caused to their metabolism associated with oxidative stress and neurotoxicity may have effects on the development of tadpoles.

HEPATOCELLULAR TOXICITY OF THE METABOLITE EMODIN PRODUCED BY THE COMMON BUCKTHORN (RHAMNUS CATHARTICA) IN GREEN FROG (LITHOBATES CLAMITANS) TADPOLES

The secondary metabolite emodin, produced by the widely distributed invasive shrub known as the common buckthorn (Rhamnus cathartica), has been shown to produce deformities and mortality in invertebrates, fish, and amphibian larvae. Here, we describe the effects on the liver of green frog (Lithobates clamitans) tadpoles after 21 d of exposure to high concentrations of emodin in a controlled environment. Histopathologic analysis showed fibrosis, bile duct proliferation, hepatocellular swelling, and accumulations of flocculent material consistent with emodin within the gall bladder and bile ducts of exposed individuals. The extensive fibrosis produced probably impeded the blood flow within the portal triads, limiting the detoxification function of the liver and resulting in hepatocellular necrosis and premature death for the individuals exposed. Exposure to emodin in the environment could represent a significant threat to developing amphibian larvae and contribute to local declines of populations.

Ecotoxicological evaluation of water from the Sorocaba River using an integrated analysis of biochemical and morphological biomarkers in bullfrog tadpoles, Lithobates catesbeianus ()

Lithobates catesbeianus tadpoles were exposed for 96 h to water from two sites of the Sorocaba River (summer and winter), Ibiúna (PI) and Itupararanga reservoir (PIR) that contained metals. In the liver, in PI, the glutathione peroxidase (GPx) decreased, and the glutathione S-transferase (GST) and carbonyl proteins (PCO) increased. In PIR, the glutathione reduced (GSH) increased, while there was a decrease in catalase (CAT), GPx, GST, PCO, and superoxide dismutase (SOD). In winter, GPx and GST increased in both points. Regarding the kidneys, lipoperoxidation (LPO) levels and GST decreased, while GSH increased in the summer. In the winter, LPO increased in PI. In the muscle, in the summer, there was an increase in GSH and GST and change in PCO. In the winter, the levels of PCO increased and CAT decreased in PIR. The area and volume of the hepatocyte and nucleus area increased in the summer and decreased in the winter. Hepatic melanin decreased in the summer after exposure to PIR water. There were the systemic effects of Sorocaba River water exposure at different times of the year with alterations in biomarkers at different levels, in which kidney shows highest Integrated Response of Biomarkers (IBR) value followed by liver and muscle. Biochemical biomarkers were more sensitive than morphological ones. The more sensitive biochemical markers were MT, PCO, GST and LPO. These effects confirm the hypothesis of metabolic alteration in bullfrog tadpoles by the Sorocaba River water.

Cadmium induced skeletal underdevelopment, liver cell apoptosis and hepatic energy metabolism disorder in Bufo gargarizans larvae by disrupting thyroid hormone signaling

Cadmium (Cd) is hazardous to human health and it is also highly detrimental to amphibian life. In this study, Bufo gargarizans larvae were exposed to environmentally relevant Cd concentrations of 5, 100 and 200 μg L^-1 from Gosner stage (Gs) 26 to Gs 42 of metamorphic climax about 6 weeks. The results showed thyroid structural injuries and thyroid signaling disruption were induced by high Cd exposure (100 and 200 μg L^-1). Moreover, tadpole skeleton including whole body, vertebrata, forelimb and hindlimb was developmentally delayed by high Cd exposure through downregulating the mRNA expressions of genes involved with skeletal ossification and growth pathway. Moreover, liver histopathological injuries were caused by high Cd exposure featured by hepatocytes malformation, nuclear degeneration and increasing melanomacrophage centers. Meanwhile, liver apoptosis rate showed on the rise in a dose-dependent way and Cd stimulated liver apoptosis by upregulating mRNA expressions of genes related to extrinsic and intrinsic apoptosis pathways. Furthermore, high Cd caused hepatic glucometabolism disorder by decreasing the genetic expressions associated with glycolysis and mitochondrial oxidative phosphorylation. In addition, liver lipid metabolism was disrupted by high Cd exposure through downregulating mRNA levels of genes related to fatty oxidation and upregulating mRNA levels of genes related to fatty acid synthesis. We suggested that Cd did great harm to tadpole health by disturbing thyroid function, skeletal growth, liver cell apoptosis signaling and hepatic energy metabolism pathway.

Differential liver histopathological responses to amphibian chytrid infection

Amphibians have been facing a pandemic caused by the deadly fungus Batrachochytrium dendrobatidis (Bd). Although studies have elucidated cutaneous and homeostatic disturbances, it is still unknown if the hepatic function can be affected or if hepatic effects differ among host species. Thus, we evaluated the effects of an experimental Bd infection on the liver (histopathology and the hepatosomatic index) of 2 anuran species (Xenopus laevis and Physalaemus albonotatus) with different susceptibilities to Bd infection and compared them to uninfected controls. Bd infection increased the melanomacrophage cell area and induced leukocyte infiltration in both species. The effects were more pronounced in the sensitive species, P. albonotatus, which showed severe reduction in glycogen stores and liver atrophy, due to energetic imbalance. Hepatocytes of P. albonotatus also showed ballooning degeneration (vacuolization), which could lead to cell death and liver failure. Our results provide evidence that although the sensitive species showed more severe effects, the tolerant species also had hepatic responses to the infection. These findings indicate that hepatic function can play an important role in detoxification and in immune responses to chytridiomycosis, and that it may be used as a new biomarker of health status in chytrid infections.

Physiological Response of Pelophylax nigromaculatus Adults to Salinity Exposure

Simple Summary

This study explored physiological resilience to and recovery from saline exposure in Pelophylax nigromaculatus, a semi-aquatic frog that is widely distributed in East Asia. Analysis of 11 serum components revealed the physiological response of frogs to either severe saline exposure for six days or moderate saline exposure for forty days, followed by a twenty day recovery period. During exposure to both severe and moderate saline conditions, serum electrolytes increased, protein concentrations in serum decreased, and creatinine, an indicator of renal function, sharply increased. However, renal tissue sampled after the study did not show renal dysfunction. Moreover, serum components that changed during exposure to salinity returned to their initial values during the recovery period. Adult anurans seem capable of resilience, to some extent, to saline conditions.

Abstract

Many freshwater ecosystems are becoming more saline, and amphibians, which have permeable skin, are sensitive to this change. We studied the physiological responses to high salinity and recovery from saline exposure in adult frogs (Pelophylax nigromaculatus). Frogs that experienced severe salinity were exposed to saline conditions for 6 days, while those in the moderate group were exposed to saline conditions for 40 days, followed by a recovery period in freshwater for 20 days. Our data showed that during exposure to saline conditions of severe and moderate groups, serum electrolytes increased, protein concentrations decreased, and creatinine, an indicator of renal function, sharply increased. However, renal tissue sampled after exposure did not show renal dysfunction. In addition, serum components that changed during exposure to salinity returned to their initial values during the recovery period. Thus, adult anurans can be resilient, to some extent, to saline conditions in habitats that experience either rapid or slow salinity changes.

Metabolic responses in bullfrog, Lithobates catesbeianus after exposure to zinc, copper and cadmium

This study investigated the activity of lactated dehydrogenase (LDH), malate dehydrogenase (MDH) enzymes and the levels of glucose, protein and triglyceride in bullfrog tadpoles after exposure to 1 μg L^-1 of zinc (Zn), copper (Cu) and cadmium (Cd) isolated and combined for 2 and 16 days. Zn, Cu + Cd and Zn + Cu + Cd increased the activity of the LDH (2 and 16 days) and MDH (2 days) enzymes in the liver; and MDH increased in the kidney after 16 days in all co-exposed groups compared to the control. Glucose increased in the liver in the Zn and Cu groups at 2 and 16 days of exposure and decreased in the kidney (groups Cd, Zn + Cd and Cu + Cd) and muscle (Cd) at 2 days of exposure. After 2 days of exposure, the protein increased in the liver (Zn), in the kidney in all groups exposed to metals except in the groups exposed to Cd and Zn + Cu + Cd, which did not change and decreased in muscle in all the groups exposed to isolated metals. Regarding triglycerides, the kidney and muscle were the most affected, leading to a decrease in the Zn, Cu and Cd groups and in the Zn + Cu (16 days) and Zn + Cu + Cd groups (2 days). The anaerobiosis and aerobiosis were activated in the liver and kidney after short-term exposure (2 days) and in the kidney, the aerobic metabolism was activated after chronic exposure (16 days). The metals caused toxicity and were higher in co-exposure to metals with a potential to cause metabolism damage in L. catesbeianus.

Biomarkers of the oxidative stress and neurotoxicity in tissues of the bullfrog, Lithobates catesbeianus to assess exposure to metals

Lithobates catesbeianus tadpoles were exposed to 1 μg L^-1 of zinc (Zn), copper (Cu) and cadmium (Cd) alone or combined (1:1 and 1:1:1) for 2 and 16 days. Results showed a significant increase in the superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST) activities in the liver, kidney and muscle (except for GPx) in the groups exposed to metal either alone or co-exposed after 2 days compared to the control. After 16 days, SOD, CAT and GST activities decreased significantly in the liver and kidney and GPx activity increased in the liver. Reduced glutathione (GSH) increased in the liver and kidney following combined exposure and decreased after 2 days of metal exposure in the muscle. There were significant increases in lipid hydroperoxide (LPO) levels in the liver, kidney and muscle (2 and 16 days), with the highest levels after metal co-exposure. Cholinesterase (ChE) activity increased significantly in the brain after 2 days of exposure but decreased in the brain (16 days) and muscle (2 days) after exposure to metals, alone and combined. The current study highlighted that the antioxidant system of L. catesbeianus was sensitive to metals and specially to the co-exposure of the three metals, despite presenting differences in the response among tissues. In addition, tadpoles were sensitive at both periods of exposure, but in different modes with stress response (activation, up-regulation) at 2 days and oppression (down-regulation) at 16 days.

The effects of chronic cadmium exposure on the gut of Bufo gargarizans larvae at metamorphic climax: Histopathological impairments, microbiota changes and intestinal remodeling disruption

Cadmium (Cd) is carcinogenic to human and it also has adverse effects on aquatic life such as amphibian larvae. However, its influences on amphibian gut morphology and development as well as intestinal microbiota are still hardly understood. In this study, we examined the effects of chronic cadmium exposure on the gut of tadpoles at Gosner stage 42 of metamorphic climax by using Bufo gargarizans as a model species. Tadpoles were exposed to cadmium concentrations at 0, 5, 100 and 200 μg L^-1 from Gosner stage 26-42. The results showed that high cadmium (100 and 200 μg L^-1) exposure caused significant decrease of body length and weight but significant increase of intestinal length and weight. Moreover, severe histopathological damages were induced by high Cd exposure. In addition, microbial communities in the gut of tadpoles in high cadmium exposure groups were remarkably different from those in control group. Unexpectedly, species diversity and richness were higher in the intestinal microbiota of 200 μg L^-1 cadmium exposure group. Furthermore, the abundance of prevalent phyla, families and genera of intestinal microbiota were changed by cadmium exposure. Meanwhile, cadmium exposure perturbed gut renewal functions and the relative mRNA expression of genes involved in canonical and non-canonical Wnt signaling pathway was seriously affected by high cadmium exposure. We concluded that cadmium could be harmful to tadpole health by inducing intestinal histopathological damages, gut remodeling inhibition and intestinal microbiota alterations.

Assessment of antioxidant system, cholinesterase activity and histopathology in Lithobates catesbeianus tadpoles exposed to water from an urban stream

Anthropogenic activities promote changes in community structure and decrease the species abundance of amphibians. The aim of this study was to assess potential alterations in the antioxidant system and cholinesterase activity, histopathological and oxidative damage in Lithobates catesbeianus tadpoles exposed to water from the Cascavel River, in Southern Brazil. Water samples (140 L each) were collected from the headwater, urban and rural areas of the river. Tadpoles were acclimated for seven days. After acclimatization tadpoles were reared in water from the river, except for the control aquarium. After seven days, a portion of the liver was removed and prepared for cholinesterase (ChE), superoxide dismutase (SOD), catalase (CAT) and lipid peroxidation (LPO) analysis; another part of the tissue was prepared for histological examination. An elevation of CAT activity was observed for water from both urban and rural environments. A decrease in LPO reaction was detected, mainly among the tadpoles exposed to water from the rural area. These alternations can cause delay the metamorphosis and lead to metabolic dysfunction, interfering in survival capacity and diminishing, not only individual fitness, but that of the whole population.

Exposure to cadmium induced gut histopathological damages and microbiota alterations of Chinese toad (Bufo gargarizans) larvae

Cadmium (Cd) is highly hazardous to both terrestrial and aquatic life and it also has multiple negative impacts on amphibian tadpoles and frogs. However, its effects on gut health of amphibian tadpoles are still poorly understood. We used Chinese toad (Bufo gargarizans) tadpoles to examine the effects of chronic cadmium exposure on gut histology and intestinal microbiota by using regular histology analysis and high-throughput sequencing techniques. Tadpoles were exposed to cadmium concentrations at 0, 5, 100 and 200 μg L^-1 from Gosner stage 26 to 38. Our results showed 100 and 200 μg L^-1 cadmium exposure caused severe gut histopathological alterations while 5 μg L^-1 cadmium exposure induced subtle intestine damage. Moreover, species diversity, taxonomic composition and community structure of gut microbiota were influenced by cadmium exposure. Species diversity and richness decreased gradually with the increase of cadmium concentration. Microbial communities of tadpoles in 100 and 200 μg L^-1 cadmium exposure groups were remarkably different from those in control group. Furthermore, the relative abundances of prevalent phyla such as Proteobacteria, Bacteroidetes and Firmicutes and dominant genera such as Klebsiella and Aeromonas were also affected by cadmium exposure. We concluded that cadmium could be harmful to tadpole health by inducing intestinal damages and gut microbiota changes.

Cadmium-calcium interference in the Rhinella arenarum oviduct

Given that the cadmium (Cd) toxicity could be due to its interference with the calcium (Ca) homeostasis, the aim of this work was to study the effect of Cd over the presence, distribution and volume density (Vv) of Ca and Ca-ATPase in the secretory cells of the pars preconvoluta (PPC) and the pars convoluta (pc) in Rhinella arenarum. The severe effect of the xenobiotic (CdCl₂ 2.5 mg/kg) in sexually matured females was evaluated. Co-localization, as well as a marked reduction of Ca and Ca-ATPase, was observed in treated animals, in the areas analyzed, compared to control. Low calcium deposits were found in the secreting granules (SG) of the epithelial (ESC) and glandular secretory cells (GSC), while an increase in their cytoplasm and intracellular space was observed. The Ca-ATPase in treated and control animals was detected at the SG and the plasmatic membrane of the ESC and GSC. In relation to the Vv estimates, a substantial reduction of Ca deposits and Ca-ATPase activity was observed in the treated group, with respect to the control. Both amounts of Vv of Ca and Ca-ATPase activity were higher in PPC than in pc, and, higher in ESC than in GSC. These results were associated with the Cd concentration in the oviductal PC, determining that it is a bioaccumulator organ. Thus, this work demonstrated that the Cd interacted with Ca-ATPase, leading to an increase of cytosolic Ca, which is responsible for the possible disruptions in cellular metabolism.

Mutagenic and histopathological effects of hexavalent chromium in tadpoles of Lithobates catesbeianus (Shaw, 1802) (Anura, Ranidae)

The potential mutagenic and histopathological effects of the hexavalent chromium were investigated in Lithobates catesbeianus tadpoles. These larvae (GS 25-31) were exposed to three nominal concentrations of potassium dichromate (4, 12, and 36 mg L^-1) and 5 mg L^-1 of Cyclophosphamide as a positive control (PC), for 24 h. A negative control (NC) was also added to the experiment. Our results showed that, in general, the micronuclei (MN) were less frequent than the erythrocyte nuclear abnormalities (ENA); there was a significant difference in the frequency of MN between the NC and all treated groups (p < 0.05) in a concentration-dependent curve, in addition the PC did not differ from the chromium treatments. Also, only PC and the group treated with potassium dichromate at 36 mg L^-1 showed significantly higher frequencies of ENA than NC (p < 0.05). Chromium treatments promoted cell retention in the Sub-G1 phase and a decrease of cells in the S and G2/M phases indicating inhibition of the cell cycle. All treatments with chromium led to liver and kidney histopathological lesions, especially with 36 mg L^-1 (greater number of lesions). In conclusion, hexavalent chromium was mutagenic to L. catesbeianus tadpoles and its toxic effects also resulted in anti-mitotic activity, besides inducing histopathological alterations in liver and kidney. Amphibians have been proven to be useful bioindicators, and we suggest that tadpoles of different species can be used to represent the environmental impacts in aquatic ecosystems.

Changes in intestinal microbiota of Bufo gargarizans and its association with body weight during metamorphosis

The assembly of intestinal microbial communities can play major roles in animal development. We hypothesized that intestinal microbial communities could mirror the developmental programs of amphibian metamorphosis. Here, we surveyed the morphological parameters of the body and intestine of Bufo gargarizans at varying developmental stages and inventoried the intestinal microbial communities of B. gargarizans at four key developmental stages via 16S rDNA gene sequencing. Firstly, our survey showed that during metamorphosis, body weight and intestinal weight were reduced by 56.8 and 91.8%, respectively. Secondly, the gut bacterial diversity of B. gargarizans decreased with metamorphosis and the composition of the tadpoles' intestinal microbiota varied across metamorphosis. Compared to aquatic larvae, terrestrial juveniles showed major shifts in microbial composition, including reduction in Proteobacteria and Actinobacteria, increases in Bacteroidetes and Fusobacteria, and the appearance of Verrucomicrobia. Firmicutes in four developmental stages showed similar abundance at the phylum level, but in each stage was driven by distinct genera. Enterobacter, Aeromonas, Mucinivorans and Bacteroides also changed in abundance and were found to be significantly correlated with loss of body or intestinal tissue during metamorphosis. These results indicate a shift in intestinal microbial community composition throughout amphibian metamorphosis.

Effects of fluoride on morphology, growth, development, and thyroid hormone of Chinese toad (Bufo gargarizans) embryos

Excessive fluoride in natural water ecosystem has the potential to detrimentally affect amphibians, but little is known of such effects or underlying mechanisms in Bufo gargarizans embryos. In the present study, the effects of fluoride exposure on B. gargarizans embryos were investigated. First, fluoride teratogenic experiment showed that the 9 days EC₅₀ of fluoride on B. gargarizans embryos was 177.62 mg/L. Then, we studied the sublethal effects of fluoride on B. gargarizans embryos at control, 0.7, 4.1, 19.6, 41.9, and 62.7 mg/L fluoride concentration. Malformation, growth, and development of embryos were monitored, and type 2 and 3 iodothyronine deiodinase (Dio2 and Dio3), thyroid hormone receptors (TRα and TRβ) mRNA levels were measured. Our results showed the morphological malformations, such as tail curvature (lordosis), edema, cuticularized ciliated cells, and hyperplasia were occurred during fluoride exposure. Growth and development were all inhibited at 19.5, 41.9, and 62.7 mg/L fluoride-treated groups after 9 days' exposure. According to real-time PCR results, exposure to fluoride upregulated Dio3 and TRβ mRNA expression and downregulated Dio2 and TRα mRNA level. All above indicated that excessive fluoride could induce morphology malformations, inhibit embryonic growth and development, and disrupt the normal function of maternal thyroid hormone in B. gargarizans embryos. Environ. Mol. Mutagen. 59:123-133, 2018. © 2017 Wiley Periodicals, Inc.

Effects of chronic cadmium exposure on metamorphosis, skeletal development, and thyroid endocrine disruption in Chinese toad Bufo gargarizans tadpoles

The present study examined the effects of chronic cadmium (Cd) exposure on metamorphosis, body size, thyroid gland, and skeletal development of Chinese toad (Bufo gargarizans) tadpoles. Tadpoles were exposed to Cd concentrations at 0, 5, 10, 50, 100, and 500 μg/L from Gosner stages 26 to 46 of completion of metamorphosis. Our results showed that 100 and 500 μg/L of Cd concentrations increased mortality and decelerated metamorphosis rate. In addition, significant body size reduction at Gosner stage 42 was observed at 100 and 500 μg/L of Cd treatments (p < 0.01). Average body length and hind-limb length were significantly decreased in the 500 μg/L of Cd group (p < 0.05) but body mass was not significantly different at Gosner stage 46. Moreover, bone formation was delayed in high Cd concentration treatments (50, 100, and 500 μg/L) at both Gosner stage 42 and 46. Histopathological changes of the thyroid gland showed that follicular cell hyperplasia and malformation were induced by high Cd concentrations (50, 100, and 500 μg/L). Furthermore, real-time polymerase chain reaction analysis suggested that the larvae exposed to high-dose Cd exhibited a significant decrease in deiodinase (Dio2) and thyroid hormone receptor (TRβ) mRNA levels at Gosner stage 42 and 46. Our investigation indicated that high-dose Cd caused metamorphic deceleration, body size reduction, and delayed skeletal development through disrupting the thyroid system in B. gargarizans larvae. Environ Toxicol Chem 2018;37:213-223. © 2017 SETAC.

Morphology and size of blood cells of Rhinella arenarum (Hensel, 1867) as environmental health assessment in disturbed aquatic ecosystem from central Argentina

Four populations of Rhinella arenarum from aquatic environments with different degrees of disturbance in central Argentina were compared to assess the ability of cytomorphology and cytomorphometry of blood cells as a hematological biomarker. A total of 93 specimens of R. arenarum (adults sexually mature) were captured during the spring. From the analysis of cell, no variations were found in terms of morphology, whereas in nuclear and cell areas and Price-Jones curves, we observed a smaller size in erythrocytes of individuals inhabiting the site most altered, "Villa Dalcar," as well as for leukocytes, lymphocytes, neutrophils, and eosinophils for the same site. This could be caused by presence of different pollutants in the lake. Furthermore, this was confirmed by the high levels of environmental variables (conductivity, total dissolved solids, and salinity) show that Villa Dalcar is the site most affected by human activities.

Chronic exposures to fungicide pyrimethanil: multi-organ effects on Italian tree frog (Hyla intermedia)

Amphibian habitats are easily contaminated by several pollutants, and in agricultural landscapes the likely exposure scenario is represented by pesticides. Many of these substances are known or suspected to act as endocrine disrupting chemicals (EDCs). The goal of the present study was to assess the effects of pyrimethanil, a common-used but also overlooked fungicide, on liver, kidney and gonadal differentiation of Hyla intermedia. Through a multi-organ evaluation, we demonstrated that a long term exposure to two environmentally relevant concentrations of pyrimethanil (5 and 50 µg/L) elicits a range of toxic responses. First we showed that pyrimethanil induces underdevelopment of ovaries and interferes with normal sexual differentiation, thus revealing the endocrine disruption potential of this fungicide. Moreover we revealed that all considered organs are seriously affected by this fungicide and both necrosis and apoptosis contribute to the histological response. This is the first report on the effects of pyrimethanil on gonads, liver and kidney histology of a non-model species and it demonstrates that the hazardous properties of this fungicide can result from several pathological processes affecting different key compartments of amphibian.

Blood cell responses and metallothionein in the liver, kidney and muscles of bullfrog tadpoles, Lithobates catesbeianus, following exposure to different metals

The hematological parameters and metallothionein (MT) levels in the liver, kidney and muscles were measured in bullfrog tadpoles, Lithobates catesbeianus, following exposures to 1 μg L^-1 of zinc (Zn), copper (Cu) and cadmium (Cd) alone or in combination (1:1 and 1:1:1) for 2 and 16 days. Metal accumulation occurred in all organs, with the highest values found in the kidney, followed by the muscles and liver. After exposure to isolated metals, the accumulation was in the following order: Cd > Zn > Cu in the liver and muscles and Cd > Cu > Zn in the kidney. Exposure to combined metals (Zn + Cu, Zn + Cd, Cu + Cd and Zn + Cu + Cd) revealed complex responses, such as metal accumulation increased or decreased over the exposure periods, suggesting possible competion at the uptake sites and/or metabolization and elimination processes in each organ. The MT concentration increased in the organs of tadpoles following metal exposure alone, mainly in the liver, for both periods. After the combined exposures, the MT levels were higher in the liver and muscles at 16 days, suggesting that the interaction between metals was additive, and the level was decreased in the kidney after 2 and 16 days of exposure. The whole blood hemoglobin content (Hb), red blood cell count (RBCs) and mean corpuscular hemoglobin (MCH) differed from the control groups after 2 and 16 days of exposure, showing changes in the improvement of oxygen transport. The number of lymphocytes increased, and the levels of neutrophils, eosinophils, basophils and monocytes were reduced after exposure to the metals. The changes in blood cells suggested that tadpoles have a mechanism to improve oxygen transport probably because of the increased oxygen demand and a general reduction in defense cells. The exposure of L. catesbeianus to metals during the larval phase can generate long-term dysfunction to a degree, which could lead to alterations in their health status.