Proximity to pollution sources and risk of amphibian limb malformation

Putting infection on the map: Using heatmaps to characterise within- and between-host distributions of trematode metacercariae

The location of parasites within individual hosts is often treated as a static trait, yet many parasite species can occur in multiple locations or organs within their hosts. Here, we apply distributional heat maps to study the within- and between-host infection patterns for four trematodes (Alaria marcianae, Cephalogonimus americanus, Echinostoma spp. and Ribeiroia ondatrae) within the amphibian hosts Pseudacris regilla and two species of Taricha. We developed heatmaps from 71 individual hosts from six locations in California, which illustrate stark differences among parasites both in their primary locations within amphibian hosts as well as their degree of location specificity. While metacercariae (i.e., cysts) of two parasites (C. americanus and A. marcianae) were relative generalists in habitat selection and often occurred throughout the host, two others (R. ondatrae and Echinostoma spp.) were highly localised to a specific organ or organ system. Comparing parasite distributions among these parasite taxa highlighted locations of overlap showing potential areas of interactions, such as the mandibular inner dermis region, chest and throat inner dermis and the tail reabsorption outer epidermis. Additionally, the within-host distribution of R. ondatrae differed between host species, with metacercariae aggregating in the anterior dermis areas of newts, compared with the posterior dermis area in frogs. The ability to measure fine-scale changes or alterations in parasite distributions has the potential to provide further insight about ecological questions concerning habitat preference, resource selection, host pathology and disease control.

Impacts of aqueous extracts of wildfire ashes on aquatic life-stages of Xenopus laevis: Influence of plant coverage

Wildfires have emerged as a global ecological concern due to their wide-ranging off-site effects. One particular consequence is the adverse impact on aquatic environments, as wildfires are acknowledged as a significant source of aquatic contamination through ash runoffs containing toxic compounds. Yet, amphibian response to this source of contamination remains largely undocumented. This study assessed how ash runoffs from Eucalyptus sp. and Pinus sp. affect early aquatic life-stages of Xenopus laevis. Embryos and tadpoles were exposed, respectively, for 96 h and 14 days to serial concentrations (26.9% - 100%) of aqueous extracts of ashes (AEAs; 10 gL-1) composed of eucalypt (ELS) and pine (PLS) ashes. Mortality and development were monitored, and biometric data (snout-to-vent, tail and total length, and weight) measured. Sub-individual endpoints regarding oxidative stress (catalase-CAT; total glutathione-TG; lipid peroxidation-TBARS), neurotoxicity (acetylcholinesterase-AChE), transformation metabolism (glutathione-S-transferase-GST) and energetic metabolism (carbohydrate, lipid and protein content and O2 consumption), were also measured. The two AEAs induced no significant lethal effects on embryos or tadpoles. However, in general, AEAs caused a developmental delay in both life stages. Effects of AEAs on biometric endpoint were only reported for tadpoles, which showed a decreased body length (snout-to-vent, tail and total) and weight (embryos were not weighed), with PLS exerting higher effect than ELS. As for the sub-individual endpoints, embryos showed mostly no alterations on the activity of the monitored parameters, except for PLS, which reduced embryos' carbohydrate content (at ≥59.2%) and increased O2 consumption (at ≥35.0%). Regarding tadpoles, AEA exposure decreased the activity of CAT and GST (at ≥26.0%) and decreased carbohydrate (at ≥26.0%) and lipid (at ≥45.5%), whereas oxygen consumption increased (at ≥26.0%) only on PLS. Overall, the tested AEAs differentially affected amphibians across life-stages, indicating that plant coverage might affect ash toxicity.

Effects of aqueous extracts of wildfire ashes on tadpoles of Pelophylax perezi: Influence of plant coverage

Wildfires have been pointed out as an important source of diffuse contamination to aquatic ecosystems, namely through the input of toxic compounds such as polycyclic aromatic hydrocarbons and metals. However, amphibians' responses to this disturbance have been largely ignored. Hence, this study intended to assess how ashes from Pinus sp. and Eucalyptus sp. plantation forests affect tadpoles of Pelophylax perezi. Tadpoles were exposed 14 days to serial concentrations (26.9 %-100 %) of aqueous extracts of ashes (AEA, with 10 g L-1 of ashes) containing Eucalypt (ELS) and Pine (PLS) ashes. The following endpoints were measured: mortality, malformations, developmental stage, body length and weight. Effects at sub-individual level were also monitored for oxidative stress, neurotoxicity, and energetic metabolism. Chemical characterization of the AEA of ELS showed higher concentrations of As, Cd, Co, Cr, Pb and V, while PLS showed higher concentrations of Cu, Mn, Ni and Zn. Concerning the lethal effects of AEAs on tadpoles, both extracts were able to induce mortality at high concentrations (76.9 and/or 100 % of AEA), although a high variability in the response was found. A significant mortality in tadpoles exposed to ELS was observed at the concentration of 76.9 %. For organisms exposed to PLS, though a mortality above 20 % was registered at the two highest tested concentrations, it was not significantly different from the control. No significant sub-lethal effects were observed in the ELS treatments. Contrasting, exposure to PLS induced a decrease in body length, weight, glutathione-S-transferase activity and an increase in oxygen consumption. Overall, the distinct effects of ELS and PLS suggest an influence of vegetation cover in ash toxicity. In conclusion, exposure to both ash extracts negatively affected sublethal responses of tadpoles of P. perezi. Future research is needed to assess how these effects at individual level may translate into effects at population level.

Nicosulfuron, a sulfonylurea herbicide, alters embryonic development and oxidative status of hatchlings at environmental concentrations in an amphibian species

The widespread use of agrochemicals for controlling pests and diseases of crops is recognized as a main threat to biodiversity. Sulfonylurea herbicides are being increasingly used and display low levels of degradation in water which suggest that they might affect non-target organisms. In a common garden experiment, eggs of a widespread amphibian (Bufo spinosus) were exposed to sublethal environmentally relevant concentrations of a widely used sulfonylurea herbicide, nicosulfuron, during the whole embryonic development. We assessed development-related traits (i.e., development duration, hatching success, hatchling size and occurrence of malformation) as well as antioxidant markers in response to contamination (i.e., SOD, GPx, catalase, thiols and relevant ratios thereof). We found that sublethal concentrations of nicosulfuron increased embryonic development duration, increased hatchling size and tended to increase malformations. Embryos exposed to nicosulfuron displayed decreased thiols and increased catalase activity suggesting alteration of oxidative status. We did not find any effect of nicosulfuron on SOD and GPx levels. Interestingly, higher catalase activity was linked to higher proportion of malformed individuals, suggesting that exposure to nicosulfuron induced teratogenic effects. Our results suggest that alteration of antioxidant levels might be one physiological mechanism through which nicosulfuron might cause detrimental effects on amphibian embryos. Sublethal effects of pesticides at environmentally relevant concentrations have been overlooked and require further investigations, especially in non-target taxa occurring in agricultural landscapes.

Histopathologic and genotoxic effects of deltamethrin on marsh frog, Pelophylax ridibundus (Anura: Ranidae)

It is known that amphibians inhabiting agricultural areas are constantly exposed to chemicals such as insecticides. Deltamethrin, a type II pyrethroid insecticide, is widely used in the world. The present study aimed to investigate the toxic effects of different concentrations (0.625, 1.25, and 2.50 mg/kg body wt) of orally applied deltamethrin to marsh frog (Pelophylax ridibundus) after 96 h of treatment. The histopathological abnormalities in liver, gastrointestinal tract, and kidney tissues were evaluated with quantitative analyses. In liver, increase of melanomacrophagic aggregates, non-homogeneous hepatocyte parenchyma, sinusoidal dilatations, infiltration, vascular epithelial degeneration, central vein degeneration, and congestion were determined in exposed frogs. In gastrointestinal tract, vacuolization, hypertrophy, congestion, infiltration, necrosis, and erosion of the epithelial layer, increasing goblet secretion, degeneration in villi, epithelial disorganization, and edema were observed in high-dose groups. In all experimental groups, glomerular shrinkage, hemorrhage, degeneration, infiltration, increase in Bowman distance, and eosinophilic-stained tubular lumens were detected in kidneys. Histopathological changes were more prominent in 1.25 and 2.50 mg/kg groups than the other groups. To determine the genotoxic effects of deltamethrin, the peripheral blood samples of the frogs were used. The erythrocytic nuclear abnormalities such as micro-nucleus, double-nucleus, kidney-shaped nucleus, notched nucleus, and bud nucleus were determined in the frogs, and the genotoxicity did not show a significant increase between control and low-dose groups, statistically. However, the genotoxic effects increased in medium- and especially high-dose groups. The results of this study showed that acute deltamethrin exposure can lead to histopathologic and genotoxic effects in P. ridibundus.

Landscape-level toxicant exposure mediates infection impacts on wildlife populations

Anthropogenic landscape modification such as urbanization can expose wildlife to toxicants, with profound behavioural and health effects. Toxicant exposure can alter the local transmission of wildlife diseases by reducing survival or altering immune defence. However, predicting the impacts of pathogens on wildlife across their ranges is complicated by heterogeneity in toxicant exposure across the landscape, especially if toxicants alter wildlife movement from toxicant-contaminated to uncontaminated habitats. We developed a mechanistic model to explore how toxicant effects on host health and movement propensity influence range-wide pathogen transmission, and zoonotic exposure risk, as an increasing fraction of the landscape is toxicant-contaminated. When toxicant-contaminated habitat is scarce on the landscape, costs to movement and survival from toxicant exposure can trap infected animals in contaminated habitat and reduce landscape-level transmission. Increasing the proportion of contaminated habitat causes host population declines from combined effects of toxicants and infection. The onset of host declines precedes an increase in the density of infected hosts in contaminated habitat and thus may serve as an early warning of increasing potential for zoonotic spillover in urbanizing landscapes. These results highlight how sublethal effects of toxicants can determine pathogen impacts on wildlife populations that may not manifest until landscape contamination is widespread.

Monitoring the morphological integrity of neotropical anurans

Amphibians are considered to be excellent bioindicators to their morphophysiological characteristics and life cycle. In this context, the present study investigated the morphological integrity of anuran larvae collected in preserved environments in the Emas National Park, in the municipality of Mineiros (Goiás state, Brazil), and in environments representative of the agricultural matrix of the Rio Verde region, also in Goiás, where there is a long history of the use of agricultural pesticides. Samples of water from temporary ponds, permanent dams, and veredas were analyzed for the presence of pesticides and, especially atrazine (5350 μg/L), found at significantly higher concentrations in the agricultural matrix. We observed a high percentage (approximately 10%) of morphological malformations including alterations of the fins in Boana albopunctatus and Scinax fuscovarius; alteration in oral structures in B. albopunctatus, Dematonotus muelleri, Physalaemus centralis, Physalaemus cuvieri, and Leptodactylus fuscus mainly in the tadpoles collected in the agricultural environment in comparison with those from the protected area (3.5%; P < 0.0001, χ² 31.75). However, changes in the eyes, mouth, intestines, and nostrils, as well as amelia were observed only in the agricultural environment. The vast majority of the observed malformations were associated with the tail and oral disc, which suggests that these anatomical parameters may be used as sensitive morphological biomarkers. Given these findings, we reinforce that areas of agricultural land may have a deleterious effect on the morphological integrity of the tadpoles and consequently, on their development, and that these features may be used as indicators of environmental quality and health.

Comportamento territorial, vocalização e biologia reprodutiva de Allobates olfersioides (Anura: Aromobatidae)

RESUMO Em anfíbios a territorialidade, o cortejo elaborado e outras formas de comportamento, parecem estar mais associados a espécies que exibem o padrão de reprodução prolongado. A vocalização é um importante aspecto biológico relacionado à reprodução e ao comportamento social dos anuros. Este é o primeiro estudo com comportamento e vocalização da rã-foguete Allobates olfersioides (Lutz, 1925) e nós registramos em etograma o comportamento de territorialidade e corte, descrevemos e analisamos o seu repertório vocal e avaliamos a influência climática na atividade acústica da espécie. Ao todo 18 machos de A. olfersioides foram observados pelo método de animal focal, registrando todas as atividades individuais durante dez minutos. Adicionalmente, nós utilizamos o playback de um canto de advertência de macho adulto para analisar as respostas territoriais exibidas por indivíduos machos durante o trabalho. Para este anuro, registramos 11 comportamentos distintos e analisamos 14 cantos de anúncio que demonstraram que o canto de A. olfersioides é um canto simples e composto por uma única nota não pulsionada com duração média de 0,02s, intervalo médio entre cantos de 0,35s e frequência dominante média de 5,67kHz. O período de atividade vocal foi registrado durante quase todos os meses do estudo (novembro de 2015 a outubro de 2016), exceto novembro e dezembro, onde os indivíduos ficaram inativos quanto às atividades acústicas. Acreditamos que A. olfersioides apresente uma reprodução contínua (com duração de aproximadamente dez meses), devido à ausência de vocalizações durante os meses mais secos em novembro e dezembro. No que se refere às atividades comportamentais, A. olfersioides apresenta padrões de comportamento semelhantes a outras espécies de Aromobatidae, como também, o padrão territorialista já visto para o grupo, demonstrando a importância dos sinais acústicos e visuais.

Follow-up ecological studies for cryptic species discoveries: Decrypting the leopard frogs of the eastern U.S

Cryptic species are a challenge for systematics, but their elucidation also may leave critical information gaps about the distribution, conservation status, and behavior of affected species. We use the leopard frogs of the eastern U.S. as a case study of this issue. We refined the known range of the recently described Rana kauffeldi, the Atlantic Coast Leopard Frog, relative to the region’s two other leopard frog species, conducted assessments of conservation status, and improved methods for separating the three species using morphological field characters. We conducted over 2,000 call and visual surveys and took photographs of and tissue samples from hundreds of frogs. Genetic analysis supported a three-species taxonomy and provided determinations for 220 individual photographed frogs. Rana kauffeldi was confirmed in eight U.S. states, from North Carolina to southern Connecticut, hewing closely to the Atlantic Coastal Plain. It can be reliably differentiated in life from R. pipiens, and from R. sphenocephala 90% of the time, based on such characters as the femoral reticulum patterning, dorsal spot size and number, and presence of a snout spot. However, the only diagnostic character separating R. kauffeldi from R. sphenocephala remains the breeding call described in 2014. Based on our field study, museum specimens, and prior survey data, we suggest that R. kauffeldi has declined substantially in the northern part of its range, but is more secure in the core of its range. We also report, for the first time, apparent extirpations of R. pipiens from the southeastern portion of its range, previously overlooked because of confusion with R. kauffeldi. We conclude with a generalized ecological research agenda for cryptic species. For R. kauffeldi, needs include descriptions of earlier life stages, studies of niche partitioning with sympatric congeners and the potential for hybridization, and identification of conservation actions to prevent further declines.

Blindness in echolocating bats

Vision in echolocating bats works complementary to their echolocation signals and is especially important in long-range orientation. Contrary to previous predictions, we report here the first case of blindness and ocular anomalies in healthy adult echolocating bats. Two anomalous individuals of Carollia perspicillata, two Artibeus planirostris and one Artibeus lituratus were captured in highly human-modified areas (urban and agricultural). One C. perspicillata was totally blind exhibiting completely closed eyelids and the others presented strong corneal opacity in their right eye. Our finding brings new insights about the habitat perception in mammals and suggests an unreported ecological compensation of the sensory system in bats.

Micronucleus cytome assay in the differential assessment of cytotoxicity and genotoxicity of cadmium and lead in Amietophrynus regularis

Amphibians are increasingly being used as bio-indicator of contamination in ecosystems due to their sensitivity to xenobiotics in the environment. Cadmium and lead compounds, ubiquitous mutagens and carcinogens, are capable of eliciting genome instability in adult toads which may enhance amphibian decline. Micronucleus cytome (MN-cyt) assay, a comprehensive cytogenetic test for the assessment of genome instability induced by xenobiotics in organisms, was utilized in the differential cytogenotoxic evaluation of Cd and Pb in adult Amietophrynus regularis. A. regularis was exposed to six concentrations (8 - 512 mg/L) of the metal solutions to determine 96 h acute toxicity. Four toads per group were exposed to five sub-lethal concentrations (5 - 75 %) of the 96 h LC50 of the metals for 14 days. At post exposure, bone marrow and peripheral erythrocytes were collected for MN-cyt analysis. The metals induced differential concentration and time-dependent increase in mortality with 96 h LC50 of 36.36 mg/L (Cd) and 112.06 mg/L (Pb). No observable effective concentrations (NOEC); Cd=8 and Pb=32 (mg/L) and Lowest observable effective concentrations (LOEC); Cd=16 and Pb=64 (mg/L) were recorded for the metals. Derived toxicity factor (TF) showed that Cd was 3.08 times more toxic to the toads than Pb. The metal solutions induced significant (p<0.05) increase in frequencies of MN, binucleated, nuclear bud, notch, lobe, vacuolated erythrocytes, apoptosis and necrosis compared to the negative control. Cd elicited 1.42 and 3.26 folds increase in MN and NAs respectively, than Pb. MN-cyt assay is a suitable cytogenetic tool for assessing genome instability in A. regularis. Increased genetic instability induced by Cd and Pb may be associated with genetic related syndromes; neoplasms, reproductive dysfunctions and mortality. This suggests threat to amphibian health and may enhance population decline.

Continental-extent patterns in amphibian malformations linked to parasites, chemical contaminants, and their interactions

Widespread observations of malformed amphibians across North America have generated both concern and controversy. Debates over the causes of such malformations-which can affect >50% of animals in a population-have continued, likely due to involvement of multiple causal factors. Here, we used a 13-year dataset encompassing 53,880 frogs and toads from 422 wetlands and 42 states in the conterminous USA to test hypotheses relating abnormalities and four categories of potential drivers: (i) chemical contaminants, (ii) land use practices, (iii) parasite infection, and (iv) targeted interactions between parasites and pesticides. Using a hierarchically nested, competing-model approach, we further examined how these associations varied spatially among geographic regions. Although malformations were rare overall (average = 1.6%), we identified 96 hotspot sites with 5%-25% abnormal individuals. Using the full dataset of 934 collections (without data on parasite infection), malformation frequency was best predicted by the presence of oil and gas wells within the watershed. Among collections also examined for parasite infection (n = 154), average parasite load and its interaction with pesticide application positively predicted malformations: wetlands with a greater abundance of the trematode Ribeiroia ondatrae were more likely to have malformed amphibians, but these effects were strongest when pesticide application was also high, consistent with prior experimental research. Importantly, however, the influence of these factors also varied regionally, helping explain divergent results from previous studies at local scales; parasite infection was more influential in the West and Northeast, whereas pesticide application and oil/gas wells correlated with abnormalities in the Northeast, Southeast, and western regions of the USA. These results, based on the largest systematic sampling of amphibian malformations, suggest that increased observations of abnormal amphibians are associated with both parasite infection and chemical contaminants, but that their relative importance and interaction strength varied with the spatial extent of the analysis.

Eye malformation baseline in Scinax fuscovarius larvae populations that inhabit agroecosystem ponds in southern Brazil

Events of mass malformations in amphibian populations that have exceeded historical records have been reported over the past thirty years. Many of these events have been linked to human activities that occurred near amphibian breeding habitats. The rise in biofuels has promoted, and continues to promote, the growth of sugarcane plantations in Brazil, with the northwest region of São Paulo State having experienced the largest sugarcane expansion over the past few decades. In this region, we sampled temporary ponds located in agroecosystems dominated to different degrees by sugarcane. We found several larvae of Scinax fuscovarius with eye malformations (anophthalmia, aphakia, microphthalmia and sub-development). In this study, we assessed whether the distance from the ponds to the nearest sugarcane crop, the proportion of sugarcane surrounding the ponds, the presence of pesticides in the ponds, or the proportion of land uses with potential teratogens that surround the ponds were related to the frequencies of amphibian eye malformations. We found pesticides present in 11 of the 18 ponds, but none of the predictor variables was associated with the frequencies of amphibian eye malformations. Thus, our results suggest that the observed frequencies of amphibian eye malformations could be a consequence of natural mutation rates, and these data could be used as a malformation baseline for the region. This malformation baseline is the first reported for amphibians in South America and may be useful in future surveys on amphibian populations in tropical agroecosystems.

Genetic damage in Rhinella marina populations in habitats affected by agriculture in the middle region of the Sinú River, Colombia

Contamination with pesticide residues affects the environmental health of agroecosystems, especially the amphibian fauna that lives in these environments. The objective of the present study was to determine pesticides concentrations in sediments of agroecosystems and to evaluate genetic damage in Rhinella marina populations living in these zones. A total of 91 individuals were collected, 51 in the group exposed in different areas of the middle region of the Sinú River (Irrigation District of Mocari 16, Irrigation District of Aguas Negras 21, Irrigation District of Cerete 14) and 40 in a control group; at the same time, 36 subsamples of sediments were taken at each sampled station to determine pesticides organochlorine by means of chromatography coupled with ISQ Thermo Scientific mass spectrometer. The micronucleus test was applied in erythrocytes of the individuals collected. Results showed the presence of persistent organochlorine pesticides (POPs) in the sediment samples (p,p'-DDT, p,p'-DDE, and p,p'-DDD) of agricultural soils. Two individuals were registered with abnormalities in their limbs at the Mocari station, representing 12.5% of the morphological malformations to this sector. Micronucleus analysis revealed statistically significant genetic damage in exposed individuals (Mocari 9.87 ± 5.1, Cerete 7.7 ± 1.7, Aguas Negras 5.6 ± 3.6) with respect to the control group (2.4 ± 1.9) (p < 0.05). Spearman correlation analysis revealed a positive association between genetic damage and POP concentrations (p < 0.05). In addition, cellular alterations such as nuclear buds, and pyknosis (cell death), were statistically significant in the exposed group compared to the control group (p < 0.05). This study suggests that there is evidence for morphological and genotoxic effects in R. marina populations inhabiting areas influenced by agriculture, possibly associated with the presence of p,p'-DDT, p,p'-DDD, and p,p'-DDE.

Habitat quality affects the incidence of morphological abnormalities in the endangered salamander Ambystoma ordinarium

Identification of early warning signals previous to the occurrence of population decline or extinction is a major challenge for the conservation of animal species. Prevalence of morphological abnormalities in a population can be one of these signals. We registered morphological abnormalities in the salamander Ambystoma ordinarium. We also evaluated the relation between habitat quality and the prevalence of abnormalities in this species. We used scores from rapid bioassessment protocols (RBPs) to assess the habitat quality of streams inhabited by A. ordinarium. A preliminary survey indicated that of 29 streams where this species has been historically registered, 13 might have few or no A. ordinarium. The association between habitat quality and the incidence of morphological abnormalities was evaluated in these 16 streams. Of 502 sampled individuals, 224 (44.62%) had at least one body abnormality. Of the 224 individuals with body abnormalities, 84 (37.5%) presented more than one abnormality. Of a total of 5,522 evaluated morphological characters, 344 (6.74%) were abnormal. Partial loss of gills and missing digits were the most frequent abnormalities. Results of a binomial logistic regression indicated that the probability of a character of an individual to be abnormal was significantly associated with habitat quality; as the levels of the quality of the habitat increased, the prevalence of morphological abnormalities decreased. These results suggest that RBPs are a quick and useful method for assessing the habitat quality of streams inhabited by A. ordinarium. Given that RBPs provide rapid and cost-effective assessments of the ecological health of aquatic ecosystems, it will be important to test if the RBPs protocols can be used to rapidly assess habitat quality for other species of stream amphibians. The negative association between habitat quality and the prevalence of morpohological abnormalities that we found indicates that habitat condition plays an important role in the high number of abnormalities registered in A. ordinarium. Therefore, our results suggest that one of the several negative effects of habitat degradation on amphibians is an increase in the frequency of morphological abnormalities with marked consequences for the survival and general fitness of aquatic amphibians.

Phalangeal bone anomalies in the European common toad Bufo bufo from polluted environments

Every spring, many of amphibians are killed by motor vehicles on roads. These road-killed animals can be used as valuable material for non-invasive studies showing the effect of environmental pollution on amphibian populations. The aims of our research were to check whether the phalanges of road-killed toads may be useful as material for histological analysis, and whether various degrees of human impact influence the level in bone abnormalities in the common toad. We also examined whether the sex and age structure of toads can differ significantly depending in the different sites. We chose three toad breeding sites where road-killed individuals had been observed: near the centre of a city, the outskirts of a city, and a rural site. We collected dead individuals during spring migration in 2013. The sex of each individual was determined and the toes were used to determine age using the skeletochronology method. While performing age estimates, we looked for abnormalities in relation to normal bone tissue structure. In urban site, females dominate males (sex ratio 2.6:1), but in populations from rural and semi-urban sites, sex ratio was reverse (1:2.2 and 1:1.4, respectively). However, we did not find any significant differences between age structure of all populations (average age of each population: approximately 4 years). We observed abnormalities in more than 80 % of all toads from the city, compared to approximately 20 % from the rural and semi-urban sites. In particular, we found hypertrophic bone cells, misaligned intercellular substance, and irregular outer edges of bones. We suggest that these malformations are caused by different pollution, e.g. with heavy metals.

Amphibian malformations and body condition across an agricultural landscape of northwest Argentina

Agricultural landscapes support large amphibian populations because they provide habitat for many species, although agriculture affects amphibians through various mechanisms. Pollution with agrochemicals is the major threat to amphibian populations after habitat loss, as chemicals alter the ecophysiology of amphibians, putting their health and survival at risk. We aimed to assess the effect of different environments, sites, width of forest buffers and sampling years on the health of amphibians, which was estimated through the prevalence of malformations and body condition. During 3 yr of pitfall trapping, we captured 4491 amphibians. The prevalence of malformations was higher in the croplands than in the forests, while the body condition was better within forests. The prevalence of malformations was higher in the narrower forest site than in the wider forest site. The prevalence of malformations and the body condition were higher in the third year. The prevalence of malformations differed by species. We found 11 types of malformation, which mainly affected limbs and were unilateral or bilaterally asymmetrical. Our results showed that the prevalence of malformations and body condition reflect different aspects of the health of amphibians and that forest individuals are healthier than those from croplands. The results also highlight the importance of spatial configuration besides the conservation of natural habitats to preserve healthy amphibians in agricultural landscapes. The types of malformation that we found suggest that agrochemicals could be an important cause of malformations.

The plasticizer bisphenol A affects somatic and sexual development, but differently in pipid, hylid and bufonid anurans

Due to their terrestrial habitats and aquatic reproduction, many amphibians are both very vulnerable and highly suitable bioindicators. The plasticizer bisphenol A (BPA) is one of the most produced chemical substances worldwide, and knowledge on its impacts on humans and animals is mounting. BPA is used for the industrial production of polycarbonate plastics and epoxy resins and found in a multitude of consumer products. Studies on BPA have involved mammals, fish and the fully aquatic anuran model Xenopus laevis. However, our knowledge about the sexual development of non-model, often semi-terrestrial anuran amphibians remains poor. Using a recently developed experimental design, we simultaneously applied BPA to two non-model species (Hyla arborea, Hylidae; Bufo viridis, Bufonidae) and the model X. laevis (Pipidae), compared their genetic and phenotypic sex for detection of sex reversals, and studied sexual development, focusing on anatomical and histological features of gonads. We compared three concentrations of BPA (0.023, 2.28 and 228 μg/L) to control groups in a high-standard flow-through-system, and tested whether conclusions, drawn from the model species, can be extrapolated to non-model anurans. In contrast to previous studies on fish and Xenopus, often involving dosages much higher than most environmental pollution data, we show that BPA causes neither the development of mixed sex nor of sex-reversed individuals (few, seemingly BPA-independent sex reversals) in all focal species. However, environmentally relevant concentrations, as low as 0.023 μg/L, were sufficient to provoke species-specific anatomically and histologically detectable impairments of gonads, and affected morphological traits of metamorphs. As the intensity of these effects differed between the three species, our data imply that BPA diversely affects amphibians with different evolutionary history, sex determination systems and larval ecologies. These results highlight the role of amphibians as a sensitive group that is responsive to environmental pollution.

Effects of long-term exposure to two fungicides, pyrimethanil and tebuconazole, on survival and life history traits of Italian tree frog (Hyla intermedia)

Over the last few years, the hazards associated with the extensive use of fungicides have become an issue of great concern but, at present, the effects of these substances on amphibians remain poorly understood. The goal of the present study was to assess the effects of two commonly used fungicides, tebuconazole and pyrimethanil, on Italian Tree Frog (Hyla intermedia), a species frequently found in agricultural areas. Tadpoles were exposed to fungicides from developmental Gosner stage 25 (GS 25) to completion of metamorphosis (GS 46) and the whole exposure period lasted 78 days. For both tested fungicides we used two concentrations (5 and 50μg/L) that are comparable to those detected in surface waters, near agricultural fields. A variety of sublethal effects-on growth, development, behavior, and physiology-may be used for evaluating alterations induced by pollutants in amphibians. We estimated whether pyrimethanil and tebuconazole exposure impacted on H. intermedia life history traits. For this purpose, survival, growth, development, initiation of metamorphosis, success and size at metamorphosis, time to metamorphosis, and frequency of morphological abnormalities were evaluated. We showed, for all considered endpoints, that the exposure to tebuconazole exerts more harmful effects on H. intermedia than does exposure to pyrimethanil. Before the onset of metamorphic climax we showed, for both fungicides, that the low concentrations (5μg/L) induced significantly greater effects than the higher ones (50μg/L) on survival and deformity incidence. During the metamorphic climax, a complete reversal of this nonlinear trend takes place, and the percentage of animals initiating metamorphosis was reduced in fungicide-exposed groups in a concentration-dependent manner. Furthermore, a strong correlation emerged between fungicide exposure and the incidence of morphological abnormalities such as tail malformations, scoliosis, edema, mouth and limb deformities. Exposure to tested fungicides also caused a reduction in developmental rates just prior to the onset of metamorphic climax, which translated to a significant delay in timing of metamorphosis. We detected a drastic decrease in the success at metamorphosis in all exposed groups, compared to control group (86.25%). In fact, the percentage of survived larvae to GS 46, in the high and low concentrations, respectively, was only 22.5% and 36.25% in tebuconazole-exposed groups and 43.75% (50μg/L) and 56.25% (5μg/L) in pyrimethanil-exposed groups. Our findings underscore the hazardous properties of these two fungicides for non-target species in the context of ecotoxicological risk assessment. No published studies have addressed the long-term effects of tebuconazole and pyrimethanil on amphibians. To date, this is one of only a few studies documenting the effects of fungicide exposure over the whole larval development.

Common toad Rhinella arenarum (Hensel, 1867) and its importance in assessing environmental health: test of micronuclei and nuclear abnormalities in erythrocytes

Anthropogenic activities may generate significant changes in the integrity of aquatic ecosystems, so long-term monitoring of populations that inhabit them is crucial. Counting micronucleated erythrocytes (MN) and erythrocytic nuclear abnormalities (ENA) in peripheral blood is a widely used method for detecting chromosomal damage due to chemical agents in the water. We analyzed MN and ENA frequency in blood obtained from the common toad Rhinella arenarum populations in sites with different degrees of environmental degradation. The results of this study indicate that there is an association between the frequency of micronuclei and nuclear abnormalities and the degree of environmental alteration recorded for the sites studied.

Heavy metal mediated immunomodulation of the Indian green frog, Euphlyctis hexadactylus (Anura:Ranidae) in urban wetlands

Impacts of heavy metal toxicity on the immune system of the Indian green frog, Euphlyctis hexadactylus, in Bellanwila Attidiya, an urban wetland polluted with high levels of heavy metals, compared to the reference site in Bolgoda, in Sri Lanka was investigated. Significantly higher accumulation of selected heavy metals, copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd) were detected by AAS in frog liver and gastrocnemius muscle, in the polluted site than in the reference site. Non-functional immunotoxicity tests; total WBC, splenocyte and bone marrow cell counts, spleen weight/body weight ratio, neutrophil/lymphocyte ratio and basal immunoglobulin levels, and phagocytic capacity of peritoneal macrophages (immune functional test) were carried out using standard methodology. Test parameters recorded significantly lower values for frogs of the polluted site compared with their reference site counterparts, indicative of lowered immune response of frogs in the former site. In vitro phagocytic assay based on NBT dye reduction, measured the stimulation index (SI) of E. hexadactylus blood leukocytes, splenocytes and peritoneal macrophages, where SIs of frogs in the polluted site were significantly lower. Also, in vitro exposure of frog phagocytes to Cu, Zn, Pb and Cd at 10(-2)-10(-10)M, showed immunomodulation i.e. low concentrations stimulated phagocytosis while increased concentrations showed a trend towards immunosuppression. IC50 values indicated Cd>Zn>Cu>Pb as the decreasing order of the potential of phagocytosis inhibition. In conclusion, this study clearly demonstrated immunomodulation of E. hexadactylus, stimulated by heavy metals. In-vitro studies evidently suggested the use of phagocytosis as a biomarker in Ecoimmunotoxicology to detect aquatic heavy metal pollution.

Pesticide concentrations in frog tissue and wetland habitats in a landscape dominated by agriculture

Habitat loss and exposure to pesticides are likely primary factors contributing to amphibian decline in agricultural landscapes. Conservation efforts have attempted to restore wetlands lost through landscape modifications to reduce contaminant loads in surface waters and providing quality habitat to wildlife. The benefits of this increased wetland area, perhaps especially for amphibians, may be negated if habitat quality is insufficient to support persistent populations. We examined the presence of pesticides and nutrients in water and sediment as indicators of habitat quality and assessed the bioaccumulation of pesticides in the tissue of two native amphibian species Pseudacris maculata (chorus frogs) and Lithobates pipiens (leopard frogs) at six wetlands (3 restored and 3 reference) in Iowa, USA. Restored wetlands are positioned on the landscape to receive subsurface tile drainage water while reference wetlands receive water from overland run-off and shallow groundwater sources. Concentrations of the pesticides frequently detected in water and sediment samples were not different between wetland types. The median concentration of atrazine in surface water was 0.2 μg/L. Reproductive abnormalities in leopard frogs have been observed in other studies at these concentrations. Nutrient concentrations were higher in the restored wetlands but lower than concentrations thought lethal to frogs. Complex mixtures of pesticides including up to 8 fungicides, some previously unreported in tissue, were detected with concentrations ranging from 0.08 to 1,500 μg/kg wet weight. No significant differences in pesticide concentrations were observed between species, although concentrations tended to be higher in leopard frogs compared to chorus frogs, possibly because of differences in life histories. Our results provide information on habitat quality in restored wetlands that will assist state and federal agencies, landowners, and resource managers in identifying and implementing conservation and management actions for these and similar wetlands in agriculturally dominated landscapes.

Pesticide residues in two frog species in a paddy agroecosystem in Palakkad district, Kerala, India

Pesticides residues were quantified in 109 frogs comprising two species (Fejervarya limnocharis and Hoplobatrachus crassus) from organic and conventional paddy farms in Kerala, India. Seven frogs from conventional but none from the organic farms revealed deformities. Levels of total Organochlorines (OCs) (33.22 ng/g) and Synthetic Pyrethroid, Fenvalerate-II (26.91/42.15 ng/g) in deformed F. limnocharis and H. crassus were significantly greater than in healthy frogs. Among OCs in healthy frogs, traces of γ (gamma)-HCH (hexachlorocyclohexane) (2.12 ng/g) were found only in F. limnocharis from organic farm. Among Organophosphates, Phorate (1.02 ng/g) and Quinalphos (2.62 ng/g) were present in traces in deformed F. limnocharis, while Parathion ethyl (1.02 ng/g) was detected in deformed H. crassus. The data indicate that the high level of pesticides may have contributed to the deformity of frogs. Therefore, an elaborative study will be essential to conserve amphibians in India.

A persistent organic pollutant related with unusual high frequency of hermaphroditism in the neotropical anuran Physalaemus cuvieri Fitzinger, 1826

Representing a reflection of anthropic activity, the level of xenobiotic compounds in aquatic ecosystems has increased in recent years, bringing severe damage to the environment. The present work reports the occurrence of malformation in gonads of Physalaemus cuvieri individuals from a population of Atlantic Forest in Southern Brazil. Twenty male specimens were collected, which had their testicles removed, immersed in Karnovsky fixative solution, included in historesin for 2 μm cuts and stained with Hematoxylin-eosin. Four specimens showed intersexual gonads condition along with the presence of sperm and oocytes. In order to test a possible contamination of water, 2L were collected from the water body to check organochlorine, organophosphate and carbamate compounds. The analysis of water showed the presence of agrotoxic Dieldrin in a concentration of 0.05 μg/L, representing a concentration above the recommended reference. This agrotoxic, in addition to acting as endocrine disrupter and commercially prohibited, has quite persistent residual effects, and may be responsible for the high frequency of P. cuvieri with intersexual gonads, which in the long term can represent a risk for this population due to the potential impact on its effective reproductive ability.

Localized hotspots drive continental geography of abnormal amphibians on U.S. wildlife refuges

Amphibians with missing, misshapen, and extra limbs have garnered public and scientific attention for two decades, yet the extent of the phenomenon remains poorly understood. Despite progress in identifying the causes of abnormalities in some regions, a lack of knowledge about their broader spatial distribution and temporal dynamics has hindered efforts to understand their implications for amphibian population declines and environmental quality. To address this data gap, we conducted a nationwide, 10-year assessment of 62,947 amphibians on U.S. National Wildlife Refuges. Analysis of a core dataset of 48,081 individuals revealed that consistent with expected background frequencies, an average of 2% were abnormal, but abnormalities exhibited marked spatial variation with a maximum prevalence of 40%. Variance partitioning analysis demonstrated that factors associated with space (rather than species or year sampled) captured 97% of the variation in abnormalities, and the amount of partitioned variance decreased with increasing spatial scale (from site to refuge to region). Consistent with this, abnormalities occurred in local to regional hotspots, clustering at scales of tens to hundreds of kilometers. We detected such hotspot clusters of high-abnormality sites in the Mississippi River Valley, California, and Alaska. Abnormality frequency was more variable within than outside of hotspot clusters. This is consistent with dynamic phenomena such as disturbance or natural enemies (pathogens or predators), whereas similarity of abnormality frequencies at scales of tens to hundreds of kilometers suggests involvement of factors that are spatially consistent at a regional scale. Our characterization of the spatial and temporal variation inherent in continent-wide amphibian abnormalities demonstrates the disproportionate contribution of local factors in predicting hotspots, and the episodic nature of their occurrence.

Accumulation of pesticides in Pacific chorus frogs (Pseudacris regilla) from California's Sierra Nevada Mountains, USA

Pesticides are receiving increasing attention as potential causes of amphibian declines, acting singly or in combination with other stressors, but limited information is available on the accumulation of current-use pesticides in tissue. The authors examined potential exposure and accumulation of currently used pesticides in pond-breeding frogs (Pseudacris regilla) collected from 7 high elevations sites in northern California. All sites sampled are located downwind of California's highly agricultural Central Valley and receive inputs of pesticides through precipitation and/or dry deposition. Whole frog tissue, water, and sediment were analyzed for more than 90 current-use pesticides and pesticide degradates using gas chromatography-mass spectrometry. Two fungicides, pyraclostrobin and tebuconazole, and one herbicide, simazine, were the most frequently detected pesticides in tissue samples. Median pesticide concentration ranged from 13 µg/kg to 235 µg/kg wet weight. Tebuconazole and pyraclostrobin were the only 2 compounds observed frequently in frog tissue and sediment. Significant spatial differences in tissue concentration were observed, which corresponded to pesticide use in the upwind counties. Data generated indicated that amphibians residing in remote locations are exposed to and capable of accumulating current-use pesticides. A comparison of P. regilla tissue concentrations with water and sediment data indicated that the frogs are accumulating pesticides and are potentially a more reliable indicator of exposure to this group of pesticides than either water or sediment.

Abnormalities in amphibian populations inhabiting agroecosystems in Northeastern Buenos Aires Province, Argentina

The occurrence of abnormalities in amphibians has been reported in many populations, and its increase could be related to environmental pollution and habitat degradation. We evaluated the type and prevalence of abnormalities in 5 amphibian populations from agroecosystems with different degrees of agricultural disturbance (cultivated and reference areas). We detected 9 types of abnormalities, of which the most frequent were those occurring in limbs. The observed prevalence of abnormality in assessed populations from cultivated and reference areas was as follows: Rhinella fernandezae (37.1 and 10.2%, respectively), Leptodactylus latrans adults (28.1 and 9.2%) and juveniles (32.9 and 15.3%), and Hypsiboas pulchellus (11.6 and 2.8%). Scinax granulatus populations did not show abnormalities. Pseudis minuta, which was only detected in the reference area, exhibited a prevalence of 13.3%. For R. fernandezae, L. latrans, and H. pulchellus, generalized linear mixed models showed that prevalence of abnormalities was significantly higher (p < 0.05) in cultivated than in reference areas. L. latrans juveniles were more vulnerable to abnormalities than adults (p < 0.05). The presence of abnormalities in some species inhabiting different agroecosystems suggests that environmental stress factors might be responsible for their occurrence. While we detected pesticides (endosulfan, cypermethrin, and chlorpyrifos) and lower dissolved oxygen levels in ponds of the cultivated area, no data are currently available on how other factors, such as injuries from predators and parasite infections, vary by land use. Further research will be necessary to evaluate possible causes of abnormalities detected in the present study mainly in the context of factor interactions.

Endosulfan effects on Rana dalmatina tadpoles: quantitative developmental and behavioural analysis

Endosulfan is an organochlorine pesticide that was recently labeled as a persistent organic pollutant, but it is still widely employed, particularly in developing countries. The goal of this study is to evaluate the acute (LC(50)) and chronic effects (developmental and behavioural traits) of this insecticide on Rana dalmatina tadpoles after exposure to ecologically relevant concentrations (0.005, 0.01, and 0.05 mg/L) by applying video-tracking techniques to evaluate the quantitative effect of endosulfan on amphibian behavioural patterns. The 96 h LC(50) value was 0.074 mg endosulfan/L. Tadpoles chronically exposed to 0.01 and 0.05 mg endosulfan/L underwent high mortality rate, decreased larval growth, delayed development, and increased incidence of malformations, and they did not reach metamorphosis by the end of the experiment. Moreover, tadpoles exposed to these concentrations exhibited several abnormalities in swimming patterns, such as shorter distance moved, swirling, resting, and unusual use of space. The exposure to 0.005 mg endosulfan/L did not cause any significant effects on behaviour, larval growth, or development, but we observed a significant decrease in both survival and time to metamorphosis. We showed that developmental abnormalities are dose-dependent and that the pesticide effects could differ depending on the endosulfan concentration and the species tested. We also validated the hypothesis that behavioural analysis, along with the use of new analytical methods, could be a useful tool in amphibian ecotoxicological studies.

Oxidation of retinoic acids in hepatic microsomes of wild bullfrogs Lithobates catesbeianus environmentally-exposed to a gradient of agricultural contamination

Agricultural contaminants are suspected of contributing to the increased incidence of deformities and the decline of amphibians populations worldwide. Many authors have further suggested that a retinoid effect could be implicated in teratogenic mechanisms since the reported deformities resemble those caused by abnormal levels of retinoic acid (RA). We previously reported altered retinoid concentrations in male bullfrogs from the Yamaska River basin (Québec, Canada) associated with moderate-to-high agricultural activity, and the findings were consistent with a possible effect on hepatic RA oxidation. An in vitro assay was therefore optimized and hepatic microsomal RA oxidation in bullfrogs was found to be quite different from that of other vertebrates. With either all-transRA (atRA) or 13cisRA as the substrate, the major metabolite generated was at4-oxo-RA. The reaction with 13cisRA as substrate, markedly greater compared with atRA, was enhanced in the presence of a reducing agent and inhibited by cytochrome P450 inhibitors in a dose-dependent manner. Hepatic RA oxidation in male bullfrogs showed significant differences between sites with no clear relationship to a gradient of agricultural activity or 13cis-4-oxo-RA quantified in plasma. In contrast, the in vitro RA oxidation in females increased with the levels of contamination and coincided in vivo with higher plasma 13cis-4-oxo-RA concentration. The levels of circulating 4-oxo-derivatives could be influenced by hepatic RA oxidative metabolism as well as isomerization conditions or RA precursor levels.

Cyanobacteria blooms produce teratogenic retinoic acids

Deformed amphibians have been observed in eutrophic habitats, and some clues point to the retinoic acids (RAs) or RA mimics. However, RAs are generally thought of as vertebrate-specific hormones, and there was no evidence that RAs exist in cyanobacteria or algae blooms. By analyzing RAs and their analogs 4-oxo-RAs in natural cyanobacteria blooms and cultures of cyanobacteria and algae, we showed that cyanobacteria blooms could produce RAs, which were powerful animal teratogens. Intracellular RAs and 4-oxo-RAs with concentrations between 0.4 and 4.2 × 10(2) ng/L were detected in all bloom materials, and extracellular concentrations measured in water from Taihu Lake, China, were as great as 2.0 × 10 ng/L, which might pose a risk to wildlife through chronic exposure. Further examination of 39 cyanobacteria and algae species revealed that 32 species could produce RAs and 4-oxo-RAs (1.6-1.4 × 10(3) ng/g dry weight), and the dominant cyanobacteria species in Taihu Lake, Microcystis flos-aquae and Microcystis aeruginosa, produced high amounts of RAs and 4-oxo-RAs with concentrations of 1.4 × 10(3) and 3.7 × 10(2) ng/g dry weight, respectively. Most genera of cyanobacteria that could produce RAs and 4-oxo-RAs, such as Microcystis, Anabaena, and Aphanizomenon, often occur dominantly in blooms. Production of RAs and 4-oxo-RAs by cyanobacteria was associated with species, origin location, and growth stage. These results represent a conclusive demonstration of endogenous production of RAs in freshwater cyanobacteria blooms. The observation of teratogenic RAs in cyanobacteria is evolutionarily and ecologically significant because RAs are vertebrate-specific hormones, and cyanobacteria form extensive and highly visible blooms in many aquatic ecosystems.

Toxicity of chlorpyrifos to larval Rana dalmatina: acute and chronic effects on survival, development, growth and gill apparatus

Chlorpyrifos [O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl)phosphorothioate] is a widely used non-systemic organophosphorus insecticide frequently detected in surface waters around the world. The goal of this study is to evaluate the acute and chronic effects of this insecticide on Rana dalmatina tadpoles. To assess the sensitivity of this species, the LC50 value (i.e. the concentration at which 50% of tadpoles die) was determined after 96 h. Our results showed that 5.174 mg L(-1) chlorpyrifos caused 50% mortality in tadpoles at Gosner stage 25. Chronic toxicity tests were also conducted to evaluate the sublethal effects of chlorpyrifos; tadpoles were exposed to three ecologically relevant concentrations (0.025, 0.05 and 0.1 mg L(-1)) in static renewal tests from Gosner stage 25 (tadpoles shortly after hatching) until completed metamorphosis (Gosner stage 46). No significant reduction was observed in survival, larval growth (mass), snout-vent length, stage development or number metamorphosed. In contrast, chlorpyrifos exhibited significant chronic toxic effects on larval development, manifested as the appearance of abnormalities, including tail flexure, skeletal and muscle defects in later stages of development in tadpoles exposed to all tested concentrations. We also evaluated the chronic effects of chlorpyrifos on gill morphology and ultrastructure. Tadpoles were sacrificed after 8 days and 30 days of exposure. Observations by both scanning (SEM) and transmission electron microscopy (TEM) showed considerable morphological and ultrastructural changes. The main gill effects recorded were mucous secretion, epithelium detachment and a degeneration phenomenon. Comparing these results with our previous findings, we demonstrate that the first effect of chlorpyrifos on R. dalmatina is gill alteration, thus supporting the role of a morphological approach in toxicological studies.

Morphological abnormalities in frogs from a rice-growing region in NSW, Australia, with investigations into pesticide exposure

Three frog species (Limnodynastes tasmaniensis, Limnodynastes fletcheri and Litoria raniformis) were surveyed in rice bays of the Coleambally Irrigation Area (CIA), NSW, Australia, during the rice-growing seasons of 2005/2006 and 2006/2007. A total external morphological abnormality index of 7.0% was observed in frogs of the CIA (n=1,209). The types and frequencies of abnormalities were typical of reports from agricultural areas with ectrodactyly being the most common aberration. A relatively low abnormality index of 1.2% was observed in L. raniformis (n=87) compared to indices of 7.1% and 8.2% observed in L. fletcheri (n=694) and L. tasmaniensis (n=428), respectively. No conclusive evidence was found of unnaturally high rates of intersex, gonadal maldevelopment or unbalanced sex ratios in any species. Rice bay surface waters differed significantly in mean pesticide concentrations of atrazine and metolachlor on farms growing rice and corn compared to farms with rice as the sole crop. However, the similar abnormality indices observed in recent metamorphs emerging from these two farm types provided no evidence to suggest a link between larval exposure to the measured pesticides and developmental malformations.

Mystery unsolved: missing limbs in deformed amphibians

Ballengee and Sessions (2009) claim that predatory attacks by small predators such as Sympetrum dragonfly larvae are sufficient to explain amphibian limb deformities in which the limb is partly or completely missing. This deformity type, the most common in nature, is not well explained by Ribeiroia infection which has also been nominated as a mechanism for limb deformities. We argue that the conclusions of the Ballanegee and Sessions study are not well founded. In part this is because the authors have provided no quantitative analysis of the association between limb deformities and predator densities. Our own data on frequencies of limb deformities suggest that missing hind limbs are often extremely rare even when Sympetrum and other small predators are common. While predatory attacks may contribute to observations of limb deformities, further study will be required to elucidate their role; other potential mechanisms deserve study as well. It is premature, and counterproductive, to draw any conclusions regarding the mechanisms behind the most common limb deformities recorded in natural populations.

Growth, development and sex ratios of Spotted Marsh Frog (Limnodynastes tasmaniensis) larvae exposed to atrazine and a herbicide mixture

Exposures of Limnodynastes tasmaniensis tadpoles to atrazine (0.1, 1, 3 and 30microgL(-1)), metolachlor (0.1, 1 and 10microgL(-1)) and thiobencarb (90, 180 and 360microgL(-1)) from Gosner stage 28 to 42 under controlled laboratory conditions gave no significant effects on tadpole growth, development and sex ratios. A binary mixture of atrazine and thiobencarb as well as a ternary mixture of all three herbicides also had no significant effects on the developing larvae to show no evidence of interactive toxicity. Abnormal gonad morphology was observed on two occasions; both from 0.1microgL(-1) atrazine treatments with one tadpole observed with testicular ovarian follicles. The low frequencies of abnormal gonadal morphology and testicular ovarian follicles did not indicate a concentration associated response to herbicide exposure. No significantly unbalanced sex ratios were observed to suggest any evidence of chemically induced feminisation. These observations suggest that environmentally relevant concentrations of atrazine, metolachlor and thiobencarb do not present a significant threat to the normal development of L. tasmaniensis larvae in surface waters of irrigated agricultural areas.

Amphibians and agricultural chemicals: review of the risks in a complex environment

Agricultural landscapes, although often highly altered in nature, provide habitat for many species of amphibian. However, the persistence and health of amphibian populations are likely to be compromised by the escalating use of pesticides and other agricultural chemicals. This review examines some of the issues relating to exposure of amphibian populations to these chemicals and places emphasis on mechanisms of toxicity. Several mechanisms are highlighted, including those that may disrupt thyroid activity, retinoid pathways, and sexual differentiation. Special emphasis is also placed on the various interactions that may occur between different agro-chemicals and between chemicals and other environmental factors. We also examine the indirect effects on amphibian populations that occur when their surrounding pond communities are altered by chemicals.

Identification of retinoic acid receptor agonists in sewage treatment plants

Retinoic acid receptor (RAR) agonists are speculated to be one possible cause for the widely observed frog deformities in North America, although little is known about the specific RAR agonists in aquatic environments. We identified the specific RAR egonists in sewage treatment plants (STPs) and receiving rivers using an RAR yeast two-hybrid bioassay. Water samples were extracted by solid-phase extract cartridges, which were successively eluted by hexane, ethyl acetate, and methanol for bioassay. Among the three fractions, the ethyl acetate fraction showed the highest RAR agonistic activities. The bioassay-derived activity, expressed as all-trans-retinoic acid (all-transRA) equivalents (ATRA-EQ) were 10.9 +/- 2.2 and 1.7 +/- 1.0 ng/L in the STP influents and effluents, respectively, while the ATRA-EQs were as high as 7.1 and 8.3 ng/L in the two rivers receiving STP effluents. Following a two-step fractionation using high-performance liquid chromatography and ultra-performance liquid chromatography (UPLC) directed by the bioassay, two bioactive fractions were obtained from Gaobeidian STP influent and all-trans-4-oxo-RA (4.7-10.4 ng/L in influents, < 0.2-0.9 ng/L in effluents) and 13-cis-4-oxo-RA (2.3-7.1 ng/L in influents, < 0.4-1.1 ng/L in effluents) were identified in these fractions with UPLC-MS/MS. The EC50 for all-trans-4-oxo-RA or 13-cis-4-oxo-RA relative to that of all-trans-RA in exhibiting RARalpha agonistic activity was calculated to be 3.87 and 0.46, respectively.

Comparative endocrinology in the 21st century

Hormones coordinate developmental, physiological, and behavioral processes within and between all living organisms. They orchestrate and shape organogenesis from early in development, regulate the acquisition, assimilation, and utilization of nutrients to support growth and metabolism, control gamete production and sexual behavior, mediate organismal responses to environmental change, and allow for communication of information between organisms. Genes that code for hormones; the enzymes that synthesize, metabolize, and transport hormones; and hormone receptors are important targets for natural selection, and variation in their expression and function is a major driving force for the evolution of morphology and life history. Hormones coordinate physiology and behavior of populations of organisms, and thus play key roles in determining the structure of populations, communities, and ecosystems. The field of endocrinology is concerned with the study of hormones and their actions. This field is rooted in the comparative study of hormones in diverse species, which has provided the foundation for the modern fields of evolutionary, environmental, and biomedical endocrinology. Comparative endocrinologists work at the cutting edge of the life sciences. They identify new hormones, hormone receptors and mechanisms of hormone action applicable to diverse species, including humans; study the impact of habitat destruction, pollution, and climatic change on populations of organisms; establish novel model systems for studying hormones and their functions; and develop new genetic strains and husbandry practices for efficient production of animal protein. While the model system approach has dominated biomedical research in recent years, and has provided extraordinary insight into many basic cellular and molecular processes, this approach is limited to investigating a small minority of organisms. Animals exhibit tremendous diversity in form and function, life-history strategies, and responses to the environment. A major challenge for life scientists in the 21st century is to understand how a changing environment impacts all life on earth. A full understanding of the capabilities of organisms to respond to environmental variation, and the resilience of organisms challenged by environmental changes and extremes, is necessary for understanding the impact of pollution and climatic change on the viability of populations. Comparative endocrinologists have a key role to play in these efforts.

Environmentally relevant concentrations of endosulfan impair development, metamorphosis and behaviour in Bufo bufo tadpoles

Endosulfan is a widely used organochlorine pesticide with well-documented neurotoxic effects in both humans and laboratory animals (mammals and fish). Neurotoxicity has been implied also in amphibians after short-term exposure to endosulfan. Little is known about effects of chronic exposure of endosulfan in amphibians. Previously, we examined the short-term toxicity of endosulfan in common toad (Bufo bufo) tadpoles and determined the LC50 value to 0.43 mg/L. In the present study, we investigated the effects of endosulfan on B. bufo tadpoles after chronic exposure to ecologically relevant concentrations. Tadpoles were exposed in a static renewal test, from shortly after hatching (Gosner stage 25) to completed metamorphosis, to 0.01, 0.05 and 0.1mg endosulfan/L (nominal). The exposure period lasted 43-52 days. Mortality, larval growth (mass), development (reached Gosner stage at various times and deformities presence), metamorphosis and behaviour (swimming activity) were monitored regularly over the entire course of larval development. Our results show that 0.05 and 0.1mg endosulfan/L caused impaired behaviour, prolonged time to metamorphosis, increased incidences of mouth and skeletal malformations as well as mortality, and reduced body weight (observed also at 0.01 mg/L) in B. bufo tadpoles. Behavioural effects occurred at exposure day 4, before any other effects occurred, indicating a neurotoxic effect. Endosulfan levels found in groundwater and surface water range from 0.1 to 100 microg/L and after extraordinary runoff events, concentrations exceed 0.5 mg/L in surface water. Our results indicate that endosulfan may negatively affect wild frog populations in agricultural areas.

Road proximity increases risk of skeletal abnormalities in wood frogs from National Wildlife Refuges in Alaska

BACKGROUND

Skeletal and eye abnormalities in amphibians are not well understood, and they appear to be increasing while global populations decline. Here, we present the first study of amphibian abnormalities in Alaska.

OBJECTIVE

In this study we investigated the relationship between anthropogenic influences and the probability of skeletal and eye abnormalities in Alaskan wood frogs (Rana sylvatica).

METHODS

From 2000 to 2006, we examined 9,269 metamorphic wood frogs from 86 breeding sites on five National Wildlife Refuges: Arctic, Innoko, Kenai, Tetlin, and Yukon Delta. Using road proximity as a proxy for human development, we tested relationships between skeletal and eye abnormalities and anthropogenic effects. We also examined a subsample of 458 frogs for the trematode parasite Ribeiroia ondatrae, a known cause of amphibian limb abnormalities.

RESULTS

Prevalence of skeletal and eye abnormalities at Alaskan refuges ranged from 1.5% to 7.9% and were as high as 20% at individual breeding sites. Proximity to roads increased the risk of skeletal abnormalities (p = 0.004) but not eye abnormalities. The only significant predictor of eye abnormalities was year sampled (p = 0.006). R. ondatrae was not detected in any Alaskan wood frogs.

CONCLUSIONS

Abnormality prevalence at road-accessible sites in the Kenai and Tetlin refuges is among the highest reported in the published literature. Proximity to roads is positively correlated with risk of skeletal abnormalities in Alaskan wood frogs.

Disruption of retinoid transport, metabolism and signaling by environmental pollutants

Although the assessment of circulatory levels of retinoids has become a widely used biomarker of exposure to environmental pollutants, the adverse effects caused by imbalance of the retinoid metabolism and signaling in wildlife are not known in detail. Retinoids play an important role in controlling such vital processes as morphogenesis, development, reproduction or apoptosis. Unlike other signaling molecules, retinoids are not strictly endogenous but they are derived from dietary sources of vitamin A or its precursors and thus they are sometimes referred to as 'dietary' hormones. Some environmental pollutants that affect embryogenesis, immunity or epithelial functions were also shown to interfere with retinoid metabolism and signaling in animals. This suggests that at least some of their toxic effects may be related to interaction with the retinoid metabolism, transport or signal transduction. This review summarizes in vivo and in vitro studies on interaction of environmental complex samples, pesticides, polychlorinated dioxins, polychlorinated biphenyls, polycyclic aromatic compounds and other organic pollutants with physiology of retinoids. It sums up contemporary knowledge about levels of interaction and mechanisms of action of the environmental contaminants.