Endocrine disruptors in breeding ponds and reproductive health of toads in agricultural, urban and natural landscapes

Population declines of a widespread amphibian in agricultural landscapes

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

Does stress make males? An experiment on the role of glucocorticoids in anuran sex reversal

Environmentally sensitive sex determination may help organisms adapt to environmental change but also makes them vulnerable to anthropogenic stressors, with diverse consequences for population dynamics and evolution. The mechanisms translating environmental stimuli to sex are controversial: although several fish experiments supported the mediator role of glucocorticoid hormones, results on some reptiles challenged it. We tested this hypothesis in amphibians by investigating the effect of corticosterone on sex determination in agile frogs (Rana dalmatina). This species is liable to environmental sex reversal whereby genetic females develop into phenotypic males. After exposing tadpoles during sex determination to waterborne corticosterone, the proportion of genetic females with testes or ovotestes increased from 11% to up to 32% at 3 out of 4 concentrations. These differences were not statistically significant except for the group treated with 10 nM corticosterone, and there was no monotonous dose-effect relationship. These findings suggest that corticosterone is unlikely to mediate sex reversal in frogs. Unexpectedly, animals originating from urban habitats had higher sex-reversal and corticosterone-release rates, reduced body mass and development speed, and lower survival compared to individuals collected from woodland habitats. Thus, anthropogenic environments may affect both sex and fitness, and the underlying mechanisms may vary across ectothermic vertebrates.

Reversing the damage: ecological restoration of polluted water bodies affected by pollutants due to anthropogenic activities

Aquatic ecosystems provide a large number of cultural, regulating, and supporting services to humans and play a pivotal role in sustaining freshwater-dependent ecosystems. However, an increase in human population coupled with economic growth in the last few decades has severely affected their functioning and ecological health. This has led to an increase in concentrations of pollutants originating from anthropogenic activities such as heavy metals, plastics, semi-volatile organic compounds, and endocrine disruptors. These pollutants provoke deleterious impacts on aquatic biodiversity and affect the water quality and functioning. In this paper, we discuss the sources and impacts of such pollutants as well as restoration techniques for reducing their impact on aquatic ecosystems. Several physical and chemical ecological restoration techniques, such as dredging, sediment capping, water diversion, adsorption, aeration, and flushing, can be employed to improve the water quality of water bodies. Additionally, biological techniques such as phytoremediation, phycoremediation, the use of biomembranes, and the construction of ecological floating beds can be employed to increase the population of aquatic organisms and improve the overall ecological health of aquatic ecosystems. Restoration techniques can effectively reduce the concentrations of suspended solids and dissolved phosphorus and increase the levels of dissolved oxygen. The restoration techniques for improving the ecological health of water bodies should not be limited to simply improving the water quality but should also focus on improving the biological processes and ecosystem functioning since it is essential to mitigate the adverse effects of pollutants and restore the vital ecosystem services provided by water bodies for future generations.

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

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

Gut Bacterial Communities Vary across Habitats and Their Diversity Increases with Increasing Glucocorticoids in Toad Tadpoles

The gut microbiome is important for host health and can be influenced by environmental and hormonal changes. We studied the interactions between anthropogenic land use, glucocorticoid hormones, and gut bacterial communities in common toads (Bufo bufo). We sampled tadpoles from ponds of three habitat types (natural, agricultural, and urban ponds), examined gut microbiome composition using amplicon sequencing of the 16S rRNA gene, and measured the associated stress physiology using water-borne hormones. Tadpoles from different habitat types significantly differed in bacterial composition. However, bacterial richness, Shannon diversity, and Firmicutes to Bacteroidota ratio did not vary with habitat type. In contrast with other studies, we found a positive correlation between baseline corticosterone release rate and bacterial diversity. Stress response and negative feedback were not significantly correlated with bacterial diversity. These results suggest that, despite alterations in the composition of intestinal bacterial communities due to land-use change, common toad tadpoles in anthropogenic habitats may maintain their physiological health in terms of the “gut-brain axis”.

Toxicity tests, bioaccumulation and residuality of pyrethroid insecticides commonly used to control conifer bark beetles in Mexico

Effectiveness of pyrethroid insecticides against pests including bark beetles (Dendroctonus spp.) is well known, but little is known about their (a) residuality and persistence in forests after application to control an outbreak and (b) ability to bioaccumulate in insects, which could cause adverse effects on the trophic chains. The 24 h lethal toxicity, bioaccumulation factors, and lethal body burdens of the pyrethroid insecticides bifenthrin, deltamethrin, and cypermethrin were evaluated in the bark beetle Dendroctonus mexicanus. The residuality and persistence of the insecticide bifenthrin in the forest ecosystem (soil, water, and sediment) was also monitored after its application in a region infested by bark beetles. We determined whether contamination of soil, water, and sediments occurred near the sanitation site. For D. mexicanus, the most toxic insecticide for adults was bifenthrin for topical application (LC₅₀ = 0.94 mg/L) and cypermethrin for bark application (LC₅₀ = 5.04 mg/L). The insecticide that bioaccumulated the most in the insect body was deltamethrin (622.41 μg g^-1 dw) and the insecticide that bioaccumulated the least amount was cypermethrin (183.09 μg g^-1 dw). However, cypermethrin was the active substance that presented the lowest body burdens, and therefore required a lower dose to cause death of D. mexicanus adults. Our results demonstrate that prolonged presence of bifenthrin in the forest ecosystem could lead to bioaccumulation in soil, sediment, and insects.

Non-destructive methods to assess health of wild tropical frogs (túngara frogs: Engystomops pustulosus) in Trinidad reveal negative impacts of agricultural land

Amphibians are threatened globally with at least 43% of species declining and the most important stressor being habitat loss or degradation. Amphibians inhabiting highly biodiverse tropical regions are disproportionately threatened; however, the effects of landscape alterations on amphibian health are virtually unknown. In this study, we utilised non-destructive techniques to compare size (weight, snout-vent length [SVL]), body condition, male secondary sexual features (forelimb width, nuptial pad length) and breeding success (egg number, fertility [percentage fertilised eggs], hatching success) in túngara frogs (Engystomops pustulosus) collected from reference (n = 5), suburban (n = 6) and agricultural (n = 4) sites in Trinidad; characterised by presence/absence of crops/houses. All measured endpoints were negatively impacted in frogs collected from agricultural sites. The largest effect was observed for hatching success (2.77-fold lower) and egg number (2.5-fold lower). Less pronounced effects were observed on male frogs (weight: 1.77-fold lower; SVL: 1.18-fold lower; forelimb width: 1.33-fold lower; nuptial pad length: 1.15-fold lower). Our findings demonstrate negative impacts of agricultural sites on túngara frog health, with the number of viable offspring reduced by almost one third. The methods outlined here are technically simple and low-cost and thereby have potential for application to other species in order to investigate the potential impacts of habitat degradation on amphibian health. Furthermore, as these methods are non-destructive, they could be used to investigate the potential contribution of frog size and/or reproductive capability as a causative factor contributing to population declines in threatened species, which is particularly pressing in tropical regions.

Impacts of endocrine disrupting chemicals on reproduction in wildlife and humans

Endocrine disrupting chemicals (EDCs) are ubiquitous in aquatic and terrestrial environments. The main objective of this review was to summarize the current knowledge of the impacts of EDCs on reproductive success in wildlife and humans. The examples selected often include a retrospective assessment of the knowledge of reproductive impacts over time to discern how the effects of EDCs have changed over the last several decades. Collectively, the evidence summarized here within reinforce the concept that reproduction in wildlife and humans is negatively impacted by anthropogenic chemicals, with several altering endocrine system function. These observations of chemicals interfering with different aspects of the reproductive endocrine axis are particularly pronounced for aquatic species and are often corroborated by laboratory-based experiments (i.e. fish, amphibians, birds). Noteworthy, many of these same indicators are also observed in epidemiological studies in mammalian wildlife and humans. Given the vast array of reproductive strategies used by animals, it is perhaps not surprising that no single disrupted target is predictive of reproductive effects. Nevertheless, there are some general features of the endocrine control of reproduction, and in particular, the critical role that steroid hormones play in these processes that confer a high degree of susceptibility to environmental chemicals. New research is needed on the implications of chemical exposures during development and the potential for long-term reproductive effects. Future emphasis on field-based observations that can form the basis of more deliberate, extensive, and long-term population level studies to monitor contaminant effects, including adverse effects on the endocrine system, are key to addressing these knowledge gaps.

A cross-species comparative approach to assessing multi- and transgenerational effects of endocrine disrupting chemicals

A wide range of chemicals have been identified as endocrine disrupting chemicals (EDCs) in vertebrate species. Most studies of EDCs have focused on exposure of both male and female adults to these chemicals; however, there is clear evidence that EDCs have dramatic effects when mature or developing gametes are exposed, and consequently are associated with in multigenerational and transgenerational effects. Several publications have reviewed such actions of EDCs in subgroups of species, e.g., fish or rodents. In this review, we take a holistic approach synthesizing knowledge of the effects of EDCs across vertebrate species, including fish, anurans, birds, and mammals, and discuss the potential mechanism(s) mediating such multi- and transgenerational effects. We also propose a series of recommendations aimed at moving the field forward in a structured and coherent manner.

Pharmaceuticals in water and sediment of small streams under the pressure of urbanization: Concentrations, interactions, and risks

Small streams are crucial but vulnerable elements of ecological networks. To better understand the occurrence of pharmaceutically active compounds (PhACs) in streams, this study focused on the occurrence, distribution, and environmental risk of 111 PhACs and 7 trace elements based on a total of 141 water and sediment samples from small streams located in the urbanizing region of Budapest, Hungary. Eighty-one PhACs were detected in the aqueous phase, whereas sixty-two compounds were detected in the sediment. Carbamazepine (CBZ) was the most frequently identified PhAC in water, and was found in 91.5% of all samples. However, the highest concentrations were measured for lamotrigine (344.8 μg·L^-1) and caffeine (221.4 μg·L^-1). Lidocaine was the most frequently occurring PhAC in sediment (73.8%), but the maximum concentrations were detected for CBZ (395.9 ng·g^-1) and tiapride (187.7 ng·g^-1). In both water and sediment, more PhACs were found downstream of the wastewater treatment plants (WWTPs) than in the samples not affected by treated wastewater, even though no relationship was observed between the total amount of treated wastewater and the number of detected PhACs. The PhAC concentrations were also independent of the distance from the WWTP effluents. PhAC-polluted samples were detected upstream of the WWTPs, thereby suggesting the relevance of diffuse emissions in addition to WWTP outlets. The most frequently detected PhACs in the sediment were usually also present in the water samples collected at the same place and time. The varying concentrations of PhACs and the fluctuating water-sediment properties resulted in a lack of correlation between the general chemical properties and the concentrations of PhACs, which makes it difficult to predict PhAC contamination and risks in urbanized small streams. The environmental risk assessment indicated that diclofenac had the highest risk in the sampling area.

Novel genetic sex markers reveal unexpected lack of, and similar susceptibility to, sex reversal in free-living common toads in both natural and anthropogenic habitats

Anthropogenic environmental changes are affecting biodiversity and microevolution worldwide. Ectothermic vertebrates are especially vulnerable, since environmental changes can disrupt their sexual development and cause sex reversal, a mismatch between genetic and phenotypic sex. This can potentially lead to sex-ratio distortion and population decline. Despite these implications, we have scarce empirical knowledge on the incidence of sex reversal in nature. Populations in anthropogenic environments may be exposed to sex-reversing stimuli more frequently, which may lead to higher sex-reversal rate, or alternatively, these populations may adapt to resist sex reversal. We developed PCR-based genetic sex markers for the common toad (Bufo bufo) to assess the prevalence of sex reversal in wild populations living in natural, agricultural and urban habitats, and the susceptibility of the same populations to two ubiquitous estrogenic pollutants in a common-garden experiment. We found negligible sex-reversal frequency in free-living adults despite the presence of various endocrine-disrupting pollutants in their breeding ponds. Individuals from different habitat types showed similar susceptibility to sex reversal in the laboratory: all genetic males developed female phenotype when exposed to 1 µg/L 17α-ethinylestradiol (EE2) during larval development, whereas no sex reversal occurred in response to 1 ng/L EE2 and a glyphosate-based herbicide with 3 µg/L or 3 mg/L glyphosate. The latter results do not support that populations in anthropogenic habitats would have either increased propensity for or higher tolerance to chemically induced sex reversal. Thus, the extremely low sex-reversal frequency in wild toads compared to other ectothermic vertebrates studied before might indicate idiosyncratic, potentially species-specific resistance to sex reversal.

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

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

A Review on Environmental Contaminants-Related Fertility Threat in Male Fishes: Effects and Possible Mechanisms of Action Learned from Wildlife and Laboratory Studies

Increasing global rates of diminished fertility in males has been suggested to be associated with exposure to environmental contaminants (ECs). The aquatic environments are the final repository of ECs. As the reproductive system is conserved in vertebrates, studies on the effects of ECs on fertility endpoints in fishes provide us with valuable information to establish biomarkers in risk assessment of ECs, and to understand the ECs-related fertility threat. The aim of the present review was to evaluate associations between ECs and fertility determinants to better understand ECs-related male fertility threat in male fishes. Wildlife studies show that the reproductive system has been affected in fishes sampled from the polluted aquatic environment. The laboratory studies show the potency of ECs including natural and synthetic hormones, alkylphenols, bisphenols, plasticizers, pesticides, pharmaceutical, alkylating, and organotin agents to affect fertility determinants, resulting in diminished fertility at environmentally relevant concentrations. Both wildlife and laboratory studies reveal that ECs adverse effects on male fertility are associated with a decrease in sperm production, damage to sperm morphology, alternations in sperm genome, and decrease in sperm motility kinetics. The efficiency of ECs to affect sperm quality and male fertility highly depends on the concentration of the contaminants and the duration of exposure. Our review highlights that the number of contaminants examined over fertility tests are much lower than the number of contaminants detected in our environment. The ECs effects on fertility are largely unknown when fishes are exposed to the contaminants at early developmental stages. The review suggests the urgent need to examine ECs effects on male fertility when a fish is exposed at different developmental stages in a single or combination protocol. The ECs effects on the sperm genome are largely unknown to understand ECs-related inheritance of reproductive disorders transmitted to the progeny. To elucidate modes of action of ECs on sperm motility, it is needed to study functional morphology of the motility apparatus and to investigate ECs-disrupted motility signaling.

Sex reversal and ontogeny under climate change and chemical pollution: are there interactions between the effects of elevated temperature and a xenoestrogen on early development in agile frogs?

Anthropogenic environmental change poses a special threat to species in which genetic sex determination can be overwritten by the thermal and chemical environment. Endocrine disrupting chemicals as well as extreme temperatures can induce sex reversal in such species, with potentially wide-ranging consequences for fitness, demography, population viability and evolution. Despite accumulating evidence suggesting that chemical and thermal effects may interact in ecological contexts, little is known about their combined effects on sex reversal. Here we assessed the simultaneous effects of high temperature (female-to-male sex-reversing agent) and 17α-ethinylestradiol (EE2), a widespread xenoestrogen (male-to-female sex-reversing agent), on sexual development and fitness-related traits in agile frogs (Rana dalmatina). We exposed tadpoles to a six-days heat wave (30 °C) and/or an ecologically relevant concentration of EE2 (30 ng/L) in one of three consecutive larval periods, and diagnosed sex reversals two months after metamorphosis using species-specific markers for genetic sexing. We found that high temperature induced female-to-male sex reversal, decreased survival, delayed metamorphosis, decreased body mass at metamorphosis, and increased the proportion of animals that had no fat bodies, while EE2 had no effect on these traits. Simultaneous exposure to heat and EE2 had non-additive effects on juvenile body mass, which were dependent on treatment timing and further complicated by a negative effect of sex reversal on body mass. These results show that environmentally relevant exposure to EE2 does not diminish the female-to-male sex-reversing effects of high temperature. Instead, our findings on growth suggest that climate change and chemical pollution may have complex consequences for individual fitness and population persistence in species with environment-sensitive sex determination.

Age, size and body condition do not equally reflect population response to habitat change in the common spadefoot toad Pelobates fuscus

Urbanization impacts biodiversity both directly through physical expansion over land, and indirectly due to land use conversion and human behaviors associated with urban areas. We assessed the response of a common spadefoot toad population (Pelobates fuscus) to habitat loss and fragmentation resulting from urban development by studying changes in size, body condition and age parameters. We compared samples collected in the early 2000s (sample A) and later on during 2012-2014 (sample B). The terrestrial habitats in the study area were severely reduced and fragmented due to the expansion of the human settlement. We found no significant differences in the age parameters between the two sampling periods; the median lifespan shortened from 3.5 (sample A) to 3.0 years (sample B), while the other age parameters were similar in both samples. In contrast, snout-vent length, body mass and body condition experienced a significant decrease over time. Our results suggest that changes in body size and body condition, rather than age parameters, better reflect the response of the common spadefoot toad population to declining habitat quality. Therefore, body measurements can provide reliable estimates of the impact of habitat degradation in amphibian populations.

Layered double hydroxides and related hybrid materials for removal of pharmaceutical pollutants from water

Pharmaceuticals and their by-products are recalcitrant contaminants in water. Moreover, the high consumption of these drugs has many detrimental effects on body waters and ecosystems. In this timely review, the advances in molecular engineering of layered double hydroxides (LDH) that have been used for the removal of pharmaceutical pollutants are discussed. The approach starts from the strategies to obtain homogeneous synthesis of LDH that allow the doping and/or surface functionalization of different metals and oxides, producing heterojunction systems as well as composites with carbon and silica-based materials with high surface area. Adsorption is considered as a traditional removal of pharmaceutical pollutants, so the kinetic and mechanism of this phenomenon are analyzed based on pH, temperature, ionic strength, in order to obtain new insights for the formation of multifunctional LDH. Advanced oxidation methodologies, mainly heterogeneous photocatalysis and Fenton-like processes, stand out as the more efficient even to obtain the mineralization of the drugs. The LDH have the advantage of structural memory that favors regeneration processes. The reconstruction of calcined LDH can be used to improve drug removal, through a combination of adsorption capacity/catalytic activity. A meticulous analysis of the persistence, toxicity and bioaccumulation of the most common pharmaceuticals has allowed us to highlight the ability of the LDH to remove recalcitrant drugs at relatively low concentrations (ppm, ppb), in contrast to other mixed oxide nanostructures and homogeneous oxidation processes. In this sense, the mechanism of drug removal by LDH is discussed based on the importance of the use of composites, scavenger agents, Fenton and electro-Fenton processes, membranes, thin films and coatings, among others. In addition, the ecotoxicity of LDH is also reviewed to indicate that these layered structures can exhibit biocompatibility or high toxicity depending on the adsorbed drug and ions/metals that compose them. Undoubtedly, the LDH have a unique flexible structure with adsorption capacity and catalytic activity, facts that explain the important reasons for their extensive use in the environmental remediation of pharmaceutical pollutants from water.

Pharmaceuticals in source waters of 95 First Nations in Canada

OBJECTIVES

Pharmaceuticals are emerging contaminants in the environment. Little has been published about the presence of pharmaceuticals in waterbodies nearby or on reserve land of First Nations in Canada. The objectives of this study were to (1) quantify the level of pharmaceuticals in First Nations' surface waters, (2) calculate the human health risks of the mixtures found, and (3) measure the exposure to pharmaceuticals in First Nations' drinking water where source water was highly contaminated.

METHODS

This participatory study measured the levels of 43 pharmaceuticals from surface water samples taken at three water sampling sites chosen by the 95 participating First Nations. The sites were in proximity to recreational areas, fishing areas, drinking water sources, and/or wastewater outflows. When elevated levels of pharmaceutical mixtures were found in samples, drinking water samples were obtained and analyzed for potential pharmaceuticals. Human health risks were calculated by an established protocol.

RESULTS

In total, 432 samples were collected at 302 water sampling sites (285 surface water, 11 drinking water, and 6 wastewater sites). Quantifiable levels of 35 pharmaceuticals were found in 79 of the 95 (83%) participating First Nations at 193 of the 285 surface water sites (68%). Overall, the levels found were comparable to or lower than those found in other studies in Canada and worldwide.

CONCLUSION

In almost all participating First Nations, there is no human health risk from consuming surface water for drinking. However, surface water in the vicinity of major urban centres should not be used as secondary untreated water sources due to the elevated human health risk associated with exposure to the mixtures of multiple pharmaceuticals detected.

Effects of the emulsifiable herbicide Dicamba on amphibian tadpoles: an underestimated toxicity risk?

The effects of exposure to the herbicide Dicamba (DIC) on tadpoles of two amphibian species, Scinax nasicus and Elachistocleis bicolor, were assessed. Mortality and biochemical sublethal effects were evaluated using acetylcholinesterase (AChE), glutathione S-transferase (GST), glutathione reductase (GR), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities and thyroid hormone (T4) levels. The LC₅₀ value at 48h was 0.859 mg L^-1 for S. nasicus and 0.221 mg L^-1 for E. bicolor tadpoles. After exposure to sublethal DIC concentrations for 48 h, GST activity increased in S. nasicus but significantly decreased in E. bicolor with respect to controls. GR activity decreased only in S. nasicus at all the tested DIC concentrations. AChE activity was significantly inhibited in both S. nasicus and E. bicolor tadpoles at 48 h. DIC also caused significant changes in transamination, as evidenced by an increase in AST and ALT activities in both amphibian species. T4 levels were higher in DIC-treated tadpoles of both species than in controls. The DIC-induced biochemical alterations in glutathione system enzymes and transaminases indicate lesions in liver tissues and cellular function. Moreover, the observed AChE inhibition could lead to the accumulation of acetylcholine, excessively stimulating postsynaptic receptors, and the increase in T4 levels in both species may indicate an overactive thyroid. The commercial DIC formulation showed a high biotoxicity in the two amphibian native species after short-term exposure, controversially differing from the toxicity level indicated in the official fact sheet data. This fact highlights the need for an urgent re-categorization and reevaluation of DIC toxicity in native species.

Clutch quality is related to embryonic development duration, hatchling body size and telomere length in the spined toad (Bufo spinosus)

Reproductive success is often related to parental quality, a parameter expressed through various traits, such as site selection, mate selection and energetic investment in the eggs or progeny. Owing to the complex interactions between environmental and parental characteristics occurring at various stages of the reproductive event, it is often complicated to tease apart the relative contributions of these different factors to reproductive success. Study systems where these complex interactions are simplified (e.g. absence of parental care) can help us to understand how metrics of parental quality (e.g. gamete and egg quality) influence reproductive success. Using such a study system in a common garden experiment, we investigated the relationships between clutch hatching success (a proxy of clutch quality) and offspring quality in an amphibian species lacking post-oviposition parental care. We found a relationship between clutch quality and embryonic development duration and hatchling phenotype. We found that hatchling telomere length was linked to hatching success. These results suggest that clutch quality is linked to early life traits in larval amphibians and that deciphering the influence of parental traits on the patterns we detected is a promising avenue of research.

Digit ratio in the common toad Bufo bufo: the effects of reduced fingers and of age dependency

INTRODUCTION

Despite the growing number of studies describing digit ratio patterns in tetrapods, knowledge concerning certain basic issues is still scarce. In lower vertebrates such as tailless amphibians (Anura), the numbering of individual fingers on the forelimbs and their homology with the fingers of other vertebrates pose an unsolved problem. Based on reviewed data on anuran limb development, we argue that the correct finger numbering scheme should be based on the assumption that the first finger, not the fifth finger, was reduced on the forelimbs. We analyzed the digit ratio in the common toad (Bufo bufo, Bufonidae), a species characterized by well-developed sexual dimorphism whereby females are larger than males, using both numbering schemes present in the literature.

RESULTS

We found that the digit ratio on hindlimbs differed significantly between the sexes only in the cases of left 2D:3D, with lower digit ratios in females, and of left 3D:4D, with lower digit ratios in males. We found that sex was the only significant variable for forelimbs, differentiating 2D:3D on the left forelimb, with lower digit ratios in females; 2D:4D on the right forelimb, with lower digit ratios in males; and 3D:4D on both forelimbs, with lower digit ratios in males. These results relate to variant II reflecting the hypothesis that the first digit was reduced during phylogenesis. There was no relationship between the body size (SVL) of individuals and any digit ratio, excluding 2D:4D on the right forelimbs in models with age variables. Additionally, for a subset of data where individual age was known, the models indicated that age was linked to significant differences in 2D:4D and 3D:4D on the left hindlimbs, while age, SVL, and sex influenced 2D:4D on the right forelimbs.

CONCLUSION

We emphasize the importance of the problem of the correct numbering of forelimb digits in Anura and, under the assumption that it was the fifth digit that was reduced, argue that earlier results on digit ratio in this group should be interpreted with caution. The detected relationship between digit ratio and age in amphibians expands our knowledge, indicating that the age of individuals should be included in future digit ratio studies. This relationship may also apply to studies using digit ratio as a noninvasive indicator of endocrine disruption in amphibians.

Pesticide exposure affects reproductive capacity of common toads (Bufo bufo) in a viticultural landscape

Amphibian populations are declining worldwide at alarming rates. Among the large variety of contributing stressors, chemical pollutants like pesticides have been identified as a major factor for this decline. Besides direct effects on aquatic and terrestrial amphibian stages, sublethal effects like impairments in reproduction can affect a population. Therefore, we investigated the reproductive capacity of common toads (Bufo bufo) in the pesticide-intensive viticultural landscape of Palatinate in Southwest Germany along a pesticide gradient. In a semi-field study, we captured reproductively active common toad pairs of five breeding ponds with different pesticide contamination level and kept them in a net cage until spawning. Toads from more contaminated ponds showed an increased fecundity (more eggs) but decreased fertilization rates (fewer hatching tadpoles) as well as lower survival rates and reduced size in Gosner stage 25, suggesting that the higher exposed populations suffer from long-term reproductive impairments. In combination with acute toxicity effects, the detected sublethal effects, which are mostly not addressed in the ecological risk assessment of pesticides, pose a serious threat on amphibian populations in agricultural landscapes.

Stressed tadpoles mount more efficient glucocorticoid negative feedback in anthropogenic habitats due to phenotypic plasticity

Coping with anthropogenic environmental change is among the greatest challenges faced by wildlife, and endocrine flexibility is a potentially crucial coping mechanism. Animals may adapt to anthropogenic environments by dampening their glucocorticoid stress response, but empirical tests of this hypothesis have provided mixed evidence. An alternative hypothesis is that a non-attenuated stress response and efficient negative feedback are favored in anthropogenic habitats. To test this idea, we non-invasively sampled corticosterone release rates of common toad (Bufo bufo) tadpoles in agricultural, urban, and natural habitats, and quantified their stress response and negative feedback by a standardized stress-and-recovery protocol. We repeated the same sampling with tadpoles raised from eggs from the same ponds in a common-garden experiment to infer if the differences observed between populations in different habitats were due to individual phenotypic plasticity rather than microevolution or transgenerational effects. We found that, compared to tadpoles in natural ponds, urban tadpoles had higher baseline and stressed corticosterone release rates, and tadpoles in agricultural ponds had similar corticosterone release rates but greater stress-induced change, indicating stronger stress responses in both types of anthropogenic habitats. As predicted, tadpoles in both agricultural and urban ponds showed more efficient negative feedback than did tadpoles in natural ponds. Water pollution levels, as indicated by the concentrations of carbamazepine and corticoid-disrupting compounds in pond water, contributed to elevating the stress response regardless of land use. Infection by neither Batrachochytrium dendrobatidis nor Ranavirus was detected in free-living tadpoles. No habitat-related glucocorticoid differences persisted in the common-garden experiment. These results suggest that toad tadpoles in anthropogenic habitats increased their glucocorticoid flexibility via phenotypic plasticity. The coupling of stronger stress response and stronger negative feedback in these habitats supports the importance of rapidly "turning on and off" the stress response as a mechanism for coping with anthropogenic environmental change.

A laboratory investigation into features of morphology and physiology for their potential to predict reproductive success in male frogs

Amphibian populations are declining globally, however, the contribution of reduced reproduction to declines is unknown. We investigated associations between morphological (weight/snout-vent length, nuptial pad colour/size, forelimb width/size) and physiological (nuptial pad/testis histomorphology, plasma hormones, gene expression) features with reproductive success in males as measured by amplexus success and fertility rate (% eggs fertilised) in laboratory maintained Silurana/Xenopus tropicalis. We explored the robustness of these features to predict amplexus success/fertility rate by investigating these associations within a sub-set of frogs exposed to anti-androgens (flutamide (50 μg/L)/linuron (9 or 45 μg/L)). In unexposed males, nuptial pad features (size/colour/number of hooks/androgen receptor mRNA) were positively associated with amplexus success, but not with fertility rate. In exposed males, many of the associations with amplexus success differed from untreated animals (they were either reversed or absent). In the exposed males forelimb width/nuptial pad morphology were also associated with fertility rate. However, a more darkly coloured nuptial pad was positively associated with amplexus success across all groups and was indicative of androgen status. Our findings demonstrate the central role for nuptial pad morphology in reproductive success in S. tropicalis, however, the lack of concordance between unexposed/exposed frogs complicates understanding of the utility of features of nuptial pad morphology as biomarkers in wild populations. In conclusion, our work has indicated that nuptial pad and forelimb morphology have potential for development as biomarkers of reproductive health in wild anurans, however, further research is needed to establish this.

Aminomethylphosphonic acid alters amphibian embryonic development at environmental concentrations

Despite intense societal and scientific debates regarding glyphosate toxicity, it remains the most widely used herbicide. The primary metabolite of glyphosate, AMPA (aminomethylphosphonic acid), is the main contaminant detected in surface waters worldwide, both because of the extensive use of glyphosate and because of other widespread sources of AMPA (i.e., industrial detergents). Studies on potential effects of glyphosate using environmentally relevant concentrations of AMPA on non-target wildlife species are lacking. We experimentally tested the effects of AMPA on embryonic development in a common European toad at concentrations spanning the range found in natural water bodies (from 0.07 to 3.57 μg l^-1). Our experimental concentrations of AMPA were 100-6000 times lower than official Predicted-No-Effect-Concentrations. We found that these low-level concentrations of AMPA decreased embryonic survival, increased development duration and influenced hatchling morphology. Response patterns were more complex than classical linear concentration-response relationships, as concentration responses were nonmonotonic, with greater effects at low-concentrations of AMPA than at high levels. Based on our results we recommend that investigators focus not only on effects of "parent compounds," but also their metabolites at environmentally relevant concentrations in order to comprehensively assess impacts of anthropogenic contaminants on the environment.

Novel genetic sex markers reveal high frequency of sex reversal in wild populations of the agile frog (Rana dalmatina) associated with anthropogenic land use

Populations of ectothermic vertebrates are vulnerable to environmental pollution and climate change because certain chemicals and extreme temperatures can cause sex reversal during early ontogeny (i.e. genetically female individuals develop male phenotype or vice versa), which may distort population sex ratios. However, we have troublingly little information on sex reversals in natural populations, due to unavailability of genetic sex markers. Here, we developed a genetic sexing method based on sex-linked single nucleotide polymorphism loci to study the prevalence and fitness consequences of sex reversal in agile frogs (Rana dalmatina). Out of 125 juveniles raised in laboratory without exposure to sex-reversing stimuli, 6 showed male phenotype but female genotype according to our markers. These individuals exhibited several signs of poor physiological condition, suggesting stress-induced sex reversal and inferior fitness prospects. Among 162 adults from 11 wild populations in North-Central Hungary, 20% of phenotypic males had female genotype according to our markers. These individuals occurred more frequently in areas of anthropogenic land use; this association was attributable to agriculture and less strongly to urban land use. Female-to-male sex-reversed adults had similar body mass as normal males. We recorded no events of male-to-female sex reversal either in the laboratory or in the wild. These results support recent suspicions that sex reversal is widespread in nature, and suggest that human-induced environmental changes may contribute to its pervasiveness. Furthermore, our findings indicate that sex reversal is associated with stress and poor health in early life, but sex-reversed individuals surviving to adulthood may participate in breeding.

Effects of two little-studied environmental pollutants on early development in anurans

Despite intensive ecotoxicological research, we still know relatively little about the ecological impacts of many environmental contaminants. Filling these knowledge gaps is particularly important regarding amphibians, because they play significant roles in freshwater and terrestrial ecosystems, and their populations are declining worldwide. In this study, we investigated two pollutants that have been poorly studied in ecotoxicology despite their widespread occurrence in surface waters: the herbicide terbuthylazine and the pharmaceutical drug carbamazepine. We exposed two anuran species throughout their larval development to each of two environmentally relevant concentrations of each pollutant, and recorded mortality and 17 sub-lethal endpoints up to several months after exposure. Mortality was low and unrelated to treatment. In agile frogs (Rana dalmatina), we found that treatment with 0.3 μg/L terbuthylazine decreased tadpole activity and reduced fat bodies in juveniles, whereas treatment with 50 μg/L carbamazepine decreased spleen size and increased spleen pigmentation. In common toads (Bufo bufo), treatment with 0.003 μg/L terbuthylazine increased body mass at metamorphosis, treatment with 0.3 μg/L terbuthylazine increased the size of optic tecta, and treatment with 0.5 μg/L carbamazepine decreased hypothalamus size. Treatment with 50 μg/L carbamazepine reduced the feeding activity of toad tadpoles, decreased their production of anti-predatory bufadienolide toxins, and increased their body mass at metamorphosis; juvenile toads in this treatment group had reduced spleen pigmentation. Neither treatments affected the time to metamorphosis, post-metamorphic body mass, or sex ratios significantly. These results show that environmental levels of both terbuthylazine and carbamazepine can have several sub-lethal effects on anurans, which may be detrimental to individual fitness and population persistence in natural conditions. Our findings further highlight that toxic effects cannot be generalized between chemicals of similar structure, because the terbuthylazine effects we found do not conform with previously reported effects of atrazine, a related and extensively studied herbicide.

Thermal baths as sources of pharmaceutical and illicit drug contamination

Despite the fact that there are tens of thousands of thermal baths in existence, knowledge about the occurrence of pharmaceutically active compounds (PhACs) in untreated thermal wastewater is very limited. Because used thermal water is typically legally discharged into surface waters without any treatment, the effluent poses environmental risks for the receiving water bodies. The aim of this study was to show the occurrence patterns and spatiotemporal characteristics of 111 PhACs in thermal wastewater. Six thermal water outflows of different thermal baths were tested in different seasons in the Budapest metropolitan region (Hungary), and diurnal analysis was performed. After solid-phase extraction, the samples were analysed and quantified by coupling supercritical fluid chromatography and mass spectrometry to perform simultaneous multi-residue drug analysis. The results confirm that water discharge pipes directly transport pharmaceuticals into surface water bodies; 34 PhACs were measured to be over the limit of quantification at least once, and 21 of them were found in more than one water sample. The local anaesthetic drug lidocaine, antiepileptic carbamazepine, analgesic derivative tramadol and illicit drug cocaine were detected in more than half of the samples. Caffeine, metoprolol and bisoprolol (cardiovascular drugs), benzoylecgonine (cocaine metabolite), diclofenac (NSAID), citalopram (antidepressant) and certain types of hormones also have a significant frequency of 30-50%. However, the occurrence and concentrations of PhACs vary according to the season and number/types of visitors. As demonstrated by the diurnal fluctuation, drug contamination of thermal waters can significantly vary, even for similar types of baths; furthermore, the quantity and types of some pollutants rapidly change in the discharged thermal wastewater.

Emerging and legacy contaminants across land-use gradients and the risk to aquatic ecosystems

Information on potentially harmful emerging and legacy chemicals is essential to understand the risks to the environment and inform regulatory actions. The objective of this study was to assess the occurrence, concentration, and distribution of emerging and legacy contaminants across a gradient of land-use intensity and determine the risk posed to aquatic ecosystems. The land-use intensity gradient considered was: background/undeveloped < low-intensity agriculture < high-intensity agriculture < urban residential < urban industrial. Twenty-five sites were sampled for surface water, sediment, and soil. A total of 218 chemicals were analyzed: pesticides, per- and poly-fluoroalkyl substances (PFAS), polybrominated biphenyls and polybrominated diphenyl ethers (PBDEs), phthalates, and short-chain chlorinated paraffins (SCCPs). The risk posed by the analyzed chemicals to the aquatic environment was measured using hazard quotients (HQs), which were calculated by dividing the maximum measured environmental concentration by a predicted no-effect concentration for each chemical. A HQ > 1 was considered to indicate a high risk of adverse effects from the given chemical. A total of 68 chemicals were detected: 19 pesticides, 18 PFAS, 28 PBDEs, two phthalates, and SCCPs (as total SCCPs). There were no significant differences in the overall chemical composition between land uses. However, the insecticide bifenthrin, PFAS, PBDEs, and phthalates were more frequently found in samples from residential and/or industrial sites, suggesting urban land uses are hotspots and potential large-scale sources of these chemicals. Nineteen chemicals had a HQ > 1; most had a restricted spatial distribution limited to high-intensity agriculture and industrial sites in Melbourne. Bifenthrin and the perfluorooctanesulfonic acid (PFOS) had the highest HQs in residential and industrial sites, suggesting an increased risk to aquatic ecosystems in urban settings. The results of this study will enhance future research, predictive methods, and effective targeting of monitoring, and will help guide regulatory management actions and mitigation solutions.

Laryngeal Demasculinization in Wild Cane Toads Varies with Land Use

Anthropogenic factors, including the spread of endocrine-disrupting chemicals, have been linked to alterations in the reproductive physiology, morphology, and behavior of wildlife. Few studies of endocrine disruption, however, focus on secondary sexual traits that affect mating signals, despite their importance for reproductive success. The larynx of many anurans (frogs and toads), for example, is larger in males than in females and is crucial for producing mating calls. We aim to determine if wild populations of cane toads (Rhinella marina) near sugarcane fields in Florida have demasculinized larynges when compared to populations near urban areas. We find evidence of demasculinization in both primary and secondary sexual traits in male toads living near sugarcane. Relative to body size, the laryngeal mass, vocal cord length, and dilator muscle width are all reduced in males from sugarcane regions compared to their urban counterparts. Strong correlations between primary and secondary male sexual traits indicate that demasculinization occurs in concert both within and across diverse organs, including the testes, larynx, and skin. Our results show that anurans near sugarcane fields have demasculinized reproductive systems, that this disruption extends to secondary sexual traits like the larynx, and that it is likely due to anthropogenic causes.

Contaminant-induced behavioural changes in amphibians: A meta-analysis

Environmental contamination contributes to the threatened status of many amphibian populations. Many contaminants alter behaviour at concentrations commonly experienced in the environment, with negative consequences for individual fitness, populations and communities. A comprehensive, quantitative evaluation of the behavioural sensitivity of amphibians is warranted to better understand the population-level and resultant ecological impacts of contaminants. We conducted a systematic review and meta-analysis evaluating behavioural changes following exposure to contaminants. Most studies were conducted in North America and Europe on larval stages, and 64% of the 116 studies focussed on the effects of insecticides. We found that a suite of contaminants influence a wide range of behaviours in amphibians, with insecticides typically invoking the strongest responses. In particular, insecticides increased rates of abnormal swimming, and reduced escape responses to simulated predator attacks. Our analysis identified five key needs for future research, in particular the need: (1) for researchers to provide more details of experimental protocols and results (2) to develop a strong research base for future quantitative reviews, (3) to broaden the suite of contaminants tested, (4) to better study and thus understand the effects of multiple stressors, and (5) to establish the ecological importance of behavioural alterations. Behavioural endpoints provide useful sub-lethal indicators of how contaminants influence amphibians, and coupled with standard ecotoxicological endpoints, can provide valuable information for population models assessing the broader ecological consequences of environmental contamination.

Anthropogenic contaminants of high concern: Existence in water resources and their adverse effects

Existence of anthropogenic contaminants (ACs) in different environmental matrices is a serious and unresolved concern. For instance, ACs from different sectors, such as industrial, agricultural, and pharmaceutical, are found in water bodies with considerable endocrine disruptors potency and can damage the biotic components of the environment. The continuous ACs exposure can cause cellular toxicity, apoptosis, genotoxicity, and alterations in sex ratios in human beings. Whereas, aquatic organisms show bioaccumulation, trophic chains, and biomagnification of ACs through different entry route. These problems have been found in many countries around the globe, making them a worldwide concern. ACs have been found in different environmental matrices, such as water reservoirs for human consumption, wastewater treatment plants (WWTPs), drinking water treatment plants (DWTPs), groundwaters, surface waters, rivers, and seas, which demonstrate their free movement within the environment in an uncontrolled manner. This work provides a detailed overview of ACs occurrence in water bodies along with their toxicological effect on living organisms. The literature data reported between 2017 and 2018 is compiled following inclusion-exclusion criteria, and the obtained information was mapped as per type and source of ACs. The most important ACs are pharmaceuticals (diclofenac, ibuprofen, naproxen, ofloxacin, acetaminophen, progesterone ranitidine, and testosterone), agricultural products or pesticides (atrazine, carbendazim, fipronil), narcotics and illegal drugs (amphetamines, cocaine, and benzoylecgonine), food industry derivatives (bisphenol A, and caffeine), and personal care products (triclosan, and other related surfactants). Considering this threatening issue, robust detection and removal strategies must be considered in the design of WWTPs and DWTPs.

Urban environment and reservoir host species are associated with Batrachochytrium dendrobatidis infection prevalence in the common toad

Human-induced changes of the environment, including landscape alteration and habitat loss, may affect wildlife disease dynamics and have important ramifications for wildlife conservation. Amphibians are among the vertebrate taxa most threatened by anthropogenic habitat change. The emerging fungal pathogen Batrachochytrium dendrobatidis (Bd) has caused extinctions and population declines in hundreds of anuran species globally. We studied how the urban landscape is associated with the prevalence of Bd infections by sampling 655 anurans of 3 species (mainly the common toad Bufo bufo) in 42 ponds surrounded by different amounts of urban habitat (defined as towns, cities or villages). We also examined the association between Bd infections and a potential reservoir host species (the moor frog Rana arvalis). We found that 38% of the sites were positive for Bd with an infection prevalence of 4.4%. The extent of urban landscape was negatively correlated with Bd infection prevalence. However, the positive association of Bd with the presence of the possible reservoir species was substantially stronger than the urban effects. The body condition index of B. bufo was negatively associated with Bd infection. This Bd effect was stronger than the negative effect of urban landscape on body condition. Our results suggest that urban environments in Sweden have a negative impact on Bd infections, while the presence of the reservoir species has a positive impact on Bd prevalence. Our study also highlights the potential importance of Bd infection on host fitness, especially in rural landscapes.

Bioassay system for the detection of aryl hydrocarbon receptor agonists in waterborne pesticides using zebrafish cyp1a1 promoter-luciferase recombinant hepatic cells

Currently used pesticides are widely distributed in surface water. Most of them are harmful to aquatic animals. In the present study, a novel recombinant hepatic cell line was developed for detecting the activity of aryl hydrocarbon receptor (AhR) agonists, and their potential bio-toxicity to aquatic animals was evaluated. First, HepG2 cells were stably transfected with a luciferase reporter plasmid containing a zebrafish (Danio rerio) cyp1a1 promoter with twelve copies of dioxin-responsive elements. The minimal detection limit was a 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) concentration of 0.3 ng/L (equivalent to 0.93 pM). The AhR agonist activity of thirty-seven pesticides was screened by measuring luciferase expression in the recombinant cells. Four pesticides (ipconazole, mepanipyrim, quinoxyfen and pencycuron) significantly induced luciferase expression. Additionally, cells treated with these four pesticides increased the cyp1a1 mRNA expression level, which further confirmed that they are AhR agonists. In conclusion, for the first time, we developed recombinant hepatic cells with a luciferase reporter plasmid containing a modified zebrafish cyp1a1 promoter. The cyp1a1 promoter luciferase reporter cells can be used as a sensitive and specific model to screen AhR agonists among currently used pesticides in water, which could be beneficial for risk assessment in aquatic environments.

Insecticide pyriproxyfen (Dragón®) damage biotransformation, thyroid hormones, heart rate, and swimming performance of Odontophrynus americanus tadpoles

Odontoprynus americanus tadpoles were used to determine the safety concentration of pyriproxyfen (PPF) insecticide by acute and sublethal toxicity tests (nominal range tested 0.01 to 10 [± 15%] PPF mg/L). Median lethal concentration (LC₅₀) and no, and lowest-observed-effect concentrations (NOEC and LOEC, respectively) were calculated. We also assessed the effect on the activities of glutathione S-transferse (GST), acetylcholinesterase (AChE), and carboxylesterase (CbE) and compared to control (CO) tadpoles. Based on the 48-h NOEC value, two sublethal concentrations of PPF (0.01 and 0.1 mg/L) were assayed to detect effects on enzymes activities (GST and CbE), thyroid hormone's levels (triiodothyronine; T3 and thyroxine; T4), heart function, and tadpoles swimming behaviour. The results showed that the LC₅₀ values of O. americanus tadpoles were 3.73 PPF mg/L and 2.51 PPF mg/L at 24-h and 48-h, respectively (NOEC = 0.1 mg/L; LOEC = 1 mg/L, for both times). PPF concentrations at 48 h, induced enzymatic activities such as GST (212.98%-242.94%), AChE (142.15%-165.08%), and CbE (141.86%-87.14%) significantly respect to COs. During the 22 days of chronic PPF exposure, GST (0.01 mg/L 88%-153% NOEC), AChE (177.82% NOEC), and T4 (70% NOEC) also significantly increased respect to COs. Similarly, heart rate (fH) and ventricular cycle length (VV interval) in CO tadpoles were significantly higher than PPF treated. Finally, at NOEC tadpoles exhibited significant effects on the behavioral endpoint (swimming distance, mean speed, and global activity; P < 0.05).

Toads phenotypically adjust their chemical defences to anthropogenic habitat change

Despite the well-documented effects of human-induced environmental changes on the morphology, physiology, behaviour and life history of wild animals, next to nothing is known about how anthropogenic habitats influence anti-predatory chemical defence, a crucial fitness component of many species. We investigated the amount and composition of defensive toxins in adult common toads (Bufo bufo) captured in natural, agricultural and urban habitats, and in their offspring raised in a common-garden experiment. We found that, compared to toads captured from natural habitats, adults from both types of anthropogenic habitats had larger toxin glands (parotoids) and their toxin secretion contained higher concentrations of bufagenins, the more potent class of bufadienolide toxins. Furthermore, urban toads had lower concentrations of bufotoxins, the compounds with lower toxicity. None of these differences were present in the captive-raised juveniles; instead, toadlets originating from agricultural habitats had smaller parotoids and lower bufotoxin concentrations. These results suggest that toads' chemical defences respond to the challenges of anthropogenic environments via phenotypic plasticity. These responses may constitute non-adaptive consequences of pollution by endocrine-disrupting chemicals as well as adaptive adjustments to the altered predator assemblages of urban and agricultural habitats.