Wild Amphibian Populations Research Articles

Non-native Amphibian Pet Trade via Internet in Poland

Abstract Overharvesting and trade in amphibian populations is one of the causes of their global decline. Online trade not only encourages the exploitation of an increasing number of rare and endangered amphibian species from all over the world but also influences the spread of invasive species. The aim of our research was to investigate the amphibian pet trade conducted in online stores and portals in Poland and determine its potential impact on native species. Between November 2013 and October 2014, we regularly (on a monthly basis) checked sale offers on the websites of the 18 biggest pet shops in the country specialised in exotic animals, on a nationwide auction portal and on three exotic pet fan portals. During the study, we reported 486 offers of 112 amphibian species in online stores and on portals. Most of the offers involved one of the four families of amphibians: poison dart frogs (Dendrobatidae), tree frogs (Hylidae), true toads (Bufonidae) and true salamanders (Salamandridae). Our data show increased interest in amphibians as pets in Poland. At least half of the offered species are possible hosts for the chytrid fungus Batrachochytrium dendrobatidis. However, only one species, the American bullfrog Lithobates catesbeianus (Shaw, 1802), appears to be a potential invasive species. To summarise, the species offered in Poland that are characterised as threatened are predominantly those that are relatively easy to breed and that are popular as pets. Further studies are required to investigate the real threat to wild amphibian populations caused by the pet trade

Trends in US Imports of Amphibians in Light of the Potential Spread of Chytrid Fungus, Batrachochytrium dendrobatidis (Bd), and Implications for Conservation

ABSTRACTAmphibian populations around the world are declining in part due to diseases from infection with the chytrid fungi Batrachochytrium dendrobatidis (Bd) and Batrachochytrium salamandrivorans (Bs). While declines in more charismatic megafauna are common sources of public awareness and concern, such as the loss of elephants to poaching or polar bears to climate change, amphibians have been suffering a dramatic decline due to the outbreak of deadly fungal diseases with relatively little public attention. Various amphibian advocacy groups work to raise awareness of the issue, but given the limited funding and resources allocated to this cause, there remains a general lack of momentum to tackle the growing conservation threats to this group of animals and to examine policy weaknesses that may need to be adapted to help ensure their conservation. The international trade in live amphibians certainly contributes towards the global spread of these pathogens, but the true extent of spread remains unknown. To determine the degree to which the importation of amphibians into the United States was correlated with presence of known vectors of Bd spread, we compared US Fish and Wildlife Service wildlife trade records for all commercially traded live animals imported to the US from 2006 to 2014 against known species-level infection susceptibility. Approximately 26,859,034 live amphibians were imported into the US for commercial purposes between January 2006 and December 2014., Of these, 59.8% were specimens of species known to be susceptible to Bd infection and therefore may have introduced Bd into the country. Our findings demonstrate significant declines in the annual import quantities of 14 Bd-susceptible species between 2006 and 2014. These reductions could be due to a variety of factors, ranging from possible increased domestic production and a reduced need for foreign-sourced animals to reduced demand from changing market behaviors to the potential disease-driven decline of wild populations and greater difficulty in supplying these specimens. Our research supports the need for continued implementation of US policy, particularly the Lacey Act, to closely regulate wildlife imports to reduce the spread of highly virulent pathogens that threaten native species. Additionally, a rapid response mechanism is needed to control the introduction and spread of wildlife disease vectors when emergencies arise. Although the impact of the wildlife trade is just one facet of the overall amphibian conservation landscape, the information we present herein provides reason to develop increasingly robust rapid-response policies to protect wild amphibian populations in the midst of an emerging global disease crisis.

Antifungal treatment of wild amphibian populations caused a transient reduction in the prevalence of the fungal pathogen, Batrachochytrium dendrobatidis

Emerging infectious diseases can drive host populations to extinction and are a major driver of biodiversity loss. Controlling diseases and mitigating their impacts is therefore a priority for conservation science and practice. Chytridiomycosis is a devastating disease of amphibians that is caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), and for which there is an urgent need to develop mitigation methods. We treated tadpoles of the common midwife toad (Alytes obstetricans) with antifungal agents using a capture-treat-release approach in the field. Antifungal treatment during the spring reduced the prevalence of Bd in the cohort of tadpoles that had overwintered and reduced transmission of Bd from this cohort to the uninfected young-of-the-year cohort. Unfortunately, the mitigation was only transient, and the antifungal treatment was unable to prevent the rapid spread of Bd through the young-of-the year cohort. During the winter, Bd prevalence reached 100% in both the control and treated ponds. In the following spring, no effects of treatment were detectable anymore. We conclude that the sporadic application of antifungal agents in the present study was not sufficient for the long-term and large-scale control of Bd in this amphibian system.

Skin Bacterial Community Reorganization Following Metamorphosis of the Fire-Bellied Toad (Bombina orientalis).

In organisms with complex life histories, dramatic changes in microbial community structure may occur with host development and immune system maturation. Amphibian host susceptibility to diseases such as chytridiomycosis may be affected by the reorganization of skin microbial community structure that occurs during metamorphosis. We tracked changes in the bacterial communities inhabiting skin of Korean fire-bellied toads (Bombina orientalis) that we infected as tadpoles with different strains of Batrachochytrium dendrobatidis (Bd), the pathogenic fungus that causes chytridiomycosis. We found that B. orientalis undergoes a major change in skin bacterial community composition between 5 and 15days following metamorphosis. Richness indices and phylogenetic diversity measures began to diverge earlier, between aquatic and terrestrial stages. Our results further reveal differences in skin bacterial community composition among infection groups, suggesting that the effect of Bd infection on skin microbiome composition may differ by Bd strain. Additional studies are needed to further investigate the structural and temporal dynamics of microbiome shifts during metamorphosis in wild and captive amphibian populations. Analyses of the ontogeny of microbiome shifts may contribute to an understanding of why amphibians vary in their susceptibility to chytridiomycosis.

Frog and Toad Habitat Occupancy across a Polychlorinated Biphenyl (PCB) Contamination Gradient

Abstract A major challenge in amphibian ecotoxicology is understanding the population-level implications of laboratory-based, dose-response studies. We contrasted habitat occupancy among five species of frogs and toads in two adjacent segments of the upper Hudson River—one heavily contaminated by polychlorinated biphenyls (PCBs, compounds reported to have adverse impacts on individual amphibians) and the other uncontaminated—while controlling for site and sampling covariates. Site occupancy was estimated via repeated night call surveys at 40 wetland sites during 2006 and 2007. Habitat occupancy varied strongly in response to whether breeding sites were hydrologically connected to the Hudson River but was independent of the degree of PCB contamination of a given river segment. The results highlight the uncertainties of extrapolating outcomes of laboratory-based, toxicological studies to wild amphibian populations.

Amphibian trade and the presence of Batrachochytrium dendrobatidis in free-ranging: dispersion in vicious circle?

The amphibian trade has an important role in Batrachochytrium dendrobatidis (Bd) persistence, for at least 28 amphibian species can serve as vectors. The objectives of this work are to evaluate the presence and prevalence of Bd in amphibian traded in two petshops in Mexico City, as well as to verify their presence in wild amphibian populations of species traded. It was found that 92% of amphibians sold in the two petshops were captured free-living, and 37.3% of these animals were infected with Bd, according to histological analysis. The prevalence of 30.8% of Bd in wild amphibians at the wild capture sites was detected by means of DNA amplification. No significant differences were found between prevalence of wild and trade amphibians, but the trend was higher for trade amphibians. The importance of amphibian management and conservation plans has been growing in the last years. The pet trade and its capture from the wild turn these trade routes and their captive management into means of pathogenic dispersion, which may increase the risk of disease outbreaks.Keywords: Chytridiomycosis, pet trade, optical microscopy, nested PCR.

Mitigating amphibian chytridiomycoses in nature.

Amphibians across the planet face the threat of population decline and extirpation caused by the disease chytridiomycosis. Despite consensus that the fungal pathogens responsible for the disease are conservation issues, strategies to mitigate their impacts in the natural world are, at best, nascent. Reducing risk associated with the movement of amphibians, non-amphibian vectors and other sources of infection remains the first line of defence and a primary objective when mitigating the threat of disease in wildlife. Amphibian-associated chytridiomycete fungi and chytridiomycosis are already widespread, though, and we therefore focus on discussing options for mitigating the threats once disease emergence has occurred in wild amphibian populations. All strategies have shortcomings that need to be overcome before implementation, including stronger efforts towards understanding and addressing ethical and legal considerations. Even if these issues can be dealt with, all currently available approaches, or those under discussion, are unlikely to yield the desired conservation outcome of disease mitigation. The decision process for establishing mitigation strategies requires integrated thinking that assesses disease mitigation options critically and embeds them within more comprehensive strategies for the conservation of amphibian populations, communities and ecosystems.This article is part of the themed issue 'Tackling emerging fungal threats to animal health, food security and ecosystem resilience'.

Investigation of Amphibian Mortality Events in Wildlife Reveals an On-Going Ranavirus Epidemic in the North of the Netherlands.

In the four years following the first detection of ranavirus (genus Ranavirus, family Iridoviridae) infection in Dutch wildlife in 2010, amphibian mortality events were investigated nationwide to detect, characterize and map ranaviruses in amphibians over time, and to establish the affected host species and the clinico-pathological presentation of the disease in these hosts. The ultimate goal was to obtain more insight into ranavirus disease emergence and ecological risk. In total 155 dead amphibians from 52 sites were submitted between 2011 and 2014, and examined using histopathology, immunohistochemistry, virus isolation and molecular genetic characterization. Ranavirus-associated amphibian mortality events occurred at 18 sites (35%), initially only in proximity of the 2010 index site. Specimens belonging to approximately half of the native amphibian species were infected, including the threatened Pelobates fuscus (spadefoot toad). Clustered massive outbreaks involving dead adult specimens and ranavirus genomic identity indicated that one common midwife toad virus (CMTV)-like ranavirus strain is emerging in provinces in the north of the Netherlands. Modelling based on the spatiotemporal pattern of spread showed a high probability that this emerging virus will continue to be detected at new sites (the discrete reproductive power of this outbreak is 0.35). Phylogenetically distinct CMTV-like ranaviruses were found in the south of the Netherlands more recently. In addition to showing that CMTV-like ranaviruses threaten wild amphibian populations not only in Spain but also in the Netherlands, the current spread and risk of establishment reiterate that understanding the underlying causes of CMTV-like ranavirus emergence requires international attention.

Detection of Batrachochytrium dendrobatidis in Amphibians Imported into the UK for the Pet Trade.

There is increasing evidence that the global spread of the fungal pathogen Batrachochytrium dendrobatidis (Bd) has been facilitated by the international trade in amphibians. Bd was first detected in the UK in 2004, and has since been detected in multiple wild amphibian populations. Most amphibians imported into the UK for the pet trade from outside the European Union enter the country via Heathrow Animal Reception Centre (HARC), where Bd-positive animals have been previously detected. Data on the volume, diversity and origin of imported amphibians were collected for 59 consignments arriving at HARC between November 2009 and June 2012, along with a surveillance study to investigate the prevalence of Bd in these animals. Forty-three amphibian genera were recorded, originating from 12 countries. It was estimated that 5000-7000 amphibians are imported through HARC into the UK annually for the pet trade. Bd was detected in consignments from the USA and Tanzania, in six genera, resulting in an overall prevalence of 3.6%. This suggests that imported amphibians are a source of Bd within the international pet trade.

Malformations and body injuries in a hybrid zone of crested newts (Caudata: Salamandridae: Triturus cristatus superspecies)

Morphological abnormalities occur frequently in wild amphibian populations. We analysed malformation and injuries in the hybrid zone of three crested newt species, in the Czech Republic. In total, 274 individuals from 35 localities in South Moravia (Czech Republic) were examined during the period 2010-2014. Malformations were found in eight newts (2.9%) from seven localities. Injuries were recorded on 59 newts (21.5%). Proportions of tail crest injuries was significantly higher (P ˂ 0.1) in males than in females and the probability of being injured was significantly higher (P ˂ 0.01) for adult individuals. We discuss gene mutation, parasitism and predation as possible explanations for our observations.

Suburbanization, estrogen contamination, and sex ratio in wild amphibian populations

Research on endocrine disruption in frog populations, such as shifts in sex ratios and feminization of males, has predominantly focused on agricultural pesticides. Recent evidence suggests that suburban landscapes harbor amphibian populations exhibiting similar levels of endocrine disruption; however the endocrine disrupting chemical (EDC) sources are unknown. Here, we show that sex ratios of metamorphosing frogs become increasingly female-dominated along a suburbanization gradient. We further show that suburban ponds are frequently contaminated by the classical estrogen estrone and a variety of EDCs produced by plants (phytoestrogens), and that the diversity of organic EDCs is correlated with the extent of developed land use and cultivated lawn and gardens around a pond. Our work also raises the possibility that trace-element contamination associated with human land use around suburban ponds may be contributing to the estrogenic load within suburban freshwaters and constitutes another source of estrogenic exposure for wildlife. These data suggest novel, unexplored pathways of EDC contamination in human-altered environments. In particular, we propose that vegetation changes associated with suburban neighborhoods (e.g., from forests to lawns and ornamental plants) increase the distribution of phytoestrogens in surface waters. The result of frog sex ratios varying as a function of human land use implicates a role for environmental modulation of sexual differentiation in amphibians, which are assumed to only have genetic sex determination. Overall, we show that endocrine disruption is widespread in suburban frog populations and that the causes are likely diverse.

Correction: Rapid Response to Evaluate the Presence of Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) and Ranavirus in Wild Amphibian Populations in Madagascar.

Correction: Rapid Response to Evaluate the Presence of Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) and Ranavirus in Wild Amphibian Populations in Madagascar.

Chytridiomycosis in Amphibians

Chytridiomycosis is an emerging fungal disease caused by members of the genus Batrachochytrium. Batrachochytrium dendrobatidis has been implicated in declines in wild amphibian populations worldwide. The pathogen is able to infect various groups of amphibians, including anurans, urodeles, and caecilians. B. dendrobatidis is one of the most common pathogens related to diseases in captive amphibian collections. A second species—Batrachochytrium salamandrivorans—was recently described as a threat for European salamanders, and appears to have originated in Asia where it is prevalent in Asian urodeles. This article presents an overview on the biology of these panzootic fungi, including pathology, diagnosis, and possible protocols for treatment and ecological aspects as well.

Do hormone-modulating chemicals impact on reproduction and development of wild amphibians?

Globally, amphibians are undergoing a precipitous decline. At the last estimate in 2004, 32% of the approximately 6000 species were threatened with extinction and 43% were experiencing significant declines. These declines have been linked with a wide range of environmental pressures from habitat loss to climate change, disease and pollution. This review evaluates the evidence that endocrine-disrupting contaminants (EDCs) - pollutants that affect hormone systems - are impacting on wild amphibians and contributing to population declines. The review is limited to anurans (frogs and toads) as data for effects of EDCs on wild urodeles (salamanders, newts) or caecilians (limbless amphibians) are extremely limited. Evidence from laboratory studies has shown that a wide range of chemicals have the ability to alter hormone systems and affect reproductive development and function in anurans, but for the most part only at concentrations exceeding those normally found in natural environments. Exceptions can be found for exposures to the herbicide atrazine and polychlorinated biphenyls in leopard frogs (Rana pipiens) and perchlorate in African clawed frogs (Xenopus laevis). These contaminants induce feminising effects on the male gonads (including 'intersex' - oocytes within testes) at concentrations measured in some aquatic environments. The most extensive data for effects of an EDC in wild amphibian populations are for feminising effects of atrazine on male gonad development in regions across the USA. Even where strong evidence has been provided for feminising effects of EDCs, however, the possible impact of these effects on fertility and breeding outcome has not been established, making inference for effects on populations difficult. Laboratory studies have shown that various chemicals, including perchlorate, polychlorinated biphenyls and bromodiphenylethers, also act as endocrine disrupters through interfering with thyroid-dependent processes that are fundamental for amphibian metamorphosis. Perchlorate has also been shown to induce these effects in wild anuran populations from perchlorate-contaminated environments. Overall, the published data available suggest that some health effects observed in wild anuran populations, most notably intersex, likely have a chemical aetiology; however they derive only from very few anuran species and for a few pesticides at field sites in the USA. To understand better the impacts of EDCs on wild anuran populations, as well as other amphibian groups, assessment of fertility in exposed animals are required. Development of non-destructive biomarkers that are indicative of specific EDC-effect mechanisms are also needed to allow the study of vulnerable populations. This will help to distinguish the effects of EDCs from other environmental and/or genetic influences on development and reproduction.

Batrachochytrium dendrobatidis detected in Kihansi spray toads at a captive breeding facility (Kihansi, Tanzania).

The chytrid fungus Batrachochytrium dendrobatidis (Bd) is the aetiological agent of amphibian chytridiomycosis, a disease associated with global amphibian population declines. In November 2012, mass mortalities of Kihansi spray toads Nectophrynoides asperginis were observed at the Kihansi captive breeding facility, located in the Udzungwa Mountains, Tanzania. Mortalities increased rapidly, and dead toads showed typical clinical signs of chytridiomycosis, including reddening of the skin that was especially evident on the toe pads. Treatment of toads with itraconazole rapidly reduced mortalities. Dead toads (n = 49) were collected and used to perform Bd-specific polymerase chain reaction and subsequent nucleotide sequencing. All toads collected at the facility were positive for Bd. The obtained Bd 5.8S rRNA gene and flanking internal transcribed spacer regions (ITS1 and ITS2) were not 100% identical to any other Bd sequences in GenBank, but closely resembled isolates from Ecuador, Japan, USA, Brazil, Korea, and South Africa. To our knowledge, this is the first study reporting molecular characteristics of Bd isolated from the Udzungwa Mountains. Strict biosecurity measures at the breeding facility and in Kihansi spray wetlands where toads have been reintroduced have been implemented. Further studies on Bd epidemiology in the Udzungwa Mountains are recommended in order to understand its origin, prevalence, and molecular characteristics in wild amphibian populations. This will be important for conservation of several endemic amphibian species in the Udzungwa Mountains, which are part of the Eastern Arc Mountains, a global biodiversity hotspot.

Amphibian intersex in suburban landscapes

Within the last decade, reproductive abnormalities have been discovered in wild amphibian populations of multiple species and in a variety of regions in North America. Predominantly, these field studies have focused on agricultural landscapes. In this study, we worked in suburban environments based on preliminary evidence showing that amphibian populations can display surprisingly high frequencies of reproductive deformities, including intersex traits. Here, we report results from 28 suburban ponds located near onsite septic systems as well as those located in sewered neighborhoods. Caffeine, an indicator of domestic wastewater contamination, was detected in more than 70% of all ponds; prevalence of contamination was indistinguishable for ponds in sewered neighborhoods and those served by onsite septic systems. Among green frogs (Rana (=Lithobates) clamitans) collected from the same ponds, intersex was detected in each population; on average, one male in five showed evidence of intersex. This frequency was insensitive to wastewater treatment mode. Given prior findings that intersex is absent or rare in less developed landscapes, our results suggest that domestic wastewater contamination in suburban contexts may be more widespread than is generally appreciated and should be investigated as a contributor to intersex in wild amphibians. This hypothesis is consistent with abundant prior research on wild riverine and estuarine fish populations associating reproductive deformities with wastewater exposure.

Fish and amphibians as potential reservoirs of Mycobacterium ulcerans, the causative agent of Buruli ulcer disease

Background: Buruli ulcer is a skin disease often associated with proximity to certain water bodies in Africa. Much remains unknown about the reservoir and transmission of this disease. Previous studies have suggested that fish may concentrate Mycobacterium ulcerans, the etiological agent of the disease, in their gills and intestines and serve as passive reservoirs of the bacterium. The objective of this study was to test the hypothesis that fish and amphibians serve as natural reservoirs of M. ulcerans or other closely related mycolactone-producing mycobacteria.Methods: Polymerase chain reaction targeting the enoyl reductase (ER) domain present in mlsA, which is required for mycolactone production, was used to screen water, fish, and amphibians from water bodies in Ghana for the presence of mycolactone-producing mycobacteria, and positive specimens were subjected to variable number tandem repeat (VNTR) typing.Results: The use of VNTR typing revealed the presence of Mycobacterium liflandii in a tadpole and a fish, and M. ulcerans in an adult frog. Similarity percentage analysis (SIMPER) showed that the predatory cichlid Hemichromis bimaculatus was associated with ER-positive water bodies. No amphibian species or fish-feeding guild served as a reliable indicator of the presence of mycolactone-producing mycobacteria in a water body, and there was no significant difference between fish and amphibian positivity rates (P-value=0.106). There was a significant difference between water bodies in the total number of ER-positive specimens (P-value=0.0164).Conclusions: Although IS2404-positive tadpoles and fish have been reported, this is the first VNTR confirmation of M. ulcerans or M. liflandii in wild amphibian and fish populations in West Africa. Results from this study suggest that amphibians should be carefully examined as potential reservoirs for M. ulcerans in West Africa, and that H. bimaculatus may be useful as an indicator of habitats likely to support mycolactone-producing mycobacteria.

Effects of Rotenone on Columbia Spotted Frogs Rana luteiventris during Field Applications in Lentic Habitats of Southwestern Montana

AbstractFisheries managers are restoring native populations by removing nonnative fishes worldwide. Increasingly, the piscicide rotenone is used to accomplish this. Fish introductions and removals change the aquatic environment, and it is important to consider the impacts of these actions on nontarget species, including amphibians. Laboratory experiments have shown that rotenone can negatively affect tadpoles. We therefore assessed the effects of rotenone used on two wild amphibian populations. The commercial piscicide formulation CFT Legumine (5% rotenone) was applied at 1 mg/L (50 μg/L rotenone) to a lake containing nonnative trout in Yellowstone National Park (YNP) in 2006 and two fishless wetlands on private lands in southwestern Montana in 2008. Amphibian surveys were conducted immediately prior to and after the rotenone treatments to obtain tadpole population estimates. Follow‐up surveys were conducted 1 year posttreatment to estimate tadpole recovery. In YNP, additional surveys were conducted 2 and 3 years postapplication to observe longer‐term effects of fish removal and the subsequent introduction of native fish. Within 24 h following application of rotenone, there was 100% mortality in gill‐breathing tadpoles, but nongill‐breathing metamorphs, juveniles, and adults were apparently unaffected. In the years following, tadpoles repopulated all waters and population levels were similar to, or, in the case of YNP because of concurrent fish removal, higher than pretreatment levels. In YNP, tadpole abundance and distribution decreased after westslope cutthroat trout Oncorhynchus clarkii lewisi were stocked in the treated lake.Received October 22, 2011; accepted May 4, 2012

Pathophysiology in mountain yellow-legged frogs (Rana muscosa) during a chytridiomycosis outbreak.

The disease chytridiomycosis is responsible for declines and extirpations of amphibians worldwide. Chytridiomycosis is caused by a fungal pathogen (Batrachochytrium dendrobatidis) that infects amphibian skin. Although we have a basic understanding of the pathophysiology from laboratory experiments, many mechanistic details remain unresolved and it is unknown if disease development is similar in wild amphibian populations. To gain a better understanding of chytridiomycosis pathophysiology in wild amphibian populations, we collected blood biochemistry measurements during an outbreak in mountain yellow-legged frogs (Rana muscosa) in the Sierra Nevada Mountains of California. We found that pathogen load is associated with disruptions in fluid and electrolyte balance, yet is not associated with fluctuations acid-base balance. These findings enhance our knowledge of the pathophysiology of this disease and indicate that disease development is consistent across multiple species and in both laboratory and natural conditions. We recommend integrating an understanding of chytridiomycosis pathophysiology with mitigation practices to improve amphibian conservation.

Disrupted Oogenesis in the Frog Xenopus tropicalis after Exposure to Environmental Progestin Concentrations1

Levonorgestrel is a synthetic progesterone commonly used in pharmaceuticals (e.g., in contraceptives). It is found in sewage treatment plant effluents at concentrations up to 30 ng/L and was recently shown to pose a threat to egg laying in fish. Information on the susceptibility of adult amphibians to progestin toxicity is lacking. The present study aimed to 1) characterize progestogenic effects on the full cycle of oogenesis (egg development) in frogs and 2) determine female amphibians' susceptibility to reproductive impacts from progestogenic compounds in the environment. Sexually mature female Xenopus tropicalis were exposed to levonorgestrel via the surrounding water for 7 days (0, 51, or 307 ng/L) or 28 days (0, 1.3, 18, 160, or 1240 ng/L). Their ovaries were analyzed histologically with respect to frequencies of immature (in early meiotic prophase I), previtellogenic, vitellogenic, mature, and atretic oocytes. The 28-day exposure caused reduced proportions of oocytes at immature, vitellogenic, and mature stages, and increased proportions of previtellogenic oocytes compared with the control. The lowest tested concentration, 1.3 ng/L, increased the proportions of previtellogenic oocytes and reduced the proportions of vitellogenic oocytes, indicating inhibited vitellogenesis. The present study shows that progestin concentrations found in the aquatic environment impaired oogenesis in adult frogs. Our results indicate that progestogenic effects on oocyte development include interrupted germ cell progression into meiosis and inhibited vitellogenesis. Considering the crucial role of oogenesis in female fertility, our results indicate that progestogenic pollutants may pose a threat to reproduction in wild amphibian populations.