Amphibian Declines Research Articles

Populations, pools, and peccaries: simulating the impact of ecosystem engineers on rainforest frogs.

"Ecosystem engineering" describes habitat alteration by an organism that affects another organism; such nontrophic interactions between organisms are a current focus in ecological research. Our study quantifies the actual impact an ecosystem engineer can have on another species by using a previously identified model system-peccaries and rainforest frogs. In a 4-year experiment, we simulated the impact of peccaries on a population of Allobates femoralis (Dendrobatidae) by installing an array of artificial pools to mimic a forest patch modified by peccaries. The data were analyzed using a gradual before-after control-impact (gBACI) model. Following the supplementation, population size almost doubled as a result of increased autochthonous recruitment driven by a higher per-capita reproduction of males and a higher proportion of reproducing females. The effect was evenly distributed across the population. The differential response of males and females reflects the reproductive behavior of A. femoralis, as only the males use the aquatic sites for tadpole deposition. Our study shows that management and conservation must consider nontrophic relationships and that human "ecosystem engineering" can play a vital role in efforts against the "global amphibian decline."

Batrachochytrium dendrobatidis in natural and farmed Louisiana crayfish populations: prevalence and implications.

The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) has been linked to global declines and extinctions of amphibians, making it one of the most devastating wildlife pathogens known. Understanding the factors that affect disease dynamics in this system is critical for mitigating infection and protecting threatened species. Crayfish are hosts of this pathogen and can transmit Bd to amphibians. Because they co-occur with susceptible amphibian communities, crayfish may be important alternative hosts for Bd. Understanding the prevalence and seasonal dynamics of crayfish infections is of agricultural and ecological interest in areas where crayfish are farmed and traded for human consumption. We conducted a survey of Bd in farmed and natural crayfish (Procambarus spp.) populations in Louisiana, USA. We found that Bd prevalence and infection intensity was low in both farmed and native populations and that prevalence varied seasonally in wild Louisiana crayfish. This seasonal pattern mirrors that seen in local amphibians. As crayfish are an important globally traded freshwater taxon, even with low prevalence, they could be an important vector in the spread of Bd.

Optimization, validation and efficacy of the phytohaemagglutinin inflammation assay for use in ecoimmunological studies of amphibians.

The global amphibian biodiversity crisis is driven by disease, habitat destruction and drastically altered ecosystems. It has given rise to an unprecedented need to understand the link between rapidly changing environments, immunocompetence and wildlife health (the nascent field of ecoimmunology). Increasing our knowledge of the ecoimmunology of amphibians necessitates the development of reliable, field-applicable methods of assessing immunocompetence in non-model species. The phytohaemagglutinin (PHA) inflammation assay uses a lectin to elicit localized inflammation that reflects an organism's capacity to mount an immune response. Although extensively used in birds to assess responses to environmental change, stress and disease, its application in amphibians has been extremely limited. We developed, validated and optimized a practical and effective phytohaemagglutinin inflammation assay in phylogenetically distant amphibians and demonstrated its suitability for use in a wide range of ecoimmunological studies. The protocol was effective for all species tested and worked equally well for both sexes and for adult and sub-adult animals. We determined that using set-force-measuring instruments resulted in a 'compression effect' that countered the inflammatory response, reinforcing the need for internal controls. We developed a novel method to determine peak response times more accurately and thereby improve assay sensitivity. Histological validation demonstrated considerable interspecies variation in the robustness of amphibian immune defences. Importantly, we applied the assay to a real-world scenario of varying environmental conditions and proved that the assay effectively detected differences in immune fitness between groups of animals exposed to ecologically meaningful levels of density stress. This provided strong evidence that one cost of metamorphic plasticity responses by tadpoles to increasing density is a reduction in post-metamorphic immune fitness and that metamorphosis does not prevent phenotypic carry-over of larval stress to the adult phenotype. This assay provides an effective tool for understanding the role of global environmental change in the amphibian extinction crisis.

Population stability in the endangered Fleay’s barred frog (Mixophyes fleayi) and a program for long-term monitoring

In the wake of the global decline in amphibians there is a need for long-term population monitoring. Previous research suggested that the endangered Fleay’s barred frog (Mixophyes fleayi) had recovered after a severe decline. We aimed to determine whether this recovery has been sustained and to test an example of a monitoring program that could be employed at intervals of five or more years to assess long-term population stability. We conducted capture–mark–recapture five years after the last detailed census at Brindle Creek in Border Ranges National Park, New South Wales. Frogs were captured along a 200 m creek transect between September 2013 and February 2014. We used program Mark to estimate demographic parameters of adult male frogs using two modelling approaches: robust design (RD) and the POPAN formulation of the Jolly–Seber model. Abundance was estimated at 38.2 ± 0.5 (s.e.) (RD) and 46.0 ± 2.7 (POPAN). Abundance in 2008 was estimated at 53.2 ± 10.0 (POPAN) male frogs. Estimates of apparent monthly survival over our five-month-long study were very high (RD: 1.0 ± 0.0; POPAN: 1.0 ± 0.02). Recapture estimates were also high (RD: 0.40 ± 0.07 to 0.72 ± 0.05 per session; POPAN: 0.84 ± 0.05 per month). These data suggest that the Brindle Creek population has remained relatively stable over a period of ~10 years.

Low humidity is a failed treatment option for chytridiomycosis in the critically endangered southern corroboree frog

Context One of the major drivers of the current worldwide amphibian decline and extinction crisis is the spread of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). Captive assurance colonies may be the only lifeline for some species. Current antifungal chemotherapies can be effective for clearing infection but may have detrimental side effects. The only non-chemotherapeutic treatment that has been clinically tested is heat, which is impractical for cold-adapted species. The fungus does not survive desiccation, and therefore a plausible alternative non-chemotherapeutic treatment would be a low-humidity regimen. Aims We tested the efficacy of a low-humidity treatment regimen for treating Bd-infected animals of the critically endangered species Pseudophryne corroboree. This species has high tolerance of dry environments, and is thus an ideal candidate for this treatment trial. Methods Forty frogs were exposed to 1 × 106 zoospores. At three weeks after exposure access to water was reduced to once daily for 10 days for 20 animals. Ten of these animals were also rinsed daily with the aim of removing zoospores. Key results The drying regimen neither increased survival nor decreased infection load, and treatment may have hastened mortality. All infected frogs died between 21 and 80 days after exposure, except one untreated frog. Conclusions Our results suggest that a drying regimen is not a viable treatment for chytridiomycosis. Infection may decrease the host’s ability to cope with water stress. Implications The failed drying treatment in P. corroboree suggests that drying is not an appropriate treatment for chytridiomycosis and treatment efforts should be focussed on chemotherapies for cold-adapted species. P. corroboree is a critically endangered species for which chytridiomycosis is the primary cause of decline, yet few experiments have been carried out on this species with regards to chytridiomycosis. All experimental information about this species and disease will benefit the management and protection of the species.

Long‐term changes in structure and function of a tropical headwater stream following a disease‐driven amphibian decline

Summary Taxonomic and functional diversity in freshwater habitats is rapidly declining, but we know little about how such declines will ultimately affect ecosystems. Neotropical streams are currently experiencing massive losses of amphibians, with many losses linked to the chytrid fungus, Batrachochytrium dendrobatidis (Bd). We examined the ecological consequences of the disease‐driven loss of amphibians from a Panamanian stream. We quantified basal resources, macroinvertebrates, N uptake and fluxes through food‐web components and ecosystem metabolism in 2012 and 2014 and compared them to pre‐decline (2006) and 2 year post‐decline (2008) values from a prior study. Epilithon biomass accrued after the decline, more than doubling between 2006 and 2012, but then decreased fivefold from 2012 to 2014. In contrast, suspended particulate organic matter (SPOM) concentrations declined continuously after the amphibian decline through 2014. Biomass of filter‐feeding, grazing and shredding macroinvertebrates decreased from 2006 to 2014, while collector–gatherers increased during the same time period. Macroinvertebrate taxa richness decreased from 2006 (52 taxa) to 2012 (30 taxa), with a subsequent increase to 51 taxa in 2014. Community respiration, which initially decreased after the amphibian decline, remained lower than pre‐decline in 2012 but was greater than pre‐decline values in 2014. Gross primary production remained low and similar among years, while uptake length in both 2012 and 2014 was longer than pre‐decline. Nitrogen flux to epilithon increased after the decline and continued to do so through 2014, but N fluxes to fine particulate organic matter and SPOM decreased and remained low. Our findings underscore the importance of studying the ecological consequences of declining biodiversity in natural systems over relatively long time periods. There was no evidence of functional redundancy or compensation by other taxa after the loss of amphibians, even after 8 years.

Assessing atrazine-induced toxicities in Bufo bufo gargarizans Cantor.

Atrazine (AZ), a widely used herbicide has drawn attentions for its potential impacts on amphibians. This study aims to investigate the toxicity of AZ in Bufo bufo gargarizans Cantor (B. bufo gargarizans), a species of toad commonly found in China and countries in East Asia. We treated tadpoles with 0.1, 1, 10 and 100μg/L AZ for 85days and examined related parameters. The results showed that the mortality of the toads in the treatment group increased dramatically in a U-shaped dose-response relationship. The hindlimb extension and metamorphosis rate of the toads were significantly inhibited by AZ at 10 and 100μg/L. Under the same condition, there were significant progressive changes in the testicular structures. Moreover, we found that AZ has no significant effects on growth, sex ratios, gonadal morphology, forelimb emergence and histology in the ovaries. Our results support the idea that environmental contaminants including AZ may be relevant to global amphibian decline.

Correlates of virulence in a frog-killing fungal pathogen: evidence from a California amphibian decline.

The fungal pathogen Batrachochytrium dendrobatidis (Bd) has caused declines and extinctions in amphibians worldwide, and there is increasing evidence that some strains of this pathogen are more virulent than others. While a number of putative virulence factors have been identified, few studies link these factors to specific epizootic events. We documented a dramatic decline in juvenile frogs in a Bd-infected population of Cascades frogs (Rana cascadae) in the mountains of northern California and used a laboratory experiment to show that Bd isolated in the midst of this decline induced higher mortality than Bd isolated from a more stable population of the same species of frog. This highly virulent Bd isolate was more toxic to immune cells and attained higher density in liquid culture than comparable isolates. Genomic analyses revealed that this isolate is nested within the global panzootic lineage and exhibited unusual genomic patterns, including increased copy numbers of many chromosomal segments. This study integrates data from multiple sources to suggest specific phenotypic and genomic characteristics of the pathogen that may be linked to disease-related declines.

Rediscovery of the Critically Endangered Streamside Frog, Craugastor Taurus (Craugastoridae), in Costa Rica

In 1987 the amphibian decline crisis reached its apex in Costa Rica when at least 17 species experienced population crashes and subsequently went undetected for decades. The amphibian declines in Costa Rica were relatively well documented and came to exemplify the current global amphibian decline crisis. The Mesoamerica endemic frog clade, the Craugastor punctariolus species group, is one of most severely affected anuran clades, experiencing a loss of 26 out of 33 species throughout Mesoamerica. Eight species of C. punctariolus group frogs occur in Costa Rica, and all declined following the 1987 die-off; despite intensive surveys over the last 14 years, most remain undetected. To date, only one species in this group, the stream-breeding frog C. ranoides, in known to have a stable population, and only in the Santa Elena Peninsula. Here we document the rediscovery of another species, the South Pacific streamside frog C. taurus, in southeastern Costa Rica, representing the first sighting after fifteen years of searching. We discovered two previously unknown populations in Punta Banco, the driest section within the historical range, in an area representing only 4% of the historical distribution. Our findings add to the short but growing list of recently rediscovered amphibian species in Costa Rica and provide encouraging news in an otherwise discouraging situation for amphibian conservation. Additional research and monitoring are urgently needed to develop long-term management plans for this and other Critically Endangered species

New information on molecular features of the dengue virus type 3, panorama of the amphibian research in Brazil, and a new extinct Cretaceous angiosperm

This last issue of the Annals of the Brazilian Academy of Sciences (AABC) contains 50 papers on a great variety of subjects, making it very hard to select those that should be highlighted in the present editorial note. This is also a result of the increasing excellence of the manuscripts that are being submitted to this journal, a developing trend in the last decade.Among the most important contributions of this issue is the paper by Jefferson J. S. Santos (FIOCRUZ, Rio de Janeiro) and collaborators that unravels new molecular aspects of the dengue virus 3 (Santos et al. 2014). That dengue viral infection is a big problem in several countries is nothing new these days. Estimates of humans that are being affected by this disease are in the millions (e.g., Kyle and Harris 2008). Therefore, several researchers are dedicating their efforts in developing new ways on how to deal with this serious health issue, ranging from studies on potential new insecticides (e.g., Oliveira et al. 2013) to a better understanding of molecular mechanisms that ultimately might lead to the development of vaccines (e.g., Blaney et al. 2004). Here, Santos and colleagues have reported a successful way to create a dengue virus 3 (DENV3) and indicate a way on how to overcome the genome instability inherent to flaviviruses (e.g., Polo et al. 1997).Over the last decades, zoologists have observed that amphibian populations are declining worldwide. Despite the fact that in several instances it is not clear which are the exact causes for this decline, there is a consensus that the main factor is related to alterations of habitats (e.g., Beebee and Griffiths 2005). This is also the case in Brazil, although researchers agree that there is a general lack of knowledge regarding several aspects of those vertebrates found in the country, including geographic ranges and population status (e.g., Pimenta et al. 2005, Pirani et al. 2013). In a thorough review of the literature published from 2001 to 2010, Felipe S. Campos (Universidade Estadual de Santa Cruz, Bahia) and colleagues have provided a panorama of the amphibian studies in Brazil (Campos et al. 2014). One of the conclusions reached by those authors is that the threat regarding amphibian extinctions in the country is underestimated due to the lack of knowledge that affects at least 25% of the known species diversity. They have also identified biases regarding research efforts, including the lack of studies about the conservation of amphibians, which is hampering the development of more effective ways to protect some critical habitats that might avoid the extinction of several endangered species.

C-1013: Cryopreservation of spermic milt in the model species Ambystoma tigrinum (Tiger salamander) for application in endangered salamanders

In the face of the amphibian extinction crisis, captive assurance colonies have been established to preserve genetic diversity. Sadly, many captive assurance colonies fail due to reproductive cues which are not entirely understood. In addition, the majority of amphibian conservation and genome banking research has focused on anurans (frogs/toads), despite the fact that caudates (salamanders/newts) face a larger threat of extinction. Therefore, it is critical that assisted reproductive technologies, such as gamete cryopreservation and artificial fertilization, be developed as conservation tools for application in genetic management of threatened caudates. It was hypothesized that a modified anuran sperm freezing protocol could be successfully used in cryopreservation of Ambystoma tigrinum (tiger salamander) sperm as a caudate model. Spermiation in male tiger salamanders was hormonally induced via injection with hCG, LHRH, or a combination of these two hormones. Average spermic milt concentrations were 2.75 × 107(±7.2 × 106)/mL. Average total motility upon collection of fresh milt was 53.6% (±17.6%). After collection and initial analysis, fresh milt samples were diluted 1:1 in chilled cryoprotectant treatment solutions. They were then frozen in 0.25 mL French straws using a stepwise slow-rate freezing process. Upon thawing, milt suspensions were diluted 1:10 with a 10% Holtfreter’s solution in order to activate the sperm for post thaw analysis. Frozen-thawed sperm in the 5% Me2SO treatment group had an average total motility of 19.1% (±15.8%) and sperm in the 5% Me2SO with 0.5% BSA treatment group had an average total motility of 21.75% (±14.8%). Early trials showed that caudate sperm are not susceptible to toxicity from several cryoprotective media. Moreover, initial fertilization trials indicate that frozen-thawed caudate sperm are capable of producing early cleavage stage embryos. Optimizing cryopreservation protocols for salamander sperm is an important step in building a global genetic resource bank for endangered caudates.

Environmental and Anthropogenic Factors Influencing Salamanders in Riparian Forests: A Review

Salamanders and riparian forests are intimately interconnected. Salamanders are integral to ecosystem functions, contributing to vertebrate biomass and complex food webs in riparian forests. In turn, these forests are critical ecosystems that perform many environmental services, facilitate high biodiversity and species richness, and provide habitat to salamander populations. Due to the global decline of amphibians, it is important to understand, as thoroughly and holistically as possible, the roles of environmental parameters and the impact of human activities on salamander abundance and diversity in riparian forests. To determine the population responses of salamanders to a variety of environmental factors and anthropogenic activities, we conducted a review of published literature that compared salamander abundance and diversity, and then summarized and synthesized the data into general patterns. We identify stream quality, leaf litter and woody debris, riparian buffer width, and soil characteristics as major environmental factors influencing salamander populations in riparian forests, describe and explain salamander responses to those factors, and discuss the effects of anthropogenic activities such as timber harvest, prescribed fires, urbanization, road construction, and habitat fragmentation. This review can assist land and natural resource managers in anticipating the consequences of human activities and preparing strategic conservation plans.

Anuran Species Composition of an Impacted Seasonal Lake in Sapele, Delta State, Nigeria.

Studies on anuran diversity in Lake Akapankpan, a seasonal Lake in Sapele, Delta State was carried out between May and October 2011. Human activities around the Lake included its use as a dumpsite and as a receptor for run-offs from mechanic activities located some few metres from it. Six anuran species which included Hoplobatrachus occipitalis, Ptychadena bibroni, P. pumilio, P. mascareniensis, Amietophyrnus (Bufo)maculatus and Afrixalus dorsalis were recorded from the Lake. Ptychadena pumilio was the most abundant species (49%) while Afrixalus dorsalis and Hoplobatrachus occipitalis were least (4%). Species diversity was low (Hꞌ = 1.37). Physico-chemical parameters of the water showed iron to be high (P<0.05). Statistical analysis was done using the one sample test. Although there are no baseline studies on the Lake, studies on similar ecological areas in Sapele showed a higher diversity (Hꞌ = 1.70). Silurana tropicalis, a completely aquatic species commonly found in waters was absent while another aquatic species Hoplobatrachus occipitalis commonly recorded in high numbers in waters recorded only 4%. There is a possibility that the low species diversity recorded could be due to the impact of human activities around the Lake. The need to minimize human activities around water bodies is highly recommended to reduce species loss and ultimately, amphibian decline.Keywords: anuran diversity, impacted seasonal Lake, species loss, amphibian decline

Meeting ultraviolet B radiation requirements of amphibians in captivity: a case study with mountain chicken frogs (Leptodactylus fallax) and general recommendations for pre-release health screening.

Conservation breeding programmes are a tool used to prevent amphibian extinctions. The husbandry requirements of amphibians are complex. Ongoing research is needed to ensure optimal management of those captive-bred animals destined, in particular, for reintroduction. The UV-B and vitamin D3 requirements of amphibians are largely unknown. Metabolic bone disease has been reported in a number of species. These include the Critically Endangered mountain chicken frog (Leptodactylus fallax) reared in captivity on diets supplemented with a high-calcium multivitamin and mineral supplement containing vitamin D3 but without UV-B provision. Captive-bred L. fallax being reared for reintroduction to Montserrat were provided with UV-B radiation from metamorphosis and were fed on insects supplemented with vitamins and minerals. Overlapping heat, light and UV-B gradients were provided, mimicking what we believe best represents the natural situation and thereby facilitated self-regulation of UV-B exposure. A subset of 10 frogs was periodically radiographed to assess skeletal health. Radiographic bone density and anatomical integrity appeared unremarkable when compared with a wild caught L. fallax. In addition to other routine health-screening, we recommend that radiography be performed to a structured schedule on a subset of all captive-bred and reared amphibians to assess skeletal health and to gauge the appropriateness of captive husbandry. We demonstrate here that, through the appropriate provision of a combination of both UV-B radiation and dietary supplementation, L. fallax can be bred and reared in captivity with healthy skeletal development.

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

Habitat loss and exposure to pesticides are likely primary factors contributing to amphibian decline in agricultural landscapes. Conservation efforts have attempted to restore wetlands lost through landscape modifications to reduce contaminant loads in surface waters and providing quality habitat to wildlife. The benefits of this increased wetland area, perhaps especially for amphibians, may be negated if habitat quality is insufficient to support persistent populations. We examined the presence of pesticides and nutrients in water and sediment as indicators of habitat quality and assessed the bioaccumulation of pesticides in the tissue of two native amphibian species Pseudacris maculata (chorus frogs) and Lithobates pipiens (leopard frogs) at six wetlands (3 restored and 3 reference) in Iowa, USA. Restored wetlands are positioned on the landscape to receive subsurface tile drainage water while reference wetlands receive water from overland run-off and shallow groundwater sources. Concentrations of the pesticides frequently detected in water and sediment samples were not different between wetland types. The median concentration of atrazine in surface water was 0.2μg/L. Reproductive abnormalities in leopard frogs have been observed in other studies at these concentrations. Nutrient concentrations were higher in the restored wetlands but lower than concentrations thought lethal to frogs. Complex mixtures of pesticides including up to 8 fungicides, some previously unreported in tissue, were detected with concentrations ranging from 0.08 to 1500μg/kg wet weight. No significant differences in pesticide concentrations were observed between species, although concentrations tended to be higher in leopard frogs compared to chorus frogs, possibly because of differences in life histories. Our results provide information on habitat quality in restored wetlands that will assist state and federal agencies, landowners, and resource managers in identifying and implementing conservation and management actions for these and similar wetlands in agriculturally dominated landscapes.

Batrachochytrium dendrobatidis infection dynamics vary seasonally in upstate New York, USA.

The amphibian disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), is a major cause of worldwide amphibian declines and extinctions. Although several studies indicate that Bd prevalence and infection intensity vary seasonally, temporal variation of Bd at high-latitude sites, such as the northeastern USA, is still poorly characterized. We screened amphibians for Bd monthly at 2 study sites in New York State from April to October 2011 and used quantitative polymerase chain reaction (qPCR) to detect and quantify temporal variability in Bd infection prevalence and intensity. We found pronounced seasonal variation in both Bd infection prevalence and intensity at the community level, and our data indicate that this pattern is due to a few species (Lithobates catesbeianus, L. clamitans, and Notophthalmus viridescens) that drive temporal variability in disease dynamics. Amphibian body mass and sex were significant predictors of infection intensity but not infection prevalence. Understanding the temporal dynamics of Bd host-pathogen interactions provides important insight into regional, seasonal, and host-specific determinants of disease outbreaks. Further, our study elucidates the most relevant and informative timing for Bd surveys in temperate amphibian assemblages. Seasonal variation of infection dynamics suggests that Bd surveys from different sampling time points are not comparable, and summer surveys to evaluate chytridiomycosis may significantly underestimate Bd prevalence and intensity, leading to false conclusions about the severity of chytridiomycosis-induced amphibian mortality and population decline.

Water quality of urban water bodies – a threat for amphibians?

Most studies on the effects of water quality on amphibians concern experimental conditions. The main aim of our study was to determine whether the quality of water bodies in urban environment may be a factor leading to local extinction of some amphibian species. We investigated the current amphibian richness in Krakow water bodies and the water quality of these water bodies. We compared our results with available historical data on amphibian richness in Krakow and we determined the number of amphibian species local extinction for each water body. Then, we compared water bodies with low amphibian extinction rates to water bodies with high amphibian extinction rates in respect to ten water quality chemical indicators. We found that the values of most chemical indicators were higher in water bodies with high amphibian extinction rates. The values of magnesium and chloride ion concentration, as well as conductivity appeared to differ the most between these two types of water bodies which is connected mainly with spring run-off into the water bodies. The results of this study demonstrate that water pollution may lead to local extinction of amphibian species.

Trematode-associated morbidity and mortality of tadpoles in Israel.

Amphibians stand at the forefront of the global biodiversity crisis. The causes of their decline are diverse and include a rise in amphibian malformations due to various factors, especially trematode infection. However, linking amphibian mortality and morbidity with trematode infection has proven to be challenging due to the complex life cycle of the trematodes and the fact that trematodes are nonfastidious in their choice of definitive hosts. In Israel, the decline in local amphibian populations has been mostly attributed to the loss and degradation of wetlands and riparian habitats. Recently, however, there have been several reports of morbidity and mortality of tadpoles with signs of edema and malformations from various localities in Israel. We collected dead and morbid tadpoles and metamorphs of Hyla savignyi and Pelophylax bedriagae, and we showed that the morbidity and the deformations observed in the field are the result of infection by trematodes. We also isolated an echinostomatid trematode from the malformed and edematous tadpoles and from the freshwater snail Bulinus truncatus, all from the same site. We further succeeded in experimentally infecting H. savignyi tadpoles by echinostomatid cercariae that were shed from the snails, and we showed that infection had significantly increased the mortality rates of these tadpoles. The combination of high trematode prevalence and their pathogenic effects suggests that in nature, the effect of echinostome infection on amphibians may be substantial and could become an emerging disease in Israel.

Impaired liver function in Xenopus tropicalis exposed to benzo[a]pyrene: transcriptomic and metabolic evidence.

BackgroundDespite numerous studies suggesting that amphibians are highly sensitive to cumulative anthropogenic stresses, the role pollutants play in the decline of amphibian populations remains unclear. Amongst the most common aquatic contaminants, polycyclic aromatic hydrocarbons (PAHs) have been shown to induce several adverse effects on amphibian species in the larval stages. Conversely, adults exposed to high concentrations of the ubiquitous PAH, benzo[a]pyrene (BaP), tolerate the compound thanks to their highly efficient hepatic detoxification mechanisms. Due to this apparent lack of toxic effect on adults, no studies have examined in depth the potential toxicological impact of PAH on the physiology of adult amphibian livers. This study sheds light on the hepatic responses of Xenopus tropicalis when exposed to high environmentally relevant concentrations of BaP, by combining a high throughput transcriptomic approach (mRNA deep sequencing) and a characterization of cellular and physiological modifications to the amphibian liver.ResultsTranscriptomic changes observed in BaP-exposed Xenopus were further characterized using a time-dependent enrichment analysis, which revealed the pollutant-dependent gene regulation of important biochemical pathways, such as cholesterol biosynthesis, insulin signaling, adipocytokines signaling, glycolysis/gluconeogenesis and MAPK signaling. These results were substantiated at the physiological level with the detection of a pronounced metabolic disorder resulting in a possible insulin resistance-like syndrome phenotype. Hepatotoxicity induced by lipid and cholesterol metabolism impairments was clearly identified in BaP-exposed individuals.ConclusionsOur data suggested that BaP may disrupt overall liver physiology, and carbohydrate and cholesterol metabolism in particular, even after short-term exposure. These results are further discussed in terms of how this deregulation of liver physiology can lead to general metabolic impairment in amphibians chronically exposed to contaminants, thereby illustrating the role xenobiotics might play in the global decline in amphibian populations.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-666) contains supplementary material, which is available to authorized users.

Spatial and temporal variation in population dynamics of Andean frogs: Effects of forest disturbance and evidence for declines

Biodiversity loss is a global phenomenon that can result in the collapse of food webs and critical ecosystem services. Amphibian population decline over the last century is a notable case of species loss because amphibians survived the last four major extinction events in global history, their current rate of extinction is unprecedented, and their rate of extinction is greater than that for most other taxonomic groups. Despite the severity of this conservation problem and its relevance to the study of global biodiversity loss, major knowledge gaps remain for many of the most threatened species and regions in the world. Rigorous estimates of population parameters are lacking for many amphibian species in the Neotropics. The goal of our study was to determine how the demography of seven species of the genus Pristimantis varied over time and space in two cloud forests in the Ecuadorian Andes. We completed a long term capture–mark–recapture study to estimate abundance, survival, and population growth rates in two cloud forests in the Ecuadorian Andes; from 2002 to 2009 at Yanayacu in the Eastern Cordillera and from 2002 to 2003 at Cashca Totoras in the Western Cordillera. Our results showed seasonal and annual variation in population parameters by species and sex. P. bicantus experienced significant reductions in abundance over the course of our study. Abundance, apparent survival, and population growth rates were lower in disturbed than in primary or mature secondary forest. The results of our study raise concerns for the population status of understudied amphibian groups and provide insights into the population dynamics of Neotropical amphibians.