Malformed Frogs Research Articles

Review of malformed frogs

This study reviewed the survey of malformed frogs and the probable causes of their deformities. It analysed the checklist and pattern of malformations in frogs and examined different malformations in frogs of selected articles. It also reviewed the causes of malformation in frogs of different articles. The reviewed showed that limb malformations with 22.41% was the most recorded malformations in frogs with pattern of publications revealed that there was varying trend in article publication which peaked in 2000 and 2023. Different malformations in frogs are abnormal skin, albinism, extra hindlimb, eye malformation. Others are lack of palms, appendages and appendicular, limb malformation, ectrodactyly, brachydactyly and ectrodactyly. The causes of malformations in frogs reviewed includes mutation, parasites, heavy metals, environmental stressors and ultraviolet light. The study concluded that human factors or anthropogenic activities played an important role in malformations in frogs reviewed.

Annotated list of anurans from the lateritic plateau of western India with notes on malformations

Lateritic plateaus of India are geographically and ecologically complex plateaus that support endemic flora and fauna. However, despite their uniqueness they are termed as “wastelands”. The plateaus’ overall treeless structure makes them susceptible to developmental activities like infrastructure growth, waste dumping, and urbanization. This paper presents a list of anurans compiled from surveys carried out in the years between 2016 and 2018 in the town of Manipal, a predominant lateritic landscape on the west coast of India. The list comprises of 19 species belonging to five different families, includes notes on microhabitat structure and associated species. We also present descriptions of malformed frogs recorded during the surveys. The growing demands for urbanization, presence of malformed frogs, and habitat complexities that support species densities highlight the need to re-evaluate our understanding towards these plateaus. We express our concern towards the need for conservation of these lesser known amphibian habitats.  

Cytochrome P450 1A transcript is a suitable biomarker of both exposure and response to diluted bitumen in developing frog embryos

In order for Alberta's thick bitumen to be transported through pipelines, condensates are added creating a diluted bitumen (dilbit) mixture. Recent pipeline expansion projects have generated concern about potential dilbit spills on aquatic wildlife health. Studies have suggested that polycyclic aromatic compounds (PACs) are toxic to aquatic vertebrates and could potentially also interfere with their endocrine system. The research objectives of this study were to investigate the toxicity of dilbit to developing frog embryos and to identify the molecular mechanisms of action involved. Fertilized embryos of Western clawed frog (Silurana tropicalis) were exposed for 72 h to water accommodated fractions (WAF; 0.7–8.9 μg/L TPACs) and chemically-enhanced WAFs (CEWAF; 0.09–56.7 μg/L TPACs) of Access Western Blend (AWB) and Cold Lake Blend (CLB) dilbits. Both dilbit's CEWAFs significantly increased embryonic mortality and malformation incidence in the highest treatments tested, while WAF treatments led to no visible toxic effects. Increases of the cytochrome P450 1A (cyp1a) mRNA levels were observed for all WAF and CEWAF dilbit treatments suggesting that phase I detoxification is activated in the dilbit-exposed larvae. When exposed to PAC concentrations ranging from 0.09 to 8.9 μg/L, the frogs displayed no observable malformations, but expressed significant increases of cyp1a mRNA levels (2- to 25-fold; indicating a suitable biomarker of exposure); however, when concentrations were of 46.6 μg/L or higher, both malformed frog phenotype and induction of cyp1a mRNA level (>250-fold) were measured (indicating a suitable biomarker of response). The expression of several genes related to cellular detoxification and endocrine disruption were also measured, but were not significantly altered by the treatments. In sum, cyp1a mRNA level is a highly sensitive endpoint to measure subtle molecular changes induced by PAC exposure in the frog embryos and larvae, and data suggest that PAC concentration higher than 46 μg/L would be toxic to the developing S. tropicalis.

Using an ecosystem‐level manipulation to understand host‐parasite interactions and how they vary with study venue

We investigated interactions between the virulent trematode Ribeiroia ondatrae, which has been linked to amphibian malformations across the United States, and its amphibian host (Pseudacris regilla) using a hierarchical approach involving multi‐year regional field surveys, replicated pond enclosures, and an unreplicated ecosystem manipulation of parasite infection. Results of this multi‐tiered approach provide strong evidence of the causal linkage between infection and malformations while offering additional insights about the influence of experimental venue on effect size. Among years and across 18 wetlands in northern California, Ribeiroia infection was a strong predictor of malformation frequency, which ranged from 0 to 77% at all sites (n = 6,511). Correspondingly, the addition of >500 Ribeiroia infected snails to an experimentally divided wetland using a three‐year Before After Control Impact (BACI) design caused sharp increases in Ribeiroia infection and severe malformations in P. regilla during the manipulation year (but not pre‐ or post‐manipulation). These results were complemented by the findings from a replicated (n = 16) enclosure/exclosure study conducted on both sides of the divided wetland (Hog Lake), which showed increased infection and malformations only among larvae within cages that allowed parasite entry and only on the manipulated side. No differences in mortality were observed among animals as a function of cage type. A comparison of the slope between observed infection and malformations as a function of venue (previous laboratory work and the two spatial scales of this study (cages and whole‐pond)) indicated that small‐scale experiments exhibit stronger effects relative to results from larger spatial extents. Multi‐year sampling also indicated that malformed frogs were unlikely to return as breeding adults, highlighting the potential for population‐level impacts associated with high Ribeiroia infections. Taken together, these results provide support for the causal relationship between Ribeiroia infection and amphibian malformations under realistic conditions while simultaneously emphasizing the influence of study venue on the strength of this relationship.

Presence of Ribeiroia ondatrae in the developing anuran limb disrupts retinoic acid levels

The widespread reports of malformed frogs have sparked interest worldwide to try and determine the causes of such malformations. Ribeiroia ondatrae is a digenetic trematode, which has been implicated as one such cause, as this parasite encysts within the developing tadpole hind limb bud and inguinal region causing dramatic limb malformations. Currently, the mechanisms involved in parasite-induced limb deformities remain unclear. We sought to investigate whether the level of retinoic acid (RA), a morphogenetic factor known to play a critical role in limb bud formation, is altered by the presence of R. ondatrae within the infected tadpole. Alteration of RA levels within the limb bud caused by the presence of the parasite may be achieved in three ways. First, metacercariae are actively secreting RA; second, cercariae, upon entering the limb/inguinal region, may release a large amount of RA; finally, the metacercariae may induce either an increase in the synthesis or a decrease in the degradation of the host's endogenous retinoic acid levels. Here, we show through high performance liquid chromatography and mass spectrometry that limb bud tissue of Lithobates sylvaticus, which has been parasitised, contains 70% more RA compared to the unparasitised control. Furthermore, parasites that have encysted within the limb buds appear to contain substantially less RA (56%) than the free swimming cercariae (defined as the infectious stage of the parasite). Taken together, these data illustrate for the first time that encystment of R. ondatrae leads to an increase in RA levels in the tadpole limb bud and may offer insight into the mechanisms involved in parasite-induced limb deformities.

Disease and the Extended Phenotype: Parasites Control Host Performance and Survival through Induced Changes in Body Plan

BackgroundBy definition, parasites harm their hosts. However, some forms of parasite-induced alterations increase parasite transmission between hosts, such that manipulated hosts can be considered extensions of the parasite's phenotype. While well accepted in principle, surprisingly few studies have quantified how parasite manipulations alter host performance and survival under field and laboratory conditions.Methodology/Principal FindingsBy interfering with limb development, the trematode Ribeiroia ondatrae causes particularly severe morphological alterations within amphibian hosts that provide an ideal system to evaluate parasite-induced changes in phenotype. Here, we coupled laboratory performance trials with a capture-mark-recapture study of 1388 Pacific chorus frogs (Pseudacris regilla) to quantify the effects of parasite-induced malformations on host locomotion, foraging, and survival. Malformations, which affected ∼50% of metamorphosing frogs in nature, caused dramatic reductions in all measures of organismal function. Malformed frogs exhibited significantly shorter jumping distances (41% reduction), slower swimming speeds (37% reduction), reduced endurance (66% reduction), and lower foraging success relative to infected hosts without malformations. Furthermore, while normal and malformed individuals had comparable survival within predator-free exclosures, deformed frogs in natural populations had 22% lower biweekly survival than normal frogs and rarely recruited to the adult population over a two-year period.Conclusions/SignificanceOur results highlight the ability of parasites to deeply alter multiple dimensions of host phenotype with important consequences for performance and survival. These patterns were best explained by malformation status, rather than infection per se, helping to decouple the direct and indirect effects of parasitism on host fitness.

Ecomorphology and disease: cryptic effects of parasitism on host habitat use, thermoregulation, and predator avoidance

Parasites can cause dramatic changes in the phenotypes of their hosts, sometimes leading to a higher probability of predation and parasite transmission. Because an organism's morphology directly affects its locomotion, even subtle changes in key morphological traits may affect survival and behavior. However, despite the ubiquity of parasites in natural communities, few studies have incorporated parasites into ecomorphological research. Here, we evaluated the effects of parasite-induced changes in host phenotype on the habitat use, thermal biology, and simulated predator-escape ability of Pacific chorus frogs (Pseudacris regilla) in natural environments. Frogs with parasite-induced limb malformations were more likely to use ground microhabitats relative to vertical refugia and selected less-angled perches closer to the ground in comparison with normal frogs. Although both groups had similar levels of infection, malformed frogs used warmer microhabitats, which resulted in higher body temperatures. Likely as a result of their morphological abnormalities, malformed frogs allowed a simulated predator to approach closer before escaping and escaped shorter distances relative to normal frogs. These data indicate that parasite-induced morphological changes can significantly alter host behavior and habitat use, highlighting the importance of incorporating the ubiquitous, albeit cryptic, role of parasites into ecomorphological research.

Malformed frogs: Bayesian and random-effect model analyses

Historical data (1958 1963) on frog malformations in Minnesota, USA, are compared to malformation data collected from 1996 to 1999, at many of the same collection sites, to investigate malformation risk changes between the study periods. We initially consider Mantel-Haenszel and simple logistic regression analyses. Potential variation in risk across data collection sites lead to random-effect logistic regression and hierarchical Bayesian models. We find clear evidence of increased malformation risk in the 1990s data collection period. The random-effect logistic regression and Bayesian logistic regression analyses produce similar point estimates of relative risk, and uncertainty, but Bayesian models allow analysts to view the impact of additional information on the inferences. Bayesian analyses programs in WinBUGS and SAS are provided.

The Meaning behind Malformed Frogs

The Meaning behind Malformed Frogs

Malformed Frogs

Malformed Frogs

Malformed frogs: the collapse of aquatic ecosystems

The widespread appearance of frogs with deformed bodies has generated much press coverage over the past decade. with extra limbs or digits, missing limbs or digits, or misaligned appendages raise an alarming question: Are deformed humans next? Taking a fresh look at this disturbing environmental problem, this reference provides a balanced overview of the science behind the malformed frog phenomenon. Bringing together data from ecology, parasitology, and other disciplines, Michael Lannoo considers the possible causes of these deformities, tells which frogs have been affected, and addresses questions about what these malformations might mean to human populations. Featuring high-quality radiographic images, Malformed Frogs suggests that our focus should be on finding practical solutions, a key component of which will be controlling chemical, nutrient, and pesticide runoff into wetlands.

Application of Xenopus laevis in ecotoxicology (I) —Introduction and quality control of laboratory animal

The aim of the series of papers is to discuss the application of Xenopus laevis, as model animal in biology, in ecotoxicology. X. laevis as model animal is wildly used in biological study and has provided a lot of relating data because of many advantages, such as living in water and being easily maintained, laying eggs in the whole year, and externally fertilizing and developing. Embryos and larvae of X. laevis like other amphibians are directly exposed in the aquatic environment and sensitive to pollutants. In addition, sex differentiation and sex organ development of X. laevis are sensitive to sex hormones and endocrine disruptors with sex hormone activities, which enable X. laevis to be used in studies on sex hormone disruption and reproductive toxicity of endocrine disruptors. Metamorphic development of X. laevis is very sensitive to thyroid hormones and thyroid disruptors, which enables X. laevis to be used for evaluating thyroid disruptors. Also, X. laevis ecotoxicology can be linked with amphibian population declines and malformed frog occurrence, being one of the hotspots in ecology. Thus, more and more laboratories have introduced X. laevis to ecotoxicological study. The quality of laboratory animals correlates with scientificity and reliability of results from animal experiments. It is especially important for toxicology. Quality control of X. laevis involving several factors such as water and food is discussed in this paper.

Low Levels of Sodium and Potassium in the Water from Wetlands in Minnesota that Contained Malformed Frogs Affect the Rate ofXenopusDevelopment

Water samples were collected between 1999 and 2000 from wetlands in Minnesota that contained malformed frogs. The water samples were analyzed for 14 minerals/ions and screened for the presence of biologically active compounds using Xenopus laevis. Results indicated that water from two sites, CWB and ROI2, induced severe retardation with embryo lengths reduced 20% after 96 hr of development. The developmental delay observed with water from ROI2 was alleviated by supplementation with sodium, while both sodium and potassium alleviated the developmental delay observed with water whose mineral content mimicked that of CWB. Seasonal fluctuations in the sodium and potassium content at ROI2 and NEY correlated with changes in the rates of Xenopus development. Xenopus embryos reared on water from ROI2 for 120 hr displayed gut malformations not present in embryos reared on a synthetic media designed to mimic the mineral content of the water from ROI2. Embryos reared on water from ROI2 supplemented with minerals at levels comparable to that routinely employed in the rearing of Xenopus were neither retarded nor malformed. It is proposed that climate driven hydrology may influence the mineral composition at selected wetlands and delay development which may alter window(s) of susceptibility towards biologically active agents and the occurrence of malformed frogs.

Photochemical characterization of water samples from Minnesota and Vermont sites with malformed frogs: potential influence of photosensitization by singlet molecular oxygen ( 1O 2) and free radicals on aquatic toxicity

Environmental pollutants activated by UV sunlight may have contributed to the recent decline in frog populations and the concomitant increase in malformations in the USA and abroad. UV radiation is able to mutate DNA and to initiate photosensitization processes that generate mutagenic and biologically disruptive oxygen transients. We have examined water from selected sites in Minnesota and Vermont using singlet molecular oxygen ( 1O 2), detected by its phosphorescence and free radicals detected by spin trapping, as markers for photosensitization. Water from a pond in Minnesota with malformed frogs, which also causes malformations in the laboratory, photosensitized more 1O 2, even though it absorbed less UV light compared to water from a site that did not cause malformations. This suggested that unknown natural or pollutant agents were present, and that photosensitization may be involved. Although UV irradiation of the two Minnesota water samples in the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) revealed the presence of the DMPO/ OH, DMPO/ H(e aq −) and DMPO/ C(unknown) adducts there were no qualitative or quantitative differences between them. We also examined water samples from several sites in Vermont, and compared them by measuring the quantum yield of 1O 2 photosensitization. While all the Vermont samples produced a small amount of 1O 2, there was no clear correlation with the incidence of frog malformations. However, the samples differed strongly in absorption spectra and the ability to quench 1O 2. These factors may determine how much UV light is absorbed and converted into chemical reactions. Our results show that photochemical characterization of 1O 2 photosensitization is possible in untreated natural water samples. Photosensitization falls into the category of global factors that may be closely associated with the effects of UV irradiation of the Earth's environments. Thus, photosensitization might be an important component in global amphibian malformation and decline. The observation of 1O 2 emission directly from natural water may also provide new opportunities to investigate the involvement of 1O 2 in other complex environmental processes.

A regional survey of malformed frogs in Minnesota (USA) (Minnesota malformed frogs).

In late 1995, school children discovered malformed frogs in a south central Minnesota pond. Press coverage resulted in numerous citizen reports of frog malformation across Minnesota in 1996. After some initial site investigation, 3 affected frog sites and 4 nearby reference sites were selected for more detailed evaluation. Field biologists made 89 visits to study sites beginning spring 1997 through fall 1999 to examine the number and type of frog malformations. Over 5,100 Leopard frogs (Rana pipiens) were captured and examined at all study sites. Water elevations and associated littoral inundation were recorded from 1997-2000. Results indicate that malformation occurred at all study sites above historical background levels. Rana pipiens malformation across all sites over three seasons averaged 7.9% and ranged from 0 to 7% at reference sites and 4 to 23% at affected sites. At one northern Minnesota site, mink frog (Rana septentrionalis) malformation was 75% in 1998. A site characteristic common to the most affected sites was an elastic zone of littoral inundation. Climate driven hydrologic variation likely influenced water depth and associated breeding locations.

Deformed frogs and environmental retinoids

Since the early 1990s, a substantial number of deformed frogs have been observed in North America, particularly in the upper Midwest and Canada. Attempts to understand the etiology of the deformed frog problem have met with limited success to date with nearly as many proposed explanations as research groups working on the problem. Models for the mechanism underlying the development of deformed frogs include parasite/predation, ultraviolet radiation, and chemical exposure. Each model has its strengths and weaknesses. Despite contentious debate among researchers, there is an overall consensus that the increasing prevalence of deformed frogs is the result of a water-borne contaminant that has recently appeared, or reached a critical concentration. Our detailed analysis of malformed frogs collected in Minnesota ponds and lakes suggested that limb patterning was being modified by the disruption of a retinoid-sensitive developmental signaling pathway. Accordingly, we focused in the identification and characterization of bioactive retinoids from lake water and showed that retinoid treatment of frog embryos at sensitive times of development could recapitulate the full spectrum of limb abnormalities observed in field specimens in the laboratory. These data have led to the conclusion that inappropriate modulation of retinoid signaling by environmental contaminants is the mechanism underlying the increased incidence of frog malformations.

Congener‐specific analysis of polychlorinated dibenzo‐p‐dioxins, dibenzofurans, and coplanar polychlorinated biphenyls in frogs and their habitats, Kitakyushu, Japan

The occurrence and fates of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (coplanar PCBs) were investigated in two species of frog, mountain brown frog (Rana ornativentris) and Japanese brown frog (Rana japonica), and in soil samples. This study was carried out as part of an investigation aimed at determining the cause of extra forelimbs in the mountain brown frog. Frogs, not including malformed ones, and soil samples were collected at three sites in Kitakyushu, Japan, including the site where the malformed frogs were found and two reference sites. All samples were analyzed for PCDDs/PCDFs and coplanar PCBs. Relatively high concentrations of PCDDs/PCDFs and coplanar PCBs were detected in the soils and frogs collected from all three sites. Comparisons of concentrations in frogs and soils indicated that bioaccumulation of PCDDs/PCDFs was much lower than that of coplanar PCBs and that 2,3,7,8-substituted PCDDs/PCDFs were more highly accumulated than non-2,3,7,8-substituted isomers. From comparison of concentrations between the sexes, it was found that concentrations of dioxins, except for PCDDs, were significantly higher in males than in females. In the present study, relatively high concentrations of dioxins in frogs were found and maternal transfer to the eggs was strongly suspected. However, no difference in dioxin concentrations in frogs between the study site and the reference sites was found, so the cause of the malformations was not dioxins and remains unknown.

Limb Malformations and Abnormal Sex Hormone Concentrations in Frogs

Declines in amphibian populations, and amphibians with gross malformations, have prompted concern regarding the biological status of many anuran species. A survey of bullfrogs, Rana catesbeiana, and green frogs, Rana clamitans, conducted in central and southern New Hampshire showed malformed frogs at 81% of the sites sampled (13 of 16 sites). Brain gonadotropin-releasing hormone (GnRH) and the synthesis of androgens and estradiol, hormones essential to reproductive processes, were measured from limb-malformed and normal (no limb malformation) frogs. Normal frogs had significantly higher concentrations (nearly 3-fold) of in vitro produced androgens and of brain GnRH than malformed frogs. Because most malformations are thought to occur during development, we propose that environmental factors or endocrine-disrupting chemicals that may cause developmental abnormalities also act during early development to ultimately cause abnormally reduced GnRH and androgen production in adult frogs. The consequences of reduced GnRH and androgens on anuran reproductive behavior and population dynamics are unknown but certainly may be profound and warrant further research.

Limb malformations and abnormal sex hormone concentrations in frogs.

Declines in amphibian populations, and amphibians with gross malformations, have prompted concern regarding the biological status of many anuran species. A survey of bullfrogs, Rana catesbeiana, and green frogs, Rana clamitans, conducted in central and southern New Hampshire showed malformed frogs at 81% of the sites sampled (13 of 16 sites). Brain gonadotropin-releasing hormone (GnRH) and the synthesis of androgens and estradiol, hormones essential to reproductive processes, were measured from limb-malformed and normal (no limb malformation) frogs. Normal frogs had significantly higher concentrations (nearly 3-fold) of in vitro produced androgens and of brain GnRH than malformed frogs. Because most malformations are thought to occur during development, we propose that environmental factors or endocrine-disrupting chemicals that may cause developmental abnormalities also act during early development to ultimately cause abnormally reduced GnRH and androgen production in adult frogs. The consequences of reduced GnRH and androgens on anuran reproductive behavior and population dynamics are unknown but certainly may be profound and warrant further research.

Malformed Frogs: Making the Leap to Humans

Research ArticleOpen AccessMalformed frogs. Making the leap to humans. J S Manuel J S Manuel Search for more papers by this author Published:1 January 2000https://doi.org/10.1289/ehp.108-a31Cited by:1AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail "Malformed frogs. Making the leap to humans.." Environmental Health Perspectives, 108(1), p. A31FiguresReferencesRelatedDetailsCited ByCarter L, Tabor M, Bonner J and Bonner L (2018) Mitogen-activated protein kinase activation by oxidative and bacterial stress in an amphibian cell culture model., Environmental Health Perspectives, 110:7, (641-645), Online publication date: 1-Jul-2002. Vol. 108, No. 1 January 2000Metrics About Article Metrics Publication History Originally published1 January 2000Published in print1 January 2000 Financial disclosures License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.