Hind limb malformations in free-living northern leopard frogs (Rana pipiens) from Maine, Minnesota, and Vermont suggest multiple etiologies

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

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

In situ effects of pesticides on amphibians in the Sierra Nevada

For more than 20 years, conservationists have agreed that amphibian populations around the world are declining. Results obtained through laboratory or mesocosm studies and measurement of contaminant concentrations in areas experiencing declines have supported a role of contaminants in these declines. The current study examines the effects of contaminant exposure to amphibians in situ in areas actually experiencing declines. Early larval Pseudacris regilla were translocated among Lassen Volcanic, Yosemite and Sequoia National Parks, California, USA and caged in wetlands in 2001 and 2002 until metamorphosis. Twenty contaminants were identified in tadpoles with an average of 1.3-5.9 (maximum = 10) contaminants per animal. Sequoia National Park, which had the greatest variety and concentrations of contaminants in 2001, also had tadpoles that experienced the greatest mortality, slowest developmental rates and lowest cholinesterase activities. Yosemite and Sequoia tadpoles and metamorphs had greater genotoxicity than those in Lassen during 2001, as determined by flow cytometry. In 2001 tadpoles at Yosemite had a significantly higher rate of malformations, characterized as hemimelia (shortened femurs), than those at the other two parks but no significant differences were observed in 2002. Fewer differences in contaminant types and concentrations existed among parks during 2002 compared to 2001. In 2002 Sequoia tadpoles had higher mortality and slower developmental rates but there was no difference among parks in cholinesterase activities. Although concentrations of most contaminants were below known lethal concentrations, simultaneous exposure to multiple chemicals and other stressors may have resulted in lethal and sublethal effects.

Indicators of the statuses of amphibian populations and their potential for exposure to atrazine in four midwestern U.S. conservation areas

Extensive corn production in the midwestern United States has physically eliminated or fragmented vast areas of historical amphibian habitat. Midwestern corn farmers also apply large quantities of fertilizers and herbicides, which can cause direct and indirect effects on amphibians. Limited field research regarding the statuses of midwestern amphibian populations near areas of corn production has left resource managers, conservation planners, and other stakeholders needing more information to improve conservation strategies and management plans. We repeatedly sampled amphibians in wetlands in four conservation areas along a gradient of proximity to corn production in Illinois, Iowa, Minnesota, and Wisconsin from 2002 to 2005 and estimated site occupancy. We measured frequencies of gross physical deformities in recent metamorphs and triazine concentrations in the water at breeding sites. We also measured trematode infection rates in kidneys of recently metamorphosed Lithobates pipiens collected from nine wetlands in 2003 and 2004. We detected all possible amphibian species in each study area. The amount of nearby row crops was limited in importance as a covariate for estimating site occupancy. We observed deformities in <5% of metamorphs sampled and proportions were not associated with triazine concentrations. Trematode infections were high in metamorphs from all sites we sampled, but not associated with site triazine concentrations, except perhaps for a subset of sites sampled in both years. We detected triazines more often and in higher concentrations in breeding wetlands closer to corn production. Triazine concentrations increased in floodplain wetlands as water levels rose after rainfall and were similar among lotic and lentic sites. Overall, our results suggest amphibian populations were not faring differently among these four conservation areas, regardless of their proximity to corn production, and that the ecological dynamics of atrazine exposure were complex.

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

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

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

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

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

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

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

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

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.

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

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

Sublethal predators and their injured prey: linking aquatic predators and severe limb abnormalities in amphibians

While many predators completely consume their prey, others feed only on blood or tissue without killing the prey, sometimes causing ecologically significant levels of injury. We investigated the importance of sublethal predator attacks in driving an emerging issue of conservation importance: missing-limb deformities in amphibians. We combined long-term field data and manipulative experiments to evaluate the role of sublethal predation in causing abnormalities in two regions of central Oregon, U.S.A. Since 1988, western toads (Bufo boreas) in Lake Aspen have exhibited abnormalities dominated by partially missing limbs and digits at annual frequencies from <1% to 35%. On Broken Top volcano, we found comparable types and frequencies of abnormalities in Cascades frogs (Rana cascadae). Field sampling and observational data implicated two aquatic predators in these abnormality phenomena: introduced sticklebacks (Gasterosteus aculeatus) at Lake Aspen and corduliid dragonfly larvae (Somatochlora albicincta) at Broken Top. In experiments, these predators produced limb abnormalities identical to those observed in the respective regions. At Lake Aspen, in situ predator exclosures effectively eliminated abnormalities in toads, while comparisons among years with low and high stickleback abundance and between wetlands with and without sticklebacks reinforced the link between fish and amphibian abnormalities. Neither trematode parasite infection nor pesticide contamination could explain observed abnormalities. Our results suggest that predators are an important explanation for missing-limb abnormalities and highlight the ecological significance of sublethal predation in nature.

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

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

Identification of retinoic acid receptor agonists in sewage treatment plants

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

The archipelago of Fernando de Noronha: an intriguing malformed toad hotspot in South America

Malformed anurans raise concern among scientists, because deformities may relate to the recent global crisis among amphibian populations, although declining populations also may be associated with other causes (e.g., diseases, over-exploitation, and land use/land cover change). We examined a sample of toads (Rhinella jimi, Bufonidae) from an introduced population in the Archipelago of Fernando de Noronha, Brazil where malformations of anurans were thought to be high. Our sample of 159 specimens from the site revealed that 44.6% of all specimens had one or more malformations. Incidence of malformed toads on the mainland sites was substantially lower: 10.5% at Itamaracá, and 3.7% at Propriá. We describe the malformations observed, including six undescribed types of malformation of anurans, and we pose possible hypotheses to explain this high incidence of malformed toads. In addition to existing hypotheses, we suggest for the first time the hypothesis that lack of predation pressures contributes to numbers of malformed toads. We indicate the need of specific studies to understand the causes of malformations in the R. jimi population of Fernando de Noronha, which is thought to be extreme foci of malformed amphibians in the world. Our results may improve local conservation action plans as this is an alien population that may be affecting endemic fauna, and may affect populations in other parts of the world, because toad species of the genus Rhinella are recognized as exceptional colonizers. More importantly, unknown variables in these toads' environment are evidently affecting toads during development, which should be a concern for all species that inhabit the area, perhaps even humans.

The contribution of habitat loss to changes in body size, allometry, and bilateral asymmetry in two Eleutherodactylus frogs from Puerto Rico

Amphibian populations have been declining worldwide and the exact mechanisms underlying these changes are not well understood. We examined environmentally induced phenotypic changes that may reflect ongoing stresses on individuals and therefore their ability to persist in increasingly changing landscapes. Specifically, we evaluated the contribution of habitat loss on the size, allometry, and levels of fluctuating asymmetry of Eleutherodactylus antillensis and E. coqui, 2 common species that are endemic to Puerto Rico. We x-rayed frogs collected at 9 sites that differed in the amount of forest cover and measured their snout-vent, radio-ulna, femur, and tibio-fibula lengths. E. antillensis and E. coqui were smaller in the highly disturbed (< or =20% forest cover) than in the intermediately (20-70% forest cover) and little-disturbed (> or =70% forest cover) landscapes. In E. antillensis but not in E. coqui, the slope and intercept of the curves relating snout-vent length with the length of the 3 bones differed with degree of forest cover, suggesting an effect of habitat loss on body shape. In E. antillensis and E. coqui, differences between right and left sides corresponded to true fluctuating asymmetry; however, only the radio-ulna length of E. coqui showed a trend toward an increase in fluctuating asymmetry with habitat loss. Because body size scales with a variety of physiological, life history, and ecological traits, conservation programs aimed at monitoring morphological changes in amphibians may help in understanding the mechanisms that contribute to their persistence in changing environments.

Chronic exposure of Rana pipiens tadpoles to UVB radiation and the estrogenic chemical 4-tert-octylphenol

While adverse effects of exposure to ultraviolet B radiation (UVBR) and environmental pollutants on amphibians have been documented, few studies examined the effects of interactions between environmental stressors on amphibian health. Here the impacts of chronic exposure to UVBR and the estrogenic chemical 4-tert-octylphenol (OP), alone and in combination, on the survival, development, growth, and metamorphosis of Rana pipiens (northern leopard frog) tadpoles are evaluated. Tadpoles were exposed to environmentally relevant levels of OP (0.01 or 10 nM), with and without exposure to UVBR (approximately 0.22 W/m2). After 8 mo of exposure, animals were transferred to a clean-water grow-out system for 3 additional mo. There was no effect of treatments on the weights of animals at wk 42 or on the age, snout-vent length (SVL), and weights of tadpoles at forelimb emergence (FLE). However, tadpoles exposed to UVBR had markedly delayed development and significantly fewer reached metamorphosis compared to control animals. Although exposure to UVBR and OP together produced the highest incidence of mortality and developmental anomalies, UVBR alone was sufficient to produce significant mortality of tadpoles, and exposure to UVBR or OP alone induced a significant increase in malformations and abnormalities. The malformations observed consisted mainly of spinal curvature. Our results show that chronic exposure to environmental levels of UVBR or OP alone exerts lethal and/or sublethal effects on R. pipiens tadpoles.

Bioremediation of tetrachloroethylene-contaminated groundwater in a model aquifer: effects on green frogs (Rana clamitans) and Xenopus laevis as potential wetland receptors

Recent regulations require that the ecological effects of microorganisms introduced into the environment, such as for groundwater bioremediation, be assessed prior to their utilization. A native anuran (Rana clamitans) and a model anuran (Xenopus laevis) were used as potential wetland receptors of tetrachloroethylene (PCE)-contaminated groundwater, undergoing three bioremediation treatments: natural attenuation (NA), biostimulation (ST), and bioaugmentation (AU). Eggs of both species were exposed acutely (96 h) to remediated effluents. Xenopus tadpoles were chronically exposed to the effluents for 100 days and were screened for the presence of bacterial pathogens. There was no impact on the survivorship of the frogs exposed either acutely or chronically to the NA, ST, or AU effluents; nor was there any evidence of bacterial infection found, with the exception of control individuals. The results of these exposures suggest that bioremediation with KB-1trade mark culture poses a minimal threat to anuran development and survivorship.

Effects of lead-contaminated sediment on Rana sphenocephala tadpoles

We exposed larval southern leopard frogs (Rana sphenocephala) to lead-contaminated sediments to determine the lethal and sublethal effects of this metal. Tadpoles were laboratory-raised from early free-swimming stage through metamorphosis at lead concentrations of 45, 75, 180, 540, 2360, 3940, 5520, and 7580 mg/kg dry weight in sediment. Corresponding pore water lead concentrations were 123, 227, 589, 1833, 8121, 13,579, 19,038, and 24,427 microg/L. Tadpoles exposed to lead concentrations in sediment of 3940 mg/kg or higher died within 2 to 5 days of exposure. At lower concentrations, mortality through metamorphosis ranged from 3.5% at 45 mg/kg lead to 37% at 2360 mg/kg lead in sediment. The LC50 value for lead in sediment was 3728 mg/kg (95% CI = 1315 to 72,847 mg/kg), which corresponded to 12,539 microg/L lead in pore water (95% CI = 4000 to 35,200 microg/L). Early growth and development were depressed at 2,360 mg/kg lead in sediment (8100 microg/L in pore water) but differences were not evident by the time of metamorphosis. The most obvious effect of lead was its pronounced influence on skeletal development. Whereas tadpoles at 45 mg/kg lead in sediment did not display permanent abnormalities, skeletal malformations increased in frequency and severity at all higher lead concentrations. By 2360 mg/kg, 100% of surviving metamorphs displayed severe spinal problems, reduced femur and humerus lengths, deformed digits, and other bone malformations. Lead concentrations in tissues correlated positively with sediment and pore water concentrations.

Proximity to pollution sources and risk of amphibian limb malformation

The cause of limb deformities in wild amphibian populations remains unclear, even though the apparent increase in prevalence of this condition may have implications for human health. Few studies have simultaneously assessed the effect of multiple exposures on the risk of limb deformities. In a cross-sectional survey of 5,264 hylid and ranid metamorphs in 42 Vermont wetlands, we assessed independent risk factors for nontraumatic limb malformation. The rate of nontraumatic limb malformation varied by location from 0 to 10.2%. Analysis of a subsample did not demonstrate any evidence of infection with the parasite Ribeiroia. We used geographic information system (GIS) land-use/land-cover data to validate field observations of land use in the proximity of study wetlands. In a multiple logistic regression model that included land use as well as developmental stage, genus, and water-quality measures, proximity to agricultural land use was associated with an increased risk of limb malformation (odds ratio = 2.26; 95% confidence interval, 1.42-3.58; p < 0.001). The overall discriminant power of the statistical model was high (C = 0.79). These findings from one of the largest systematic surveys to date provide support for the role of chemical toxicants in the development of amphibian limb malformation and demonstrate the value of an epidemiologic approach to this problem.

Plasma retinoid profile in bullfrogs, Rana catesbeiana, in relation to agricultural intensity of sub-watersheds in the Yamaska River drainage basin, Québec, Canada

Amphibian populations are decreasing globally and the causes are presently unclear. Retinoids have been extensively studied in other vertebrate classes where they are associated with pleiotropic effects such as susceptibility to disease (including cancer and parasitic infections), deformities and reproduction. To investigate the hypothesis that retinoid homeostasis is influenced by agricultural activities, blood samples were collected from adult bullfrogs, Rana catesbeiana, at each of six sub-watersheds chosen to represent a gradient of agricultural intensity within the Yamaska River drainage basin. Samples of surface water were collected at each of the study sites approximately 1 month after spraying and analyzed for 53 pesticides. Male body weight was significantly different (p<0.001) between study sites with the smallest bullfrogs captured from the Rivière à la Barbue sub-watershed associated with high agricultural intensity. A significant linear regression (p<0.001; R2=0.176) was obtained between plasma retinol and body weight. Plasma retinol concentrations were significantly different between study sites (p<0.001) being lowest at both Rivière Noire and Rivière à la Barbue. More than 60% of the land area in these sub-watersheds is under intensive corn-soya cultivation and surface water contained the highest concentrations of the herbicides atrazine, deethyl-atrazine, simazine, metolachlor, dimethenamide, chlopyralide, dicamba and bentazone. Plasma 13-cis-4-oxo-retinoic acid was significantly different (p<0.001) between sub-watersheds, however this effect was apparently unrelated to agricultural intensity. Plasma retinol was negatively correlated (p=0.026; r=-0.237) with plasma 13-cis-4-oxo-retinoic acid. These results suggest that retinoid homeostasis in bullfrogs may be influenced by agricultural practices.

Dietary retinoic acid induces hindlimb and eye deformities in Xenopus laevis

This study investigated the effects of dietary retinoic acid (RA) on frog hindlimb development. Xenopus laevis (African clawed frog) tadpoles were fed a diet supplemented with 0, 1, 10, or 100 microg of RA/g of food for 2 or 5 d at different stages of metamorphosis. Hindlimb deformities were induced in the group fed 100 microg of RA/g of diet for 5 d. Exposures beginning at mid-hindlimb bud development induced bilaterally bent tibiafibula (bony triangles), while exposures later in hindlimb development induced deformities of the feet, including fusion of the 1st and 2nd clawed digits and reduced length of the 4th and 5th digits (due to reduced, missing, or misplaced phalanges). There were also cases of extra phalanges in the 5th digit. The eye was another target of RA exposure. In one experiment, 58% of the tadpoles fed 10 microg of RA/g had a smaller or absent right eye. Additionally, 11% of the tadpoles fed 100 microg of RA/g of diet developed a smaller or absent left eye. Waterborne heavy metals (Zn or Cu) modified RA effects on the hindlimb and eye. Co-exposure to metals and RA resulted in cases of unilateral bony triangles and reduced rates of smaller eyes. There were also cases of extra hindlimb digits in Zn-exposed animals. Dietary RA exposure in tadpoles can cause some deformities that differ from waterborne RA exposures in previous studies. RA also induced deformities that resemble those in affected wild frog populations (bony triangles), although the patterns of other deformities and missing segments (phalanges and metatarsals) are not similar to those documented in the wild.

Ectrodactyly in a West Highland white terrier

A case of monomelic forelimb ectrodactyly (lobster-claw deformity) in a West Highland white terrier is reported. Clinical and radiographic findings are described. The dog was treated with a soft tissue reconstruction of the cleft. It later developed a slight varus-type deformity at the carpus but remained sound with occasional bouts of mild lameness following vigorous exercise. To the author's knowledge, this is the first reported case of canine ectrodactyly treated by simple cleft reconstruction, and only the second report of ectrodactyly in this breed.

Assessment of environmental stressors potentially responsible for malformations in North American anuran amphibians

Several species of anuran amphibians from different regions across North America have recently exhibited an increased occurrence of malformations, predominantly of the hindlimb. Research concerning the potential causes of these malformations has focused extensively on three stressors: chemical contaminants, ultraviolet (UV) radiation, and parasitic trematodes. In this overview of recent work with each of these stressors, we assess their plausibility as contributors to the malformations observed in field-collected amphibians. There is as yet little evidence that chemical contaminants are responsible for the limb malformations. This includes chemicals, such as the pesticide methoprene, that could affect retinoid-signaling pathways that are critical to limb development. Exposure to UV radiation also seems to be an unlikely explanation for hindlimb malformations in amphibians. Although solar UV can cause hindlimb deficiencies in amphibians, a probabilistic assessment based on empirical dose-response and exposure data indicates that UV exposures sufficient to induce limb defects would be uncommon in most wetlands. Results of controlled studies conducted with some affected species and field-monitoring work suggest infection by digenetic trematodes as a promising explanation for the malformations observed in anurans collected from many field sites. Controlled experimentation with additional species and monitoring across a broader range of affected sites are required to assess fully the role of trematodes in relation to other stressors in causing limb malformations. If trematode infestations are indeed related to the recent increases in malformed amphibians, then the question remains as to what alterations in the environment might be causing changes in the distribution and abundance of the parasites.

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.

Influence of Ribeiroia ondatrae (Trematoda: Digenea) infection on limb development and survival of northern leopard frogs (Rana pipiens): effects of host stage and parasite-exposure level

Recent evidence suggests that infection by larvae of the trematode Ribeiroia ondatrae accounts for a significant proportion of limb malformations currently observed in amphibian populations of North America. However, the effects of R. ondatrae infection on northern leopard frogs (Rana pipiens), one of the species most frequently reported with malformations, have not been adequately explored. Moreover, the risk factors associated with R. ondatrae-induced malformations have not been clearly identified. We examined the effects of timing of infection on tadpole survival and limb development. Rana pipiens tadpoles were individually exposed to R. ondatrae cercariae at the pre-limb-bud (Gosner stages 24 and 25), limb-bud (Gosner stages 27 and 28), or paddle (Gosner stages 31–33) stages of development and monitored through metamorphosis. The effects of infection were stage-specific. Infections acquired at the pre-limb-bud stage resulted in a high mortality rate (47.5–97.5%), whereas tadpoles infected at the limb-bud stage displayed a high malformation rate (16% overall), and the magnitude of effects increased with the level of exposure to cercariae. In contrast, infections acquired at the paddle stage had no effect on limb development or tadpole survival, which suggests that the timing of R. ondatrae infection in relation to the stage structure of tadpole populations in the wild is an important determinant of the degree to which populations are affected by R. ondatrae.

How trematodes cause limb deformities in amphibians

We used trematode cyst infestation to induce limb deformities in two species of frogs of the genus Rana and compared them to deformities induced by surgical limb bud rotations. The specific deformities produced by both treatments closely resemble those of wild-caught deformed amphibians and are consistent with a known developmental response to disruption of the spatial organization of cells in developing limb buds. Histological analysis showed that trematode cysts cause massive disruption and abnormal cellular growth involving the limb buds of infected individuals. Our results indicate that trematode cyst infestation causes deformities in frogs by perturbation of the positional relationships of cells in developing limb buds. The crippling effects of cyst-infection on frogs may reflect complex co-evolutionary interactions among trematodes, frogs, and other hosts in the trematode's life cycle.

Amelia/ectromelia in association with scoliosis in three commercial layer hens (Gallus gallus forma domestica)

Three wingless "healthy" pullet hens were serendipitously discovered at a grow-out facility for an egg-production ranch. Two of the birds were amelic and one was ectromelic. The defect in these chickens differs from the previously reported wingless mutations in that all three affected birds also had scoliosis. The birds also differed from previously reported scolitic mutant chickens in that they were wingless. Although the combination of amelia and scoliosis has been reported in humans, this is the first report of the combination in an animal species.

Assessment of the risk of solar ultraviolet radiation to amphibians. I. Dose-dependent induction of hindlimb malformations in the northern leopard frog (Rana pipiens)

A number of environmental stressors have been hypothesized as responsible for recent increases in limb malformations in several species of North American amphibians. The purpose of this study was to generate dose-response data suitable for assessing the potential role of solar ultraviolet (UV) radiation in causing limb malformations in a species in which this phenomenon seemingly is particularly prevalent, the northern leopard frog (Rana pipiens). Frogs were exposed from early embryonic stages through complete metamorphosis to varying natural sunlight regimes, including unaltered (100%) sunlight, sunlight subjected to neutral density filtration to achieve relative intensities of 85%, 75%, 65%, 50%, and 25% of unaltered sunlight, and sunlight filtered with glass or acrylamide to attenuate, respectively, the UVB (290-320 nm) and UVB plus UVA (290-380 nm) portions of the spectrum. The experiments were conducted in a controlled setting, with continual monitoring of UVB, UVA, and visible light to support a robust exposure assessment. Full sunlight caused approximately 50% mortality of the frogs during early larval development; no significant treatment-related mortality occurred under any of the other exposure regimes, including 100% sunlight with glass or acrylamide filtration. There was a dose-dependent (p < 0.0001) induction of hindlimb malformations in the frogs, with the percentage of affected animals ranging from about 97% under unaltered sunlight to 0% in the 25% neutral density treatment. Malformations were comprised mostly of missing or truncated digits, and generally were bilateral as well as symmetrical. Filtration of sunlight with either glass or acrylamide both significantly reduced the incidence of malformed limbs. The estimated sunlight dose resulting in a 50% limb malformation rate (ED50) was 63.5%. The limb ED50 values based on measured sunlight intensities corresponded to average daily doses of 4.5 and 100 Wh x m(-2) for UVB and UVA, respectively. Exposure to sunlight also resulted in increased eye malformations in R. pipiens, however, the dose-response relationship for this endpoint was not monotonic. The results of this study, in conjunction with measured or predicted exposure data from natural settings, provide a basis for quantitative prediction of the risk of solar UV radiation to amphibians.

Frog decline, frog malformations, and a comparison of frog and human health

The decline in frog populations and the increase in the frequency of frog malformations are discussed. Topics considered for analysis include chytridiomycosis, retinoids, UV-B radiation, chemical contaminants, environmental threats, introduced invasive species and predation, unsustainable use, and enigmatic decline. Care must be taken to distinguish between hypotheses, laboratory experiments, and the findings in feral frog populations. Clearly, the causes of population decline and malformations are heterogeneous. The subject of frogs and humans is addressed under three subheadings: the importance of frogs to human societies, medical implications of frog studies, and a comparison of frog and human disease factors.

Leaping lopsided: a review of the current hypotheses regarding etiologies of limb malformations in frogs

Recent progress in the investigation of limb malformations in free-living frogs has underlined the wide range in the types of limb malformations and the apparent spatiotemporal clustering of their occurrence. Here, we review the current understanding of normal and abnormal vertebrate limb development and regeneration and discuss some of the molecular events that may bring about limb malformation. Consideration of the differences between limb development and regeneration in amphibians has led us to the hypothesis that some of the observed limb malformations come about through misdirected regeneration. We report the results of a pilot study that supports this hypothesis. In this study, the distal aspect of the right hindlimb buds of X. laevis tadpoles was amputated at the pre-foot paddle stage. The tadpoles were raised in water from a pond in Minnesota at which 7% of surveyed newly metamorphosed feral frogs had malformations. Six percent (6 of 100) of the right limbs of the tadpoles raised in pond water developed abnormally. One truncated right limb was the only malformation in the control group, which was raised in dechlorinated municipal water. All unamputated limbs developed normally in both groups. Three major factors under consideration for effecting the limb malformations are discussed. These factors include environmental chemicals (primarily agrichemicals), encysted larvae (metacercariae) of trematode parasites, and increased levels of ultraviolet light. Emphasis is placed on the necessary intersection of environmental stressors and developmental events to bring about the specific malformations that are observed in free-living frog populations.

Ecological developmental biology: developmental biology meets the real world

The production of phenotype is regulated by differential gene expression. However, the regulators of gene expression need not all reside within the embryo. Environmental factors, such as temperature, photoperiod, diet, population density, or the presence of predators, can produce specific phenotypes, presumably by altering gene-expression patterns. The field of ecological developmental biology seeks to look at development in the real world of predators, competitors, and changing seasons. Ecological concerns had played a major role in the formation of experimental embryology, and they are returning as the need for knowledge about the effects of environmental change on embryos and larvae becomes crucial. This essay reviews some of the areas of ecological developmental biology, concentrating on new studies of amphibia and Homo.

Getting the problem of endocrine disruption into focus: the need for a pause for thought

The study of chemically-induced endocrine disruption in mammals is a relatively new field of endeavour, and it has been assailed by an unusual level of disagreement among investigators regarding the developmental effects produced by chemicals in animals. This article discusses the several sources of uncertainty in endocrine toxicity studies, and the intrinsic variability of many of the key experimental parameters. It is concluded that current uncertainties are due to the absence of an extensive agreed control database for the developmental parameters under study, coupled to the established intrinsic variability of these parameters between strains/species of test animals and test protocols. Only when these factors are generally accepted and well studied will it be possible to design studies capable of distinguishing the possible subtle endocrine toxicity of chemicals and chance observations that cannot be independently reproduced.