Prevalence of skeletal and eye malformations in frogs from north-central United States: estimations based on collections from randomly selected sites

Osteological description of Indian Skipper Frog Euphlyctis cyanophlyctis (Anura: Dicroglossidae) from the Western Ghats of India

The present study provides description of the osteology of Skipper Frog Euphlyctis cyanophlyctis.  Seven adult specimens of E. cyanophlyctis from northern Western Ghats of India were cleared and double stained for studying osteological characteristics.  The baseline description of osteological characters of cranial and post-cranial elements (paired nasals, tubular sphenethmoid, well-developed vomerine teeth, arciferal pectoral girdle, fan-shaped omosternum, cartilaginous W-shaped xiphisternum, hind limb with longest cylindrical humerus, V-shaped pectoral girdle and phalangeal appendages) provided in present study will help in further taxonomic investigations of the genus Euphlyctis.  Further, the baseline information on osteology of Skipper frog will serve as a reference material for investigations related to malformations, either in this or related species.  We also provide first observation on sacro-pelvic malformation in one of the studied specimens. 

Radiographic and histological evidence of metabolic bone disease in gliding leaf frogs (Agalychnis spurrelli)

Bone alterations due to metabolic bone disease in captive animal populations can have a negative impact on repopulation and research initiatives. This investigation has the purpose of describing the principal radiographic and anatomopathological findings present in nine gliding leaf frogs (Agalychnis spurrelli) kept in captivity with alterations in their spines and long bones. The observed histopathological findings were in the canalis vertebralis, paraspinal muscle and long bones, and included deformed bones with alteration of the adjacent tissues, alterations in the ossification process, bone degeneration and resorption, decreased number of osteocytes and deposition of osteoid and fibrous material in the compact bone tissue. Additionally, the spinal cord showed compressed white matter, chronic meningitis in the duramater, alteration in the number of glial cells and loss of delimitation between the gray and white matter. Radiographical changes were found mainly in the long bones and included moth-eaten osteolysis, solid periosteal reaction, bone deformities, cortical tunneling and inflammation of adjacent soft tissues. Also, pathological fractures of the femur and urostyle were observed together with spinal column deviations with increased bone density.

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.

Effects of tributyltin (TBT) on Xenopus tropicalis embryos at environmentally relevant concentrations

Tributyltin (TBT) has been widely used as a biocide in antifouling paints and is a known endocrine disrupting chemical. In this paper, we exposed embryos of Xenopus tropicalis to 50-400ngL(-1) tributyltin chloride. TBT significantly decreased the survival rate, reduced the body length and retarded the development of embryos after 24, 36 and 48h of exposure. These effects of TBT were concentration- and time-dependent. Embryos treated with TBT showed multiple malformations. The most obvious alterations were abnormal eyes, enlarged proctodaeum, narrow fins, and skin hypopigmentation. Enlarged proctodaeum and narrow fins were mainly observed after 36 and 48h of exposure. The loss of eye pigmentation or the absence of external eyes occurred after 24 and 36h of exposure, while extended lenses or edemas of eyes were more commonly observed after 48h of exposure. Additional malformations included: small anterior region of heads, pericardial edemas, enlarged trunks, and bent tails. These results suggested that TBT is very toxic to X. tropicalis embryos at environmentally relevant concentrations.

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.

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.

Road proximity increases risk of skeletal abnormalities in wood frogs from National Wildlife Refuges in Alaska

BACKGROUND

Skeletal and eye abnormalities in amphibians are not well understood, and they appear to be increasing while global populations decline. Here, we present the first study of amphibian abnormalities in Alaska.

OBJECTIVE

In this study we investigated the relationship between anthropogenic influences and the probability of skeletal and eye abnormalities in Alaskan wood frogs (Rana sylvatica).

METHODS

From 2000 to 2006, we examined 9,269 metamorphic wood frogs from 86 breeding sites on five National Wildlife Refuges: Arctic, Innoko, Kenai, Tetlin, and Yukon Delta. Using road proximity as a proxy for human development, we tested relationships between skeletal and eye abnormalities and anthropogenic effects. We also examined a subsample of 458 frogs for the trematode parasite Ribeiroia ondatrae, a known cause of amphibian limb abnormalities.

RESULTS

Prevalence of skeletal and eye abnormalities at Alaskan refuges ranged from 1.5% to 7.9% and were as high as 20% at individual breeding sites. Proximity to roads increased the risk of skeletal abnormalities (p = 0.004) but not eye abnormalities. The only significant predictor of eye abnormalities was year sampled (p = 0.006). R. ondatrae was not detected in any Alaskan wood frogs.

CONCLUSIONS

Abnormality prevalence at road-accessible sites in the Kenai and Tetlin refuges is among the highest reported in the published literature. Proximity to roads is positively correlated with risk of skeletal abnormalities in Alaskan wood frogs.

A Ribeiroia spp. (class: Trematoda)--specific PCR-based diagnostic

Increased reporting of amphibian malformations in North America has been noted with concern in light of reports that amphibian numbers and species are declining worldwide. Ribeiroia ondatrae has been shown to cause a variety of types of malformations in amphibians. However, little is known about the prevalence of R. ondatrae in North America. To aid in conducting field studies of Ribeiroia spp., we have developed a polymerase chain reaction (PCR)-based diagnostic. Herein, we describe the development of an accurate, rapid, simple, and cost-effective diagnostic for detection of Ribeiroia spp. infection in snails (Planorbella trivolvis). Candidate oligonucleotide primers for PCR were designed via DNA sequence analyses of multiple ribosomal internal transcribed spacer-2 regions from Ribeiroia spp. and Echinostoma spp. Comparison of consensus sequences determined from both genera identified areas of sequence potentially unique to Ribeiroia spp. The PCR reliably produced a diagnostic 290-base pair (bp) product in the presence of a wide concentration range of snail or frog DNA. Sensitivity was examined with DNA extracted from single R. ondatrae cercaria. The single-tube PCR could routinely detect less than 1 cercariae equivalent, because DNA isolated from a single cercaria could be diluted at least 1:50 and still yield a positive result via gel electrophoresis. An even more sensitive nested PCR also was developed that routinely detected 100 fg of the 290-bp fragment. The assay did not detect furcocercous cercariae of certain Schistosomatidae, Echinostoma sp., or Sphaeridiotrema globulus nor adults of Clinostomum sp. or Cyathocotyle bushiensis. Field testing of 137 P. trivolvis identified 3 positives with no overt environmental cross-reactivity, and results concurred with microscopic examinations in all cases.

Skeletal morphology and postmetamorphic ontogeny ofAcris crepitans (Anura: Hylidae): A case of miniaturization in frogs

Acris crepitans is a small, semiaquatic member of the treefrog family Hylidae. Much recent attention has been paid to this species because of reports of population declines and malformations, yet few works have considered the skeletal anatomy of this common North American frog. Herein, we provide a detailed description of the morphology and adult ontogeny of the skeleton of A. crepitans, and discuss novel morphologies, interesting postmetamorphic developmental patterns, and intraspecific skeletal variation. The reduced amount of adult ossification, as well as several novel morphologies present in this species, are consistent with patterns of miniaturization seen in other anurans. For example, the skull is poorly ossified, but most of the cranial cartilages are heavily mineralized, the nasal bones are fused to endochondral ossification of the tectum nasi, the palatines are reduced, and the prootics and exoccipitals are not fused to one another (although the prootics are well-developed and ornamented). In addition, several specimens exhibit abnormalities, which might indicate that: (1) the population was under an acute malformation outbreak, (2) a high incidence of small skeletal malformations is normal in this species, (3) the population is under stress because of habitat fragmentation, (4) there is environmental deterioration in the region where the specimens were collected, and/or (5) the species is now showing signs of decline in southern Missouri. Regardless of the cause, it is clear that further examination of skeletal variability in A. crepitans, including ossification patterns and the frequency of abnormalities, is warranted.

ENVIRONMENTAL FACTORS INFLUENCING TREMATODE PREVALENCE IN GREY TREE FROG (HYLA VERSICOLOR) TADPOLES IN SOUTHERN ONTARIO

The emergence or increased prevalence of various parasites may be linked to alterations in host-parasite interactions caused by environmental changes. We investigated prevalence of trematode infections in grey tree frog (Hyla versicolor) tadpoles from ponds in nonagricultural settings versus ponds adjacent to cornfields in southern Ontario. We found that agricultural activity was a significant factor in determining the percentage of tadpoles infected by 1 or more trematodes from 1 or more species (combined trematode infection). However, we found no associations between combined trematode infection and forest cover; pond size; road density; and measures of water quality, such as nitrate level and the presence of the herbicide atrazine. Although combined trematode prevalence was associated only with agricultural activity, prevalence of Alaria species showed a positive association with forest cover. This latter result probably reflects the importance of habitat suitability for the canid definitive hosts of this trematode species.

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.

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.