Deformity Levels in Wild Populations of the Wood Frog (Rana sylvatica) in Three Ecoregions of Western Canada

Ontogenetic development of the oral apparatus and oropharyngeal cavity in bullfrog tadpoles (Lithobates catesbeianus, Shaw 1802)

OBJECTIVE

The present study aimed to describe the morphology of oral apparatus and oral cavity of bullfrog tadpoles during their development and metamorphosis.

DESIGN

The oral apparatus and oropharyngeal cavity of tadpoles from hatching up to metamorphosis stage was dissected for further analysis. These structures were fixed in Karnovsky solution, afterwards in osmium tetroxide and metalized in palladium gold and electron-micrographed using the scanning electron microscope.

RESULTS

The development of oral apparatus started with the formation and keratinization of the jaw sheaths and labial teeth followed by the formation of marginal and sub-marginal papillae. Degeneration of oral apparatus and formation of mouth was observed during metamorphosis. From stage-42 (metamorphic climax) to stage-43, the jaw sheath and labial tooth rows were disappeared progressively while the size and number of labial papillae were decreased. At stage-44, mouth formation started with the development of anterior and posterior labium though the labial papillae were still present. At stage-45 and 46, mouth was already formed, being very similar to the adult and characterized by the progressive increase in size.

CONCLUSION

The sequence of events that happen during the development of oral apparatus of Lithobates catesbeianus Shaw, 1802 tadpoles follows the same pattern as occur in other anuran species but metamorphic atrophy of the oral apparatus follows the sequence of morphogenesis.

Habitat quality affects the incidence of morphological abnormalities in the endangered salamander Ambystoma ordinarium

Identification of early warning signals previous to the occurrence of population decline or extinction is a major challenge for the conservation of animal species. Prevalence of morphological abnormalities in a population can be one of these signals. We registered morphological abnormalities in the salamander Ambystoma ordinarium. We also evaluated the relation between habitat quality and the prevalence of abnormalities in this species. We used scores from rapid bioassessment protocols (RBPs) to assess the habitat quality of streams inhabited by A. ordinarium. A preliminary survey indicated that of 29 streams where this species has been historically registered, 13 might have few or no A. ordinarium. The association between habitat quality and the incidence of morphological abnormalities was evaluated in these 16 streams. Of 502 sampled individuals, 224 (44.62%) had at least one body abnormality. Of the 224 individuals with body abnormalities, 84 (37.5%) presented more than one abnormality. Of a total of 5,522 evaluated morphological characters, 344 (6.74%) were abnormal. Partial loss of gills and missing digits were the most frequent abnormalities. Results of a binomial logistic regression indicated that the probability of a character of an individual to be abnormal was significantly associated with habitat quality; as the levels of the quality of the habitat increased, the prevalence of morphological abnormalities decreased. These results suggest that RBPs are a quick and useful method for assessing the habitat quality of streams inhabited by A. ordinarium. Given that RBPs provide rapid and cost-effective assessments of the ecological health of aquatic ecosystems, it will be important to test if the RBPs protocols can be used to rapidly assess habitat quality for other species of stream amphibians. The negative association between habitat quality and the prevalence of morpohological abnormalities that we found indicates that habitat condition plays an important role in the high number of abnormalities registered in A. ordinarium. Therefore, our results suggest that one of the several negative effects of habitat degradation on amphibians is an increase in the frequency of morphological abnormalities with marked consequences for the survival and general fitness of aquatic amphibians.

Amphibian malformations and body condition across an agricultural landscape of northwest Argentina

Agricultural landscapes support large amphibian populations because they provide habitat for many species, although agriculture affects amphibians through various mechanisms. Pollution with agrochemicals is the major threat to amphibian populations after habitat loss, as chemicals alter the ecophysiology of amphibians, putting their health and survival at risk. We aimed to assess the effect of different environments, sites, width of forest buffers and sampling years on the health of amphibians, which was estimated through the prevalence of malformations and body condition. During 3 yr of pitfall trapping, we captured 4491 amphibians. The prevalence of malformations was higher in the croplands than in the forests, while the body condition was better within forests. The prevalence of malformations was higher in the narrower forest site than in the wider forest site. The prevalence of malformations and the body condition were higher in the third year. The prevalence of malformations differed by species. We found 11 types of malformation, which mainly affected limbs and were unilateral or bilaterally asymmetrical. Our results showed that the prevalence of malformations and body condition reflect different aspects of the health of amphibians and that forest individuals are healthier than those from croplands. The results also highlight the importance of spatial configuration besides the conservation of natural habitats to preserve healthy amphibians in agricultural landscapes. The types of malformation that we found suggest that agrochemicals could be an important cause of malformations.

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.

Ribeiroia ondatrae causes limb abnormalities in a Canadian amphibian community

A parasitic flatworm ( Ribeiroia ondatrae Price, 1931) is known to cause severe limb abnormalities and high mortality levels in American amphibian populations. The distributional pattern of this parasite—its main dispersal agent being birds—correlates with the boundaries of migratory flyways in the USA. Yet thus far, R. ondatrae have not been found in Canadian amphibians, which is surprising, considering that said flyways extend well into northern Canada. In this study, we report on a lake in British Columbia that is known to support amphibians with abnormalities similar to those induced by R. ondatrae. To determine if the parasite was present and if it was the cause of the abnormalities, we collected and necropsied metamorphs of the Columbia Spotted Frog ( Rana luteiventris Thompson, 1913) and the Pacific Chorus Frog ( Pseudacris regilla (Baird and Girard, 1852)), and we set up field enclosures to protect larvae from R. ondatrae. Abnormality levels were high in both species (>20%), with the vast majority being found in close proximity to the metacercariae of R. ondatrae. Moreover, the types of abnormalities closely matched those previously recorded in field and laboratory exposures of amphibians to R. ondatrae. Finally, larvae that developed in the same lake, but were protected from R. ondatrae by an enclosure, did not develop abnormalities. Collectively, these results demonstrate that R. ondatrae are both present in an amphibian community in Canada and responsible for causing limb abnormalities.

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.

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.

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.