Amphibian

Ecosystem Responses to Mercury Contamination Indicators of Change 

Desirable characteristics of candidate biomonitor species and ranking according to characteristic 

Based on the scoring in Table 5.1 (summing scores for each species), candidate bioindicator species can be ranked within a taxonomic group according to suitability for a mercury monitoring program for North America  

Terrestrial and aquatic mammals, from highest to lowest mink, raccoon, river otter, bats. 

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The amphibian metamorphosis test is based on the abiUty of thyroid hormones to induce precocious transformation of a tadpole into a frog or of the axolod into a salamander. It is rarely used because of solubiUty problems and the difficulty of applying the results to humans. 

There is some evidence for chemically mediated endocrine disruption in amphibians. The egg yolk protein, vitellogenin, is inducible in amphibians by exposure to DDT. " Males of the short clawed toad Xenopus laevis given 250 fig/g or 1 fig/g o,p -DDT for seven days have been shown to produce vitellogenin, although the induction was less than that achieved by treatment with 1 fig/g of either 17/1-oestradiol or diethylstilboestrol. Research has also shown that endocrine disrupting chemicals can alter sex ratios in wild populations of certain species PCB congeners and organochlorine compounds have been linked with male domination of sex ratios in polluted compared to unpolluted sites. ... 

Amphibians. Amphibians are highly susceptible to endocrine disruption during development of the larval form and during metamorphosis. The action of metamorphosis is triggered and controlled by the thyroid gland via an increase in triiodothyronine and a decrease in thyroxine, and differs greatly between oviparous and viviparous species. Experimentally, it has been shown that disruption during this sensitive period can lead to malformations and adverse impacts on immune and reproductive functions. 

Amphibians. Immunosuppression has been shown to occur during metamorphosis in several amphibians, and appears to be hormonally regulated. The disappearance of 11 populations of toad from Colorado was associated with immune suppression, and frog mortalities have been associated with infection by a commonly occurring bacteria, Aeromonas hydrophila the cause of the immunosuppression in these animals has not been elucidated. " ... 

Carborvlerous) 320 Coal forests, nsects. amphibians, reptiles... 

Apelins and the Apelin Receptor. Figure 2 Sequence alignment of mammalian and amphibian apelin-36 amino-acid sequences, indicates residues conserved across all the species shown. Residues which differfrom the human sequence are highlighted in red. 

Amphibians such as frogs and salamanders depend heavily on temporary ponds for breeding. These ponds are highly vulnerable to the "acid shock" events associated with storms or snowmelt. In several studies, reproduction of amphibians has been shown to be seriously restricted when acidity of their habitat decreases to a pH value of less than 5 14). 

Devonian 400 Myr Continents collide at end of period. Asteroid probably collides with Earth. Diversification of bony and cartilaginous fishes trilobites diversify origin of ammonoids, amphibians, insects first forests. Mass extinction at end of period (ca. 75% of species disappear)... 

Carboniferous 345 Myr Climate cools, marked latitudinal gradients. Extensive forests of early vascular plants, especially club mosses, horsetails, ferns. Coal beds form. Amphibians diversify first reptiles appear. Radiation of early insect orders... 

Phylum Chordata Tunicates, sharks, bony fishes, amphibians, reptiles, birds, mammals... 

Mcmenamin SK, Hadly EA, Wright CK (2008) Climatic change and wetland desiccation cause amphibian decline in Yellowstone National Park. Proc Natl Acad Sci USA 105 16988-16993... 

LeNoir J, Aston L, Datta S, et al. 1998. Pesticides and polychlorinated biphenyls in Sierra Nevada ecosystems Potential relationship to decline of amphibians. Division of Environmental Chemistry Preprints of Extended Abstracts 38(2) 264-266. 

Excretory processes for xenobiotics are best understood for mammals, with far less work having been done on birds, reptiles, and amphibians. Highly lipophilic compounds show little tendency to be excreted unchanged. In the absence of effective metabolism, they tend to have very long biological half-lives in depot fat. Thus, half-lives of about 1 year have been reported for p,p -DDE in birds, whereas higher... 

There is strong evidence that DNA adduction by these bulky reactive metabolites of PAHs is far from random, and that there are certain hot spots that are preferentially attacked. Differential steric hindrance and the differential operation of DNA repair mechanisms ensure that particular sites on DNA are subject to stable adduct formation (Purchase 1994). DNA repair mechanisms clearly remove many PAH/ guanine adducts very quickly, but studies with P postlabeling have shown that certain adducts can be very persistent—certainly over many weeks. Evidence for this has been produced in studies on fish and Xenopus (an amphibian Reichert et al. 1991 Waters et al. 1994). 

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