Amphibian chytridiomycosis

Amphibian chytridiomycosis is a fungal disease caused by the chytrid fungus Batrachochytrium dendrobatidis. It is arguably the most significant recorded infectious disease of any vertebrate class. The disease is reducing amphibian biodiversity across most continents and regions of the world, affecting the resilience of surviving populations and driving multiple species to extinction. It is now recognised by the World Organisation for Animal Health (OIE) as an internationally notifiable disease. Collaborative research in areas including the development of diagnostic assays, distribution and impact of the disease, and management (treatment and policy) has assisted in leading a paradigm shift in accepting infectious disease as a major factor influencing wildlife population stability and biodiversity.     

Amphibian tachykinin precursor

The precursor of amphibian tachykinin has not been found although more than 30 tachykinins have been isolated from amphibians since 1964. In this report, two tachykinin-like peptides are identified from the skin secretions of the frog, Odorrana grahami. Their amino acid sequences are DDTEDLANKFIGLM-NH(2) (named tachykinin OG1) and DDASDRAKKFYGLM-NH(2) that is the same with ranamargarin found in Rana margaretae, respectively, with a conserved FXGLM-NH(2) C-terminal consensus motif. By cDNA cloning, their precursors were screened from the skin cDNA library of O. grahami. The precursors are composed of 61 amino acid (aa) residues including a signal peptide followed by an acidic spacer peptide and one copy of mature tachykinin-like peptide. Their overall structure is different from structures of other tachykinin precursors such as human protachykinin 1 precursor containing 143 aa including one copy of substance P (SP) and neurokinin A (NKA), and ascidian tachykinin 1 precursor containing 164 aa including two copies of tachykinin-like peptides. The current results demonstrate that the biosynthesis mode of tachykinins in amphibians is different from other animals.     

湖北省两栖动物资源概况

通过总结文献资料并结合作者等近20余年调查积累的资料,从区系特点、地理分布、保护级别等方面总结了湖北省两栖动物的资源概况.湖北省现有两栖动物2目10科28属69种,其中东洋界61种,占88.4%,古北界4种,占5.8%,广布种4种, 占5.8%;国家Ⅱ保护动物 3种,即大鲵Andrias davidianus、细痣疣螈Tylototriton asperrimus、虎纹蛙Hoplobatrachus rugulosus,占4.3%;列入<中国濒危动物红皮书>的珍稀濒危物种8种,占11.6%;省级重点保护动物23种,占33.3%.可见湖北省两栖动物资源具有以东洋界华中区种类为主、省内各区分布不均、濒危保护种类丰富等特点.     

Hormonal Interaction in Amphibian Metamorphosis

SYNOPSIS. The climactic stages of amphibian metamorphosis constitutea period characterized by radical morphological changes thatare driven primarily by the thyroidal hormones. Radioimmunoassaysshow that levels of thyroid hormones (TH) rise to a peak duringmetamorphic climax. Accompanying peaks are reported for ACTH,adrenal corticoids (AC), insulin (I) and prolacdn (PRL). ACenhance the metamorphic action of TH by increasing their bindingto nuclei of target cells. TH, in turn, act to raise levelsof AC by stimulating the differentiation of the median eminencethus facilitating the flow of a CRF from the hypothalamus tothe adenohypophysis, by synergizing with ACTH and bystimulationof the interrenals through some other route. During the metamorphicperiod, at least as far as climax, PRL antagonizes TH, perhapsat the thyroidal level and certainly at the level of targetcells. PRL may antagonize by inhibiting induction of hydrolyticenzymes by TH, by alteration of hydromineral responses or byaltering levels of binding of TH to receptors. The antagonisticaction of PRL is mimicked by cAMP. A surge of PRL that is releasedinto the plasma during metamorphic climax seemingly producesno antagonistic effect on thyroidal actions.     

Passive Intercellular Pathway in Amphibian Epithelia

PHYSIOLOGIC studies of transporting epithelia generally indicate that passive shunts (or “leak” pathways for water and ions) exist in parallel with transport systems. Most notably, Ussing^1–3 defines this pathway as an extracellular channel in amphibian skin and has shown that a hypertonic external bath decreases the transepithelial electrical resistance, whereas a hypertonic internal bath has the opposite effect. Similar results have been obtained with toad urinary bladder⁴, but in virtually all of the epithelia studied by electron microscopy, tight junctions⁵ have been found at the luminal end of intercellular spaces. Apparent fusion of adjacent plasma membranes and the inability of electron-dense tracer molecules to pass through such regions^5–8 suggest that they may be tight seals, preventing extracellular transepithelial flow. It is shown that these junctions are reproducibly altered when electrical resistance is changed by hypertonic solutions.     

Microtubules and Microfilaments in Amphibian Neurulation

In the salamander embryo, the morphogenetic movements of neurulationare correlated with two cell shape changes in the neural epithelium:elongation and apical constriction of the columnar neural platecells. Cells first elongate to form the flat open neural plateand then constrict apically as the plate rolls up to form theneural tube. Evidence is presented that these cell shape changesare intrinsic to the cells themselves and that they play a causalrole in the morphogenetic movements. Neural plate cells containnumerous microtubules oriented parallel to the axis of elongation.These microtubules are critical to the elongation process. Possiblemechanisms for microtubule function in cell elongation are considered.During apical constriction the cells contain bundles of microfilamentswhich encircle the cell apex in purse-string fashion. Evidenceis presented which suggests that microfilament bundles playan active role in apical constriction, and that this localizedcontraction is produced by filament sliding.     

Amphibian biology and husbandry

Extant amphibians comprise three lineages-- salamanders (Urodela or Caudata), frogs and toads (Anura), and caecilians (Gymnophiona, Apoda, or Caecilia)--which contain more than 6,000 species. Fewer than a dozen species of amphibians are commonly maintained in laboratory colonies, and the husbandry requirements for the vast majority of amphibians are poorly known. For these species, a review of basic characteristics of amphibian biology supplemented by inferences drawn from the morphological and physiological characteristics of the species in question provides a basis for decisions about housing and feeding. Amphibians are ectotherms, and their skin is permeable to water, ions, and respiratory gases. Most species are secretive and, in many cases, nocturnal. The essential characteristics of their environment include appropriate levels of humidity, temperature, and lighting as well as retreat sites. Terrestrial and arboreal species require moist substrates, water dishes, and high relative humidity. Because temperature requirements for most species are poorly known, it is advisable to use a temperature mosaic that will allow an animal to find an appropriate temperature within its cage. Photoperiod may affect physiology and behavior (especially reproduction and hibernation), and although the importance of ultraviolet light for calcium metabolism by amphibians is not yet known, ecological observations suggest that it might be important for some species of frogs. Some amphibians are territorial, and some use olfactory cues to mark their territory and to recognize other individuals of their species. All amphibians are carnivorous as adults, and the feeding response of many species is elicited by the movement of prey. Diets should include a mixture of prey species, and it may be advisable to load prey with vitamins and minerals.     

Amphibian malformations and inbreeding

Inbreeding may lead to morphological malformations in a wide variety of taxa. We used genetic markers to evaluate whether malformed urodeles were more inbred and/or had less genetic diversity than normal salamanders. We captured 687 adult and 1259 larval tiger salamanders (Ambystoma tigrinum tigrinum), assessed each individual for gross malformations, and surveyed genetic variation among malformed and normal individuals using both cytoplasmic and nuclear markers. The most common malformations in both adults and larvae were brachydactyly, ectrodactyly and polyphalangy. The overall frequency of adults with malformations was 0.078 compared to 0.081 in larval samples. Genetic diversity was high in both normal and malformed salamanders, and there were no significant difference in measures of inbreeding (f and F), allele frequencies, mean individual heterozygosity or mean internal relatedness. Environmental contaminants or other extrinsic factors may lead to genome alternations that ultimately cause malformations, but our data indicate that inbreeding is not a causal mechanism.     

Amphibian sympathetic ganglia in tissue culture

1. A culture medium has been developed for amphibian sympathetic nervous tissue but it is suggested that the ionic values should be adjusted to correspond to the concentrations of salts in the plasma of particular species. 2. The morphology, monoamine fluorescence, growth and differentiation of sympathetic ganglia of the frog, Limnodynastes dumerili, have been studied in culture. 3. Two types of neuron could be distinguished largely according to size, namely small, 18 X 20 mum and large, 38 X 42 mum. The possibility that these represent one type at different stages in development or represent functionally distinct neurons is discussed. 4. The sympathetic neurons are extremely sensitive to nerve growth factor (NGF) which caused an increase in the size of the cell bodies, the number of nerve fibres regenerating, the rate of axonal growth and synthesis of catecholamines. 5. Various other cell types appearing in the cultures have been described, including chromaffin, satellite, Schwann, multipolar and epithelial cells as well as fibroblasts, melanocytes and macrophages. The epithelial cells show slow contractions and changes in shape.     

Amphibian development in the fossil record

Ontogenetic series of extinct taxa are extremely rare and when preserved often incomplete and difficult to interpret. However, the fossil record of amphibians includes a number of well-preserved ontogenetic sequences for temnospondyl and lepospondyl taxa, which have provided valuable information about the development of these extinct groups. Here we summarize the current knowledge on fossil ontogenies of amphibians, their potential and limitations for relationship assessments, and discuss the insights they have provided for our understanding of the anatomy, life history, and ecology of extinct amphibians.     

Amphibian Pathogen Batrachochytrium dendrobatidis Is Inhibited by the Cutaneous Bacteria of Amphibian Species

Population declines of amphibian species in many parts of the world are associated with a lethal fungal pathogen, Batrachochytrium dendrobatidis. Using laboratory challenge assays, we describe the inhibition of B. dendrobatidis by members of eight genera of bacteria isolated from the skin of two amphibian species that exhibit parental care behavior (Plethodon cinereus and Hemidactylium scutatum). We found that members of three genera of bacteria isolated from the skins of the salamander P. cinereus and members of seven genera isolated from the salamander H. scutatum inhibited the growth of B. dendrobatidis. Understanding how B. dendrobatidis interacts with an ecological community of cutaneous flora may be important in explaining and preventing amphibian population declines.     

Amphibian Pathogens in Southeast Asian Frog Trade

Amphibian trade is known to facilitate the geographic spread of pathogens. Here we assess the health of amphibians traded in Southeast Asia for food or as pets, focusing on Batrachochytrium dendrobatidis (Bd), ranavirus and general clinical condition. Samples were collected from 2,389 individual animals at 51 sites in Lao PDR, Cambodia, Vietnam and Singapore for Bd screening, and 74 animals in Cambodia and Vietnam for ranavirus screening. Bd was found in one frog (n = 347) in Cambodia and 13 in Singapore (n = 419). No Bd was found in Lao PDR (n = 1,126) or Vietnam (n = 497), and no ranavirus was found in Cambodia (n = 70) or Vietnam (n = 4). Mild to severe dermatological lesions were observed in all East Asian bullfrogs Hoplobatrachus rugolosus (n = 497) sampled in farms in Vietnam. Histologic lesions consistent with sepsis were found within the lesions of three frogs and bacterial sepsis in two (n = 4); one had Gram-negative bacilli and one had acid-fast organisms consistent with mycobacterium sp. These results confirm that Bd is currently rare in amphibian trade in Southeast Asia. The presence of Mycobacterium-associated disease in farmed H. rugolosus is a cause for concern, as it may have public health implications and indicates the need for improved biosecurity in amphibian farming and trade.     

Mechanisms of Melanophore Induction in Amphibian Development

Induction of melanophores was examined by the sandwich method of explantation with embryonic tissues of Xenopus laevis +/+ and the white mutant, a^P/a^P. Interspecific combinations of tissues of Triturus taeniatus and Xenopus borealis were also used. The ectoderm used as the reacting system was taken from embriyos at various stages and combined with various tissues known to be melanogenic inductors. The following results were obtained: 1) The sources of melanophore induction in both +/+ and a^p/a^p studied by sandwich explantation were the same in both retinal pigmented epithelium and dermal melanophores: 2) Melanophores were induced in epidermal material from embryos at stages from the early gastrula to the late tail bud stage: 3) The presence of melanoblasts together with other ectomesenchymal cells in the neural crest is not sine qua non for their determination and differentiation: 4) On isolation of reacting material from the late gastrula, melanophores appeared in all cases. This shows that two hours contact between inductor tissues and the ectoderm is necessary and sufficient for melanophore induction: 5) Melanophore induction is not species-specific, but occurred in Xenopus ectoderm under the action of endomesoderm of Tr. taeniatus or X. borealis , and vice versa. The shapes and structures of melanophores induced were typical for the species from which the ectoderm was taken: 6) Melanogenic activity in the late gastrula stage has a gradient of distribution with a maximum in the prechordal plate: 7) In the mutant only the primary source of melanogenic inductors, the prechordal plate (PrP1), was active in stages both before and after its invagination: 8) Despite the fact that skin melanophores and retinal melanocytes have different genesis in development, all the present data suggest the identity of the mechanisms of melanin synthesizing machinery in the two.     

贵州雷公山自然保护区两栖动物调查报告

2005年5月~2006年11月,对贵州雷公山自然保护区的两栖动物进行了5次野外调查,根据实际地形调查采用样线法或样方法,调查地点为毛坪、平祥、雷公山工区、格头、小丹江、昂英、桥歪、雷公坪、西江、桃江、高岩、交腊等地。结果显示,保护区共有36种两栖动物,隶属2目8科19属,其中国家II级保护动物2种,即大鲵和细痣疣螈。分析了保护区两栖动物的物种组成、区系特征、垂直分布和雷公山模式产地的种类。     

Determination of Extracellular Space in Amphibian Muscle

The volumes of distribution of inulin and dextran in the sartorius, stomach, and cardiac muscle of the frog agree rather closely. That these spaces represent the volume of extracellular water is supported by the observation that efflux of sucrose can be divided into a fast and a slow phase and that the fast-moving fraction corresponds closely with inulin space determined in the same muscle. These and other findings confirm that sugars and related substances penetrate slowly into part of the fiber water and that, therefore, their volume of distribution does not accurately represent the volume of extracellular water. The kinetics of efflux of sucrose is consistent with the assumption that the movement of sugars is determined by the resistance of the cell surface as well as by internal diffusion. In connective tissue, sucrose and inulin are excluded only from a small part of the total water.