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排序方式: 共有450条查询结果,搜索用时 15 毫秒
1.
Effects of roads and land use on frog distributions across spatial scales and regions in the Eastern and Central United States 下载免费PDF全文
David M. Marsh Bradley J. Cosentino Kara S. Jones Joseph J. Apodaca Karen H. Beard Jane Margaret Bell Christine Bozarth Derrick Carper Julie F. Charbonnier Andreia Dantas Elizabeth A. Forys Miran Foster Jaquelyn General Kristen S. Genet Macie Hanneken Kyle R. Hess Shane A. Hill Faisal Iqbal Nancy E. Karraker Eran S. Kilpatrick Tom A. Langen James Langford Kathryn Lauer Alison J. McCarthy Joseph Neale Saumya Patel Austin Patton Cherie Southwick Nathaniel Stearrett Nicholas Steijn Mohammad Tasleem Joseph M. Taylor James R. Vonesh 《Diversity & distributions》2017,23(2):158-170
2.
Selective deposition of BaSO4 in the tight junctions (TJs) of frog skins led to profound and reversible functional alterations of these structures, as revealed by changes of tissue conductance (G), clamping current (I), and fluxes of extracellular markers (sulfate (JSO
4) and sucrose (JSUC)). Experiments were performed with nominally Ca2+ -free simple salt solutions on the apical side (usually KCl) and Na2SO4-Ringer on the inner side of skins. The deposition of BaSO4 in the TJs was obtained by diffusion and/or migration through the paracellular path of Ba2+ from the apical solution and SO
4
2–
from the inner solution. A brief presence (2 to 6 min) of apical Ba2+ (Ba2+ pulse) is followed (i.e., when Ba2+ is removed from the apical fluid) by a large increase of G, I, JSO
4 and JSUC, above pre-Ba2+ levels. These attain a steady state within 15 to 30 min (overshoot phase), characterizing a conspicuous increase of the paracellular permeability. During the overshoot phase, a second Ba2+ pulse blocks the paracellular route while apical Ba2+ is present, leading to a new and larger overshoot when the Ba2+ pulse is terminated. Addition of apical Ca2+ triggers the resealing of the TJs, resulting in a full recovery of G, I, JSO
4 and JSUC. This Ca2+ -induced recovery persists when apical Ca2+ is removed. The presence of a normal Ca2+ concentration in the inner bathing Ringer does not induce the recovery process. Tissues remain viable after being submitted to the Ba2+ treatment and the subsequent overshoot. Experiments performed in the urinary bladder of Rana catesbeiana and skins and urinary bladders of Bufo marinus indicate that Ba2+ effect can also be elicited in these tissues. The above results seem to report general properties of the TJs. Incidentally, they warn about the use of Ba2+ as an ion channel blocker in epithelial membranes in association with SO
4
2–
-containing solutions on the contralateral side.This project was supported by grants from Fundação de Amparo à Pesquisa do Estado de São Paulo (91/0293-7 to F.L.V., and 90/1788-1 to A.S.), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (410068/90-0 and 303633-85/BF to F.L.V.). J.A.C. received a doctoral fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior/Fundação Universidade do Rio Grande. We thank Dr. Alice T. Ferreira for help in the measurements of free Ca2+ concentration. 相似文献
3.
Gentile Francesco Ficetola Dario Furlani Giorgio Colombo Fiorenza De Bernardi 《Biodiversity and Conservation》2008,17(9):2185-2195
Secondary forests constitute a growing portion of forested areas worldwide. They might have a substantial role for the conservation
of biodiversity in tropical areas, but there is little information on their potential to support forest species and the recovery
of faunal communities. We studied two forest frogs (Eleutherodactylus diastema and E. fitzingeri) in an area of Costa Rica composed of a mosaic of primary forest, young secondary forest and pasture, and we compared the
density of calling males in areas with different forest alteration. Autoregressive models were used to compensate for potentially
undesired effects of spatial autocorrelation and pseudoreplication. Both species were most abundant in riparian, primary forest.
However, E. fitzingeri was also abundant in riparian secondary forests, and its density far from the river was similar in primary and secondary
forest, suggesting that river proximity can influence the recovery of secondary forest for amphibians. Conversely, the density
of E. diastema was similar in secondary forest and pasture, stressing interspecific differences for recovery rate. These frogs have a keystone
role in nutrient cycling and food webs, and their prompt recovery might represent an important step for the functional recovery
of forests. Nevertheless, the strong interspecific differences stress the complexity of these processes. 相似文献
4.
Summary AHG-associated protein (AHG-a.p.), the antigen of the blood-clotting factor VIII complex, is a specific endothelial cell marker. Primary (p-XTH) and established (XTH-2) endothelial cells from the hearts of Xenopus laevis tadpoles were assayed for the presence of this marker by means of immunological cross-reaction (recognition of common antigenic sites) with antiserum against human AHG-a.p. Radial imtnunodiffusion and rocket immunoelectrophoresis proved to be insufficiently sensitive, whereas immunofluorescence and a newly evaluated ELISA technique gave positive results. The very high sensitivity of the ELISA (less than 1/240000 of the AHG-a.p. in 0.1 ml human standard plasma can be detected) and the removal of interfering proteins by gel filtration also revealed the presence of AHG-a.p. in the fetal calf serum used in the culture medium; earlier investigations into this subject by a one-step radioimmunoassay had reported negative results. Specially adapted XTH-2 cells were grown in a proteinand serum-free hydrolysate medium in order to demonstrate the presence of a Xenopus-derived antigen that was immunoreactive with the anti-human AHG-a.p. 相似文献
5.
A ‘big’ frog (Rana esculenta) neurophysin, encompassing sequences homologous to mammalian MSEL-neurophysin and copeptin, has been passed through a trypsin-Sepharose column in order to compare its conformation with that of the two-domain intermediate precursor isolated from guinea pig. Whereas the polypeptide possesses 8 arginine residues, only two cleavages were observed located in a putative inter-domain sequence (at Arg-94 and Arg-114). Because free vasotocin has been isolated from the frog, it is assumed that pro-vasotocin has a three-domain conformation similar to that of pro-vasopressin but processing in amphibians involves only one step rather than two steps as in mammals. 相似文献
6.
Fabián Michelangeli Dalia M. Sulcas Marie-Christine Ruiz 《Cell and tissue research》1987,250(2):413-419
Summary This study is concerned with electron-microscopic observations on endocrine or paracrine cells in the fundic gastric mucosa of the bullfrog. Also, an attempt was made to identify the histamine-releasing cells involved in the secretagogue response. At least three distinct endocrine-like cell types were found. The classification is based on the appearance of secretory granules and other organelles, and the relationship of endocrine-like cells with other cells in the tissue. The amphibian endocrine-like cells resemble the ECL, D and EC cells of mammals. Type-I (ECL) cells showed degranulation after repeated stimulation with tetragastrin (TG), acetylcholine (ACh) and K+ depolarizing solution, all of which release histamine. 相似文献
7.
《Cryobiology》2019
Global amphibian declines have fueled an increased interest in amphibian assisted reproductive technologies. Within the genus Rhaebo, half of the species are experiencing decreasing population trends; however, insufficient information is available on many of these species’ reproductive biology. Using the smooth-sided toad, Rhaebo guttatus, we present effective methods for collecting and cryopreserving an example of Rhaebo sperm. Specifically, our findings show that administering 10 IU/g body weight of hCG (human chorionic gonadotropin) yields the most motile and concentrated sperm and that cryopreserving spermic urine in a solution of 5% DMFA (N,N-Dimethylformamide) and 10% trehalose returns sperm with a 33 ± 3% average post-thaw motility. These findings may represent an important step forward in developing techniques that can be safely applied to other, more vulnerable species within the Rhaebo genus. 相似文献
8.
Andrew R. Blaustein John M. Romansic Joseph M. Kiesecker Audrey C. Hatch 《Diversity & distributions》2003,9(2):123-140
Abstract. As part of an overall ‘biodiversity crisis’, many amphibian populations are in decline throughout the world. Numerous factors have contributed to these declines, including habitat destruction, pathogens, increasing ultraviolet (UV) radiation, introduced non‐native species and contaminants. In this paper we review the contribution of increasing UV radiation and environmental contamination to the global decline of amphibian populations. Both UV radiation and environmental contaminants can affect amphibians at all life stages. Exposure to UV radiation and to certain contaminants can kill amphibians and induce sublethal affects in embryos, larvae and adults. Moreover, UV radiation and contaminants may interact with one another synergistically. Synergistic interactions of UV radiation with contaminants can enhance the detrimental effects of the contaminant and UV radiation. 相似文献
9.
Albert S. Feng Peter M. Narins 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2008,194(2):159-167
The concave-eared torrent frogs (Amolops tormotus) have highly unusual ear morphology--in males the eardrums are embedded deep inside ear cavities. In collaboration with our colleagues we investigated the functional significance of this morphological feature in hearing. Sound recordings in the field showed that males of A. tormotus produce diverse bird-like melodic calls with pronounced frequency modulations and non-linear phenomena (e.g., frequency jumps, different orders of subharmonics, and chaos) that often contain spectral energy in the ultrasonic range. The audible as well as the ultrasonic components of the species call could effectively evoke males' vocal responses, demonstrating that they can hear and respond to ultrasound. Electrophysiological recordings from the auditory midbrain confirmed the ultrasonic hearing capacity of these frogs. The recessed tympana and extremely thin tympanic membranes are adaptations for hearing ultrasound--this sensitivity may have evolved in response to the intense, predominately low-frequency ambient noise from local streams. Finally, results from the isolated laryngeal preparation in euthanized frogs revealed that the origin of call complexity and diversity lies with having a vocal system with nonlinear properties. 相似文献
10.
Jeremy M. Cohen Taegan A. McMahon Chloe Ramsay Elizabeth A. Roznik Erin L. Sauer Scott Bessler David J. Civitello Bryan K. Delius Neal Halstead Sarah A. Knutie Karena H. Nguyen Nicole Ortega Brittany Sears Matthew D. Venesky Suzanne Young Jason R. Rohr 《Ecology letters》2019,22(5):817-825
Global climate change is increasing the frequency of unpredictable weather conditions; however, it remains unclear how species‐level and geographic factors, including body size and latitude, moderate impacts of unusually warm or cool temperatures on disease. Because larger and lower‐latitude hosts generally have slower acclimation times than smaller and higher‐latitude hosts, we hypothesised that their disease susceptibility increases under ‘thermal mismatches’ or differences between baseline climate and the temperature during surveying for disease. Here, we examined how thermal mismatches interact with body size, life stage, habitat, latitude, elevation, phylogeny and International Union for Conservation of Nature (IUCN) conservation status to predict infection prevalence of the chytrid fungus Batrachochytrium dendrobatidis (Bd) in a global analysis of 32 291 amphibian hosts. As hypothesised, we found that the susceptibility of larger hosts and hosts from lower latitudes to Bd was influenced by thermal mismatches. Furthermore, hosts of conservation concern were more susceptible than others following thermal mismatches, suggesting that thermal mismatches might have contributed to recent amphibian declines. 相似文献