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PubMed1994

Visual lexical access is initially phonological: 1. Evidence from associative priming by words, homophones, and pseudohomophones.

In 9 experiments, a target word (e.g., frog) was named following an associate (TOAD), or a word (e.g., TOWED) or nonword (e.g., TODE) homophonic with the associate. At brief (e.g., 50 ms) stimulus onset asynchronies (SOAs), the 3 primes produced equal associative priming. At a long SOA (250 ms), priming by TOAD was matched by TODE but not by TOWED. Equal priming at brief SOAs by the 3 primes and no priming by orthographic controls (TOLD, TORD) suggests that lexical access is initially phonological. TOWED priming less than TODE at SOA = 250 ms suggests that phonologically activated representations whose input orthography does not match the addressed spelling (available only for words) are eventually suppressed. Phonological constraints on lexical access precede and set the stage for orthographic constraints.

Adult↗
PubMed1999

Genetic structure of island populations of the anurans rana temporaria and bufo bufo

Amphibians have traditionally been considered to have low dispersal ability and they have become a model for studies on the effects of man-made habitat fragmentation on genetic variation and population differentiation. This study examined the genetic population structure in the common frog (Rana temporaria) and the common toad (Bufo bufo) in an archipelago of the northern Baltic Sea. Heterozygosity was not correlated with distance of the island from the mainland nor, in R. temporaria, with effective population size based on census estimates. Generally, no inbreeding was detected in island populations. The overall differentiation among islands was weak, but the FST values were significantly larger in R. temporaria (FST = 0.068) than in B. bufo (FST = 0.019). Most of the differentiation was a result of differences among groups of islands, differentiation within them playing a minor role. Thus, assuming Wright's island model of migration, gene flow was rather high among closely located islands, but longer distances seemed to form a slight dispersal barrier for R. temporaria. Strong gene flow within the study area was confirmed by lack of isolation by distance. The estimated effective population sizes in R. temporaria were small, the average being 32 breeding females per island. The results indicate that gene flow between island populations across the matrix of open, brackish-water sea is extensive and suggest that the anurans are well able to disperse in this natural metapopulation system.

Journal Article↗
PubMed1999

An electrophoretic study of myosin heavy chain expression in skeletal muscles of the toad Bufo marinus.

In this study we developed an SDS-PAGE protocol which for the first time separates effectively all myosin heavy chain (MHC) isoforms expected to be expressed in iliofibularis (IF), pyriformis (PYR), cruralis (CRU) and sartorius (SAR) muscles of the toad Bufo marinus on the basis of previously reported fibre type composition. The main feature of the method is the use of alanine instead of glycine both in the separating gel and in the running buffer. The correlation between the MHC isoform composition of IF, SAR and PYR muscles determined in this study and the previously reported fibre type composition of IF and SAR muscles in the toad and of PYR muscle in the frog was used to tentatively identify the MHC isoforms expressed by twitch fibre types 1, 2 and 3 and by tonic fibres. The alanine-SDS electrophoretic method was employed to examine changes in the MHC composition of IF, PYR, CRU and SAR muscles with the ontogenetic growth of the toad from post-natal life (body weight < 1 g) to late adulthood (body weight 200-450 g). The developmental changes in the MHC isoform composition of the toad IF muscle observed in this study are in very good agreement with those in the fibre type composition of the developing IF muscle reported in the literature.

Animals↗
PubMed1991

Prostaglandin regulation of H+ secretion in amphibian epithelia.

The role of prostaglandins in regulating H+ excretion in amphibian epithelia was investigated. The abdominal skin of the southern leopard frog Rana pipiens and the urinary bladder of the toad Bufo marinus were used to measure proton excretion across their mucosal surface. Prostaglandin F2 alpha (PGF2 alpha) produced a dose-dependent inhibition of H+ excretion across the frog skin. Frogs pretreated with ibuprofen (30 mg.kg-1.day-1 for 3 days) showed an enhanced proton excretion similar to that observed when frogs are placed in chronic metabolic acidosis. The number of mitochondria-rich cells, the cells responsible for proton excretion, was also increased in frog skins after chronic metabolic acidosis or ibuprofen treatment. Mezerein and the phorbol ester 4 beta-phorbol 12-myristate 13-acetate (4 beta-PMA), activators of protein kinase C (PCK), decreased H+ excretion in frog skin, whereas the inactive phorbol 4 alpha-PMA was without an effect. The inhibition of proton excretion was similar to that observed with PGF2 alpha and suggested that the effects of PGF2 alpha and activation of PKC were mediated through a common pathway. Frogs pretreated with ibuprofen not only had an enhanced proton excretion rate but also had a decrease in cytosolic PKC activity. In another amphibian tissue, the toad urinary bladder, PGE2 inhibited proton excretion at low doses but enhanced H+ excretion at higher doses. Toads maintained under chronic metabolic acidosis had enhanced proton excretion rates and also had a threefold increase in cellular PGE2 concentration, which was consistent with the observation that PGE2 enhanced proton excretion at high doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Amphibians↗
PubMed2006

Alien mink predation induces prolonged declines in archipelago amphibians.

Amphibians are undergoing enigmatic global declines variously attributed to a complex web of anthropogenic forces. Alien predators pose a fundamental threat to biodiversity generally that is predicted to be most acute in island ecosystems. While amphibian eggs and tadpoles are vulnerable to aquatic predators, the effect of predators on adult, reproducing frogs, which most influence amphibian population processes, is unknown. Here, we report on the responses of amphibian populations in the outer Finnish Archipelago to a long-term, large-scale removal of American mink (Mustela vison Schreb.), an invasive predator linked to recent biodiversity loss across Europe. Removal increased both the densities and distribution of common frogs (Rana temporaria L.) but not those of common toads (Bufo bufo L.), which appear to escape mink predation because of their unpalatable skin. Importantly, the largest benefits of mink removal to frog recovery were slow to appear as frogs apparently have a delayed maturation in these harsh environments, which means we must be cautious about reliance upon short-term results.

Animals↗
PubMed1975

Behavior of sperm nuclei injected into intact ripening and ripe toad oocytes and into oocytes ripening after removal of the germinal vesicle.

The behavior of frog sperm nuclei (obtained by treating a sperm suspension with pronase) in the cytoplasm of intact ripening and ripe toad oocytes and in the cytoplasm of oocytes ripening after removal of the germinal vesicle was studied. Sperm nuclei treated with pronase in the cytoplasm of intact ripe oocytes behave like the nuclei of sperm cells penetrating during normal fertilization: they increase in volume, synthesize DNA, and start to divide. They undergo no changes in the cytoplasm of oocytes ripening in the absence of karyoplasm. Transformations of sperm nuclei into pronuclei and DNA synthesis in them are found initially at the metaphase stage of the second maturation division.

Animals↗
PubMed1985

The activity of hepatic gamma-glutamyltranspeptidase in various animal species.

The activity of gamma-glutamyltranspeptidase was determined in liver homogenates derived from various animals belonging to different phylogenetic groups. Although gamma-glutamyltranspeptidase was present in all livers studied, the activity varied greatly, with the order of activity being: guinea pig much greater than frog much greater than rabbit greater than toad greater than dog congruent to cat = duck greater than hamster = budgerigar = goldfish congruent to rat = mouse. There was no trend with respect to enzyme activity, phylogeny, diet, or habitat.

Animals↗
PubMed1985

An investigation of the alarm response in Bufo boreas and Rana cascadae tadpoles.

Tadpoles of the western toad (Bufo boreas) and of the Cascades frog (Rana cascadae) show an alarm reaction to an extract containing chemical cues from damaged conspecifics. The mean time spent by individual B. boreas tadpoles in the half of the test tank to which the extract solution was added was significantly lower than expected by chance. Activity was also significantly greater in Bufo extract tests than in control tests. Tadpoles did not avoid an extract of another tadpole species (Hyla regilla). Rana cascadae tadpoles did not avoid areas containing Rana extract but did significantly increase their level of activity in response to the extract. These results suggest that the R. cascadae tadpole alarm reaction exists but differs from the B. boreas reaction.

Animals↗
PubMedDate not supplied

[Dynamics of the intensity of respiration in early embryogenesis of amphibians].

We studied growth and respiration rate during early ontogenesis of the axolotl Ambystoma mexicanum, Bosca's newt Triturus waltlii, the green toad Bufo viridis, and the smooth clawed frog Xenopus laevis. The respiration rate in these amphibian species increases during embryonal and larval development, peaks after transition to active feeding, and decreases at later stages of ontogenesis. The patterns of dynamics of this energy metabolism index in tailed and tailless amphibians have some differences related to their specific development. The changes in respiration rate in the embryos and larvae are correlated with the concentrations of mitochondria.

Amphibians↗
PubMed1987

A sensitive in vitro toad skin bioassay for melanotropic peptides.

1. An in vitro bioassay for melanotropic peptide utilizing reflectance measurements of toad skin (Bufo ictericus ictericus) is described as an alternative to the commonly used Rana pipiens bioassay. 2. The toad skin bioassay is as sensitive to melanotropins and melanin concentrating hormone (MCH) as the frog bioassay. 3. On the basis of parallel dose-response curves obtained with the toad skin assay we found that beta-MSH is slightly less active than alpha-MSH, whereas the synthetic analogue [Nle4-D-Phe7]-alpha-MSH is about 10 times more potent and exhibits prolonged biological activity. 4. MCH, a putative neurohormone, can also be bioassayed in the in vitro toad skin bioassay, since it has alpha-MSH-like activity on amphibian melanocytes. 5. Since neither adreno- nor cholinoceptors are present in the toad melanocytes, the assay provides great specificity and sensitivity for the determination of melanotropin activity in tissue or blood.

Animals↗
PubMed1988

Electrophysiological analysis of sodium-transport in the colon of the frog (Rana esculenta). Modulation of apical membrane properties by antidiuretic hormone.

Sodium transport and apical bioelectrical membrane properties were investigated in frog colonic epithelium in the absence and presence of the antidiuretic hormone arginine-vasotocin (AVT). Apical Na-permeability and intracellular Na-activity were evaluated by analysis of current-voltage relationships in the serosally K-depolarized tissue. Tissue- and apical membrane capacitance were measured by voltages step analysis. The frog colon was found to be a tight epithelium with a transepithelial resistance of 2.63 +/- 0.25 k omega.muF (n = 17). 85-90% of short circuit current (11.2 +/- 1.1 microA.microF.l-1; n = 17) was related to electrogenic Na-transport from mucosa to serosa. Graded doses of amiloride (less than 50 mumol.l-1) induced Michaelis-Menten-type inhibition kinetics. Serosal addition of 10(-6) mol.l-1 AVT induced a significant increase in sodium current (25%), apical sodium permeability (19%) and tissue capacitance (4.3%) whereas intracellular Na-activity remained unchanged. There was a good correlation between increased Na-current and apical Na-permeability. No correlation was found between Na-current and membrane capacitance. Our results demonstrate that in contrast to other species the amphibian colon shows a natriferic reaction to AVT. We suggest that the regulation of Na-transport in frog colon is similar to that in the toad urinary bladder. It is caused by an activation of preexisting apical Na-channels and not by fusion of subapical cytoplasmic vesicles with the apical membrane.

Amiloride↗
PubMed2004

Comparison of liver mixed-function oxygenase and antioxidant enzymes in vertebrates.

We performed a comparative analysis of cytochrome P450, cytochrome b5, MFO associated enzymes and cytosolic antioxidant enzymes in hepatic microsomes and cytosolic fractions prepared from five animal species representing three vertebrate classes living in tropical conditions (Brazil). The data obtained show that rats have higher hepato-somatic index, specific cytochrome b5 concentration, and NADPH-dependent cytochrome c (P450) activity compared to ectothermic species, SOD activity similar to those in amphibians, and specific concentration of cytochrome P450 and catalase activity lower than in a toad, but higher than in fishes and a frog. Our data indicate that tropical fishes may have reduced xenobiotic-metabolizing ability compared to the rat and amphibians. In contrast to fish and rat, amphibians have a low ratio (< 0.5) of cytochrome b5 concentration to that of P450. Most species showed cytochrome b5 sensitivity to oxygen. Thus, the use of sodium dithionate as a reducer, rather than NADPH, may be preferential in b5 determinations.

Animals↗
PubMed2002

Cladistic analysis of anuran POMC sequences.

Procedures for performing cladistic analyses can provide powerful tools for understanding the evolution of neuropeptide and polypeptide hormone coding genes. These analyses can be done on either amino acid data sets or nucleotide data sets and can utilize several different algorithms that are dependent on distinct sets of operating assumptions and constraints. In some cases, the results of these analyses can be used to gauge phylogenetic relationships between taxa. Selecting the proper cladistic analysis strategy is dependent on the taxonomic level of analysis and the rate of evolution within the orthologous genes being evaluated. For example, previous studies have shown that the amino acid sequence of proopiomelanocortin (POMC), the common precursor for the melanocortins and beta-endorphin, can be used to resolve phylogenetic relationships at the class and order level. This study tested the hypothesis that POMC sequences could be used to resolve phylogenetic relationships at the family taxonomic level. Cladistic analyses were performed on amphibian POMC sequences characterized from the marine toad, Bufo marinus (family Bufonidae; this study), the spadefoot toad, Spea multiplicatus (family Pelobatidae), the African clawed frog, Xenopus laevis (family Pipidae) and the laughing frog, Rana ridibunda (family Ranidae). In these analyses the sequence of Australian lungfish POMC was used as the outgroup. The analyses were done at the amino acid level using the maximum parsimony algorithm and at the nucleotide level using the maximum likelihood algorithm. For the anuran POMC genes, analysis at the nucleotide level using the maximum likelihood algorithm generated a cladogram with higher bootstrap values than the maximum parsimony analysis of the POMC amino acid data set. For anuran POMC sequences, analysis of nucleotide sequences using the maximum likelihood algorithm would appear to be the preferred strategy for resolving phylogenetic relationships at the family taxonomic level.

Amino Acid Sequence↗