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At least 199 records · Page 11Linked to original sources
PubMed1986

Acetazolamide does not disrupt limb regenerate morphogenesis in the salamander, Plethodon cinereus.

Acetazolamide, a potent and highly specific inhibitor of carbonic anhydrase, is teratogenic in mammalian embryos and when administered during early limb development causes unique limb defects in a time- and dose-dependent manner. The regenerating urodele limb is often considered to be a good experimental analog of limb development and, if it employs the same mechanisms of tissue interactions during pattern formation, should be susceptible to teratogens which selectively disrupt developmental limb patterning. This study demonstrates that while carbonic anhydrase inhibition is toxic to the red-backed salamander, Plethodon cinereus, it does not have the same teratogenic effect on limb regeneration as seen in mammalian limb development. Several points are considered as to why the regenerating limb, at least in this salamander species, may not be suitable for studying this class of teratogen.

Acetazolamide↗
PubMed1997

Differential effects of mate competition and mate choice on eastern tiger salamanders

Male tiger salamanders, Ambystoma tigrinum tigrinumare slightly larger in body size and have considerably higher and longer tails than females. To determine how these dimorphic traits affected reproductive performance and success, we conducted breeding trials using 12 males and six females per trial and monitored male-female and male-male interactions. Larger males had an advantage in most aspects of mate competition investigated. Males with higher tails had no advantage in either mate competition or mate choice. Males with longer tails also had no advantage in mate competition but were preferred as mates by females. Larger males interrupted courting males more often than smaller males did. The form of male-male interference was conditional on body size and not on either tail dimension. If the intruder was larger than the courting male, it would shove the female away from the courting male and initiate courtship; if the intruder was smaller, it adopted a female mimicry tactic in which it positioned itself between the courting male and female and performed female behaviours to the courting male while simultaneously courting the female. Our trials indicated that the two components of sexual selection may influence the evolution of different male morphological traits in tiger salamanders. Mate competition may favour increased male body length; mate choice may select for greater male tail length.

Journal Article↗
PubMed1998

Habitat-contingent reproductive behaviour in radio-implanted salamanders: a model and test.

All tiger salamanders, Ambystoma tigrinum, entering a small pond in New York state were given radio-implants and tracked throughout breeding to determine whether reproductive behaviour in nature differs from that described in laboratory studies. I formed an extended model of adult reproductive behaviour that included male and female strategies and differential use of habitat components in the breeding pond, and then tested four key predictions regarding adult movement using the sequence of positions of all salamanders between pond entry and exit. An unexpected, female-biased sex ratio during most courtship activity led to departures from the predicted behaviour, but in all other respects the behaviour of the males and females followed from the predictions. Apparent mate scanning in clear water, and weather assessment in pond-edge shallows just prior to emergence, are new indications for caudate amphibians. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1994

Plasma androgen levels, spermatogenesis, and secondary sexual characteristics in two species of plethodontid salamanders with dissociated reproductive patterns.

In the summer of 1991 (late May to early September), I measured seasonal levels of plasma androgens in two species of plethodontid salamanders to assess the temporal relationship of elevated plasma androgen levels with spermatogenic events and with sexual behavior. In both species, spermatogenesis occurs in the spring and summer. In one species, Plethodon jordani, mating occurs in the fall. In the other species, Desmognathus ochrophaeus, the mating season is prolonged, occurring both in the fall and in the spring. In P. jordani, plasma testosterone (T) levels were lowest in June and highest in late August, such that elevated plasma T levels coincided with the development of secondary sexual characteristics and the time when mating behavior occurs. Plasma dihydrotestosterone (DHT) levels for P. jordani were lowest in June and rose significantly in mid July when spermiation began. In D. ochrophaeus, plasma T and DHT levels were lowest during June and July and highest in late August. Elevated T and DHT levels coincided with spermiation and with the period when mating behavior occurs. Data for these two salamander species indicate that maximally elevated plasma androgens were temporally dissociated from the peak of spermatogenesis; maximal androgen levels were more closely associated with spermiation and the development of secondary sexual characteristics.

Androgens↗
PubMed2000

Pre-pleistocene refugia and differentiation between populations of the caucasian salamander (Mertensiella caucasica).

A 350-bp fragment of the mitochondrial cytochrome-b gene was sequenced in the Caucasian salamander, Mertensiella caucasica, representing 10 populations from across its range along the Black Sea coast. Five haplotypes were discovered among 65 fragments analyzed, differing at 2-50 positions. The highest differentiation between haplotypes was observed in animals from the eastern part of the species' range (Borjomi) compared to those from the remainder of the species' range. Randomly amplified nuclear DNA revealed a pattern of spatial genetic variation similar to that of the mitochondrial genome. M. caucasica, as currently known, represents two evolutionary lineages that evolved independently, perhaps since the lower Pliocene. These lineages represent taxa, possibly to be described as species, distributed in the Borjomi area in central Georgia and in southwestern Georgia and northeastern Turkey. The multivariate analysis of morphological data did not reveal significant differences between the taxa. However, substantial morphological differentiation was observed within both lineages, showing parallel patterns in body proportions and coloration patterns. This variation is possibly associated with extant ecological conditions. Salamanders with reduced pigmentation from southwestern Georgia were not genetically distinguishable from neighboring populations.

Animals↗
PubMed2001

Molecular phylogenetics and historical biogeography among salamandrids of the "true" salamander clade: rapid branching of numerous highly divergent lineages in Mertensiella luschani associated with the rise of Anatolia.

Phylogenetic relationships among salamandrids of the "true" salamander clade are investigated using 2019 aligned base positions (713 parsimony informative) of 20 mitochondrial DNA sequences from the genes encoding ND1 (subunit one of NADH dehydrogenase), tRNA(Ile), tRNA(Gln), tRNA(Met), ND2, tRNA(Trp), tRNA(Ala), tRNA(Asn), tRNA(Cys), tRNA(Tyr), and COI (subunit I of cytochrome c oxidase), plus the origin for light-strand replication (O(L)) between the tRNA(Asn) and the tRNA(Cys) genes. Parsimony analysis produces a robust phylogenetic estimate for the relationships of the major groups of "true" salamanders. Strong support is provided for the sister taxon relationship of Chioglossa and Mertensiella caucasica and for the placement of Salamandra and Mertensiella luschani as sister taxa. These relationships suggest two vicariant events between Europe and Anatolia caused by the formation of seaways in the Mediterranean Basin. Molecular divergence indicates an Early Miocene separation of Chioglossa and M. caucasica and a Late Miocene separation of Salamandra and M. luschani. The traditional phylogenetic hypothesis of a monophyletic Mertensiella is statistically rejected, indicating that southwestern and northeastern Anatolian populations have separate historical biogeographic origins. Therefore, we recommend placement of M. luschani in the genus Salamandra. Within M. luschani, six highly divergent lineages showing 7.6 to 10.1% pairwise sequence divergence are identified. Tests using four-taxon subsamples suggest that these lineages diverged nearly simultaneously in the Late Miocene, approximately 6 to 8 million years ago, when extensive uplifting of Anatolia occurred in response to the Arabian collision.

Africa, Northern↗
PubMed1993

A model of the saccadic sensorimotor system of salamanders.

A model of the saccadic system of salamanders on the basis of electrophysiological and anatomical results is presented. The model includes centers found to be significant for the guidance of saccades in these comparatively simple vertebrates. In particular, these are the optic tectum, the bulbar reticular formation and the motor system. The latter consists of two pairs of neck-muscles, an epaxial and a hypaxial one driven by their respective motoneurons. The model includes a visual, a sensori-motor, and a motor level. At the sensory level, the retinal coordinates are transferred to the optic tectum to establish an orthogonal map of visual angles. A secondary visual map of the ipsilateral eye with a pointsymmetrical organization exists in addition. The premotor system of the tectum was modelled according to an ensemble-coding principle. Thus, local activation of the visual map results in recruitment of an appropriate number of tectal premotor units. Simulation of the model reproduces correct metric properties of salamander saccades under varying stimulus presentations.

Animals↗
PubMed1978

Ultrastructural and morphometric study of the lung of the European salamander, Salamandra salamandra L.

Ultrastructural and morphometric investigations were performed on the lung of the European salamander, Salamandra salamandra L. Folds of first and second order are covered with a ciliated epithelium containing goblet cells. The respiratory surface of the lung is lined by a single type of cell which, in amphibians, combines features of type I and type II alveolar cells of the mammalian lung. In the salamander the respiratory and ciliated epithelial cells as well as goblet cells possess electron dense and lucent vesicles in their cytoplasm as well as lamellar bodies. A small amount of surfactant, composed most probably of phospholipids and mucopolysaccharides, was observed covering the entire inner surface of the lung. Morphometric methods were used to determine the dimensions of the perinuclear region of pneumocytes, the thickness of the air-blood barrier and lung wall, and also the diameter of capillaries. The thickness of the respiratory air-blood barrier was found to be considerably higher than that of the corresponding barrier in mammals.

Animals↗
PubMed1988

Cell dynamics in the olfactory epithelium of the tiger salamander: a morphometric analysis.

The factors controlling neurogenesis and differentiation of olfactory receptor cells in adults are poorly understood, although it is often stated that these cells undergo continual turnover after a predetermined lifespan. An interesting model in which to study mechanisms which control olfactory receptor neurogenesis and cell turnover is the tiger salamander, since basal cell mitosis varies with epithelial thickness and location in the nasal cavity. This paper presents a quantitative light-microscopic study of the different cell types within the ventral olfactory epithelium of the tiger salamander using a computer-assisted morphometric analysis of 2 micron sections. The results show that the surface density of olfactory vesicles remained constant throughout most of the epithelium and was independent of nasal cavity location, epithelial thickness and the total number of nuclei per unit epithelial surface area. Histological classification of nuclei into different cell types indicated that the increase in total cell number with epithelial thickness was mainly due to an increase in the number of immature receptor cells since the number of supporting cells varied only slightly and the numbers of basal cells and mature receptor cells remained constant except in the thinnest, most caudally located epithelium. It is concluded that the rate of maturation of receptor cells may be limited by an optimal surface density of olfactory vesicles. That is, when this density reaches 4.5 x 10(4) vesicles per mm2 there is a physical or chemical mechanism which prevents the final maturation of newly developing receptor cells, leading to their accumulation. This mechanism may also account for the variations in basal cell mitosis in this species.

Animals↗
PubMed1994

Immunocytochemical survey of the neuroepithelial endocrine system in the respiratory tract of the Tokyo salamander, Hynobius nebulosus tokyoensis TAgo.

The epithelial lining of the respiratory tract of urodeles has been shown to harbor an innervated system of neuroepithelial endocrine (NEE) cells. Even between phylogenetically closely related species, large differences have been reported in the appearance and chemical coding of the NEE system. Although urodeles are well suited for the purpose, none of the prior studies have provided an immunocytochemical survey of the NEE system in all parts of the respiratory tract. In the present study, many bioactive substances and a general marker were immunocytochemically demonstrated in serial sections of the entire respiratory tract of the Tokyo salamander, Hynobius nebulosus tokyoensis, a species in which neuroepithelial bodies (NEBs) were previously characterized at the electron microscopic level. In the current study, serotonin-immunoreactive solitary NEE cells were observed in variable numbers in the larynx, in all parts of the trachea, and in areas of the lungs covered with ciliomucous epithelium. Serotonin-containing NEBs, however, were detected in small cranial areas of the lung only. Solitary NEE cells were seen in the trachea and lungs of H. nebulosus tokyoensis by immunocytochemical staining for somatostatin, calcitonin, calcitonin gene-related peptide, and bombesin, but the number, localization, and appearance of the labeled NEE cells differed considerably. Only calcitonin-like immunoreactivity was also noted in some NEB-like cell clusters in the cranial parts of the lungs. Unlike many other vertebrates, neuron specific enolase was found to be a poor marker for the NEE system in the salamander species used in this investigation. It may be concluded that the NEE system of H. nebulosus tokyoensis contains at least five different bioactive substances.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Control theory predictions of reproductive allocation in female dusky salamanders.

A model of the reproductive ecology of female dusky salamanders was used to investigate the allocation scheme that a female might use to maximize her reproductive success. Analysis of the model with techniques of optimal control theory suggests that fecundity is maximized either by allocating food resources to reproduction for the entire time period prior to egg laying, or by growing first, then switching to reproduction later in the year. The analysis also indicates that egg mortality will be minimized if the female provides maternal care at the maximum level throughout egg brooding. These results are not specific to dusky salamanders, but can be extended to other organisms with similar reproductive characteristics.

Animals↗
PubMed1994

The composition and function of the pulmonary surfactant system during metamorphosis in the tiger salamander Ambystoma tigrinum.

Mammalian lungs secrete a mixture of surface-active lipids (surfactant), which greatly reduces the surface tension of the fluid coating the inner lung surface, thereby reducing the risk of collapse upon deflation and increasing compliance upon inflation. During foetal lung maturation, these lipids become enriched in the primary and active ingredient, a disaturated phospholipid. However, disaturated phospholipids exist in their inactive gel-like form at temperatures below 37 degrees C and thus are inappropriate for controlling surface tension in the lungs of many ectotherms. We examined the development of the composition and function of the surfactant system of the tiger salamander (Ambystoma tigrinum) during metamorphosis from the fully aquatic larva (termed stage I) through an intermediate air-breathing larval form (stage IV) to the terrestrial adult (stage VII). Biochemical analysis of lung washings from these three life stages revealed a decrease in the percentage of disaturated phospholipid per total phospholipid (23.03 versus 15.92%) with lung maturity. The relative cholesterol content remained constant. The increased level of phospholipid saturation in the fully aquatic larvae may reflect their generally higher body temperature and the higher external hydrostatic compression forces exerted on the lungs, compared to the terrestrial adults. Opening pressure (pressure required for initial lung opening) prior to lavage decreased from larval to adult salamanders (7.96 versus 4.69 cm H2O), indicating a decrease in resistance to opening with lung development.(ABSTRACT TRUNCATED AT 250 WORDS)

Ambystoma↗
PubMed1993

Distribution of NCAM-180 and polysialic acid in the developing tectum mesencephali of the frog Discoglossus pictus and the salamander Pleurodeles waltl.

The 180 kDa component of the neural cell adhesion molecule (NCAM-180), total NCAM (NCAM-total) and the polysialic acid modification of NCAM (PSA) show similar temporal and spatial regulation in the developing tecta of Pleurodeles waltl (salamander) and Discoglossus pictus (frog). Whereas NCAM-total is found throughout the tectal tissue on neurons and glia, NCAM-180 is only found on non-proliferating neurons and in fiber layers. PSA is expressed by a subset of NCAM-180-positive cells. Western blots show that there is little polysialylated NCAM-140 in the developing amphibian tectum. Regions unstained for PSA and NCAM-180 correspond precisely to the growth zones of the tectum. NCAM-180 and PSA are not present in tecta of early larvae. Staining intensity is strongest at midlarval stages for both antigens. At metamorphosis, PSA is strongly downregulated, whereas NCAM-180 is downregulated in juvenile animals. Both antigens are still present in fiber layers of adult animals. In dissociated tissue culture of the frog tectum, NCAM-180 is not present on astrocytes, but on neuronal cells. Expression is enhanced at cell contact sites, suggesting that NCAM-180 is involved in cell contact stabilization. This study shows that general features of temporal and spatial regulation of NCAM isoforms and PSA are highly conserved in frog and salamander tecta, despite large differences in the rate of cell migration and the degree of lamination in these homologous brain regions.

Animals↗
PubMed1988

Miniaturization, genome size and the origin of functional constraints in the visual system of salamanders.

During their evolution, many species of lungless salamanders (fam. Plethodontidae) have experienced a great increase in genome size and consequently in the size of their cells, including sensory receptors and neurons. In addition, some have become extremely miniaturized. The consequences of these events and the morphological compensatory processes are studied in the visual system of juvenile and adult salamanders.

Animals↗
PubMed1986

Cytophotometric evidence of variation in genome size of desmognathine salamanders.

The amount of DNA per haploid genome, the C-value, is often directly correlated with nuclear and cell volume, but inversely correlated with cell replication rate. Also, rates of cellular growth sometimes appear to be correlated with organismal developmental rates and life history patterns. Among vertebrates, salamanders exhibit the greatest variation in genome size. In the present study we have examined interspecific and intraspecific variation in blood cell DNA levels in the genus Desmognathus, which shows greater variation in life history traits than any other salamander genus. Specimens of Desmognathus quadramaculatus, D. monticola, D. ochrophaeus and D. wrighti were collected from nature at two localities in the southern Appalachian Mountains. Estimates of genome size in pg of DNA were obtained from blood smears by DNA-Feulgen cytophotometry, using erythrocyte nuclei of Xenopus laevis as an internal reference standard of 6.35 pg DNA per cell. C-values of Desmognathus are the smallest in the order Caudata. Although significant variation in DNA levels was found among the four species, the differences were small, and do not support previously proposed relationships between C-value and life-history variation.

Animals↗
PubMed1988

A comparison of the discriminatory ability and sensitivity of the trigeminal and olfactory systems to chemical stimuli in the tiger salamander.

Trigeminal receptors can respond to a wide variety of chemical stimuli, but it is unknown whether these receptors mediate discrimination between chemical stimuli matched for equal perceptual intensity. The present electrophysiological and behavioral experiments address this issue using tiger salamanders, Ambystoma tigrinum, and four compounds (amyl acetate, cyclohexanone, butanol, and d-limonene). In addition, the relative sensitivities of the trigeminal and olfactory systems to these compounds are compared. In electrophysiological cross-adaptation experiments (amyl acetate vs cyclohexanone; butanol vs d-limonene), there was complete cross adaptation such that only concentrations above the background (cross-adapting) stimulus concentration elicited responses, suggesting that chemical stimuli may stimulate trigeminal receptors nonspecifically. In behavioral experiments (amyl acetate vs cyclohexanone; butanol vs d-limonene), only animals with intact olfactory nerves could discriminate between perceptually equivalent concentrations, that is concentrations that elicited the same level of responding. Both electrophysiologically and behaviorally, the trigeminal system exhibited higher thresholds than the olfactory system. We conclude that trigeminal chemoreceptors, at least in salamanders, are unable to discriminate between these two pairs of compounds when matched for equal perceptual intensity, and that trigeminal chemoreceptors are less sensitive than olfactory receptors.

Action Potentials↗
PubMed2007

Population dynamics and regulation in the cave salamander Speleomantes strinatii.

Time series analysis has been used to evaluate the mechanisms regulating population dynamics of mammals and insects, but has been rarely applied to amphibian populations. In this study, the influence of endogenous (density-dependent) and exogenous (density-independent) factors regulating population dynamics of the terrestrial plethodontid salamander Speleomantes strinatii was analysed by means of time series and multiple regression analyses. During the period 1993-2005, S. strinatii population abundance, estimated by a standardised temporary removal method, displayed relatively low fluctuations, and the autocorrelation function (ACF) analysis showed that the time series had a noncyclic structure. The partial rate correlation function (PRCF) indicated that a strong first-order negative feedback dominated the endogenous dynamics. Stepwise multiple regression analysis showed that the only climatic factor influencing population growth rate was the minimum winter temperature. Thus, at least during the study period, endogenous, density-dependent negative feedback was the main factor affecting the growth rate of the salamander population, whereas stochastic environmental variables, such as temperature and rainfall, seemed to play a minor role in regulation. These results stress the importance of considering both exogenous and endogenous factors when analysing amphibian long-term population dynamics.

Animals↗
PubMed2004

Toxicologic and histopathologic response of the terrestrial salamander Plethodon cinereus to soil exposures of 1,3,5-trinitrohexahydro-1,3,5-triazine.

Red-backed salamanders (Plethodon cinereus) were exposed to four different concentrations of 1,3,5-trinitrohexahydro-1,3,5-triazine (RDX) in soil under controlled laboratory conditions for 28 days. Wild-caught P. cinereus (N = 20/treatment) were exposed to target concentrations of 5,000, 1000, 100, 10, and 0 mg RDX/kg soil (dry wt) using a microcosm design. Animals were fed 5 to 10 uncontaminated mutant Drosophila flies every 3 days and monitored daily. Animals were weighed 1 day before being placed in treatment and weekly thereafter. RDX concentrations in soil were analytically determined after the compound was added and mixed at the beginning, the midpoint, and the end of exposure. RDX soil concentrations were relatively stable throughout the exposure period. Signs of overt toxicity were observed primarily in the highest exposure group. Salamanders exposed to 5,000 mg RDX/kg soil exhibited signs of neuromuscular effects (lethargy, gaping, hypersensitivity, tremors) and exhibited significant weight loss. A single moribund animal from this group lost >20% of its original body weight and was killed. Animals in this exposure group also lost weight relative to animals in other treatments. Histopathologic evaluations, including an evaluation of melanomacrophage parameters, indicated no strong treatment-related findings. This study provided information regarding the effects from subchronic dermal exposure of a terrestrial amphibian species to RDX in soil and provides a microcosm approach to the evaluation of toxicity of contaminants in soil to a terrestrial vertebrate.

Administration, Cutaneous↗