EXPERIMENTAL PRODUCTION OF GIGANTISM BY FEEDING THE ANTERIOR LOBE OF THE HYPOPHYSIS

1. Metamorphosed salamanders of the species Ambystoma opacum and Ambystoma tigrinum were fed on a pure diet of the anterior lobe of the hypophysis of cattle; the controls were fed on an abundant diet of earthworms. 2. The rate of growth of the animals fed on the anterior lobe of the hypophysis was greatly increased over the rate of growth of normal animals. 3. Growth of the animals fed on anterior lobe did not cease after they had reached the normal "maximum" size of the species, and experimental giants were produced. 4. The largest animal of the species Ambystoma opacum fed on anterior lobe of the hypophysis was 19 mm. larger than the largest normal animal of this species known to the writer; the largest animal of the species Ambystoma tigrinum fed on anterior lobe is at present about 28 mm. larger than the largest normal animal of the eastern race of this species known to the writer.     

Cross-species axial signaling, with realignment of retinal axes, in embryonic Xenopus eyes

The locus specificities which enable retinal ganglion cells to assemble a topographic retinotectal map are patterned about a pair of (anteroposterior and dorsoventral) retinal axes set down in the early eye bud. We have transplanted a Xenopus laevis eye bud, at stage $\text{23}\text{24}$ when the retinal field is still responsive to the axial signals from the surrounding tissues, into the enucleated eye socket of a comparable stage Ambystoma maculatum embryo. Three days later, when the Xenopus eye had reached early larval stages and was no longer responsive to extraocular signals, the eye was retransplanted into the socket of the Xenopus final carrier embryo. The pattern of retinotectal connections between the eye and the carrier's optic tectum was examined by electrophysiological analysis of the visuotectal projections. The results indicated that many of the retinae had patterned locus specificities about axes derived from the salamander intermediate host. We infer that axial signaling involves fundamental cellular processes which have been highly conserved during evolution.     

THE ANTAGONISM BETWEEN THYROID AND PARATHYROID GLANDS

From the facts stated in this paper it is evident that the thymus gland of mammals contains a substance which is capable of producing tetany when fed to the larvæ of certain species of salamanders (Ambystoma opacum and Ambystoma maculatum). As long as the larvæ have not developed their own thymus glands, they are able, by means of some mechanism, to counterbalance the tetanic action of the thymus substance introduced in their food. When, however, the secretion from their own thymus glands is added to the thymus material introduced with the food, this mechanism of preventing tetany becomes inadequate and tetany ensues. In the larva of a third species of salamander, Ambystoma tigrinum, this mechanism will prevent tetany even when the larvæ are fed on thymus. In mammals the parathyroids are known to prevent tetany and are supposed either to absorb the tetany-producing substance and thus prevent its action or to change it into another non-toxic substance. It is at least probable that in the amphibians the parathyroids play the same rôle. Larvæ of anuran amphibians, which develop their parathyroids soon after hatching, never show tetanic convulsions if they are fed on thymus, but in certain species of salamanders, whose parathyroids develop only during metamorphosis, the larvæ invariably have tetanic convulsions upon thymus feeding, while the metamorphosed animals never show tetany. But in addition to the parathyroids the salamanders must possess still another mechanism which during the larval period inhibits the production of tetany by the animal''s own thymus glands. In the larvæ of Ambystoma opacum and Ambystoma maculatum this mechanism is sufficient only to prevent tetany from the animal''s own thymus, while in the larvæ of Ambystoma tigrinum it is capable of preventing tetany even when the larvæ are fed with thymus. If the thymus is the organ by whose action tetany is produced, we can understand why tetany in human beings occurs far more frequently in children than in adults, since in the latter the thymus gland is replaced, at least to a great extent, by connective tissue. The relation of thymus to tetany may also possibly explain the occurrence of tetany during pregnancy; while the parathyroids of the mother may be sufficient to prevent tetany from her largely atrophied thymus, they may not be sufficient to prevent tetany from the excess of thymus substance furnished by the fetus to the blood of the mother.     

Ammonia: basis for algal symbiosis in salamander egg masses

The nitrogenous waste product ammonia, excreted by laval stages of the salamander, $\text{Ambystoma gracilis}$ (Baird), is removed from the perivitelline fluid by a symbiotic green alga, $\text{Chlamydomonas}$ sp. The alga stores the excess nitrogen as membrane-bound proteinaceous bodies, which partially explains the accelerated rate of development in the algal-inhabited egg masses.     

A scanning electron microscopic study of the appearance and localization of cell surface material during amphibian gastrulation.

Cell surface material (CSM) has been implicated in a wide variety of morphogenetic processes. We describe here its discrete appearance at the blastoporal region throughout gastrulation in the salamander Ambystoma mexicanum. The CSM becomes visible in the scanning electron microscope after treatment with Alcian blue and lanthanum nitrate which reportedly attests to the presence of mucopolysaccharides. The possible importance of this CSM is underscored by its correlative appearance on tissue undergoing morphogenetic movement and induction.     

Antigenotoxic Effect of Ascorbic Acid and Resveratrol in Erythrocytes of Ambystoma mexicanum,Oreochromis niloticus and Human Lymphocytes Exposed to Glyphosate

Glyphosate is a controversial herbicide. Its genotoxicity and presence in various ecosystems have been reported. The use of ascorbic acid and resveratrol could protect different organisms from glyphosate-induced genetic damage. In the present study, specific genetic damage induced by glyphosate was evaluated in erythrocytes of Oreochromis niloticus, Ambystoma mexicanum and human lymphocytes. Simultaneously, the antigenotoxic capacity of various concentrations of ascorbic acid and resveratrol was evaluated by means of pretreatment and simultaneous treatment protocols. The 0.03, 0.05 and 0.07 mM concentrations of glyphosate induced significant genotoxic activity (p < 0.05) in human lymphocytes and in erythrocytes of the species studied, and could cause genomic instability in these populations. The reduction in genetic damage observed in human lymphocytes exposed to high concentrations of glyphosate is only apparent: excessive genetic damage was associated with undetectable excessive tail migration length. A significant (p < 0.05) antigenotoxic effect of ascorbic acid and resveratrol was observed in all concentrations, organisms and protocols used. Both ascorbic acid and resveratrol play an important role in maintaining the integrity of DNA. Ascorbic acid in Oreochromis niloticus, Ambystoma mexicanum reduced glyphosate-induced genetic damage to a basal level. Therefore, our data indicate that these antioxidants could help preserve the integrity of the DNA of organisms exposed to glyphosate. The consumption of antioxidants is a useful tool against the genotoxicity of glyphosate.     

A nonlethal method of identification of Ambystoma laterale,A. jeffersonianum and sympatric unisexuals

Unisexual salamanders in the genus Ambystoma live in obligate sympatry with the sexual species Ambystoma laterale or Ambystoma jeffersonianum, from which they are not easily distinguished. Because the sexual species are protected in many parts of their range, accurate identification of sexual and unisexual individuals is required for conservation purposes. Unisexual individuals are currently identified using isozyme electrophoresis, which requires sacrificing the animal. Here we present a nonlethal method of identification for members of the A. laterale–jeffersonianum part of the Ambystoma complex utilizing genome‐specific microsatellites with or without the addition of flow cytometry.     

Biochemical studies on muscaranic receptors in the salamander olfactory epithelium

Muscarinic cholinergic receptors in the olfactory epithelium of the salamander, Ambystoma tigrinum, were studied via binding of 3-[³H]quinuclidinyl benzilate. The receptors are present on the olfactory receptor cells in the epithelium to an amount of 0.08 pmol/mg homogenate protein. Both choline acetyltransferase and acetylcholine esterase are present in the salamander olfactory epithelium.     

Ontogeny of cranial ossification in the small-mouthed salamander, Ambystoma texanum (Matthes)

The ontogenetic sequence of cranial bony structure from initial ossifications through metamorphosis in Ambystoma texanum is described on the basis of 128 cleared and stained specimens. For convenience of discussion nine stages are recognized on the basis of conspicuous events. Cranial bones ossify and are modified in a definite sequence, and comparisons of complete sequences among groups of salamanders may prove useful in classification and in better understanding of relationships.     

An Electron Microscope Study of the Salamander Thyroid during Hormonal Stimulation

Cytological changes in thyroid glands following administration of thyroid-stimulating hormone (TSH), were studied in adult salamanders, Ambystoma tigrinum, Triturus torosus, and Triturus viridescens by electron and light microscopy. Thyroids from untreated salamanders contained large follicles, faintly basophilic colloid, low follicle cells with flattened nuclei, and scant, slightly basophilic cytoplasm. After TSH administration the cell height and nuclear volume increased. Cytoplasmic basophilia was markedly increased and follicle lumina were reduced. In electron micrographs, stacks of ergastoplasmic lamellae appeared near the nucleus occasionally in contact with the nuclear membrane. In more advanced stages of stimulation, lamellar arrays were largely replaced by small disoriented vesicles and larger vacuoles containing colloid-like material. Sections of obliquely oriented ergastoplasmic membranes contained rows of extremely fine particles. Microvilli increased in size and number and Golgi structures became more extensive. Homogeneous osmiophilic droplets increased in size and abundance. Some of the smaller droplets were seen associated with the Golgi zone. Droplets similar in size and density frequently contained closely packed, whorled lamellae. Mitochondria showed no structural changes but occurred in aggregates interposed between the nucleus and highly folded portions of the basal cell membrane.     

When can embryos learn? A test of the timing of learning in embryonic amphibians

Learning is crucial to the survival of organisms across their life span, including during embryonic development. We set out to determine when learning becomes possible in amphibian development by exposing spotted salamander (Ambystoma maculatum) embryos to chemical stimuli from a predator (Ambystoma opacum), nonpredator (Lithobates clamitans), or control at developmental stages 16–21 or 36–38 (Harrison 1969 ). Once exposures were completed and embryos hatched, we recorded the number of movements and time spent moving of individuals in both groups and all treatments. There was no significant difference in number of movements or time spent moving among any of the treatments. The groups that were exposed to predator stimuli and a blank control at stages 36–38 were also tested to determine whether there was a difference in refuge preference or difference in survivorship when exposed to a predator (marbled salamander). There was no difference in survival or refuge preference between individuals; however, all individuals preferred vegetated over open areas regardless of treatment type. We discuss hypotheses for the absence of embryonic learning in this species and suggest it may be the result of the intensity of the predator–prey interaction between the predator, large marbled salamander larvae, and the prey, spotted salamander larvae.     

Life cycle separates Puccinia pachycephala from P. metanarthecii

Puccinia metanarthecii and P. pachycephala differed in their heteroecious life cycle. The former rust fungus formed spermogonial/aecial stages on Ixeris dentata and uredinial/telial stages on Metanarthecium luteo-viride or Aletris foliata. The latter formed spermogonial/aecial stages on Ligularia hodgsonii and uredinial/telial stages on Veratrum maackii var. longibracteatum and V. maackii var. parviflorum. Puccinia pachycephala and P. metanarthecii can also be differentiated by aeciospore and teliospore morphology.     

Criconemella spp. in Pennsylvania Peach Orchards with Morphological Observations of C. curvata and C. ornata

Criconemella xenoplax and C. curvata, previously associated with decline of peach trees in other parts of the United States, were found in 20 of 25 Pennsylvania peach orchards. Population densities were high in some samples. Morphometrics of juveniles and adult females of Criconemella curvata and C. ornata, are provided. Cuticular crenations were observed on J2 and J3 stages of C. curvata and J2-J4 stages of C. ornata.     

An examination of multiple factors affecting community structure in an aquatic amphibian community

Summary The potential effects of multiple factors structuring certain larval amphibian communities were studied using a pen experiment in a natural pond. Potential factors (predation and competition from other species) were allowed to act in a stepwise fashion such that their relative importance could be evaluated. Based on a previous study, it was hypothesized that predation by Ambystoma salamander larvae on other larval amphibian species would be the most important factor. Survival of Ambystoma jeffersonianum salamander larvae and Rana sylvatica tadpoles was significantly depressed only by Ambystoma opacum predation. Survival of Ambystoma maculatum salamander larvae was significantly greater in the absence of both A. opacum and A. jeffersonianum predators. The virtual elimination of Hyla chrysoscelis larvae in all treatments also can be largely attributed to Ambystoma predation. Thus, Ambystoma predation was the dominant factor determining larval survival of four amphibian prey species in the experimental communities.     

Evolution mediates the effects of apex predation on aquatic food webs

Ecological and evolutionary mechanisms are increasingly thought to shape local community dynamics. Here, I evaluate if the local adaptation of a meso-predator to an apex predator alters local food webs. The marbled salamander (Ambystoma opacum) is an apex predator that consumes both the spotted salamander (Ambystoma maculatum) and shared zooplankton prey. Common garden experiments reveal that spotted salamander populations which co-occur with marbled salamanders forage more intensely than those that face other predator species. These foraging differences, in turn, alter the diversity, abundance and composition of zooplankton communities in common garden experiments and natural ponds. Locally adapted spotted salamanders exacerbate prey biomass declines associated with apex predation, but dampen the top-down effects of apex predation on prey diversity. Countergradient selection on foraging explains why locally adapted spotted salamanders exacerbate prey biomass declines. The two salamander species prefer different prey species, which explains why adapted spotted salamanders buffer changes in prey composition owing to apex predation. Results suggest that local adaptation can strongly mediate effects from apex predation on local food webs. Community ecologists might often need to consider the evolutionary history of populations to understand local diversity patterns, food web dynamics, resource gradients and their responses to disturbance.     

THE INFLUENCE OF FEEDING THE ANTERIOR LOBE OF THE HYPOPHYSIS ON THE SIZE OF AMBYSTOMA TIGRINUM

1. Animals of the species Ambystoma tigrinum when fed anterior lobe can reach a size far in excess of that of animals fed earthworms and presumably also of that of liver-fed animals. 2. Liver produces a rate of growth as high as that resulting from anterior lobe-feeding, but maintains growth only, until the animals reach a definite size far below that of anterior lobe-fed animals.     

Calmodulin during development and metamorphosis in urodelan amphibians

Calmodulin isolated and purified to homogeneity from young larvae is very similar to that obtained from adult Pleurodeles waltlii and these proteins are almost identical to previously described vertebrate calmodulins. During P. waltlii development, an increase in total individual calmodulin content is observed after the heart beating stage. In dorsal axial muscle, calmodulin level which is very high at the beginning of larval life (premetamorphosis) decreases strikingly in the first part of prometamorphosis. Such an evolution is observed in Ambystoma mexicanum too. Then, a significant increase occurs during metamorphosis. In contrast, calmodulin level in P. waltlii cardiac ventricular muscle increases continuously from hatching to the end of metamorphic climax. Thyroxine treatment which promotes precocious metamorphosis in P. waltlii and experimental metamorphosis in neotenic A. mexicanum, induces a rapid and significant increase in muscle calmodulin concentration.