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Complete nucleotide sequence and gene rearrangement of the mitochondrial genome of the bell-ring frog, Buergeria buergeri (family Rhacophoridae).

In this study we determined the complete nucleotide sequence (19,959 bp) of the mitochondrial DNA of the rhacophorid frog Buergeria buergeri. The gene content, nucleotide composition, and codon usage of B. buergeri conformed to those of typical vertebrate patterns. However, due to an accumulation of lengthy repetitive sequences in the D-loop region, this species possesses the largest mitochondrial genome among all the vertebrates examined so far. Comparison of the gene organizations among amphibian species (Rana, Xenopus, salamanders and caecilians) revealed that the positioning of four tRNA genes and the ND5 gene in the mtDNA of B. buergeri diverged from the common vertebrate gene arrangement shared by Xenopus, salamanders and caecilians. The unique positions of the tRNA genes in B. buergeri are shared by ranid frogs, indicating that the rearrangements of the tRNA genes occurred in a common ancestral lineage of ranids and rhacophorids. On the other hand, the novel position of the ND5 gene seems to have arisen in a lineage leading to rhacophorids (and other closely related taxa) after ranid divergence. Phylogenetic analysis based on nucleotide sequence data of all mitochondrial genes also supported the gene rearrangement pathway.

Animals↗

Exposure, postexposure, and density-mediated effects of atrazine on amphibians: breaking down net effects into their parts.

Most toxicology studies focus on effects of contaminants during exposure. This is disconcerting because subsequent survival may be affected. For instance, contaminant-induced mortality can be later ameliorated by reduced competition among the survivors, a concept we refer to as "density-mediated compensation." Alternatively, it can be exacerbated by toxicant effects that persist or appear after exposure, a phenomenon we term "carryover effects." We developed a laboratory framework for testing the contribution of exposure, density-mediated, and carryover effects to net survival, by exposing embryos and larvae of the streamside salamander (Ambystoma barbouri) to atrazine (0, 4, 40, 400 ppb; 3 ppb is the U.S. drinking water maximum) and quantifying survival during and 14 months after exposure. Atrazine is the most commonly used herbicide in the United States and a documented endocrine disruptor. We show that atrazine-induced mortality during exposure was ameliorated by density-dependent survival after exposure, but complete density-mediated compensation was precluded by significant carryover effects of atrazine. Consequently, salamanders exposed to >or=4 ppb of atrazine had significantly lower survival than did control animals 14 months postexposure. The greatest change in survival occurred at low exposure concentrations. These nonlinear, long-term, postexposure effects of atrazine have similarities to effects of early development exposure to other endocrine disruptors. Together with evidence of low levels of atrazine impairing amphibian gonadal development, the results here raise concerns about the role of atrazine in amphibian declines and highlight the importance of considering persistent, postexposure effects when evaluating the impact of xenobiotics on environmental health.

Animals↗

Food habit of the juvenile of the Japanese newt Cynops pyrrhogaster.

The previous study showed that the red coloration of the ventral skin of the Japanese newt Cynops pyrrhogaster was associated with the number of carotenoid vesicles and the content of carotenoid in the pigment cell of the skin. To elucidate the mechanism for the red coloration of the skin of the newt, we studied the food habit of the juvenile from the Japanese newt Cynops pyrrhogaster. Sixty-two juveniles were collected in Fukue Island in Nagasaki Prefecture from November 2000 to May 2002 and divided into 2 groups according to the snout-vent length (SVL). Over 400 prey animals were obtained from the juveniles by stomach flushing. In the larger group (SVL>30.0mm), Collembola (45.4%) and Acari (12.6%), which are very common species of soil animals, were the prey animals dominant in number. In the group with the smaller SVL (<29.9mm), Collembola (30.4%) and Acari (25.4%) were in number as well. We also studied the food habit of the Japanese clouded salamander, Hynobius nebulosus. In the salamander, Doratodesmidae (56.5%) and Amphipoda (13%) were the prey animals dominant in number. Our results, taken together, suggest that the Japanese juvenile C. pyrrhogaster does not change its food habit as it grows, and that it eats soil animals common in its habitat. Moreover, the food habit of juvenile C. pyrrhogaster differs from that of H. nebulosus, although the juveniles of both species live in the same area.

Animals↗

Immunologic conservation of the fiber cell beaded filament.

Lenses were obtained from the eyes of four different classes of Chordates, including Mammalia (rat, mouse, cow, human), Aves (chicken), Amphibia (tiger salamander), and Osteichthyes (steelhead), as well as from one Mollusca (squid). Buffer soluble, urea soluble and urea insoluble fractions were prepared from each, and probed by western blot analysis for the presence of the lens fiber cell 115 and 49 kD beaded filament proteins. Application of both polyclonal and monoclonal antibodies revealed that an immunologic homologue to the bovine fiber cell 115 kD protein is present in all examples of Chordates tested, and that this homologue possessed properties very similar to those of its bovine counterpart. Both monoclonal and polyclonal antibodies revealed an immunologically cross-reactive homologue in squid as well, but suggested that the squid protein had a native molecular weight of closer to 70-80 kD. A monoclonal antibody to the bovine 49 kD beaded filament protein was successful at identifying an immunologic homologue to this protein in mouse, chicken, and tiger salamander. Ultrastructural analysis of rat, human, and fish lenses showed that a beaded filament was present in these lenses, which was indistinguishable from that seen in the bovine lens. In the squid a filamentous, beaded structure was observed, but it differed from that seen in the bovine lens. We conclude from the data presented that the beaded filament, and its constituent proteins, are well-conserved. This data should facilitate the identification of lens cytoskeletal proteins and structure in a wide range of animal models, and establish that probes for these proteins may be of broad applicability.

Animals↗

Spore dispersal of a resupinate ectomycorrhizal fungus, Tomentella sublilacina, via soil food webs.

Patterns of fungal spore dispersal affect gene flow, population structure and fungal community structure. Many Basidiomycota produce resupinate (crust-like) basidiocarps buried in the soil. Although spores are actively discharged, they often do not appear to be well positioned for aerial dispersal. We investigated the potential spore dispersal mechanisms of one exemplar of this growth form, Tomentella sublilacina. It is a widespread ectomycorrhizal fungus that sporulates in the soil organic horizon, can establish from the spore bank shortly after disturbance, but also can be a dominant species in mature forest stands. We investigated whether its spores could be dispersed via spore-based food webs. We examined external surfaces, gut contents and feces from arthropod fungivores (mites, springtails, millipedes, beetles, fly larvae) and arthropod and vertebrate predators (centipedes, salamanders) from on and around T. sublilacina sporocarps. Spore densities were high in the guts of many individuals from all fungivore groups. Centipede gut contents, centipede feces and salamander feces contained undigested invertebrate exoskeletons and many apparently intact spores. DAPI staining of spores from feces of fungivores indicated that 7-73% of spores contained intact nuclei, whereas spores from predators had lower percentages of intact nuclei. The spiny spores often were lodged on invertebrate exoskeletons. To test the viability of spores that had passed through invertebrate guts we used fecal droppings of the millipede Harpaphe haydeniana to successfully inoculate seedlings of Pinus muricata (Bishop pine). These results indicate the potential for T. sublilacina spore dispersal via invertebrates and their predators in soil food webs and might help to explain the widespread distribution of this species. It is likely that this is a general mechanism of dispersal for fungi producing resupinate sporocarps, indicating a need to develop a fuller understanding of the linkages of soil food webs and spore dispersal.

Animals↗

[Paul-Louis Simond and coccidia].

In 1880, during a sojourn at Constantine, Alphonse Laveran discovered the etiological agent of human malaria. During his microscopic observations of the parasite in freshly collected blood, Laveran's attention was attracted to the movement of flagellar bodies in the preparations. For Laveran these flagellar bodies corresponded to living organisms, in fact he considered them the most characteristic stage of the parasite; perhaps the sexual form of the parasite. In 1884, back in Paris at the military hospital Val de Grâce, A. Laveran showed these flagellated bodies to Pasteur, Roux and Chamberland who all thought that is was impossible not to recognize a living body in this mass of protoplasm displacing the surrounding red blood cells with its protruding flagella. As early as 1890, Elie Metchnikoff established a link between the flagellar bodies of Laveran and the stealthy stage of parasitic Coccidia infecting the intestinal epithelium of salamanders. It was the Pasteuriens and a few others scientists like Danilewski and Pfeiffer who firmly believed that the flagellar forms were indeed a normal stage during the hematozoan life cycle. On the contrary, Grassi and the Italian school, as well as the French protozoologist Labbé were convinced that the flagellar bodies corresponded to a degenerative form of the parasite provoked by the exposure of the parasites to air during slide preparation. In early 1896, P-L Simond joined Metchnikoff's laboratory and was assigned to study salamander coccidia in order to clarify the nature of the flagellar bodies. In a very short period of time, Simond clearly demonstrated that the coccidia had two types of life cycles; one of which resulted in the formation of flagellar bodies. Simond called the flagellar bodies "chromatozoites" due to the important quantities of chromatin twisted around the flagellum. From these observations and the sperm-like movement of the chromatozoites, Simond put forth the hypothesis that the chromatozoites were the male sexual forms of the parasite. He noted that they were found in all species of coccidia, as well as in the different species of malaria causing hematozoans of man and birds. Simond went even further in his interpretation to suggest that malaria parasites undergo sexual reproduction. This was indeed true, but Simond thought erroneously that sexual reproduction in hematozoans would result in the formation of resistant spores like in the Coccidia. The sexual reproduction hypothesis of malaria parasites was also formulated independently a year later by W. G. MacCallum (1898) working in the United States on Halteridium, a hematozoan infecting crows. Initially MacCallum was not aware of Simond's work, but later gave Simond full credit for his work on Coccidia. Furthermore, MacCallum observed for the first time the chromatozoite (microgamete) enter a female element (macrogamete) to form a mobile worm-like stage of the parasite know today as the ookinete. In his writings Simond is very modest, giving most of the credit to his mentors Metchnikoff and Laveran, but Laveran in an article which appeared in 1899 recognizes P.-L. Simond as the first person having put forth the hypothesis that the flagellar bodies of hematozoans causing human and bird malaria were the male forms of the parasite destined to fertilize the female elements.

Animals↗

Metamorphosis and neoteny: alternative pathways in an extinct amphibian clade.

The Branchiosauridae was a clade of small amphibians from the Permo-Carboniferous with an overall salamander-like appearance. The clade is distinguished by an extraordinary fossil record that comprises hundreds of well-preserved specimens, representing a wide range of ontogenetic stages. Branchiosaurids had external gills and weakly ossified skeletons, and due to this larval appearance their status as neotenic (perennibranchiate) forms has long been accepted. Despite their extensive fossil record large specimens with an adult morphology appeared to be lacking altogether, but recently two adult specimens were identified in a rich sample of Apateon gracilis collected in the 19th century from a locality near Dresden, Saxony. These specimens are unique among branchiosaurids in showing a high level of ossification, including bones that have never been reported in a branchiosaur. These highlight the successive formation of features believed to indicate terrestrial locomotion, as well as feeding on larger prey items. Moreover, these transformations occurred in a small time window (whereas the degree of size increase is used as a proxy of time) and the degree of concentration of developmental events in branchiosaurids is unique among tetrapods outside the lissamphibians. These specimens are compared with large adults of the neotenic branchiosaurid Apateon caducus from the Saar-Nahe Basin, which despite their larger body size lack the features found in the adult A. gracilis specimens. These specimens give new insight into patterns of metamorphosis (morphological transformation) in branchiosaurids that are believed to be correlated to a change of habitat, and clearly show that different life-history pathways comparable to those of modern salamanders were already established in this Paleozoic clade.

Amphibians↗

[Metamorphosis in the Urodelan amphibians: patterns, regulation mechanisms, and evolution].

Patterns of metamorphosis and mechanisms of its regulation in primitive and advanced salamanders are compared. It is found that urodelan evolution was characterised by the following trends: 1) increase in the number of metamorphosing systems; 2) increase in the amplitude of metamorphic transformations of each particular system due to the progressive divergence of the larval and the adult morphology; 3) synchronization of metamorphic transformations and their concentration within a relatively short period of ontogeny; 4) increase in the role of the thyroid hormones (TH) in the regulation of metamorphosis. Structures that are induced by factors other than TH and develop independently of TH in primitive Urodela species acquire TH-dependence in phyletically more advanced salamanders. For instance, morphogenetic induction as a mechanism of ontogeny regulation is substituted by endocrine induction with TH as the inducing factor. The switch from morphogenetic to endocrine induction stimulates the following events: 1) optimization of ontogeny; 2) reduction of the metamorphosis duration; 3) formation of the dissociability of larval and post-metamorphic stages of ontogeny, which, in its turn, is a precondition for the swith to necrobiotic metamorphosis and to the direct development.

Animals↗

Anatomical connections and electrophysiological properties of toral and dorsal tegmental neurons in the terrestrial urodele Salamandra salamandra.

Fire salamanders (Salamandra salamandra) are strictly terrestrial urodele amphibians, having lost electroreception and the lateral line system during metamorphosis. The present study demonstrates that (i) the lateral lemniscus is supplied by fibers of the medullary acoustic nucleus (nucleus intermedius) and the superior olive; (ii) the subtectal dorsal tegmentum can be clearly separated into a dorsally located torus semicircularis and a ventrally situated dorsal tegmental nucleus, the former processing auditory and vibratory, the latter vestibular signals; and (iii) the hearing capabilities of this animal, as estimated from the tuning of toral units, are comparable to those of anurans with extratympanic sound transmission. It is concluded that vibration sensitivity and hearing are involved in defensive reactions in the non-vocalizing fire salamander. The vestibular cells in the dorsal tegmentum probably relay a head-velocity input to the optic tectum, thus providing a self-motion signal for the visual localization center.

Action Potentials↗

Temperature sex-reversal in amphibians and reptiles.

The sexual differentiation of gonads has been shown to be temperature-sensitive in many species of amphibians and reptiles. In two close species of salamanders, Pleurodeles poireti and P. waltl, both displaying a ZZ/ZW mechanism of genotypic sex determination (GSD), the rearing of larvae at high temperatures (30 degrees-32 degrees C) produces opposite effects: ZZ genotypic males of Pleurodeles poireti become phenotypic females whereas ZW genotypic females of P. waltl become phenotypic males. Sex-reversal of these individuals has been irrefutably demonstrated through genetic, cytogenetic, enzymatic and immunological studies. In many turtles, both sexes differentiate only within a critical range of temperature: above this range, all the individuals become phenotypic females, whereas below it, 100% become phenotypic males. The inverse occurs in some crocodiles and lizards. In many species of these three orders of reptiles, females are obtained at low and high temperatures, and males at intermediate ones. Preliminary studies in turtles (Emys orbicularis) indicate that within the critical range of temperature, sexual phenotype conforms with GSD, but that above and below this range, GSD is overriden. Temperature shifts during larval development in salamanders and during embryonic development in reptiles allowed the determination of thermosensitive stages for gonadal differentiation. Estrogens synthesized in the gonads at these stages appear to be involved in their sexual differentiation, higher levels being produced at feminizing temperatures than at masculinizing ones. The phenomenon of temperature sensitivity of gonadal differentiation occurs in species showing a very early stage in the evolution of sex chromosomes. Its adaptive value, chiefly in reptiles, remains an open question.

Amphibians↗

Distribution of potassium conductance in mammalian Müller (glial) cells: a comparative study.

The distribution of K+ conductance across the surface of retinal Müller cells was determined in 5 mammalian species--rabbit, guinea pig, mouse, owl monkey, and cat--and in tiger salamander. Potassium conductance was measured by monitoring cell depolarizations evoked by focal ejections of a high-K+ solution onto the surface of freshly dissociated cells. This technique measured the total K+ conductance of a given cell region (regional conductance), i.e., the specific K+ conductance times the total surface area in that region. In mammalian species with avascular retinas (rabbit, guinea pig), the regional K+ conductance within the middle portion of the cell was only a fraction (10.6-28.9%) of the endfoot conductance, while the conductance of the distal (photo-receptor) end of the cell was approximately half (41.2-49.8%) the endfoot conductance. In 2 species with vascularized retinas (mouse and owl monkey), by contrast, the regional K+ conductance within the middle portion of the cell was as large as 125.5-129.8% of the endfoot conductance. In these cells the K+ conductance of the distal end was 68.3-82.9% of the endfoot value. In cat, a third vascularized species, the K+ conductance was highest (187.1% of the endfoot value) at the distal end of the cell. In tiger salamander, which has an avascular retina, the regional K+ conductance of all regions distal to the endfoot was only 2.4-15.7% of the endfoot value. Differences in the distributions of regional K+ conductance observed in the 6 species raise the possibility that in vascularized mammalian retinas, the high-K+ conductance of the middle portion of Müller cells is associated with retinal blood vessels. The results are consistent with the hypothesis that, in avascular species, Müller cells aid in regulating extracellular K+ levels by transferring (siphoning) excess K+ principally into the vitreous humor, while in at least some vascularized species (mouse, monkey), excess K+ is transferred by Müller cells into retinal capillaries, as well as into the vitreous.

Animals↗

Size dependence during the development of the amphibian foot. Colchicine-induced digital loss and reduction.

Localized treatment of the limb buds of the frog, Xenopus laevis, and the salamander, Ambystoma mexicanum, with the mitotic inhibitor colchicine results in limbs that, when compared with the contralateral control, are smaller in size and have lost skeletal elements. There is a very well defined pattern in terms of what elements are most likely to be lost. For example, frogs that have lost a toe always lose the first toe, while salamanders always lose the fifth. These differences correspond to qualitative differences in developmental sequence of digital differentiation in anurans as compared to urodeles. We propose a hypothesis in which the digital pattern is indirectly affected by reduction in the number of mesenchymal cells in the embryonic field.

Ambystoma mexicanum↗

New host records for Myxidium serotinum (Protozoa: Myxosporea) from North American amphibians.

Three hundred twenty-five amphibians (80 salamanders, 245 frogs and toads) from Arkansas and Texas, representing 28 species within 9 families (Ambystomatidae, Plethodontidae, Salamandridae, Sirenidae, Bufonidae, Hylidae, Leptodacytlidae, Microhylidae, Ranidae) were examined for gall bladder myxosporeans. Of these, 32 (10%) were found to harbor Myxidium serotinum Kudo and Sprague, 1940, including 3 (4%) of the salamanders and 29 (12%) of the frogs and toads. This report documents 6 new host records for M. serotinum in Ambystoma opacum, Bufo americanus charlesmithi, Bufo speciosus, Acris crepitans blanchardi, Gastrophryne olivacea, and Pseudacris streckeri illinoensis. In addition, the Great Plains narrowmouth toad G. olivacea represents the first microhylid host of Myxidium spp. worldwide.

Amphibians↗

Novel requirements in peripheral structures of the extended satellite 2 hammerhead.

A number of RNAs that infect plants self-cleave using a domain called the hammerhead. The consensus plant hammerhead has three base paired stem structures. Stems I and III flank the cleaved phosphodiester and are connected to stem II by two unpaired and highly conserved sequences. We demonstrated previously that satellite 2 transcripts from the newt, Notophthalmus viridescens, use a modified hammerhead structure for self-cleavage. Here we show that hammerheads with similar modifications occur in satellite 2 from species representing two additional families of salamanders (Ambystoma talpoideum and Amphiuma tridactylum). The distinctive features of the modified satellite 2 hammerheads include unusually short stem III regions and internally looped extensions to stem I that are required for cleavage. However, despite the strict nucleotide requirement in the internal stem I loop of the newt hammerhead, the details of the stem I extensions differ in the three salamanders. An analysis of chimeric transcripts indicated that, in order for a specific stem I extension to be functional, it must be compatible with other regions of the modified satellite 2 hammerhead. One such region is stem II, and a mutational analysis has confirmed that there are specific sequence and/or structural requirements in stem II.

Animals↗

How does the urodele ear develop?

An overview is provided of the structural and molecular events causing the transformation of undifferentiated epidermal cells together with the underlying mesenchyme to become the complex, three-dimensional ear. While tremendous progress has been achieved in a few model systems, enough is not yet known about the comparative embryology of ear development to provide causal explanations of the adult structural differences among species. It is hoped that the changes in selector and/or structural genes, as well as changes in the spatiotemporal induction of structural gene activation, and possible changes in the interaction between the various embryonic sources which contribute to the ear, will soon be understood. The most promising new avenue for research appears to be studies which combine classical transplantation tissue experiments with modern gene expression analyses and modern in vitro assays of the role of putative morphogens or trophic factors. It is emphasized that it is not understood what is missing in the developmental program of those salamanders which have lost a basilar papilla. Direct comparison of gene expression patterns and xenoplastic transplantations in salamanders of comparable stages which either do or do not develop this organ should help to clarify the molecular events that have led to this major evolutionary novel feature of the vertebrate ear.

Ambystoma mexicanum↗

What insights into the developmental traits of urodeles does the study of interspecific hybrids provide?

Natural and artificial hybrids represent an important source of material for developmental and evolutionary studies of urodeles. We review the available literature on hybrid salamanders, emphasizing the unique developmental insights that these organisms provide. Of particular interest is the application of new molecular tools to identify DNA markers for traditional characters in developmental research, and we discuss our own results using Bulk Segregant Analysis to identify RAPD markers for the white phenotype in the axolotl. We pay particular attention to the inferences that can be drawn from the many disparate crosses between ambystomatid salamanders that vary in their metamorphic response. These crossing experiments suggest that 1) metamorphosis is dominant to paedomorphosis, 2) that different ambystomatids use different genetic mechanisms to block metamorphosis and become sexually mature, larval paedomorphs, and 3) metamorphosis may be controlled by a few genetic loci. As increasingly sophisticated molecular approaches are applied to these and other hybrid crossing schemes, it should be possible to understand the mechanistic basis of a wide variety of developmental characters that differentiate urodele species.

Ambystoma↗

The electrogenic Na/HCO3 cotransporter.

The electrogenic Na/HCO3 cotransporter (symporter) is the major HCO3- transporter of the renal proximal tubule (PiT), located at the basolateral membrane (BLM), and also plays a noteworthy role in Na+ reabsorption. HCO3 transporters are important for regulation of intracellular pH (pHi) in most cells and also thereby regulate blood pH. This electrogenic Na/HCO3 cotransporter was first discovered using perfused Ambystoma tigrinum (salamander) renal, proximal tubules. This novel cotransporter mediates the movement of one Na+ ion with several HCO3- ions, making it electrogenic, is blocked by stilbene compounds, but does not depend on intra- or extracellular Cl-. This and similar cotransporters have been found in a number of tissues and cell types. Recently, we used Xenopus-laevis oocytes to expression clone the salamander renal electrogenic Na Bicarbonate Cotransporter (NBC). Using microelectrodes to monitor membrane potential (Vm) and intracellular pH (pHi), we followed oocyte expression after injecting poly (A)+, fractioned poly (A)+, or cRNA. All experimental solutions contained 100 microM ouabain to block the Na+/K+ pump. Our expression assay was to apply 1.5% CO2/10 mM HCO3- (pH 7.5), allow pHi to stabilize from the CO2-induced acidification, and then remove bath Na+. Removing bath Na+ from native oocytes and water-injected controls, hyperpolarized the oocytes by approximately 5 mV and had no effect on pHi. However, for oocytes injected with poly (A)+ RNA, removing Na+ transiently depolarized the cell by approximately 10 mV and caused pHi to decrease; both effects were blocked by 4,4'-diisothiocyano-2,2'-stilbenedisulfonate (DIDS) and required HCO3-. Electrophoretic fractionation of the poly (A)+ RNA, enriched the expression signal. From the optimal expression-fraction, we constructed a size-selected cDNA library in pSPORT1. Screening our Ambystoma library yielded a single clone (aNBC). We could detect expression 3 days after injection of NBC cRNA. In aNBC-expressing oocytes, adding CO2/HCO3-elicited a large (> 50mV) and rapid hyperpolarization, followed by a partial relaxation as pHi stabilized. Na+ removal in CO2/HCO3-depolarized the cell by > 40mV and decreased pHi, aNBC encodes a protein of 1035 amino acids with several putative membrane-spanning domains, and has a low level of amino-acid homology (approximately 30% to the AE family of Cl-HCO3 exchangers. aNBC is the first member of a new family of Na(+)-linked HCO3- transporters and, together with the AE family, defines a new superfamily of HCO3- transporters. Using aNBC to screen a rat-kidney cDNA library, we identified a full-length cDNA clone (rNBC), rNBC encodes a protein of 1035 amino acids, is 86% identical to aNBC, and can be functionally expressed in oocytes.

Acid-Base Equilibrium↗

[Change of a releasing mechanism involved in pre-catching behavior during the development of Salamandra salamandra (L.)].

Preycatching behaviour in salamanders (Salamandra salamandra L.) was studied before (60 larvae) and after metamorphosis (50 juveniles) to find out whether there are differences in releasing mechanisms depending on the developmental stage. Responses to prey dummies of different size, shape and orientation were recorded. With advancing age salamanders respond more selectively, preferring "wormlike" dummies. The releasing mechanism is narrowed down during 10 months after metamorphosis. This is not caused by learning processes.

Animals↗