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PubMed1979

Ultrastructural and histochemical features of the thymus glands of the adult lungless salamander, Plethodon glutinosus (Caudata: Plethodontidae).

The thymus glands of adult slimy salamanders (Plethodon glutinosus) were examined by light and electron microscopy with the objective of describing the populations of epithelial cells believed to be secretory. The results of various histochemical procedures designed to demonstrate nucleic acids, proteins, lipids, and mucosubstances were evaluated by light microscopy. Each thymus is incompletely subdivided into a variable number of interconnected lobules by trabeculae extending inward from a thin capsule composed of connective tissues. The thymic parenchyma lacks distinct cortical and medullary regions, although developing lymphocytes and plasma cells tend to accumulate in larger numbers in the outermost portions of the glands. Basophils are found regularly in the capsule and trabeculae, but only very rarely within the thymic parenchyma. The epithelial cells of the thymus can be classified into five categories: epithelial reticular cells; three varieties of granulated cells (types I, II, and III), and myoid cells. Epithelial reticular cells form a three-dimensional network which extends throughout all portions of the thymus. Type I and type II granulated cells can be distinguished from one another by various morphological criteria at the ultrastructural level, but only small differences in the composition of their inclusions can be demonstrated histochemically. Both types of granules are composed principally of a proteinaceous material containing an abundance of primary amino and guanidyl groups. In addition, most type I inclusions possess a lipid component that cannot be demonstrated in type II granules. Type III granulated cells possess very small cytoplasmic inclusions resembling those of gastroenteric endocrine cells. Myoid cells contain concentrically arranged myofibrils composed of sarcomeres. In favorably oriented material, small cysts can be identified whose walls are composed of mixtures of type I cells, type II cells, and epithelial reticular cells. Groups of degenerating epithelial cells form lamellated structures corresponding to Hassall's (thymic) corpuscles.

Animals↗
PubMed1986

Comparative features of the surface morphology of the basilar papilla in five families of salamanders (Amphibia; Caudata).

The surface morphology of the basilar recess and papilla was examined in 14 species of newts and salamanders selected from the five families of urodeles (Ambystomatidae, Salamandridae, Hynobiidae, Cryptobranchidae, and Amphiumidae) known to have this end-organ. In this sampling, the general organization of basilar structures is essentially similar across species investigated. The recess forms a tubular diverticulum of the proximal part of the lagena. One wall of the recess is associated with a diverticulum of the intracapsular periotic sac, and an adjacent wall is occupied by the basilar papilla. The papilla contained from as few as five hair cells in specimens of Taricha torosa to over 200 hair cells in Cryptobranchus allegheniensis. In most species, the papilla showed a morphological continuum between tall centrally or distally placed ciliary bundles and short ciliary bundles near the papillar margins. In certain species examined, tall bundles had kinocilia with swellings near their tips. Most forms showed a tendency to have groups of ciliary bundles morphologically polarized either toward or away from the saccule. In Cryptobranchus and Dicamptodon, many bundles had a random orientation. The gross and fine structural features of the basilar complex are compared in urodeles and anurans, and "generalized" features for the amphibian basilar complex are suggested. The basilar complex of Cryptobranchus is interpreted as being most generalized, representing a structural form from which most features of the basilar complex in other urodeles and anurans can be derived.

Ambystomatidae↗
PubMed2001

Molecular systematics of Plethodon and Aneides (Caudata: Plethodontidae: Plethodontini): phylogenetic analysis of an old and rapid radiation.

The closely related salamander genera Plethodon and Aneides (Plethodontidae) differ in morphology, behavior, and ecology. Although the systematics of these taxa has been the focus of much study, many details remain unresolved. To generate an hypothesis for the relationships among these taxa, I sequenced a segment of the mitochondrial protein-coding gene ND4 and portions of mitochondrial tRNAs. Taxa sampled were 5 species of Aneides, 7 species of western Plethodon, and 13 species of eastern Plethodon. Ensatina eschscholtzii was used as the outgroup. Phylogenetic analyses using maximum-parsimony, neighbor-joining, and maximum-likelihood consistently recovered some relationships. The eastern species of Plethodon are a robust, well-supported clade. Sister taxon relationships of P. elongatus and P. stormi, of P. dunni and P. vehiculum, and of A. hardii and the three west coast species of Aneides were also consistently resolved with good support. The monophyly of Aneides was only weakly supported in some analyses and there is no evidence for the monophyly of Plethodon or of the western species of Plethodon. Excluding the relatively distant outgroup, down-weighting saturated substitutions, and analyzing conserved data partitions did not yield additional resolution or support among the lineages of western Plethodon and Aneides. These results are consistent either with saturation of sequences, due to the age of the lineages, or with relatively rapid radiation. An old, rapid radiation is consistent with the results of previous studies. An analysis of current taxonomy within the phylogenetic framework presented here retains Aneides and recognizes Plethodon as a metataxon (indicated with an asterisk, Plethodon*).

Animals↗
PubMed2005

Testing hypotheses of speciation timing in Dicamptodon copei and Dicamptodon aterrimus (Caudata: Dicamptodontidae).

Giant salamanders of the genus Dicamptodon are members of the mesic forest ecosystem that occurs in the Pacific Northwest of North America. We estimate the phylogeny of the genus to test several hypotheses concerning speciation and the origin of current species distributions. Specifically, we test competing a priori hypotheses of dispersal and vicariance to explain the disjunct inland distribution of the Idaho giant salamander (D. aterrimus) and to test the hypothesis of Pleistocene speciation of Cope's giant salamander (D. copei) using Bayesian hypothesis testing. We determined that available outgroups were too divergent to root the phylogeny effectively, and we calculated Bayesian posterior probabilities for each of the 15 possible root placements for this four-taxon group. This analysis placed the root on the branch leading to D. aterrimus, indicating that current distribution and speciation of D. aterrimus fit the ancient vicariance hypothesis and are attributable to the orogeny of the Cascade Mountains rather than recent inland dispersal. Furthermore, test results indicate that D. copei is distantly related to other coastal lineages and likely originated much earlier than the Pleistocene. These results suggest that speciation within the genus is attributable to ancient geologic events, while more recent Pleistocene glaciation has shaped genetic variation and distributions within the extant species.

Animals↗
PubMed2005

Phylogenetic relationships of Hynobius naevius (Amphibia: Caudata) as revealed by mitochondrial 12S and 16S rRNA genes.

Using mitochondrial 12S and 16S rRNA sequences, we investigated phylogenetic relationships among populations of the endemic Japanese salamander Hynobius naevius. Monophyly of this species was recovered only in the maximum parsimony tree and was unresolved in maximum likelihood and Bayesian trees. Instead the following four haplotype clades consistently emerged clearly: Clade 1 from northwestern Kyushu, Clade 2 from Chugoku and northeastern Kyushu, Clade 3 from western Shikoku and Kyushu, and Clade 4 from Chubu-Kinki and central-eastern Shikoku. Of these, Clades 1 and 2, and Clades 3 and 4, respectively, correspond to Groups A and B previously recognized from the analyses of allozyme data in this species, but monophyly of these groups was not strongly supported. Unlike the previous results, the western and eastern samples from Shikoku did not form a clade, and were grouped with Kyushu-B in Clade 3 and Chubu-Kinki in Clade 4, respectively. The reason for this conflict between mtDNA and allozyme results is unknown, but might be related to retention of ancestral mtDNA polymorphism in Shikoku populations. Nearly simultaneous divergence of as many as four lineages in wide-ranging H. naevius is inferred for the late Miocene-Pliocene history of this taxon.

Animals↗
PubMed2000

Allozymic variation of Hynobius kimurae Dunn (Amphibia, Caudata).

An electrophoretic survey was conducted to examine genetic divergence among 21 populations of a lotic-breeding salamander Hynobius kimurae from Honshu, Japan. Genetically H. kimurae proved to be specifically distinct from H. naevius. Hynobius kimurae is divided genetically into two groups of local populations, and the five populations from the eastern area are genetically distinct from the remaining populations of the central and western areas. Less prominent genetic differentiation was revealed between the western and central populations. Separation of the eastern and central-western groups are discussed in relation to the formation of the Japanese mainland.

Animals↗
PubMed2003

The complete mitochondrial genome of the Chinese giant salamander, Andrias davidianus (Amphibia: Caudata).

The mitochondrial genome of the Chinese giant salamander Andrias davidianus was isolated using the long-and-accurate polymerase chain reaction (LA PCR) method. The sequencing work adopted the shotgun strategy accompanying with seven internal primers to cover the gaps where overlapping clones were not available. The entire mtDNA sequence is 16,503 bp long, with a gene content of 13 protein-coding, two ribosomal RNA and 22 transfer RNA genes, and order identical to that observed in most other vertebrates except for an additional 318 bp non-coding sequence between tRNA-Thr and tRNA-Pro genes. In order to carry out molecular phylogenetic analyses, all 13 protein sequences deduced from whole mitochondrial genomes for eight vertebrate species (six amphibians, two lobe-finned fishes) were combined to a single data set. This data set was refined by the program Gblocks using a stringent parameter setting and then subjected to MP, ML and NJ analyses. Thus phylogenetic relationships among living amphibians were discussed.

Animals↗
PubMedDate not supplied

Variation of repetitive DNA and its phylogenetic relation in Hynobiidae (Caudata).

Middle repetitive (MR) DNA comprising about 35% of the genomic DNA of Hynobius retardatus was isolated and used as mixed probes. A 1.3-kb Bam HI fragment, the major repeating unit of the extensively amplified sequences in H. retardatus, was cloned, sequenced, and used as a probe. Dot blot hybridization under the conditions of probe excess revealed that the MR DNA sequences were shared among the three salamander genera belonging to the family Hynobiidae. However, a large difference in the amount of common sequences was found between Hynobius and Salamandrella, and large differences in both amounts and sequence similarity were found between Hynobius and Onychodactylus. Even among species belonging to the genus Hynobius, relative contents of sequences common to the H. retardatus MR DNA were 20% to 50%. Partially related sequences to the 1.3-kb sequence seemed to be present in all the species of Hynobius and Salamandrella, but the extensive amplification was found only in H. retardatus. Based on the relative contents of the common MR DNA and previously reported chromosomal banding characteristics, species in the genus Hynobius are classified into at least three groups. An evolutionary aspect of the emergence of the amplified sequence in H. retardatus is discussed.

Animals↗
PubMed2000

Neoteny and progenesis as two heterochronic processes involved in paedomorphosis in Triturus alpestris (Amphibia: Caudata).

Current theories on the evolution of paedomorphosis suppose that several ontogenetic pathways have appeared according to different selective pressures. The aim of this study was to find out whether two distinct processes can lead to paedomorphosis in the Alpine newt, Triturus alpestris. In this respect, we compared age structures of paedomorphic and metamorphic individuals in two newt populations where the two forms lived syntopically. Whereas paedomorphosis resulted in a slower rate of somatic development in one population, it resulted in an acceleration of sexual maturation in the other population. These processes correspond to neoteny and progenesis, respectively. These results suggest that phenotypic plasticity can result from contrasted ontogenetic pathways between two populations of the same species. They give support to models that consider gonadic development as the target of selection under different environmental pressures.

Animals↗
PubMed2000

Kamegainema cingulum (Linstow, 1902) n. gen., n. comb. (Nematoda: Dracunculidae), a subcutaneous parasite of cryptobranchids (Amphibia: Caudata).

The monotypic Kamegainema n. gen. is proposed for Filaria cingula, a subcutaneous parasite of cryptobranchids. Examination of female specimens recently collected from the Japanese giant salamander, Andrias japonicus, revealed that it belongs to Dracunculidae. Kamegainema is closest to Protenema Petter and Planelles, 1986, the only other dracunculid genus known from Amphibia, but is readily distinguished by having prominent cuticular bosses. Kamegainema cingulum is redescribed.

Animals↗