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At least 523 records · Page 29Linked to original sources
PubMed2003

Chromosome banding in Amphibia. XXVIII. Homomorphic XY sex chromosomes and a derived Y-autosome translocation in Eleutherodactylus riveroi (Anura, Leptodactylidae).

Extensive cytogenetic analyses on a population of the leptodactylid frog Eleutherodactylus riveroi in northern Venezuela revealed the existence of multiple XXAA male/XYAA female/XAA(Y) female sex chromosomes. The XAA(Y) karyotype originated by a centric (Robertsonian) fusion between the original, free Y chromosome and an autosome. 46.2% of the male individuals in this population are carriers of this Y-autosome fusion. In male meiosis the XAA(Y) sex chromosomes pair in the expected trivalent configuration. In the same population 53.8% of the male animals still possess the original, free XY sex chromosomes. E. riveroi is only the second vertebrate species discovered in which a derived Y-autosome fusion coexists with the ancestral free XY sex chromosomes. The free XY sex chromosomes, as well as the multiple XA(Y) sex chromosomes are still in a very primitive (homomorphic) stage of differentiation. With no banding technique applied it is possible to distinguish the Y from the X. Various banding techniques and in situ hybridizations have been carried out to characterize the karyotypes. DNA flow cytometric measurements show that the genome size of E. riveroi resembles that of other Eleutherodactylus species. The cytogenetic data obtained in E. riveroi are compared with those of the sole other vertebrate known to possess the extremely rare, multiple XXAA male/XYAA female/XAA(Y) female sex chromosomes. Surprisingly enough, this vertebrate again is a frog belonging to the genus Eleutherodactylus [E. ((maussi) biporcatus] which lives exactly in the same habitat in northern Venezuela as does E. riveroi.

Animals↗
PubMed2003

Chromosome banding in Amphibia. XXIX. The primitive XY/XX sex chromosomes of Hyla femoralis (Anura, Hylidae).

The karyotype of the pine woods treefrog, Hyla femoralis, is characterized by primitive XY female/XX male sex chromosomes. The sole difference between the X and the Y is the presence of a nucleolus organizer region (NOR) in the X. Due to a deletion of the NOR in the Y, this chromosome is distinctly smaller than the X. Since no autosomal NORs exist in the karyotype of this species, the NOR deletion in the Y results in a sex-specific difference in the number of ribosomal RNA genes, with a female:male ratio of about 2:1. Interphase nuclei of male animals contain always one silver-stained nucleolus, whereas most nuclei of female specimens exhibit two nucleoli. This is in agreement with the absence of dosage compensation for sex-linked genes in amphibian cells. The consequences of the loss of about 50% of ribosomal RNA genes for the viability of male individuals and spermatogenesis are discussed.

Animals↗
PubMed2006

Distribution of neuropeptide FF-like immunoreactivity in the brain of Dermophis mexicanus (Amphibia; Gymnophiona): comparison with FMRFamide immunoreactivity.

Neuropeptide FF (NPFF) is an FMRFamide-related peptide widely distributed in the mammalian brain. NPFF immunohistochemistry labeled cell bodies in a few locations and dense fiber networks throughout the brain. Recently, the distribution of NPFF immunoreactive (NPFF-ir) cells and fibers in the brain of anuran and urodele amphibians was studied and, as in mammals, significant species differences were noted. To further assess general and derived features of the NPFF-containing neuron system in amphibians, we have investigated the distribution of NPFF-ir cell bodies and fibers in the brain of the gymnophionan Dermophis mexicanus by means of an antiserum against bovine NPFF. This distribution was compared to that of FMRFamide immunoreactivity. Major traits shared with anurans and urodeles were the abundant fiber labeling in the ventral telencephalon, hypothalamus, isthmus, ventrolateral medulla and dorsal spinal cord. In addition, in the three amphibian orders the majority of the NPFF-ir cells were located in the preoptic-hypothalamic region. However, distinct particular features were present in the gymnophionan such as the lack of NPFF-ir cells in the telencephalon, brainstem and spinal cord and the absence of NPFF-ir fibers in the hypophysis and the olfactory bulbs. This pattern was distinct from that observed for FMRFamide distribution. Striking differences were noted in the pallium, caudal hypothalamus and midbrain tegmentum where FMRFamide-containing cells were localized. The present results in Dermophis support the idea that data from gymnophionans must be included when stating the amphibian condition of a given system because important variations are obvious when gymnophionans are compared with anurans and urodeles.

Amphibians↗
PubMed1985

Pretectal and accessory-optic visual nuclei of fish, amphibia and reptiles: theme and variations.

The organization of the accessory optic and pretectal circuits is surveyed in a variety of poikilotherms and the conclusion drawn that a common organizational pattern exists. This pattern consists of the presence of three optic pretectal nuclei located rostrocaudally in lateral-superficial, central and dorsomedial (or periventricular) positions. Furthermore, a well-defined basal optic tract and ventrolaterally placed terminal field at the level of the oculomotor nucleus appears to be a consistent feature among bony fish, amphibians and reptiles. The possible role of these circuits in in visuomotor behaviors is discussed.

Afferent Pathways↗
PubMed1981

Nucleolar organizer regions and constitutive heterochromatin in polyploid species of the genus Odontophrynus (Amphibia, Anura).

Chromosome banding patterns obtained by ammoniacal silver staining (Ag-AS) and alkaline Giemsa (CBG) have been analysed in several amphibian species of the genus Odontophrynus from South America. Ag-AS bands were found at secondary constrictions, mainly of chromosomes 4 and 11. The CBG technique revealed centromeric and telomeric constitutive heterochromatin on almost all chromosomes of these species. Moreover, intercalary bands were found at particular sites of several chromosomes. Some inter- and intra-population polymorphisms were found for the Ag-AS and C-banding patterns. The species variability in the number and position of the Ag-AS bands, known to be regions of active ribosomal cistrons, as well as the specific sites of intercalary heterochromatin, are used to discuss the possible evolutionary relationships among these species.

Animals↗
PubMed1982

Chromosomal evolution in allopatric populations of the Odontophrynus occidentalis group (Amphibia, Anura) from western Argentina.

A karyological study of some populations of the Odontophrynus occidentalis group (2n = 22) from Argentina is reported. Ammoniacal silver (Ag-AS) and alkaline Giemsa (CBG) staining have been performed on specimens from La Rioja, Mendoza, Malargue, Tamelen, Tapiluque, Valcheta, and Meseta de Somuncura. All populations showed active ribosomal cistrons (NORs) on chromosome 11. Some metaphases of three specimens from Mendoza and five from La Rioja also showed bands on 9. Centromeric and telomeric C-bands were common to all populations, and a block of heterochromatin on both sides of the centromere of 2 was remarkable in all but the La Rioja populations. The specimens from La Rioja showed a similar block of heterochromatin on the short arm of 1. Taxonomic studies of several specimens from these localities revealed differences in larval development, glandular pattern, the size of specimens, etc. As a whole, biological as well as karyological features suggest that the isolated population at La Rioja is a separate entity, at the species level, as described elsewhere.

Animals↗
PubMed1993

Chromosome banding in Amphibia. XVIII. Karyotype evolution and genomic size variation in Pleurodema (Anura, Leptodactylidae).

DNA flow cytophotometric measurements demonstrate that the quantity of nuclear DNA of the South American leptodactylid frog Pleurodema brachyops is 3.4 times greater than that of P. thaul. Nevertheless, the conventionally stained karyotypes of both species are nearly identical. In the metaphase chromosomes of P. brachyops, the chromatin has a distinctly higher degree of packaging than in those of P. thaul. C-banding reveals that almost 6 times the constitutive heterochromatin is present in the karyotype of P. brachyops than in the karyotype of P. thaul. Analysis of fluorescence banding patterns shows that the chromosomes of P. brachyops contain AT- and GC-rich heterochromatin, whereas the karyotype of P. thaul is devoid of brightly fluorescing heterochromatin. The substantial differences in the genome sizes of Pleurodema is explained by homogeneous, symmetrical changes in the amounts of all DNA sequence classes along all chromosomes, which preserved the ancestral morphology of the chromosomes.

Animals↗
PubMed1993

Chromosome banding in Amphibia. XIX. Primitive ZW/ZZ sex chromosomes in Buergeria buergeri (Anura, Rhacophoridae).

The karyotype of the common bell-ring frog, Buergeria buergeri, is characterized by primitive ZW/ZZ (female/male) sex chromosomes. The only difference between the Z and W is the presence of a nucleolus organizer region (NOR) and its associated constitutive heterochromatin in the Z. This causes a sex-specific difference in the number of ribosomal RNA genes, with a male:female ratio of about 2:1. In the cell nuclei of the various tissues analyzed the NORs on both Z chromosomes are transcriptionally active. During meiosis in females, the ZW chromosomes form a characteristic lampbrush sex bivalent with a conspicuous absence of chiasmata along half of their long arms. No further morphological differences are present in these primitive sex chromosomes. The results indicate that there is no Z-chromosome inactivation mechanism operating in this amphibian. Experimental sex reversal of genetic (ZW) females to functional males was achieved by estrogen treatment of tadpoles. Mating of sex-reversed females with normal females yields the expected 25% lethal nucleoli-less WW embryos, which die at the tail-bud stage. The sex of the remaining viable embryos with one or two nucleoli determined after metamorphosis was in a female:male ratio of 1.57:1. These genetic experiments confirm that a primitive ZW/ZZ (female/male) type of chromosomal sex determination operates in this species.

Animals↗
PubMed1995

Chromosome banding in Amphibia. XXI. Inversion polymorphism and multiple nucleolus organizer regions in Agalychnis callidryas (Anura, Hylidae).

Cytogenetic analyses were performed on several populations of the Central American tree frog Agalychnis callidryas, using conventional methods and banding techniques. The karyotype of this species is distinguished by an inversion polymorphism in chromosome 9, which is either submetacentric or telocentric. The populations examined are in Hardy-Weinberg equilibrium with respect to the two alternative morphs of chromosome 9. This is the first report of the occurrence of an intrapopulational chromosomal inversion polymorphism in the order Anura. In male meiosis, the two chromosomes 9 form a bivalent exhibiting a ring-like pairing configuration with terminal chiasmata in both arms, regardless of whether the paired homologs are heteromorphic or homomorphic. Furthermore, individual specimens of A. callidryas exhibit one or two unexpected 18S + 28S ribosomal RNA gene clusters, in addition to the standard nucleolus organizers. The chromosomal localization of these extra nucleolus organizers is identical in all metaphases from the same specimen and shows a specific intraindividual pattern. The karyotype evolution in the phyllomedusine hylids, the structure of the various classes of heterochromatin, and the occurrence and possible origin of the rare inversion polymorphisms and multiple nucleolus organizers in A. callidryas and a few other amphibian species are discussed.

Animals↗
PubMed1977

Morphological and functional aspects of the arrangement of connective tissue and muscle fibres in the tail of the Mexican axolotl, Siredon mexicanum (Shaw) (Amphibia, Urodela).

In the lateral musculature of the axolotl tail a multipennate arrangement of muscle fibres is found in the 3rd postanal myomere and all following myomeres. This arrangement appears in larval stages as soon as the myomeres concerned are fully differentiated. Within a myomere a uniform degree of contraction of the muscle fibres may be achieved either by helical arrangement as seen in Teleosts, by diminishing fibre length in medial direction or by a combination of both phenomena. The relation between muscle fibre length and angle of insertion in the myomeres showing pennate arrangement is approximated by the Benninghoff and Roll-häuser equation but the values recorded deviated systematically from the values calculated. In the rather slender tail of the axolotl the transition from the helical or parallel fibre system into the pennate arrangement will be in favour of the development of relatively strong bending moments in the region concerned while a reasonable uniformity of the rate of contraction is maintained.

Ambystoma↗