Chromosome banding in Amphibia

Abstract

A 15-year cytogenetic survey on one population of the leaf litter frog Eleutherodactylus maussi in northern Venezuela confirmed the existence of multiple XXAA♂/XAA^Y♀ sex chromosomes which originated by a centric (Robertsonian) fusion between the original Y chromosome and an autosome. 95% 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, 5% of the male animals still possess the original, free XY sex chromosomes. In a second population of E. maussi analyzed, all male specimens are characterized by these ancestral XY chromosomes which form normal bivalents in meiosis. E. maussi apparently represents the first vertebrate species discovered in which a derived Y-autosome fusion still 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. DNA flow cytometric measurements show that the genome of E. maussi is among the largest in the anuran family Leptodactylidae. The present study also supplies further data on differential chromosome banding and fluorescence in situ hybridization experiments in this amphibian species.

Nucleolus Organizer Regions in Physalaemus Cuvieri (Anura, Leptodactylidae), with Evidence of a Unique Case of Ag-NOR Variability

“…This agrees with that previously described by BECAK et al (1970) It has been shown that a general feature in anurans is the presence of a single pair of Ag-NORs, almost always conservatively localized in homoeologous chromosome pairs in species belonging to the same or to closely related species groups (SCHMID 1982;KING 1990;SCHMID et al 1990). Contrary to this finding, the analysis of ten specimens of P. cuuieri from different localities showed a very unusual intraspecific variation in the Ag-stained nucleolus organizer regions.…”

Chromosome banding in Amphibia

“…As in all other Anura examined (Schmid and Guttenbach, 1988;Schmid et al, 1990), the euchromatic segments of E. euphronides chromosomes fluoresce with uniform intensity. All those regions fluorescing either brighter or fainter than the euchromatin are composed of constitutive heterochromatin or represent the nucleolus organizer regions (Fig.…”

Five new species of Pristimantis (Anura: Strabomantidae) from the coastal cloud forest of the Península de Paria, Venezuela

“…Analysis of additional male individuals will be necessary to determine if this fusion chromosome, designated as cfu (11;18), represents a Y-autosomal fusion that characterizes the karyotype of some male individuals in this population. Such Y-autosomal fusions have been described in two other species in the Terrarana, Strabomantis biporcatus (Schmid et al 1992(Schmid et al , 2002 and Pristimantis riveroi (Schmid et al 2003). Three other Pristimantis species and one Eleutherodactylus species have confirmed Y-autosomal fusions, and in one Pristimantis species and five Eleutherodactylus species they are suspected to exist (Schmid et al 2010).…”