Complex sex chromosome system in Eigenmannia sp. (Pisces, Gymnotiformes)

Abstract

Chromosomes of Eigenmannia sp. (7 males and 15 females) collected from the Tiet~ River in Botucatu (SP, Brazil) were examined from gill, kidney and testicular cells. The diploid chromosome number in males was 2n = 3 ! and in females, 2n = 32. In both sexes the number of chromosomal arms was 40. The difference in diploid number was due to the fusion of two acrocentrics. Mitotic and meiotic studies suggested that one of the fused acrocentrics was the Y chromosome. The sex-determining mechanism in Eigenmannia sp. could therefore be XX, AA in the female and X, YA A in the males. One of the males presented 2n = 30 chromosomes due to the occurrence of another fusion of acrocentrics. C-banding analysis of the mitotic chromosomes revealed constitutive heterochromatin in the centromeric regions of all acrocentrics. However, small metacentrics were C-band negative. The YA chromosome is C-band negative except for a small amount of heterochromatin in the centromeric region. The nucleolar organizer region as identified by Ag-staining is present in the interstitial region of chromosome pair No. 10.

Comparative cytogenetics among sympatric species of Characidium (Pisces, Characiformes). Diversity analysis with the description of a ZW sex chromosome system and natural triploidy

“…Among the neotropical fish different kinds of sex chromosome systems can be found, even among species of a same family, such as in Erythrinidae (BERTOLLO et al 1979(BERTOLLO et al , 1983 and Parodontidae (MOREIRA-FILHO et al 1993), or even among species of a same genus, such as in Hoplias (BERTOLLO et al 2000) and in Eigenmannia (ALMEIDA-TOLEDO et al 1984). The diversity of these systems indicates their distinct origins, as well as that they took place at different times, as it is known that the isolation of the distinct Brazilian hydrographic basins was not a concomitant event.…”

Chromosome banding in Amphibia

“…At least 20 species belonging to the orders Cypriniformes, Cyprinodontiformes, Perciformes, Salmoniformes and Tetraodontiformes are distinguished by remarkable XXAAY/XAA Y = or ZZAA=/ZAA W Y sex chromosomes (for reviews see Moreira et al, 1980;Almeida-Toledo et al, 1984Saitoh, 1989;Morescalchi et al, 1992aMorescalchi et al, , 1992b. In all these fishes, the original free Y or W sex chromosomes have become attached to an autosome either by a centric fusion (like in E. maussi), or alternatively by a tandem fusion.…”

Chromosome banding in Amphibia

“…However, previous reports describe the origin of similar unusual multiple sex chromosomes in fishes. At least 20 species belonging to the orders Cypriniformes, Cyprinodontiformes, Perciformes, Salmoniformes and Tetraodontiformes are distinguished by remarkable XXAAY/XAA Y = or ZZAA=/ ZAA W Ysex chromosomes (for reviews see Moreira et al, 1980;de Almeida Toledo et al, 1984;Almeida Toledo et al, 1988;Saitoh, 1989;Morescalchi et al, 1992aMorescalchi et al, , 1992b. In all these fishes, the original free Y or W sex chromosomes have become attached to an autosome either by a centric fusion (like in E. riveroi and E. (maussi) biporcatus), or by a tandem fusion.…”