Distribution of repetitive DNAs and the hybrid origin of the red vizcacha rat (Octodontidae).

Great genome size (GS) variations described in desert-specialist octodontid rodents include diploid species ( Octomys mimax and Octodontomys gliroides ) and putative tetraploid species ( Tympanoctomys barrerae and Pipanacoctomys aureus ). Because of its high DNA content, elevated chromosome number, and gigas effect, the genome of T. barrerae is claimed to have resulted from tetraploidy. Alternatively, the origin of its GS has been attributed to the accumulation of repetitive sequences. To better characterize the extent and origin of these repetitive DNA, self-genomic in situ hybridization (self-GISH), whole-comparative genomic hybridization (W-CGH), and conventional GISH were conducted in mitotic and meiotic chromosomes. Self-GISH on T. barrerae mitotic plates together with comparative self-GISH (using its closest relatives) discriminate a pericentromeric and a telomeric DNA fraction. As most of the repetitive sequences are pericentromeric, it seems that the large GS of T. barrerae is not due to highly repeated sequences accumulated along chromosomes arms. W-CGH using red-labeled P. aureus DNA and green-labeled O. mimax DNA simultaneously on chromosomes of T. barrerae revealed a yellow-orange fluorescence over a repetitive fraction of the karyotype. However, distinctive red-only fluorescent signals were also detected at some centromeres and telomeres, indicating closer homology with the DNA sequences of P. aureus. Conventional GISH using an excess of blocking DNA from either P. aureus or O. mimax labeled only a fraction of the T. barrerae genome, indicating its double genome composition. These data point to a hybrid nature of the T. barrerae karyotype, suggesting a hybridization event in the origin of this species.

Molecular cytogenetics and allotetraploidy in the red vizcacha rat, Tympanoctomys barrerae (Rodentia, Octodontidae).

The theoretical impossibility of polyploidy in mammals was overturned by the discovery of tetraploidy in the red vizcacha rat, Tympanoctomys barrerae (2n = 102). As a consequence of genome duplication, remarkably increased cell dimensions are observed in the spermatozoa and in different somatic cell lines of this species. Locus duplication had been previously demonstrated by in situ PCR and Southern blot analysis of single-copy genes. Here, we corroborate duplication of loci in multiple-copy (major rDNAs) and single-copy (Hoxc8) genes by fluorescence in situ hybridization. We also demonstrate that nucleolar dominance, a large-scale epigenetic silencing phenomenon characteristic of allopolyploids, explains the presence of only one Ag-NOR chromosome pair in T. barrerae. Nucleolar dominance, together with the chromosomal heteromorphism detected in the G-banding pattern and synaptonemal complexes of the species' diploid-like meiosis, consistently indicates allotetraploidy. Allotetraploidization can coherently explain the peculiarities of gene silencing, cell dimensions, and karyotypic features of T. barrerae that remain unexplained by assuming diploidy and a large genome size attained by the dispersion of repetitive sequences.

[Two new fleas (Siphonaptera: Rhopalopsyllidae: Parapsyllinae) of Argentina, from Abrocoma uspallata Braun and Mares, 2002, (Rodentia: Abrocomidae)]. / Deux puces nouvelles (Siphonaptera: Rhopalopsyllidae: Parapsylunae) d'Argentine, parasites d'Abrocoma uspallata Braun et Mares, 2002 (Rod.: Abrocomidae).

Ectinorus (E.) uspallatae n. sp. and Delostichus ojedai n. sp. are described from the rodent Abrocomid, Abrocoma uspallata Braun and Mares, 2002, a new small mammal of Argentina.

[Two new species of fleas from Chile and Argentina(Insecta-Siphonaptera: Stephanocircidae and Rhopalopsyllidae) and raising of a new sub-genus of Plocopsylla Jordan, 1931]. / Deux puces nouvelles du Chili et d'Argentine (Insecta-Siphonaptera: Stephanocircidae et Rhopalopsyllidae) et érection d'un sous-genre chez Plocopsylla Jordan 1931.

A new subgenus of Plocopsylla is raised, Schrammapsylla Beaucournu and Ménier from the entire group B of Schramm & Lewis, 1988 and two new fleas from Chile and Argentina are described: Plocopsylla (S.) muruai n. sp. Beaucournu and Gallardo and Ectinorus (E.) mimacydis n. sp. Beaucournu and Gallardo. These two taxa are only known by the male sex.

Gradual and quantum genome size shifts in the hystricognath rodents.

We assessed genome size variation by flow cytometry within and among 31 species of nine families of African and South American hystricognath rodents. Interspecific variation was extensive and genome size was relatively high among the South American radiation whereas only moderate variation and smaller estimates of genome size were observed in the African counterparts. The largest genome size, indicating tetraploidy was recorded in the South American octodontid, Tympanoctomys barrerae (16.8 pg DNA). This quantum shift in DNA content represents a novel mechanism of genome evolution in mammals. As expected in polyploid organisms, varying nucleotypic effects were observed in the dimensions of the sperm cells and lymphocytes of T. barrerae. The role of control mechanisms that influence cell dimensions in polyploid organisms is discussed.

Chromosomal homology in southern Akodon.

Differential staining (G and C) of southern South American Akodon are presented. A. olivaceus, A. longipilis and A. sanborni all have the same karyotype (2n = 52, NF = 58). A virtually identical band sequence is observed. This situation is interpreted using the canalization model of chromosomal evolution which stresses an optimum karyotype for each adaptive zone. Despite the high degree of conservation of the chromosome structures, the specific status of these species is supported by maintenance of distinctness when they occur in areas of sympatry.