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3 Acta Theriologica

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A new species of sigmodontine rodent from the Atlantic forest of Eastern Brazil

100%

De O. J. A. , Bonvicino C. R.

nr 3

We describe a new sigmodontine species on the basis of three specimens obtained from a high-altitude locality in the Atlantic forest of eastern Brazil. This new form, a small-bodied pentalophodont with tail longer than head and body, long soft fur, and a brownish ochraceous dorsum, is diagnosed by the presence of an open slit in the suture between the frontal bones in prepared skulls, and by a reduced diploid number of 20 coupled with a relatively high fundamental number of 34. Although the low diploid number suggests a derived sigmodontine, analyses of morphological characters and DNA sequence data (720 bp of the cytochrome-6 gene) point to its placement within the recently described genus Juliomys González, 2000, a taxon regarded as belonging to an old and independent sigmodontine lineage. This finding reinforces current hypotheses of the Atlantic forest domain as an important center of diversification for a primitive sigmodontine stock. It also suggests that at least some surviving lineages, often considered rather ancient and unspeciose relicts, were subject to relatively more recent speciation events.

The Wilfredomys pictipes [Rodentia: Sigmodontinae] karyotype with comments on the karyosystematics of Brazilian Thomasomyini

100%

Bonvicino C. R. , Otazu I.

Acta Theriologica

1999

tom 44

nr 3

Karyotypic analysis of two specimens of Wilfredornys pictipes (Osgood, 1933), collected in the Atlantic forest of Sao Paulo State, Brazil, showed 2n = 36 / FN = 34. Comparative karyologic analysis indicated that W. pictipes was very different from species belonging to the tribe Oryzomyini and to the genus Delomys but similar to Rhipidomys species. These findings indicated that the tribe Thomasomyini is not a karyotypically homogeneous taxon. The low diploid number of W. pictipes is likely to be a derived trait among sigmodontine rodents.

Karyologic diversification and phylogenetic relationships of the genus Thalpomys (Rodentia, Sigmodontinae)

80%

De A. A. F. B. , Bonvicino C. R. , Briani D. C. , Kasahara S.

2004

tom 49

nr 2

We describe the karyotype of Thalpomys species, from different Brazilian localities of the Cerrado. Thalpomys cerradensis Herskovitz, 1990 showed 2n = 36, FN = 34 and T. lasiotis Thomas, .1916 2n = 38, FN = 38. Comparisons of G-band karyotypes showed evident inter-specific homologies indicating that their chromosome complements could be derived from one another by two presumed rearrangements. Both species showed pericentromeric C-band regions in almost all chromosomes but a comparison with CMA3/DA/DAPI staining indicated that the molecular content of heterochromatic regions was different. T. lasiotis specimens from two different localities differed in the morphology of the X chromosome due to the presence of a short heterochromatic arm. These chromosome types are apparently fixed in each population rather than maintained as a polymorphic variation. Phylogenetic analyses supported the monophyly of the genus Thalpomys but was not capable of elucidating its phylogenetic relationship to other Akodontini rodents. These analyses also showed inter-individual variation in T. lasiotis, even within a given population. Phylogenetic analyses placed T. lasiotis specimens with different karyotypes in different monophyletic branches. Molecular and karyologic data confirmed the identity of the genus Thalpomys.