title: Comparative cytogenetics of  spiny rats of the genus Proechimys (Rodentia, Echimyidae) from the  Amazon region.
abstract: We made  a comparative analysis of the cytogenetics of spiny rat species of the genus Proechimys collected from several sites of the Madeira River basin (Amazonas State,  Brazil) and Jari River valley (Pará State, Brazil). Individuals were assigned  to three groups based on diploid and fundamental numbers: 2n = 28, FN = 46 (P.  cuvieri and P. gr. longicaudatus); 2n = 38, FN = 52 (Proechimys gr. guyannensis), and 2n = 40, FN = 54 (P. gardneri). The  nucleolar organizer region (NOR) was interstitial on the long arm of one  submetacentric pair, as seen in all species of Proechimys analyzed thus  far. However, its position in the karyotype was variable. A duplication of the  NOR in one of the homologues was detected in P. gr. longicaudatus from  the Aripuanã basin along the mid Madeira. The C-band pattern varied between  species and, together with the NOR, allowed the identification of two  evolutionary units in P. gr. longicaudatus in the region of the  mid Madeira River (cytotypes A and B). The morphology and banding of the sex  chromosomes were species specific. A range extension is suggested for the  geographic distribution of P. gardneri and P. gr. longicaudatus.  Moreover, we suggest that species of Proechimys with 2n = 38 chromosomes  are restricted to east of the Negro River and north of the Amazon River. We  also revised the published chromosome data available for Proechimys.
authors.affiliation: Laboratório de Genética Animal, Instituto Nacional de Pesquisa da Amazônia, Manaus, AM, Brasil. edueler@yahoo.com.br
authors.forename: E S
authors.initials: ES
authors.lastname: Eler
authors.forename: M N F
authors.initials: MN
authors.lastname: da Silva
authors.forename: C E F
authors.initials: CE
authors.lastname: Silva
authors.forename: E
authors.initials: E
authors.lastname: Feldberg
mesh_terms: D000818:Animals; D001938:Brazil; D002871:Chromosome Banding; D007621:Karyotyping; D012377:Rodentia / Q000235:genetics*