B chromosome system in populations of Oryzomys flavescens (Rodentia, Cricetidae) from southern Brazil

Abstract

1991. B chromosome system in populations of Oryzomys flavescens (Rodentia, Cricetidae) from southern Brazil. Acta theriol. 36: 193-199. Chromosome studies on 49 specimens collected from 11 Brazilian populations of the rodent species Oryzomys flavescens (Waterhouse, 1837) disclosed 2n = 64 in 25 individuals, 2n = 65 in 9, 2n = 66 in 12, and 2n = 64/65 mosaics in 3. This chromosome variation was due to the occurrence of one or two extra small heterochromatic acrocentrics, interpreted as B chromosomes. Comparisons made between our data and those previously reported for O. flavescens from Uruguay and Argentina, O.fornesi from Paraguay, and Oryzomys sp. from Sao Paulo, Brazil, revealed that these taxa share similar karyotypes, suggesting they belong to a single cytotaxonomic group.