The chromosomes of 14 specimens of the genus Reithrodon from three different localities of Argentina and two localities of Uruguay were studied using G- and C-banding techniques. Specimens of Uruguay showed a karyotype of 2n = 28 chromosomes having a large metacentric X, and a telocentric Y chromosome. This karyotype is very similar to that recently described in a sample from southern Brazil, differing only in the nature of the Y chromosome, which is metacentric in the Brazilian form. All specimens from Argentina showed a 2n = 34 karyotype, differing from the Brazilian karyotype by two centric fusions, an acquisition of chromosome material, and at least one pericentric inversion, and by the telocentric nature of both the X and the Y chromosomes. G- and C-banding suggest that the metacentric gonosomes in the Brazilian form resulted from a double autosomal-X-Y Robertsonian translocation. The Uruguayan cytotype is interpreted as derived from a hypothetical neo-X/Y1Y2 ancestral form by the secondary loss of the Y1 chromosome. The karyotypic differences between the Brazilian-Uruguayan and the Argentinian forms afford evidence of species differentiation. It is proposed to assign the former to Reithrodon typicus, and the later to R. auritus.
Crocidura in captivity. A cta theriol., 24, 5: 61-68. -D ip p en aar N. J. (1979). N otes on th e ea rly p o st-n a ta l developm ent and b eh av io u r of th e tin y m u sk sh rew Crocidura bicolor Bocage, 1889 (In sectívo ra : Soricidae). M am m alia 43: 83-92. -Fons R. (1972). L a m usaraigne m usette, Crocidura russula (H erm ann, 1780 Study of th e seasonal v aria tio n in th e stom ach co n ten ts of coney rats, R eithrodon a uritus (Fischer, 1914), collected in a n a tiv e g rasslan d of th e so u th e ast of Buenos A ires P rovince, show s th a t diet of th is sm all ro d en t is exclusively constitued of p la n t m a terials, m ostly grasses. L olium m u ltiflo ru m and Poa spp. w ere tw o d o m in an t species w hich com posed a 74%> of th e stom ach contents dry w eight. T he n u m b er of item s found in th e diets w ere d ram a tic ally low er th a n th e n u m b er of species in th e p asture.
Plant Composition of Coney Rat's (Reithrodon auritus) Diet S K Ł A D D IETY R O Ś L IN N E J U REITH RO D ON AU R IT U SO
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