A large geographic differentiation has been reported in Sylvilagus brasiliensis based on external characters of a small number of specimens. A new karyotype with 2n = 40 and FNa = 74 from Rio de Janeiro is herein reported. Phylogenetic analyses based on cytochrome b DNA of eight samples from the states of Paraíba, Tocantins, Goiás, Minas Gerais and Rio de Janeiro suggested a strongly structured population. Altogether, molecular and karyotypic data suggested that the diversity of Sylvilagus in eastern Brazil may be larger than the one reported in the literature on the basis of external characters.
Morphologic, molecular and karyologic analyses of Callicebus lugens (Humboldt, 1811) of known geographic origin supported the proposition that this is a valid species. Morphologic and morphometric analyses showed evident differences between C. lugens and two other related taxa of the same group (Callicebus purinus and Callicebus torquatus). Cytochrome b DNA analyses (maximum parsimony, neighbour joining and maximum likelihood) were congruent in showing a strong association between C. lugens and Callicebus sp. of the torquatus group in one branch and a sister branch further divided into two clades: one with species of the personatus group and another, with species of the moloch group. Karyotypic analysis showed that C. lugens has the lowest diploid chromosome number of the primate order (2n = 16). Comparisons with other congeneric species clearly supported the proposition that C. lugens is karyotypically similar to others of the torquatus group.
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