Detailed characterizations of the karyotypes of the Brazilian leptodactylid
frogs Pleurodema diplolistris, the only species of Pleurodema not studied
cytogenetically so far, and Physalaemus nattereri, a species in the Ph.
biligonigerus group, are presented. Both karyotypes had 2n = 22 and their
chromosomes had a very similar morphology, except for pair 11, which was
metacentric in Pl. diplolistris and telocentric in Ph. nattereri. The
localization of nucleolar organizer regions (NORs) and heterochromatic bands
allowed the differentiation of chromosomes that were morphologically
indistinguishable between these species, such as pairs 1, 3 and 10, which
showed interstitial C-bands in Ph. nattereri, and pair 8, that had an NOR
and an adjacent C-band in Pl. diplolistris. Pair 8 also has NOR-bearing
chromosomes in many other Pleurodema species. However, in these species, the
NOR is located proximal to the centromere on the short arm, while in Pl.
diplolistris it occurred distally on the long arm, a condition that may be
considered a derived state. In Ph. nattereri, the NOR occurred on chromosome
11 and differed from the other species of the Ph. biligonigerus group. In
contrast, C-banding revealed a heterochromatic block near the centromere on
the short arm of pair 3, a characteristic common to all members of this
group of Physalaemus.