Abstract
We performed cytogenetic analyses on specimens from three population samples of Proceratophrys boiei from southeastern and northeastern Brazil. We stained chromosomes of mitotic and meiotic cells with Giemsa, C-banding and Ag-NOR methods. All specimens of P. boiei presented a karyotype with a full chromosome complement of 2n=22, metacentric and submetacentric. We observed the secondary constriction within the short arm of pair 8, which was in the same position of the nucleolus organizer region (NOR). NOR heteromorphism was observed within two specimens from the municipality of Mata de São João (northeastern Bahia State). The C-banding evidenced an unusual heterochromatic pattern in the genome of P. boiei. In the southern most population samples (São Paulo State), we observed large blocks of heterochromatin in the centromeric regions of all chromosomes, whereas the northernmost samples (Bahia State) presented a small amount of constitutive heterochromatin. We suppose that this geographic variation in heterochromatin quantities could be due to heterochromatinization of some chromosome regions in the genome of the São Paulo samples. Furthermore, females from São Paulo presented, within chromosome pair 1 from C-banded karyotypes, one homologous chromosome almost heterochromatic, whereas males had heterochromatin restricted to the centromeric region. This unusual heterochromatic arrangement led us to assume that P. boiei owns a ZZ/ZW type of sexual determination system. This finding is very important, as this is the first record of ZZ/ZW sex chromosomes within Cycloramphidae. We believe that the cytogenetic differences found between southeastern and northeastern Brazilian population samples of P. boiei strongly supports the existence of a species complex under the name P. boiei, and the requirement of taxonomic and systematic reviews by morphological, bioacoustical, molecular, and cytogenetic data could define this taxonomic issue in the future.
Highlights
IntroductionFemales from Sao Paulo presented, within chromosome pair 1 from C-banded karyotypes, one homologous chromosome almost heterochromatic, whereas males had heterochromatin restricted to the centromeric region
We performed cytogenetic analyses on specimens from three population samples of Proceratophrys boiei from southeastern and northeastern Brazil
We considered that more comprehensive data on the cytogenetics of P. boiei could contribute to the understanding of the geographic variation of this taxon, as cytogenetics of the frog genus Proceratophrys is poorly known and restricted to the description of a 2n 022 karyotype for P. boiei and P. appendiculata (BEC AK et al 1970; SILVA et al 2003), and to the localization of the nucleolar organizer region in P. boiei (SILVA et al 2003)
Summary
Females from Sao Paulo presented, within chromosome pair 1 from C-banded karyotypes, one homologous chromosome almost heterochromatic, whereas males had heterochromatin restricted to the centromeric region This unusual heterochromatic arrangement led us to assume that P. boiei owns a ZZ/ZW type of sexual determination system. We considered that more comprehensive data on the cytogenetics of P. boiei could contribute to the understanding of the geographic variation of this taxon, as cytogenetics of the frog genus Proceratophrys is poorly known and restricted to the description of a 2n 022 karyotype for P. boiei and P. appendiculata (BEC AK et al 1970; SILVA et al 2003), and to the localization of the nucleolar organizer region in P. boiei (SILVA et al 2003) This issue led us to compare karyotypes of specimens of P. boiei from population samples of the State of Sao Paulo, southeastern Brazil, with that from. The finding and description of an additional Neotropical species owning heteromorphic ZZ/ZW sex chromosomes, P. boiei, is very important
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