Abstract
Specimens of Bufo ictericus, Bufo paracnemis and a third type, considered an intermediate subgroup between these species, were cytogenetically studied by conventional Giemsa staining, C-banding and staining of the nucleolus organizer region (NOR). The nuclear DNA content and seroproteins were also analyzed to characterize these species, and verify the possibility of hybridization between them. Karyotypes and cytogenetic markers were essentially equal on the basis of the methods used. The DNA nuclear content found was 6.25 ± 0.30 pg/DNA in Bufo ictericus; 7.57 ± 0.40 pg/DNA in Bufo paracnemis and 7.04 ± 0.29 pg/DNA in the intermediate subgroup. Eletrophoresis of total blood serum in Bufo ictericus, Bufo paracnemis and the intermediate specimens revealed a remarkable difference in the patterns of the protein bands whose molecular weight corresponded to that of albumin. While the parental species presented two different bands, the intermediate form presented 4. However, only three of these bands were seen in each specimen. The results obtained pointed to a high probability for natural hybridization between Bufo ictericus and Bufo paracnemis in the site and specimens studied.
Highlights
Anura have usually been studied from the morphological and ecological point of view
The purpose of this study was to enable a better understanding of the relationships between Bufo species and taxonomic studies of the group by characterizing the B. ictericus and B. paracnemis samples found in the region of Botucatu, São Paulo, Brazil, and to test the hypothesis of hybridization between these species by comparing the results obtained from samples considered as parentals and supposedly hybrids
The diploid number was 2n = 22 in Bufo ictericus, B. paracnemis and the individuals considered as intermediate forms
Summary
Anura have usually been studied from the morphological and ecological point of view. The Bufo genus is of particular interest for studies regarding evolution and reproductive isolation mechanisms (Haddad et al, 1990), due to its cosmopolitan distribution and easy interbreeding in nature. Many authors have reported hybridization among the members of this genus in areas of sympatry (Blair, 1941; Thornton, 1955; Sullivan, 1986; Schlyter et al, 1991; Gergus et al, 1999 and Malmos et al, 2001). According to Wells (1977), the high frequency of hybridization can be explained by the reproductive mechanisms, such as external fertilization or the non-territoriality of observed in the group. Hybrids are not very successful due to sterility, or either partial or total lack of viability
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