Revisiting the polyploidy in the genus Odontophrynus (Anura: Odontophrynidae)

The genus Odontophrynus, composed of ten species, is found in practically the entire south of South America. Odontophrynus americanus was the first vertebrate registered to present natural polyploidy, considering that most individuals have 2N = 4x = 44 chromosomes, although having 2N = 2x = 22 chromosomes is considered the ancestral condition for all genera of the family Odontophrynidae. The present study aimed to analyze the karyotype of O. americanus, providing a detailed and comparative description of conventional chromosomal markers, with focus on a possible diploidization process operating in this polyploid genome. The individuals were collected in a fragment of Atlantic Forest in the south-central region of Paraná State, Brazil. The analyzed individuals presented the tetraploid pattern, with biarmed chromosomes. The C-banding showed heterochromatic regions restricted to centromeres and telomeres. Among homologous chromosomes of the same quartet, small differences were observed in morphology, possibly the result of differentiation after the polyploidization event. Finally, the 45S rDNA (Nucleolar Organizer Regions) was mapped in the short arm of quartet 11, showing the nucleolus organizing regions active in the four homologous chromosomes. This genome, although structurally polyploid, may be undergoing a process of diploidization, by becoming functionally equivalent to a diploid genome, via chromosomal rearrangements, epigenetic mechanisms, and/or repetitive DNA dynamics.