Although the genetic makeup of the vast majority of Vertebrates is diploid, some remarkable exceptions exist. Among these, Amphibians occupy a prominent position: about 50 Anuran species, indeed, have been described as polyploid.

In a work that will be published in the next issue of Acta Herpetologica, the origin of polyploidy in the Odontophrynus americanus complex was studied. This group of species, widely distributed in the South-eastern part of South America, is composed of 3 diploid species (2N = 22) and 1 polyploid species (2N = 44). Diploidy is considered to be the ancestral condition, since it is the most frequent condition among the species belonging to the complex.

In order to reconstruct the evolution of the ploidy in the group, cytogenetic analyses were carried out on 6 juvenile individuals of O. americanus. The analyses of the chromosomal arrangement during the mitotic metaphase revealed translocations and transpositions in the genotype of polyploid specimens. However, such karyotype differentiation is interpreted by the authors as a series of post-polyploid events, linked to the wide geographic distribution of the species.  Polyploidy in the O. americanus complex was putatively originated by intra-specific duplication of the whole genome (a phenomenon called autopolyploidy). However, the possibility of allopolyploidy (i.e., a duplication of the genome derivating by hybridization) could not be completely ruled out, because of the complex scenario of mechanism influencing the genetic makeup of species and populations. Independently of its origin, however, polyploidy carries fitness benefits that are stabilized, generation after generation, by a variety of DNA dynamics.

Discover more about polyploidy in O. americanus complex here.

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