Naturally occurring triploids in contact zones between diploid/tetraploid Odontophrynus cordobae and O. americanus (Anura, Odontophrynidae)

Abstract

Polyploidization plays an important role in speciation and evolution in anurans. However, a few stable triploid populations and some isolated triploid individuals have been reported. Here, we report the discovery of naturally occurring triploids in contact zones between diploid Odontophrynus cordobae and tetraploid O. americanus from Central Argentina, and propose values of erythrocyte area for the distinction of ploidy levels. A total of 101 individuals from three contact zones were studied and ploidy of each specimen was identified by mean chromosome count and erythrocyte size. Twenty three adult triploid specimens (males: n = 21; females: n = 2) from two contact sites were identified (percentage of individuals per ploidy level: site S2, 2n = 40.6%, 3n = 12.5%, 4n = 46.9%; site S3: 2n = 44.7%, 3n = 40.4%, 4n = 14.9%). The limit values of erythrocyte nuclear area used to distinguish between different ploidy levels were 23.62 μm2 (probability to be assigned to a respective ploidy level = 94.78%) for separating diploids and triploids and 27.67 μm2 (98.62%) for triploids and tetraploids. The high number of adult triploids occurring in more than one contact site between O. cordobae and O. americanus indicates that is not an isolated event. However, further studies are necessary to provide a hypothesis on the origin and evaluate the possible maintenance of triploids in syntopy with O. cordobae and O. americanus.