Discovery of triploidy in Palearctic green toads (Anura: Bufonidae) from Iran with indications for a reproductive system involving diploids and triploids

Palearctic green toads (Bufo viridis subgroup) represent one of the few vertebrate systems with three bisexually reproducing ploidy levels that can form population systems where up to three ploidy levels interact reproductively. However, especially from Western Central Asia, very few cytogenetic data are available. Therefore, we investigated the cytogenetic status and ploidy of 15 populations of the Bufo viridis subgroup, represented by diploid (2n) B. variabilis, 2n B. turanensis, as well as tetraploid (4n) B. oblongus in Iran. Karyotypes of 70 individual toads revealed three ploidy levels. While diploids (2n = 22) were found at 10 localities mostly from Northeastern (Kopet–Dagh range) and a population of 2n B. variabilis from Western Iran, tetraploid (4n = 44) B. oblongus were detected in four populations from Central and Eastern Central Iran. For the first time, we report triploid green toads (3n = 33) from Iran that were detected at two localities at the Eastern slopes of the Kopet–Dagh range (Yekkeh Bid, and Bazangan). These triploids probably do not appear to result from primary diploid–tetraploid hybridizations. Instead, co-occurrence of triploids with diploids may indicate a population system, in which both (2n and 3n) interact reproductively. These findings, which we compare with knowledge from other diploid–triploid vertebrate reproductive systems, deserve further investigations and raise evolutionary questions regarding origin and interaction of green toads of different ploidy levels in Iran.