A bisexually reproducing all-triploid vertebrate

Green toads are common in the Palaearctic region, where they have differentiated into several taxa(1,2). The toads exist with variable amounts of ploidy, similar to other anuran species(3) or reptiles(4). In vertebrate biology, the very rare occurrence of triploidy is coupled with infertility or unisexuality, or requires the coexistence of individuals of different ploidy in a reproductive community. The reproduction of naturally occurring triploids has been reported to occur only through parthenogenesis, gynogenesis or hybridogenesis. The bisexual reproduction of pure triploids has been considered to be impossible because of the problem of equally distributing three chromosome sets in meiosis. Here we report geographically isolated populations of green toads (Bufo viridis complex) that are all-triploid and reproduce bisexually.