Abstract

This review summarizes the current status of the known extant genuine polyploid anuran and urodelan species, as well as spontaneously originated and/or experimentally produced amphibian polyploids. The mechanisms by which polyploids can originate, the meiotic pairing configurations, the diploidization processes operating in polyploid genomes, the phenomenon of hybridogenesis, and the relationship between polyploidization and sex chromosome evolution are discussed. The polyploid systems in some important amphibian taxa are described in more detail.

Frequent Occurrence of Bisexual Polyploid Amphibians

Polyploidization has been documented across a wide range of animal taxa. These include turbellarians, annelids, mollusks, crustaceans, and insects [Gregory and Mable, 2005], teleost fishes [Schultz, 1980; Le Comber and Smith, 2004], reptiles [Gregory and Mable, 2005], and amphibians [Bogart, 1980; Kawamura, 1984; King, 1990; Schmid et al., 2010; Evans et al., 2012]. In parthenogenetically reproducing animal species, polyploidy is observed relatively frequently [for reviews, see White, 1973; Fujita and Moritz, 2009]. In sexually reproducing animals, however, polyploid species are rare. Possible barriers to polyploidization include the presence of sex chromosomes [Muller, 1925], the prevalence of cross-fertilization [White, 1973], and the histological complexity of advanced animals [Stebbins, 1950]. These barriers may explain why polyploidy is much rarer in animals than in plants [Orr, 1990; Otto and Whitton, 2000].