Polyploidization and sex chromosome evolution in amphibians

Genome duplication, including polyploid speciation and spontaneous polyploidy in diploid species, occurs more frequently in amphibians than mammals. One possible explanation is that some amphibians, unlike almost all mammals, have young sex chromosomes that carry a similar suite of genes (apart from the genetic trigger for sex determination). These species potentially can experience genome duplication without disrupting dosage stoichiometry between interacting proteins encoded by genes on the sex chromosomes and autosomal chromosomes. To explore this possibility, we performed a permutation aimed at testing whether amphibian species that experienced polyploid speciation or spontaneous polyploidy have younger sex chromosomes than other amphibians. While the most conservative permutation was not significant, the frog genera Xenopus and Leiopelma provide anecdotal support for a negative correlation between the age of sex chromosomes and a species' propensity to undergo genome duplication. This study also points to more frequent turnover of sex chromosomes than previously proposed, and suggests a lack of statistical support for male versus female heterogamy in the most recent common ancestors of frogs, salamanders, and amphibians in general. Future advances in genomics undoubtedly will further illuminate the relationship between amphibian sex chromosome degeneration and genome duplication.