Subgenome evolution and sex chromosome conservation through multiple allotetraploidization events in the African clawed frogs (Xenopus)

African clawed frogs (Xenopus) have a high rate of sex chromosome turnover, wherein closely related species oftentimes have nonhomologous sex chromosomes. One possible explanation is that genome duplication (polyploidization) – which occurred many times in the genus Xenopus – catalyzes sex chromosome turnover. To explore this possibility, we evaluated the number of independent allotetraploidization events and sex-linked regions within the subgenus Silurana, which includes one diploid and three allotetraploid species, using whole-genome sequencing (WGS) data and reduced representation genome sequences. We then explored how sex-linkage varies among natural populations of the diploid species X. tropicalis. Our results suggest at least two separate allotetraploidization events occurred to generate these allotetraploid species, and that the sex-linked regions in all three allotetraploids remained unchanged compared to a diploid ancestor. Analysis of population structures identifies a X. tropicalis sample from Liberia with substantial genetic differentiation from other X. tropicalis samples. Additionally, our analyses also identify geographic variation in sex-linked regions over the range of the diploid X. tropicalis in west Africa. Together, these results contextualize the relative timing of diploid population differentiation, allotetraploidization, and sex chromosome evolution in these frogs, and are inconsistent with polyploidization being a major catalyst for sex chromosome turnover – at least in Xenopus. We also studied how subgenomes of the allotetraploid species, X. laevis, changed in southern Africa in relation to geography and climate.