Fig. 1.

Phylogenetic affinities of at least eight nonhomologous sex-linked regions exist in Xenopus. The sex-linked regions (SLR) are on chromosomes that are indicated with numbers, and letters after these numbers refer to subgenomes (L or S for allotetraploids in subgenus Xenopus, L1, L2, S1, or S2 for allooctoploids in subgenus Xenopus, α or β for allotetraploids in subgenus Silurana; Evans et al. 2005, 2015). The heterogametic sex (hetero) is indicated with ZW for female heterogamety and XY for male heterogamety, or ZWY for X. tropicalis (see main text). The time-calibrated phylogeny was estimated from complete mitochondrial genomes (Evans et al. 2019) that do not reflect reticulating relationships among allopolyploid species. Scale bars illustrate variation in date estimates when analyses are performed using mitochondrial (Evans et al. 2019) and nuclear DNA (Evans et al. 2015). Black dots indicate unknown information from some species that were surveyed using RRGS data in this study; dashes indicate species for which RRGS data are not currently available. Results from X. laevis, X. borealis, X. tropicalis, X. mellotropicalis, P. parva, and Hymenochirus sp. (H. sp. as Hymenochirus boettgeri) were previously reported (Yoshimoto et al. 2008; Olmstead et al. 2010; Roco et al. 2015; Furman and Evans 2016; Cauret et al. 2020, 2023).