Sympatry and hybridization between the clawed frogs Xenopus laevis laevis and Xenopus muelleri (Pipidae)

Though most Xenopus species are polyploid and can be hybridized in the labo ratory, natural hybridization seems to be restricted to hybrids of X. laevi s laevis x X. gilli. A parapatric distribution pattern between X. I laevis and X. muelleri seems to prevent interbreeding. We found X. l. laevis and X . muelleri living sympatrically in water bodies in the Republic of South Af rica west of Kruger Park and report a natural hybrid of X. l. laevis x X. m uelleri. Natural occurrence of such a hybrid has not been reported previous ly. The hybrid character was confirmed by analysis of its advertisement cal ls, which were intermediate between those of the parental species, by analy sis of its serum albumin pattern, and by determination of the nuclear DNA c ontent of its erythrocytes. The results indicate that this specimen is all F-1 hybrid between X. l. laevis and X. muelleri. Backcrossing with both par ental species indicated that the hybrid is sterile. It is discussed why sym patry between X. l. laevis and X. muelleri though possible might be rare.