Two germ cell lineages with genomes of different species in one and the same animal.

Cytological evidence for two germ cell lineages, each with the DNA-content of one of the parental species only, was obtained for certain males of the hybridogenic water frog Rana esculenta (R. ridibunda x R. lessonae) by means of DNA flow cytometry. The approach was based on the 16 +/- 2% difference in the DNA-content of genomes of the parental species. Two types of germ cells were observed in six out of 39 males studied from populations where such males did exist. The term 'hybrid amphispermy' is proposed for the phenomenon. Occurrence of the 'hybrid amphispermy' suggests that the direction of elimination (i.e., which genome being eliminated) is determined in R. esculenta by the relative activity of putative elimination-inducing factor(s) in each of the parental genomes, which can alternate from cell to cell.