AMPHIDIPLOIDY RECOVERS THE VIABILITY OF HYBRIDS OF EUROPEAN AND EAST-ASIAN WATER FROGS

Reciprocal diploid hybrids, artificially produced from crosses between Rana nigromaculata and Rana lessonae, die at the stage from neurula t o tailbud. We found in a previous study that triploid hybrids having t wo R. nigromaculata genomes and one R. lessonae genome in R. nigromacu lata cytoplasm grow into mature frogs, whereas triploid hybrids compos ed of the other combinations of genome and cytoplasm arrest before hat ching. In this study, we made amphidiploid hybrids with two R. nigroma culata and two R. lessonae genomes in the cytoplasm of either species and examined their viability to discover the interaction between paren tal genomes in each cytoplasm. The amphidiploids with R. nigromaculata cytoplasm developed into mature frogs, whereas ones with R. lessonae cytoplasm arrested at almost the same embryo stage as the lethal tripl oid hybrids. These findings suggest that the arrest of the reciprocal diploid hybrids is not caused only by the incompatibility between the R. nigromaculata genome and the R. lessonae genome. Taking these toget her with the results of the triploid hybrids, we suppose that the leth ality of the hybrids is mainly due to the incompatibility between the egg cytoplasm and foreign genome(s). With the R. nigromaculata cytopla sm, doubling the maternal genome can ease this incompatibility, but it cannot with the R. lessonae cytoplasm. (C) 1997 Wiley-Liss, Inc.