Genetic analysis of developmental arrest in an amphibian hybrid ( Rana catesbeiana, Rana clamitans)

Abstract

The importance of nucleocytoplasmic interactions in early development is illustrated by the embryonic lethality of many hybrid combinations between species. In order to investigate these interactions genetically, I used hybrids between the frogs Rana catesbeiana and Rana clamitans which exhibit unilateral incompatibility. Embryos from the cross R. catesbeiana ♀ × R. clamitans ♂ are arrested as exogastrulae, while the reciprocal cross yields fertile adults. When a hybrid male was backcrossed to a R. catesbeiana female, half of the embryos developed while half were arrested early in development, many as exogastrulae. The viable backcross animals were diploid, and carried isozyme alleles that, for the most part, reflected normal inheritance from their hybrid father. The backcross animals had a normal sex ratio, and the locus for lactate dehydrogenase B was sexlinked. When a hybrid female was backcrossed to a R. catesbeiana male, all of the embryos lived. When backcrossed to a R. clamitans male, however, about half lived and about half were arrested, some as exogastrulae. Isozyme analysis using three loci indicated normal inheritance from the hybrid female. Taken together, the results suggest that in this lethal cross, the nucleocytoplasmic interaction involves a single R. clamitans chromosome in the sperm, a chromosome in the egg pronucleus, and a cytoplasmic component of the R. catesbeiana egg.