UNREDUCED DIPLOID EGGS PRODUCED BY INTERSPECIFIC HYBRIDS BETWEEN ORYZIAS-LATIPES AND O-CURVINOTUS

Male hybrids produced from reciprocal crosses between Oryzias latipes and O. curvinotus are sterile, whereas females do lay eggs. Fertilized by the sperm of one of the parental species, such eggs develop into triploid males and females. We examined allozyme patterns of triploids that developed from the eggs fertilized by sperms of non-parental strains of O. latipes or a closely related species, O. luzonensis. Expression of three allelic products in triploid offsprings indicated unreduced diploidy of the eggs produced by the hybrid females. In order to test the clonality of the diploid eggs produced by the hybrid females, we examined the progeny of hybrid females for their immunological clonality and DNA content. Progeny of a hybrid female crossed with a male of an inbred strain of O. latipes was demonstrated to belong to a single immunological clone. Differences in frequency of hypotriploidy and mosaicism were observed between strains of O. latipes that produced hybrid females. Because O. latipes is a fish that is used widely as a model organism in experimental biology, the hybrid females that produce unreduced diploid eggs provide a unique model with which to examine the underlying causes of polyploidy and clonal reproduction in vertebrates. (C) 1993 Wiley-Liss, Inc.