THE DEVELOPMENT OF RECIPROCAL ANDROGENETIC FROG HYBRIDS

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Abstract
The development of 112 androgenetic R. pipiens and 148 androgenetic R. palustris embryos is briefly descr. 204 androgenetic hybrids between R. pipiens female x R. palustris male developed uniformly to an early neural fold stage, then differentiation ceased, the neural plate cells were sloughed off, and the embryos died. A gut with a small lumen and a mesodermal layer were present. Notochord and liver were absent. Pycnotic nuclei were present in the anterior neural ectoderm. 304 androgenetic hybrids between R. palustris female x R. pipiens male developed uniformly until early gastrulae. Thereafter their development was highly variable. Gastrulation was usually incomplete, and a short neural plate may be formed. In a few embryos closure of the neural folds occurred and neuroid and neural tissue were formed. An occasional embryo was capable of slightly further differentiation, with an abnormal brain and neural tube, optic and otic vesicles. Gut, notochord and an occasional subnotochordal rod were present. The liver was absent. Pycnosis and edema were sometimes present. The results obtained suggest that the abnormal development and death of haploid amphibian embryos is due to both haploidy per se and to unmasked lethal and semi-lethal genes. In androgenetic hybrid development not only may these two factors be operative but, in addition, the cytoplasmic substrates may play a role.